WINTER POPULATION DYNAMICS OF PHYTOPLANKTON IN COOS BAY, OREGON by PETER C , FREEMAN Presented to the Department of Biology and the Honors College of the University of Dregon in partial fulfillment of the requirements for the degree of Bachelor of Arts (Honors College) June 1979 Dedication I would like to dedicate this paper to my parents , Molly M. Freeman and Richard W. Freeman, without whose love and support I would have never reached this point . I would also like to thank Dr. . Paul P . Rudy , for his irreplaceable help , patience and understanding . Thanks also to the entire staff at the Oregon Institute of Marine Biology, especially Jean Hanna and Bob Ellis. i Contents Page Introduction 1 Materials a nd Methods 7 Results · 9 Conclusions 10 Tables, Graphs 23 Appendix 32 Refer ences 33 Bibliography 35 ii Tables and Graphs Table 1: Phytoplankton Cells per Liter 23 Table 2 : Phytoplankton Cells per Liter(24 hr . series ) 24 Table J : Phytoplankton Percent Composition 25 Figure 1: Map of Coos Bay 26 Figure 2 : Total, Phytoplankton 27 Figure J: Whittaker Percent Similarity 28 Figure 4: S~asonal .Variation in Tem9 . and Sal. 29 Figure 5: Reproduction vs . Exchange Ratio JO Figure 6 : Seasonal Relationships 31 This study is concerned with the early winter (October , November , December ) dynamics of phytoplankton populations in the South Slough of the Coos Bay estuary . A student study, conducted at the Oregon Institute of Marine Biology in July and August 1973 established the size , location and make-up of the phytoplankton population present during the summer months . It is hoped that this study , when combined with the findings of the OIMB summer study, will lead to the formulation of a summer- fall-winter trend in the phytoplankton populations in the South Slough . Coos ~ ay is _located in Coos County , Oregon , about 200 miles south of the Columbia River and about 445 miles north of the San Francisco Bay. The Coos Bay watershed area en- compasses about 82q square miles and consists primarily of coniferous forests . At mean high tide , the Coos Bay estuary, including the South Slough, contains approximately 10, 500 acres , and ip reduced to about 5 , 000 acres at mean low tide . The Coos Bay estuary, as far as salinity is con- cerned, varies from a partly mixed to a well mixed or vertically homogeneous estuary depending on the season and location within the estuary . This study is-prima~ily concerned with the phytoplankton population of the South Slough , which drains an area of approximately 26 square miles . Much of the South Sl~ugh is composed of marsh areas and extensive mud flats which lie exposed at low tides . Carex sp . and Di s tichli s sp . are the prominent marsh plants present. 2 The South Slough is connected to Coos Bay through a narrow channel 50- 75 yards wide, deep enough to allow small fishing vessels to pass through . The channel leading into the South Slough is very near the mouth of Coos Bay , and there is a great influx of sea water a.t incoming tides . The salinity 0£ the South Slough is therefore very near that of pure sea water , 33-35 ppt (o/oo) , and varies season- ally with increased runoff . Very little is known of the hydrography and physiography of the South Slough , It remains in a pristine condition in most of ·its upper reaches . The annual freshwater r unoff from South Slough drainage basin was estimated to be 98 cfs. The monthl y values ranged from 6 cfs in August to 232 cfs in February . The annual average precipi~ation of 54,82 inches resul ted in 42 , 58 equivalent inches of runoff. Harris , et al . (1979) , For the purpos~s of t hi s study, the smaller South Slough estuary will be treated as a part of the greater Coo s Bay estuary, with respect to hydrography and physi ography . Phytopl ankton is a general class of or ganisms ; those organisms which float and drift in the water layers . The phytoplankton is composed, of an array of plant species , incapable of movement against the tides and currents , which contain chlorophyll and a re thus able to perform photosyn- t hesis , Part of the phytoplankton community is made up of the benthic forms , which by definition dwell primarily on t he bottom of the estuary. The other part of the community 3 consists of the free floating forms, found in the upper parts of the water column, where light intensity and wavelength are adequate for their survival . The most obvious and usually most numerous form of phytoplankton is the diatom. The diatoms are unicellular and possess a unique skeleton of silica and pectin, com- posed of two parts or valves, the hypotheca and epitheca. In one group of diatoms, referred to as the pennate forms, many species have -a characteristic slit (raphe) through which the protoplasm may be in contact with the water . Raymont (1967). Most marine speci~s belong to the centric group of diatoms that have no raphe, but