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The physical oceanographic factors governing the plankton distribution in the British Columbia inlets LeBrasseur, Robin John 1954

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THE PHYSICAL OCEANOGRAPHIC FACTORS GOVERNING THE PLANKTON DISTRIBUTION IN THE BRITISH COLUMBIA INLETS by ROBIN JOHN LEBRASSEUR A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS ih the Department of ZOOLOGY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF ARTS Members of the Department of Zoology THE UNIVERSITY OF BRITISH COLUMBIA Apri l , 1954. ABSTRACT The major constituents of the plankton, phyto-plankton, cladocera, copepods and chaetognaths, sampled in the 1951 oceanographic survey of the British Columbia Inlets are reported in concentrations per cubic meter of water. Horizontal plankton tows sampled four depths, 5, 21, 32 and 47 feet, respectively. The distribution of each group i s discussed in relation to the hydrographic data and the pre-sent theory of inlet circulation. The inlets investigated f a l l into two general groups, (a) those which are long and have a large freshwater discharge at the head and (b) those which have a small freshwater discharge and are short. The data from six inlets making up the former have been grouped together and are discussed as the Average Inlet. Those inlets making up the latter group are classified under the general heading of atypical inlets; each i s discussed separately. In the Average Inlet the plankton volumes were the greatest at the mouth, particularly towards the surface. The con-centration of plankton i s shown to be a result of local phytoplankton production. In the absence of currents the phytoplankton are shown to be limited v e r t i c a l l y by density. The zooplankton are divided into three groups on the basis of their response to the physical factors. The distribution of cladocera indicates that i t i s positively phototropic while that of the copepods and chaetognaths indicate that that they are negatively phototropic. The chaetognaths are found to be absent from a l l the atypical inlets, the cladocera from three. The copepods are concentrated at the depth which i s associated with the compensation light inten-sit y . Attention i s drawn to the fact that this report i s a qualitative description of the relationship between the distribution of the plankton and the physical oceanographic conditions. Future surveys w i l l have to sample more exten-sively and intensively. ACKNOWLEDGMENTS The writer wishes to acknowledge with thanks financial assistance made available from National Research Council funds by Dr. G. L. Pickard for the i n i t i a l examina-tion of the plankton samples collected during the 1951 Inlet Survey. Personal thanks are due to Dr. G.L. Pickard for his assistance in obtaining the hydrographic data before i t was available for publication. Thanks, also, are due to the other students associated with the Institute of Oceano-graphy for their unfailing interest, co-operation, and sug-gestions throughout the preparation of this paper. Help i s also acknowledged in the fin a l preparation of the diagrams. Finally, the writer would like to thank Dr. W^M?. Cameron, under whose supervision this work was carried out, for determining the vertical current velocities reported here and for his encouragement and assistance in the preparation of the f i n a l draft of this paper. TABLE OF CONTENTS Page INTRODUCTION 1 MATERIALS AND METHODS i 4 Collection of data 4 Calibration of samplers 4 Examination of material . . . . . . . . 6 Significance of data . . . . . . . . 8 RESULTS AND DISCUSSION 9 Average Inlet 9 Factors affecting distribution of plankton . . . . 9 Light 9 Temperature 12 Salinity 14 Oxygen 15 Currents 20 Plankton distribution in the Average Inlet . . . . 23 Atypical Inlets 30 Belize Inlet 32 Pendrell Sound 35 Laredo Inlet 39 Surf Inlet 41 CONCLUSIONS AND SUMMARY 44 REFERENCES 49 - I — 130° I 2 5 ° W Figure I. THE PHYSICAL OCEANOGRAPHIC FACTORS GOVERNING THE PLANKTON DISTRIBUTION IN THE BRITISH COLUMBIA INLETS INTRODUCTION During the summer of 1951 the Institute of Oceano-graphy of the University of British Columbia undertook an exploratory survey of the coast of British Columbia. In the course of i t s investigations observations were made in seventeen (17) inlets along the mainland coast. (Figure 1). Although the main purpose of the survey was physical oceano-graphy, an opportunity was afforded to make certain plank-ton collections. British Columbia coast has received considerable attention since the pioneer work of Hutchinson and Lucas (1928, 1929, and 1931) in the Strait of Georgia. They dis-cussed the distribution of plankton on the basis of the know-ledge of the physical conditions available at that time. Carter (1933) gave a general description of the physical oceanography and plankton of three southern in l e t s . He found the inlets less productive at the head than at the 1 2 mouth, and less productive than the Strait of Georgia. Unfor-tunately, his data have not been published so comparisons with the other inlets cannot be made. Tully (1936, 1942 and 1949), Thompson and Barkley (1938), Pickard (1953), and Tabata (1954) have reported on the physical characteristics of inlets, and Cameron (1951) has discussed their dynamics on a theoretical basis. With the exception of Carter's work, no report on the biological phenomena of Br i t i s h Columbia inlets has been forthcoming. This lack has stemmed primarily from the concentration on the physical phenomena. In view of the extensive scope of both the physical and biological data of the 1951 expedition, i t i s proposed to summarize the gross features of the plankton distributions and to interpret them in the light of the more recent and adequate observational and theoretical material. Pickard (1953) has described the main physical fea-tures of the inlets. The inlets are long, narrow, deep and generally without beaches. A short river of glacial origin discharges into the head of the majority of the inlets. The salinity of the surface water increases to the seaward, vary-ing from 0 °/oo a t the head to 28 °/oo at the mouth. Below 60 feet the salinity i s comparatively constant. The tempera-ture of the surface water generally increases down the i n l e t , while that of the deep water remains nearly constant. Most of the inlets have direct access to the coastal waters so that there i s l i t t l e opportunity for stagnation to occur; the only inlet this paper deals with that has evidence of stagnation 3 i s Belize Inlet. The gross biological features can be similarly described. Six inlets, Bute, Knight, Dean, Gardner, Douglas and Portland, which in their average conform to Pickard 1s description, have been summarized. We shall f i r s t submit a parallel description of the biological conditions in the Average Inlet, then analyse their features in the light of the physical observations available, and indicate the im-portant physical characteristics which determine the plank-tonic distribution. Finally, atypical inlets w i l l be des-cribed and the departures from the norm w i l l be discussed. 4 MATERIALS AND METHODS Collection: A total of 98 plankton stations were made in 17 inlets and adjacent waters. Horizontal ten-minute tows with Clarke-Bumpus Plankton Samplers at four depths provided the material, which consists of 398 samples. The depths sampled were 5, 21, 32, and 47 feet with an approximate error of 14 °/b either way. The samples were preserved for examina-tion at the Institute of Oceanography. Calibration of the Samplers The flow meters were calibrated independently over a range of 0.8 to 2 knots by towing the samplers without nets a 20 meter distance in times ranging from 20 to 50 seconds. The volume f i l t e r e d per revolution of the meter was calcul-ated from the cross-sectional area of the sampler and the distance travelled per revolution. Reference to Table 1 TABLE 1 CALIBRATION OP FLOW METERS NET NO. 1 ' NET NO. 2 DATE Meters/Rev. Liters/Rev. Meters/Rev. Liters/Rev. May 20 0.449 5.39 0.435 5.20 May 31 0.409 4.91 June 21 0.418 5.03 0.410 4.92 July 20 0.412 4.95 0.419 5.04 indicates that after the i n i t i a l breaking in period during the f i r s t ten days, the flow meters consistently recorded an approximate volume of five l i t e r s of water per revolution The range of the calibration ratings are well within the 5% variation suggested by Clarke and Bumpus (1950) for the esti mated towing speeds. 