Relationships between porewater nutrients and seagrasses in a subtropical carbonate environment

The feeding, diet and egg production of the copepod Acartia tonsa were dermined during ten experiments in Los Angeles Harbor, California, between November 1986 and October 1987. Copepods were incubated in situ, in quasi-natural food environments. Water temperatures ranged from 14.6 to 21.5°C. Particulate organic carbon and nitrogen (POC and PON) were high (534 to 3710 g Cl^-1, 51 to 459 Nl^-1) but dominated by small (<8 m diam) particles. Plankton (phytoplankton and microzooplankton) C-biomass composed about 10% of the total POC and was usually dominated by particles >8 m. Plankton biomass was always low. Daily ingestion rates ranged from 3 to 96% of body C; egg production ranged from 4 to 35% of body carbon. Mean ingestion and egg production rates during spring-summer were 1.9 and 1.5 times higher than average for the entire study, respectively. The average gross efficiency of egg production for the study was 80%; the spring-summer mean was 41%. Bivariate and multiple-regression analyses revealed that the ingestion rate was dependent upon both temperature and food availability, but that, below 21°C, egg production depended more upon temperature than upon food concentration. To detect dietary preferences, the composition of diet was compared with that of the food supply. Selective feeding was infrequent, but the diet was often dominated by dinoflagellates and ciliates. It would appear that within metabolic limits governed by temperature, the feeding response of A. tonsa is dependent upon food concentration, while egg production depends more on qualitative attributes of the food supply.     

Food limitation stimulates metamorphosis of competent larvae and alters postmetamorphic growth rate in the marine prosobranch gastropodCrepidula fornicata

The effects of food limitation on growth rates and survival of marine invertebrate larvae have been studied for many years. Far less is known about how food limitation during the larval stage influences length of larval life or postmetamorphic performance. This paper documents the effects of food limitation during larval development (1) on how long the larvae ofCrepidula fornicata (L.) can delay metamorphosis in the laboratory after they have become competent to metamorphose and (2) on postmetamorphic growth rate. To assess the magnitude of nutritional stress imposed by different food concentrations, we measured growth rates (as changes in shell length and ash-free dry weight) for larvae reared in either 0.45-m filtered seawater or at phytoplankton concentrations (Isoehrysis galbana, clone T-ISO) of 1 × l0³, 1 × 10⁴, or 1.8 × 10⁵ cells ml^–1. Larvae increased both shell length and biomass at 1 × 10⁴ cells ml^–1, although significantly more slowly than at the highest food concentration. Larvae did not significantly increase (p > 0.10) mean shell length in filtered seawater or at a phytoplankton concentration of only 1 × 10³ cells ml^–1, and in fact lost weight under these conditions. To assess the influence of food limitation on the ability of competent individuals to postpone metamorphosis, larvae were first reared to metamorphic competence on a high food concentration ofI. galbana (1.8 × 10⁵ cells ml^–1). When at least 80% of subsampled larvae were competent to metamorphose, as assessed by the numbers of indlviduals metamorphosing in response to elevated K⁺ concentration in seawater, remaining larvae were transferred either to 0.45-m filtered seawater or to suspensions of reduced phytoplankton concentration (1 × 10³, 1 × 10⁴, or 5 × 10⁴ cells ml^–1), or were maintained at 1.8 × 10⁵ cells ml^–1. All larvae were monitored daily for metamorphosis. Individuals that metamorphosed in each food treatment were transferred to high ration conditions (1.8 × 10⁵ tells ml^–1) for four additional days to monitor postmetamorphic growth. Competent larvae responded to all food-limiting conditions by metamorphosing precociously, typically 1 wk or more before larvae metamorphosed when maintained at the highest food ration. Surprisingly, juveniles reared at full ration grew more slowly if they had spent 2 or 3 d under food-limiting conditions as competent larvae. The data show that a rapid decline in phytoplankton concentration during the larval development ofC. fornicata stimulates metamorphosis, foreshortening the larval dispersal period, and may also reduce the ability of postmetamorphic individuals to grow rapidly even when food concentrations increase.     