show characteristic patterns of pores in the exoskeleton. Within the valves, cytoplasm forms a lining surrounding a large vacuole ' filled with cell sap. The nucleus is usually central, with numerous chromatophores found through- out. The chromatophores contain a mixture of chlorophylls a and .Q, with several carotenoids, mainly ~ -carotene and oe-xanthophyll, Raymont (1967), which absorb light at wavelengths different from the chlorophylls and consequently allow the organism to photosynthesize over a greater range of light wavelengths. The range of size in diatoms is relatively l arge , with some approaching dimensions as great as 400 microns in diameter and 150 microns in length, while many species are as small as 10 microns or less. Part of this variation in size is due to the method of reproduction: at each cell 4 division, the valves separate, one going to each daughter cell, where both the hypotheca and epitheca from the orig- inal diatom form the epitheca for the daughter cells. With this method of reproduction, the average size of the indi- viduals of a continually dividing population must dec.r ease as division continues. H.H . Gran has shown division rates for various diatom species to be considerabl y faster than one division per day. However, growth conditions in the ocean and estuary are hardly ever as favorable as those in culture , and a division rate of once every one or two days is probably nearer the maxjmum. Raymont (1967). Rates of division do vary from species to species, and will also depend on environmental conditions such as temperature, light, salinity, and available nutrients , In general, reproduction rates of phytoplankton decrease with decreasing temperature, while a critical level of light for a population "bloom" has been suggested by Riley (1967), and Castenholtz (1964) has shown the ability to use light in some species is regulated by the time of exposure and salinity . Pratt (1965) has con- cluded that the nutrients Silicon and Nitrogen regu~ate the maximum abundance and termination of the winter-spring phytoplankton bloo~ in Narragansett Bay. With long periods of reproductive activity, the average size of the diatom cell ~ill decrease rapidly. The restor- ation to maximum size is achieved by the formation of an auxospore , during which the cell throws off the old valves 5 and increase greatly in size . A membrane of pectin and silica is formed around·the enlarging cytoplasm and new valves consistent with the increase d size are formed. Oils produced as an end product of the photosynthetic process are stored within the valves and may be useful in the control of ·bouyancy. Both salinity and temperature affect the specific gravity of seawater, and these two factors undoubtedly -play a part in the sinking of phyto- plankton . Raymont- ( 1967 ) . The .flushing rate of the estuary also plays a major role in the composition of the popu_lations of phytoplankton within the estuary . The flushing rate is the period of time it takes the freshwater input to the estuary to replace the tidal volume , and is usually expressed in terms of river flow in a ratio·to the volume of water in the area considered in conjunction with the ratio of fresh to salt water in the area . If S0 is the salinity of the water outside the estuary which is avai lable for mixing, and Sis the salinity at any point inside , the fresh water content is given by : f = S0 - S So and the accumulated_ fresh~ater volume is the n ~iven by: J0 F = fd(vol ) vol where the integration is carrie·d out over the total volume . If R is the rate of influx of fresh w' ater , the. flushing time , t , .can be determined by: t = F R 6 where Fis the total freshwater volume from above . The flushing number technique , used by Harris , et al . (1979 ) yielded extreme values of flushing numbers of O.OJO for February and 0 . 001 for August. Low values indicate very little stratification. The tidal prism in the estuary is the difference in volume of the estuary due to the tidal highs and lows . .H arris et al (1979) used three independent methods to estimate the volume of the tidal prism and obtained a value of J . J x 108 ft3 for the South Slough . The classification of an estuary, with regard to salinity, is calculated as the ratio of river flow per tidal cycle to the tidal prism. ·When this ratio is 0 .1 or less, .the . estuary is classified as well mixed. A ratio of 0 .1 to 0.5 indicates a partly mixed system, and above 0.5 a highly stratified system . Dyer (1973). The ratio of freshwater volume per tide cycle to tidal prism, described by Harris et al (1979), gave extreme values of J,05% for February and 0.09% for•August. The Coos Bay estuary is well mixed during the summer months, and changes to partly mixed during the winter, be - cause of the increased river flow . Salinities within t he estuary range from O ppt ~fresh water) in the uppermost