40 of the 136 samples discussed in this report were obtained with a No. 10 mesh net, the remainder with No. 2 mesh. An evaluation of the relative f i l t e r i n g e f f i -ciencies of these two meshes was necessary before their res-pective plankton volumes could be compared. Unfortunately, c in experiments designed to sample the same volumn of water simultaneously with the two nets the opening and closing mechanism of the sampler failed to operate. Consequently, i t was assumed that the total volume of plankton was approxi mately the same in a l l the inlets over the depths sampled. The samples and the respective volumes of water f i l t e r e d taken with each net were averaged and the volume of plankton per cubic meter calculated. The results given in Table 2 indicate that the smaller mesh nets, Nos. 10 and 20, retain nearly twice as much plankton as does No. 2 mesh. A 20% variation in the total plankton was found for the inlets, which i s s u f f i -ciently small enough to justify the assumption made earlier. On the basis of this, a l l the plankton volumes are dis-cussed in terms of the f i l t e r i n g capacity of No. 2 mesh. Where the organisms are reported as absolute numbers per 6 cubic meter no correction was applied, since these organisms were large enough to be caught in equal numbers by any of the nets. TABLE 2 COMPARISON OF FILTERING EFFICIENCY OF MESHES NO. 2, 10, AND 20 Mesh Size Volume of Water Volume of Plankton Vol.Plankton Filtered (m3) Filtered (c8) /m3 5.6 6.7 1.14 6.4 13.1 2.0 5.7 11.7 2.1 Examination of Material The settling volume of each plankton sample was determined, and for comparison with other data, sixty samples were chosen randomly for the determination of displacement volumes. The settling volumes were found to be approximately four times greater than the displacement volumes (Sverdrup et a l pg. 935 gives a value of 4.9 times as great). The plankton volumes were expressed as cubic centimeters of plankton per cubic meter of water. A 10 ml. sub sample was taken from every sample for examination under a low power binocular microscope. The major groups of plankton were identified and the quantity of each group was estimated as a percentage of the total volume. 2 10 20 7 Usually where a group of plankters was less than one per cent of the total volume, each organism was counted. The plankton were classified under the following headings: A Phytoplankton ±2 Zooplankton Coelenterata - Hydrozoa - Siphonophora Ctenophora Mollusca Annelida A Crustacea - Cladocera - Ostracoda - Cirrepedia - Copepoda - Mysidacea - Amphipoda - Euphausidacea - Decapoda A Chaetognatha Tunicata Pisces Eggs The starred groups (A) are the ones discussed in this paper. 8 Significance of data: Before discussing the relative volumes and d i s t r i -bution of the plankton the actual significance of the results should be stressed. The 1951 Inlet Survey was designed to emphasize the common attributes of the inlets which are independent of local peculiarities. In the collection of the plankton samples the effect of variables such as distance, time and weather were sacrificed to achieve the overall plan. The interrelationships and behavior of the plankton also had to be overlooked. The plankton observations w i l l deal with a pre-liminary evaluation of the qualitative relationships found between them and the oceanographic factors. Accordingly, the inlets which were oceanographically similar, and which had a maximum of reliable plankton observations were chosen for analysis. In appreciation of the fact that plankton sampling i s , even under ideal conditions, subject to large sampling errors the data were grouped under one heading, the Average Inlet; and in order to minimize local peculiarities only three positions were examined c r i t i c a l l y , the mouth, middle, and head of the in l e t . The f i n a l result i s a picture of the gross biological and physical conditions found in the typi-cal British Columbia inlets during the spring and summer months. 9 RESULTS AND DISCUSSION 1. Average Inlet Riley (1946) has shown for ecological investiga-tions a variation in one factor directly, or i n d i r e c t l y / affects the other factors. Consequently, i t i s d i f f i c u l t to assess the relative importance of any one factor. The overall distribution of the total plankton for the upper 60 feet in the inl e t i s shown in Figure 2. Atten-tion i s called to the significant increase of the total volume of plankton from the head to the mouth. There i s also an increase of the volumes towards the surface at the mouth. The explanation of these variations with depth and position w i l l he sought for in the variations of the physical environment. The observations of light, temperature, sal-inity and oxygen w i l l be presented. Their individual and combined effects on the plankton, w i l l be discussed. The circulation and i t s probable effect on the inlet plankton w i l l be described. Finally, on the basis of the physical observations a theoretical distribution of the plankton w i l l be compared to their actual distribution. 1) Physical Characteristics A. Light: The penetration of light was restricted by the s i l t and debris carried in by the tributary at the head of the inl e t . Secchi disc readings ranged from less than one MOUTH MIDDLE HEAD 2Cf 30H 40 501 ui ° l i o -20 30 FIGURE 2 i AVERAGE INLET-DISTRIBUTION OF PLANKTON (cc/m 3) Ui ° 40 50»-COMPENSATION DEPTH *0 .07 FIGURE 3. AVERAGE INLET-DISTRIBUTION OF LIGHT INTENSITY (flm.col/cnf/hr) 10 20-30 40-50-B RAKISH ZONE < REGION OF NO HORIZONTAL MOTION [ / / / / / / ^ 4 INTERMEDIATE ZONE FIGURE 4. AVERAGE INLET - CURRENT DISTRIBUTION (SCHEMATIC) 10 foot at the head to 25 and more feet at the mouth. A strong positive correlation was found between the secchi disc read-ing and the s a l i n i t y along the i n l e t . This confirms the impression that the increasing secchi disc readings from the head towards the mouth are a function of the increasing dilution of the s i l t laden river water towards the mouth. Figure 3 showing distribution of light intensity with depth along the inlet is based on the assumption that the light scattering quality of the water column i s homogeneous. In actual practice where the secchi disc readings are very small this was not found to be the case. The lack of further obser-vational data has prevented correcting for this phenomena. Light intensity is the prime factor directly influencing plankton production. For the low light inten-s i t i e s , Jenkin (1937) has demonstrated a nearly linear relationship with the phot©synthetic rate of the diatom, Cosinodiscns excentricus Ehr. Sverdrnp et a l (pg. 781) re-port that different species of diatoms have different opti-mum light intensities; these values are between 1.0 and 0.1 gm/cal/cm2/hr. ( 1 gm/cal/hr.•= 7750 luxes). Below the region of optimum light intensity is a point at which the light i s sufficiently strong for the phyto-plankton to survive, but insufficient for i t to grow. This point is called the compensation point. For mixed plank-ton in a Swedish fjord Sverdrup et a l (pg. 782) report that Pettersson et a l (1934) found the compensation light 2 intensity to be about 0.07 gm/cal/cm /nr. Assuming this to be a good approximation of the light intensity required by the British Columbia diatoms the depth at which this l i e s can be calculated from the secchi disc readings from the relationship:-l o g i n I. . l o g 1 0 I - 1 , 7 x Lm (Sverdrup et al pg. 80,82) 2.3 D m I 0 = light intensity at the sea surface (cm2) = 1.8 gm./cal/cm2/hr. (Riley et a l . 1949, Fig.l) I 1 - light intensity at compensation depth r. i pg. 782) = 0.07 gm/cal/cm /h  (Sverdrup et a l , Lffl = depth in meters of compensation depth Dffl = depth in meters of secchi disc reading. These values calculated for the Average Inlet are shown in Table 3, they represent the lower boundary of lig h t inten-sity shown in Figure 3. Light stimulates and regulates zooplankton movement. Russel (1927), Clarke (1934) and Bogorov (1946) have demon-strated a correlation between the intensity of light and the distribution of zooplankton. The optimum light intensity varies from species to species, for different ages and sexes, and for changes in the physical environment. There are also marked vertical migrations which are thought to be brought about by a change in the light intensity. However, generally speaking, the members of any one group are consistently found in the same photic zone. For example, the cladocera are positively phototrophic and are found near the surface where the light intensities are the strongest, Jorgensen (1934). Bogorov's observations (1946) of the arctic summer plankton showed that the organisms maintained an invariable vertical distribution, in spite of temperature and salinity fluctuations. On the basis of light then, the plankton can be expected to show a variable distribution in the Average Inlet, where the light intensity varies with depth and from station to station. Those zooplankton which tend to remain at a constant light intensity w i l l be nearest the surface towards the head where light penetration i s the least. The phytoplankton can be expected to be the most abundant towards the mouth where the depth range of optimum light intensities i