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UBC Theses and Dissertations

A preliminary quantitative study of the zooplankton of the water of the Strait of Georgia Campbell, Mildred Helena 1928

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U . B . C . LIBRARY j CAT «*0. L ( i g j L & f l I acc. HO. A PRELIMINARY QUANTITATIVE STUDY OF THE ZOOPLANKTON OF THE WATER OF THE STRAIT OF GEORGIA. -by- ; : MILDRED HELENA CAMPBELL. A Thesis submitted for the Degree of MASTER OF ARTS in the Department of ZOOLOGY. A PRELIMINARY QUANTITATIVE STUDY OP THE ZOOPLANKTON OF THE WATER OF THE STRAIT OP GEORGIA. The economic importance of an investigation such as is described in this paper, and of the results obtained from it, cannot be overestimated. It is obvious that an attempt at a solution of the general problem of the migration of fish is dependent, to a large extent, on an understanding of the food supply, its whereabouts and contents. An appreciation of the central and commanding position occupied by the plankton in the metabolism of the ocean is ably expressed in the introduction to "Marine Plankton" , (Johnstone Scott & Chadwick 1924) by W. A. Kerdman. Willey (1919) makes the following statement concerning the Gopepods and it may be applied generally to the zoo-plankton, of which the Copepods form the most important con-stituent . "Copepoda are small crustacea less than 5 mm. in length, whose abundance in the sea is a measure of their importance as a direct source of food supply for the commercial fishes. In addition, they are preeminently the food of the herring which in turn is preyed upon by larger fishes. Accordingly, the investigation of their distribution as governed by depth, season, currents, salinity and temperature is generally rec-ognized as having an economic bearing, for fishes will nec-essarily assemble in places where their food supply is plen-tiful". Facilities for the study of the zooplankton of the Strait of Georgia were provided by the Biological Board of Canada and the problem itself was suggested by Dr. W. A. Clemens, director of the Pacific Biological Station. His helpful suggestions as to methods of attacking the problem and assis-tance in procuring literature are much appreciated. The results recorded were obtained from an examination of the material collected during the summer months of 1926'by Dr. A. H. Hutchinson and Mr. Colin Lucas. Though not pres-ent when these samples were taken, opportunity was afforded to assist in the collecting of similar samples during the summer of 1927• The occurrence of the phytoplankton of the 1926 collections, in relation to the physical and chemical factors has already been reported on in the publication, "A Bio-Hydrographical Investigation of the Sea Adjacent to the Praser River Mouth", (Hutchinson and Lucas I927). My thanks are due to Dr. Hutchinson and Mr. Colin Lucas for valuable advice and kindly suggestions. The w/ork was commenced in the summer of 1927 at the Bio-logical Station and was continued throughout the year at the University of British Colombia. During the University session the investigation has been directed almost entirely by Dr. C. McLean Eraser and my sincere gratitude and thanks are due to him. His kindly suggestions, interest and valuable criticism are much appreciated. Water and plankton samples were taken at various stations in the open strait, as well as in narrow channels, and inshore points. The vertical hauls were obtained by means of a closing net of ft "bolting cloth and for the surface samples a smaller net of ft bolting silk was used. All readings for the hauls taken at various depths have been standardized to represent the number of organisms in the number of gallons (24) strained through the net, if hauled through ten yards. In the case of the surface hauls ten gal-lons were poured through the net and consequently all original counts, to be standardized, were multiplied by 2.4. The stan-dardized readings alone are used in this paper. The plankton samples were preserved in a mixture of B.C. Fixative (2 parts) and 10% Formalin (1 part). Formula for B. C. Fixative: Alcohol 95% - 50 parts H20 - 10 parts Formalin 40%- 2-§- parts Olacial Acetic-1 part This preservative proved very satisfactory for many of the forms but the majority of the ciliates, silico-flagellates and some of the softer forms disintegrated. Counting was done by means of a Rafter cell and numbers used in plotting graphs represent the average of five counts. The high power of the binocular only was used (32 mm. objec-tive , eye piece) and consequently many of the very minute forns of Protozoa were missed entirely. This is but a mere preliminary attempt to arrive at an understanding of the fundamental underlying principles of the problem. The results obtained serve to indicate some of the phases which offer a promising field for a more detailed in-vestigation . One cannot hope for consistent results when samples were never taken at the same stations under similar conditions. Attempting to compare depth occurrence curves for animals collected from several stations seems hopeless if one stops to consider the possibility of varieties of conditions. There are many factors to be considered and doubtless one will be more influential than either of the others at one particu-lar station. Esterly (1912) even considers that attempting to adjust for different nets in regard to distance and rate of hauling, amount of water filtered and like factors is at least unnecessary when the nets are used at different times and under different condition's. Por these several reasons including the possibility of faulty collecting and preserving, results as to distribution must be accepted with reserve and NN a i - ' -5-considered as tentative merely. In all the samples counted, the following forms were al-most always present and in appreciable numbers—Copepoda, Uauplii, Tintinnidae , Peridinia. Consequently, these have been considered in most detail and the graphs which accompany this paper are concerned with these forms only. Many other organ-isms, of course, were present also, but they occurred so in-frequently and in such a scarcity of numbers, that they will be treated only very generally. The conclusions arrived at are based chiefly on observa-tions of the Copepods - these animals are by far the most ab-undant metozoa in the sea - they dominate the plankton and form its most stable constituent. The following is Johnstone's (1908) appreciation of the importance of this group. "Estimates of the abundance of Copepoda furnished by quantita-tive plankton investigations are more reliable than those