reaches of the bay to greater than JO ppt (sea water) at the mouth. The temperature varies seasonally, and averages 8° - 12° during the early winter (fig. 4). The . tides are caused by gravitational force s of the moon 7 and sun acti~g upon a rotating earth. The tide height reached for any day depends upon the moon- sun alignment . When the moon and sun are in line, their forces complement each other and an increased tide range results. A decreased range re sults , therefore, when the moon and ·sun are not in line (the first ani last moon quarters). The tides follow a diurnal cycle, resulting in two high and two low tides within an approximate 24 h·our period. The moon passes through a given meridian at .mean intervals of 24 hours 50 minutes , called a Lunar Day, thus it passes a particular meridian 50 minutes later each day. Therefore each day the tides rise on an average 50 minutes later. The interval between t he passing of the moon and the rise of the tides is constant for any given coastal position. The position of the moon affects not only the time of the tides , but also . the height and mass of the water involved in the tidal current, creating the higher high , lower low, lower high and higher low tides experienced within an approx- imate 24 hour period (24 hours 50 minutes), MATERIAL~ AND METHODS Surface plankton samples were taken during the daylight high and low slack tides on six days during the period be- I g inning October 31, 1977 and ending on December 4, 1977. Two samples were taken, high and low tides on October 31, November 12, November 14, November 16_, November 28 ; and December · 4 , 1977, A series of samples was also taken during 8 the 24 hour ·period of December J - 4 , 1977 , One sample was taken every three hours during the 24 hour pe r iod . . A total of 20 samples were taken , with eight samples composi ng the 24 hour series , and the remaining twelve composing the high-low population compar ison. The samples were collecte d by allowing 500 milliliter(ml) Erlenmeyer flasks to fill when submerged just below the surface of the water. The undiluted samples were treated in the laboratory with Lugol' s Solution-Weigert ' s variation, in the proportions 1 : 2 , 000 or 0 , 05 ml per 100 ml 0£ sample. Lugol ' s solution was added to act both as a preservative and -a dye in the case of the clear silica val ves of the diatoms . The samples were filtered , using a standard suction apparatus , ont o a 4 ,5 x 10- 4mm (0 .45 micron) Millipore HA membrane filter . The filters chosen, from standard stock , were equipped with gridding for use as a counting aid . After filtering , the samples were allowed to dry in a Thermo- dyne hot plate oven . For handling , the filters were placed on glass microscope slides . A small amount of immersion oil •Was applied to the dried filter , which effectively c·leare d the filter for microscopic viewing and counting of the or- ganisms present . T~e organisms were counted on American, Optical-Spencer compouDd microscopes . A counting field on .the slide was defined to have the ! dimens ions 6.o mm x 20 . 0 mm . Vertical sweeps , each 0 . 95 mm wide were used to scan and count every 2.0 mm across the 9 slide . The -organism count was extrapolated to include the entire surface area of the filter. Organisms were counted as single cells only , and in the case of chain type diatoms , individual cells within the chain were counted, rather than counting the chain as.a solitary organism . Organisms present were identified to genera only , due to the extreme difficulty of identification of species and the high magnification necessary to discern characteristic pore patterns, etc., needed for species identification . RESULTS The ma jor genera identified included Coscinodiscus, Melosira , Skeletonema, Fragillaria , Thallasiosira, and Nitzschia . Other genera_ identified were Biddulphia and Grammatophora. Three other classifications were used in place of further identification : dinoflagellates , pennates, and stars (an unidentified organism) . Coscinodiscus sp . comprised the major portion of all samples taken, dominating the populati ons at both high and . low tides . By individual count , Coscinodiscus sp . averaged 54.8% of the number o! cells collected at low tides, and 74 ,6% at high tides . The range of percentages varied from I 49 . 2 to 60 .5% at low tide , and from 44.9 to 87,9% at high tide, Melosira sp. , second to Coscinodiscus in cell pe~centage per sample , comprised an average of 20 ,5% at low tides , and 10 only 1 . 8% at high tides , varying from 1J. 6 to 30 . 