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Some aspects of the demography of Iridaea splendens Dyck, Leonard James 1991

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SOME ASPECTS OF THE DEMOGRAPHY OF IRIDAEA SPLENDENS by L E O N A R D J A M E S D Y C K B.Sc, The University of British Columbia, 1978 A THESIS SUBMITTED IN P A R T I A L F U L F I L M E N T OF T H E R E Q U I R E M E N T S FOR T H E D E G R E E O F M A S T E R OF SCIENCE in T H E F A C U L T Y OF G R A D U A T E STUDIES Department of Botany We accept this thesis as conforming to the required standard T H E UNIVERSITY O F BRITISH C O L U M B I A 2 October 1991 ® Leonard James Dyck, 1991 In presenting this thesis in part ia l ful f i lment of the requirements for an advanced degree at The Un ivers i t y of Br i t i sh Co lumbia , I agree that the L ib ra ry shal l make it freely avai lable for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Depar tment or by his or her representatives. It is understood that copying or publication of this thesis for f inancial gain shal l not be allowed without my wri t ten permission. Depar tment of Botany The Un ivers i ty of Br i t i sh Columbia 2075 Wesbrook Place Vancouver , Canada V 6 T 1W5 Date: 9 October 1991 ABSTRACT A population of lridaea splendens at Brockton Point, Vancouver , Br i t i sh Columbia was examined. The persistent alternation between diploid dominance in winter and haploid dominance in summer (DeWreede and Green, 1990) at this site was produced by differential rates of increase and decrease in density of the alternate phases. M a x i m u m density of both phases occurred in June and m in imum density in February . Densi ty increase began earl ier in spr ing for gametophytes and proceeded at a higher rate than for tetrasporophytes result ing in gametophyte dominance in summer. The rate of decreasing density in fal l was also higher for gametophytes resul t ing in equal densities of the alternate phases in November and tetrasporophyte dominance in winter. The reproductively mature stages were also temporal ly segregated, wi th cystocarpic plants predominating in, summer and tetrasporangial plants in winter. The alternate reproductively mature stages appeared in the population at the same time (June). Increase in density of cystocarpic plants began immediately while increase in density of tetrasporangial plants began two months later. Surv ivorship of tagged blades of lridaea splendens was type II (Deevey, 1947) for three separate size classes (2 - 5 cm, 5 - 15 cm, 15+ cm) of both gametophytes and tetrasporophytes, indicating blades in al l categories had an equal chance of death over t ime. Calculat ion of rates of addition of new blades to the population indicated that in fal l tetrasporophytes produced new blades at a higher rate than gametophytes (the reverse of the situat ion in spring), thereby decreasing in density at a lesser rate. i i TABLE OF CONTENTS Abst ract i i L i s t of Tables , v L i s t of F igures ; v i i Acknowlegement ix Chapter 1: General Introduction 1 Chapter 2: Seasonal Dynamics of Genets and Modules of Iridaea splendens .. 26 Introduction 26 Methods and Mater ia ls 35 Results 43 Discussion 61 Chapter 3: Seasonal Dynamics of Nonfert i le, Tetrasporangia l and Cystocarpic Genets of Iridaea splendens ; 73 Introduction 73 Methods and Mater ia ls 76 Results 78 Discussion 92 Chapter 4: The Fate of Individual Modules of Iridaea splendens 99 Introduction 99 Methods and Mater ia ls 102 Results 104 Discussion 133 Chapter 5: Genera l Discussion 137 References 145 Appendix A : Tables of results f rom the permanent sites examined on a per site basis (data not adjusted for surface area) 156 ii i Appendix B : Figures examin ing results f rom the permanent sites on a per site basis (data not adjusted for surface area) 172 Appendix C : Supplementary f igures for the dynamics of reproductively mature stages of lridaea splendens 179 Appendix D: Supplementary tables for the dynamics of reproductively mature stages of lridaea splendens 182 Appendix E : L i fe tables for the separate size classes of gametophyte and tetrasporophyte blades of lridaea splendens tagged in June , 1989 189 Appendix F : L i fe tables for blades of lridaea splendens tagged in November , 1989 196 Appendix G : Depletion and surv ivorship curves for the separate size classes in the June , 1989, cohort of lridaea splendens 202 Appendix H : Depletion and survivorship curves for the November, 1989, tagging of lridaea splendens 221 Appendix I: Tables of results f rom the permanent sites, data adjusted to compensate for unequal surface areas of sites 240 Appendix J : Tables for the dynamics of reproductively mature stages of lridaea splendens 258 iv LIST OF TABLES Table 2.1: Gametophyte vs . tetrasporophyte genets wi th in sampl ing periods in permanent sites adjusted for surface area. 54 Table 2.2: Gametophyte vs . tetrasporophyte modules wi th in sampl ing periods in permanent sites adjusted for surface area. 55 Table 3.1: Densi ty of tetrasporangial vs. cystocarpic genets wi th in each sampl ing period in the contiguous transects. 85 Table 3.2: Densi ty of tetrasporangial vs. nonferti le genets wi th in each sampl ing period in the contiguous transects. 86 Table 3.3: Densi ty of cystocarpic vs . nonfertile genets within each sampl ing period in the contiguous transects. 87 Table 3.4: Densi ty of tetrasporangial vs. cystocarpic genets wi th in each sampl ing period in the permanent sites. 89 Table 3.5: Densi ty of tetrasporangial vs. nonferti le genets wi th in each sampl ing period in the permanent sites. 90 Table 3.6: Densi ty of cystocarpic vs . nonfertile genets wi th in each sampl ing period in the permanent sites. 91 Table 4 .1 : L i fe table for al l blades tagged in June , 1989. 105 Table 4.2: L i fe table for al l gametophyte blades tagged in June , 1989. 106 Table 4.3: L i fe table for al l tetrasporophyte blades tagged in June , 1989. 107 Table 4.4: Rates of loss among al l tagged blades. 121 Table 4.5: Rates of loss in tagged gametophyte blades. 122 Table 4.6: Rates of loss in tagged tetrasporophyte blades. 123 Table 4.7: Observed vs. expected rates of blade loss in the permanent sites. 124 Table 4.8: Rates of addition of blades in the permanent sites. 125 v i LIST OF FIGURES Figure 2.1: Four possible mechanisms, in terms of seasonal f luctuation in density of lridaea splendens, by which seasonal alternation of phase dominance m a y occur. 34 Figure 2.2: The vert ical extension of each of the 36 permanent sites in relation to Canad ian Char t Da tum. 38 Figure 2.3: Seasonal change in density of modules and genets of lridaea splendens in the contiguous transects. 45 Figure 2.4: Seasonal change in modules and genets of lridaea splendens in the permanent sites. 47 Figure 2.5: Seasonal changes in genet density in gametophytes vs . tetrasporophytes of lridaea splendens in the permanent sites. 50 Figure 2.6: Seasonal change in module density in gametophytes vs. tetrasporophytes of lridaea splendens in the permanent sites. 53 Figure 2.7: Seasonal change in number of modules per genet for gametophytes vs. tetrasporophytes of lridaea splendens. 58 Figure 2.8: Seasonal change in number of modules per genet of lridaea splendens in the contiguous transects and the permanent sites. 60 Figure 3.1: Seasonal change in density of nonferti le, tetrasporangial and cystocarpic genets of lridaea splendens in the contiguous transects. 80 vn Figure 3.2: Seasonal change in density of nonferti le, tetrasporangial and cystocarpic genets of lridaea splendens in the permanent sites. 84 Figure 4 .1 : Loss of modules over t ime in lridaea splendens tagged in June , 1989. 109 F igure 4.2: Surv ivorship of modules of lridaea splendens tagged in June , 1989. I l l Figure 4.3: Loss of gametophyte modules of lridaea splendens tagged in June , 1989. 113 Figure 4.4: Loss of tetrasporophyte modules of lridaea splendens tagged in June , 1989. 115 Figure 4.5: Surv ivorship of gametophyte modules of lridaea splendens tagged in June , 1989. 117 Figure 4.6: Surv ivorship of tetrasporophyte modules of lridaea splendens tagged in June , 1989. 119 vi i i A C K N O W L E G E M E N T I would like to thank m y supervisor Dr . Robert E . DeWreede for providing me wi th the opportunity to do this study and for his continual support throughout. Thanks also to the other members of m y supervisory committee -Dr . M ike Hawkes , Dr . G a r y Bradf ie ld and Dr . P a u l G . Har r i son for their assistance and editorial comments. A special thank-you to Helen and M o m and Dad for support both moral and mater ia l . To Pu t A n g and F r a n k Shaughnessey, thanks for al l the discussions. They were most helpful dur ing both the research and the wr i t ing up. Thanks to D r . Roy Turk ington for helping wi th references , to Rosemary Mason for exhibi t ing tolerance, and to D r . Jack Maze for candid comments, stat ist ical consultation and bravely assist ing wi th al l those hamsters. ix CHAPTER 1: GENERAL INTRODUCTION Plants stand sti l l and wai t to be counted, as J . L. Ha rpe r is fond of say ing (Harper, 1977), yet the actual demography of plants has accounted for a relat ively smal l proportion of the work done to date in plant ecology. Two reasons for this are advanced by Crawley (1990). The first is the longevity of certain plants and the impract ical i ty of plott ing mortal i ty in species which may survive many human lifetimes. The second involves the phenotypic plast ici ty of plants. The same individual, depending on var iat ion in factors such as available moisture and nutr ients, may va ry several orders of magnitude in fecundity f rom year to year . In addition plants are modular in construction and may lose biomass in t imes of stress so that, while modules die the genetic indiv idual may not (Harper, 1977). A s a consequence the demographic picture may be very different depending on whether the births and deaths being enumerated are modules or genetic individuals. The value of the information gleaned by demographic methods has sometimes been questioned. Watk inson (1986) has pointed out that monitor ing the fates of individuals rarely reveals the causes of death and general ly only provides informat ion on how fecundity and morta l i ty va ry wi th age and size. Whi le this contention is arguably correct, it seems rather to underscore the need for demographic work to precede exper imental studies. Since demography demonstrates the var iat ion in fecundity and mortal i ty wi th size, age and season, it wi l l highl ight those cases where either fecundity or morta l i ty are strongly correlated with a part icular age, size or t ime of year. In doing so it may be 1 2 able to el iminate a number of potential causes of fecundity or mortal i ty. If, for example, mortal i ty proved to be consistently high (for some species X) in a part icular size class dur ing a part icular t ime of year , it may wel l be possible to narrow the field of potential agents of mortal i ty to be considered in experimental studies to those most l ikely to operate dur ing that season on that size class. In this way demography lays a foundation for studies of herbivory, competition, and the interaction between plants and the physical environment. Demography of mar ine macroalgae has generally lagged behind demography of terrestr ia l plants. Near l y al l formal demographic studies of seaweed populations have been reported since 1980 (Chapman, 1986), and estimates of rates of bir th and death, the most obvious regulators of plant numbers, are few. In algal population biology the measurement of biomass has usual ly been stressed over density. Chapman (1986) points out that this is l ikely due to commercial enterprise being interested pr imar i l y in weight of plant mater ia l present rather than numbers of individuals. Sustainable y ield, however, is dependant on natal i ty and morta l i ty rates and detailed demography is esential here as wel l . lridaea splendens is an alga which has been studied for its commercial potential (Waaland, 1973, 1978, Mumford and Waa land , 1980, as lridaea cordata) and which has also been the subject of demographic studies which raised a number of questions. This study wi l l pay close attention to one part icular population of lridaea splendens near Vancouver in the hope of achieving a detailed picture of its demography. 3 Iridaea splendens (Setchell et Gardner) Papenfuss is a red alga in the order Gigart inales. Nomenclature in this genus has, for some t ime, been in a state of f lux. W h a t follows is a brief history of these nomenclatural and taxonomic changes. Th is genus, part icular ly common along the Pacif ic coast of No r th Amer i ca , has been referred to both as Iridaea (Ky l in , 1928) and as Iridophycus (Setchell and Gardner , 1937). A total of eighteen species were reported for this area by Setchell and Gardner (1937), K y l i n (1941) and Doty (1947). A n assessment of these eighteen species by Abbott (1971) resulted in several synonymies. A total of seven species were subsequently recognized, one of them, Iridaea cordata, wi th two variet ies, var . cordata and var . splendens. A n analysis of the plast ici ty of the characters used in delineating species of Iridaea led Abbott (1972) to support further reduction in number of species. Such a reduction, however, was not carr ied out at that t ime. In a series of ecological experiments Foster (1982) observed that some plants, recruited from Iridaea flaccida spores had Iridaea cordata characterist ics. Foster suggested from this that Iridaea flaccida and Iridaea cordata were conspecific. Le is ter (1977) argued that the type locality of Iridaea cordata was Isla de las Estados Argent ina, rather than Banks Is land, Br i t i sh Columbia, and that the name Iridaea cordata should therefore be applied to plants from the southern hemisphere. Leister proposed that the name Iridaea splendens be applied to plants f rom the northern hemisphere previously referred to as Iridaea cordata, and this name was used by S i lva (1979). Scagel et al. (1989), in the most recent 4 synopsis of the benthic mar ine algae of Br i t i sh Columbia, Southeast A l a s k a , Washington and Oregon, have adopted the name lridaea splendens to refer to taxa previously designated as lridaea cordata (both var . cordata and var . splendens) and lridaea flaccida, and it is on this basis that I use the name lridaea splendens. The life history of lridaea splendens consists of an alternation of isomorphic generations. Dioecious gametophytes give rise to non-flagellated spermat ia in male thal l i , and fert i l ization is presumed to take place in situ on the female gametophyte. Zygote ampl i f icat ion, again in situ on the female gametophyte, gives rise to a diploid carposporophyte, releasing diploid carpospores. These germinate to form the tetrasporophyte generation. The presumed site of meiosis is in sori near the surface of the tetrasporophyte blade, producing haploid tetraspores which, when released, settle and germinate into gametophytes. Haploid chromosome numbers of n = 4 have been found for male and female gametophyte tissue by Fra l ick and Cole (1973, as lridaea cordata) who also recorded a diploid number of n = 8 for tetrasporophyte t issue. Gametophytes in which cystocarps have not formed can not be dist inguished, by morphology, f rom tetrasporophytes which have not formed sporangia. It has been demonstrated, however, (McCandless et al., 1975; Waa land , 1975; as lridaea cordata) that gametophytes of lridaea splendens have a predominance of kappa-carrageenan while lambda-carrageenan predominates in tetrasporophytes. Craigie and Le igh (1978) developed a test for kappa-carrageenan ut i l iz ing a resorcinol reagent or iginal ly used b}' Yaphe and Arsenau l t (1965) to 5 test for fructose and 3,6-anhydrogalactose. Kappa-carrageenan consists of units of alpha 1,3-linked galactose-4-sulphate alternat ing wi th beta 1,4-linked anhydrogalactose, while lambda-carrageenan is alpha 1,3-linked galactose or galactose-2-sulphate al ternat ing wi th beta 1,4-linked galactose-2,6-disulphate. The resorcinal reagent produces a red colour in the presence of kappa-carrageenan, presumably the result of a reaction wi th the anhydrogalactose. The red colour is not produced in reaction wi th lambda-carrageenan. Th is method has been used by Craigie and Pr ingle (1978) to determine the numbers of gametophytes and tetrasporoph3 rtes in populations of Chondrus crispus, and for populations of Iridaea splendens by Dyck et al. (1985, as Iridaea cordata), and by DeWreede and Green (1990). Iridaea splendens is the most widespread species of Iridaea in the northeastern Pacif ic (Abbott, 1972; as Iridaea cordata), occurr ing from A l a s k a to central Cal i forn ia. It occupies sites wi th a var iety of wave exposures from protected to open coast (Hannach and Waa land , 1986; as Iridaea cordata), and is typical ly found in the low intert idal to shallow subtidal zones, extending in vert ical range f rom 0.5 to 1.0 m above M L L W (U.S . Cha r t Datum) (Abbott, 1971; as Iridaea flaccida) to 1.5 m below M L L W (U.S . Char t Datum) (Hruby, 1976; Hansen , 1977; both as Iridaea cordata). The lower l imi ts of distr ibution m a y be determined by competition w i th kelps, as was suggested for a population in the state of Washington by H r u b y (1976). Tha l l i of Iridaea are of mul t iax ia l construction (Norr is and K i m , 1972). There is a smal l crustose holdfast which is perennial , and upr ight blades which 6 arise at various t imes of year and survive for various lengths of t ime, usual l j 7 less than one year (Hansen, 1977). Populat ion studies on lridaea and related genera. The population structure of four Cal i forn ia populations of lridaea splendens was studied by Hansen and Doyle (1976, as lridaea cordata) in order to observe aspects of the life history in situ. Measurements were made on seasonal var iat ion in standing crop, density, and size class distr ibution of the life history stages. Stages were identified by the presence of reproductive structures, so four groups were recognized; tetrasporangial , cystocarpic, juveni le, and combined immature and male. Juveni le thal l i (less than 3 cm) dominated, in terms of density, throughout the year. Combined immature and male thal l i were next most numerous. Tetrasporangia l thal l i signif icantly outnumbered cystocarpic thal l i throughout the year. Juveni le density was highest in winter and lowest in late summer to au tumn, and was the only stage which showed signif icant f luctuation wi th season. Standing crop was dominated by the tetrasporangial stage through most of the year , but replaced by the combined immature and male thal l i in spr ing. Cystocarpic thal l i consistently represented only a smal l f ract ion of the total. Examina t ion of size class distr ibutions demonstrated loss of large tetrasporangial thal l i in autumn, wi th further attr i t ion in winter. This resulted in an increasingly large smal l size class composed of stubs of the formerly mature tetrasporangial blades. The proportion of tetrasporangial thal l i in the larger size classes increased 7 in spr ing and peaked in summer. Th is same pattern was present in cystocarpic thal l i and in the combined immature and male thal l i . Hansen and Doyle (1976) found that, throughout the year , gametangial and tetrasporangial stages were present wi th min imal seasonal f luctuation in density. The tetrasporangial stage dominated over the gametangial stage year round, wi th the exception of spr ing when combined immature and male plants were dominant. Carrageenan extracted f rom randomly collected batches of the immature and male blades was p redominan t^ lambda, indicat ing that the major i ty of this category were also tetrasporophytes. According to Hansen and Doyle (1976) possible explanations for this continued dominance by the tetrasporophyte generation were high morta l i ty of tetraspores, or apomeiosis which had been shown to occur in Iridaea splendens in culture (K im, 1976; as Iridaea cordata). Growth of Iridaea splendens was also studied in several populations in Cal i forn ia (Hansen, 1977; as Iridaea cordata). Growth rates for gametangial and tetrasporangial plants were s imi lar . Juveni le blades tagged in late winter to early spr ing consistently showed growth rates one to two orders of magnitude higher than juveni les tagged dur ing other months. In addition spring-tagged blades proved to have the longest life spans (9 - 12 mo), as opposed to blades tagged dur ing summer or au tumn (6 - 8 mo). Changes in growth rate were not correlated to changes in i r radiat ion, daylength, surface seawater temperature, or to changes in ammon ium, ni trate, nitr i te, and phosphate concentrations. The greatest period of growth, however, did coincide wi th the spr ing increase in irradiance and 8 daylength. Senescence occurred in individual blades throughout the year but was most prevalent in autumn. The rate of loss was highly var iable. Hansen (1977) contended that new blades originated pr imar i ly by vegetative means, that is, perennation f rom a basal crust. Ba re spots on the subst ratum were not actively colonized by lridaea splendens. Th is suggested that the success of sporelings in an established population was marg ina l . Extensive maturat ion of thal l i was observed, however, such that at the end of the growing season the population consisted almost exclusively of reproductively mature thal l i , the major i ty of which were tetrasporangial . Hansen (1977) noted the paradox of a plant expending such a large amount of energy producing reproductive structures, mostly tetrasporangial , while recrui t ing relat ively few sporelings and remain ing predominant ly tetrasporophytic in population structure. One explanation offered was that the tetrasporangial crusts are tougher and longer-l ived. Another explanat ion was apomeiosis, providing for the continued recrui tment of the diploid generation f rom tetraspores. Studies on lridaea splendens in the Stra i t of Georgia, Br i t i sh Columbia (Adams, 1979; as lridaea cordata) showed dynamics somewhat different f rom those in Cal i forn ia. Standing crop peaked in the period f rom June through J u l y , followed by rapid decline and low winter levels, and a rapid rise again in spr ing. Blades over 10 cm accounted for 90% of the biomass. Seasonal var iat ion in density was large and followed the same pattern as standing crop. The density of cystocarpic blades was higher than the density of tetrasporangial blades f rom M a y through Ju l y . The situation then reversed and the density of 9 tetrasporangial blades was higher than that of cystocarpic blades from August through December. In a location sl ightly to the south (Victor ia, Br i t i sh Columbia), Aus t i n and Adams (1971) found cystocarpic blades dominant to tetrasporangial blades f rom June through September and the reverse situation from October through February . This alternation of dominant life history stage wi th time of year was in contrast to the situation reported in Cal i forn ia . A d a m s (1979) speculated that this might be attributable to differential growth and maturat ion of blades in Br i t i sh Columbian waters but did not discuss which differences between the Br i t i sh Columbian and Cal i forn ian environments might contribute to differential growth. Sampl ing of lridaea splendens done in Bark ley Sound, Br i t i sh Columbia (Dyck et al., 1985; as lridaea cordata), dur ing the spring and summer of 1981 showed var iat ion in proportions of gametophytes and tetrasporophytes at the same site, and also between sites at the same t ime. Ut i l i z ing the resorcinol test for kappa-carrageenan, it was discovered that gametophytic blades were most common overal l , ranging from 55 to 90%. S imi la r work done in Vancouver harbour dur ing the spr ing of 1981 also showed a predominance (80%) of gametophytic blades. Th is indicated that the dominance of cystocarpic over tetrasporangial blades in ear ly spr ing and summer, noted by A d a m s (1979), was also present in vegetative thal l i . Du r i ng J u l y , 1982, lridaea splendens in twelve sites on the Oregon and Cal i forn ia coasts were sampled and analyzed using the resorcinol method (Dyck et al., 1985; as lridaea cordata). The intention was to discover i f a cline in 1 0 dominance existed from gametophyte dominance in Br i t i sh Columbia, to tetrasporophyte dominance in Cal i forn ia. Considerable variat ion in proportions of gametophytes and tetrasporophytes was seen from site to site. The data as a whole (albeit wi th some anomalies) suggested a trend which was the reverse of the one expected, tetrasporophyte dominance in northern Oregon, grading to gametophyte dominance in central Cal i forn ia. The sampl ing in Cal i forn ia included a site previously sampled by Hansen and Doyle (1976) which now showed an 86% gametophyte dominance instead of the tetrasporophyte dominance previously recorded. C lear ly tetrasporophyte dominance was not a permanent feature of Iridaea splendens in Cal i forn ia. In lieu of apomeiosis or competit ively superior tetrasporophyte crusts, Dyck et al., (1985) proposed a stochastic model in which space is held by the perennial crust. A part icular ratio of gametophyte and tetrasporophyte stages would change very little unt i l some disturbance (e.g. massive graz ing, or very low tides combined wi th hot weather) ki l led large numbers of crusts. The ratio of carpospores and tetraspores then present in the water column would determine the new ratio of gametophytes to tetrasporophytes sett l ing and germinat ing on the newly cleared space. The new ratio, maintained again by perennation unt i l the next disturbance, might wel l be the opposite of the ratio present before the disturbance. Work on a related genus, Chondrus crispus, (Mathieson and Burns , 1975) found cystocarpic plants to be the most abundant type, on a year-round basis, in two of three N e w Hampsh i re populations studied. Cystocarpic abundance itself peaked dur ing fal l and winter. Tetrasporangia l abundance was more errat ic w i th m a x i m a occurr ing in any season f rom site to site, and abundance vary ing from 11 rare to common between sites. Cystocarpic and tetrasporangial m a x i m a at one site were offset in a manner which could suggest temporal segregation of reproductive act iv i ty, but this was less than clear at the other two sites. Ver t ica l segregation of cystocarpic and tetrasporangial stages was seen, wi th cystocarpic plants occupying a higher zone than tetrasporangial plants. Studies of Chondrus crispus in P lymouth , Massachuset ts (Prince and K ingsbury , 1973) indicated that densit j ' var ied wi th season. M a x i m a were in summer and min ima in winter, a s imi lar situation to that described for lridaea splendens in the Stra i t of Georgia (Adams, 1979; as lridaea cordata). A burst of growth in this population of Chondrus crispus was observed by Pr ince and K ingsbury (1973) in late Februa ry , wi th growth rates reaching a max imum in summer and dropping to a m in imum in November and December. Ut i l i z ing the resorcinol test for kappa-carrageenan, Craig ie and Pringle (1978) examined three populations of Chondrus crispus on Pr ince Edward Island and found gametophyte predominance ranging from 69 to 78%. One population sampled in N o v a Scotia, however, showed a tetrasporophyte predominance of 51%. On San J u a n Island in Washington a population of lridaea splendens was examined dur ing three consecutive spr ing-summer periods f rom 1980 to 1982 (May , 1986; as lridaea cordata). B lades were tested for kappa-carrageenan. The population exhibited gametophyte dominance which var ied little f rom year to year , spanning a range from 84.6% in 1980 to 82.3% in 1982. Th is was simi lar to spr ing-summer values obtained for Bark ley Sound and for Vancouver harbour 12 during 1981 (Dj'ck et al., 1985; as lridaea cordata). Th is spr ing-summer predominance of gametophytes also corresponded to the period in which cystocarpic blades were