of diatoms or protozoa, for the crustaceans are more evenly dis-tributed throughout the sea and are so large that all are re-tained by the meshes of the silk nets employed". Bigelow (1926) reports that the plankton of the Gulf of Maine consists chiefly of Copepods. As far as the horizontal distribution is concerned Hutchinson (1927) indicates a maximum occurrence of diatoms (phytoplankton) in two definite regions, one north of the Fraser and the other south of the river mouth. He attributes this occurrence to the fact that optimum conditions for dia-toms were provided in those regions where the salt and fresh water mixed to the best advantage. No correlation between horizontal surface distribution of the zooplankton and phytoplankton is apparent from the examin-ation of the samples from-the Strait of Georgia. Neither is there any apparent correlation between the horizontal distri-bution of the zooplankton and the physical and chemical fac-tors. More extensive data from a greater range of locations, .may, however, yield more comparative results. In more than half the stations studied, a definite corr-elation is found to exist between the occurrence of the zoo-plankton animals and depth. Organisms increase in numbers with a decrease in depth (but not proportionately) and attain a max-imum at 2._5 yds. from the surface. Here a decidedly abrupt decrease in numbers is noted. Many other investigators record an abundance of plankton animals in the upper strata of water. This applies equally to the distribution of the organisms in.fresh water as well as to marine forms, e.g. Adamstone (1924) found the 0-1 m. stratum least productive and an increase in abundance from 1-40 m. McKay (1924) in his studies of the bays of Lake Nipigon found plankton concentrated in the 10-30 m. stratum. In Biaok Sturgeon Bay, the plankton was more abundant in the 0-j? m. stratum--this was the case in Humbolt Outer Bay, but in the -vv • - . 1 -7-Inner Bay more animals were observed in the 0-1 m. stratum. Here, as for the vertical distribution of marine plankton, the chemical condition of the deeper water may differ greatly from that of the upper layer. Juday (1922) believed;as did McKay (1924) that the absence of oxygen made the lower strata of water uninhabitable for plankton crustacea. Bigelow (1926) reported swarms of Oalanus in I5-0 fathom hauls. He observed that Calanus during the months of July, August and September was more abundant in the 2.5-100 m. hauls. He found greater •catches in the 30-0 than in the 83-Q m. haul. He also re-corded numerous specimens of Temora longicornis in the 40-0 m. level while McMurrich recorded all of this species in the upper 7 meters. Bigelow gives no idea of just where the max-imum occurrence is reached; the hauls taken in the Strait of Georgia were throagh much shorter distances, e.g. 30-10 yds; 10-5 yds. and J5-0 yds. If the zooplankton and temperature curves are studied, a correlation is obvious up to 2.5 yds. The temperature of the water increases with a decrease in depth but not in direct proportion with it, reaching a maximum at the surface. The temperature and zooplankton curves are by no means parallel but it is significant that they both show increases toward the upper strata of water. ±t is logical to conclude from the above that temperature plays an important role in the vertical distribution of the plankton animals up to 2.5 yds. There are no definite or conclusive results which point to pH or salinity as limiting factors. The temperature seems to act as a limiting factor up to 2.5 yds. and here the more powerful light factor interferes. The full intensity of the sunlight is felt only at the surface of the water and its intensity decreases very rapidly wfi. th the increase in depth. At the surface the sunlight is the deter-mining factor in distribution, and acts as a repellent force which overcomes the influence of the temperature factor. When a depth of 2.5 yds. is reached, the effectiveness is lost and the temperature becomes the determining factor. It is a general well known fact among fishermen that on bright sunny days, scanty catches are obtained. May not this be due to the absence of a food supply (the bulk of which con-sists of plankton organisms) which shuns the surface stratum of water, and is to be found at lower depths? Some argue that the scarcity of the catch is due to the fact that on bright clear days the fish are able to see the nets and consciously avoid them. Huntsman (1924) performed some very interesting experi-ments by submitting certain marine animals to direct light. He demonstrated that Copepods and Euphausia died from the effects of these direct light rays in 2-3 days. Some of the Copepods, however, were found to be very resistant to the light after being exposed for a certain length of time, their numbers remaining constant. He makes the statement that the "vast majority of animals in the sea live at some distance from the surface where the light intensity is greatly diminished, or if living near the surface, either retreat to the deeper water during the day or are sheltered by rocks, seaweed or other ob-jects from the direct rays of the sun." Huntsman, in the same publication, states that Copepods are very resistant to high temperatures. They do not die until O o temperatures as high as 26.5 - 29*5 C. are reached. None of the surface temperatures for the stations in the Strait of ° O e Georgia exceeded 20, they averaged 17 - I9.C This leads one to believe that in all probability the optimum temperature is never attained and the animals would continue to increase to the surface, were it not for the interference of the more in-fluential light factor. Pearse (1926) says "An animal cannot survive supramaximal or supraminimal temperatures, but the optimum rate of metab-olism is usually much closer to the maximum than to the mini-mum. Within certain limits, the higher the temperature, the more rapid the rate of metabolism." He believes temperature to be the primary cause of vertical and horizontal zonation that animals show in their distribution. Esterly (1924) found little if any consistent relation between the temperature and the occurrence of Calanus at the surface. He observed Copepods over a period which included June, July and August and recorded them as more abundant at 18.1° - 21./ C. and less abundant at 16° - 18°C. Bigelow (I923) did not find Ca-lanus in water warmer than 62.5° F (16.9°C.) at the surface. They varied from 42°- 76°F. i (5./C. - 24.4° G.) and in 1924 he found Temora longicornis in temperatures 2°- 20°G. Bigelow (1926) attributes the disappearance of the large blue