3% at low tides and from Oto 3 , 9% at highs , The r emaining genera composed no greater than 29% (Fragillaria sp .) of any sample , and averaged between 1 and 10% in each sample . Overall concentrations of cells per Liter (c/L) varied for an individual· genera , betwe·en 10 c/L and 2 , 600 c/L ; and betw:en JOO c/L and J , 000 c/L for total cell concentrations , Coscinodiscus also dominated the population samples taken at high tides during the 24 hour sampling , December J - 4 , 1977, For the two high tides sampled , Coscinodiscus comprised 87% and 84% of the total c€lls per Liter , Melo- sira fol~owe~ as above , comprising only 4% and 5% of the sample at the same tide . Total cell concentrations during the 24 hour sampling . period varied from 380 c/L to 1 , 000 c/L . The physical results of the samplings, both raw cell counts and the relati~e per cent compositions of each genera are furnished in tables _1_ through _J_. Population and relative abund~nce comparisons, carried out in hope of finding distinct populations within the es- tuary were calculated using the Whittaker Percent Similarity Index (appendix) . The results of these calculations are summarized in figure 3 , CONCLUSIONS . The · OIMB student ' s study, summer 1973 , found an upper bay phytoplankton assemblage dominated by Skeletonema sp. and Melosira sp.; and a lower bay assemblage dominated by Chaetoceros, Skeletonema , and Thallasiosira. The samples taken during the twenty-four (24) hour· period of December 3-4, 1977, show a distinct upper South Slough assemblage dominated by Melosira , Coscinodiscus , and Fragillaria. This dominance by Melosira, etc ., during the early winter months of 1977 is interesting when compared with the results from summer 1973, In that study , Melosira and Coscinodiscus (that study was also confined to identificati on to genera only) each comprised less than five . (5) percent of the samples. OIMB students (1973) , As shown above, in the winter of 1977, Melosira and Coscinodiscus comprise up to thirty (JO) per- cent and eighty-eight ( 88 ) percent respectively. The population _figures and composition suggested by the same should be viewed discerningly, as the figures were ob- tained using identification only to genus level , which may introduce an error into the actual population size and com- position . The major constituent of all samples was the genus Coscinodiscus, which is readily identified t o that level by its characteristic valve. Species identification, however , has become increasingly complex , with a much greater level of magnification necessary than was readily available . Many species are now differentiated only br the number or pattern of pores ~n their exoskeleton . 12 As a r esult , the large percentage of Coscinodiscus present, which for the purposes of this study were counted as a single group , may be found to be comprised. of a number of different species , perhaps composing entirely different upper and lower bay assemblages . This possible error may al~o be reflected in the percent similarity computed , using Whittaker's Index. The large num- ber of Coscinodiscus present in every sample almost immed- iately makes the populations sampled similar; when as shown above, the Coscinodiscus populations at high and low·tides may be composed of completely different species, or a mixture of popula. tion. s. The Whittaker Percent Similarity Index also fails to take into account areas in the populations where a type of organism is represented in one population and not in the other . For the purposes of percent similarity, this difference in the populations is ign9red (i.e. it contributes or subtracts nothing to the total percent similarity, despite evidencing a difference in the population) . ~he similari ty computed in this fashio·n is based solely on the percent composition of each population of organisms present in both populations. Coscinodiscus is known to reach into the hundreds of microns in diame~er, yet a majority of the organisms c~unted from the winter 1977 samples were on the order of 50 microns or less , with a· sub~tantial portion considerably smaller . This may ·be evidence of a continually dividing population, ' 1' 1.3 with subsequent decrease in t he average individual ~ize , or evidence of preferential predation . In either of these cases , furt her evidence of one or the other would most likely have been observed. With a continually di viding populatioD, some individuals will remain at the large original size , no indiv- iduals of such size were noted in the samples , and wit h predation, a number of predator zooplankton would also have been found in the sampl$, as no filtering other than through the membrane Millipore filter was performed . The succession of dominance fro~ Chaetoceros , Skeletonema , Thallasiosira, and Melosira during t he summer in the Coos Bay estuary to Coscinodiscus and Melosira during t he early winter should in no way be considered unique. Scott and Chadwick (1924) found after years of study in the Irish sea , that during the winter when the phytoplankton concentration is low, the populations are dominated by Coscinodiscus , and s omewhat later by Biddulphia . The spring