numerical ly dominant to tetrasporangial blades in lridaea splendens near V ic tor ia , Br i t i sh Columbia (Aust in and A d a m s , 1971; as lridaea cordata). Since winter sampl ing was not undertaken by M a y (1986) the seasonal segregation of cystocarpic and tetrasporangial blades observed by Aus t in and Adams (1971) could not be confirmed or denied for the San J u a n population. M a y (1986) also mapped indiv idual holdfasts, and demonstrated that 80% of the blades ar is ing annual ly did so from perennial holdfasts whi le only 20% were recruited from spores. Blades ar is ing from perennating holdfasts also predominated in the . larger size classes over blades ar is ing from spores, such that 90% of the blade area, at peak density, was attributable to regeneration from holdfasts. M a y (1986) speculated that, given equal number and viabi l i ty of carpospores and tetraspores per blade, the population she observed should be producing larger numbers of carpospores than tetraspores. F r o m this, she argued, there should be increasingly larger numbers of tetrasporophytes in the population from year to year , as tetrasporophytes would make up approximately 80% of the new recruits. Since the proportion of tetrasporophytes in the population did not change appreciably f rom year to year , M a y (1986) postulated differential recrui tment of gametophyte sporelings, in addition to perennation, to account for the long term stabil i ty in the San J u a n Island population. M a y (1986) concluded that the stochastic model, proposed by Dyck et al. (1985) to account for the radical shift in population structure at Pidgeon Point, Ca l i fo rn ia , was not applicable to the situation on San J u a n Island. Instead, a mechanist ic model was 13 favored, in which ecological differences between life history stages would result in a population structure which would remain stable over t ime. Such ecological differences have been examined in Iridaea laminarioides and Iridaea ciliata f rom Pe lancura , Chi le (Hannach and Santelices, 1985). Both species showed a marked seasonality for biomass values, wi th peaks in summer and min ima in winter. Fo r Iridaea laminarioides sterile and male thal l i showed a marked increase near the end of spring at high and middle intert idal levels, but almost no seasonal i ty at the lower level. Cystocarpic thal l i peaked in biomass dur ing summer. Once again, the effect was much more pronounced at the high and middle intert idal levels. Tetrasporangial thal l i had a more marked seasonality than the cystocarpic thal l i , and this effect was most pronounced at the middle and lower levels. Iridaea ciliata showed a s imi lar temporal segregation between the reproductive phases. The overal l density of both species showed a seasonal trend s imi lar to that for biomass. Tetrasporangial thal l i of Iridaea laminarioides showed a marked seasonality at both middle and low tidal levels, w i th peaks in abundance during the fa l l . The peak abundance in cystocarpic thal l i was earl ier than for tetrasporangial thal l i , and var iat ion was greatest at the middle level. In Iridaea ciliata abundance of the combined sterile and male thal l i peaked in spr ing while both cystocarpic and tetrasporangial thal l i peaked in fal l . The overwhelming majori ty of this var iat ion took place at the lower t idal level. Each of the two species exhibited a part icular pattern of var iat ion in 14 density of the reproductive stages wi th t idal height. Cystocarpic blades of Iridaea laminarioides were more prevalant at the higher and middle levels, while abundance of tetrasporangial blades increased markedly at the lower level. Wi th Iridaea ciliata tetrasporangial blades predominated in the upper part of its range, while cystocarpic blades were more frequent in the lower part. For both species, the sterile and male category was composed pr imar i ly of smal l (2 to 4 cm) thal l i year round. Cystocarpic thal l i of both species were signif icantly larger in summer than in winter. Tetrasporangial thal l i were larger in summer than in winter, and tetrasporangial thal l i were signif icant ly larger than cystocarpic thal l i , only for Iridaea laminarioides. Cul ture of sporelings of both gametophytes and tetrasporophytes of Iridaea laminarioides and Iridaea ciliata, however, demonstrated no signif icant differences in growth opt ima in response to temperature, l ight intensity, water movement, or sal in i ty. Hannach and Santel ices (1985) suggested that the larger f luctuations experienced by the tetrasporangial blades implies that this stage is more sensitive to seasonal changes than the cystocarpic stage. Fur thermore, the temporal differences in m a x i m u m abundance between cystocarpic and tetrasporangial thal l i suggested that the two stages were responding to different envi ronmental factors correlated wi th changing season. The dominance of cystocarpic plants of Iridaea laminarioides in the upper and middle intert idal zones, areas of greater environmental f luctuation, caused Hannach and Santelices (1985) to call into question the general val id i ty of the prevalent notion (Stebbins and . H i l l , 1980; Stansf ield, 1977; Bar i lo t t i , 1971) that a diploid organism wil l show greater 15 adaptabi l i ty in the face of increased environmental var iat ion. Work on the ecological differences between life historj ' stages of lridaea laminarioides was continued by Luxoro and Santelices (1989). Tetrasporophytes responded differently than gametophytes to dessication stress, showing higher mortal i ty in response to emersion periods of 3 hours. The opt imum temperature for growth of gametophytes was 20 C while the opt imum for tetrasporophytes was at 15 C . Tetrasporophytes showed signif icantly higher growth rates in 12 hours of l ight than in 8, but did not further increase their growth rate when placed in a 16 hour daylength. The growth rate of gametophytes, on the other hand, was signif icantly higher in the 16 hour daylength than in either of the other two photoperiods. Food preference studies conducted wi th several herbivores indicated a consistent preference for young tetrasporophytes over young gametophytes. Differences in consumption of older ferti le fronds were not signif icant. There was no signif icant difference in the total number of spores produced by the two phases over a single year. However , in a single unreplicated observation, the number of carpospores released wi th in a 20 hour period was four orders of magnitude higher than the number of tetraspores released dur ing the same period. F r o m October 1982, to September 1983, Chondrus crispus was sampled monthly at Pubnico Point, N o v a Scotia (Bhat tacharya, 1985). A n extremely high numerical dominance (91%) of gametophytes over tetrasporophytes (anatyzed wi th 16 the resorcinol test for kappa-carrageenan) was found. This result was similar to the work of Wright (1981) who sampled Chondrus crispus in Halifax County, Nova Scotia. Wright found gametophyte proportions of 90 and 94% intertidally, and, in a subtidal collection taken from a depth of 10 meters, found 98% gametophyte dominance. Demographic analysis by Bhattacharya (1985) indicated that fronds emerged from winter with a low death risk, but that the chance of mortality increased with the onset of spring and accelerated growth. Mortality increased among the larger size classes as the year progressed and this appeared to be a result of bearing sori. Of mature thalli, between September and December, 19 to 33% were cystocarpic and 1.5 to 6% were tetrasporangial. Gametophytes grew more quickly than tetrasporophytes during all periods of measurement except June and July. It is to this increased growth rate that Bhattacharya (1985) attributed much of the dominance of gametophytes, since gametophytes and tetrasporophytes were very nearly equal in terms of survivorship and number of spores released. Higher growth rates in gametophytes (Bhattacharya, 1985) is in contrast to a difference in net photosynthetic rate observed by Mathieson and Norall (1975). In this latter study, during which both stages were collected subtidally, tetrasporangial thalli exhibited a higher net photosynthetic rate than cystocarpic thalli. Mathieson and Norall (1975) hypothesized that in the subtidal environment tetrasporangial fronds would grow faster than their cystocarpic counterparts. This would explain the predominance of tetrasporangial fronds of Chondrus crispus which Mathieson and Norall had found at depth in their study site. Bhattacharya (1985) indicated that the reverse appears to have happened in the intert idal. Whi le temporal segregation of gametophytes and tetrasporophytes appears not to have happened in this instance, vert ical segregation in response to differing environmental factors seems to have occurred. A s wi th Hannach and Santelices (1985) gametophytes once again p re fe ren t ia l l y occupy the upper par t of the species vert ical range and tetrasporophytes, the lower. Dissent on the idea of ecological differences between life history phases of Chondrus crispus comes from Lazo et al. (1989). Extensive sampl ing of six areas on Pr ince Edward Island was undertaken for the period from M a y through September dur ing 1985 and 1986. The overal l ratio of gametophytes to tetrasporophytes proved to be very close to unit}', wi th a slight predominance of gametophytes. When the areas were examined separately dominance by any stage was patchy, vary ing from site to site and wi th in a site over t ime. Lazo et al. argued that this patchiness calls into question previous work showing gametophyte dominance, as these studies may have involved isolated patches (dominated by gametophytes) and therefore may not be representative of the larger picture. The differences between the populations of Chondrus crispus in N o v a Scotia and those in Pr ince Edward Is land, however, appear more consistent and Lazo et al. (1989) have suggested that the two regions are substant ial ly different wi th respect to population structure. Lazo et al. (1989) have again raised the question of whether single phase dominance of a population could possibly be a stable feature, also cit ing the shift in dominance at Pidgeon Point, Cal i forn ia, for lridaea splendens (Dyck et al., 18 1985; as lridaea cordata). In the absence of extreme disturbance, argue Lazo et al. (1989), one generation would eventual ly predominate through intraspecif ic interaction in a manner s imi lar to the competitive exclusion principle for interspecific interaction (Si lvertown, 1982). The under ly ing assumption of this model is that the two phases would behave demographical ly as separate species, mutual ly independent and competing for resources in v i r tua l l j ' the same manner. A s a l l environments are disturbed to a greater or lesser degree, over a large area one should find patches wi th var ious proportions of the life history phases, some wi th a clear predominance of one stage, some dominated by the other. The proportions should be dependent to some extent on the level, frequency, and t iming of disturbance. Through this the overal l structure of the population would be mainta ined, wi th degree of disturbance from area to area causing considerable local and temporal var iat ion. Lazo et al. (1989) argue that this is the case for Pr ince Edward Is land, where entire plants, along wi th a superf icial layer of the soft l imestone subst ra tum, are frequently dislodged. DeWreede and Green (1990) have reported temporal differences in proportions of gametophytes and tetrasporophytes which persist f rom one year to the next. Sampl ing of lridaea splendens took place at four sites in Vancouver harbour, monthly dur ing the periods f rom M a y through Augus t and from November through February , from 1985 through 1987. A l though, once again, values var ied from site to site, there was a clear predominance of gametophytes at al l sites dur ing the summer and an equally clear predominance of tetrasporophytes dur ing the winter. This pattern persisted over three consecutive 19 years. S imi la r calculations, made by enumerat ing reproductive plants only, yielded the same pattern. Three size classes (0 - 5 cm., 5 - 15 cm. , and over 20 cm.) were each examined. Proport ions of the life history stages were stat ist ical ly s imi lar in al l three size classes, each paral le l ing the seasonal change in proportions of gametophytes and tetrasporophytes. Recolonization of cleared substratum by Iridaea splendens (Green, 1989; as Iridaea cordata) was slow for plots cleared in summer. Approx imate ly one year passed before new thal l i appeared. B y contrast, new recruits were observed on plots cleared dur ing the winter wi th in 4 - 6 months after clearing. Tetrasporophyte blades which became fertile in winter had almost twice the density of sori apparent in tetrasporophytes becoming fertile in summer. However , w i th the larger surface areas of summer blades, net numbers of sori produced in summer vs. winter were stat ist ical ly equal. S imi la r ly for cystocarpic blades, the increased surface area present dur ing their period of peak abundance led to a simi lar net number of reproductive structures per blade as were found on tetrasporangial blades dur ing their period of peak abundance. In theory then, the seasonally dominant phase releases the majori ty of the spores dur ing that season. G iven the longer t ime needed to recruit new plants f rom spores released in summer (predominantly carpospores giv ing rise to tetrasporophytes), compared to faster rates of establ ishment f rom winter released spores (predominantly tetraspores giv ing rise to gametophytes), most recruits of both phases should appear simultaneously in spr ing. I f numbers of spores produced and released are nearly equal between phases, differential recrui tment of 20 gametophytes would explain gametophyte dominance of a population. Given the rate of recrui tment measured by M a y (1986), however, differential recruitment alone could not explain the seasonal alternation between gametophyte and tetrasporophyte dominance. To account for such a seasonal alternation differential growth rates, differential rates of addition of new blades to the population either f rom spores or from perennial crusts, differential morta l i ty , or some combination of the preceeding, must be invoked. Appl icat ion of demography to lridaea splendens Demograplvy deals in the description of changes wi th in a population, over t ime, as a consequence of the births and deaths of individuals. Harper and Whi te (1974) deal at length wi th some of the common problems encountered in plant demography. Demography has never received the same attention among botanists as it has among zoologists, and as a consequence much of the theory in p lant demography has been derived from work in an imal demography. One of the fundamental differences addressed by Harpe r and Whi te (1974) is that growth in plants frequently involves the accumulat ion of structural units. This has given rise to the notion of plants as "modular organ isms" or as " a population of par ts " since the parts, e.g. leaves on a deciduous tree, may have cycles of b i r th, maturat ion, and death quite apart f rom the bir th, maturat ion and death of the genetic indiv idual (Bazzaz and Harper , 1977). lridaea splendens is such a plant. Its perennial crust can grow f rom one to several blades which m a y surv ive for vary ing amounts of time (usually one year or less) (Hansen, 1977; as lridaea cordata). Temporal patterns which arise due to births and deaths of blades (modules) may differ f rom those which arise f rom the births 21 and deaths of the perennial crusts (the genetic individuals or genets). If the genets of a part icular phase, either gametophyte or tetrasporophyte, produce a consistently higher number of modules than the other phase, predominance itself might var j ' depending on whether modules or genets were the unit being enumerated. Work on Ranunculus repens (Sarukhan and Harper , 1973) has shown that fluctuations in population density, over t ime, can appear smal l i f the number of plants in a permanent plot is s imply counted at time one and again at t ime two. Dur ing the interval between counting, however, the number of plants recruited into, and lost f rom the plot, may be very high (if one has followed the fate of individuals). A rapid turnover at one level is masked by the appearance of less var iat ion i f measurements are taken at a different scale. The seasonal switch f rom gametophyte dominance in summer to tetrasporophyte dominance in winter , documented by DeWreede and Green (1990), was based on random sampl ing of near ly equal sample sizes dur ing al l periods when measurements were made. Measurements of seasonal changes in density were not made and Green (1989) notes that it would be of interest to establ ish, i f there is seasonal f luctuation in density, to what extent the relat ive abundances of gametophytes and tetrasporophytes contribute to the overal l var iat ion. Tha t there would be seasonal f luctuation in abundance of Iridaea splendens in Vancouver harbour seems l ikely, since A d a m s (1979, as Iridaea cordata) found such seasonal f luctuations of the reproductively mature stages in the nearby St ra i t of Georgia. 22 The discovery of demographic differences, in which rates of addition or loss of modules or genets of Iridaea splendens differed seasonally for the alternate life history stages, would further reinforce the idea of ecological differences between isomorphic life history stages. In addit ion, the fluctuation in births and deaths of modules and genets wi l l suggest, at the scale in which the module or genet is the indivisable unit of measurement, the mechanism undertying the seasonal al ternation in dominance observed by DeWreede and Green (1990). It is the description of that alternation in dominance, in terms of the under ly ing fluctuations in numbers of individuals, which is the pr imary purpose of my study. The site chosen for this study was Brockton Point in Vancouver harbour, as this work builds on what is already known about the population in that area. Sampl ing was done by contiguous quadrats along a transect and also b3 r fol lowing the progress in permanent sites selected haphazard ly around Brockton Point. These transects were sampled in order to check demographic trends in the permanent sites, which remained static, against demographic trends in the rest of Brockton Point. The sampl ing itself was done as near to monthly as tides would permit. Genets of Iridaea splendens appeared as one or more blades ar is ing f rom a common spot on a rock and closely bunched together. In the contiguous transects the number of genets was counted in each quadrat, wi th the number of modules and the reproductive condition noted for each genet. In the permanent sites the number of genets was counted in each site, wi th the number of 23 modules, reproductive condition, and life histor3 r phase, noted for each genet. The contiguous transects served as a means of comparison of the dynamics within the permanent sites to the dynamics in the rest of the population, indicating, at least to some extent, how wel l the permanent sites reflect the demographic act iv i ty of lridaea splendens at Brockton Point. Since the period of data collection (slightly more than one year) was short and the smal l perennial crusts could not be followed wi th any accuracy when not producing upr ights, this study is essential ly a demography of modules. There are, however, useful observations which can be made concerning short term behavior of genets in the population. The situation in which, for example, all genets might produce a blade at roughly the same time of year and hence the subsequent density increase is due entirely to increase in number of modules, is different f rom the situation in which more and more genets are observed producing modules as density increases. Genets then, for the purposes of this study, show themselves at var ious t imes of the year by producing one or more modules, and disappear again when al l their modules are lost. Whether or not the perennial crust remains alive at that point is unknown, although, given the smal l recrui tment rate observed by M a y (1986), it seems reasonable to assume that the overwhelming majori ty of crusts last more than one seasonal cycle. In this study it is only the modules which can be spoken of as being t ru ly gained or lost in the population. The module is the unit which was "born" and suffered mortal i ty dur ing the seasonal cycle observed, whi le genets may only accurately be discussed as hav ing appeared and disappeared. Ut i l i z ing the data obtained f rom the contiguous transects and permanent 24 sites, I intend to address the fol lowing questions; In Chapter 2: 1. Is there seasonal change in density of Iridaea splendens at Brockton Point? 2. Is var ia t ion in density a function of gain and loss of modules, appearance and disappearance of genets, or a combination of both effects? 3. A r e the dynamics described in 2 different for gametophytes and tetrasporophytes? 4. Wha t are the relative rates of seasonal increase and decrease for gametophytes and tetrasporophytes in terms of gain and loss of modules and appearance and disappearance of genets? 5. W h a t are the relat ive contributions of appearance and disappearance of genets vs gain and loss of modules to the overal l dynamics of gametophytes and tetrasporophytes? 6. A re there signif icantly more modules per genet for either phase and does such an effect, if present, va ry wi th season? In Chapter 3: 1. Wha t is the temporal pattern of the onset, peak and decline of reproductive matur i ty for cystocarpic and tetrasporangial plants? 2. Wha t are the relat ive proportions of female gametophytes and tetrasporophytes which become reproductively mature? 3. How do the dynamics of cystocarpic and tetrasporangial blades compare to the dynamics of vegetative blades? The data avai lable f rom the permanent sites wi l l facil i tate comparison of the numbers of modules and genets which are apparent f rom month to month in a • specific area, but wi l l not follow the fate of individuals dur ing the interval between measurements. It is apparent f rom Sarukhan and Harper (1973) that the results of this sort can mask potential ly higher rates of gain and loss. A site which has, for example, 20 blades in M a y and 30 in June may have gained an addit ional 10 blades dur ing the in terval , provided the ini t ial 20 all surv ived the interval . If some of the or iginal blades were lost to mortal i ty dur ing the in terval , however, the actual gain would be higher than the perceived gain. To address this problem adequately would involve fol lowing the fate of each individual blade in a site from when it is f i rst visible to when it is lost. The logistical problems wi th an enterprise of this magnitude are such that it has been attempted infrequently, even for terrestr ial p lants, and the problems are compounded by the time restrict ions imposed on sampl ing by ebbing and r is ing tides. However , for this study, two haphazard ly chosen groups of blades were successfully tagged, one in spr ing and another in fa l l . The mortal i ty rates obtained f rom these groups wi l l be employed, in Chapter 4, to suggest in some pre l iminary fashion what sort of modifications may be necessary to the results obtained from the permanent sites and contiguous transects in order to more accurately reflect the true rates of module gain and loss in lridaea splendens at Brockton Point. CHAPTER 2: SEASONAL DYNAMICS OF GENETS AND MODULES OF IRIDAEA SPLENDENS Introduction Al ternat ion in phase dominance in Iridaea splendens has been observed (Adams, 1979, as Iridaea cordata, DeWreede and Green, 1990) but the underly ing demographic mechanism is as yet unknown. Seasonal patterns of change in density and biomass, when they do occur, often show little consistency from species to species mak ing prediction in new situations difficult. This is evident in the fol lowing studies of other species, where questions s imi lar to those I am asking about Iridaea splendens were posed. Seasonal var iat ion, in both density and biomass, occurs in a var iety of marine algae. In Chordaria flagelliformis in N o v a Scotia (Rice and Chapman, 1982) decrease in density was observed over a period from late spr ing (June 2) to ear ly fal l (September 23). Concurrent wi th decrease in density per square meter came an increase in biomass per square meter, as the mean weight of individual plants increased while plants were lost f rom the population. Gunni l l (1980a), work ing in southern Cal i fo rn ia , observed that total numbers of individuals of Pelvetia fastigiata were general ly greatest f rom June to Augus t and lowest in Ap r i l and M a y . Whi le peak abundances occurred at near ly the same time each year (the period of study covered 1974 through 1977) var iat ion in the magnitude of the peak abundance from year to year was high. Cystoseira osmundacea and Halidrys dioica, studied at L a Jo l la , Cal i forn ia, (Gunni l l , 1980b) f rom 1973 to 26 1977, showed numbers of individuals, in their respective populations, increasing steadily over the entire period of the study in one site (Gunni l l , 1986), while at another rate of recruitment appeared to balance morta l i ty , resul t ing in little overal l change dur ing the course of the study. Individuals of Codium fragile, also studied at L a Jo l l a , Cal i forn ia, (Gunni l l , 1980b) were most abundant f rom August to October and least abundant in M a r c h and A p r i l . M i n i m a and m a x i m a were s imi lar between sites but varied in magnitude from year to year . Peaks in abundance generalty coincided wi th peaks in recruitment. S imi la r patterns were seen in Egregia laevigata and Eisenia arborea (Gunni l l , 1980b). Examina t ion of changes in mean densities of Laminaria longicruris and Laminaria digitata in southwest N o v a Scotia (Chapman, 1984) f rom August , 1981, to August , 1982, showed values for Laminaria longicruris remain ing fa i r ly constant over the period of study. The density of Laminaria digitata was more var iable over t ime wi th a peak in October, 1981, and a subsequent decline to J a n u a r y , 1982. Densi ty in February , 1982 was 1.8 times that of J a n u a r y , wi th the decline occurr ing in M a r c h . F r o m M a r c h to J u l y of 1982 density increased, peaking in J u l y , wi th a slight (14%) decrease in August , 1982. A l though density var ied over the course of the year , a clear seasonal pattern was not immed ia te^ evident. Observ ing growth rate in Ascophyllum nodosum and Fucus vesiculosus in estuarine populations, Sh ipman et al. (1976) noted seasonal differences, wi th m a x i m a in spr ing and fa l l , dur ing two consecutive years. Whi le increased growth rate may at times be related to increased standing crop in a part icular 28 population, this need not be the case i f increased thal lus size is responsible for increased r isk of mortal i ty. Seasonal change in standing crop was examined for three species of Sargassum in H a w a i i , by DeWreede (1976). Var ia t ion occurred between sites in terms of the t iming of m a x i m a and min ima, as well as the relat ive magnitude of the m a x i m u m standing crop. Standing crop in Sargassum oligocystum remained at a low stable level over a three year period wi th a relat ively slight m a x i m u m in Ju l y -Augus t of one year. A t a second site a m a x i m u m approximately 10 times that year 's m in imum, occurred during February of the f i rst year , and a peak of sl ightly less magnitude dur ing Februa ry -Apr i l of the second year. A t a thi rd site max imum standing crop occurred from February to m id -May . Sargassum obtusifolium had m a x i m u m standing crop in September-November in one year and Augus t to September in the year fol lowing at one site. A t another, standing crop peaked from February to M a y . Sargassum polyphyllum, over