cope pod Anornalocera to the cooling of the surface waters of the Gulf of Maine. Bigelow (1926) also considers that physical factors offer no apparent explanation of the comparative scarcity of Calanus in the deeper water as compared with intermediate levels as the temperature and salinity are well within the optimum of it-he believes the cause to lie in the distribution of the food supply, Calanus tending to congregate at levels where the mi-croscopic plants on which it feeds are most abundant. This is certainly the case with the phytoplankton and zooplankton studied from the Gulf of Georgia. The Copepods are always found in maximum abundance at the 2.3 yds. level where the dia-toms are also numerous. Almost as frequently is the maximum occurrence of the phytoplankton at the surface, and it has been suggested that the zooplankton, at a slightly lower level, feed on the diatoms as they sink. Bigelow (1926) says "much evidence has accumulated to the effect that somewhat cooler water offers a more favorable en-vironment for Calanus, whether as it affects the growth of the -11-Copepod itself, its reporduction or food supply, in spite of the fact that Calanus can exist in such temperatures as 24.44° C.H Huntsman (1919) agrees with this statement and re-ports more plankton in the deeper and colder waters and less in warmer, more superficial strata. In many cases the hauls were taken through long distances 20-0, 40-0, 70-0 m. etc.--it is consequently difficult to judge where the true maximum abun-dance occurs—it may be near the 70 m, level, or, on the other hand, very close to the surface. If hauls through shorter distances were examined it may be that the optimum would be found to occur in the upper stratum. Few of the hauls taken in the Gulf of Georgia were deeper than ^0 yds. and rarely were samples taken from the 100 yds. level. In all cases the zooplankton exhibited a decided decrease in numbers below the 10 yd. level. Johnstone (1908) reports more abundant though perhaps less varied plankton in cold water than in warmer water. rie states that the quantity of the plankton catch varies inver-sely as the temperature. Esterly (1912) says that hauls show as much variation in abundance.at low temperatures as at medium and high tempera-tures. One table shows the animals least abundant at a low temperature and an increase in abundance to the maximum at O O 18 - 19. lie concludes that temperature is not important, however, as a determining factor for the distribution of Calanus at the surface. Johnstone, Scott and Chadwick (1924) report a dense abun-dant plankton of relatively few species in the Arctic regions in contrast to a much less dense animal plankton, with greater numbers of species, in the tropical seas--this merely refers to relatively cold waters as a whole, and does not imply that plankton decreases with increase in temperature. if'raser (1918) found very few Copepods, on, or near the surface of Departure -bay during the winter months. If temper-ature is a limiting factor, i.e. if Copepods prefer warmer regions, and if it is here that they occur in greatest numbers, this migration to lower depths, during the winter months, is explained. At this time of year, the surface layer of water is appreciably colder and even freezes over at times, while the underlying layers have a distinctly warmer temperature. The light factor must not be ignored, however, Few Copepods are found right at the surface during the day and their ab-sence during the winter may be due to light influence primar-ily, and not so much to temperature changes. .tfirge and Juday (1922) record similar results in their in-vestigation of the plankton of Lake Llendota. During the winter months, when the lake became covered with ice, they found greater numbers of Crustacea in the strata below the surface, where the water was warmer. In spite of the evidence that plankton animals (i.e. Copepods) prefer colder water to warmer within certain limits, as is contended by several investigators, it is conclusive from the examination of the samples collected in the Strait of Georgia that temperature increases result in increase in abun-dance of the plankton organisms. Graphs showing depth-occurr-ence curves are inserted and if they are compared with the depth-temperature curves submitted by Lucas (1927) for the same stations, the correlation is obvious. Huntsman (1919) found that the plankton as a whole seeks a deeper level at night than'during the day. Ssterly (I912) and Bigelow, on the contrary, report that a diurnal migration occurs ana that in the case of Copepods, all species move toward the upper layers of water at night. Specifically, Ssterly studied the distribution of nineteen species of Copepods and from his data, came to the obvious conclusion that a greater abundance, of every species, occurred at night in the surface stratum, than during the day. 3sterly (1912) mentions Franz's observa-tions (1911)- Franz attributed the habits of organisms only partly to light but said it was difficult to avoid the con-clusion that a reaction to light was the primary cause of the upward movement. If surface temperatures which are decidedly higher than those of the intermediate water layers, do not provide more favorable conditions for the Copepods, why this definite migration to the surface, when the light factor is eliminated? To quote Bigelow (1926) , "In the daytime the stock of Calanus at say 10-30 meter level becomes enriched by the tend-, ency of the little crustaceans to sink when the sun is high--at night it is correspondingly impoverished". It is impossible to base any statement for or against the theory of diurnal migrations on this investigation. No hauls were made in the Strait of Georgia, for the purpose of study-ing this phenomenon. It yet remains to be seen whether data obtained from examination of plankton hauls taken hourly throu-ghout 24 hr. periods will yield similar results. During the summer of 1927, a twenty-four hour series was taken at a Station in Active Pass-- the material has not yet been worked over for zooplankton, but it is quite probable that it will yield interesting results. Bigelow believes that the increasing intensity of the sunlight as well as the progressive warming of the water which accompanies the advance of the season results in a surface stratum which is less favorable to Calanus. However, as men-tioned before, Copepods have- been found lacking from the sur-face during the winter months also. The fact that Bigelow obtained abundant hauls at the sur-face on certain occasions when the sun was high, caused him to doubt that sunlight is the only