bloom was charac- terized by species of Chaetoceros toge_ther with Thallasiosira and Lauderia . Raymont (1967 ). Lillick (1940) studying phyt oplankton in the Gul f of Maine found the winter .flora to be dominated by Coscinodiscus , with the spring bloom consisting predominantly of Thallassiosira , which is sue- ceeded by a sharp bloom of Chaetoceros . During the late summer Rhizosolenia arid Skeletonema take over, fo·11owed again i by the winter domination· of Coscinodiscus . Raymont (1967 ). In a strikingly similar study, Cassin and McLaughlin 14 (1972) found annual maxima in phytoplankton biomass to occur in summer ; with minor peaks in January and May , dominated by the diatoms , particularly Centrales (Coscinodiscus , Actino- discus , Chaetoceros , and Biddulphia) . . The winter community consisted mainly of Skeletonema costatum, Thal,l asios i ra baltica, L gravida , L halina , Leptocylindrus sp ., Rhizo- solenia sp. , Chaetoceros sp ., and Asterionella j aponica . Takahashi , et a l . ; (1976 ), found Thal lasiosira sp . and Chaetoceros sp. to be dominant in spring and summer popula- t ions . in Saanich Inlet, B. C. Canad~ , with their· numbers dropping off s harply in autumn . Smayda (1973) found Skele- tonema costatum to be the dominant species in Narragansett Bay in the winter-spring bloom , and to usually be the initiating species in that bloom. A number of natural factors play a major role in the size and compositior of the phytoplankton community , includ- ing temperature , inc.ident light , nutrient levels, avai lable nutrients , and sali nity . These factors may cont ribute independently or jointly in their effects on the popul ation . Gran (1929b) and Scott and Chadwick (1924) expressed the bel ief that temperature ~as the chief factor in the seasonal succession of phytoplankton . Raymont comments : Species succession would appear to be a very wide- spread phenomenon among phytoplankton. Although tem- perature , and to a lesser· extent light intensity, and perhaps nutrient concentration may play- a part in. the changes , more subtle differences , particularly the biologi cal history of the water ,· have an important role. Raymont ( 1967). 15 Phytoplankton cells respond to temperature by changing their rate of division and assimilation number . Both division rate ·and assimilation number increase wi t h temperatur e until unfavorably high temperat~res are r eached . This is because metabolic rates , including the dark reaction rate s of photo- synthesis , are temperature dependent. Phytoplankton also respond to temperature with a change in the composition · of their cells. Skeletonema costatum cells increase photosynthetic enzymes and organic matter at low temperatures and double their carbon content per cell as temperature decreases from 20°c to 7°c. The increase in carbon per cell and carbon per unit chlorophyll a with de- creasing temperature appear s to be a characteristic of marine phytoplankton. Jirgenson (1968). Since cell division and dark reaction rates of photo-· synthesis depend upon rates of enzymatic processes , an increase in amount of cellular enzymes per cell offsets to s ome extent the decrease of enzymatic activity with the de- crease in temperature . Figure 4 shows the high _and low extremes for temperature and salinity over a-nineteen (19) year period, at the same site from which the winter 1977 samples were taken . The temperature varies from a high of 15°c in July to a low of s0 c in October through April . This small variation in tem- perature over the year is not large enough to be the exclusive reason for the seasonal succession in Coos Bay , al t hough it 16 does appear to be large enough to cause differing rates of division within the organi sms and to cause increases -in the amount of Carbon per cell and per unit chlorophyll . Castenholtz (1964 ) found the growth of Fragillaria striatula and Synedra tabulata to be daylength dependent , and the doubling rates of these organisms were significantly lower during short days than during long days , both above and below the saturating light intensity. Melosira moniliformis showed less dependence on daylength , but was inhibited by high light intensities during 15 hour periods . The rate of cell division is dependent upon the supply of photosynthetically produced carbon and is therefore light dependent . At very low light intensities , cellular carbon is used faster than it is produced . The rate of production is equal to its rate of use at the compensation intensity . Further increases in light intensity increase divis ion until unfavorably high light intensities are reached or until some other factor becomes limiting . Rice and Ferguson (1975) , Phtoplankton adapt to changEEin light intensity by changing the amounts of pigments or amounts of photosynthetic enzymes in the cells, Decreasing the chlorophyll a content of the cell increases