a three year period, had peaks in October, October-November, and in December. McCour t (1984) examined seasonal patterns in Sargassum johnstonii, Sargassum herporhizum and Sargassum sinicola var . camouii in the Gu l f of Cal i forn ia near Sonora, Mexico. Seasonal var iat ion in canopy cover was present, w i th al l three species reaching m a x i m a between Februa ry and A p r i l as . temperatures began to rise. Sargassum sinicola also showed a second peak in the fal l . The macroscopic sporophyte of Leathesia difformis is present for only three 29 months dur ing the summer in N o v a Scotia (Chapman and Goudey, 1983). P lants appear at approximately the beginning of June and density increases rapidly unti l near the end of June. Increase in density f rom the beginning to the end of J u l y is slight, followed by rapid decrease in density f rom the beginning of Augus t to the beginning of September. Fur ther decline is sl ight f rom the beginning of September to mid-way through the month when the last of the macrothal lus population usual ly dissappears. The macroscopic sporophyte alternates wi th a filamentous gametophyte which is not recognizable in the field, mak ing it impossible to say whether there is temporal segregation of the alternate phases, or whether only the sporophyte is temporal ly constrained. Seasonal abundance of the upright forms of Petalonia fascia and Scytosiphon lomentaria were followed for one year near Fo r t Const i tut ion, N e w Hampsh i re (Shannon et al., 1988), as were the alternate crustose forms. M e a n percent cover in permanent plots showed a s imi lar pattern for both genera. Scarci ty in ear ly autumn was followed b}r m a x i m u m abundance in December and scarcity again in late winter. Both genera also showed a second, smal ler peak in abundance, Petalonia fascia in spr ing and Scytosiphon lomentaria in ear ly summer. Abundance of the crustose form showed no clear seasonal pattern. These examples demonstrate no pattern of seasonal abundance common to mar ine macroalgae in general. In addition there is frequently wide var iat ion wi th in a part icular species f rom site to site. In lridaea splendens standing crop has shown seasonal var iat ion, w i th summer values five to six t imes higher than winter values (Hansen and Doyle, 1976, as lridaea cordata). This pattern for 30 Iridaea splendens in Cal i forn ia appears also to hold true for Iridaea laminarioides in central Chi le (Hannach and Santel ices, 1985). In Iridaea splendens in central Cal i forn ia , density of vegetative thal l i peaked in winter, while density of cystocarpic thal l i peaked in spr ing and summer, and density of tetrasporangial thal l i peaked in fal l (Hansen and Doyle, 1976; Hansen , 1977, as Iridaea cordata). In the St ra i t of Georgia, Br i t i sh Columbia, (as mentioned in Chapter 1) Iridaea splendens showed a peak in standing crop f rom June through J u l y . Pr ior to the peak there was a rapid spr ing increase in standing crop, and fol lowing the peak a rapid fal l decline to low winter levels. Seasonal change in density followed the same pattern, wi th peak densities of cystocarpic and tetrasporic thal l i s imi lar to those in Cal i forn ia (Adams, 1979, as Iridaea cordata). A t Brockton Point in Vancouver Harbour , Br i t i sh Columbia, DeWreede and Green (1990) found a regular alternation in the population structure of Iridaea splendens between gametophyte dominance f rom June through Augus t to tetrasporophyte dominance from December through February . The pattern persisted over three consecutive years. A l though seasonal f luctuation in standing crop need not be directly related to f luctuation in density, it seems from the work of Hansen and Doyle ( i976) , Hansen (1977), and Adams (1979) that it is l ikely to be an approximately direct relat ionship in Iridaea splendens. If the pattern bf seasonal var iat ion in density at Brockton Point follows the pattern in the Stra i t of Georg ia, wi th wide f luctuation f rom min ima in winter to m a x i m a in summer, there appear to be four basic ways in which densities of gametophytes and tetrasporophytes could 31 va ry to produce the pattern of seasonal alternation of phase dominance observed by DeWreede and Green (1990). 1. Gametophyte density may fluctuate widety while tetrasporophyte density mainta ins a lower but very steady level (Fig. 2.1, No . 1). 2. Gametophyte density may fluctuate widely while tetrasporophyte density f luctuates less widely. Tetrasporophyte density peaks dur ing the winter while gametophyte density peaks in summer (Fig. 2.1, No . 2). 3. Gametophyte density may fluctuate widely while tetrasporophyte density f luctuates less widely. Rates of density increase and decrease may be lower for tetrasporophytes than for gametophytes so that, whi le m in ima and m a x i m a are in the same seasonal position for both phases, the magnitude of the gametophyte peak is greater in summer and the m in imum lower in winter, than the respective max imum and m in imum of the tetrasporophytes (Fig. 2 .1 , No . 3). 4. F ina l l y , the situation may be as mentioned in No . 3, but wi th a time lag offsetting either the spr ing density increase or the fal l decrease, or both, in the tetrasporophyte component of the population. A lag might indicate response to a different environmental tr igger in tetrasporophytes rather than simply a slower physiological response to the same st imul i (Fig. 2.1, No . 4). In this chapter I w i l l describe overal l f luctuations in density of lridaea splendens at Brockton Point, both in terms of numbers of genets present and in terms of modules. This overall var iat ion wi l l be broken down into seasonal 32 patterns of var iat ion wi th in the gametophyte and tetrasporophyte components of the population, wi th the intention of examin ing which of the four models (Fig. 2.1) best describes the way in which alternation of phase dominance occurs wi th changing density. 33 Figure 2.1 Four possible mechanisms, in terms of seasonal f luctuation in density of gametophytes and tetrasporophytes of Iridaea splendens, by which seasonal alternation of phase dominance may occur. Gametophytes -Tetrasporophytes maxl (TJ w max [3] min maxl (4) J F M A M J J A S O N D J F M A M J J A S O N D TIME 34 Methods and Materials Permanent sites at Brockton Point were chosen haphazardly f rom the total set of areas in which Iridaea splendens was present. In order not to introduce a seasonal bias in the permanent sites, roughly hal f were chosen dur ing the summer and hal f dur ing the winter. Seventeen sites were chosen dur ing August , 1988, and another nineteen in December, 1988. Each permanent site was on the vert ical or sloping face of a rock large enough to be in no danger of being displaced by wave action. The upper edge of the rock face and the lower intersection of rock and sandy substratum formed the upper and lower boundaries of each site. The r ight and left boundaries were marked wi th 1 cm diam. steel reinforcement rod, 50 cm in length, dr iven 35 cm into the sandy substratum. A piece of 5 cm d iam. P V C tubing, 20 cm in length, was placed over the protruding end of the rod and secured to the rod by f i l l ing it w i th fast setting concrete. N e a r each site an addit ional rod was dr iven into the substratum. To this a 50 - 60 cm long piece of 2 m m diam. plastic coated wire was attached. A t the tip of the wire a plastic tag wi th the number of the site and 15 - 20 cm of orange f lagging tape was attached, increasing visibi l i ty of the site locations for low tides dur ing the night in winter. The 36 permanent sites were sampled 12 times over the period from J a n u a r y 1, 1989, to February 28, 1990. The dates of sampl ing were J a n u a r y 5 - 11, Februa ry 3 - 5, Ap r i l 7 - 8, M a y 4 - 8, June 1 - 6, June 29 - J u l y 5, J u l y 28 - Augus t 1, October 17 - 19, November 12 - 15 and December 10 -12 during 1989, and J a n u a r y 8 - 1 3 and February 6 - 7 in 1990. A l l 36 permanent sites were between 0.1 and 0.8 meters above Canad ian Char t Da tum (Anonymous, 1989, 1990). Dates of sampl ing were constrained by those periods dur ing which the sites would be emersed. The height each site occupied in the intert idal is given in F i g . 2.2. In each site, each blade present was sampled by removal of a 0.5 cm d iam. disk wi th a single hole paper punch. A l l disks were wrapped in tissue paper for dry ing. Only disks taken from blades presumed to be par t of a single genet were wrapped together. In this way the number of genets, and number of modules (blades) for each genet, were calculated for each site dur ing each sampl ing period. Fo r the months f rom A p r i l , 1989, to Februa ry , 1990, the reproductive condition of each genet was also noted. 37 Figure 2.2 The vert ical range of each of the 36 permanent sites in relation to Canadian Char t Da tum. oo 2 D < 0 h < X o z < Q < z < o UJ > o CQ < I-X CJ UJ X 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 21 2 2 23 24 25 26 27 28 29 30 31 32 33 34 35 36 S I T E N U M B E R 39 The dried disks were analyzed wi th resorcinol reagent (Craigie and Le igh , 1978) according to the modifications by Dyck et al. (1985). A i r dried disks of tissue were each placed in individual test tubes. Two ml of resorcinol reagent was added to each tube. The tubes were then placed in a hot water bath heated to 80 C for 2 - 3 minutes. Posit ively react ing thal l i (gametophytes containing predominantly kappa-carrageenan) turned a deep red. Negat ive ly react ing thal l i (tetrasporophytes containing predominant ly lambda-carrageenan) were colourless to pale pink. Reproductively mature tissue of both gametophytes and tetrasporophytes was included wi th each batch of samples to ensure that the reagent was giving the correct results. Shaughnessy and DeWreede (1991) have demonstrated this to be an extremely reliable tool for identi fying the isomorphic non-reproductively mature phases of three species of Iridaea including Iridaea splendens. Contiguous transects were also sampled in order to check whether the demographic patterns seen in the permanent sites were representative of the demographic patterns in Iridaea splendens over Brockton Point as a whole. The patterns in the 36 permanent sites were compared to the pattern in plants encountered in a lateral wa lk around the point fol lowing the path of ebbing and ris ing tide. 2 A la teral transect of contiguous 0.25 m quadrats was sampled approximately monthly. Since the number of days that the population of Iridaea splendens was emersed var ied between cycles of low tides, there were periods when only enough days were avai lable to examine the permanent sites wi th no 40 t ime remain ing to sample a contiguous transect. This was the case in A p r i l , 1989, and in February , 1990. In total there were eight dates sampled by contiguous transect, February 5, M a y 9, June 6, J u l y 4, October 19, November 14, and December 12 in 1989, and J a n u a r y 10, 1990. E a c h transect was begun paral lel to the viewpoint at the southern end of Brockton Point. Sampl ing took place dur ing the time from one hal f hour before lowest low water to one hal f hour after. The path of the quadrats followed the path of lowest low water f rom below the viewpoint nor thward to just below the 2 l ighthouse. E a c h transect consisted of 230 - 240 0.25 m quadrats, and s imi lar distances were covered for each date. E a c h contiguous transect was done when lower low water would be as near to 0.5 m as was possible in that t idal cycle to ensure that the same general area of the intert idal was sampled each period. Placement of quadrats along each contiguous transect was free f rom personal bias in that it was dictated by the path traced by the ebbing and r is ing tide. In each quadrat the number of genets was counted wi th the number of modules per genet and reproductive condition was noted. 2 Change in density of genets and modules per 0.25 m surface area of subst ra tum, regardless of substratum type, was calculated using data from the contiguous transects. Sampl ing periods were compared pairwise to determine the time frame over which stat ist ical ly signif icant change (probability equal to or less than 0.05) occurred. Signif icant values are indicated in the tables by an asterisk. Bar t le t t 's tests for homogeneity of var iance indicated that homogeneity of var iance was present infrequently. Cer ta in data sets also did not improve in normal i ty of distribution fol lowing transformat ion. In the interest of consistency, therefore, al l comparisons were done using the M a n n Whi tney U Test (Sokal and Rohlf, 1973), a non-parametr ic, distr ibution free method. Rates of density increase or decrease between sampl ing periods were calculated as change in mean number of genets 2 or modules per 0.25 m per month. 2 Change in density of genets and modules per 0.25 m of substratum known to be support ing Iridaea splendens was examined using data f rom the permanent sites. The surface area of each site was measured and the count of 2 genets and modules for each site adjusted to the number per 0.25 m of site surface. Sampl ing periods were compared pairwise to determine the time frame over which stat ist ical l j ' signif icant change (probability equal to or less than 0.05) occurred. A g a i n Bart let t 's tests showed little homogeneity of variance and transformat ion of data was not universal ly successful so that comparisons were made wi th the M a n n Whi tney U Test. Rates of density increase or decrease were calculated as for the contiguous transects. A l l manipulat ions performed wi th the data f rom the permanent sites, which had been adjusted for surface area, were repeated wi th the non-adjusted data to observe i f there was any change in trends. Rates of increase and decrease were calculated on a per site basis us ing the non-adjusted data. Densi ty differences between modules and genets wi th in each sampl ing period were examined for data obtained f rom the contiguous transects and from the permanent sites. Comparisons were made using the M a n n Whi tney U Test. Since wi th in month calculations concerned only the densities of genets and modules relat ive to each other, quadrats and sites containing no plants were not included in the analysis. U s i n g this same procedure, densities of gametophytes were compared to those of tetrasporophytes wi th in each month sampled. Comparisons were done for both genets and modules using the data adjusted for surface area. S imi lar comparisons were made using the data not adjusted for surface area although density was not calculated in the absence of a unit area base. The presence of the same demographic patterns on a per unit area basis and on a per site basis would indicate that the same fundamental demographic pattern is repeated, on average, f rom site to site. U s i n g data from the permanent sites the number of modules per genet, for gametophytes vs. tetrasporophytes, was compared wi th in each sampl ing period. Change in number of modules per genet over t ime was observed using both data f rom the contiguous transects and f rom the permanent sites. A l l analyses were performed wi th the M a n n Whi tney U Test. 43 Results o Genets and modules in the contiguous transects. The results of the temporal comparisons performed on data f rom the contiguous transects are detailed in Appendix L (Table 1 for genets and Table 2 2 for modules). The pattern of mean number of genets per 0.25 m of substratum consistently followed the pattern of change in modules (Fig. 2.3), although alwa3's at a lower rate. Th is same pattern was evident when the combined totals for al l quadrats sampled dur ing a part icular month were followed over time (Appendix A , F i g . 1) The most conspicuous difference between the results f rom the contiguous transects and those from the permanent sites was the stat ist ical ly signif icant increase in density of genets and modules from October, 1989, to November , 1989, present in the data from the contiguous transects but not in that f rom the permanent sites. Genets and modules in the permanent sites. The results f rom the permanent sites, adjusted for surface area, also showed density change in genets paral le l ing that of modules (Fig. 2.4). These results are detailed in Appendix I (Table 3 for genets and Table 4 for modules). The results f rom the permanent sites, not adjusted to compensate for unequal surface areas between sites, showed a very s imi lar pattern (Appendix B, F i g . 1) to that in the adjusted data. The results of the comparisons between sampl ing periods are detailed in Appendix A , Table 1 (for genets) and Appendix A , Table 2 (for modules). 44 Figure 2.3 Seasonal change in density of modules and genets of lridaea splendens over all substrata (data from the contiguous transects). Means (modules or genets/0.25 2 m ) plus and minus one standard error. 4 6 Figure 2.4 Seasonal change in modules and genets of Iridaea splendens in the permanent sites (Data adjusted to compensate for unequal surface areas between sites). 2 Means (modules or genets/0.25 m ) plus and minus one standard error. J F A M J J A O N D J F S A M P L I N G P E R I O D 48 Gametophyte vs. tetrasporophyte genets in the permanent sites. Seasonal changes in mean density of gametophyte and tetrasporophyte genets (using data from the permanent sites, adjusted for surface area) produced a pattern where the predominant proportion of the population was tetrasporophyte f rom December, 1989, to February , 1990, and the predominant proportion of the population was gametophytic f rom A p r i l to October, 1989 (Fig. 2.5). The change f rom tetrasporophyte to gametophyte dominance occurred in the interval between February and Ap r i l and the reversal occurred in November. The results of the comparisons between sampl ing periods are detailed in Appendix I (Table 5 for gametophytes and Table 6 for tetrasporophytes). Relat ive changes in the number of gametophyte and tetrasporophyte genets per site (Appendix B, F i g . 2) followed the same pattern as the results based on density. The details of comparisons between sampl ing periods are given in Appendix A , Table 4 (for tetrasporophytes) and Appendix A , Table 3 (for gametophytes). One instance of a stat ist ical ly signif icant increase changed as a result of examinat ion on a per site basis. November - December, 1989, which had a P-value of 0.038 using the data adjusted for surface area, had a P-value of 0.063 using the non adjusted data. 49 Figure 2.5 Seasonal changes in genet density in gametophytes vs. tetrasporophytes of lridaea splendens in the permanent sites (data adjusted for surface area). Means 2 (genets/0.25 m ) plus and minus one standard error. J F A M J J A O N D J F S A M P L I N G P E R I O D 51 Gametophyte vs. tetrasporophyte modules in the permanent sites. Relat ive change in the mean densities of gametophyte and tetrasporophyte modules in the permanent sites, adjusted for surface area (Fig. 2.6), followed a very s imi lar pattern to that previously seen for gametophyte and tetrasporophyte genets (Fig. 2.5). Detai ls of the comparisons between sampl ing periods are given in Appendix I (Table 7 for gametophytes and Table 8 for tetrasporophytes). Relat ive changes in the mean number of gametophyte and tetrasporophyte. modules per site (Appendix B , F i g 3) followed the same pattern as the results based on density. Detai ls of the comparisons are given in Appendix A , Table 5 (for gametophytes) and Appendix A , Table 6 (for tetrasporophytes). Compar isons wi th in sampl ing periods When comparing the distr ibutions of gametophyte vs. tetrasporophyte genets wi th in individual sampl ing periods, results f rom the permanent sites, adjusted for surface area (Table 2.1), showed signif icant differences in al l periods except J a n u a r y , October and November, 1989. The same comparisons made wi th the non-adjusted data (Appendix A , Table 8) showed an identical pattern. Results for modules (Table 2.2) were the same as for genets wi th the exception of Janua ry , 1989 which showed a signif icant difference for modules but not for genets. The results for modules when the non-adjusted data was used (Appendix A , Table 9) were s imi lar . 52 Figure 2.6 Seasonal change in module density in gametophytes vs. tetrasporophytes of lridaea splendens in the permanent sites (data adjusted for surface area). Means 2 (modules/0.25 m ) plus and minus one standard error. J F A M J J A O N D J F S A M P L I N G P E R I O D 54 T A B L E 2.1 Gametophyte vs. tetrasporophyte genets within sampling periods in permanent sites adjusted for surface area Comparisons of the distribution of gametophyte and tetrasporophyte genets within each sampling period. Given with each comparison are the means, standard errors, and the probability of the null hypothesis that the distributions are equivalent. Sampling Comparison Mean S. E . P-Value Period January/89 Gam. •2.21 0.44 Tet. 2.68 0.39 0.152 February/89 Gam. 0.35 0.15 * Tet. 2.00 0.34 0.000 April/89 Gam. 7.54 1.43 * Tet. 2.79 0.68 0.000 May/89 Gam. 11.62 2.38 * Tet. 6.08 1.35 0.019 June/89 Gam. 13.12 2.57 * Tet. 6.51 1.50 0.006 July/89 Gam. 10.41 2.70 * Tet. 5.06 1.16 0.009 August/89 Gam. 11.08 2.95 * Tet. 5.16 1.52 0.002 October/89 Gam. 4.89 1.19 Tet. 4.05 0.86 0.664 November/89 Gam. 3.49 1.14 Tet. 3.53 0.79 0.387 December/89 Gam. 2.13 0.77 * Tet.. 3.81 0.72 0.002 January/90 Gam. 0.71 0.15 * Tet. 2.70 0.47 0.000 February/90 Gam. 0.40 0.12 Tet. 2.06 0.47 0.000 T A B L E 2.2 Gametophyte vs. tetrasprophyte modules wi th in sampl ing periods in permanent sites adjusted for surface area Comparisons of the distr ibution of gametophyte and tetrasporophyte modules wi th in each sampl ing period. G iven wi th each comparison are the means, standard errors, and the probabil i ty of the nul l hypothesis, that the distributions are equivalent. Sampl ing Compar ison M e a n S. E . P-Value Period Januar j r /89 G a m . 2.95 0.57 * Tet. 4.84 0.68 0.023 February /89 G a m . 0.46 0.18 * Tet. 3.28 0.60 0.000 Apr i l / 89 G a m . 14.18 2.76 * Tet. 6.35 1.62 0.003 M a y / 8 9 G a m . 20.40 3.77 * Tet. 10.58 2.08 0.029 June/89 G a m . 21.37 3.77 Tet. 11.14 2.13 0.019 Ju l y /89 G a m . 14.45 3.16 * Tet. 7.62 1.54 0.016 Augus t /89 . G a m . 15.29 3.46 * Tet. 7,89 1.89 0.014 October/89 G a m . 6.84 1.61 Tet. 5.23 0.95 0.787 November/89 G a m . 4.12 1.18 Tet. 4.51 0.89 0.204 December/89 G a m . 2.54 0.81 * Tet. 4.68 0.79 0.002 Janua ry /90 G a m . 0.80 0.18 * Tet. 3.37 0.52 0.000 February /90 G a m . 0.45 0.14 * Tet. 2.55 0.56 0.000 56 Number of modules per genet Compar ing the distr ibution of modules per genet in the permanent sites between gametophytes and tetrasporophytes wi th in each sampl ing period (Appendix I, Table 9) showed stat ist ical ly signif icant differences in two periods, Janua ry and November, 1989. Change in number of modules per genet in the contiguous transects followed a s imi lar pattern over time for both gametophytes and tetrasporophytes (Fig. 2.7). Change in number of modules per genet over t ime, using data f rom the contiguous transects (Appendix I, Table 10) showed signif icant decreases from M a y to June , 1989, and from J u l y to October, 1989. No periods of signif icant increase were evident. D a t a f rom the permanent sites (Appendix I, Table 11) showed a signif icant increase f rom Februa ry to A p r i l , 1989, and signif icant decreases in mean number of modules per genet f rom M a y to June , 1989, f rom June to J u l y , 1989, and f rom Augus t to October, 1989. The pattern of change in modules per genet was s imi lar in the contiguous transects and the permanent sites (Fig. 2.8) for the two signif icant periods of decrease. The mean number of modules per genet in Feb rua ry , 1989, however, was much higher in the data f rom the contiguous transects than for the same period in the permanent sites; and the period from October, 1989, to J a n u a r y , 1990, showed wider f luctuation in the contiguous transects than in the permanent sites, where change after November, 1989, was min imal . 57 Figure 2.7 Seasonal change in number of modules per genet for gametophytes vs. tetrasporophytes of lridaea splendens. 59 Figure 2.8 Seasonal change in number of modules per genet of Iridaea splendens (both phases combined) in data from the contiguous transects and the permanent sites. 61 Discussion The pattern of overal l density change in Iridaea splendens, at Brockton Point, followed the pattern observed by A d a m s (1979) in the Strai t of Georgia, w i th density lowest in winter and highest in summer. Th is basic pattern was the same in the data from the contiguous transects (Fig. 2.3), and for the data f rom the permanent sites, both when adjusted for surface area (Fig. 2.4) and when not adjusted (Appendix B, F i g . 1). This symmet ry suggests that the pattern is not l ikely to be an art i fact of sampl ing certain areas of Brockton Point rather than others. This same overal l pattern was observed for both modules and genets wi th some var iat ion in rates of increase and decrease. Densi ty on substratum known to be supportive of Iridaea splendens (data f rom the permanent sites) was consistently higher than on al l substratum regardless of type (data f rom the contiguous transects). Since the permanent sites 3 consisted of large rocks (0.02 m or larger) while the contiguous transects included sand, gravel , cobble and large rocks, this indicates that larger rocks better support the growth of Iridaea splendens. Because the persistence of Iridaea splendens at a site is thought to be largely a result of perennation (Hansen, 1977, M a y , 1986, as Iridaea cordata) and since new recruits may take six to twelve months to appear (Green, 1989, as Iridaea cordata), i t seems l ikely that plants would persist most ly on larger rocks which would be less l ikely to shift due to wave action and bury or abrade crusts, holdfasts, or new recruits. One difference between the dynamics seen in the contiguous transects and 62 those in the permanent sites is the increase f rom October to November, 1989, seen only in the contiguous transects. The increased density in November, 1989, might be a chance product of the path taken by the transect, possibly t ravel l ing through a larger number of patches of Iridaea splendens dur ing that month than previously or subsequently. If this November increase was not an art i fact, the question arises as to why it did not appear in the results f rom the permanent sites. One possibil i ty is that, through the loss of some canopy species, Iridaea splendens previously exist ing as minute juveni les might then grow sufficiently (to a length greater than 5 cm) to be counted in the next month, producing a peak. Laminaria sp. which were present at Brockton Point f rom summer to early fal l and were more frequently encountered in the contiguous transects than in the permanent sites, and may be a pr imary candidate for such a canopy species. Ava i lab le data on c growth rates in Iridaea splendens, however, do not support this speculation. Whi le rapid growth has been observed for Iridaea splendens in spr ing (Hansen, 1977, as Iridaea cordata) the autumn growth rates in the Cal i forn ia populations were the lowest of the year. Unless autumn-winter growth rates prove higher in Br i t i sh Co lumbia than in Cal i forn ia one month growing time may not be sufficient to produce a noticable increase after removal of canopy plants. In the results f rom the permanent sites the spring increase can be broken into two stat ist ical ly signif icant periods of increase. The f irst period, Feb rua ry -Ap r i l , 1989, showed lower rates of increase for both modules and genets than the second period, A p r i l - M a y , 1989. Whether or not ini t ia l spr ing 63 rates of increase in densit37 are actual ly lower than those later in spr ing is not known since there were no tides low enough for sampl ing dur ing the month of M a r c h , 1989. If density remained at the winter low unti l the beginning of M a r c h and then started to increase there would be little difference in rates between the two periods. In the fal l decrease in density the periods August-October, 1989, October, 1989-January , 1990, and January -Feb rua ry , 1990 (each showing a stat ist ical ly signif icant decrease for both modules and genets) showed progressively lower rates of decrease wi th each successive period. It is possible that the major i ty of those blades not hardy enough to wi thstand the increased wave action that occurs wi th the onset of fal l storms are removed earl ier in the fal l leaving the hardier individuals to be lost at lesser rates as winter progresses. The pattern of change in density of gametophytes of lridaea splendens was simi lar for both genets and modules, and remained consistent for analyses performed on the data adjusted for surface area (Fig. 2.5, 2.6) and on the non-adjusted data (Appendix B , F igs . 