s the greatest. B. Temperature: Figure 5 shows the temperature distribution. The temperatures increased from the deep zone towards the surface, a slight thermocline occurring from 20 feet to the surface. The surface water temperatures immediately adjacent to entrance of the river were the coldest temperatures en-countered. The low temperature of the river tended to mod-erate the surface temperature the length of the i n l e t . The variation in temperature caused a 30% variation in the mole-cular viscosity of the water. FIGURE 7. AVERAGE INLET-DISTRIBUTION OF OXYGEN (V.) 13 Temperature influences the growth and metabolism of plankton. According to von Hoff»s Law a 10°C rise in temperature w i l l increase the rate of metabolism 2 to 3 o times. A 6 C difference in temperature from the surface to f i f t y feet was found. Those organisms which occupy the surface zone should have a correspondingly more rapid meta-bolism and growth rate. However, no observations were made of this phenomena. The rate of sinking, for an organism whose density is nearly equal to that of i t s environment, is inversely proportional to the molecular viscosity of the water which in turn is inversely proportional to the temperature. Con-sequently, i n the region of a thermocline there would be a concentration of non motile forms because they would sink into the thermocline faster than they would sink out. Another effect of thermoclines is to limit the vertical movement of the stenothermic zooplankton, and other marine organisms, Sverdrup et a l (pg. 838). Reference to Figure 5 indicates that the thermocline i s not as sharp as the halocline, Fig-ure 6, therefore i t seems l i k e l y that the effect of molecular viscosity and the thermocline w i l l be overshadowed by that of s a l i n i t y , or possibly light. The temperature may limit or modify an organism's response to other environmental conditions. For example, considering the effect of temperature and light intensity, Russel (1928) working with the copepod, Calanns finmarchius (Qunnerus), found i t to be negatively phototropic to light at 20°C but at 13°C i t became positively phototropic and strongly so at 10GC. Temperature in the Average Inlet may possibly play a modifying role such as this. C. Salinity: The variation in s a l i n i t y with depth and posi-tion was the most outstanding characteristic of the inlet waters, Figure 6. Above 60 feet the s a l i n i t y ranged from less than 5 °/oo at the head to more than 30 °/oo at the mouth. Below 60 feet the salinity showed less than 3 °/o variation. The density and the salt content of the surface waters w i l l show a corresponding variation. The osmotic balance existing between the sea water and the body fluids of the inlet plankton i s related to the salt content of the water. Typically, the sa l i n i t y shows only a slight variation from oceanic to coastal waters. In the inlets there i s an 80 percent variation. Adolph (1925) pointed out how comparatively easy oceanic forms can main-tain their salt balance when compared to the coastal forms. He assumes that the organisms maintain an osmotic e q u i l i -brium with the water. Gross (1940) found evidence to sug-gest that some diatoms are in fact hypotonic to the sea water. However, until more work of this nature i s done i t seems reasonable to conclude that only euryhaline planktonic forms are going to be found in the surface zone of the i n l e t . The density of a planktonic form i s generally very similar to that of i t s environment. A 2 percent variation in density was found. Such a variation in density w i l l limit the distribution of the non motile plankton. For, unless there are supporting currents, these plankters must sink to their own density level. 15 In the Average Inlet the character of the plankton and to a certain extent the vertical position they occupy can be attributed to the salinity. The maximum number of species should, therefore, be found towards the mouth, and on the basis of density the non motile forms would show a uniform distribution over a greater depth range than at the head. D. Oxygen: Waldichuck (1953) has reported the distribut-ion of oxygen for the Strait of Georgia. His findings, supersaturation towards the surface and decreasing concen-trations with depth, are similar to those of the Average Inlet, Figure 7. Supersaturation of oxygen i s attributed to the photosynthetic activity of phytoplankton while ASur-prisingly high oxygen concentration in the deep zone, greater than 40 percent, i s a result of vertical mixing. In the North Pacific an oxygen minimum layer i s found between 600 and 800 meters. Here values of 1 ml/liter are found, Sverdrup et al (pg. 729). In the British Columbia inlets the lowest concentration of oxygen was 0.25 ml/liter while the lowest concentrations normally encountered were greater than 3 ml/liter. Sverdrup et al (pg. 872) report that planktonic l i f e exists in the minimum oxygen layer in the Pacific. They also report that l i t t l e i s known of the relationship existing between the pelagic l i f e and the oxygen 16 deficient areas. Sverdrup et a l (pg. 872) report that Bogorov (1932) found copepods and other planktonic forms in a region of complete oxygen depletion in the Barents and White Sea. Similarly, the oxygen concentrations found in the British Columbia inlets cannot be expected to have a limiting effect on the total plankton. It is quite con-ceivable, however, that particular groups or species are susceptible to the lower oxygen concentrations. Oxygen is frequently reported as a percentage saturation, the amount of oxygen capable of being held in solution decreasing with increasing temperature. Frequently, areas of supersaturation are encountered in the surface zone. Since oxygen is a by-product of the photosynthetic processes of phytoplankton, regions of oxygen maxima probably define regions of phytoplankton blooming, Sverdrup et a l (pg. 780). However, bacterial activity and the respiration of marine animals tend to reduce the oxygen concentration, and diffus-ion and currents tend to distribute the oxygen away from i t s center of production. Therefore, unless a l l these factors are known, i t becomes impossible to make a specific statement about phytoplankton activity and the oxygen concentration. In the Average Inlet the distribution of oxygen does not appear to be associated with, any one biological phenomena. As Riley (1946) has pointed out, only rarely one environmental factor acts to the exclusion of a l l others. Generally, each factor modifies or is modified by the other factors. 17 In a preliminary investigation of a Swedish fjord Hansen (1951) considered the factors, temperature and s a l i -nity, and indirectly light, as dividing the plankton com-munity into four groups according to the biological character-i s t i c s arid sensitivity of separate species. The thermocline and halocline form what he ca l l s the discontinuity layer. The group of organisms found distributed throughout the whole of a vertical water column are the true eurythermic, euryhaline forms. The copepods are the best representa-tives of this group. The group found in the surface water with the discontinuity layer as i t s chief boundary are also euryhaline and, to certain extent, eurythermic. The plank-tonic larval stages, and cladocera are representatives of this group. Those organisms which are sensitive to wide temperature, or salinity changes, w i l l be limited v e r t i c a l l y by the discontinuity layer. These are the stenothermic and stenohaline forms made up of some adult copepods and chaetognaths. The fourth group i s generally found in the discontinuity layer i t s e l f . Free floating forms and copepods are the most numer-ous organisms occupying this region. In order to evaluate the effect of light Hansen made comparative day and night tows in each zone. He found that the volume of plankton in the surface zone increased more than three times at night. In the discontinuity layer the volume of plankton was reduced to one third the day volume. Below the discontinuity layer the volumes remained comparatively constant. 