the cell ' s resistance to extreme light intensities. As light intensity decreases , chlorophyll a concentration increases , and assimilation number and compen- sation level are reduced. These adaptive changes ~llow cells to utilize light of l ower !intensity than cells which have not been adapted. Rice and Ferguson (1975) , 17 Riley (1967) suggested that the radiation level" during the period from December to March was the most important fac - tor in the onset of the winter phytoplankton bloom . He further suggested that the critical level for the initiation of the bloom is about 40 g-cal day-1 • Assuming a thorough mixing of a column of water between the surface and~ depth z, which may be the total depth of water in a shallow area , or may be a discontinuity layer which limits further downward mixing , the mean amount of light received by each cell will equal the mean amount of light I in the water column above depth z, which is given by: I= I /kz (1 - e - kz) 0 where k is the extinction coefficient and I is the incident 0 radiation in g-cal/cm-2/day- 1 . Riley (1967). This formula suggests that in some very shallow waters, growth may never be seriously limited by winter reduction in radiation. Hitchcock and Smayda (1975) found that light intensity and available light greatly influenced phytoplankton winter growth in Narragansett Bay, contradi cting previous studies : Pratt (1965) suggesting that a relaxation of grazing pressure determined the date - of the winter bloom inception . In this particular study, the winter bloom was delayed 6 weeks past the usual date of its inception, until late January . The delay being attributed to subcritical light intensities in December . 18 The nutrient level in the estuary is the result of a number of modes of input . Fresh water runoff from the water- shed area introduces nitrogen , phosphorus , and silicon, as well as trace amounts of other elements. There has be~n shown to exist in some estuarie s , a salt wedge , which com- pensates for the net seaward movement of fresh water by moving inward below the'surface , carrying detritus and n~trients brought up from deeper waters , Man ' s presence is also heavily felt· in the estuary , with increased runoff from developed or disturbed natural areas , industrial effluents , heated water , nutrients from fertilized farmlands , as well as many toxic substances including pesticides . Nutrients in the estuary are limiting factors in the growth of pytoplankton, which may be present at such low levels that no cell division occurs ; as compared to a con- trolling factor such as temperature, which affects the rate at which phytoplankton utilize available energy supplies and nutrients , The concentration of a nutrient can be a limiting or a lethal factor to phytoplankton . In general only one .nutrient will be limiting to cell division at any given time and this deficiency of a single essential element will pre- vent cell division . The concentration of a nutrient becomes I limiting when it is low enough to preclude uptake at adequate rates for cell maintenanc~ or high enough to be toxic . Nitro- 1 gen and Phosphorus tend to be the limiting nutrients in estuaries, as opposed to inorganic carbon, trace metals or 19 silicon. Rice and Ferguson (1975 ). Figure 6 r elates amounts of light , nitrogen, and phos- phate to the phytoplankton population s i ze throughout the yearly cycle . Clearly shown are t he spring and fall maximums. With ~he spring· bloom, t he levels of N and P drop seve r ely , perhaps a llowing a different organism to dominate the popu- lation at that time . · The summertime utilization of N and P keeps their leve1s ·1ow, gradually climbing with t he onset of winter and lower population levels , with increased flow into the estuary of fresh water supplies.and greater nutrient s uppl ies from increased runoff . The high l eve ls of light in the summer months do not appear to aid the phytoplankton populations in growth, as they are limited in t his s ituation by nutrient levels . The thermocline established during the summer prevents nutrients from being drawn up from the bottom, and thus the planktoD is unable to use all the incident light . Maddux and Jones (1964) working with Nitzschia closterium and Tetraselmis sp . demonstrated that these organisms have a l ower optimum light inten sity when g rown at l ower level s of nit rate and phosphate . Nitzschia was shown to increase its optimum temperature fo+ growth when cultured at high nu- t rient· and light intensity levels from 16 to 23°c . In exper- iments with increasing light intensity, at lower concentrations of nitrate and phosphate the organisms were particularly susceptible to t he increased light . Grazing has been shown to have marked effects on the 20 overall size of the phytoplankton community, and can be con- sidered to have an effect on the average size of the