3,5). Densi ty change in gametophytes was simi lar to the pattern of overal l change. There was a rapid spr ing increase in density, wi th a peak dur ing the summer. The fal l decrease in density of gametophytes, l ike the overal l decrease, had rates of decrease lessening over t ime. The pattern of change in density of tetrasporophytes of lridaea splendens was s imi lar for both genets and modules and for analyses performed on the data 64 adjusted for surface area (Figs. 2.5, 2.6) and on the non-adjusted data (Appendix B, F igs . 3,5). Un l ike gametophytes, tetrasporophyte modules and genets showed no signif icant increase in the late winter-early spr ing (February-Apr i l , 1989). The sharp spr ing increase in densit j ' was delayed unti l Apr i l -Ma3 ' , 1989, dur ing which the rate of mean increase i n . tetrasporophyte genets was slightty less than that for gametophytes. The spr ing increase in density was not only delayed in the tetrasporophyte portion of the population, but rates of increase were lower as wel l , more marked ly so for modules (Fig. 2.6) than for genets (Fig. 2.5). The fal l decline in density proceeded at a much slower rate for tetrasporophytes than for gametophytes. There was a signif icant decrease in density of tetrasporophyte genets between June and November, 1989 and a signif icant decrease in tetrasporophyte modules between June and October, 1989. Both modules and genets showed a relat ively slow steady rate of loss for the period from August to December, 1989, followed by a more rapid decrease f rom December, 1989, to February , 1990. Rate of decrease in density of tetrasporophytes dur ing this last period was higher than the rate of decrease for gametophytes but the tetrasporophyte portion of the population never reached the very low density levels characterist ic of the gametophyte portion. The pattern discussed above corresponds best to the last of the four models proposed in the introduction to this chapter (Fig. 2.1 No . 4). The pattern of alternation of phase dominance observed in this study corresponds to the pattern observed by DeWreede and Green (1990) over a three year period, wi th gametophyte dominance in spr ing and summer, and tetrasporophyte dominance in winter. It also corresponds to the summer gametophyte dominance observed on San J u a n Island (May, 1986, as Iridaea cordata). Examinat ion of the distributions of gametophytes and tetrasporophytes wi th in each sampl ing period (Table 2.1, 2.2) supports the argument that these two phases of the population follow different seasonal dynamics. The distributions were signif icantly different wi thin al l sampl ing periods except October and November, 1989, the period dur ing which the fal l crossover between gametophyte and tetrasporophyte dominance took place. In examin ing whether either phase produced more modules per genet than the other, signif icant differences were found only for J a n u a r y and November, 1989 (Appendix I, Table 9; F i g . 2.7). Both indicated a larger number of modules per genet for tetrasporophytes, and this was the case for the non-signif icant comparisons as well (with the single exception of December, 1989). However , given the fact that the signif icant difference seen in J a n u a r y , 1989, was not repeated in Januar3', 1990, and the large number of comparisons which were not signif icant ly different, it appears prudent to conclude at this t ime that neither phase produces more modules per genet, overal l , than the other. The differences . in seasonal dynamics between gametophytes and tetrasporophytes of Iridaea splendens adds to the evidence f rom DeWreede and Green (1990) in suggesting that Iridaea splendens, l ike Iridaea laminarioides and Iridaea ciliata (Hannach and Santel ices, 1985), shows ecological differences between the isomorphic phases. Whi le Hannach and Santelices (1985) worked wi th reproductively mature blades, showing a peak abundance of cystocarpic blades 66 prior to the peak in tetrasporangial blades, m in imum and max imum densities of gametophytes and tetrasporophytes (regardless of reproductive matur i ty) of lridaea splendens at Brockton Point occurred at the same t ime, but wi th density of gametophytes f luctuat ing more widely over the year than density of tetrasporophytes. In contrast to lridaea laminarioides (Hannach and Santel ices, 1985) which showed the greatest magnitude of f luctuation in tetrasporangial blades, lridaea splendens displayed the largest magnitude of f luctuation in gametophytes. Fol lowing the argument made by Hannach and Santelices (1985) this suggests that it is the gametophyte of lridaea splendens which is more sensitive to seasonal conditions than the tetrasporophyte. W i th lridaea laminarioides in Chi le (Hannach and Santel ices, 1985), cystocarpic blades both exhibited less seasonal f luctuation, and were more abundant over the year than tetrasporangial blades. Th is caused Hannach and Santelices (1985) to question the general val id i ty of a series of common statements about the -adaptive advantages of diploidy over haploidy (Stebbins and H i l l , 1980; Stansf ield, 1977; Bar i lo t t i , 1971). The situation is less clear for lridaea splendens at Brockton Point. Overa l l , gametophytes outnumbered tetrasporophytes by virtue of the high densities reached dur ing the summer peak. Tetrasporophytes however, by hav ing less seasonal f luctuation, seem less sensitive to the environmental changes occurr ing wi th season, and therefore appear hardier. Th is makes the matter of adaptive advantage for either phase of lridaea splendens much more of an open question than w i th lridaea laminarioides. Gametophytes of lridaea laminarioides showed opt imum growth at higher 67 temperatures and longer daylengths than tetrasporophytes (Luxoro and Santelices, 1989). W i th Iridaea splendens however, the rapid appearance of genets and addition of modules occurred f i rst among gametophytes. The delay in increased densit j ' of tetrasporophytes in spr ing indicates that the opt imum growth conditions for gametophytes and tetrasporophytes of Iridaea splendens may be different f rom those of Iridaea laminarioides not only in terms of the part icular values of the opt ima, but in terms of which phase responds preferential ly to higher temperature and longer daylength. A l ternat ive ly , tetrasporophytes may require a photoperiod of a certain length to init iate the rapid spr ing increase in density. A photoperiodic response in i t iat ing production of macrothal l i f rom a crustose microthal lus has been demonstrated for Dumontia contorta (Reitema, 1982), which responded to a period of 31 or more short-day cj'cles. Tetrasporophytes of Iridaea splendens may respond wi th a sharp increase in the rate of init iat ion of new blades in the longer A p r i l - M a y photoperiods while gametophytes are able to respond to the shorter daylengths in Ma rch -Ap r i l . St i l l another possibil i ty is, since the sampl ing took place over 14 months f rom J a n u a r y , 1989, to February , 1990, and the February -Apr i l period was not replicated, that there is var iat ion in the onset of the spr ing density increase for both gametophytes and tetrasporophytes. F a l l and winter are frequently associated wi th storms and increased wave act iv i ty. The lower rates of decrease in density of tetrasporophytes vs. gametophytes in fal l and ear ly w in te r . may reflect an increased abil i ty on the par t of tetrasporophytes to wi thstand wave action. Th is is consistent wi th observations made by Dyck et al. (1985) in which signif icantly larger numbers of tetrasporophytes were found in areas of higher wave exposure, while 68 gametophytes predominated in areas of lower wave exposure (at F i r s t Beach, Ba rk ley Sound). In J u l y , 1982, at Otter Rock, Cal i forn ia, sampl ing of both attached blades at the site, and blades in the drift, revealed attached blades to be 11% gametophytic while blades f rom the drift were 68% gametophytic (Dyck et al., 1985, as Iridaea cordata). Th is provides another indication that tetrasporophytes of Iridaea splendens may be more resistant to removal by wave action than gametophytes. Both the pattern of density change wi th season, for modules and genets of both phases of Iridaea splendens combined, and the pattern of density change in modules and genets of gametophytes vs. tetrasporophytes, are unambiguous. The pattern of change in the number of modules per genet over t ime is less so. The number of modules per genet f rom the contiguous transects (Fig. 2.8) showed a signif icant decline dur ing M a y - J u n e , 1989, and July-October, 1989, and no stat ist ical ly signif icant changes in any other period. Results f rom the permanent sites (Fig. 2.9) showed a signif icant increase in number of modules per genet dur ing Feb rua ry -Ap r i l , 1989, and signif icant decreases in May -June , June -Ju l y , and August-October, 1989. Both sets of results showed a signif icant decrease in modules per genet dur ing the M a y - J u n e period and another in the late summer-ear ly fal l (July-October for the contiguous transects, August-October for the permanent sites). In both sets of results the rates of decrease in spring - ear ly summer are higher than those in late summer - fa l l . In both sets of results there was no signif icant change in number of modules per genet dur ing the winter. 69 Diff icult ies arise in comparing the results from the contiguous transects wi th those f rom the permanent sites for the period from late winter to ear ly spr ing. The decline in modules per genet which begins in Ap r i l in the permanent sites, and in M a y in the contiguous transects, may s imply be due to the absence of sampl ing a contiguous transect in A p r i l . However , the signif icant Feb rua ry -Apr i l increase in modules per genet, present in the results f rom the permanent sites, is absent in the results f rom the contiguous transects. In addition, the number of modules per genet occupied roughly the same range in J a n u a r y and February , 1989, as in Janua ry and February , 1990, for the results f rom the permanent sites, while winter f igures for the contiguous transects were very different comparing February , 1989, wi th Janua ry , 1990. There is no apparent reason why number of modules per genet should be different when considering substrata of al l types (the contiguous transects) as opposed to larger rocks (the permanent sites). A l though the values for winter, 1989, are quite different between the two sets of results, they are much closer in the second winter. Th is suggests there wi l l be var iat ion in the pattern from year to year . The sharp decline in modules per genet in spr ing and ear ly summer , and the lesser rate of decline in late summer and fal l , however, were evident . in both the data f rom the contiguous transects and from the permanent sites. Therefore, even though there is ambiguity in other aspects, there does appear to be a trend of decline in number of modules per genet. This decline begins in A p r i l - M a y wi th an in i t ia l ly high rate which changes to a lesser rate of decline f rom Ju l y -Augus t to October-November. 70 For there to be a decline in modules per genet f rom a spr ing high to a winter low there must be some increase during another season (allowing that var iat ion in number of modules per genet is in fact a cycl ical , seasonal occurrance). F o r this reason it seems that the results f rom the permanent sites may be more useful in approximat ing the trend in the population than those from the contiguous transects. Examin ing the slopes of the lines for modules vs. genets dur ing the spring density increase (Fig. 2.4) showed the slope of the line for module density was 1.9 t imes that for genet density f rom February to A p r i l , 1989. F r o m A p r i l to M a y , 1989, the slope of the module line was 1.59 times that of the genet l ine; and f rom M a y to June, 1989, the slope of the module line was 1.22 times that of the genet l ine. This is another indication that the number of modules per genet becomes progressively fewer in the months following Ap r i l . Th is trend, to the degree that it is an accurate reflection of seasonal var iat ion in numbers of modules per genet of lridaea splendens, indicates that, concurrent wi th the rapid spr ing increases in density of modules and genets, there is an increase in numbers of modules per genet. Th is increase, however, appears very short-l ived in that the number of modules per genet peaks between Ap r i l and M a y , subsequently decl ining unt i l February . Green (1989) observed that on rocks cleared in June , 1989, it took near ly 12 months for lridaea splendens (as lridaea cordata) to become re-established. Rocks cleared in November, 1986, showed new growth of lridaea splendens by M a y , 1987, as did rocks cleared in Janua ry , 1987. G iven this required t ime for germination and production of one or more noticeable uprights, most new recruits in the population would show up in M a y or later. If the majority of the density increase in modules and genets dur ing the earl ier par t of the spr ing were due to regeneration f rom perennial crusts whi le the establ ishment of new recruits became increasingly important later in spr ing, and if regenerating plants have signif icantly more modules per genet than new recruits, then the decline in number of modules per genet may be due to an increasing contribution of new recruits to the change in density as spr ing progresses. M a y (1986) found regeneration contributed 80%, and recrui tment 20%, to a population of Iridaea splendens (as Iridaea cordata) on San J u a n Is land, Washington. If the peak in terms of modules per genet for Iridaea splendens at Brockton Point were in the month of M a y (as is the case in the results f rom the contiguous transects) the subsequent decline in numbers of modules per genet would correspond well to when the Brockton Point population reached approximately 80% of its June m a x i m u m . It would also correspond to when new recruits were most l ikely to appear (Green, 1989). If the peak number of modules per genet is in A p r i l (as is suggested by the results f rom the permanent sites) the decline in number of modules per genet would not correspond as wel l to the expected percentage of the population result ing f rom regeneration (genets in A p r i l were 53% of the June max imum) or to the expected time of appearance of new recruits. T ime needed for germinat ion and production of uprights, however, may vary f rom year to year , and there may be considerable overlap in the contributions of regeneration and recrui tment to increasing spr ing density. The proportions of the contributions of recrui tment and regeneration to the population at Brockton Point may also be different f rom those on San J u a n Island, and so this explanation need not be ruled out. 72 In conclusion, there is marked seasonal change in density of both genet and modules of lridaea splendens at Brockton Point, Vancouver . The same general pattern is followed by both modules and genets, wi th m a x i m a in June and min ima in February . Both gametophytes and tetrasporophytes follow this pat tern, but the spr ing increase comes later for tetrasporophytes than for gametophytes, and the fal l decrease and spr ing increase in density are much more pronounced in gametophytes than in tetrasporophytes. Th is results in tetrasporophytes hav ing lower summer peak densities and higher winter m in imum densities than gametophytes, and brings about a seasonal alternation of phase dominance wi th gametophytes predominating in summer and tetrasporophytes in winter. Th is is the demographic mechanism under ly ing the observations of DeWreede and Green (1990) of a persistant seasonal alternation of phase dominance in lridaea splendens. CHAPTER 3: SEASONAL DYNAMICS OF NONFERTILE, TETRASPORANGIAL AND CYSTOCARPIC GENETS OF IRIDAEA SPLENDENS Introduction Pr io r to the use of the resorcinol reagent to dist inguish gametophytes and tetrasporophytes of Chondrus and lridaea on the basis of their constituent carrageenans, dominance of one or the other phase in a part icular population was inferred by the enumerat ion of reproductively mature thal l i . Observations on Chondrus- crispus in New Hampsh i re (Mathieson and Bu rns , 1975) found cystocarpic thal l i most abundant throughout the year wi th a peak in fal l-winter. Tetrasporangia l thal l i showed more errat ic f luctuations, wi th fa l l , winter and spr ing m a x i m a , depending on site. lridaea laminarioides in central Chi le (Hannach and Santel ices, 1985) showed a marked increase in the number of nonfertile thal l i near the end of spr ing. Nonfert i le thal l i continued to dominate the population throughout the year . Among fertile thal l i , cystocarpic plants dominated in summer and tetrasporangial plants in fal l . Studies on lridaea splendens in Cal i forn ia (Hansen and Doyle, 1976, as lridaea cordata) also found nonferti le thal l i to predominate in spr ing. Dur ing the rest of the year tetrasporangial thal l i predominated. Tha l l i became reproductively mature throughout the year (Hansen, 1977, as lridaea cordata) apparent ly irrespective of growth rate or size, and growth did not cease w i th the onset of reproductive maturat ion. When previously harvested plots were allowed to grow 73 74 undisturbed for one year, 90% of the population present at the end of that year was reproductively mature. Further work on Iridaea splendens in the Strait of Georgia, British Columbia, (Adams, 1979, as Iridaea cordata) showed density of nonfertile thalli increasing rapidly in early spring and summer, then declining to very low levels in winter. Of the reproductively mature stages, cystocarpic densities were higher from May through July, and tetrasporangial thalli predominated from August through December. This pattern was also observed near Victoria, British Columbia, (Austin and Adams, 1971, as Iridaea cordata) where cystocarpic thalli predominated (among the reproductively mature thalli) from June through September, and tetrasporangial thalli predominated from October through February. The gametophyte dominance in summer and tetrasporophyte dominance in winter seen at Brockton Point (DeWreede and Green, 1990) was mirrored in the summer predominance of cystocarpic thalli and winter predominance of tetrasporangial thalli observed in the Strait of Georgia (Adams, 1979) and near Victoria (Austin and Adams, 1971). This suggests that reproductively mature thalli at Brockton Point may follow the dynamics observed by Adams (1979). However, population structure in Iridaea splendens has shown considerable geographic variation (Dyck et al., 1985, as Iridaea cordata) and the same may be true of its phenology. It remains to be determined, therefore, whether the demographic pattern of reproductively mature stages seen in the Strait of Georgia (Adams, 1979) holds for Brockton Point, and if so, how similar the timing of events is to those from the Strait of Georgia and Victoria. This chapter wi l l investigate the dynamics of nonferti le, cystocarpic, and tetrasporangial plants at Brockton Point. Cystocarpic and tetrasporangial thal l i may become mature at different t imes wi th s imi lar rates of addition and loss from the population, or the alternate reproductively mature phases may appear at the same time wi th differential rates of appearance and dissapearance of thal l i f rom the population accounting for the seasonal segregation of peak densities. In the preceeding chapter I showed that the seasonal dynamics of gametophytes and tetrasporophytes of lridaea splendens are quite different. In this chapter I wi l l compare those dynamics to the dynamics of cystocarpic and tetrasporangial plants. 76 Methods and Materials Both the contiguous transects and the permanent sites, outlined in Chapter 2, were sampled. Sampl ing dates were those listed in Chapter 2. Wi th in each quadrat or site the number of genets w i th one or more mature cystocarpic or tetrasporangial blades was counted. The contiguous transects were . sampled from February , 1989, through J a n u a r y , 1990. The permanent sites were sampled from A p r i l , 1989, through February , 1990. Changes in density of tetrasporangial , cystocarpic, and nonferti le genets per 2 0.25 m of substratum, over al l substratum types, were calculated using data f rom the contiguous transects. Changes in density of fertile and non-fertile genets per 0.25 m of substratum known to be supporting lridaea splendens were calculated us ing data f rom the permanent sites. Sampl ing periods were compared pairwise to determine the time f rame over which stat ist ical ly signif icant change (P=0.05) occurred. A l l comparisons were done using the M a n n Whi tney U Test (Sokal and Rholf, 1973). Rates of increase and decrease in density between sampl ing periods were also calculated for tetrasporangial , cystocarpic, and nonferti le genets. Ana lys i s was done both on data adjusted for the unequal surface areas of the permanent sites (surface area adjustment outlined in Chapter 2), and on the non-adjusted data. Densi ty differences between tetrasporangial , cystocarpic, and nonferti le genets were examined wi th in each sampl ing period. Th is was done using data f rom the contiguous transects and from the permanent sites (both 77 adjusted and non-adjusted). A l l comparisons were made using the M a n n Whi tney U Test. 78 Results Results f rom the contiguous transects The results of the temporal comparisons of nonfertile genets (using data f rom the contiguous transects) are detailed in Appendix J , Table 1. Comparisons of tetrasporangial genets are detailed in Appendix J , Table 2, and cystocarpic genets in Appendix J , Table 3. The overal l pat tern (Fig. 3.1) showed declining fertile genets and rapidly increasing numbers of non-fertile genets dur ing late winter - ear ly spr ing. Fert i le genets were absent in spr ing with the f irst appearance of cystocarpic genets occurr ing in J u l y and f irst appearance of tetrasporangial genets in . October. M e a n density of cystocarpic genets peaked in November , 1989, and tetrasporangial density in December, wi th tetrasporangial density remain ing 2 to 4 t imes higher than cystocarpic density f rom November, 1989 to J a n u a r y , 1990. Dur ing this period mean density of nonfertile genets declined below the mean density of tetrasporangial genets but remained higher than the mean density of cystocarpic plants. 79 Figure 3.1 Seasonal change in density of nonferti le, tetrasporangial and cystocarpic genets of Iridaea splendens over al l available substrata (data from the contiguous transects). 2 Means (genets/0.25 m ) plus and minus one standard error. 8 1 Results f rom the permanent sites. The results of the temporal comparisons using data f rom the permanent sites, adjusted for surface area, are detailed in Appendix J (Table 4 for nonferti le genets, Table 5 for tetrasporangial genets and Table 6 for cystocarpic genets). The overal l pattern (Fig. 3.2) was of rapidly increasing numbers of nonferti le genets in spr ing whi le fertile plants were absent. Cystocarpic numbers increased steadily f rom M a y to August , 1989, while tetrasporangial genet numbers f luctuated at low levels (May-Ju ly) and then increased steadily from J u l y to December, 1989. Decrease in numbers of nonfertile genets was continuous from June , 1989, to Februa ry , 1990. M e a n density of tetrasporangial genets decreased from December, 1989,. to February , 1990. The results of the temporal comparisons between sampl ing periods using data f rom the permanent sites, not adjusted for surface area, are detailed in Appendix D, Table 1 (for nonfertile genets), Appendix D, Table 2 (for tetrasporangial genets) and Appendix D, Table 3 (for cystocarpic genets). Patterns of increase and decrease, and periods over which density differences were signif icant ly different, were identical to those observed when using the data adjusted for surface area. The overal l pattern for the non-adjusted data (Appendix C, F i g . 1) was s imi lar in most regards to that found in the adjusted data (Fig. 3.2). One difference was that, in the October, 1989 sampl ing period, the adjusted data showed a mean density of cystocarpic genets sl ight ly higher than for 82 tetrasporangial genets. Us ing the non-adjusted data this situation was reversed. Wi th the non-adjusted data, the February , 1990 values for mean density were s imi lar for non-fertile and tetrasporangial genets while the value for cystocarpic genets was lower. This was not the case for the adjusted data, where the mean values in February , 1990 were closer for nonferti le and cystocarpic genets while the value for tetrasporangial genets was higher. Comparisons wi th in sampl ing periods in the contiguous transects U s i n g the data f rom the contiguous transects, the densities of tetrasporangial and cystocarpic genets were compared wi th in each sampl ing period (Table 3.1). Densit ies of the two fertile phases were signif icantly different wi thin al l periods except M a y and June , 1989, when no fertile thal l i were observed, and in October, 1989. The densities of tetrasporangial vs. nonferti le genets (Table 3.2) were signif icantly different wi th in al l periods except February , 1989. The densities of cystocarpic vs. nonferti le genets (Table 3.3) were signif icant ly different wi th in al l periods except November and December, 1989. 83 Figure 3.2 Seasonal change in density of nonfertile, tetrasporangial and cystocarpic genets of lridaea splendens in the permanent sites (data adjusted to compensate for unequal 2 surface areas between sites). Means (genets/0.25 m ) plus and minus one standard error. Nonfertile SAMPLING PERIOD T A B L E 3.1 Densi ty of tetrasporangial vs. cystocarpic genets within each sampl ing period in the contiguous transects Pa i rw ise comparison of the density of tetrasporangial vs. cystocarpic genets wi th in eagh sampl ing period. Given wi th each comparison are the means (in genets/0.25 m ) and standard errors for each stage and the probabil i ty of the nul l hypothesis that the distributions for the two stages are equivalent. Mon th Compar ison M e a n S. E . P-Va lue February /89 Tet. 0.23 0.05 * Cyst . 0.03 0.01 0.000 M a y / 8 9 Tet. 0.00 0.00 Cyst . 0.00 0.00 1.000 June/89 Tet. 0.00 0.00 Cyst . 0.00 0.00 1.000 Ju l y /89 Tet. 0.00 0.00 Cyst . 0.07 0.03 0.001 October/89 Tet. 0.27 0.03 Cyst . 0.19 0.04 0.319 November/89 Tet. 0.55 0.06 * Cyst . 0.25 0.05 0.000 December/89 Tet. 0.58 0.07 * Cyst . 0.13 0.03 0.000 Janua ry /90 Tet. 0.48 0.07 * Cyst . 0.10 0.02 0.000 T A B L E 3.2 Densi ty of tetrasporangial vs. nonfertile genets wi th in each sampl ing period in the contiguous transects. Pa i rw ise comparison of the density of tetrasporangial vs. nonfertile genets wi th in each sampl ing period. Given wi th each comparison are the means (in genets/0.25 m ) and standard errors for each stage and the probabil i ty of the nul l hypothesis that the distributions for the two stages are equivalent. Mon th Compar ison M e a n S. E . P-Value February /89 Tet. 0.23 0.05 N . F . 0.23 0.06 0.295 M a y / 8 9 Tet. 0.00 0.00 * N . F . 