influential factor in play. These instances may be considered as exceptional, in spite of the fact that the hauls were obtained in regions of weak ver--15-tioal striatin and not in situations where tidal currents would account for the increase in abundance at the surface. Most of the other surface catches which were really "rich" were made during the hours 6-7 P.M.; 8-10 P.M.; 10:30-22:00 P.M. 1-2 A.M.; 6 A.M. Bigelow (1926) found Calanus occurring regularly and plentifully at the surface during the winter and explained it on the basis that the cooling of the water and the lessening intensity of the sun's rays provided a more favorable envir-onment. He believed temperature combined with light to be a factor worth considering: said "Calanus may tend to sink in warm, brightly illuminated water but to rise in pale ill-umination irrespective of its temperature". Praser (1918) found just the opposite conditions to exist. His observations are duplicated by Gran (Huntsman, 1919). Pearse (1926) attributes the abundance of Copepods found at the surface during the month of May to the bright sunshine, and disregards the temperature whether it be high or low. Bigelow (I9I3) reports a similar observation i.e. Copepods which were very scarce during April, appeared as swarms of Hauplii and older larvae during May 1913 while June hauls gave almost pure Calanus. Bigelow (1926) confirms his former observations and reports that Copepods reach their high water mark early in June and constitute almost the total plankton taken in hauls during May and June. The decrease . -f-, - ^ I* I " 1r ~ Jr . • it'** " , . „. : -17-from 5-8 P.M. Palolo worms found in the Gulf of Mexico ex-hibit this interesting characteristic also. May it not be that the biological factor at this time of \ year comes more into consideration and exerts such a powerful influence that the effects of physical factors such as temp-erature and light are nullified to such an extent that the plankton animals are to be found at the very surface? Loeb (Ssterly 1919) considers light as the most impor-tant factor. He states "A change in tropism because of a change in external conditions is the principal factor in the periodical depth migration". Giesbrecht (Willjr 1919) reports that the nauplius larva is positively heliotropic and as soon as it hatches from the egg, ascends toward the light, all Gopepod nauplji being positively heliotropic. Bigelow (I9I5) records somewhat similar observations stating that "it is interesting to note the scarcity of adult pelogic animals which make up the Galanus community at the surface during daylight hours of summer. Nets usually yield little plankton except larvae forms, smallest crustaceans and phytoplankton, while surface tows made during hours of dark-ness, especially if near midnight, have usually yielded an abundance of calanoid Copepods, even including the deep water genus Suchaeta". However, hauls were taken by'Bigelow at four stations which ?/ere occupied at daylight and three after dark. Galanus was very rare in all the hauls. This shows --18-that its absence from the surface, in the regions where it swarms in deeper waters does not depend altogether on sun-light, though the latter may be one of the factors which con-fines it to deeper levels. There is no evidence from the examination of the plankton samples collected in the Strait of Georgia, that this is the case, that is, that larval stages are found more abundantly at the surface, than are adult Copepods. This may be due, however, to insufficient data, from which to draw results that can be accepted without reserve. It is quite possible that Copepods, or even plankton an-imals in general, may be positively heliotropic during one period of their life history, as is evidenced by Bigelow and Loeb, only to become negatively heliotropic when they attain the adult.stage. Groom and Loeb, (Loeb 1918) , noticed that larvae of the barnacle upon hatching go directly to the light and gather at the light side of the dish, but that sooner or later the pos-itive heliotropism may give way to an equally pronounced neg-ative heliotropism. Groom and Loeb, (Loeb 1893), state that Balanus perforatus is positively heliotropic in weak light and if exposed to strong light becomes negatively heliotropic. That this may ex-plain the periodical migration, is their belief. In the even-ing and often during the night, the light reflected from the -19-sky is very weak and the animals are forced to move vertically upwards. At daybreak, as soon as the light becomes sufficient-ly intense, the animal becomes negatively heliotropic and must move vertically downward. Yerkes (1900) says there is slight evidence of a positive movement on the part of Copepods when subjected to light. It seems probable to him that Cyclops would respond photopathi-cally; if for example the light were exceedingly bright, it would not be surprising if the animals exhibited a negative tendency. It is also conceivable that at different stages of growth, light would affect the organism in different ways, for physiological conditions, as well as varieties in the stimuli, determine the reactions of an animal. Towle (1900) experimented with Ostracods 'and light and found that individuals at first responded positively when sub-jected to diffuse daylight, but there later followed an accum-ulation at the negative end of the trough. Other interesting experiments have been performed by Loeb. Previous to 1918 he demonstrated that the sense of heliotrcpism in marine crustaceons and in marine annelid larvae could be reversed by changes in the osmotic pressure (i.e. salinity) of the sea water. With an increase of O.P., the negative forms became positive. Deeper layers of water are more saline than the surface stratum and here the animals may respond positively to light but in the superficial stratum, the tropism becomes negative. Other experiments performed by the same investigator dem-onstrated that marine Copepods became positive on lowering the temperature. Similar effects were produced with Balanus larvae. These results may be used as evidence in favor of the important role played by temperature and light in regard to bathymetrical distribution. Copepods may be positively heliotropic at great-er depths where the temperature is low and tend to become more numerous toward the light, but when they reach decidedly warmer regions, they react negatively to the light rays. Esterly (1919) reports similar results to Loeb's (1918). He found that Calanus finmarchious became positively helio-tropic in water of lev; temperature. It seemed to him that the high salinity counteracted, to