diatoms composing the community . Pratt (1965) hypothesized that grazing was respons ible for the initiation of the winter- spring bloom of phytoplankton in Narragansett Bay. The curves for phytoplankton concentrations are paral- leled (with .a short lag or delay ) by the curves for t he concentrations of zooplankton , most notably copepods . The summer 1973 dominant organisms were largely chain type (i . e . Skeletonema , Thallasiosira , and Chaetoceros), and . it is possible that this may play a major role in the•winter . s urvival of the organisms. It has besn suggested by Gran that certain modifications in chain type organisms found in the Northern Atlantic , such as Chaetoceros decipiens, aid in the organism ' s flotation and thus aid winter survival. Gran has shown that these organisms actually modify the thickness of their cell wall , the stoutness of the setae , and the size of the interstitial spa?es. These modifications , presumably for flotation , offer a mechanism for adjusting to the different densities that occur with the seasonal variations in the water temperature . The chain type nature of these organisms may subject them to a greater chance of being carried out of the estuary and its protection in the winter , when the increased river flow partially stratifies the water column, creating a salt wedge. Under the conditions of a salt wedge , there is a net flow of fresh water out of t he estuary , which floats on top of the I 21 heavier, mor~ saline water. To replace the flow of outward bound water , there is a net movement of salt water inward , below the surface of the estuary . The large chain organisms are more likely to be picked up and floated outward with the flow of fresh water , while the centric diatoms sink to a greater degree and are carried inward on the salt wedge . This phenomenon is relatively minor in effect when cqmpared to the effect of varying reproduction rates and grazing . A number of physical factors have been introduced which may influence the size and composition of the phytoplankton community and its seasonal succession within the estuary. Each may play an individual role , such as a limiting nutrient , or may wo~k i~ conjunction with another to hinder or accel- erate planktonic growth. It has also been shown that the individual organisms adapt to varying conditions to which they are exposed , in apparent attempts to maximize growth under any set of condi- tions . The overall yearly success of such adaptations may be measured by the presence of the organism in the estuary the year ar0und . The extent to which such individuals com- pose the population is a reflection of the success of their adaptations . The interplay of the physical factors in the estuary, the phytoplankton' s ability to adapt to varying conditions, and the basic requirements of the individual organisms (which may vary greatly fro~ species -to species , in terms of light and nutrients ) for growth and reproduction, results in the 22 seasonal succession of pytoplankton seen to exist in the Coos Bay estuary. No one factor may be said to be responsible for the yearly succession, but rather , all contribute to the overall set of conditions responsible for the. succession . .r 23 PHYTOPLANKTON CELLS PER LITER ... )~ . GENERA 10/..Jl 11L12 11L14 11L16 11L28 12/4 low high low high low high low high low high low high MELOSIRA 200 645 2.5 475 · 10 295 40 355 JO 70 15 CQSCINODISCUS 685 465 1605 1015 1740 ·1475 705 2665 575 395 265 335 SKELETONEMA 10 10 15 40 60 35 50 10 5 FRAGILLARIA 10 120 JO 40 12C JO 70 255 55 NITZSCHIA 170 JO · 70 JO 120 10 45 20 20 THALLASSOSIRA 90 JO 100 55 120 50 110 JO 50 100 20 15 BIDDULPHIA 10 20 40 10 10 50 GRAMMATOPHORA 10 10 20 20 PENNATE 120 70 140 20 10 20 80 10 35 DINO FLAG ELL ATE 110 60 60 120 150 20 110 JO JO 15 STAR 40 45 JO JO 20 60 10 15 15 TOTAL 1335 605 2670 1345 2875 1955 1250 3035 1170 880 515 385 Table 1 24 PHYTOPLANKTON CELLS PER LITER(24 Hr . Series) GENERA1 11:}0AM 2 :}0PM 2:}0PM 8:}0PM 11 : JOPM 2:JOAM ,2 : JOAM 8 : JOAM 11 : JOAM MELOSIRA 7.Q 142 15 198 163 213 21 208 367 COSCINODISCUS 265 269 335 605 255 184 3~9 337 417 SKELETONEMA 5 10 50 20 FRAGILLARIA '55 21 218 57 7 10 40 NITZSCHIA 20 35 10 21 21 7 10 80 THALLASSIOSIRA 20 7 15 7 20 BIDDULPHIA 10 GRAMMATOPHORA 20 PENNA.TE 35 DINOFLAGELLATE 15 10 7 STAR 15 21 15 7 28 10 20 TOTAL 515 495 385 1051 503 432 382 645 954 Table 2 . . .. ··. . . 25 PHYTOPLANKTON PERCENT COMPOSITION 10/3i 11/12 11/14 11/16 11/28 12/04 l ow high low high lo~ high . low high 1.£'!! high low high Mel osira 14 , 9 24 . 1 1.8 16 . 5 0.5 23 .6 1,3 J0 . 3 3 .4 13. 6 .3 . 9 Coscinodiscus 51,.3 77,0 60 . 2 75 .6 60 .5 75.5 56 . 4 87 . 9 49 . 2 44 . 9 .51. 4 2 7 . o Skel etonema 0.7 0 . 4 1.1 1.4 3.1 2 .8 1. 6 0.8 1.3 Fragillaria 0 . 7 4. 5 . 2.-2 1.4 6. 1 1.0 6. o 29 . 0 10.7 Nitzschia 12 . 7 4 . 9 2 .6 2. 2 4 . 2 0.5 3. 6 o. 6 3.,9 Thalassiothrix .6 . 