18 In the Average Inlet the distribution of total plankton can be expected to show a similar grouping. The absence of night samples w i l l make i t d i f f i c u l t to determine the effect of salinity on the zooplankton. However, i t i s f e l t that the reaction to light w i l l be of more importance than Hansen has indicated. Jorgenson (1934) and Ostenfeld (1931) report that cladocera are invariably found in the photic zone regardless of the sea temperature or salinity. Similarly, Russel (1927, 1935) reports that the larval and juvenile stages of plankton are generally postively photo-tropic. Hansen's observations (loc. c i t . ) seem to indicate that the organisms in the discontinuity layer are there be-cause of a negative phototropic response to strong light intensities rather than the avoidance of low s a l i n i t i e s and high temperatures found in the surface region that he sug-gests. Before introducing the other environmental var-iable, circulation, the overall effect of light, tempera-ture and salinity w i l l be discussed. A distribution or grouping of the planktonic community such as Hansen found may be expected to be present in the British Columbia Inlets which have similar variables. The low density brought about by the river discharge w i l l separate the non motile phyto-plankton from the motile zooplankton. The phytoplankton should be associated with the discontinuity layer since this i s the region where their rate of sinking w i l l be decreased. The cladocera, because of their characteristics of motility, 19 euryhalinity, eurythermism, and positive phototropism, w i l l be the representatives of the surface region. The copepods which show a varied response to the variables and are gen-erally negatively phototropic, w i l l represent the group found throughout the water column. The chaetognath, Sagitta elegans. v e r r i l , w i l l represent those organisms found below the discontinuity layer. Although Hansen re-ported the chaetognaths as avoiding variations in tempera-ture and s a l i n i t y , Michael (1913) and Clarek (1934) found that they migrate vertically at night which means they pro-bably encounter differences in temperature and s a l i n i t y . The limiting factor(s) w i l l have to be determined by future ob-servations. Reference to the physical observations, Figures 3, 5, and 6, indicates that the cladocera w i l l be distributed over a greater depth at the mouth than at the head. The phytoplankton w i l l , generally, show a similar distribution since the density, and light intensities show the least variation with depth at the mouth. The adult copepods and chaetognaths which are negatively phototropic to strong light intensities w i l l be found below the discontinuity layer, there-fore they should be found nearer the surface at the head than at the mouth. In comparing the actual observations, Figures 8, 9, 10 and Table 3, with the theoretical, the impression i s that the distribution of zooplankters approximates what was expected. The phytoplankton, however, are concentrated in nearly the opposite manner to what was expected. A more 20 detailed examination w i l l be presented after the circulation has been described. E. Currents: The circulation of water in an inlet has been des-cribed by previous workers, particularly Tully (1949), Cameron (1951), and Pickard (1953). Although a l l the de-t a i l s of the current system in an inlet are not yet known, enough has been written to present a picture of the average conditions. Figure 4 illustrates the present concept of the inl e t circulation. As the runoff waters flow seaward, the resulting f r i c t i o n a l forces tend to drag the underlying inter-mediate water along with i t . More and more mixing takes place so that the runoff water becomes increasingly more saline to-wards the mouth. The thickness of this layer appears to remain comparatively constant a l l along the in l e t in spite of the addition of water from the intermediate zone. The seaward velocity of the runoff water must, and does, increase towards the mouth to compensate for the increasing volume of mixed water. The water lost to the surface layer i s replaced by an inward movement of seawater by way of the intermediate zone. Vertical mixing takes place between the runoff water and the intermediate water along the in l e t . Therefore as the mixing progresses the surface salinity approaches that of the intermediate zone. The boundary between the inflowing and outflowing water i s termed the region of no horizontal motion and i s thought (Pickard, 1953) to coincide with the 21 lower limit of the halocline. The lower limit of the halo-cline in the Average Inlet varies between 18 and 36 feet, the average being about 25 feet. The tides are known to effect the velocities of the currents, however their effect i s gen-erally averaged out over a long period so only the net flow of water is considered. The mean seaward velocity of the surface water at the mouth of the Alberni Inlet during a freshet has been observed to be in the order of magnitude of 0.57 meters per second at the surface which decreases to zero at 8 meters. The observed inward velocities for 30 meters, 70 meters, and 100 meters are 0.04, 0.01 and 0.02 meters per second respectively, Cameron (1951). The maxi-mum inward velocity which is about one third that of the outward velocity is found about 15 meters (personal comm.). The mean vertical velocity above 20 meters in Cameron's interpretation of these data is 1.2 meters per hour, (per-sonal communication). Reliable measurements of velocities at positions further removed from the mouth have not been made. It is sufficient to say that these calculations are in agreement with the present observational data. In the Average Inlet the mean current velocities would probably be in the same order of magnitude. Inasmuch as the rivers are of glacial origin, and have a comparatively small drainage area, they cannot be expected to bring much in the way of nutrients into the inlet. Howeveri the rivers are important in i n i t i a t i n g the inward flow of seawater and i t s subsequent mixing. The data from Table 4 indicates that the phosphate concentrat ions in 22 the coast waters are sufficiently high to provide a source of nutrients for phytoplankton activity in the i n l e t . TABLE 4 PHOSPHATE CONCENTRATIONS ALONG THE COAST OF BRITISH COLUMBIA DURING EARLY SUMMER (After Igelsrud et a l , 1936) Concentration Phosphorous ( g atoms P/liter) Position Depth Open Ocean Continental Shelf Str. of Georgia Off Fraser River °m 0.23 0.44 0.46 0.63 10 0.23 1.25 1.30 0.79 25 0.25 1.40 1.35 1.10 50 0.65 1.90 1.50 1.60 100 1.62 2.2 1.75 1.75 Ketchum (1939) in experiments with the diatom, Nitzschia  closterium, found the minimal phosphate requirements to be 0.55 microgram; atoms P/ l i t e r . Igelsrud 1 s figures, Table 4 indicate that the phosphorus values are more than twice the minimal requirements f o r N. closterium .Cfik*4. The role of nutrients, such as nitrates and phosphates, as growth pro-moting and, in some cases, limiting factors have been investi-gated by Riley (1946), Pratt (1950), and Goldberg et a l , (1953). 23 In general, they found that the plants could store phosphorus for later use, the phosphorus content in the plants depended upon the phosphorus content of their environment, and phos-phate and nitrate depletion i s associated with phytoplankton blooms. In the Average Inlet the surface water, where the phytoplankton activity would be the greatest, i s constantly being replaced by nutrient rich water from below. Consequently, i t i s unlikely, except very near the river, that the nutrients would be a controlling factor. 2) Distribution of the plankton It w i l l be recalled that the overall effect of the physical factors, light, temperature and salinity, was to separate the plankton into four groups depending on their response to these variables. It was found that, in general, the different groups of plankton showed l i t t l e variation from the expected distribution. The phytoplankton were a notable exception. In order to explain the distribution more completely the other variable, circulation, was described. In considering the effect of the currents i t w i l l be con-venient to divide the plankton into two groups, 1) the non motile phytoplankton, and 2) the motile zooplankton. Phytoplankton The most immediate and obvious effect of the seaward flowing surface current i s that i t w i l l carry a l l the surface phytoplankton out of the inlet. It was observed, 24 however, that the phytoplankton were most abundant in the surface region which, i f we assume this represents the steady state, suggests that an outside source replaces the phyto-plankton as i t i s carried away. The explanation i s thought to l i e in the current system of the inlet. F i r s t we must assume that the phytoplankton are not of local origin, and second we must assume that they f a i l to reproduce after entering the photic zone. On the basis of these assumptions then i t i s not unreasonable to postulate that phytoplankton enter the inlet the same way the salt does, that i s to say they enter the inlet via the inward flowing sub-surface current and thence to the surface zone. L i t t l e i s known regarding the mechanism of mixing in the inlets. At present, i t i s assumed that a l l properties of the water mix in a manner similar to that of salt. Since the assumption i s also made, that in the Average Inlet the distribution of salt indicates the steady state maintained by the processes of advection and mixing, i t must be concluded that an unvaried distribution of phytoplankton requires