1.97 0.24 0.000 June/89 Tet. 0.00 0.00 * N . F . 2.67 0.32 0.000 J u l y / 8 9 Tet. 0.00 0.00 * N . F . 2.20 0.31 0.000 October/89 Tet. 0.27 0.03 * N . F . 0.58 0.11 0.019 November/89 Tet. 0.55 0.06 N . F . 0.39 0.08 o.ooo' December/89 Tet. 0.58 0.07 * N . F . . 0.20 0.07 0.000 Janua ry /90 Tet. 0.48 0.07 * N . F . 0.27 0.05 0.003 87 T A B L E 3.3 Densi ty of cystocarpic vs. nonferti le genets within each sampl ing period in the contiguous transects. Pa i rw ise comparison of the density of cystocarpic vs. nonferti le genets wi th in eacji sampl ing period. G iven wi th each comparison are the means (in. genets/0.25 m ) and standard errors for each stage and the probabil i ty of the nul l hypothesis that the distributions for the two stages are equivalent. Mon th Compar ison M e a n S. E . P-Value Februa ry /89 Cys t . 0.03 0.01 * N . F . 0.23 0.06 0.000 M a y / 8 9 Cys t . 0.00 0.00 * N . F . 1.97 0.24 0.000 June /89 Cys t . 0.00 0.00 * N . F . 2.67 0.32 0.000 J u l y / 8 9 Cys t . 0.07 0.03 N . F . 2.20 0.31 0.000 October/89 Cys t . 0.19 0.04 * N . F . 0.58 0.11 0.001 November /89 Cys t . 0.25 0.05 N . F . 0.39 0.08 0.298 December/89 Cys t . 0.13 0.03 N . F . 0.20 0.07 0.807 J a n u a r y / 9 0 Cys t . 0.10 0.02 * N . F . 0.27 0.05 0.008 88 Comparisons wi th in sampl ing periods in the permanent sites The densities of the two fertile phases were signif icantly different in J u l y and August , 1989, and from November, 1989, through Februa ry , 1990 (Table 3.4). The densities of tetrasporangial and nonfertile genets (Table 3.5) were signif icantly different wi th in al l periods except October, November, and December, 1989. The densities of cystocarpic and nonferti le genets (Table 3.6) were signif icantly different wi thin al l periods except October, 1989, and J a n u a r y , 1990. U s i n g the data from the permanent sites, not adjusted for surface area, the distributions of tetrasporangial and cystocarpic genets were compared wi th in each sampl ing period (Appendix D, Table 4). The pattern of stat ist ical ly signif icant differences was identical to that in the data which had been adjusted, as was the case for the comparison of tetrasporangial and nonferti le genets (Appendix D, Table 5). The comparison of cystocarpic and nonfertile genets (Appendix D, Table. 6) produced signif icant differences wi th in al l periods except October, 1989. Janua ry , 1990, wi th a non-signif icant difference using the adjusted data, showed a signif icant difference using the non-adjusted data. T A B L E 3.4 Densi ty of tetrasporangial vs . cystocarpic genets wi th in each sampl ing period in the permanent sites (adjusted for surface area). Pa i rw ise comparison of the density of tetrasporangial vs. cystocarpic genets wi th in eagh sampl ing period. G iven wi th each comparison are the means (in genets/0.25 m ) and standard errors for each stage and the probabil i ty of the nul l hypothesis that the distributions for the two phases are equivalent. Mon th Compar ison M e a n S. E . P-Value Apr i l / 89 Tet. 0.00 0.00 Cyst . 0.00 0.00 1.000 M a y / 8 9 Tet. 0.00 0.00 Cyst . 0.00 0.00 1.000 June /89 Tet. 0.14 0.08 Cyst . 0.43 0.16 0.068 J u l y / 8 9 Tet. 0.01 0.01 * ' Cys t . 1.29 0.29 0.000 Augus t /89 Tet. 0.81 0.28 * Cyst . 2.32 0.72 0.036 October/89 Tet. 1.74 0.31 Cyst . 2.18 0.58 0.729 November/89 Tet. 1.96 0.40 * Cyst . 1.27 0.36 0.032 December/89 Tet. 2.49 0.55 * Cyst . 0.74 0.20 •0.001 J a n u a r y / 9 0 Tet. 2.13 0.40 * Cyst . 0.27 0.09 0.000 Februa ry /90 Tet. 1.32. 0.32 * Cyst . 0.08 0.05 0.000 T A B L E 3.5 Densi ty of tetrasporangial vs . nonfertile genets within each sampl ing period in the  permanent sites (adjusted for surface area). Pa i rw ise comparison of the density of tetrasporangial vs. nonferti le genets wi th in eagh sampl ing period. Given w i th each comparison are the means (in genets/0.25 m ) and standard errors for each stage and the probabil i ty of the nul l hypothesis that the distributions for the two phases are equivalent. Mon th Compar ison M e a n S. E . P-Va lue Apr i l / 89 Tet. 0.00 0.00 * N . F . 8.59 1.80 0.000 M a y / 8 9 Tet. 0.00 0.00 N . F . 16.79 3.41 0.000 June/89 Tet. 0.14 0.08 * N . F . 18.54 • 3.81 0.000 Ju l y /89 Tet. 0.01 0.01 * N . F . 13.73 3.49 0.000 August /89 Tet. 0.81 0.28 * N . F . 13.27 3.56 0.000 October/89 Tet. 1.74 0.31 N . F . 4.65 1.29 0.256 November/89 Tet. 1.96 0.40 N . F . 3.59 1.09 0.914 December/89 Tet. 2.49 0.55 N . F . 1.91 0.53 0.165 Janua ry /90 Tet. 2.13 0.40 * N . F . 0.62 0.15 0.000 February /90 Tet. 1.32 0.32 * N . F . 0.38 0.11 0.003 91 T A B L E 3.6 Density of cystocarpic vs. nonfertile genets within each sampling period in the  permanent sites (adjusted for surface area). Pairwise comparison of the density of cystocarpic vs. nonfertile genets within eac j i sampling period. Given with each comparison are the means (in genets/0.25 m ) and standard errors for each stage and the probability of the null hypothesis that the distributions of the two phases are equivalent. Month Comparison Mean S. E . P-Value April/89 Cyst. 0.00 0.00 * N.F. 8.59 1.80 0.000 May/89 Cyst. 0.00 0.00 * N.F . 16.79 3.41 0.000 June/89 Cyst. 0.43 0.16 * N.F. 18.54 3.81 0.000 July/89 Cyst. 1.29 0.29 * N.F. 13.73 3.49 0.000 August/89 Cyst. 2.32 0.72 N.F. 13.27 3.56 0.000 October/89 Cyst. 2.18 0.58 N.F . 4.65 1.29 0.190 November/89 Cyst. 1.27 0.36 N.F . 3.59 1.09 0.023 December/89 Cyst. 0.74 0.20 * N.F . 1.91 0.53 0.044 January/90 Cyst. • 0.27 0.09 N.F . 0.62 0.15 0.059 February/90 Cyst. 0.08 0.05 * N.F . 0.38 0.11 0.017 Discussion The general , pattern observed by A d a m s (1979) in the St ra i t of Georgia (predominance of nonferti le thal l i in spr ing and summer and fertile thal l i in winter, w i th cystocarpic thal l i predominating, among fertile thal l i , in summer and tetrasporangial thal l i in fal l and winter) appears to hold generally for Brockton Point as wel l . This basic pattern (albeit wi th differences in the t iming of certain events) held for the results from the contiguous transects and for the results f rom the permanent sites (both adjusted for surface area and non-adjusted). Once again, as discussed in Chapter 2, the basic pattern is not an art i fact of sampl ing certain areas of Brockton Point rather than others. The trend seen in the changing density of nonferti le genets wi th season was the most consistent one between the results f rom the contiguous transects and those from the permanent sites. In both cases there was a rapid spr ing increase in genet density, peaking in June , and followed by a rapid decline from June through October. F r o m October to December, 1989, there was a period of decrease at a lesser rate than f rom June to October. The point at which the results f rom the permanent sites and those f rom the contiguous transects differed was the period from December, 1989, to J a n u a r y , 1990, dur ing which the results f rom the contiguous transects showed a slight, non-signif icant increase while the results f rom the permanent sites showed continuous decrease. Since the increase seen in the results f rom the contiguous transects was non-signif icant, it seems wel l w i th in the range of stochastic f luctuations to be expected. A s imi lar situation occurred in compar ing the data f rom the permanent sites which had been 93 adjusted for surface area to the non-adjusted data. In the non-adjusted results there was a slight, non-signif icant increase in nonfertile genet density from J a n u a r y to February , 1990, while using the adjusted results showed a slight, non-signif icant decrease. In examining the changes in density of cystocarpic and tetrasporangial genets over t ime, larger differences emerged between the results f rom the contiguous transects and those f rom the permanent sites. The f i rst appearance of ferti le genets in the permanent sites occurred in June , 1989, wi th both cystocarpic and tetrasporangial genets mak ing their appearance at the same time. In the results f rom the contiguous transects, cystocarpic thal l i appeared f irst in J u l y , 1989, while tetrasporangial thal l i appeared in October, 1989. Densit ies of ferti le genets dur ing June, however, were very low in the permanent sites (0.43 2 2 genets/0.25 m for cystocarpic genets; 0.14 genets/0.25 m for tetrasporangial genets) and may have been missed by chance in the placing of quadrats in the contiguous transect. In Ju l y , 1989, cystocarpic genets were found in both the results f rom the contiguous transects and those f rom the permanent sites. Once again the density of tetrasporangial genets found in the permanent sites was 2 very low (0.01 genets/0.25 m ) and could have been missed by chance in the contiguous transect (accounting for their absence there). In Augus t , 1989, a contiguous transect was not sampled. Results f rom the permanent sites for this period showed a tetrasporangial genet density near ly two thirds that of the J u l y , 1989, cystocarpic genet density, It seems f rom this that the f i rst appearances of the fertile stages are later in the contiguous transects than in the permanent sites through chance and absence of a sample set, and not due to some 94 difference inherent in sampl ing over al l avai lable substrata vs. sampl ing only substrata known to support Iridaea splendens. The pattern of mean change in cystocarpic genet density also differed between the contiguous transects and the permanent sites. The f irst difference was the absence, in the contiguous transects, of the August , 1989, peak in density seen in the permanent sites which was l ikely missed because the contiguous transect was not sampled dur ing that period. The second difference was the non-signif icant increase dur ing October-November, 1989, result ing in the November peak density. This was concurrent wi th a tetrasporangial genet density increase in this same period and wi th the increased genet density previously mentioned (Chapter 2). Since al l three appear l inked, it is l ikely that the reasons for the pat tern in fertile blades is the same as those discussed in Chapter 2 for the pattern of genets in general. The onset of reproductive matur i ty in both cystocarpic and tetrasporangial genets occurred when densities of gametophyte and tetrasporophyte genets were at their seasonal max imum (June, 1989). A t this point only 3.4% of avai lable gametophytes were reproductively mature. The proportion of female gametophytes which this represents remains unknown since, due to the diff iculty of identi fying male plants, there was no enumerat ion of male gametangial thal l i in this study. A d a m s (1979, as Iridaea cordata) found cystocarpic and male gametangial thal l i in approximately equal densities (although wi th considerable var iat ion from site to site) in spr ing, w i th male gametangial densities exceeding those of cystocarpic thal l i in summer (almost twice the density at one site). If a 1:1 ratio of male 95 gametangial to cystocarpic thalli is the case for Brockton Point it would mean that a relatively small percentage of male gametophytes would become sexually mature during June as well, leaving the vast majoritj' of gametophytes nonfertile. In August, 1989, cystocarpic genets, at their peak density, made up 21% of the mean gametophyte genet density. Since mean density of gametophyte genets declined continuously from August to October, 1989, while cystocarpic genet density declined very little, cystocarpic genets accounted for 46% of mean gametophyte genet density in October. As mean density of gametophyte genets declined from October, 1989, to January, 1990, cystocarpic genets declined at similar rates remaining 46 to 37% of mean gametophyte genet density. In February, 1990, cystocarpic genets made up 28% of the mean density of gametophyte genets. As was argued in Chapter 1, the actual rates of increase and decrease in mean density of cystocarpic genets depend largely on the underlying turnover rate of cystocarpic plants. If, from June to October, 1989, cystocarpic genets were disappearing at rates proportional to those at which gametophyte genets overall were disappearing, the actual rates of increase in numbers of new cystocarpic genets would need to be much higher than those observed to account for the increasing density of cystocarpic genets while plants are continually being lost. If however, cystocarpic plants were not subject to the same dynamics as gametophyte genets overall, and were not lost until some discrete event (such as a synchronous shedding of spores) had occurred, thereafter declining proportionately to overall gametophyte decline, the actual pattern would more closely resemble the pattern apparent in the data. Green (1989, as lridaea 96 cordata). noted that during the period of cystocarpic dominance (summer) 2 carposporangia released more spores per cm of thallus than tetrasporangia, and that the reverse occurred in winter when tetrasporangial thalli predominated. This suggests that a certain ammount of synchronization of spore release does occur. Little is known about the underlying turnover rates of fertile and nonfertile blades, and further investigation is necessary in resolving this question. It is apparent, however, that the majority of gametophyte thalli of Iridaea splendens were lost before reaching reproductive maturity. Mature tetrasporangial genets made up 2.2% of the June, 1989, seasonal maximum in mean tetrasporophyte genet density described in Chapter 2. This increased to 15.7% of available tetrasporophyte genets in August, 44% in October, 57% in November, 76% in December, 95% in January, and then dropped to 88% in February, 1990. A greater proportion of available tetrasporophytes became fertile than gametophytes. The peak mean density of cystocarpic genets in August, 1989, however, was not significantly different from the peak mean density of tetrasporangial genets in December (P=0.163). As demonstrated in Chapter 2, there was no significant difference in number of modules per genet between gametophytes and tetrasporophytes. Whether this is also true for reproductively mature genets was not examined in this study. If it is, the number of cystocarpic and tetrasporangial modules produced also would not differ significantly. Once again the question of whether more cystocarpic or tetrasporangial thalli are produced during the course of the year is dependant on the underlying turnover rates of the fertile stages. In the simplest scenario (fertile blades are long lived and continue to accumulate until an approximately 97 synchronous spore release, declining thereafter), roughly the same numbers of cystocarpic and tetrasporangial thalli would be produced during the course of the year. If, however, cystocarpic and tetrasporangial thalli were releasing spores and being gained and lost from the population throughout their respective cycles of increasing and decreasing density, and if these processes were proceeding at different rates for the alternate stages, it would be impossible to asses (from the available data) which of the two has produced the larger number of thalli over the course of the year. For lridaea laminarioides (Luxoro and Santelices, 1989) no significant differences were found in the number of spores produced by either cystocarps or tetrasporangial sori the total number of spores produced per unit surface area of rocky substratum, or the total number of sori produced per plant. The significantly larger number of sori per unit of thallus surface, found in sporophytic blades, was balanced by the larger size, larger number of fertile blades per genet, and increased abundance of cystocarpic plants in the population. For lridaea splendens (Green, 1989, as lridaea cordata) there was a significantly lower density of reproductive structures on cystocarpic than on tetrasporangial blades, however, cystocarpic blades also had significantly larger surface areas than tetrasporangial blades, resulting in no significant difference in number of reproductive structures per blade. The analysis compared cystocarpic blades collected during their period of dominance with tetrasporangial blades collected during their period of dominance. Carposporangia were observed to release up to 18 times as many spores per unit area of thallus as 98 tetrasporangia, so that, even if mean numbers of sori produced, and mean numbers of spores produced per sorus were indeed the same for the tetrasporangial and cystocarpic components of the population, this need not ensure equal numbers of spores released. Similarly larger numbers of spores released need not necessarily translate into larger numbers of recruits. What is most apparent in examining the demography of the reproductively mature stages of Iridaea splendens is another level of differences between gametophytes and tetrasporophytes. The first is the seasonal separation in maximum densities of the two reproductively mature stages, previously observed in the Strait of Georgia by Adams (1979, as Iridaea cordata). The second is the fact that a much larger proportion of available tetrasporophyte genets become reproductively mature than do gametophytes, so that the maximum densities achieved by both cystocarpic and tetrasporangial genets at their respective peaks are not significantly different. If the number of fertile modules per genet are not significant^ different for the two stages, if turnover rates are uniform, and if spore release is approximately equal, then the gametophyte dominance seen during spring and summer could not be maintained in that proportion of the population which are new recruits without some selective mechanism acting after spore release. Further demographic work, concentrating on the reproductively mature stages and on spore production and release would be useful in resolving whether this is the case. CHAPTER 4: THE FATE OF INDIVIDUAL MODULES OF IRIDAEA SPLENDENS Introduction The rates of gain and loss of modules and genets discussed in Chapter 2 assumed that increases and decreases in density from one period of observation to the next were the result of simple addition or loss of blades. In the spring increase in density, each subsequent measurement was treated as if a number of blades had been added to the population without loss of any which were present in the previous measurement. In the fall density decrease, density in each subsequent measurement was treated as if a number of blades, present in the previous measurement, had been lost while assuming no new blades were added to the population during this time. Sarukan and Harper (1973) have shown that these assumptions can be mistaken. Populations which would appear static if simply enumerated each month can show high turnover rates when the fate of individuals is followed. In this chapter I will discuss some preliminary work on the fate of individual modules of lridaea splendens using two groups, one tagged in spring, 1989, and the other in fall of the same year. Rates of loss based on the fate of individuals will be compared to the rates of increasing and decreasing density from Chapter 2. Cohort studies of animals have frequently followed organisms from birth through their age classes, noting mortality from one age class to the next 99 100 (Deevej', 1947) and age class work has been done for certain marine algae (Parke, 1948, Kawashima, 1972, Rosenthal et al, 1974, DeWreede, 1984). It has been argued, however, (Harper, 1977) that many of the demographic events in the life of a plant are more closely correlated with size than with age. Mortality in the Petrocelis stage of Mastocarpus papillatus has been shown to be more closely related to size than to age (Paine et al., 1979). The same has been argued for corals (Hughes, 1984). The term "cohort" is usually used to denote a particular group of organisms all of the same age (Begon et al., 1986). In this case, however, the blades tagged were of unknown age but were followed over time in the manner in which a cohort would be followed. In this chapter each haphazardly tagged cohort will be examined to compare patterns of mortality between spring and fall, between gametophytes and tetrasporophytes within each season, and between three size classes within each life history phase. Patterns of mortality within the size classes will be compared to mortality within the alternate phases regardless of size class, and to overall mortality in the spring and fall cohorts. This will provide a preliminary indication of whether patterns of mortality differ for different size classes and alternate life history phases. Onset of fertility will also be examined in this chapter. DeWreede and Klinger (1988) argue that, if reproduction imposes a cost on an organism, then it is likely that the organism must attain a certain size before beginning reproduction, that reduction or cessation of growth accompanies the onset of reproduction, and that an organism is more likely to die after producing and 101 releasing reproductive structures or propagules. There is evidence from certain algae that a resource trade-off may occur, e.g. sexual reproduction in Halimeda is followed immediately by death of the adult (Hillis-Colinvaux, 1980). However for Iridaea splendens, Hansen (1977, as Iridaea cordata) has observed the continued growth of blades after becoming reproductive. At Brockton Point the onset of reproductive maturity was noted for each tagged blade which was not already reproductively mature. DeWreede and Green (1990) reported that the less than 5 cm size class of Iridaea splendens never contained thalli with either carposporangia or tetrasporangia and that these were also rare in the 5 - 15 cm class. Most blades which became reproductively mature were larger than 20 cm in length. My study will provide some additional data on whether a certain size class must be attained by blades of Iridaea splendens before reproductive activity can begin. The length of time blades remain reproductive before being lost will be examined to suggest whether the onset of reproductive maturity increases the likelihood of mortality. Any blades at Brockton Point which increase in size class after the onset of reproductive maturity would corroborate the observations of Hansen (1977); however, if it appears that a particular size class must be reached before reproductive activity can begin or that reproduction increases the chance of death, then there is the possibility that some form of resource trade-off between growth and reproduction occurs in Iridaea splendens. 102 Methods and Materials One hundred and sixteen individual blades were haphazardly tagged at 9 sites at Brockton Point between June 18 and June 22, 1989, Tagging was done with plastic cable ties to which numbered nylon clip sleeve wire markers had been epoxied. Two tags were fastened around the stipe of each blade. Each tagged blade had a 3 mm diameter disk removed using a single-hole paper punch. Each disk was kept in a separate pouch labelled with the number of the tag and the site at which it was located. Disks were analyzed using the resorcinol test for kappa-carrageenan as described in Chapter 2. The sites were re-examined for the presence or absence of the tagged blades on June 29 - July 4, 1989, July 16-17, 1989, July 28-30, 1989, August 15, 1989, October 17-19, 1989, November 13-15, 1989, December 10-12, 1989, January 8-10, 1990, and February 6, 1990. During November 14-15, 1989, 88 additional blades were haphazardly tagged at Brockton Point. The tagging took place at 10 sites, 7 of which were sites used in June. Tagging procedures were identical to those used in June, 1989. Disks were removed and subjected to carrageenan analysis. The sites were re-examined for the presence or absence of tagged blades on December 10-12, 1989, January 8-10, 1990, and February 6, 1990. Based on blade length all blades in both the June and November cohorts were grouped as small (2-5 cm), medium (6-15 cm), or large (>15 cm). One life table was constructed for all blades tagged during June 18-22, 1989, and another 103 for all blades tagged during November 14-15, 1989. Within each of these groups separate life tables were constructed for gametophytes and tetrasporophytes, and within each phase, separate tables for small, medium and large blades. For each life table a depletion curve, showing simple loss of individual blades over time, and a survivorship curve were plotted. The Ix values were scaled to 1000 before plotting log Ix over time. Rates of loss for gametophytes and tetrasporophytes were calculated and compared to the rates calculated in Chapter 2 in order to arrive at an estimate of the rates at which new blades were introduced into the population. . Size class was measured for each blade still present in each observation subsequent to the initial tagging. The number of blades lost without changing size class was noted for each group previously mentioned, as well as the number lost after losing or gaining one or two size classes. Onset of fertility was noted for each blade, as was the duration of reproductive maturity before the blade was lost. 104 Results The results of the 116 blades, tagged in June, 1989, treated as a single cohort, are summarized in Table 4.1. The depletion curve (Fig. 4.1) produced by plotting loss of blades over time approximates the hyperbolic shape expected when the probability of death remains constant over time. The survivorship curve plotted for the same group of blades (Fig. 4.2) also most closely approximates a type II curve (Deevey, 1947) representing equal probability of death over time. Examination of this group of blades as two separate cohorts, one of 86 gametophytes (Table 4.2), the other of 30 tetrasporophytes (Table 4.3), produced similar results for both the depletion curves (Fig. 4.3 for gametophytes, Fig. 4.4 for tetrasporophytes) and the survivorship curves (Fig. 4.5 for gametophytes, Fig. 4.6 for tetrasporophytes). The life tables for large, medium and small blades as separate cohorts within each life history phase may be found in Appendix E . Life tables for the various groupings of the 88 blades tagged in November, 1989, are in Appendix F. The depletion and survivorship curves plotted for each size class within each phase (for blades tagged in June) showed the same trend as did all blades tagged in June treated as a single cohort (Appendix G). This same pattern of depletion and survivorship curves, indicating equal probability of mortality over time, was also evident in the results of the blades tagged in November, 1989 (Appendix H), with the exception of the large gametophyte class which consisted of an initial cohort of only 3 individuals and therefore has insufficient data. 105 T A B L E 4.1 Life table for all blades tagged in June, 1989. X - X l is the interval between enumerations of the tagged plants (in days). Dx refers to the number of days in the interval and Nx to the number of tagged blades present at the beginning of the interval. Zx is the proportion of the original cohort surviving to day X. dx is the proportion of the original cohort dying during the interval, qx is the proportion of those blades present at the beginning proportion of the lost per interval which day. were lost during the interval. qx/Dx is X - X l Dx Nx Ix dx <7x/Dx 0-10 10 116 1.0000 0.2069 0.2069 0.0207 10-25 15 92 0.7931 0.2328 0.2935 0.0196 25-38 13 65 0.5603 0.1206 0.2152 0.0166 38-55 17 5! 0.4397 0.1552 0.3530 0.0207 55-120 65 33 0.2845 0.1724 0.6060 0.0093 120-147 27 13 0.1121 0.0345 0.3078 0.0114 147-174 27 9 0.0776 0.0086 0.1108 0.0041 174-203 29 8 0.0690 0.0173 0.2057 0.0086 203-231 28 6 0.0517 0.0431 0.8336 0.0298 231- 1 0.0086 TABLE 4.2 Life table for all gametophyte blades tagged in June, 1989. Abbreviations as for Table 4.1 X - X l 0-10 10-25 25-38 38-55 55-120 120-147 147-174 174-203 203-231 231-Dx 10 15 13 17 65 27 27 29 28 Nx 86 70 48 37 26 9 6 5 4 1 Jx 1.0000 0.8140 0.5581 0.4302 0.3023 0.1047 0.0698 0.0581 0.0465 0.0116 dx 0.1860 0.2559 0.1279 0.1279 0.1976 0.0349 0.0117 0.0117 0.0349 0.1860 0.3144 0.2292 0.2779 0.6537 0.3333 0.1676 0.2014 0.7654 qxfDx 0.0186 0.0210 0.0176 0.0163 0.0101 0.0123 0.0062 0.0069 0.0273 107 T A B L E 4.3 Life table for all tetrasporophyte blades tagged in June, 1989. Abbreviations as for Table 4.1 X-Xl 0-10 10-25 25-38 38-55 55-120 120-147 147-174 174-203 203-231 Dx 10 15 13 17 65 27 27 29 .28 Nx 30 22 17 14 7 4 3 3 2 Jx 1.0000 0.7333 0.5667 0.4667 0.2333 0.1333 0.1000 0.1000 0.0666 dx 0.2667 0.1666 0.1000 0.2334 0.1000 0.0333 0.0000 0.0334 0.0666 _22L 0.2667 0.2272 0.1796 0.5001 0.4286 0.2498 0.0000 0.3340 1.0000 qxfDx 0.0267 0.0151 0.0138 0.0294 0.0066 0.0093 0.0000 0.0115 0.0357 108 Figure 4.1 Number of individual modules over time in Iridaea splendens tagged in June, 1989. o CM O LO O l O O tf)0«00 C M O O J ^ t O ^ f C O * -SlVnaiAIQNI JO ON 109 Figure 4.2 ' Survivorship of modules of Iridaea splendens tagged in June, 1989. 