Influence of algal and suspended sediment concentrations on the feeding physiology of the hard clam Mercenaria mercenaria

Short-term laboratory feeding experiments were conducted to determine the response of the hard clam Mercenaria mercenaria (L.) (32 mm in mean shell length) to increasing sediment concentrations. Clams were fed mixed suspensions of Pseudoisochrysis paradoxa (50 and 150 cells l^-1) and bottom sediments (0 to 44 mg l^-1). Algal ingestion rate deelined with increasing sediment loads. This resulted primarily from a reduction in clearance rate, which declined by 0.08 l h^-1 g^-1 (1.3%) for every 1 mg l^-1 increase in sediment load. This reduction was of similar magnitude for juvenile (13 mm) clams. At the algal concentrations tested, pseudofaeces production was intermittent and inconspicuous below about 10 mg silt l^-1. Loss of algae in pseudofaeces increased with increasing sediment loads; however, even at the highest silt and algal concentrations, clams lost a maximum of only 18% of the algae cleared from suspension. Thus, pseudofaeces production is not expected to cause significant loss of algal food at the sediment concentrations normally encountered in the natural environment ( ca 40 mg silt l^-1). Absorption rate of total organic matter remained constant, at least up to silt concentrations of 20 mg l^-1. Experiments using dual ⁵¹Cr:¹⁴C-formaldehyde-labelled sediment indicated that clams were able to counteract the dilution of algae by absorbing a considerable fraction (21 to 22%) of detrital sedimentary organics. Absorption efficiency of pure P. paradoxa ranged from 82% at 50 cells l^-1 to 58% at 150 cells l^-1. Integration of physiological rate measurements suggests that at moderate to high algal concentrations (300 g Cl^-1), growth improvement by the addition of silt, documented in mussels, surf clams and oysters, is unlikely to occur in M. mercenaria. It is suggested that a suspension-feeding bivalve's success in maximizing its energy gain in a turbid environment depends on the combination of two features: a high selection efficiency and a high rate of pseudofaeces production. It is proposed that species which regulate ingestion primarily by producing pseudofaeces are better adapted to cope with high suspended sediment loads than species such as M. mercenaria, which control ingestion mainly by reducing clearance rate.Contribution No. 451 from the Marine Sciences Research Center, State University of New York at Stony Brook, USA     

Grazing of Acartia hudsonica (A. clausi) on Skeletonema costatum in Narragansett Bay (USA): Influence of food concentration and temperature

Grazing experiments were performed with temperatureacclimated Acartia hudsonica fed the diatom Skeletonema costatum in concentrations ranging from 50 to 3×10⁴ cell ml^-1 at 5°, 10° and 15°C. The ingestion data were best fit by an Ivlev equation. Feeding threshold values of 39 and 59 cells ml^-1 were not significantly different from zero; however, filtration rates were depressed at low food concentrations. Maximum filtration rates increased exponentially with temperature, reaching a maximum with copepods collected at 14°–15°C, and then declining. Both the increase in ingestion rate with increasing food concentration and the maximum ingestion rate were significantly greater as experimental temperature was increased. Maximum ingestion rates were reached at concentrations greater than 6×10³ cells ml^-1. Percent of body carbon ingested per day at 5 g C L^-1 increased from 1.5% at 5°C to 6.7% at 15°C. At 500 g C L^-1, the ingestion increased from 84% (5°C) to 660% (15°C). Percent of body nitrogen at 0.5 g N L^-1 increased from 0.6% per day at 5°C to 2.5% per day at 15°C. At 50 g N L^-1, the ingestion was 42% body nitrogen at 5°C and 250% at 15°C. The influence of grazing by A. hudsonica on phytoplankton in Narragansett Bay, USA was estimated for 1972–1977. The percent of standing stock removed by grazing rarely exceeded 5% per day except during the late spring when S. costatum growth becomes nutrient limited and higher temperatures favor the rapid population growth of A. hudsonica.     

The effect of low concentrations of phenol and ammonia on egg production rates,fecal pellet production and egg viability of the calanoid copepod Acartia clausi

Estimates of daily fecundity, hatching success and fecal pellet production are reported for Acartia clausi females exposed for 10 d to low levels of phenol and ammonia. Copepods were collected in 1991 and 1992 from a southern coastal area of the Mar Grande of Taranto (southern Italy). A reduction in egg numbers and fecal pellet production was observed for females after 8 d of exposure to 500 g l^-1 phenol concentration. Ammonia (120 g l^-1) produced a significant increment in egg production, but hatching success was reduced by about 50% after nine exposure days. A. clausi was more sensitive to ammonia than phenol at high concentrations (24-h LC₅₀ phenol-32.26 mg l^-1; 24-h LC₅₀ ammonia=0.91 mg l^-1). At low concentrations, only long-term exposure to phenol determined a reduction in fecundity.     