some extent, the effect of the low temperature. He reports that Calanus responds negatively to light of all intensities except when the water is cooled. He does not believe that a change in geotropism, with a change in light intensity or in temperature is general enough to be considered as of wide significance. Loeb also noted that Copepods and the Amphipod Gammarus , when indifferent to light, can be made intensely positively' heliotropic by adding acid to the water, thereby decreasing the pH. Depth pH curves show the surface layer of water in the Strait of Georgia to be more alkaline than the deeper strata (Lucas 1927)'- ';-'he same arguments hold here as do for the ex--21-periments with temperature and salinity as outlined above. Franz (Esterly 1919) contends that vertical migrations do not occur; he considers the reason for the larger numbers at the surface at night, as shown by collections, is that the an-imals cannot see the nets then to avoid them. He believes them to be really as abundant at the surface during the day as at night, but they escape the nets when it is light enough for them to see. Bigelow (1913) suggests the possibility that the density of the water may affect the bathymetrical distribution of the Copepods by its effect on flotation as is the case with fish eggs. Parker (19J2) believes the phenomenon of diurnial migra-tion to be controlled chiefly by the light factor, but states that the reaction to gravity has not been shown to be without influence and heat and density of the sea water may play sub-ordinate parts. Parker found the S.G. of habidocera aestiva to be higher than that of sea water. The explanation of diurnal migrations, on the basis that light controls the movement, has been offered by many workers. The puzzling side of the question is the fact that maximum numbers of Copepods are found in surface hauls for the four hours before midnight (Esterly 1912) and (Michael cf Esterly 1912) to be followed by a decided decrease from that time until morning. One v;ould not expect the light to be of suff--22--icient intensity to be effective so soon after midnight. If Copepods are positively heliotropic to light of less intensity what accounts for the habit of the crustaceans to seek lower depths so shortly after midnight? As mentioned previously, there is very little evidence which points to pH or salinity as limiting factors in the dis-tribution of plankton forms in the Strait of Georgia. In gen-eral,, more animals are found at a pH of 8.5 or thereabouts, but as nearly all the hauls,great or small , were found to have a pK very near that, little significance can be attached to the observation. Powers (1920) lays stress on the importance of pH. He refers to Loeb's and Moore's estimation of the impor-tance of the pH of sea water for the first stages of the dev-elopment of certain marine animals. McLendon (1918) reports that certain marine animals die if subjected to a pH of too great a range. McKay (1924) suggests that the Copepod increase in Orient Bay (in L. Nipigon) around the middle of July was due to the high pH and bi-carbonate concentration there at that time of the year. As regards salinity, there is some evidence at least, for assuming that sea water of definite concentration of salt pres-ents optimum conditions for marine animals. Examination of the plankton samples collected from the Strait of Georgia show greatest numbers of animals in water with a salinity of -23-13-15-5 of grams halide (chloride) dissolved in 1000 grams of sea-water. (Salinity can be cslculated by formula S°/oo = 1.8050 Gl°/00 -+- 0.03,0) ) . This does not hold to be true for all samples. At a salinity of I3.6 very large numbers of Copepods were obtained in the 5-0 yds. haul at Station 10; at Station 45, with a salinity of 12.6, they also occurred abun-dantly. Equally disturbing results are recorded for the Tin-tinnidae and Uauplii. These two forms were found in large numbers in the 5-0 yd. hauls at Station 22, with a salinity of 11.5, and at Station 10 with a salinity of I3.5 Esterly (1924) states that Copepods were found in lesser numbers at a low salinity. Bigelow (I9I5) reports the lowest salinity for Calanus at the surface as 31.8 (17.6°/OO CI.) and the highest at 20-0 fathoms as 35 (l?.3l°/oo 01.). The majority were found- to occur at a salinity of 32.7 - 33.4 (l8.09°/oo Cl-18.48°/00 CL). Bigelow (1926) reports that Calanus finmarchicus was un-affected by changes of salinity within wide limits. However, he does not find this form to be regularly abundant anywhere in water more saline than 35.3°/oo (l9.53°/oo CI). He says "High salinity may be a more effective barrier to its dispersal than is high temperature , but to quote Willy (1919) 'the factor that determines the limits of southern dispersion of Calanus fi nmarchicuB is clearly neither a simple physical constant nor a single organic tropism, but includes the biological factors -24-of food supply and propagation™. A species like C. finmarchicus (Esterly 1912) in its diurnal migrations probably passes through as many different physical conditions as would be encountered in a horizontal journey of many miles. Praser (1914) suggests a greater effect of salinity on sessile or slow moving forms. As Copepods are free moving animals they can migrate to a more favorable environment and would meet with a moderate range of salinity in their wander-ings. Johnstone, Scott and Chadwick (1924) emphasize that plankton animals drift passively about the sea. Doubtless they are carried to a great extent by currents, but they are capable of moving up and down and would have to withstand differences in salinity. • Willey (1919) believed Calanus finmarchicus to be indepen-dent of ordinary diurnal and seasonal fluctuations of temper-ature and salinity. As stated previously, a general increase in Zooplankton was observed from examination of the collections from the Strait of Georgia, up to 2.5 yds. where a falling off in num-bers occurred. In two cases only did the Copedods continue to increase above the 2.5 yd. level. At both stations the numbers of animals counted were very few and consequently the increases may be considered as almost negligible. To be more specific ,--at Station 7 (between Thormanb y Island and the -25-Mainland) the increase was from 1 - 2, and at Station 48 (off Roberts Bank, south of the mouth of the Eraser) the increase was from 2.5 - 2.8. When so few animals per count are consid-ered, the possibility of error eliminates any significance in these increases. Also, the situation of the first Station mentioned (7) is sufficient to expect disruption of normal