112 Figure 4.3 Number of individual gametophyte modules over time in lridaea splendens tagged in June, 1989. £11 114 Figure 4.4 Number of individual tetrasporophyte modules over time in Iridaea splendens tagged in June, 1989. 116 Figure 4.5 Survivorship of gametophj'te modules of lridaea splendens tagged in June, 1989. 118 Figure 4.6 Survivorship of tetrasporophyte modules of lridaea splendens tagged in June, 1989. 120 Rates of loss of blades in the intervals between observation periods are presented in Table 4.4. Rates for the period from June 18-22, 1989, to November 13-15, 1989, were calculated using the cohort tagged in June and rates for the period from November 13-15, 1989, to February 6, 1990, were calculated using the cohort tagged in November. Rates for gametophytes only are given in Table 4.5 and rates for tetrasporophytes only in Table 4.6. The rates for the two life history phases were not significantly different (compared by t-test, P = 0.756). Two periods during the course of the year had different rates of loss. From June to August, 1989 (Table 4.4), mean rate of loss was 2% per day. From August, 1989, to February, 1990, it was 1% per day. This pattern also held when gametophytes and tetrasporophytes were considered separately (Table 4.5, Table 4.6). The apparent rates of loss for gametophyte and tetrasporophyte modules from Chapter 2 were adjusted using the rates of blade loss of the tagged plants from the June and November cohorts (Table 4.7). Rates of loss observed in the permanent sites were compared, using t-tests, to the expected rates of loss for each period based on rate of loss of tagged blades. For gametophyte blades, from August, 1989 to February, 1990, the observed and expected rates were not significantly different (P=0.206) while observed and expected rates for tetrasporophytes, during the same period differed significantly (P = 0.018). Using these rates an estimate was made of the rate of addition of new blades to the population (Table 4.8). Rates of addition were high from June to August, 1989, and much lower from August, 1989, to February, 1990. This pattern also held for gametophytes and tetrasporophytes considered separately. 121 T A B L E 4.4 Rates of loss among all tagged blades. "Period" denotes the period over which the blades were lost. "Prop. Lost" refers to the proportion of the blades which were present at the beginning of the period lost during the period. "Rate" is the proportion lost per day. Period Prop. Lost Rate June 18-22/89 June 29 - July 4/89 0.207 0.021 June29 - July 4/89 July 16-17/89 0.293 0.020 July 16-17/89 July 28-30/89 0.215 0.017 July 28-30/89 Aug. 15/89 0.353 0.021 Aug. 15/89 Oct. 17-19/89 0.606 0.009 Oct.. 17-19/89 Nov. 13-15/89 0.308 0.011 Nov. 13-15/89 Dec. 10-12/89 0.216 0.009 Dec. 10-12/89 Jan. 8-10/89 0.290 0.009 Jan. 8-10/90 Feb. 6/90 0.367 0.013 122 T A B L E 4.5 Rates of loss in tagged gametophyte blades. "Period" denotes the interval over which the blades were lost. "Prop. Lost" refers to the proportion of blades which were present at the beginning of the period lost during the period. "Rate" is the proportion lost per day. Period Prop. Lost Rate June 18-22/89 June 29 - July 4/89 0.186 0.019 June 29 - July 4/89 July 16-17/89 0.314 0.021 July 16-17/89 July 28-30/89 0.229 0.018 July 28-30/89 Aug. 15/89 0.297 0.016 Aug. 15/89 Oct. 17-19/89 0.654 0.010 Oct. 17-19/89 Nov. 13-15/89 0.333 0.012 Nov. 13-15/89 Dec. 10-12/89 0.225 0.008 Dec. 10-12/89 Jan. 8-10/90 0.323 0.011 Jan. 8-10/90 Feb. 6/90 0.286 0.010 123 T A B L E 4.6 Rates of loss of tagged tetrasporophyte blades. "Period" denotes the interval during which the blades were lost. "Prop. Lost" refers to the proportion of blades present at the beginning of the period which were lost during the period. "Rate" is the proportion lost per day. Period Prop". Lost Rate June 18-22/89 June 29 - July 4/89 0.267 0.027 June 29- July 4/89 July 16-17/89 July 16-17/89 July 28-30/89 July 28-30/89 Aug. 15/89 Aug. 15/89 Oct. 17-19/89 Oct. 17-19/89 Nov. 13-15/89 Nov. 13-15/89 Dec. 10-12/89 Dec. 10-12/89 Jan. 8-10/90 0.227 0.176 0.500 0.429 0.250 0.208 0.263 0.015 0.014 0.029 0.007 0.009 0.008 0.009 Jan. 8-10/90 Feb. 6/90 0.429 0.016 124 T A B L E 4.7 Observed vs. expected rates of blade loss in the permanent sites. "Period" denotes the time interval between which blades were enumerated. "Obs.Gam." is the observed rate of loss of gametophyte blades from the permanent sites (Chapter 2). "Exp.Gam." is the expected rate of loss of gametophyte blades in the permanent sites based on rates of loss of tagged blades. "Obs.Tet." is the observed rate of loss of tetrasporophyte blades from the permanent sites. "Exp.Tet." is the expected rate of loss of tetrasporophyte blades in the permanent sites based on rate of loss of tagged blades. Period Obs.Gam. Exp.Gam. Obs.Tet. Exp.Tet. June - July/89 -6.72 -12.46 -3.42 -6.50 July - Aug./89 + 1.24 -8.43 + 0.48 -4.45 Aug. - Oct./89 -3.46 -4.59 -1.13 -2.37 Oct. - Nov./89 -2.64 -2.00 -0.70 -1.52 Nov. - Dec/89 -1.82 -1.20 -0.35 -1.31 Dec./89-Jan./90 -1.52 -0.65 -1.22 -1.21 Jan. - Feb./90 -0.34 -0.20 -0.97 -0.84 Oct. - Dec/89 -2.23 -1.99 -0.53 -1.52 Nov./89-Jan./90 -1.67 -1.20 -0.79 -1.31 Dec./89-Feb./90 -0.93 -0.65 -1.10 -1.21 125 T A B L E 4.8 Rates of addition of blades in the permanent sites. "Period" denotes the time interval between which blades were enumerated. "Rate All" refers to the rate at which both gametophyte and tetrasporophyte blades are being added. "Rate Gam." is the rate at which gametophyte blades are being added. "Rate Tet." is the rate ^t which tetrasporophyte blades are being added. All rates are in modules/0.25 m /month. Negative rates are the result of periods where the observed loss in the permanent sites was greater than the expected loss based on rates of loss among the tagged blades. Period Rate All Rate Gam. Rate Tet. June - July/89 + 8.42 + 5.72 + 3.08 July - Aug./89 + 14.66 + 9.67 + 4.93 Aug. - Oct./89 + 2.38 + 1.13 + 1.24 Oct. - Nov./89 + 0.18 -0.65 + 0.82 Nov. - Dec/89 + 0.37 -0.62 + 0.96 Dec/89 - Jan./90 -0.89 -0.86 -0.01 Jan. - Feb./90 -0.28 -0.14 -0.13 Oct. - Dec/89 -0.77 -0.24 + 0.99 Nov./89 ' - Jan./90 + 0.06 -0.47 + 0.52 Dec/89 - Feb./90 -0.18 -0.28 + 0.11 126 In following the 116 blades tagged in June, 1989, through to February 6, 1990, only 10 blades were ever found with only one tag present instead of the original two. In each of these cases, what remained of the plant was 1-2 cm of stipe, and the apophysis and blade were entirely missing. This was also the case for the 5 out of 88 blades tagged in November, 1989, which were found with only one tag in the course of following the cohort till February 6, 1990. This indicates that tag loss without loss of the tagged blade was minimal. Blades of both life history phases were lost rapidly so there were fewer than 50% which' changed size class. Of the gametophyte blades tagged in June, 1989, 37 of the 38 large blades were lost by February 6, 1990. Of these 37, 19 were lost without changing size class, 10 were reduced to medium blades and 8 were reduced to small blades before loss. The single blade not lost over the course of the observations was reduced to small size by February. The longer lived blades tended to be those reduced in size class. All 38 medium sized gametophyte blades were lost by February 6, 1990. Of these 20 were lost without any change in size class, 12 first grew into large blades, and 6 were reduced to small blades. In both size classes the trend in longer lived blades was toward reduction in size class. All 10 small gametophyte blades tagged in June, 1989, were lost by November 14, 1989. Eight did not change size class and 2 grew to medium size. Of the large tetrasporophyte blades tagged in June, 1989, all 10 blades were lost by February 6, 1990, 6 without reduction in size class and 4 after being reduced to small blades. All 15 medium sized tetrasporophyte blades tagged 127 in June, 1989, were lost by January 9, 1990, 12 without any change in size class, and 3 after growing into large blades. All 5 small tetrasporophyte blades were also lost by January 9, 1990, 4 without changing size class and 1 after growing to a medium sized blade. The trends seen in the blades tagged in June continued in the blades tagged November 14-15, 1989. Two of the 3 large blades 2 were lost by February 6, 1990, 1 after being reduced to a medium sized blade and 1 after reduction to a small blade. The blade remaining in February was reduced to medium size. Eleven of the 15 medium sized gametophyte blades were lost by February 6, 1990, 7 without changing size class and 4 after being reduced to small blades. Of the 4 medium sized blades remaining in February, 1 remained medium sized and the other 3 were reduced to small blades. Of 22 small gametophyte blades l l were lost by February 6, 1990, 9 without changing size class and 2 after growing to medium size. Eleven small blades remained in February. Six were still small and 5 had grown to medium size. Seven of 8 large tetrasporophyte blades were lost by February 6, 1990, 6 without changing size class and 1 after being reduced to a small blade. The blade which remained in February had been reduced to medium size. Of the 21 medium sized tetrasporophyte blades 13 were lost by February 6, 1990, 11 without changing size class and 2 after reduction to small blades. Eight blades remained in February. Seven had not changed size class and 1 blade was reduced to the small class. Thirteen of 19 small tetrasporophyte blades were lost by February 6, 1990, 12 without changing size class and 1 after growing to a 128 medium size. Of the six blades remaining in February, 5 remained small and 1 had grown to medium size. High rates of loss caused most blades tagged in June, 1989, to be lost before becoming reproductively mature. Thirty of 37 large gametophyte blades were lost without becoming cystocarpic. Of the 7 which became cystocarpic, 2 were lost immediately without changing size class and 1 after 13 days of reproductive maturity, changing from a large to a medium blade before loss. One was lost after 15 days of reproductive maturity, changing from a large to a small blade. Two were lost after 28 days of reproductive maturity without changing size class and 1 blade was lost after 208 days of reproductive maturity, changing from a large to a small blade. The blade which was not lost over the course of the observations was reproductively mature for 236 days, and changed from the large to the small size class. Thirty-two of the 38 medium sized gametophyte blades lost were lost without becoming cystocarpic. Of the . 6 which became cystocarpic, 1 was lost immediately without changing size class and 1 was lost immediately, but with reproductive maturity coinciding with reaching large size. One blade was lost after 17 days of reproductive maturity and reaching the large size class. One blade was lost after 17 days of reproductive maturity and both growing to large size and being reduced to small. The final blade was lost after 134 days of reproductive maturity. In total, 5 of the medium sized blades grew to large size before becoming cystocarpic and 1 did not. The 10 small gametophyte blades were all lost without becoming cystocarpic. 129 Seven of the 10 large tetrasporophyte blades lost were lost without becoming reproductively mature. Of the 3 which formed tetrasporangia, 1 was reproductively mature for 13 days and then lost without changing size class. One was reproductively mature for 17 days and was reduced to a small blade before loss. The final blade was reproductively mature for 116 days and was reduced to the small size class before loss. Of the 15 medium sized tetrasporophyte blades lost, 14 were lost without becoming reproductively mature. The blade which developed tetrasporangia did so on growing to large size and was lost immediately. All 5 small tetrasporophyte blades were lost without reaching reproductive maturity. Twenty-eight per cent of gametophyte blades and 54% of tetrasporophyte blades tagged in November, 1989, were reproductively mature at time of tagging. Both of the 2 large gametophyte blades lost were cystocarpic. One was reproductively mature for 27 days and reduced to medium size before loss. The other was reproductively mature for 56 days before loss and was reduced to small size. One blade, which was not lost, was reproductively mature for 84 days, and reduced to medium size. Of the 11 medium sized gametophyte blades lost, 6 were lost without becoming reproductively mature. Of the 5 which formed cystocarps, 4 were lost immediately after the onset of fertility without changing size class. One was lost after 27 days of fertility and reduction to a small blade. One blade which was not lost was reproductively mature for 84 days and did not change size class. 130 Ten of the 12 small gametophyte blades lost were lost without becoming reproductively mature. Of the 2 which were cystocarpic 1 was lost immediately and the other was fertile for 56 days before loss. Neither blade changed size class. Five blades became reproductively mature but were not lost. Two were fertile for 84 days and did not change size class. Three became fertile after increasing to medium size. One of these was fertile for 28 days, 1 for 56 days, and 1 became fertile during the last (February 6, 1990) observation. None of the 7 large tetrasporophyte blades lost were nonfertile. One blade was lost immediately. One blade was fertile for 27 days and reduced to the small size class before loss. Four blades were fertile for 27 days and lost without changing size class, and 1 blade was fertile for 56 days and lost without changing size class. The fertile blade which was not lost during the course of observation was reduced to medium size. Two of the 13 medium sized tetrasporophyte blades lost were lost without becoming reproductively mature. Of the 11 which formed tetrasporangia, 7 were lost immediately (absent in the next observation period) without changing size class. Two were lost after 27 days of fertility, one without change in size class, the other after reduction to a small blade. Seven fertile blades were not lost. One was fertile 28 days and did not change size class. Two were fertile 56 days, one remaining medium sized and the other reduced to a small blade. Four were fertile for 84 days. Three of these remained medium sized and 1 was reduced to a small blade. 131 Eight of the 13 small tetrasporophyte blades lost were lost without becoming reproductively mature. Of the 5 which formed tetrasporangia 2 were lost immediately without change in size class, 1 was lost after 27 days of fertility without change in size class, and 1 was lost after 56 days of fertility, also without change in size class. One blade was lost after 29 days of fertility and growing to medium size. Two fertile blades were not lost during the period of observation. One was fertile for 84 days and did not change size class. The other became fertile in the last observation period (February 6, 1990) concurrent with growth to medium size. During most periods from July, 1989, to February, 1990, some previously nonfertile thalli became reproductively mature. At the time of tagging in June none of the blades were cystocarpic or tetrasporangial. By July 1-3, 1989, 6 cystocarpic blades, 5 in the large size class and 1 medium, were present. On July 16, 1989, 3 previously nonfertile gametophytes became cystocarpic, 2 tagged as large blades and 1 medium now grown to large size. In this same period 1 large tetrasporophyte blade was observed with tetraporangia. From July 29 -August 1, 1989, 4 previously nonfertile gametophytes became cystocarpic, 2 in the large class and two medium blades grown into large size. One previously nonfertile large tetrasporophyte blade developed tetrasporangia. On August 15, 1989, 3 previously nonfertile tetrasporophytes developed tetrasporangia, 2 in the large class and 1 medium blade grown to large size. No previously nonfertile gametophytes became cystocarpic in this period and no previously nonfertile blade, tagged in June, 1989, became reproductively mature beyond this date. 132 At the time of tagging in November-, 1989, 3 large, 4 medium, and 4 small gametophytes tagged were cystocarpic. Eight large, 13 medium, and 5 small tetrasporophytes tagged were reproductively mature at this time. In the i observations made December 10-11, 1989, 2 previously nonfertile gametophytes became cystocarpic, 1 medium sized and 1 small blade grown to medium size, Four previously nonfertile tetrasporophytes became reproductively mature during this period, 3 medium sized blades and one small blade grown to medium size. Observations during January 8-9, 1990, showed that 2 previously nonfertile gametophytes had become cystocarpic, 1 medium sized blade and 1 small blade now grown to medium size. During this same period 2 previously nonfertile tetrasporophytes developed tetrasporangia. Both were medium sized. On February 6, 1990, 1 previously nonfertile gametophyte blade developed cystocarps. The blade was small when tagged but grew to medium size before becoming fertile. The same was true for the single tetrasporophyte blade which developed tetrasporangia. 133 Discussion The similarity of survivorship curves (all type II (Deevey, 1947)) for most of the size classes of both gametophytes and tetrasporophytes, in both the spring and fall cohorts, indicates that all these groups have an equal probability of death over time. No blades smaller than 2 cm in length were tagged, however, so this result applies only to mortality of blades above 2 cm. A previously proposed agent of mortality in Iridaea splendens is wave action (Dyck et al., 1985, as Iridaea cordata). Higher proportions of tetrasporophytes were observed in populations of Iridaea splendens in exposed sites while higher proportions of gametophytes were present in sheltered sites at First Beach, Barkley Sound, B.C. , Canada. From this, the potentially higher wave action in winter was considered in Chapter 2 as a. possible mechanism for increasing the loss of gametophyte over tetrasporophyte blades. The rates of loss of modules from the cohorts of gametophytes and tetrasporophytes at Brockton Point, however, were very similar over the period of study. Rates of loss were also higher, for both, gametophytes and tetrasporophytes, from June to August, 1989, and lower from August, 1989, to February, 1990. If indeed wave, action is higher in winter than in summer at Brockton Point, the difference between the summer and winter rates of loss suggest that factors likely to cause mortality in summer, such as desiccation, are more effective at killing blades of Iridaea splendens than any winter increase in wave exposure. The similarity in rates of blade loss for gametophytes and tetrasporophytes, during both fall and winter, also indicates that winter causes of 134 mortality do not selectively remove one or the other life history phase. Examination of the estimated rate of addition of new modules to the population showed that addition of new gametophytes occurred at a higher rate than tetrasporophytes from June to August. From October, 1989, to February, 1990, however, addition of new tetrasporophyte blades to the population continued while addition of new gametophyte blades was virtually at a standstill. This suggests that the mechanism underlying the apparent differential loss of blades in Chapter 2 (Fig. 2.5) may not be differential rates of loss of blades but rather differential rates of addition. This mechanism can produce the same results as differential blade loss between the phases. The majority of blades of both life history phases, regardless of size when tagged or season in which tagging was done, were lost from the population without changing size class. This again suggests that, at Brockton Point, it is not primarily wave action (which presumably would selectively remove larger blades because of the greater resistance caused by increased surface area) that is responsible for the mortality of modules of Iridaea splendens. The trend among the large blades of both phases in both the spring and fall cohorts was that the few longer lived blades were those which were reduced in size with time. Of the medium sized blades, tagged in June, which were lost after changing size class, larger numbers of both gametophytes and tetrasporophytes grew to large size before being lost than were reduced to small size before loss. In contrast none of the medium sized blades tagged in November, of either phase, grew into the large class before loss. This pattern, 135 which suggests higher growth rates for both phases in summer than in winter was not, however, present among the small blades tagged in June and November which grew to medium size. Hansen (1977) has shown higher growth rates of lridaea splendens (as lridaea cordata) in spring-summer vs. fall-winter in California and it is intuitively appealing that the highest growth rates would be correlated with the longer periods of irradiance present in summer. Since the pattern suggesting higher summer growth rates is restricted to the medium size class at Brockton Point and not evident in the growth of small blades it is not consistent enough to confirm or deny the existence of higher summer growth rates. A large majority of the gametophytes and tetrasporophytes tagged in June were lost before becoming reproductively mature. Of those which became reproductively mature there was no apparent correlation of blade loss with a particular period of time spent as a fertile blade. After achieving reproductive maturity blades were short, intermediate, and long lived. The majority of the large and medium sized tetrasporophyte blades tagged in November, 1989, were already reproductively mature when tagging took place, as were the large gametophytes. Once again blade loss did not appear to coincide with a particular period of reproductive maturity. This was also true for medium sized blades, tagged in November, which became reproductively mature during the course of the observations. On the surface this would suggest that the production of reproductive structures does not increase the likelihood of death for lridaea splendens. The release of spores, however, was not considered in this study and it may be that senescence begins immediately after spore release, the timing of which may vary from blade to blade regardless of the timing of the onset of 136 reproductive matur i ty . Seven medium sized blades (6 gametophytes and 1 tetrasporophyte) tagged in June became reproductively mature. S ix grew into large blades before the onset of reproductive matur i ty . Seven medium sized blades tagged in November (2 gametophytes and 5 tetrasporophytes) became reproductively mature without growing into large blades (no medium sized blades tagged in November grew into the large size class). F ive smal l blades tagged in November (3 gametophytes and 2 tetrasporophytes) became reproductively mature after growing into medium sized blades. Sma l l reproductively mature blades, both gametophyte and tetrasporophyte, were present in the November cohort. None of these blades grew into the next size class and immature smal l blades did not develop reproductive structures without f i rst growing to medium size. It seems l ikely that the reproductively mature smal l blades were the remnants of larger mature thal l i which had lost a portion of their blade. It seems f rom the avai lable data that Iridaea splendens may become reproductive only after at ta in ing a certain size class although the part icular size necessary may differ f rom large (>15 cm) in summer to medium (5-15 cm) in winter. Th is suggests that reproduction may indeed impose some cost on Iridaea splendens (DeWreede and Kl inger , 1988) although cessation of growth and increased likelihood of death wi th the onset of reproductive matur i ty were not directly observed in m y study. This is of necessity a tentative conclusion since the numbers involved were smal l . Fur ther study of the fate of individuals over t ime would be valuable in resolving this point. CHAPTER 5: GENERAL DISCUSSION The demography of lridaea splendens presented in my study has been essentially a demography of modules. The individual blades are the units which were gained and lost by the population, and while genets appeared (when they produced a blade) or disappeared (when they lost all their blades), the births and deaths of the small perennial crusts were not directly observed. The life span of these crusts remains unknown and their demography in terms of patterns of recruitment and mortalitj7 remains unknown. Density of modules of lridaea splendens in populations in the Strait of Georgia (Adams, 1979, as lridaea cordata) and biomass of lridaea splendens in populations near Ano Nuevo Point, California (Hansen, 1977, as lridaea cordata) both increased in spring, reached maximum in summer, and decreased through fall to a winter minimum. Although certain demographic patterns in lridaea splendens vary geographically, e.g. population structure (Dyck et al., 1985, as lridaea cordata), the pattern of seasonal abundance of blades seen in the Strait of Georgia and in California was also evident at Brockton Point. The pattern of appearance and disappearance of genets paralleled the pattern of gain and loss of modules in the population at Brockton Point. From the study of tagged blades (Chapter 4) it appears that any blade, regardless of size class or life history phase, has an equal probability of death at any time. Because of this pattern of blade loss genets may lose all their blades and disappear from the population at any time as well. To what extent the continued 137 138 appearance of genets in the population is the product of recruitment vs. perennation is not known. Study along these lines (May, 1986) has estimated recruitment rate at 20%: Increased growth rate of new blades in response to longer periods of irradiance has been demonstrated for lridaea splendens in California (Hansen, 1977, as lridaea cordata) and was observed in my study for the medium (5-15 cm) size class but not in the small (2-5 cm) size class. While increased growth rates in response to increased irradiance remains likely (and is consistent with the majority of the data in my study and in Hansen, 1977) the spring density increase could also have been produced by simply increasing the number of blades produced per genet without altering growth rate of individual blades. Variation in the population structure of lridaea splendens has been a source of some debate, given the differences in population structure seen in California by Hansen and Doyle (1976, as lridaea cordata) and Dyck et al. (1985, as lridaea cordata) and the comparison of that situation to the one in the pacific northwest (Adams, 1979,. May, 1986, as lridaea cordata). Although some of these studies used the presence of reproductive structures to assign life history phase while others used the resorcinol test for kappa-carrageenan to determine the proportions of the alternate life history phases in the population the results produced by either method are similar. DeWreede and Green (1990) concluded that while the magnitude of change may appear different using the two methods, either method will give the same pattern 139 of change. The pattern of seasonal alternation of phase dominance, in British Columbia, is present consistently from 1975 (Adams, 1979) through to my data for 1989 - 1990. To account for the change in population structure at Pidgeon Point, California, Dyck et al. (1985) proposed a stochastic model in which massive recruitment after a catastrophic loss of perennial crusts would establish a new population structure which would then persist largely by perennation. If such a mechanism is indeed operating in some populations of Iridaea splendens what other factors might account for the stability of the annual cycle of alternating phase dominance over the past fifteen years in British Columbia? One possibility is that, in British Columbia, seasonal variation in environmental conditions may be higher than interannual variation and each of the life history stages predominates in that set of conditions to which it is best suited. If seasonal variation is low enough near Monterey that either stage could predominate in both summer and winter, such a population might be more susceptable to changing population structure after a catastrophic removal rather than returning to a regular cycle. In addition it is possible that periodic catastrophic events, e.g. low spring tides concurrent with clear hot weather, or El Nino, occur with greater frequency near Monterey than in British Columbia, making such a change during the past fifteen years more likely at Pidgeon Point than at any of the British Columbian locations studied. While the seasonal alternation of gametophyte and tetrasporophyte dominance at Brockton Point has been well documented (Green, 1989, DeWreede 140 and Green, 1990) the underlying demographic mechanism was not known. In Chapter 2 of my study I demonstrated that the spring increase in density of gametophytes began earlier and proceeded at a higher rate than the spring increase in density of tetrasporophytes resulting in a summer gametophyte dominance. During the decrease in density, beginning in summer and proceeding til late . winter, gametophyte density decreased at a higher rate than tetrasporophyte density resulting in nearly equal densities in November and tetrasporophyte dominance in winter. Although both phases had essentially the same pattern (increasing density from February to June, peak density in June and declining density from June to February) the variation in rates of density increase and decrease produced a seasonal alternation in phase dominance. Initially, in Chapter 2, I attributed the lower rate of density decrease in tetrasporophytes during the late summer, fall and winter to increased resistance of tetrasporophyte blades over gametophyte blades to removal by wave action. Tetrasporophytes have been shown to predominate in exposed vs. sheltered areas at First Beach, Barkley Sound, and at Otter Rock, Oregon, 68% of blades in a sample of drift plants were gametophytes while in the attached population at this site gametophytes made up 11% (Dyck et al., 1985). Both of these results indicated that gametophytes may be more susceptable to removal by waves than tetrasporophytes. Since fall and winter bring storms with increased wave activity I proposed that the higher rate of density decrease found in gametophytes during this part of the year might be due to higher rates of gametophyte blade loss to wave action. 