Comparison of gut-evacuation rates of feeding and non-feeding Calanus marshallae

Gut-evacuation rates were compared for feeding and non-feeding Calanus marshallae collected near Yaquina Bay, Oregon (44°37N; 124°04W) from June 1986 through May 1987. Evacuation rates were measured at four concentrations of Thalassiosira weissflogii from the decline of gut-pigment fluorescence following transfer of copepods to filtered seawater and from the loss of cells labelled with 68-germanium, a radioactive analog of silicon. There was no significant difference between gut-evacuation rates of feeding and non-feeding copepods over both short-term (20 min) and long-term (90 min) evacuation times. Furthermore there was no difference between rates obtained using either pigment or ⁶⁸Ge as tracers of gut food-passage. These results are discussed in the light of possible dilution of tracer in the guts of feeding copepods due to mixing with unlabelled food. Gut-evacuation rates measured at food concentrations ranging from 500 to 4000 cells ml^-1 were not significantly different, regardless of the technique employed.     

Potential effects of a resuspension event on the vertical distribution of copepod eggs in the sea bed: a laboratory simulation

Adult female Acartia tonsa and Labidocera aestiva were obtained from inshore marine waters near Turkey Point, Florida (29°54.5N;84°31W) during April and May 1991. For each species, eggs spawned overnight in the laboratory were collected, mixed with sediment, and added to a plastic tube (26 to 29 cm longx5 cm diam) to yield a 2 cm-thick layer. This tube was connected to a 245 cm-long tube, seawater was added and the contents were thoroughly mixed by turning the assembly end-over-end several times. The vertical distribution of eggs in the sediments following resuspension varied according to the grain size of the sediments. For sediments of 125 m particle-diameter, 68 to 72%, and 70 to 73% of the eggs of A. tonsa and L. aestiva, respectively, occurred in the upper 4 mm.For sediments 63 to <125 m particle-diameter, 34 to 36% of the eggs of A. tonsa and L. aestiva, respectively, occurred in the upper 4 mm. For sediments of <63 m particle-diameter, egg distribution was uniform for both species throughout the 2 cm layer. The results indicate that the vertical distribution of eggs in the sea bed following a resuspension event should be highly dependent upon the grain-size composition of the sediments.     

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 g carbon l^-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 g C l^-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 m to 10 m diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.     

Nutritional value of Phaeocystis pouchetii (Prymnesiophyceae) and other phytoplankton for Acartia spp. (Copepoda): ingestion,egg production,and growth of nauplii

Ingestion and egg production by Acartia hudsonica (5°C) and A. tonsa (10°C) from Narragansett Bay, Rhode Island, USA, was measured in the laboratory over a range of concentrations of the prymnesiophyte Phaeocystis pouchetii and the diatom Skeletonema costatum. Both Acartia species reproduced well when fed unialgal diets of S. costatum. Egg production by females fed P. pouchetii, either as gelatioous colonies (primarily >200 m in diameter) or solitary cells (3 to 5 m), was not significantly different than that of starved females. Acartia spp. fed selectively on S. costatum in multialgal treatments. The presence of P. pouchetii did not reduce ingestion of S. costatum; the availability of S. costatum did not increase ingestion of P. pouchetii. Nauplii of A. hudsonica grew equally well on separate diets of P. pouchetii and Isochrysis galbana, two flagellates of similar size. Adult Acartia spp. reproduced poorly when fed these phytoplankton, suggesting that particle size may be more important than food quality in describing the responses. Grazing by Acartia spp. does not directly impact the dynamics of P. pouchetii, but may indirectly contribute to blooms of this prymnesiophyte by removal of competing phytoplankton.     