that i t show no varia-tion of concentration with position or a variation identical with that of salt. The observations, however, show the con-centration of phytoplankton to vary with position and depth and in a manner dissimilar to that of sa l i n i t y . The validity of our assumptions are open to question. The possibility of local production i s real enough at the beginning of the sea-son when no current system has been established. However, once the circulation i s established the surface water and a l l forms floating in i t move seaward. Therefore, the effect of any i n i t i a l population or spores already in the inlet i s n u l l i f i e d . The second assumption was based on the premise that i f n volumes of water move into the inlet at least n volumes of water must flow out, similarly for the plankton. However, what we actually observed was a greater volume of plankton moving out than was observed coming in, Figures 2 and 8. This indicates that our second assump-tion i s invalid and that in fact there i s production of phytoplankton. The reasons for the greatest concentrations to be found towards the mouth have already been indicated to be a result of the greater depth of optimum light intensity coupled with a constant supply of nutrients. Vertical advection, which increases towards the mouth, (Figure 4), w i l l be responsible, also, for maintaining the phytoplankton in the low densities found in the surface region. The pre-sence of phytoplankton towards the head of the in l e t i s another indication of how currents influence their d i s t r i -bution. At the head the upward movement of water i s pro-bably too slight to do more than balance their sinking rate. Consequently, they must inevitably perish in the absence of optimum li g h t intensities. Zooplankton The nature of the response to light intensity, salinity and, to a lesser extent, temperature was shown to MOUTH HEAD 26 separate the zooplankton into three groups. Each group was concentrated where the variation from i t s optimum condition was the least. In the presence of strong currents the abi-l i t y to remain in this region becomes important, therefore, the degree of motility can be used to separate the zooplankton into different groups. The weakest swimmers, cladocera, w i l l show a distribution similar to that of the non motile forms and therefore, they w i l l occasionally be found where the con-ditions are unfavourable. The strongest swimmers, chaeto-gnaths, w i l l probably be able to avoid unfavorable conditions. The copepods are intermediate in swimming a b i l i t y , and con-sequently they too w i l l usually be able to occupy their opti-mum environment. The horizontal swimming speed of the copepod, Centropages typicus. has been experimentally determined by Welsh (1933) to be about 0.022 meters per second (136 cms/min.) while that of decapod larvae have been found to be sl i g h t l y greater than 1 meter per second, Poxbn (1934), as measured in a current. Observations of the swimming rate of clado-cera and chaetognath are lacking, but they are probably in the same order of magnitude as that reported for Centropages. Assuming that this is the case, the zooplank-ton in the surface zone w i l l be transported out of the inlet. Recruitment w i l l come from organisms in the inter-mediate inward moving zone. The copepods and chaetognaths are capable of maintaining a particular vertical position even at the mouth where the vertical advection i s the greatest. Zoo-plankters, which undergo daily diurnal migrations w i l l pro-bably be distributed in a manner analagous to that found by Hardy (1936). In a plankton community different species and different stages of the same species show marked differences in their movements, Russel (1935). Consequently, their hori-zontal distribution from any one fixed point in the inlet w i l l be dependent on how long they stay in each zone. Over a long period of time the community w i l l become separated into distinct subgroups composed of similar individuals. Unless the zooplankton live most of their entire l i f e cycle below the surface zone, the species must inevitably die out or be re-placed by others moving in. Local recruitment i s unlikely since spawning invariably takes place in the surface zone and developing larvae are typically positively phototropic, Russel (1927), Marshall et a l (1952). The distribution of cladocera, Figure 9, was very close to the expected distribution. Salinity and temperature are known to have no controlling influence on their d i s t r i -bution, Ostenfeld (1931), Jorgenson (1933). Their concen-tration towards the surface region at the mouth suggests that their distribution can be attributed directly to the range of high light intensities at the mouth and the v e r t i -cal currents. Their near absence from the regions of lower light intensities serves to emphasize this point. Since the cladocera are closely associated with the seaward movement of surface water they are probably replaced by way of the intermediate zone in a manner similar to that suggested for the phytoplankton. 2 8 The copepods are very definitely limited in their vertical distribution, Figure 10. It was indicated earlier that their response to light would probably be responsible for this distribution. It w i l l be recalled that the swim-ming speed of Centropages indicated that they were capable of maintaining a fixed vertical position in spite of the vertical currents. The effect of the horizontal currents has been described as depending on the length of time they spend in the moving layers. The plankton samples closest to mouth were composed of a greater proportion of small cope-pods than those taken further up the in l e t . The unexpect-edly high surface volume of copepods taken at mouth suggests that these small copepods, probably juvenile stages, are less negatively phototropic than the larger ones or, pos-sibly, they are not as capable swimmers. The chaetognatha, Table 3, made up of Sagitta  elegans V e r r i l , show by comparison with the cladocera and copepods a narrower range of optimal conditions. They are restricted to low light intensity, temperature and salinity. Furthermore, their absence from the surface zone indicates that they are capable of maintaining themselves in this region. Their concentrations were never particularly large, consequently, very l i t t l e may be inferred of their horizontal distribution. The Currents become, in the f i n a l analysis, the most influential factor controlling the plankton. The river TABLE 3 = THE AVERAGE INLET Comp. Position Depth (ft) Depth of Sampl-ing (feet) Temp. V Salinity % o Oxygen Total PI. cc/m3 Phyto-plankton cc/m3 Zoop. cc/ m3 Clado-cera cc/m3 Cope-poda cc/m3 Chaetog-natha numbers /m3 Mouth 40 5 54.3 16.2 112 4.8 3.3 1.5 0.47 0.57 0 21 49.6 26.1 103 2.2 0.91 1.29 0.26 0.59 6 32 48.0 27.8 93 1.54 0.27 1.27 0.10 0.97 5 47 45.7 30.1 76 1.04 0.33 0.71 0.03 0.69 3 Middle 20 5 54.8 8.4 106 1.22 1.1 0.12 0.10 0.02 0 21 49.0 25.5 93 1.67 0.01 1.66 0.123 1.12 16 32 46.6 28.2 76 1.67 0.33 1.34 0.122 0.92 2 47 45.2 29.6 73 0.54 0.02 0.52 0.01 0.41 2 Head 2 5 51.5 4 100 0.15 0.015 0.14 0.08 0.005 0 21 47.0 16.9 95 1.24 0.1 1.14 0.11 0.80 20 32 45.1 26.8 97 1.15 0.01 1.14 0.06 0.35 12 47 43.4 29.8 79 0.52 0.0 0.52 0.002 0.34 4 to CO 30 runoff limits the light penetration, decreases the tempera-ture and salinity, and i t initiates the circulation. The surface current transports plankton out the in l e t , and i t provides for their return via of the intermediate water. The inward movement prevents depletion of oxygen and nut-rients and i t ensures a continual supply of plankton. 