con-ditions due to water currents from different sources. The sample at Station 48 was taken at the first phase of the ebb tide, and if the increase may not be considered as negligible, the mixing of the different layers of the water at this time would account for any irregularities in the depth-occurrence curves. Although most of the discussion has concerned Copepods, the most plentiful and constant members of the plankton, the other forms are worthy of some consideration. Bigelow1 s (I9I5) general observations of Peridinia agree generally with those recorded for Copepods. "These protozoa were noted in nearly every sample, i.e. were practically univ-ersally distributed in the Gulf of Maine, except when diatoms flowered abundantly". Even then, he suggests that they may be present but are overshadowed by the masses of diatoms. Perid-inia were noticed in abundance in the samples from the waters adjacent to the Eraser River mouth. They exhibited the charac-teristic decrease in numbers at 2.5 yds. except at five stations. The increase at three of these locations was appreciable , but due to the small size of these protozoa, the data cannot be con--26-as conclusive as that derived for larger forms such as Copepods. Specifically, the Peridinia increased as follows; The hauls at Station 1 were taken at the turn of the t'ide when abnormalities in the distribution of the plankton organ-isms are to be expected due to the mixing of the waters. As the station is situated in the open strait, where most normal conditions exist, this is the only possible explanation. At Station 51, one may expect irregularities. Subjected as it is to currents of water from several directions, a con-sistency in the occurrence of the zooplankton is not to be ex-pected. It is interesting to note that at this station two different series of hauls revealed negligible quantities of phytoplankton. Usually the animal and plant constituents of the plankton are found together. Off Snake Island (Sta. 13) , currents from all sources meet and instability in the water layers is•sufficient to account for the irregularities in the distribution of the animals of the plankton. In two other instances the increases in numbers of Peridinia were so slight as to be insignificant. They were as follows:-Sta. 1 (open strait) Sta. 51 (Sansum Harrows) Sta. 13 (near Snake Is.) 4.5-7.O 6.5-12.0 10-11.5 Station 7 (.5-.7) Station 20 (0-.49) , " f t . Si ' ' • ' -27-In nearly all the samples examined from the Strait of Georgia, the TintinnicLae were conspicuous in their numbers and varieties. BigeloiAr (1915) reports these Protozoa to be ex-pected anywhere in the Gulf of Maine, but scarce as a rule. He suggests that they may have been overlooked in his hauls. Eauplii were also observed in fairly large numbers in the majority of the hauls. The depth-occurrence curves for these members of the plankton, as for the Tintinnidae, exhibit the characteristic vertical distribution outlined above in the discussion of Copepods and Peridinia. Sight other groups of plankton animals occurred in app-reciably large numbers in the collections from the Strait of Georgia. Their absence entirely in certain hauls, made it difficult to demonstrate their occurrence by means of graphs. They will be discussed briefly from the frequency of occurrence standpoint, rather than quantitatively. Ascidians. The interesting larval stages of the Ascidians were con-spicuous members of the zooplankton and were fairly uniformly distributed at all depths. The^ were found most frequently in surface hauls (observed at 88^ of the stations) and in the 5-0 yd. hauls where they were noticed at 76^ of the stations. Gastropods. The Gastropods may be considered next to the Ascidians for frequency of occurrence. They were observed in all the y. J * *5j. r5 ' ft 1 " < / ' • -28-200-100 yds. hauls, but as very few stations were sampled from such depths, conclusions based on such scanty data are open to criticism. Gastropods were also found at 75% of the stations in the 100-50 yd. and 30-20 yd. hauls. Bigelow) (1926) found Pteropods in the 5O-O m. hauls. Pelecypods. Bi-valve larvae occurred frequently in the 30-10 yd. and IOO-5O yd. hauls--they were present at these depths at 68% and 50% of the stations respectively. They were not observed in collections from any of the stations in the 200-100 yd. hauls. . Rotifers. This group was conspicuous in all the surface samples where they were present in very large numbers. At over half the stations they were noticed in the 5-0 yd. hauls. Hone were found at any of the .stations below 50 yds. Polyzoa. Polyzoa larvae were very infrequently met with in the sur-face catches, but were noticed at 70% of the stations in the 5-0 yd. hauls. They were observed from this depth to the 200 yd. level at about half of the stations. Anne11ds (larvae). Few or no hauls at 200-50 yds. revealed annelid larvae. They were recorded at about one-third of the stations in the 50-30 yd. stratum and occurred slightly less frequently above -2 9-this depth. Echinoderms. Echinoderm larvae were found at 60% of the stations at 30-20 yds. and at 40% of the stations at 50-30 yds. Hone were noticed below this depth and they were observed less frequently above 20 yds. Medusae. These conspicuous members of the zooplankton were observed more often in samples collected at 30-10 yds., but very few specimens were noted at any depth. The following groups appeared very rarely. Tomopteris. One or two adult annelids were found in the few deep hauls taken at IOO-5O yds. Amphlpods. An odd specimen of this group was observed in one or two 100-50 yd. hauls. Bigelow (1926) reported them in l60-0 m. hauls. At one time he also noted juvenile amphipods at the surface in appreciable numbers. Euphausia. Euphausia occurred as frequently as Amphipods and in hauls from the same depths. Smith, Woods, Warburton (I909) reported Euphausia to be universally distributed. They were never not-iced above the 50 yd. level in the Strait of Georgia. Bigelow (1926) found numerous specimens of this group in 10J-0 yd.hauls. -30-Sagltta. Odd specimens of arrow worms were noted at two stations in the 100-.50 yd. hauls. Huntsman (1919) reports several species of Sagitta to occur only below the 100 m. level. He found Sagitta elegans nearer the top at 30 m. and some even at the surface. Ostracods. One or two specimens recorded in 200-100 yd. hauls. Oeratium. These Protozoa were more frequent in surface hauls. Very few specimens were seen at any depth. Other investigators mention Oeratium as a conspicuous constituent of the plankton. Their apparent absence in practically all the Strait