8 4,9 3, 7 4 . 1 4.2 2. 5 8 . 8 1,0 4.J 11.4 3 .9 3 . 9 Biddulphia 0 . 7 3.3 1.4 0.5 0. 8 0.3 5.7 ., Grammatophora 0.7 0 . .3 1,0 .3.9 . Pennate 4.5 5.2 4,9 1,0 0.8 0 . 6 6. 8 1.1 6.8 Dinofl agellate 8 . .3 9 . 9 4 , 5 4 . 2 7 , 8 1, 6 3. 6 2. 6 3. 4 2 .9 Unidentified 3 . 0 3 . .3 1.0 1,5 1. 6 2. 1 1.1 2 .9 .3 . 9 TOTAL 100 100 100 100 100 100 100 100 100 100 100 100 Table .3 26 Map of the Coos Bay Estuary i N I Pacific Ocean Coos 1977 Sampling Site South Slough Figure 1 Source ; DEQ Checkpoint Stations 27 TOTAL PHYTOPLANKTON 3000 • 2 000 . Cells/ Lit er \. Total Season 1000 •\ . ,,'/\, , • ""· x,,,,.,,,, ,x 24 Hr. Seri es . ' ' ~ / . 5 • 00 ¥-----,t.. • I I ' .... ,c__ _,, / •.·.. ...... ... .... I - ----- _...,.,. ,,, ° _ "• L , H L H L H L H L H L H 10/31 11/ 12 11/ 14 11/16 11/28 12/4 Ti des a.nd Dates Figure 2 SOUTH SLOUGH ASSEMBLAGE DATA 28 24 Hr. Series Whittaker percent similarity ~:][I=: L 14:}◊ID:=J::r :c::::.::i 17: JOL• ---1- fi:~f•J. ..........sL':--:---=-•:1Ac•..J~J _......... _-- z 0 20: 3o_1L _• _____.._ 1·. ..rbJ...~....,.,...,..,.~ --.-...._ J,,-_ "-'-~ __-_ _._. _____ : p) p.. (D 23I,3· o.u. :=t:J- ·---l:::LI__ _.,_____~ ·_,_ __ _ i~ I-'· ~ p.. I-'· 0 p) c+ (D 5:30 ,~l. Fig ure J 29 Seasonal Variation in Temperature and Salinity (High and Low Extremes over a 19 year period) 4 0 8 . .. .. . ., . ~ ~~~- ·i!w Pi Pi 30 ~ 20 •r-l - s:::: •r-4 rl ct! 10 U2 0 15 u 0 Q) $...i 10 ~ +' ct! $...i Q) 5 ~ E Q) 8 J F M A M J J A s 0 N D MONTH Figure 4 JO Reproduction vs . Exchange Ratio ct, 20 I Q.) 0 s:: ;::s rl 0 A CJ +' •rl s:: 0 +' ~ A CJ Q.) CJ •rl ;::s Populati on will 10 ct; CJ 'O r4 0 cu •rl 0 2.0 increase ct; 'O H s:: •rl ct; A 0 Q.) Q.) 5 +' 0:: •rl 0 0 + ..c: cu' CJ 'O 1.0 CJ cu •rl Q.) Q.) H rl •rl A Population 2 s:: ;::s •rl 0 ~ will decrease +' •ri rl Q.) ;::s + 0:: cu ' :s rl 0 0.5 1 .. 0 Exchange Ratio I Source: E , J. Perki ns . p. 75 Figure 5 J1 Seasonal Relationships Between Phytoplankton , Light, and ~utrients ./ --. '-. LIGHT I ./ \ .\ . . \ I \ \N&P \ '' DJFMAMJ JASOND Diagrammatic representation of the seasonal cycles in light, nitrate and phosphate, and phytoplankton in a typical northern temper~ ate sea. Figure 6 · source: Raymont . p, 194 J2 Appendix The Whittaker Percent Similarity Index. The percent similarity index is used to determine the degree of similarity -between two populations. The percentage ·composition of individuals for each population must be calculated, and then may be applied to the formula: where L(P1 ,P2 ) is the smaller of the two percentage figures for the same individual in the populations being compared. ex. organism num. in pop. 1 num, in pop. 2 A:. ; 20 10 20 20 20 B JO 10 JO 40 JO C 20 20 20 40 40 100 50 90 The calculated percent similarity for the above example is 90%. 33 References Cassin, Joseph M. and John J .A. McLaughlin . 1973 . Phyto- plankton of Goose Creek, New York . In: Estuarine Microbial Ecology (Harold Stevenson and R. R. Colwell eds .), pp . 365-379 . South Carolina : University of South Carolina Press. · Castenholz , R.W. 1964. The Effect of Daylength and Light Intensity on the Growth of Littoral Marine Diatoms i n Culture. Physiol . Plant . 17 :951-953 . Dyer,___ 1973 . Estuaries : A Physical Introduction . N. P . : John Wiley and Sons . Furnas , Miles J. , Gary Hitchcock , and Theodore Smayda . 1976 . Nutrient-Phytopl ankton Relationships in Narragansett Bay during the 1974 Summer Bloom . In : Estuarine Proc- esses V. I (Martin Wiley , ed. ), pp . 118- 133 , New Yor k : Academic Press . · Harris , David W., William G. McDougal , William A. Patton , and Nasser Talebbeydokhti . 1979 . Hydrologic Study for South Slough Estuarine Sanctuary, Coos Bay, Oregon . Corvallis , Oregon: · Water Resources Research Institute , Oregon State University M. S . Hitchcock , Gary L. · and Theodore Smayda . 1977. The Impor- tance of light in the Initiation of the 1972-1973 Winter- Spring Diatom Bloom in Narragansett Bay , Limnol. Oceanogr . 22 :126- 131 . __________ and________ 1977 . Bioassay of Lower Narragansett Bay Waters During the 1972- 1973 Winter-Spring Bloom using the Diatom Skeletonema costatum. Limnol. Oceanogr . 22 :132- 139 • Jassby, Ala~ D. and Trevor Platt . 1976. Mathematical Form- ulation of the Relationship between Photosynthesis and Light for Phytoplankton . Limnol. Oceanogr. Ketchum , Bostwick H. 1967. Phytoplankton Nutrients in Es- tuaries . In : Estuaries {G ,H. Lauff e d .), pp . 329-335 , Washington D. C. : American Association for the Advance- ment of Science . Maddux , William S. and Raymond F . Jones. 1964 . Some Inter- actions of Temperature , Light Intensity, and Nutrient Concentration during the Continuous Culture of Nitzschia closterium and Tetraselmis sp . Limnol . Oceanogr . 9 : 79-86. Morita , Richa~d Y., Larry P . Jones , Robert P. Griffiths , and Thomas E . Stacey . 1_973 . 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