2. Atypical Inlet Attention i s called to the fact that the observa-tions describing the conditions for the atypical inlets are based on discrete samples, not averages. For any one inlet there were a maximum of 12 plankton observations as com-pared to maximum of 120 observations on the Average Inlet. However, i t w i l l be assumed, as i t was for the Average Inlet, that the observations for any one of the atypical inlets represent the steady state. The results w i l l be discussed accordingly. The atypical inlet i s comparatively short (10 to 35 miles) and has no appreciable volume of fresh water flow-ing in at the head. The circulation, temperature, salinity, and oxygen distributions are different from those of the average inlet (see Tables 5, 6, 7, and 8). What circula-tion there i s , i s due largely to the wind and tide and the nature of the entrance to the inlet. The mouth of the inlet i s the region of most intensive mixing, since the tidal forces are greatest there, while the water towards the head may become stagnant, depending on the length of the inlet and how sheltered i t i s from winds. The temperatures are higher and they are not as variable as those reported for the Aver-age Inlet. The s a l i n i t i e s varied only half as much as they did in the Average Inlet. The density and molecular v i s -cosity of the atypical inlet was correspondingly more uni-form. Oxygen concentrations were of the same magnitude as those found in the other inlets, Belize Inlet being the exception to this. The region towards the mouth has! the greatest volumes of plankton. However, away from the mouth the distribution of plankton i s very erratic and no general pattern seems to exist. The concentrations of plankton varied from inlet to inlet, Surf Inlet having the greatest volumes. The cladocera were absent from three of the inlets while the chaetognatha were absent from a l l four. The phytoplankton concentrations varied with depth and position along the inl e t . The greatest concentrations of copepods were towards the mouth at depths of 20-35 feet. Riley (1942) has shown that low production and blooms of plankton are generally characteristic of areas which have l i t t l e or no circulation, while those areas with an established circulation are generally uniformly high in their production of plankton. As there was not an esta-blished circulation within these inlets the plankton w i l l be concentrated in the most optimal area. While the absence of a current system, such as there was in the Average Inlet, provides the opportunity for endemic forms to develop and reproduce, i t f a i l s to ensure a continuous supply of oxygen and nutrients. Consequently the production of plankton may be limited in some areas. In other words, the production of plankton in the atypical inlets w i l l be unpredictable and w i l l depend on the requirements of the individual species. Belize Inlet Belize Inlet i s situated on the mainland coast off the north end of Vancouver Island. The approach to the inlet is through a narrow passage, which i s shared in part by Sey-mour Inlet. In some parts the channel i s less than 200 yards wide and less than 200 feet deep. The ebb and flow of water over the tidal cycle through this channel provides opportunity for thorough mixing. However, the entrance i s also respon-sible for dampening the effect of the tide so that only small tides are found towards the head of the inl e t , which i s about 35 miles from the entrance. Of the atypical inlets, Belize Inlet i s the most similar to the Average Inlet in i t s hydro-graphic characteristics. Figures 11 - 18 show the distribu-tion of the physical and biological observations. The temp-erature i s relatively constant with depth at the mouth while at the head there i s a sharp thermocline between the surface and 30 feet. The salinity varies from 16 °/oo to 30°/oo over the depth sampled. Longitudinally, the salinity varies less than 3 °/oo. TABLE 5 - BELIZE INLET Position Corap. 0. Depth (feet) Temp. o p Salinity /oo Oxygen Plankton °/o CC/m3 Phyto-plankton cc/m3 Zoopl. cc/m3 Clado-cera cc/m3 Cope-. poda cc/m3 Mouth 25 5 57.9 19.6 110 4.2 1.44 2.76 1.26 21 53.0 28.1 88 6.3 3.7 2.6 0.06 0.63 32 52.1 28.2 87 3.5 1.6 1.9 0.009 0.4 47 48.9 29.3 82 0.9 0.14 0.76 - 0.45 Middle 25 5 58.8 15.9 80 1.5 0.15 1.35 0.8 0.06 21 56 .O 26.7 64 0.7 0.007 0.693 mm 0.69 32 52.0 27.9 62 1.9 0.002 1.898 - 1.8 47 47.8 29.0 73 0.7 0.007 0.7 - 0.69 Head 32 5 61.8 16.0 85 0.3 0.003 0.297 0.18 0.012 21 46.7 28.3 59 0.3 - 0.3 - 0.27 32 46.0 28.7 55 0.2 - 0.2 - 0.18 47 45.2 29-© 42 0.2 - 0.2 — 0.18 CO CO FIGURE II. BELIZE INLET — DISTRIBUTION OF TEMPERATURE i f ) FIGURE 12. BELIZE INLET DISTRIBUTION OF SALINITY FIGURE 13. BELIZE INLET — DISTRIBUTION OF OXYGEN (vi) 34 The low values of oxygen, particularly towards the sur-face at the head, are unusual and are suggestive of stagnation. The compensation depth i s found to be at a nearly constant level, permitting phytoplankton production from the mouth to the head down to depths of 30 feet. The distribution of plank* ton shows the typical decrease in concentration from the head to the mouth. The characteristic rate of decrease, however, is much more rapid than was found for the Average Inlet where the circulation tends to distribute the plankton more uni-formly over the length of the inlet. This i s probably a mani-festation of the absence of a circulation in Belize Inlet and i t i s indicative of the dependence of non motile forms on cur-rents for their distribution. The phytoplankton and cladocera are confined almost entirely to the area near the mouth where currents are the strongest, Figures 15 and 17. The phyto-plankton occupy the region between 10 and 30 feet while the cladocera are found above 20 feet. In comparison, the cope-pods, which are moderately strong swimmers, are found in the greatest concentrations in the intermediate zone, the maxi-mum concentration occurring near the middle station, Figure 18. The chaetognatha are absent. In the Average Inlet the chaeto-gnaths were associated with the inward moving intermediate zone. In Belize there i s no evidence of an inward moving zone. Therefore, unless there i s an endemic population of arrow we*ws, they cannot be expected to be as numerous as they were in the Average Inlet. However, this f a i l s to explain o r — 1 0 -2 0 " 3 0 " 40 -5C-MIDDLE HEAD 0 10 UI UI u. 20 z r-0. 30 UI o F I G U R E 14 B E L I Z E I N L E T - D I S T R I B U T I O N O F P L A N K T O N /(cc/tn3) i > * — — T 4 0 r 50h \ .3.0 2.0 1.0 - . 0.1 <• 0 007 r _ c^inpensatlM F I G U R E 15. BELIZE INLET-DlSTRlBl/TION-OF P H Y T O P L A N J O N (cc/m3) Oi < • i > 1 0 -2 0 " 3 C -4 0 5 0 \ 2.5 20 FBURE 1 6 . BELIZE INLET - DISTRIBUTION OF ZOOPLANKTON - (cc/tn3) 35 their complete absence, as do the other physical factors. At f i r s t the low oxygen concentrations found in the deep zone were suspected. However, in additional hauls, which sampled down to 500 feet, copepods and other zooplankton were found. Therefore on the basis of these observations oxygen could no longer be considered the factor limiting the distribution of chaetognaths. Hansen (1951) has stated that Sagitta elegans avoids both very high and very low s a l i n i t i e s , i t s optimum being between 29 and 32 °/oo. Russel (1939) and Clarke et al (1943) have both reported that S. elegans i s always associated with mixed oceanic and coastal water. This dis-tribution i s not related to the actual process of mixing but is dependent on some unknown organisms or element associated with this water; (Clarke et a l , loc. c i t . ) . Our observations also indicate that S. elegans i s associated with mixed water,but i t was not always present where mixed water was found. Pendrell Sound Pendrell Sound is short, less than 10 miles long, and there i s no river discharge into i t . However, the entrance i s in direct contact with the north end of the Strait of Georgia and adjacent waters. The presence of low s a l i n i t i e s (18 - 28 °/oo, Figure 20) has been attributed to a movement of water into the sound from Toba or Bute Inlet during the spring freshet. The distribution of temperature and salinity (Figures 19 and 20) suggests vertical s t a b i l i t y ; FIGURE 21. PENDRELL SOUND — DISTRIBUTION OF OXYGEN (V.) TABLE 6 - PENDRELL SOUND Position Comp.Depth (feet) Sampling Depth (feet) Temp. °P Salinity % o Oxygen °/oo Plankton cc/m3 Phytoplankton cc/m3 Copepods Mouth 50 5 69.8 19.1 104.4 0.37 0.04 0.37 21 65.1 23.7 112.0 1.35 0.05 1.2 32 59.8 26.8 123,0 1.15 0.02 1.0 47 55.04 27.68 123.9 0.7 0.01 0.6 Head 50 5 72.3 19.07 99.8 0.55 0.005 0.33 21 71.0 24.7 143.2 0.50 0.025 0.47 32 65.7 25.9 158-0 0.81 0.16 0.61 47 60.8 27.28 155.2 0.87 0.52 0.32 CO CT> 37 the isotherms and isohalines run nearly parallel to the sur-face. The temperatures were the highest encountered along the coast, maximum of 72°F. The oxygen concentrations are a striking departure from the average, values as high as 154 °/o saturation were found, Figure 21. The coincidence of maximum phytoplankton concentration with the maximum oxygen concentration suggests a possible relationship, particularly, since there is no circulation to distribute either the oxygen or phytoplankton. If we assume that high oxygen concentrations are generally associated with high phytoplankton concentrations the effect of currents in transporting oxygen out of the region is striking when we compare the phytoplankton volumes found in the Average Inlet with those of Pendrell Sound. The volume of phyto-plankton in Pendrell Sound is less than six times that found in the Average Inlet yet i t has more than one and a half times as much oxygen. The difference between the two values can probably be attributed to the effects of c i r -culation. The increased depth of optimum light intensities in Pendrell Sound is,also, probably a contributing factor. Figures 21 and 22 show the distribution of copepods and phytoplankton. They are concentrated at different depths and at opposite ends of the sound. The phytoplankton have probably developed locally while the copepods are possibly moving in from some outside source