of Georgia samples may be due to disintegration in the preserva-tive . Phoronis. Phoronis larvae (Actinotrocha) were observed in scanty, numbers at about one-third of the stations in t he 50-30 yd. hauls. Hoctiluca. These Cystoflagellates were conspicuous in the surface samples at nearly all the stations. Eggs of various sorts, especially those of Copepods and rotifers were abundant in the majority of the surface hauls and were also noticed in the deeper catches. -31-Upon examination of the depth-occurrence curves for zoo-plankton and Phytoplankton in samples from the Strait of Georgia, a correlation is obvious up to 2.5 yds. from the sur-face. Frequently, at this depth, the diatoms attain their maximum abundance, which occurrence is dependent on salinity rather than any other factor, (Hutchinson I927) but they also are found in large numbers at the surface. This occurs when there is no marked change in the salinity or temperature be-tween the surface and deeper waters. In the case of the diatoms, the surface layer pf water provides optimum conditions, for it is in this region only that the full intensity of the sun's rays is felt. Here, trie phytoplankton can carry or, its life processes to the best advantage. The decrease in the zooplankton at 2.5 yds. has already been discussed. Very rarely is the animal plankton present in abundance and the vegetable plankton conspicuous by its absence below 2.5 yds. This, however, was the case'at Station 51 in Sansum Harrows. Plankton samples taken both in the summer of 1926 and in 1927, at this station, revealed a scarcity of diatoms, while in the 1926 sample at least, an abundance of crustaceans was noted. The 1927 sample has not yet been examined for zoo-plankton. The situation of this station in a tide swept pas-sage may account for the scarcity of diatoms, but this ex--32-planation is not convincing. Bigelow (I9I5) states that when the quantity of animal plankton decreases to its annual minimum, it coincides with the vernal augmentation of the vegetable plankton, a change soon followed by a wave of reproduction on the part of the Copepods. Fish (I925) holds that normal diatom maxima have no not-iceable effect on the larger plankton forms. He records, how-ever, that when the unusually large swarms of phytoplankton appear, the zooplankton decreases rapidly and may even totally disappear for a time. He also states that Copepods are always present in abundance except in seasons of maximum diatom abun-dance . As no samples were collected in the Strait of Georgia earlier than the month of June, i.e. during the period of max-imum abundance of phytoplankton, there is no evidence as to the quantity of zooplankton to be found there at that time of the year. The stations for which graphs are inserted will be mention-ed specifically. 1. Stations at which depth occurrence curves for Zooplank-ton and Diatoms exhibit almost perfect parallelism. They are located in the open strait and their curves may be considered as typical of normal conditions. Staticn 10. Copepods, Peridinia, Tintinnidae and Nauplii show an in--33-crease up to 2.5 yds. where the decrease occurs. Diatoms ex-hibit steady increase to surface. Stati on 16. Zooplankton and Phytoplankton increase to 2.5 yd. level and at this point all exhibit the decrease in numbers. Station 60. All four groups of zooplankton as well as phytoplankton are most abundant at 2.5 yds. from the surface. Below the 15 yd. level, the zooplmkton organisms decrease slightly in num-bers. The greatest decrease occurs in the Tintinnidae end as they are easily overlooked when counting, this decrease is not of grec-.t significance. 11. Stations at whi jh samples we re taken at time of a change of tide - positions where there is a marked tidal curr-ent. Irregularities in depth occurrence curves are explained on this basis. Station 22. Curves show evidence of enupp;r and lower current in opposite directions. Two maxima are noticed - one at 2.5 yds. and the other at 2 0 yds. Station 11. Curves for zooplankton as well as phytoplankton are ab-normal. Copepods decrease to the surface from a maximum at 20 yds.; diatoms exhibit an irregular decrease at 2.5 yds. -34-Bamples were collected at the 6th phase of the flow tide -instability of the water layers would be expected. 111. Stations whose abnormal curves cannot be explained from a consideration of the data so frr obtained. Station 13. 1'he tide 1 ;-• at the 5th phase of the ebb; Copepods and Nauplii show fairly characteristic curves; Peridinia show a slight increase at the surface. The Tintin.nidae show greatest irregularity - they decrease to the surface i-rom a maximum at the 25 yd. level. The station is situated off Snake Island and is probably affected by currents of water from different sources, i.e. through Dodd's Narrows, from the north as well as from the open strait itself. SmilARY. 1. A. study of the plankton material collected from the Strait of Georgia revealed:- Zooplankton most abundant at 2.5 yds. from the surface. Above this level a sudden decrease in numbers is the rule. 2. Temperature seems to act as a limiting factor - zoo-plankton increases with an increase in ternperature. 3. Light overcomes the effect of temperature factor at 2.3 yds. from the surface, t od becomes the determining factor. -35-4. Salinity and pH do not appear to be limiting factors. Zooplankton and Phytoplankton depth-occurrence curves show general agreement up to 2.5 yds. in all samples from the Strait of Georgia, a decrease in Zooplankton was noted at this level while this is not generally the case with the phyto-plankton . UBC Scanned by UBC Library -36-BI3L]OGRAPHY. Only those papers with a direct bearing on the subject as treated, are listed below. Adamstone, F. B. 1924. "The distribution and economic importance of the bottom fauna of Lake Nipigon with an appendix on the bottom fauna of Lake Ontario". University of Toronto Studies, Pub. Ont. Pish. Research Lab. No. 24. Bigelow, Henry, B. Exploration of the Coast ^ater between Nova Scotia and Chesapeake Bay, July and August 1913, by the U.S. Fisheries Schoonc r Gratiipus. Oceanography and Plankton. Bull, of I'us. Compar. Zool. Harvard, Vol. L1X, No. 4, Cambridge. Plankton of the off-shore waters of the Gulf of Llai ne . Dept. Comm. Bur. of Fisheries, No.968, 1926. Reprinted from Bull. Bur. of Pish. Vol. IIL, 1924, Part 11. Kc , . and Juday, Chancey. 1922 . The Inland Lakes of Wisconsin. 1915. 