141 Examination of blades tagged in both June and November (Chapter 4), however, showed that rates of blade loss (as a proportion lost per day) were not significantly different for gametophytes vs. tetrasporophytes. As well, survivorship curves drawn for the separate size classes of gametophytes vs. tetrasporophytes in both the June and November taggings, all most closely approximated a type II curve (Deevey, 1947) indicating equal probability of death over time for any blade in any size class regardless of life history phase. These results are incompatible with the idea of differential loss of gametophyte blades to wave action. When the expected rates of loss in the permanent sites at Brockton Point were calculated based on the rates of loss observed in the tagged blades comparison with the observed rates of loss permitted the rates of addition of new modules to be approximated. Rate of addition of new modules was higher for gametophytes from June to August. This is consistent with the proposition that the predominance of gametophytes in spring is the product of a higher rate of addition of gametophyte modules and appearance of gametophyte genets. Rates of addition of new blades were nearly equal for the alternate phases from August to October with the rate of addition of new tetrasporophytes slightly higher than that for gametophytes. From October to February addition of new gametophyte blades to the population virtually stopped while tetrasoprophytes continued to give rise to new blades. In light of the results obtained from the tagged blades it now appears likely that the change in phase dominance is not due to differential loss of 142 blades from the gametophyte portion of the population but rather to the ability of tetrasporophytes to continue producing new blades after gametophytes have ceased to do so. Ecological differences in two species of Iridaea in Chile have been examined by Hannach and Santelices (1985). Both Iridaea laminarioides and Iridaea ciliata showed temporal segregation of the reproductive stages. This pattern, with abundance of cystocarpic thalli peaking earlier in the year than tetrasporangial thalli, was also observed for Iridaea splendens in the Strait of Georgia (Adams, 1979, as Iridaea cordata) and at Brockton Point by DeWreede and Green (1990) and in my own study (Chapter 3). Although the cystocarpic and tetrasporangial • plants I studied reached peak densities at different times of year the peak densities themselves were similar for the two reproductively mature stages. Comparison of these dynamics with the dynamics of gametophytes and tetrasporophj'tes (whether fertile or not) from Chapter 2 points to another potential difference between the stages. A greater proportion of tetrasporophytes become tetrasporangial during the course of the year than the proportion of gametophytes which becomes cystocarpic. A problem with this interpretation lies in the fact that reproductively mature males were not enumerated in my study. If reproductively mature males and cystocarpic females exist in a 1:1 ratio, as suggested by Adams (1979), the number of reproductively mature gametophytes (both male and cystocarpic) would reach a peak density approximately twice that of the peak density of tetrasporangial blades. If this were the case the proportions of available gametophytes and tetrasporophytes which become reproductively mature would be more nearly equivalent. 143 Luxoro and Santelices (1989) found that tetrasporophytes of lridaea laminarioides were more sensitive to desiccation than gametophytes and that higher temperatures and longer daylength provided optimum growth for gametophytes while optima for tetrasporophytes were at lower temperatures and somewhat shorter daylength. Such differences in growth optima could be present in lridaea splendens since addition of gametophyte blades to the population proceeded more rapidly in spring and summer than the addition of tetrasporophyte blades while the reverse was true in fall and winter. Rates of blade loss based on the blades tagged in June and November were twice as high in summer as in fall and winter suggesting that the causes of mortality in summer (e.g. desiccation) are more effective at killing blades than those in winter (e.g. increased wave action). Rates of blade loss (as a proportion lost per day), however, are similar for both gametophytes and tetrasporophytes and therefore do not indicate differing tolerances to the summer causes of mortality to which desiccation would intuitively seem to be an important contributor. Although the population structure of lridaea splendens has been observed to vary a great deal geographically (Dyck et al., 1985, as lridaea cordata) the seasonal alternation between summer gametophyte dominance and winter tetrasporophyte dominance appears consistently in the data from British Columbia over the past fifteen years. This pattern is also consistent with the summer gametophyte dominance reported from Washington (May, 1986, as lridaea cordata). It seems likely, therefore, that the underlying demographic patterns discovered in my study have wider application than the population at Brockton Point. Further examination of the fate of individuals is essential in determining 144 the applicability of module gain (vs. module loss) as the mechanism responsible for the seasonal alternation of phase dominance in other areas of British Columbia where this pattern has been reported. REFERENCES Abbott, Isabella A. , 1971. 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Publ., Oxford, pp. 137 - 184. Wright, E . C . , 1981. The distribution and morphological varaiation of the tetrasporophyte phase of the isomorphic alga Chondrus crispus Stackhouse. B.Sc. Honours Thesis, Dalhousie University, Nova Scotia. 21 pp. 155 Yaphe, W., and G.P. Arsenault, 1965. Improved resorcinol reagent for determination of fructose and 3,6-anhydrogalactose in polysaccharides. Anal. Bioch. 13: 143 - 148. A P P E N D I X A : T A B L E S O F R E S U L T S F R O M T H E P E R M A N E N T SITES E X A M I N E D O N A P E R S I T E B A S I S ( D A T A N O T A D J U S T E D F O R S U R F A C E A R E A ) . 156 157 T A B L E 1 Change in genet numbers in permanent sites not adjusted for surface area Pairwise comparison of the differences in number of genets per site between sampling periods. Given with each comparison are the means (in genets/site) and standard errors for each sampling period, and the probability of the null hypothesis that the distributions for the two periods are equivilant. The rate of mean increase or decrease was calculated as the change in mean number of genets per site per month. Comparison Mean S. E . P-Value Rate January/89 4.58 0.55 * February/89 1.97 0.35 0.000 -2.61 February/89 1.97 0.35 * April/89 9.33 1.75 0.000 + 3.68 April/89 9.33 1.75 * May/89 16.56 2.79 0.035 + 7.23 May/89 16.56 2.97 June/89 19.47 3.11 0.420 + 2.91 June/89 19.47 3.11 July/89 13.72 1.86 0.257 -5.75 July/89 13.72 1.86 August/89 14.67 2.00 0.739 + 0.95 August/89 14.67 2.00 * October/89 8.25 1.46 0.010 -2.57 October/89 8.25 1.45 November/89 6.39 1.24 0.251 -1.86 November/89 6.39 1.24 December/89 5.08 0.96 0.415 -1.31 December/89 5.08 0.96 January/90 3.22 0.56 0.087 -1.86 January/90 3.22 0.56 * February/90 1.94 0.44 0.037 -1.28 T A B L E 1 Continued. Comparison Mean S. E . P-Value Rate October/89 8.25 1.46 December/89 5.08 0.96 0.062 -1.59 November/89 6.39 1.24 : | ; January/90 3.22 0.56 0.011 -1.59 December/89 5.08 0.96 * February/90 1.94 0.44 0.001 -1.57 159 T A B L E 2 Change in module numbers in permanent sites not adjusted for surface area Pairwise comparison of the differences in numbers of modules per site between sampling periods. Given with each comparison are the means (in modules/site) and standard errors for each sampling period and the probability of the null hypothesis that the distributions for the two periods are equivilant. The rate of mean increase or decrease over the intervals were calculated as change in mean number of modules per site per month. Comparison Mean S. E . P-Value Rate January/89 6.97 0.76 * February/89 2.94 0.50 0.000 -4.03 February/89 2.94 0.50 * April/89 18.72 3.79 0.000 + 7.89 April/89 18.72 3.79 May/89 31.33 5.60 0.082 + 12.61 May/89 31.33 5.60 June/89 33.72 5.62 0.488 + 2.39 April/89 18.72 3.79 * June/89 33.72 5.62 0.014 + 7.50 June/89 33.72 5.62 July/89 20.08 2.77 0.107 -13.64 July/89 20.08 2.77 August/89 22.22 3.05 0.714 + 2.14 August/89 22.22 3.05 * October/89 11.06 1.74 0.005 -4.46 October/89 11.05 1.74 November/89 8.03 1.41 0.135 -3.03 November/89 8.03 1.41 December/89 6.31 1.13 0.315 -1.72 December/89 6.31 1.13 January/90 3.97 0.62 0.062 -2.34 T A B L E 2 Continued. > Comparison Mean S. E . P-Value Rate January/90 3.97 0.62 February/90 2.39 0.53 0.020 -1.58 October/89 11.06 1.74 December/89 6.31 1.13 0.019 -2.38 November/89 8.03 1.41 January/90 3.97 0.62 0.006 -2.03 December/89 6.31 1.13 February/90 2.39 0.53 0.000 -1.96 161 T A B L E 3 Change in number of gametophyte genets per site in permanent sites not adjusted for surface area Pairwise comparison of the differences in number of gametophyte genets per site between sampling periods. Given with each comparison are the means (in genets/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivilant, and the rate of mean increase or decrease over the interval (in genets per site, per month). Comparison Mean S. E . P-Value Rate January/89 1.94 0.34 * February/89 0.28 0.11 0.000 -1.66 February/89 0.28 0.11 * April/89 6.92 1.22 0.000 + 3.32 April/89 6.92 1.22 May/89 11.22 1.95 0.136 + 4.30 May/89 11.22 1.95 June/89 13.06 2.16 0.502 + 1.86 April/89 6.92 1.22 * June/89 13.06 2.16 0.018 + 3.07 June/89 13.06 2.16 July/89 8.94 1.29 0.286 -4.12 July/89 8.94 1.29 August/89 9.92 1.43 0.636 + 0.98 August/89 9.92 1.43 * October/89 4.33 0.78 0.001 -2.24 October/89 4.33 0.78 November/89 2.89 0.61 0.104 -1.45 November/89 2.89 0.61 December/89 1.53 0.35 0.063 -1.45 T A B L E 3 Continued. Comparison Mean December/89 1.53 January/90 0.67 January/90 0.67 February/90 0.31 October/89 4.33 December/89 1.53 November/89 2.89 January/90 0.67 December/89 1.53 February/90 . 0.31 S. E . P-Value Rate 0.35 0.14 0.073 -0.86 0.14 0.09 0.059 -0.36 0.78 , : 0.35 0.001 -1.40 0.61 ,.. 0.14 0.000 -1.11 0.35 * 0.09 0.001 -0.61 T A B L E 4 Change in number of tetrasporophyte genets per site in permanent sites not adjusted for surface area Pairwise comparisons of the differences in number of tetrasporophyte genets per site between sampling periods. Given with each comparison are the means (in genets/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivilant, and the rate of mean increase or decrease over the interval (in genets per site, per month). Comparison Mean S. E . P-Value Rate January/89 2.58 0.35 * February/89 1.69 0.30 0.036 -0.89 February/89 1.69 0.30 April/89 2.44 0.59 0.945 + 0.38 April/89 2.44 0.59 * May/89 5.36 1.01 0.013 + 2.92 May/89 5.36 1.01 June/89 6.42 1.20 0.502 + 1.06 June/89 6.42 1.20 July/89 4.78 0.75 0.406 -1.64 July/89 4.78 0.75 August/89 4.75 0.70 0.910 -0.03 August/89 4.75 0.70 October/89 3.92 0.74 0.383 -0.33 June/89 6.42 1.20 October/89 3.92 0.74 0.096 -0.46 October/89 3.92 0.74 November/89 3.50 0.72 0.661 -0.42 June/89 6.42 1.20 * November/89 3.50 0.72 0.034 -0.53 November/89 3.50 0.72 December/89 3.56 0.68 0.842 + 0.06 T A B L E 4 Continued. Comparison Mean S. E . P-Value Rate December/89 3.56 0.68 January/90 2.56 0.49 0.180 -1.00 January/90 2.56 0.49 February/90 1.64 0.44 0.056 -0.92 October/89 3.92 0.74 December/89 3.56 0.68 0.750 -0.18 November/89 3.50 0.72 January/90 2.56 0.49 0.192 -0.47 August/89 4.75 0.70 December/89 3.56 0.68 0.236 -0.22 June/89 6.42 1.20 :|. December/89 3.56 0.68 0.041 -0.44 December/89 3.56 0.68 February/90 1.64 0.44 0.003 -0.96 * 165 T A B L E 5 Change in number of gametophyte modules per site in permanent sites not adjusted for surface area Pairwise comparisons of the differences in number of gametophyte modules per site between sampling periods. Given with each comparison are the means (in modules/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivilant, and the rate of mean increase or decrease over the interval (in modules per site, per month). Comparison Mean S. E . P-Value Rate January/89 2.50 0.41 * February/89 0.36 0.14 0.000 -2.14 February/89 0.36 0.14 * April/89 13.19 2.59 0.000 + 6.42 April/89 13.19 2.59 May/89 21.06 3.86 0.162 + 7.87 May/89 21.06 3.86 June/89 22.47 4.04 0.636 + 1.41 April/89 13.19 2.59 June/89 22.47 4.04 0.053 + 4.64 June/89 22.47 4.04 July/89 12.81 1.87 0.124 -9.66 July/89 12.81 1.87 August/89 14.47 2.16 0.640 + 1.66 August/89 14.47 2.16 * October/89 5.86 1.07 0.001 -3.45 October/89 5.86 1.07 November/89 3.44 0.70 0.075 -2.42 November/89 3.44 0.70 December/89 1.94 0.45 0.071 -1.50 December/89 1.94 0.45 * January/90 0.75 0.16 0.036 -1.19 T A B L E 5 Continued. Comparison Mean January/90 0.75 February/90 0.33 October/89 5.86 December/89 1.94 November/89 3.44 January/90 0.75 December/89 1.94 February/90 0.33 S. E . P-Value Rate 0.16 0.10 0.054 -0.42 1-07 „ 0.45 0.001 -1.96 0.70 ; | : 0.16 0.000 -1.35 0.45 : ] : 0.10 0.000 -0.81 T A B L E 6 Change in number of tetrasporophyte modules in permanent sites not adjusted for surface area Pairwise comparisons of the differences in number of tetrasporophyte modules per site between sampling periods. Given with each comparison are the means (in modules/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivilant, and the rate of mean increase or decrease over the interval (in modules per site, per month). Comparison Mean S. E . P-Value Rate January/89 4.47 0.60 February/89 2.58 0.42 0.018 -1.89 February/89 2.58 0.42 April/89 5.53 1.42 0.752 + 1.48 April/89 5.53 1.42 * May/89 10.28 1.97 0.041 + 4.75 May/89 10.28 1.97 June/89 11.25 1.86 0.505 + 0.97 June/89 11.25 1.86 July/89 7.28 1.14 0.155 -3.97 July/89 7.28 1.14 August/89 7.75 1.09 0.668 + 0.47 August/89 7.75 1.09 October/89 5.19 0.80 0.123 -1.03 June/89 11.25 1.86 * October/89 5.19 0.80 0.013 -1.10 October/89 5.19 0.80 November/89 4.58 0.83 0.358 -0.61 November/89 4.58 0.83 December/89 4.36 0.76 0.856 -0.22 December/89 4.36 January/90 3.22 0.76 0.54 0:213 -1.14 T A B L E 6 Continued. Comparison Mean S. E . P-Value Rate January/90 3.22 0.54 :1: February/90 2.06 0.53 0.037 -1.16 October/89 5.19 0.80 December/89 4.36 0.76 0.392 -0.42 October/89 5.19 0.80 : | ! January/90 3.22 0.54 0.030 -0.66 November/89 4.58 0.83 January/90 3.22 0.54 0.132 -0.68 December/89 4.36 0.76 February/90 2.06 0.53 0.002 -1.15 169 T A B L E 7 Genets vs. modules within sampling periods in permanent sites not adjusted for surface area Comparisons of the distribution of genets to that of modules within each sampling period. Given with each comparison are the means, standard errors, and the probability of the null hypothesis that the distributions are equivalent. Sampling Comparison Mean S. E . P-Value Period January/89 Genets 4.85 0.54 * Modules 7.38 0.75 0.017 February/89 Genets 2.45 0.38 * Modules 3.66 0.54 0.031 April/89 Genets 11.20 1.93 Modules 22.47 4.24 0.069 May/89 Genets 18.06 2.90 * Modules 34.18 5.86 0.040 June/89 Genets 20.03 3.15 * Modules 34.69 5.70 0.048 July/89 Genets 14.11 1.87 Modules 20.66 2.79 0.116 August/89 Genets 14.67 2.00 Modules 22.22 3.05 0.095 October/89 Genets 8.49 1.48 Modules 11.37 1.77 0.130 November/89 Genets 6.57 1.26 Modules 8.26 1.43 0.197 December/89 Genets 5.90 1.05 Modules 7.32 1.21 0.168 January/90 Genets 3.87 0.61 Modules 4.77 0.65 0.120 February/90 Genets 2.69 0.54 Modules 3.31 0.65 0.213 T A B L E 8 Gametophyte vs. tetrasporophyte genets within sampling periods in permanent sites not adjusted for surface area Comparisons of the distribution of gametophyte and tetrasporophyte genets within each sampling period. Given with each comparison are the means, standard errors, and the probability of the null hypothesis that the distributions equivalent. Sampling Comparison Mean S. E . P-Value Period January/89 Gam. 2.06 0.35 Tet. 2.74 0.36 0.106 February/89 Gam. 0.35 0.13 * Tet. 2.10 0.33 0.000 April/89 Gam. 8.30 1.32 * Tet. 2.93 0.68 0.000 May/89 Gam. 12.24 2.03 * Tet. 5.85 1.06 0.014 June/89 Gam. 13.43 2.19 * Tet. 6.60 1.22 0.010 July/89 Gam. 9.20 1.30 * Tet. 4.91 0.76 0.016 August/89 Gam. 9.92 1.43 * Tet. 4.75 0.70 0.005 October/89 Gam. 4.46 0.79 Tet. 4.03 0.75 0.873 November/89 Gam. 2.97 0.62 Tet. 3.60 0.72 0.142 December/89 Gam. 1.77 0.39 * Tet. 4.13 0.74 0.000 January/90 Gam. 0.80 0.16 * Tet. 3.07 0.54 0.000 February/90 Gam. 0.42 0.11 * Tet. 2.27 0.56 0.000 171 T A B L E 9 Gametophyte vs. tetrasporophyte modules within sampling periods in permanent sites not adjusted for surface area Comparisons of the distribution of gametophyte and tetrasporophyte modules within each sampling period. Given with each comparison are the means, standard errors, and the probability of the null hypothesis that the distributions are equivalent. Sampling Comparison Mean S. E . P-Value Period January/89 Gam. 2.65 . 0.42 * Tet. 4.74 0.60 0.011 February/89 Gam. 0.45 0.17 * Tet. 3.21 0.46 0.000 April/89 Gam. 15.83 2.87 * Tet. 6.63 1.63 0.003 May/89 Gam. 22.79 4.05 * Tet. 11.21 2.08 0.041 June/89 Gam. 23.11 4.11 Tet. 11.57 1.88 0.042 July/89 Gam. 13.17 1.89 * Tet. 7.49 1.15 0.030 August/89 Gam. 14.47 2.16 * Tet. 7.75 1.09 0.032 October/89 Gam. 6.03 1.09 Tet. 5.34 0.81 0.934 November/89 Gam. 3.54 0.72 Tet. 4.71 0.84 0.123 December/89 Gam. 2.26 0.50 * Tet. 5.07 0.81 0.000 January/90 Gam. 0.90 0.18 * Tet. 3.87 0.57 0.000 February/90 Gam. 0.46 0.13 * Tet. 2.85 0.68 0.000 APPENDIX B: FIGURES EXAMINING RESULTS FROM THE PERMANENT SITES ON A PER SITE BASIS (DATA NOT ADJUSTED FOR SURFACE AREA). 172 173 Figure 1 • Seasonal change in numbers of modules and genets of Iridaea splendens in the permanent sites on a per site basis (data not adjusted for surface area). Means (modules or genets/site) plus and minus one standard error. 175 Figure 2 Seasonal changes in number of genets per site in gametophytes vs. tetrasporophytes of lridaea splendens in the permanent sites (data not adjusted for surface area). Means (genets/site) plus and minus one standard error. J F A M J J A O N D J F S A M P L I N G P E R I O D 177 Figure 3 Seasonal change in number of modules per site in gametophytes vs. tetrasporophytes of Iridaea splendens in the permanent sites (data not adjusted for surface area). Means (modules/site) plus and minus one standard error. Gametophytes J F A M J J A O N D J F SAMPLING PERIOD APPENDIX C: SUPPLEMENTARY FIGURES FOR THE DYNAMICS OF REPRODUCTIVELY MATURE STAGES OF IRIDAEA SPLENDENS 179 180 Figure 1 Seasonal change in number of nonfertile, tetrasporangial and cystocarpic genets of Iridaea splendens per site in the permanent sites (data not adjusted for surface area). Means (genets/site) plus and minus one standard error. Nonfertile Tetrasporic -Cystocarpic S A M P L I N G PERIOD APPENDIX D: SUPPLEMENTARY TABLES FOR THE DYNAMICS OF REPRODUCTIVELY MATURE STAGES OF IRIDAEA SPLENDENS 182 183 T A B L E 1 Change in number of nonfertile genets per site in the permanent sites (not adjusted for surface area). Pairwise comparison of the differences in mean number of nonfertile genets between sampling periods. Given with each comparison are the means (in genets/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equal, and the rate of mean increase or decrease over the interval (in genets/site/month). Comparison Mean S. E . P-Value Rate April/89 9.33 1.75 * May/89 16.56 2.79 0.035 + 7.23 May/89 16.56 2.79 June/89 18.94 3.06 0.524 + 2.38 June/89 18.94 3.06 July/89 12.50 1.70 0.164 -6.44 July/89 12.50 1.70 August/89 12.14 1.70 0.848 -0.36 June/89 18.94 3.06 August/89 12.14 1.70 0.124 -3.40 August/89 12.14 1.70 * October/89 4.72 1.17 0.000 -2.98 October/89 4.72 1.17 November/89 3.42 0.95 0.454 -1.30 November/89 3.42 0.95 December/89 1.86 0.46 0.145 -1.56 October/89 4.72 1.17 December/89 1.86 0.46 0.060 -1.43 December/89 1.86 0.46 * January/90 0.75 0.18 0.042 -1.11 January/90 0.75 0.18 February/90 1.03 0.61 0.264 + 0.28 T A B L E 2 184 Change in mean number of tetrasporangial genets per site in the permanent sites (not adjusted for surface area). Pairwise comparison of the differences in mean number of tetrasporangial genets per site between sampling periods. Given with each comparison are the means (in genets/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the rate of mean increase or decrease over the interval (in genets/site/month). Comparison Mean S. E . P-Value Rate April/89 0.00 0.00 May/89 0.00 0.00 1.000 0.00 May/89 0.00 0.00 * June/89 0.11 0.05 0.041 + 0.11 June/89 0.11 0.05 July/89 0.03 0.03 0.167 -0.08 July/89 0.03 0.03 * August/89 0.61 0.15 0.000 + 0.58 August/89 0.61 0.15 * October/89 1.89 0.24 0.000 + 0.51 October/89 1.89 0.24 November/89 1.97 0.25 0.889 + 0.08 November/89 1.97 0.25 December/89 2.56 0.43 0.573 + 0.59 October/89 1.89 0.24 December/89 2.56 0.43 0.482 + 0.34 December/89 2.56 0.43 January/90 2.39 0.44 0.731 -0.17 January/90 2.39 0.44 * February/90 1.39 0.36 0.026 -1.00 185 T A B L E 3 Change in mean number of cystocarpic genets per site in the permanent sites (not adjusted for surface area). Pairwise comparison of the differences in mean number of cystocarpic genets per site between sampling periods. Given with each comparison are the means (in genets/site) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the rate of mean increase or decrease over the interval (in genets/ site/month). Comparison Mean S. E . P-Value Rate April/89 0.00 0.00 May/89 0.00 0.00 1.000 0.00 May/89 0.00 0.00 * June/89 0.42 0.14 0.001 + 0.42 June/89 0.42 0.14 * July/89 1.19 0.28 0.011 + 0.77 July/89 1.19 0.28 August/89 1.92 0.45 0.309 + 0.73 June/89 0.42 0.14 * August/89 1.92 0.45 0.001 + 0.75 August/89 1.92 0.45 October/89 1.75 0.34 0.732 -0.07 October/89 1.75 0.34 November/89 1.00 0.21 0.106 -0.75 November/89 1.00 0.21 December/89 0.67 0.20 0.061 -0.33 October/89 1.75 0.34 * December/89 0.67 0.20 0.003 -0.54 December/89 0.67 0.20 January/90 0.28 0.09 0.129 -0.39 January/90 0.28 0.09 February/90 0.08 0.05 0.056 -0.20 December/89 0.67 0.20 * February/90 0.08 0.05 0.002 -0.29 186 T A B L E 4 Number of tetrasporangial vs. cystocarpic genets per site in the permanent sites (not adjusted for surface area). Pairwise comparisons of the number of tetrasporangial vs. cystocarpic genets per site within each sampling period. Given with each comparison are the means genets/site) and standard errors for each stage and the probability of the hypothesis that the distributions i of the two stages are equivalent. Month Comparison Mean S. E . P-Value April/89 Tet. 0.00 0.00 Cyst. 0.00 0.00 1.000 May/89 Tet. 0.00 0.00 Cyst. 0.00 0.00 1.000 June/89 Tet. 0.11 0.05 Cyst. 0.42 0.14 0.062 July/89 Tet. 0.03 0.03 * Cyst. 1.19 0.28 0.000 August/89 Tet. 0.61 0.15 * Cyst. 1.92 0.45 0.017 October/89 Tet. 1.89 0.24 Cyst. 1.75 0.34 0.235 November/89 Tet. 1.97 0.25 • * Cyst. 1.00 0.21 0.001 December/89 Tet. 2.56 0.43 Cyst. 0.67 0.20 0.000 January/90 Tet. 2.39 0.44 * Cyst. 0.28 0.09 0.000 February/90 Tet. 1.39 0.36 * Cyst. 0.08 0.05 0.000 187 T A B L E 5 Number of tetrasporangial vs. nonfertile genets per site in the permanent sites (not adjusted for surface area). Pairwise comparsion of the number of tetrasporangial vs. nonfertile genets per site within each sampling period. Given with each comparison are the means (in genets/site) and standard errors for the two stages and the probability of the null hypothesis that the distributions for the two stages are equivalent. Month Comparison Mean S. E . P-Value April/89 Tet. 0.00 0.00 * N.F . 9.33 1.75 0.000 May/89 Tet. 0.00 0.00 * N.F . 16.56 2.79 0.000 June/89 Tet. 0.11 0.05 * N.F . 18.94 3.06 0.000 July/89 Tet. 0.03 0.03 * N.F. 12.50 1.70 0.000 August/89 Tet. 0.61 0.15 * N.F. 12.14 1.70 0.000 October/89 Tet. 1.89 0.24 N . F > 4.72 1.17 0.291 November/89 Tet. 1.97 0.25 N.F . 3.42 0.95 0.904 December/89 Tet. 2.56 0.43 N.F . 1.86 0.46 0.101 January/90 Tet. 2.39 0.44 * N.F . 0.75 0.18 0.000 February/90 Tet. 1.39 0.36 N.F . 1.03 0.61 0.005 188 T A B L E 6 Number of cystocarpic vs. nonfertile genets per site in the permanent sites (not adjusted for surface area). Pairwise comparsion of the number of cystocarpic vs. nonfertile genets per site within each sampling period. Given with each comparison are the means (in genets/site) and the standard errors for each of the two stages and the probability of the null hypothesis that the distributions of the two stages are equivalent. Month Comparison Mean S. E . P-Value April/89 Cyst. 0.00 0.00 N.F. 9.33 1.75 0.000 May/89 Cyst. 0.00 0.00 * N.F. 16.56 2.79 0.000 June/89 Cyst. 0.42 0.14 N.F. 18.94 3.06 0.000~ July/89 Cyst. 1.19 0.28 * N.F. 12.50 1.70 0.000 August/89 Cyst. 1.92 0.45 * N.F . 12.14 1.70 0.000 October/89 Cyst. 1.75 0.34 N.F . 4.72 1.17 0.077 November/89 Cyst. 1.00 0.21 * N.F. 3.42 0.95 0.009 December/89 Cyst. 0.67 0.20 * N.F . 1.86 0.46 0.017 January/90 Cyst. 0.28 0.09 * N.F. 0.75 0.18 0.049 February/90 Cyst. 0.08 0.05 * N.F . 