through random swimming. The copepods are in a much higher light intensity than has FIGURE 22. PENDRELL SOUND - DISTRIBUTION OF PLANKTON (c c/m^ FIGURE 23 PENDRELL SOUND-DISTRIBUTION OF PHYTOPLANKTON (cc/m3) FIGURE 24.PENDRELL SOUND —DISTRIBUTION OF COPEPOOA (cc/m9) 38 been found previously. The presence of a large proportion of larval stages in copepod volumes are assumed to be respon-sible for the apparent change in response to light inten-sit y . The phytoplankton are distributed much lower than usual. The increased depth to which photosynthesis can be carried on and the low density of the surface water are thought to contribute to this distribution. The absence of cladocera cannot be readily explained from the physical data. Their dependence on the currents for a horizontal distribution has been demonstrated in the Average and Belize Inlets. However, they are capable of movement and should, like the copepods, gradually penetrate into the i n l e t . A possible explanation i s predation. In the Average Inlet the constant recruitment and the currents eliminated the possi-b i l i t y of predation being a limiting factor. In Pendrell Sound where the cladocera would have to develop from an endemic population or swim in, predation could play a very important role; for, unless there was a bloom of cladocera, i t i s quite conceivable that carnivorous zooplankton could remove a l l the cladocera as they appear. Another possible explanation which should be mentioned is that this phenomena is a seasonal one, particularly as the other two inlets, Surf and Laredo, which have no cladocera, were sampled only one week earlier, middle of summer. However, plankton samples were taken in Pendrell Sound in the spring, and although the closing mechanism on the samplers was not working properly, samples were obtained from the surface to 50 feet. Ho cladocera were found; copepods and decapod larvae were very numerous, and one chaetognatha was also found, therefore i t seems unlikely that this is a seasonal phenomena. Laredo Inlet Laredo Inlet is situated on the west coast of Princess Royal Island. The approach to entrance of the inlet i s protected from the open ocean by a group of islands Very l i t t l e fresh water is discharged into the i n l e t . The small, progressive increase in sal i n i t y towards the mouth suggests very l i t t l e mixing, Figure 26, the increase in o, -sa l i n i t y is less than 4 /oo. The temperature shows even less variation along the in l e t , Figure 25. The physical observations and the nature of the entrance indicate that there i s very l i t t l e circulation in the inlet. Unlike Pendrell Sound, there is no well defined pattern of oxygen concentration, Figure 27. Instead, nearly a l l the samples were between 100 and 110 percent saturated. The phytoplankton were present in a l l the samples, the maximum concentration being in surface waters at the mouth, Figure 29. Although the oxygen and phytoplankton maxima do not coincide, there is some indication that they may have been associated in the immediate past. In obser-ving plankton populations i t is customarily found that the TABLE 7 - LAREDO INLET Comp. Station Depth (Feet) Samp-ling Depth (feet) Temp. o F Salinity °/oo Oxygen 0/ /o Plankton cc/m3 Phytoplankton cc/m3 Copepods / 3 cc/m 1 39 5 59.2 30.8 110 0.95 0.85 0.057 20 58.6 31.0 108 0.3 0.18 0.12 30 57.5 31 .o 107 0.3 0.03 0.21 40 54.6 31.2 105 0.45 0.0045 0.40 3 36 5 60.6 28.3 112 0.15 0.01 0.022 20 59.0 30.0 112 0.35 0.035 0.204 30 58.3 30.8 112 0.45 0.008 0.40 40 56.2 31,0 112 0.20 0.004 0.19 5 42 5 61.7 28.1 109 0.1 0.001 0.095 20 59.0 29.9 113 0.15 0.0015 0.149 30 56.0 30.5 120 0.30 0.003 0.28 40 52.0 31.1 108 0.60 0.006 0.57 O MOUTH MIDDLE HEAD FIGURE 25.LAREDO INLET - DISTRIBUTION OF TEMPERATURE (T) -r-1 0 2 0 r -3 0 4 0 5 0 h FIGURE 2ft. LAREDO INLET - DISTRIBUTION OF SALINITY (%•) 1 — ; » IK) 110 1 0 0 ^ — i o o ^ * y FI6URE 27.LAREDO INLET- DISTRIBUTION OF OXYGEN (%) MOUTH HEAD 10-20-30-4 0 -501- "7 Q20 FIGURE 28. LAREDO INLET - DISTRIBUTION OF PLANKTON (cc/m3) 50U 10" 2 0 -30-4C- — £0.03 7 0.001 COMPENSATION DEPTH FIGURE 29. LAREDO INLET - DISTRIBUTION OF PHYTOPLANKTON (cc/m3) i c L 20L-30 40i-501-FlCURE30. LAREDO INLET - DISTRIBUTION OF COPEPODA (cc/m") 41 phytoplankton bloom f i r s t , then the herbivore plankton slowly increase in the area by actively moving up the phytoplankton gradients and through reproduction, Nielsen (1937) and Flem-ing (1939). In this case, the oxygen and copepod maxima are in the same region (Figures 25 and 30) indicating, perhaps, that the copepods have been grazing on the phytoplankton for some time and have almost removed them. The volumes of plankton are the lowest encountered in any of the inlets, Figure 28. This is probably a result of poor circulation and the consequent depletion of nutrients. The absence of the cladocera and chaetognath has already been discussed. Surf Inlet Surf Inlet is situated just north of Laredo. It, too, has only a small fresh water discharge. However, Surf Inlet is different in that i t s entrance is f u l l y exposed to the ocean. The biological and physical characteristics of Surf Inlet are strikingly different from those found ih Laredo, Table 8, Figures 31-36. The sal i n i t y variation is o / less than 2 /oo; the isohalines are nearly parallel to the o surface. The temperatures are nearly 7 F colder than those found near the surface in Laredo which suggests that there is some vertical mixing. The oxygen distribution can probably be attributed to the phytoplankton activity since the two maxima occur together near the surface at the head of the TABLE 8 - SURF INLET Station Comp. Depth Sampling Temp. Salinity Oxygen Plankton Phytoplankton Copepods (feet) Depth o o/ 0/ / 3 /3 / 3 (feet) F /°° '° cc/m cc/m cc/m 2 5 57.0 31.0 112 0.7 0.035 0.6 24 20 55.1 31.2 106 1.5 0.07 1.35 30 54.9 31.2 105 1.8 0.09 1.65 40 54.1 31.3 102 1.2 0.06 1.10 4 5 55 0 29.8 134 2.8 0.28 2.52 31 20 53.3 31.1 123 4.5 1.57 2.93 30 51.7 31.2 108 3.7 1.29 2.41 40 49.0 31.6 89 1.8 0.54 1.34 FIGURE 34.SURF INLET —DISTRIBUTION OF PLANKTON (cc/m3) FiGURE 36. SURF INLET-DISTRIBUTION OF COPEPODA (cc/m3) 43 i n l e t . The copepods are also most abundant towards the head. These samples have a very high proportion of juvenile stages indicative of an endemic copepod population. When local spawning or blooming of plankton occurred in an inlet there would probably be decreasing gradients of plankton away from the main center of spawning. The copepods in both Surf and Laredo show this type of distribution. The plankton volumes are from 3-5 times greater than those found in Laredo Inlet and suggestive of much richer waters, which could be accounted for by the evidence of vertical mixing. 44 CONCLUSIONS AND SUMMARY The physical factors known to control the d i s t r i -bution of plankton in the ocean are also found to be opera-tive in the British Columbia inlets. The range of light penetration, salinity, and current velocity gradients greatly exceed those normally found in the ocean, and i t i s these factors which produce the greatest effect on the inlet plankton. Of the environmental factors,the circulation was the most obvious in importance. The surface current res-tricted movement into the i n l e t . Any plankton in the sur-face zone or which migrated to the surface for extended periods would eventually be transported to the sea. Simi-l a r l y , eggs and larvae developing in the surface zone would be removed by the surface current from the inl e t . The in -ward flowing subsurface current was responsible for main-taining the stocks of plankton, and for ensuring a constant supply of nutrients. Those areas in which higher than average phytoplankton concentrations were observed were in general, regions showing evidence of moderate vertical move-ment of water. The areas of lower than average concentra-tions were those showing l i t t l e evidence of circulation. Assuming that the observations represent the steady state, we have indicated that in the former case considerable local production must be maintained, and in the latter, that pro-duction i s low. The literature does not contain any reference 45 to the relationship between phytoplankton and density. The data in Table 9 summarizes the conditions that were found in the inlets. For comparison with another region,Hutchinson's observations for the Strait of Georgia have been interpreted and included with these. Reference to the data indicates that the phytoplankton in the Average Inlet are associated with a much lower density than they are in the other inlets. The rate of vertical advection at the mouth of the Average Inlet i s greater than the sinking rate than inert of diatoms (28.8 meters/day vs 6 meters/day for diatoms, Sverdrup et a l , pg. 893); consequently, i t would appear that the vertical advection maintains the phytoplankton in a region i t might otherwise sink out of. Light intensity was suggested as the prime factor influencing the vertical distribution of the zooplankton. Phototropism and the currents brought about their horizontal distribution. The copepods, which were present in a l l the inlets, showed a nearly similar vertical distribution along the coast. Their horizontal distribution was variable. In the Average Inlet this was attributed to vertical migrations and the currents. In the atypical inlets their distribution was thought to reflect their origin. The argument was that i f the copepods are moving randomly into the inlet their greatest concentration w i l l be at the mouth. If they developed within the inlet they would probably show a gradient in the other direction. TABLE 9. DENSITY FOR REGIONS OF PHYTOPLANKTON MAXIMA Locality Density Water Column Phytoplankton Maximum Average Inlet 1.012 - 1.024. 