1926. -37-1. Plankton - Quantity and Chemical Com-positi on, Wise. Geological and Nat. Hist. Sur-vey, Bull. No. 64, Sc. Ser. No. lj. Clemens, W. A., Dymond, J. R. , Bigelow, N. K. 1924. Pood Studies of Lake Nipigon Pishes. Univ. Toronto Studies, ft23 Pub. Ont. Pish. Research Lab. Davidson, V. II., and Huntsman, A.. G. 1926. The Causation of Diatom Maxima. Trans. Royal Soc. Canada. Third Series, Vol XX, Sect. 3. Ssterly, C. 0. 1911. Vertical Distribution of gv:calanus ^lone-atus in the San Diego region during I909• Univ. calif. Pub. Zool.Vol.8,pp.1-7 1912. Occurrence and vertical distribution of Copepocs of the San Diego region with particular reference to 19 species. Univ. of Calif. Pub.Zool.Vol.9, pp. 253-340. .--erkeley. 1919. Reactions of various plankton animals with refer-ence to their diurnal migration. Univ. Oali f. Pub. 2 col. Vol. 19, pp. 1 -83, 1919-1920. -38-1924. .Free-swimming Copepoda of San Francisco Bay. Univ. of Calif. Pub. Zool. Zol.26. pp. 81-129, 1923-1925. Pish, C. J. 1925. Seasonal Distribution of the Plankton of the Wool's Pole Region. Dept. of Commerce, Bur. of Fisheries, Document 972, from Bull. U.S. Bur. Pish. Vol. XII, 1925. Wash. Fowle r, K. 1912. Science of the Sea. - prepared by the Challenger Society. London. John Murray, 1912. Praser, C. McLean. 1914. Marine Biology in B.C. Papers reed before the B.C.'Academy of Science, 1910-1913. 1913. The Sv/arming of Cdontosyllis. Trans. Royal Soc. Can. Series 111. Vol.It ,1915• 1918. Migrations of'Marine Animals. ' Trans. 3oy*l Qoc.-^an. Ser.lll, Vol .XI1, 1918. 1921, Some Apparent Effects of Severe "'eather on Marine Organisms in 'the vicinity of Departure Bay, B.C. Contrib. Can. Biol. 1918-1920. 1922. Pacific Perring. Contrib. Can. ?icl. 1921. -39-Fraser, 0. McLean. 1923. Ichthyol0gical Uotes. Contrib. Ca^Biol. U.S. Vol. 1, pp. 285-295 ,1923 . Gran, H. £. 1919. Quantitative Investigations as to toplankton and Pelagic Protozoa in the Golf of St. Lawrence and outside the same. Can. Pish. Exp. I914-I9I5. Investigations in the Gulf of St. Lawrence and Atlantic 'waters of Canada. Huntsman, A. 5. 1919. Some quantitative and qualitative studies of the eastern Canadian plankton. Can. Pish Exp. I914-I9I5, Dept.of Naval service 1924. Limiting Factors for Marine Animals. (1) Lethal Effect of Sunlight. Contrib. Can.Biol. U.S. Vol. 11, 1924. 1924. Limiting Factors for Marine Animals. (2) Resistance of Larval Lobsters to Extremes of Temperature. Contrib. Can. Biol. Vol. 11, 1924 . Huntsman, A. G., Sparks, M. I. 1924. Limiting Factors for i.arine Animals. (3) Relative Resistance to high temperature. C. at rib. Can. Biol. 1! .3. Vol. 11, 1924. -40-Johnstone, Jas. 190d. Some Results of the International Fishery Investiga-tions . Journ. Mac. Biol, of United Hingdom. 11.3. vol. 7, no. 1904-1906. 1908. Conditions of Life in the Sea . Fisheries Lab. Liverpool IT. Camb. Univ. Press 1908. Johnstone, J., Scott, A., Chad.vicl-, H. C. 1924. The Marine Plankton with special reference to inves-tigations in:-.de at Port Erin, Isle of Man, during 1907-1914. Univer. Press. Liverpool. Loeb, Jacques. 1894. Cn the influence of lijht on the p-.-ri olioal depth mi-grations of pelogic animals. Bull. U.S. Pish. Comm.Vol.XI11 for 1893. 1918. Forced Movements t Tropisms and Animal Conduct. Monogri-ph on E x ^ ri:..ental Biology. Lippin,'ott .Co. , Phil. L London. Lucas, C. C. and Hutchinson, A. h. I927. A 3ic-H„drographicai Investigation of the Sea Adjacent to the Eraser Riwr mo .th. Trans. Royal Soc. Can.Series 111. Vol. 21 U t • I » I -41-LicSwen, George, 'F. 1916. Summary and interpretation of the Hydrographic obser-vations made by the Scripps Institute for the Biolo-gi cal Research of the University of California, I90O-I5. Univ. of Calif. Bub. Zool. Vol. 15, I915-I9I6. IJcxIay, He c 10 r , H. 1924. A quantitative study of the plankton ofthe shallow bays of Lake Uipigon. Univ. of Toronto Studies, Biol. Ser. Jo. 26. Bub. Ont. Fish. Research Lab. LIcLendon, J. F. 1918. Changes in the s.a and their relation to organisms. Pub. Carnegie Instit. ,.ash. Dept. of Biol. 12, 215-258. Llct.lurrich, J. P. 1916. Notes on the plankton of the 3. C. Coast. Trans. Royal Soc. Can. Ser.Ill, Vol. Sect. 5, 75-89. Llichael, B. L. and IlcBwen, 0. F. I9I5. Hydrographic, plankton and dredg'ng records Scripps Institution for Biological Research University of California 19J1-1?12. Univ.of Calif. Bub.Zool. Vol.15, 1. Parker, G. 11. 1902. Reactions of Copepods to various stimuli and the bear-ing of this on depth migrations. 10, of the of the 1916,15,207. -42-Bull. U.S. Pish. Comm. Vol. 21(pp.IO3-I23) "Wash. 1902. Pearse , A. 5. 1926. Animal Ecology. McGraw-Hill Book Co. liew York. Powers, 5. B. 1920. The variation of the condition of sea-water especially the Hydrogen-ion conjentrati on and its relation to marine organisms. Pah. Paget Sound 3iol. Sta. Vol. 2. 1921. Experiments and observations on the behavior of marine fishes toward Hydrogen-ion concent rati on of t:.e sea-water in relation to their migratory movements and habits. Pub. Paget Sound Biol. Sta. Vol. 2. Smith, 0 ods, ..'arburton , Shipley Thompson. I909. Crustacea and Arachnids. Cambridge Hat. Hist. I909. LIcLlillan. Towle , Elizabeth, E. 1903. A study of the Heliotropisrn of Cypridopis. Amer. Joar. Physiol. Vol. 3, 1899-1900. Ward. H. B. and chippie, G. C. 1913. Fresh v/ater Biology. John Mile'j 6, Sons, ilew York; Chapman L Hall London. -43-Willey. Arthur. I919. Report on the Gopepoda obtained in the Gulf of St. Lawrence and adjacent waters. Can. PishZxp. I914-I3. Dept. Naval Service. 1921. Arctic Copepoda in Pasama^uoddy Bay. Studies fran Biol. Stations - Biol. Board Can. No. 3« Reprint from - Proceeding's of Airier. Arts d. Sciences. Vol. 36; No. 3, 1921, pp.183-196 Boston. wolfenden, R. II. 1904. Notes on Copepoda of the North Atlantic Sea and Faroe Channel. Jo urn. Mar. Biol. Ass. U.S. Vol. 7; 1904-1906. No. 1, April 1902, 110, 146, Plymouth, Zag. bright, R. Ramsay. 1907 . The Plankton of Zastern Nova Scotia V/aters. An account of floating organisms upon which young food f ishes tnc inly subsist. Contrib. Gan. Biol. 1902-190$. Yerkes, R. LI. 1899. Reaction of Rntomostroca to Stimulation by Light. Amer. Joiar. Physiol, Vol. 3, No. IV, 1899-1900. -00-Vn VN IV) M Vn Cn H> u O o o o c 1 3 CD I 1 1 1 1 o 'O ro ro M M Vn \ o o o O Pi CO • t3 h; a te; ^  »x: o tei 1-3 h: o • 3 t-c O • * • • • * • • • » » • CO (—1 M VOVJI HVJI H OsVn VN vm ro h-> P Vn co rv> co \JD CTvVnVn as 4^  r\3 r\3 4^  OVn * « « « <• <• « « « <• • « « <• J « M ooro r\3 rv> ro o corv) coo a o VJIH-J^ O o o o o O O 4^  CO o o o o as as os o 1 1 1 o o o o o o o o O O C O o o c c te! ^  i-c1 o teld^O t4 l-J hj CD K3 h. o « »-3 hi o ! • • • • • • • • • • » • • « * • • • • • CO c+ Vn (—1 M ro M M P M Vn 4^ Vn so ro vO H1 --0 M • - Vn js. 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