1.03 0.61 0.013 APPENDIX E: LIFE TABLES FOR THE SEPARATE SIZE CLASSES OF GAMETOPHYTE AND TETRASPOROPHYTE BLADES OF IRIDAEA SPLENDENS TAGGED IN JUNE, 1989 189 190 T A B L E 1 Life table for large gametophyte modules tagged in June, 1989. X - X l is the interval between enumerations of the tagged plants (in days). Dx refers to the number of days in the interval and Nx to the number of tagged blades present at the beginning of the interval. Ix is the proportion of the original cohort surviving to day X. dx is is the proportion of the original cohort dying during the interval, qx is the proportion of those blades present at the beginning proportion of the lost per interval which day. were lost during the interval. qxfDx is X - X l Dx Nx Ix dx _2x qxfDx 0-10 10 38 1.0000 0.1316 0'.1316 0.0132 10-25 15 33 0.8686 0.1842 0.2121 0.0141 25-38 13 26 0.6842 0.1579 0.2308 0.0178 38-55 17 20 0.5263 0.1052 0.1999 0.0118 55-120 65 16 0.4211 0.263 0.6250 0.0096 120-147 27 6 0.1579 0.0263 0.1666 0.0062 147-174 27 5 0.1316 0.0263 0.1998 0.0074 174-203 29 4 0.1053 0.0000 0.0000 0.0000 203-231 28 4 0.1053 0.0790 0.7502 0.0268 231- 1 0.0263 -TABLE 2 Life table for medium gametophyte modules tagged in June, 1989. Abbreviations as for Table 1. X-Xl 0-10 10-25 25-38 38-55 55-120 120-147 147-174 174-203 203-231 Dx 10 15 13 17 65 27 27 29 28 Nx 38 29 21 14 9 2 1 1 0 1.0000 0.7632 0.5526 0.3684 0.2368 0.0526 0.0263 0.0263 0.0000 dx 0.2368 0.2106 0.1842 0.1316 0.1842 0.0263 0.0000 0.0263 -2* 0.2363 0.2759 0.3333 0.3572 0.7779 0.5000 0.0000 1.0000 qxfDx 0.0237 0.0184 0.0256 0.0210 0.0120 0.0185 0.0000 0.0345 192 T A B L E 3 Life table for small gametophyte modules tagged in June, 1989. Abbreviations as for Table 1. X - X l Dx Nx J x dx _gx_ qxfDx 0-10 10 10 1.0000 0.2000 0.2000 0.0200 10-25 15 8 0.8000 0.1000 0.1250 0.0083 25-38 13 7 0.7000 0.2000 0.2857 0.0220 38-55 17 5 0.5000 0.2000 0.4000 0.0235 55-120 65 3 0.3000 0.1000 0.3333 0.0051 120-147 27 2 0.2000 0.2000 1.0000 0.0370 147-174 27 0 0.0000 T A B L E 4 Life table for large tetrasporophyte modules tagged in June, 1989. Abbreviations as for Table 1. X-Xl 0-10 10-25 25-38 38-55 55-120 120-147 147-174 174-203 203-231 231-Dx 10 15 13 17 65 27 27 29 28 Nx 10 9 8 . 7 3 1 1 1 1 0 Jx 1.0000 0.9000 0.8000 0.7000 0.3000 0.1000 0.1000 0.1000 0.1000 0.0000 dx 0.1000 0.1000 0.1000 0.4000 0.2000 0.0000 0.0000 0.0000 0.1000 _gx 0.1000 0.1111 0.1250 0.5714 0.6667 0.0000 0.0000 0.0000 1.0000 qxfDx 0.0100 0.0074 0.0096 0.0336 0.0103 0.0000 0.0000 0.0000 0.0357 TABLE 5 Life table for medium tetrasporophyte i modules tagged in June, 1989. Abbreviations as for Table 1. X-Xl. Dx Nx Ix dx _£X qxfDx 0-10 10 15 1.0000 0.3333 0.3333 0.0333 10-25 15 10 0.6667 0.3334 0.5001 0.0333 25-38 13 5 0.3333 0.0666 0.1998 0.0154 38-55 17 4 0.2667 0.1334 0.5002 0.0294 55-120 65 2 0.1333 0.0666 0.4996 0.0077 120-147 27 1 0.0667 0.0000 0.0000 0.0000 147-174 27 1 0.0667 0.0000 0.0000 0.0000 174-203 29 1 0.0667 0.0667 1.0000 0.0345 203-231 28 0 0.0000 T A B L E 6 Life table for small tetrasporophyte modules tagged in June, 1989. Abbreviations as for Table 1. X - X l Dx Nx Ix dx -22L qxfDx 0-10 10 5 1.0000 0.4000 0.4000 0.0400 10-25 15 3 0.6000 0.2000 0.3333 0.0222 25-38 13 2 0.4000 0.0000 0.0000 0.0000 38-55 17 2 0.4000 0.0000 0.0000 0.0000 55-120 65 2 0.4000 0.2000 0.5000 0.0076 120-147 27 1 0.2000 0.0000 0.0000 0.0000 147-174 27 1 0.2000 0.0000 0.0000 0.0000 174-203 29 1 0.2000 0.2000 1.0000 0.0345 203-231 28 0 0.0000 APPENDIX F: LIFE TABLES FOR BLADES OF IRIDAEA SPLENDENS TAGGED IN NOVEMBER, 1989. 196 197 T A B L E 1 Life table for all modules tagged in November, 1989. X - X l is the interval between enumeration of the tagged plants (in days). Dx refers to the number of days in the interval and Nx to the number of tagged blades present at the beginning of the interval. Ix is the proportion of the original cohort surviving to day X. dx is the proportion of the original cohort dying during the interval, qx is the proportion of those blades present at the beginning of the interval which were lost during the interval. qxfDx is the proportion lost per day. X - X l Dx Nx J x dx _2X qxfDx 0-27 27 88 . 1.0000 0.2519 0.2519 0.0093 27-56 29 69 0.7481 0.1913 0.2557 0.0088 56-84 28 49 0.5568 0.2046 0.3675 0.0131 84- 31 0.3522 T A B L E 2 Life table for all gametophyte modules tagged in November, 1989. Abbreviations as for Table 1. X - X l Dx Nx J x dx _S2L qxfDx 0-27 27 40 1.0000 0.2250 0.2250 0.0083 27-56 29 31 0.7750 0.2500 0.3226 0.0111 56-84 28 21 0.5250 0.1500 0.2857 0.0102 84- 15 0.3750 198 T A B L E 3 Life table for all tetrasporophyte modules tagged in November, 1989. Abbreviations as for Table 1. X - X l Dx Nx Ix dx _2x qxfDx 0-27 27 48 1.0000 0.2083 0.2083 0.0077 27-56 29 38 0.7917 0.2084 0.2632 0.0091 56-84 28 28 0.5833 0.2500 0.4586 0.0164 84- 16 0.3333 T A B L E 4 Life table for large gametophyte modules tagged in November, 1989. Abbreviations as for Table 1. X - X l Dx Nx Ix dx _92L qxfDx 0-27 27 3 1.0000 0.0000 0.0000 0.0000 27-56 29 3 1.0000 0^3333 0.3333 0.0115 56-84 28 2 0.6667 0.3334 0.5001 0.0179 84- 1 0.3333 199 T A B L E 5 Life table for medium gametophyte modules tagged in November, 1989. Abbreviations as for Table 1. X - X l Dx Nx J x dx _22L qxfDx 0-27 27 15 1.0000 0.3334 0.3334 0.0246 27-56 29 10 0.6667 0.2667 0.4000 0.0138 56-84 28 6 0.4000 0.2667 0.6668 0.0238 84- 2 0.1333 T A B L E 6 Life table for small gametophyte modules tagged in November, 1989. Abbreviations as for Table 1. X - X l Dx Nx J x dx qxfDx 0-27 27 22 1.0000 0.1818 0.1818 0.0067 27-56 29 18 0.8182 0.1364 0.1667 0.0057 56-84 28 15 0.6818 0.1818 0.2666 0.0095 84- 11 0.5000 200 T A B L E 7 Li fe table for large tetrasporophyte modules tagged in November . 1989. Abbreviat ions as for Table 1. X - X l Dx Nx J x dx _22L qxfDx 0-27 27 8 1.0000 0.1250 0.1250 0.0046 27-56 29 7 0.8750 0.6250 0.7143 0.0246 56-84 28 2 0.2500 0.1250 0.5000 0.0178 84- 1 0.1250 T A B L E 8 Li fe table for medium tetrasporophyte modules tagged in November, 1989. Abbreviat ions as for Table 1. X - X l Dx N x Ix dx qxfDx 0-27 27 21 1.0000 0.2857 0.2857 0.0106 27-56 29 15 0.7143 0.2381 0.3333 0.0115 56-84 28 10 0.4762 0.0952 0.1999 0.0071 84- 8 0.3810 T A B L E 9 Life table for small tetrasporophyte modules tagged in November, 1989. Abbreviations as for Table 1. X - X l Dx Nx J x dx _gx qxfDx 0-27 27 19 1.0000 0.2632 0.2632 0.0097 27-56 29 14 0.7368 0.2105 0.2857 0.0099 56-84 28 10 0.5263 0.2105 0.4000 0.0143 84- 6 0.3158 APPENDIX G: DEPLETION AND SURVIVORSHIP CURVES FOR THE SEPARATE SIZE CLASSES IN THE JUNE, 1989, COHORT OF IRIDAEA SPLENDENS 202 203 Figure 1 Number of individuals over time in large gametophj'te modules tagged in June, 1989. 40 0 20 40 60 80 100 120 140 160 180 200 220 240 TIME (DAYS] Figure 2 Survivorship of large gametophyte modules tagged in June, 1989. 207 Figure 3 Number of individuals over time in medium gametophyte modules tagged in June, 1989. 208 209 Figure 4 Survivorship of medium gametophyte modules tagged in June, 1989. 211 Top Figure 5 Number of individuals over time in small gametophyte modules tagged in June, 1989. Bottom Figure 6 Survivorship of small gametophyte modules tagged in June, 1989. 10 2.25 K 1.50 o o 0.75 0 20 40 60 80 100 120 212 213 Figure 7 Number of individuals over time in large tetrasporophyte modules tagged in June, 1989. 215 Figure 8 Survivorship of large tetrasporophyte modules tagged in June, 1989. 217 Top Figure 9 Number of individuals over time in medium tetrasporophyte modules tagged in June, 1989. Bottom Figure 10 Survivorship of medium tetrasporophyte modules tagged in June, 1989. 218 219 Top Figure 11 Number of individuals over time in small tetrasporophyte blades tagged in June, 1989. Bottom Figure 12 Survivorship of small tetrasporophyte modules tagged in June, 1989. 5.00 0 3.00 20 40 60 80 100 T I M E I DAYS] 120 140 160 180 2.25 1.50 O 0.75 0 I — 0 20 40 60 80 100 120 140 160 180 220 APPENDIX H: DEPLETION AND SURVIVORSHIP CURVES FOR THE NOVEMBER, 1989, TAGGING OF IRIDAEA SPLENDENS 221 222 Top Figure 1 Number of individuals over time in modules tagged in November, 1989. Bottom Figure 2 Survivorship of modules tagged in November, 1989. 96 0.75 20 40 223 60 80 224 Top Figure 3 Number of individuals over time in gametophyte modules tagged in November, 1989. Bottom Figure 4 Survivorship of gametophyte modules tagged in November, 1989. 226 Top Figure 5 Number of individuals over time in tetrasporophyte modules tagged in November, 1989. Bottom Figure 6 Survivorship of tetrasporophyte modules tagged in November, 1989. 2.25 X J0 1-50' o 0.75 0 I- • 0 20 40 60 80 227 228 Top Figure 7 Number of individuals over time in large gametophyte modules tagged in November, 1989. Bottom Figure 8 Survivorship of large gametophyte modules tagged in November, 1989. 229 230 Top Figure 9 Number of individuals over time in medium gametophyte modules tagged in November, 1989. Bottom Figure 10 Survivorship of medium gametophyte modules tagged in November, 1989. 232 Top Figure 11 Number of individuals over time in small gametophyte modules tagged in November, 1989. Bottom Figure 12 Survivorship of small gametophyte modules tagged in November, 1989. 233 234 Top Figure 13 Number of individuals over time in large tetrasporophyte modules tagged in November, 1989. Bottom Figure 14 Survivorship of large tetrasporophyte modules tagged in November, 1989. 235 236 Top Figure 15 Number of individuals over time in medium tetrasporophyte modules tagged in November, 1989. Bottom Figure 16 Survivorship of medium tetrasporophyte modules tagged in November, 1989. 238 Top Figure 17 Number of individuals over time in small tetrasporophyte modules tagged in November, 1989. Bottom Figure 18 Survivorship of small tetrasporophyte modules tagged in November, 1989. APPENDIX I: TABLES OF RESULTS FROM THE PERMANENT SITES, DATA ADJUSTED TO COMPENSATE FOR UNEQUAL SURFACE AREAS OF SITES. 240 241 T A B L E 1 Genet density change in contiguous transects Pairwise comparison of the differences in genet density between ^sampling periods. Given with each comparison are the means (in genets/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are e q u i v a l e n t , and the rate of mean increase or decrease over the interval (in genets/0.25 m /month. Comparison Mean S. E . P-Value Rate February/89 0.50 0.08 * May/89 1.97 0.24 0.000 + 0.49 May/89 1.97 0.24 June/89 2.66 0.32 0.184 + 0.67 June/89 2.66 0.32 July/89 2.22 0.31 0.141 -0.44 July/89 2.22 0.31 * October/89 0.95 0.14 0.008 -0.36 October/89 0.95 0.14 * November/89 1.18 0.14 0.019 + 0.23 November/89 1.18 0.14 * December/89 0.92 0.12 0.023 -0.26 December/89 0.92 0.12 January/90 0.84 0.11 0.510 -0.08 October/89 0.95 0.14 December/89 0.92 0.12 0.972 -0.03 October/89 0.95 0.14 January/90 0.84 0.11 0.533 -0.11 242 T A B L E 2 Module density change in contiguous transects Pairwise comparison of the differences in module density between sampling periods. Given with each comparison are the means (in modules/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent^ and the rate of mean increase or decrease over the interval (in modules/0.25 m /month). Comparison Mean S. E . P-Value Rate February/89 0.96 0.17 * May/89 3.94 0.45 0.000 + 0.99 May/89 3.94 0.45 June/89 4.35 0.52 0.450 + 0.41 June/89 4.35 0.52 July/89 3.44 0.50 0.081 -0.91 July/89 3.44 0.50 * October/89 1.30 0.18 0.006 -0.86 October/89 1.30 0.18 November/89 1.68 0.20 0.027 + 0.38 November/89 1.68 0.20 December/89 1.23 0.16 0.018 -0.47 December/89 1.23 0.16 January/90 1.16 0.16 0.522 -0.07 October/89 1.30 0.18 December/89 1.23 0.16 0.907 -0.04 October/89 1.30 0.18 January/90 1.16 0.16 0.457 -0.05 243 T A B L E 3 Genet density change in permanent sites adjusted for surface area Pairwise comparison of the differences in genet density between ^sampling periods. Given with each comparison are the means (in genets/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the rate of mean increase or decrease over the interval (in modules/0.25 m /month). Comparison Mean S. E . P-Value Rate January/89 4.66 0.65 * February/89 1.89 0.32 0.000 -2.95 February/89 1.89 0.32 * April/89 8.59 1.80 0.000 + 3.35 April/89 8.59 1.80 * May/89 16.08 3.35 0.017 + 7.49 May/89 16.08 3.35 June/89 19.08 3.84 0.362 + 3.00 June/89 19.08 3.84 July/89 15.03 3.65 0.191 -4.05 July/89 15.03 3.65 August/89 16.24 4.39 0.839 + 1.21 August/89 16.24 4.39 * October/89 8.71 1.95 0.011 -3.01 October/89 8.71 1.95 November/89 6.82 1.71 0.154 -1.89 November/89 6.82 1.71 December/89 5.13 1.19 0.255 -1.69 December/89 5.13 1.19 January/90 2.84 0.49 0.155 -2.29 January/90 2.84 0.49 * February/90 1.78 0.37 0.049 -1.06 T A B L E 3 Continued. Comparison Mean October/89 8.71 December/89 5.13 November/89 6.82 January/90 2.84 December/89 5.13 February/90 1.78 S. E . P-Value Rate 1.95 • * 1.19 0.024 -1.79 1.71 0.49 0.003 -1.99 1.19 0.37 0.002 -1.64 245 T A B L E 4 Module density change in permanent sites adjusted for surface area Pairwise comparison of the differences in module density between sampling periods. Given with each comparison are the means (in modules/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalen^ and the rate of mean increase or decrease over the interval (in modules/0.25 m /month). Comparison Mean S. E . P-Value Rate Januar3'/89 7.36 1.05 * February/89 3.01 0.55 0.000 -4.35 February/89 3.01 0.55 * April/89 17.11 3.48 0.000 + 7.05 April/89 17.11 3.48 May/89 28.39 5.22 0.056 + 11.28 May/89 28.39 5.22 June/89 32.24 5.51 0.430 + 3.85 April/89 17.11 3.48 * June/89 32.24 5.51 0.008 + 7.57 June/89 32.24 5.51 July/89 21.32 4.45 0;076 -10.92 July/89 21.32 4.45 August/89 23.19 5.18 0.628 + 1.87 August/89 23.19 5.18 * October/89 11.73 2.39 0.004 -4.58 October/89 11.73 2.39 November/89 8.39 1.83 0.062 -3.34 November/89 8.39 1.83 December/89 6.24 1.30 0.191 -2.15 December/89 6.24 1.30 January/90 3.48 0.56 0.149 -2.76 T A B L E 4 Continued. Comparison Mean January/90 3.48 February/90 2.16 October/89 11.73 December/89 6.24 November/89 8.39 January/90 3.48 December/89 6.24 February/90 2.16 S. E . P-Value Rate 0.56 ^ ; 0.45 0.039 -1.32 2.39 : | ; 1.30 0.006 -2.75 1.83 , : 0.56 0.002 -2.46 1.30 :]; 0.45 0.001 -2.04 247 T A B L E 5 Change in gametophyte genet density in permanent sites adjusted for surface area Pairwise comparison of the differences in gametophyte genet density betweeg sampling periods. Given with each comparison are the means (in genets/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and thg rate of mean increase or decrease over the interval (in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate January/89 2.09 0.42 * February/89 0.29 0.12 0.000 -1.80 February/89 0.29 0.12 * April/89 6.28 1.28 0.000 + 2.99 April/89 6.28 1.28 May/89 10.65 2.25 0.133 + 4.37 May/89 10.65 2.25 June/89 12.76 2.53 0.404 + 2.11 April/89 6.28 1.28 * June/89 12.76 2.53 0.014 + 3.24 June/89 12.76 2.53 July/89 10.12 2.64 0.251 -2.64 July/89 10.12 2.64 August/89 11.08 2.95 0.581 + 0.96 August/89 11.08 2.95 * October/89 4.75 1.16 0.002 -2.53 October/89 4.75 1.16 November/89 3.39 1.11 0.109 -1.36 November/89 3.39 1.11 * December/89 1.83 0.67 0.038 -1.56 T A B L E 5 Continued. Comparison Mean S. E . P-Value Rate December/89 1.83 0.67 January/90 0.59 0.13 0.110 -1.24 January/90 0.59 0.13 February/90 0.29 0.09 0.073 -0.30 October/89 4.75 1.16 December/89 1.83 0.67 0.001 -1.46 November/89 3.39 1.11 January/90 0.59 0.13 0.000 -1.40 December/89 1.83 0.67 February/90 0.29 0.09 0.002 -0.77 * 249 T A B L E 6 Change in tetrasporophyte genet density in permanent sites adjusted for surface area Pairwise comparison of the differences in tetrasporophyte genet density betweeg sampling periods. Given with each comparison are the means (in genets/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the, rate of mean increase or decrease over the interval (in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate January/89 2.53 0.39 : | ; February/89 1.61 0.30 0.026 -0.97 February/89 1.61 0.30 April/89 2.32 0.59 0.986 +0.36 * April/89 2.32 0.59 May/89 5.58 1.27 0.020 +3.26 May/89 5.58 1.27 June/89 6.33 1.47 0.595 +0.75 June/89 6.33 1.47 July/89 4.92 1.14 0.352 -1.41 July/89 4.92 1.14 August/89 5.16 1.52 0.991 +0.24 August/89 5.16 1.52 October/89 3.94 0.85 0.573 -0.49 June/89 6.33 1.47 October/89 3.94 0.85 0.091 -0.44 October/89 3.94 0.85 November/89 3.43 0.78 0.347 -0.51 June/89 6.33 1.47 , : November/89 3.43 0.78 0.026 -0.45 November/89 3.43 0.78 December/89 3.28 0.66 0.901 -0.15 T A B L E 6 Continued. Comparison Mean S. E . P-Value Rate December/89 3.28 0.66 Jamuary/90 2.25 0.42 0.301 -1.03 January/90 2.25 0.42 February/90 1.49 0.37 0.074 -0.76 October/89 3.94 0.85 December/89 3.28 0.66 0.470 -0.33 August/89 5.16 1.52 December/89 3.28 0.66 0.266 -0.34 January/90 2 5 42 034 45November/89 3.43 0.78 January/90 2.25 0.42 0.304 -0.59 October/89 3.94 0.85 January/90 2.25 0.42 0.063 -0.56 December/89 3.28 0.66 * February/90 1.49 0.37 0.008 -0.89 251 T A B L E 7 Change in gametophyte module density in permanent sites adjusted for surface area Pairwise comparison of the differences in gametophyte module density between sampling periods. Given with each comparison are the means (in modules/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the rate of mean increase or decrease over the interval (in modules/0.25 m /month). Comparison Mean S. E . P-Value Rate January/89 2.79 0.55 * February/89 0.37 0.15 0.000 -2.42 February/89 0.37 0.15 * April/89 11.81 2.46 0.000 + 5.72 April/89 11.81 2.46 May/89 18.70 3.58 0.129 + 6.89 May/89 18.70 3.58 June/89 20.77 3.71 0.521 + 2.07 April/89 11.81 2.46 * June/89 20.77 3.71 0.029 + 4.48 June/89 20.77 3.71 July/89 14.05 3.10 0.171 -6.72 July/89 14.05 3.10 August/89 15.29 3.46 0.689 + 1.24 August/89 15.29 3.46 * October/89 6.65 1.58 0.002 -3.46 October/89 6.65 1.58 November/89 4.01 1.16 0.071 -2.64 November/89 4.01 1.16 * December/89 2.19 0.71 0.044 -1.82 T A B L E 7 Continued. Comparison Mean S. E . F-Value Rate December/89 2.19 0.71 January/90 0.67 0.15 0.074 -1.52 January/90 0.67 0.15 February/90 0.33 0.11 0.069 -0.34 October/89 6.65 1.58 December/89 2.19 0.71 0.001 -2.23 November/89 4.01 1.16 : | : January/90 0.67 0.15 0.000 -1.67 December/89 2.19 0.71 February/90 0.33 0.11 0.001 -0.93 T A B L E 8 253 Change in tetrasporophyte module density in permanent sites adjusted for surface area Pairwise comparisons of the differences in tetrasporophyte module density between sampling periods. Given with each comparison are the means (in modules/0.25 m of substratum) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the rate of mean increase or decrease over the interval (in modules/0.25 m /month). Comparison Mean S. E . P-Value Rate January/89 4.57 0.67 * February/89 2.64 0.53 0.021 -1.93 February/89 2.64 0.53 April/89 5.29 1.41 0.846 + 1.33 April/89 5.29 1.41 * May/89 9.70 1.97 0.041 + 4.41 May/89 9.70 1.97 June/89 10.83 2.10 0.527 + 1.13 June/89 10.83 2.10 July/89 7.41 1.51 0.215 -3.42 July/89 7.41 1.51 August/89 7.89 1.89 0.800 + 0.48 August/89 7.89 1.89 October/89 5.08 0.93 0.191 -1.13 June/89 10.83 2.10 * October/89 5.08 0.93 0.028 -1.05 October/89 5.08 0.93 November/89 4.38 0.87 0.364 -0.70 November/89 4.38 0.87 December/89 4.03 0.73 0.735 -0.35 December/89 4.03 0.73 January/90 2.81 0.48 0.309 -1.22 T A B L E 8 Continued. Comparison Mean S. E . P-Value Rate January/90 2.81 0.48 February/90 1.84 0.45 0.040 -0.97 October/89 5.08 0.93 December/89 4.03 0.73 0.299 -0.53 August/89 7.89 1.89 December/89 4.03 0.73 0.043 ' -0.70 November/89 4.38 0.87 January/90 2.81 0.48 0.173 -0.79 October/89 5.08 0.93 January/90 2.81 0.48 0.037 -0.76 December/89 4.03 0.73 February/90 1.84 0.45 0.006 -1.10 255 T A B L E 9 Differences in number of modules per genet, between alternate phases, within  individual sampling periods, in permanent sites. A comparison of the distribution of modules per genet in gametophytes vs. tetrasporophytes within each sampling period. Given with each comparison are the means, standard errors, and the probability of the null hypothesis that the distributions are equivalent. Sampling Comparison Mean S. E . P-Value Period January/89 Gam. 1.25 0.06 * Tet. 1.72 0.11 0.004 February/89 Gam. 1.30 0.21 Tet. 1.53 0.09 0.251 April/89 Gam. 1.92 0.09 Tet. 2.24 0.18 0.164 May/89 Gam. 1.88 0.07 Tet. 1.89 0.11 0.376 June/89 Gam. 1.72 0.05 Tet. 1.75 0.10 0.189 July/89 Gam. 1.42 0.05 Tet. 1.53 0.09 0.732 August/89 Gam. 1.46 0.05 Tet. 1.64 0.10 0.346 October/89 Gam. 1.34 0.06 Tet. 1.35 0.06 0.832 November/89 Gam. 1.19 0.05 * Tet. 1.31 0.05 0.036 December/89 Gam. 1.26 0.08 Tet. 1.23 0.05 0.684 January/90 Gam. 1.13 0.07 Tet. 1.26 0.06 0.392 February/90 Gam. 1.10 0.10 Tet. 1.25 0.08 0.497 256 T A B L E 10 Change in number of modules per genet in contiguous transects Pairwise comparison of the number of modules per genet between sampling periods. Given with each comparison are the means, standard errors, the probability of the null hypothesis that the distributions are equivalent, and the rates of mean increase or decrease over the interval (in Modules per Genet per month). Comparison Mean S. E . P-Value Rate February/89 1.92 0.12 May/89 2.00 0.07 0.706 + 0.04 May/89 2.00 0.07 * June/89 1.63 0.04 0.000 -0.37 June/89 1.63 0.04 July/89 1.56 0.04 0.336 -0.07 July/89 1.56 0.04 * October/89 1.36 0.05 0.009 -0.06 October/89 1.36 0.05 November/89 1.42 0.05 0.696 + 0.06 November/89 1.42 0.05 December/89 1.33 0.05 0.061 -0.09 December/89 1.33 0.05 January/90 1.39 0.05 0.081 + 0.06 257 T A B L E 11 Change in number of modules per genet in permanent sites. Pairwise comparison of the differences in number of modules per genet between sampling periods. Given with each comparison are the means, standard errors, the probability of the null hypothesis that the distributions are equivalent, and the rates of mean increase or decrease over the interval (in Modules per per month). Comparison Mean S. E . P-Value Rate January/89 1.52 0.07 February/89 1.50 0.09 0.647 -0.02 February/89 1.50 0.09 * April/89 2.00 0.08 0.017 + 0.25 April/89 2.00 0.08 May/89 1.89 0.06 0.109 -0.11 May/89 1.89 0.06 * June/89 1.73 0.05 0.022 -0.16 June/89 1.73 0.05 * July/89 1.46 0.05 0.000 -0.27 July/89 1.46 0.05 August/89 1.52 0.05 0.244 + 0.06 August/89 1.52 0.05 * October/89 1.35 0.04 0.049 -0.07 October/89 1.35 0.04 November/89 1.26 0.04 0.207 -0.09 November/89 1.26 0.04 December/89 1.24 0.04 0.636 -0.02 December/89 1.24 0.04 January/90 1.23 0.05 0.988 -0.01 January/90 1.23 0.05 February/90 1.23 0.07 0.891 0.00 APPENDIX J : TABLES FOR T H E DYNAMICS OF REPRODUCTIVELY MATURE STAGES OF IRIDAEA SPLENDENS 258 259 T A B L E 1 Change in mean density of nonfertile genets in the contiguous transects. Pairwise comparison of the differences in genet density between sampling periods. Given with each comparison are the means (in genets/0.25 m ) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalen^, and the rate of mean increase or decrease over the interval (in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate February/89 0.23 0.06 * May/89 1.97 0.24 0.000 + 0.58 May/89 1.97 0.24 June/89 2.67 0.32 0.182 + 0.70 June/89 2.67 0.32 July/89 2.20 0.31 0.117 -0.47 July/89 2.20 0.31 * October/89 0.58 0.11 0.000 -0.46 October/89 0.58 0.11 November/89 0.39 0.08 0.160 -0.19 November/89 0.39 0.08 * December/89 0.20 0.07 0.018 -0.19 December/89 0.20 0.07 January/90 0.27 0.05 0.102 + 0.07 260 T A B L E 2 Change in mean density of tetrasporangial genets in the contiguous transects. Pairwise comparison of the differences in genet density between sampling periods. Given with each comparison are the means (in genets/0.25 m ) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent,^ and the rate of mean increase or decrease over the interval ( in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate February/89 0.23 0.05 * May/89 0.00 0.00 0.000 -0.08 May/89 0.00 0.00 June/89 0.00 0.00 1.000 0.00 June/89 0.00 0.00 July/89 0.00 0.00 1.000 0.00 July/89 0.00 0.00 * October/89 0.27 0.03 0.000 + 0.08 October/89 0.27 0.03 * November/89 0.55 0.06 0.000 + 0.28 November/89 0.55 0.06 December/89 0.58 0.07 0.621 + 0.01 December/89 0.58 0.07 January/90 0.48 0.07 0.188 -0.03 261 T A B L E 3 Change in mean density of cystocarpic genets in the contiguous transects. Pairwise comparison of the differences in genet density between sampling periods. Given with each comparison are the means (in genets/0.25 m ) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalen^, and the rate of mean increase or decrease over the interval (in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate February/8 9 0.03 0.01 * May/89 0.00 0.00 0.014 -0.01 May/89 0.00 0.00 June/89 0.00 0.00 1.00 0.00 June/89 0.00 0.00 * July/89 0.07 0.03 0.002 + 0.02 July/89 0.07 0.03 * October/89 0.19 0.04 0.002 + 0.04 October/89 0.19 0.04 November/89 0.25 0.05 0.395 + 0.06 November/89 0.25 0.05 December/89 0.13 0.03 0.101 -0.12 December/89 0.13 0.03 January/90 0.10 0.02 0.432 -0.03 November/89 0.25 0.05 January/90 0.10 0.02 0.017' -0.08 262 T A B L E 4 Change in mean density of nonfertile genets in the permanent sites (data adjusted for surface area). Pairwise comparison of the differences in nonfertile genet density between sampling periods. Given with each comparison are the means (in genets/).25 m ) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalen|, and the mean rate of increase or decrease over the interval (in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate April/89 8.59 1.80 * May/89 16.79 3.41 0.013 + 8.20 May/89 16.79 3.41 June/89 18.54 3.81 0.562 + 1.75 June/89 18.54 3.81 July/89 13.73 3.49 0.093 -4.81 July/89 13.73 3.49 August/89 13.27 3.56 0.809 -0.46 June/89 18.54 3.81 August/89 13.27 3.56 0.067 -2.64 August/89 13.27 3.56 * October/89 4.65 1.29 0.000 -3.45 October/89 4.65 1.29 November/89 3.59 1.09 0.511 -1.06 November/89 3.59 1.09 December/89 1.91 0.53 0.173 -1.68 October/89 4.65 1.29 December/89 1.91 0.53 0.063 -1.37 December/89 1.91 0.53 January/90 0.62 0.15 0.040 -1.29 January/90 0.62 0.15 February/90 0.38 0.11 0.233 -0.24 263 T A B L E 5 Change in mean density of tetrasporangial genets in the permanent sites (adjusted for surface area). Pairwise comparison of the differences in mean tetrasporangial genet density between sampling periods. Given with each comparison are the means (in genets/0.25 m ) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are equivalent, and the, rate of mean increase or decrease over the interval (in g€ m /month). Comparison Mean S. E . P-Value Rate April/89 0.00 0.00 May/89 0.00 0.00 1.000 0.00 May/89 0.00 0.00 * June/89 0.14 0.08 0.041 + 0.14 June/89 0.14 0.08 July/89 0.01 0.01 0.152 -0.13 July/89 0.01 0.01 * August/89 0.81 0.28 0.000 + 0.80 August/89 0.81 0.29 * October/89 1.74 0.31 0.000 + 0.37 October/89 1.74 0.31 November/89 1.96 0.40 0.982 + 0.22 November/89 1.96 0.40 December/89 2.49 0.55 0.587 + 0.53 October/89 1.74 0.31 December/89 2.49 0.55 0.548 + 0.38 December/89 2.49 0.55 January/90 2.13 0.40 0.977 -0.36 January/90 2.13 0.40 February/90 1.32 0.32 0.051 -0.81 December/89 2.49 0.55 * February/90 1.32 0.32 0.027 -0.59 264 T A B L E 6 Change in mean density of cystocarpic genets in t h e permanent sites (adjusted for surface area). Pairwise comparison of the differences in mean cystocarpic genet density between sampling periods. Given with each comparison are the means (in genets/0.25 m ) and standard errors for each sampling period, the probability of the null hypothesis that the distributions for the two periods are e q u i v a l e n t , and the rate of mean increase or decrease over the interval (in genets/0.25 m /month). Comparison Mean S. E . P-Value Rate April/89 0.00 0.00 May/89 0.00 0.00 1.000 0.00 May/89 0.00 0.00 * June/89 0.43 0.16 0.001 + 0.43 June/89 0.43 0.16 * July/89 1.29 0.29 0.012 + 0.86 July/89 1.29 0.29 August/89 2.32 0.72 0.430 + 1.03 June/89 0.43 0.16 August/89 2.32 0.72 0.002 + 0.95 August/89 2.32 0.72 October/89 2.18 0.58 0.582 -0.06 October/89 2.18 0.58 November/89 1.27 0.36 0.185 -0.91 November/89 1.27 0.36 December/89 0.74 0.20 0.086 -0.53 October/89 2.18 0.58 December/89 0.74 0.20 0.005 -0.72 December/89 0.74 0.20 January/90 0.27 0.09 0.108 -0.47 January/90 0.27 0.09 February/90 0.08 0.05 0.054 -0.19 December/89 0.74 0.20 * February/90 0.08 0.05 0.001 -0.33 

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