1.012 Belize Inlet 1.014 - 1.026 1.019 Pendrell Sound 1.013 - 1.020 1.019 Laredo Inlet 1.022 - 1.023 1.023 Surf Inlet 1.022 - 1.024 1.023 Active Pass* 1.011 - 1.023 1.020 1931). (Interpreted from Hutchinson's data, 1928, 47 The factors, salinity and light intensity, were positively correlated in the Average Inlet in which case, the effect of salinity alone could not be evaluated. In the other inlets the range of salinity was insufficient to demon-strate a variation in plankton distribution which could be attributed to salinity. As was mentioned earlier, salinity affects the density of the water which in turn influences the sinking rate of plankton. Nowhere was the effect of temperature observed to influence the plankton. Oxygen concentration was not found to do more than suggest regions of high phytoplankton activity and low c i r -culation . The purpose of this paper was to describe the inlet plankton in terms of their relationship to the physical environment. In so doing tfee important biological factors have had to be overlooked. However, i t is realized that such factors as predation play a very important role in determining the constituents of a plankton community. In one case, pre-dation was put forth as a possible explanation for the absence of cladocera. The explanation for the absence of the chaetognaths must also await further investigations. It i s interesting to note that comparison of the total plankton with the physical factors i s frequently mean-ingless. It is only when the plankton are divided into phytoplankton and zooplankton and the zooplankton into i t s 48 constituent groups that positive relationships become apparent. The preliminary examination of the physical oceano-graphic factors and the distribution of plankton has shown that there i s a relationship between the two. Until con-firmatory work has been done in two or three inlets of diver-gent characteristics the generalizations and assumptions made in this paper must be considered as unproven, qualitative, descriptions of one set of data. The future investigations must have a sound s t a t i s t i c a l basis. This would imply more extensive sampling at different depths and over several twenty-four hour periods. 49 REFERENCES Adolph, E. F. 1925. Some physiological distinctions between freshwater and marine organisms. Bi o l . Bull., 48, 327-335. Bogorov, B. G. 1941. Scheme of diurnal vertical migrations of zooplankton at different latitudes. J. Mar. Res. 6 (1), 29-32. Cameron, W. M. 1951. On dynamics of inlet circulation. Doctoral Dissertation. Carter, N. 1933. The physiography and oceanography of some B. C. Fiords. Fifth Pacific Sci. Congress, 1 IV(3). Clarke, G. L. 1934. Factors affecting the vertical d i s t r i -bution of copepods. Ecol. Monogr., 4, 530-540. Clarke, G. L. & D. F. Bumpus. 1950. The plankton sampler -An instrument for quantitative plankton investi-gations. Amer. Soc. Limn. & Ocean. Special publication (5), 1-8. Clarke, G. L., E. L. Pierce, and D. F. Bumpus. 1943. The distribution and reproduction of Sagitta elegans on Georges Bank in relation to hydrographical conditions. Biol. Bull. 85 (3), 201-226. Data Report No. 1 - British Columbia Inlet Study 1951. Institute of Oceanography of the University of British Columbia, Vancouver, B. C. Fleming, R. H. 1939. The control of diatoms by grazing. J. Cons. int. Explox. Mer. 14, 210-227. Foxon, G.E.H. 1934 -Notes on the swimming methods and habits of certain crustacean larvae. J. Mar. B i o l . Ass. U.K. N.S. 19, 328-346. Goldberg, E. D., T. J. Walker, and A. Whisenand. 1951. Phosphate utilization by diatoms. Biol. B u l l . 101 (3), 274-288. Gross, F. 1940. The osmotic relations of the plankton diatom. Ditylum brightwelli (West) J. Mar. B i o l . Ass. U.K. N.S. 24^ 381-415. 50 Hansen, K. V. 1951. On the diurnal migration of zooplankton in relation to the discontinuity layer. J. Cons. int * . Explor. Mer. 17 (3), 231-241. Hardy, A.C. 1935. The plankton of the South Georgia whaling grounds and adjacent waters 1926-1927, pt. 5., The plankton community, the whale f i s h -eries and the hypothesis of animal exclusion. Discovery Repts. 11, 273-370. Hutchinson, A. H. 1928. A Bio-hydrographical investigation of the sea adjacent to the Fraser River mouth. Trans. Roy. Soc. Can. 22, V, 293-310. Hutchinson, A.H., Lucas, C. C. and M. McPhail. 1929. Sea-sonal variations in the chemical and physical pro-perties of the waters of the Strait of Georgia in relation to phytoplankton. Trans. Roy. Soc. Can. 23. V. 177-188. Hutchinson, A. H., and C. C. Lucas. 1931. The epithalassa of the Strait of Georgia. Can. Jour. Res. 5, 231-284. Igelsrud, I., R. J. Robinson and T. G; Thompson. 1936. The distribution of phosphates in the sea water of Northeast Pacific. Univ. of Wash. Public, in Ocean. 3 (1), 1-34. Jenkins, P. M. 1937. Oxygen production by the diatom Cosinodiscns excentricus Ehr. in relation to submarine illumination in the English Channel. J. Mar. Biol. Ass. U.K. N.S. 22, 301-342. Jorgenson, 0. M. 1933. Cladocera from Northumbrian plankton. J. Mar. Bi o l . Ass. U.K. N.S. 19, 177-226. Ketchum, B. H. 1939. The adsorption of phosphate and nitrate by illuminated cultures of Nitzchia closterium. Amer. Jour. Bot. 26, 397-407. Marshall, S. M. and A. P. Orr. 1952. On biology of Calanus  finmarchius VII Factors affecting egg production. J. Mar. Bi o l . Ass. U.K. N.S. 30 (3), 527-548. Michael, E. L. 1913. Vertical distribution of the chaeto-gnaths of the San Diego region. Amer. Naturalist 47, 17-49. Nielsen, E. S. 1937. Oh the relation between quantities of phytoplankton and zooplankton in the sea. J. Cons. int . Explor. Mer. 12.147-154. 51 Ostenfeld, C. H. 1931. Resume des observations sur le plank-ton des mers explorees par le Conseil pendant les Anees 1902-1908. Cons. Explor. Mer., Bull. Trim (N), 601#672. Pickard, G. L. 1953. Oceanography of the British Columbia inlets I Water characteristics. Pac. Prog. Rep. Fish. Res. Bd.t Can. No. 96, 3-6. 1953. II Currents Ibid.. No. 97, 12-13. Pratt, D. M. 1950. Experimental study of the phosphorus cycle in f e r t i l i z e d sea water. J. Mar. Res. 9 (1), 29-54. Riley, G. A. 1942. The relationship of vertical turbulence and spring diatom flowering. J. Mar. Res. 5, 67-87. 1946. Factors controlling phytoplankton populations on Georges Bank. Ibid.. 6. 54-73. Riley, G. A., H. Stommel, and D. F. Bumpus. 1949. Quantita-tive ecology of the plankton of Western North Atlantic. Bu l l . Bingham Oceanogr. Coll., 12 (3), 1-169. Russel, F. S. 1927. The vertical distribution of plankton in the sea. Bi o l . Rev. 2 (3), 213-262. Russel, F. S. 1928. The vertical distribution of marine macroplankton. 7 Observations on the behavior of Calanns finmarchius. J. Mar. B i o l . Ass. U.K. N.S. 15.(3), 429-454. 1935. A review of some aspects of zooplankton research. Reports int. Cons. Explor. Mer. 9j>, 3-30. 1939. Hydrographical and biological conditions in the North Sea as indicated by plankton organismsv J. Cons. int. Explor. Mer. 14, 170-192. Sverdrup, H. U., M. W. Johnson, and R. H. Fleming. 1946. The Oceans, Their Physics, Chemistry and General Biology. Prentice-Hall Inc. New York, 1087 pp. Tabata, S. 1954. The physical oceanography of Bute Inlet. Masters Thesis, University of British Columbia. 52 Thompson, T. G., and K. T. Barkely. 1938. Observations on fjord waters. Univ. of Wash. Publ. Oceanogr. supp. series No. 76. Tully, J. P. 1936. Oceanography of Nootka Sound. J. B i o l . Bd. Can. 3 (1), 43-69. 1942. Surface non-tidal currents in the approaches to Juan de Fuca s t r a i t . J. Fish. Res. Bd. Can. 5_ (4), 398-409. 1949. Oceanography and prediction of pulp mill pollution in Alberni Inlet. J. Fish. Res. Bd. Can. B u l l . 83, 1-169. Waldichuck, M. 1953. Oceanography of the Strait of Georgia. IV Dissolved oxygen distribution. Pac. Prog. Rep. Fish. Res. Bd. Can. 96, 6-10. Welsh, J. H. 1933. Light intensity and the extent of a c t i -v i t y of locomotor muscles as opposed to c i l i a . B i o l . Bull.65, 168-174. 

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