Reductions in photosynthetic carbon uptake in epiphytic diatoms by water-soluble extracts of leaves of Zostera marina

A water-soluble fraction of green leaves of Zostera marina L. decreased carbon uptake rates in diatoms found as epiphytes at Roberts Bank (Lat 49°2N; Long. 123°8W) on the west coast of Canada. Extract concentrations of 11 to 1 g dry leaf ml^-1, added immediately before ¹⁴C-uptake was measured over a 3-h period, reduced uptake to 36 to 80% of controls, respectively. A lower concentration (0.6 g dry leaf ml^-1) reduced uptake significantly in only one of four cultures. Addition of the whole extract 3 d before carbon uptake was measured or in one-third doses, 0, 1, and 2 d before, resulted in inhibition similar to that observed when the whole extract was added immediately before the ¹⁴C.     

Mechanisms of production and fate of organic phosphorus in the northern Adriatic Sea

In the period from 1980 to 1984 organic phosphorus, nutrients, primary production rates (¹⁴C), chlorophyll a (chl a) standing crops, and basic oceanographic parameters were measured during 23 cruises at six stations in the open waters of the northern Adriatic Sea. These waters are significantly influenced by polluted Po River discharge. Organic phosphorus was correlated with several parameters which characterize phytoplankton activity and organic matter decomposition processes. In the late winter-spring period, organic phosphorus is produced during phytoplankton blooms. It is hypothesized that microzooplankton grazing is the main factor increasing the organic phosphorus concentrations in summer (up to 1.1 mol 1^-1). Fall and winter had much lower values (below 0.3 mol 1^-1) due to remineralization processes and an increased water mass exchange between the northern and central Adriatic regions. The direct contribution of organic phosphorus by freshwater discharge was not found to be significant. The higher organic phosphorus concentrations that can occur in low salinity waters are most likely due to their increased capability to support primary production.     

Phytoplankton ecology and production in the Red Sea off Jiddah,Saudi Arabia

Phytoplankton species diversity was generally high throughout the year at two stations in the central Red Sea (Lat. 21°30N), and species of Mediterranean and Indian Ocean origin were represented, reflecting seasonal monsoonal influence. Low phytoplankton cell numbers accompanying high production rates suggest the significance of nanoplankton or picoplankton which were not enumerated. Production was high year-round, and averaged 390 gC m^-2 yr^-1, despite the virtual lack of nutrient additions from rainfall or land runoff or demonstrable upwelling. Highest nutrient levels followed the first seasonal peak of production. Biomass and production were seasonally bi- or tri-modal, with major peaks in December–February and June–August, 1977–1978. The first peak of production, populated by diatoms, occurred at the onset of seasonal stratification, but the second peak, populated by Trichodesmium spp., occurred at the height of seasonal stratification and lowest nutrient concentrations. There is no clear relationship between the timing of monsoon activity and the annual production cycle.     

Population dynamics and secondary production in an estuarine population of Caulleriella caputesocis (Polychaeta: Cirratulidae)

Between July 1978 and March 1980, the distribution, population dynamics and secondary production of Caulleriella caputesocis St. Joseph, 1864, in Southampton Water, South England, were investigated. The distribution of the polychaete was related to amount of silt and copper-content of the sediment, the highest densities occurring in sediment containing 60 to 100% silt and less than 50 ppm copper. Breeding occurred at a low level throughout the year, usually when the worms were over one year old, with peak breeding between May and September. C. caputesocis in Southampton Water is monotelic, and oocytes measured 120 to 160 m in diameter at spawning. Unshed oocytes were resorbed. Annual secondary production varied between 0.01 and 5.90 g C m^-2 yr^-1 and P:B ratio of the species ranged between 0.84 and 7.09.     

Spatial mesoscale patterns of West Pacific picophytoplankton as analyzed by flow cytometry: their contribution to subsurface chlorophyll maxima

Vertical distributions of picophytoplankton (ppp) (<2 m) were studied by ship-board flow cytometry during two cruises in Western Pacific waters to Palau and to Australia in 1990. Weak red-fluorescing small ppp, supposed to be free-living prochlorophytes (Chisholm et al. 1988), were abundant in the area surveyed. These ppp, designated the prochlorophytes, were abundant in the surface waters (>10⁴ cells ml^-1) at the northern region (27°03N; 7°11N) in November, whereas in December at the southern tropical stations (0°23.54S; 9°20.30S; 13°50.6S), they formed subsurface maximum layers (>10⁵ cells ml^-1) on a nitracline at a depth of 3.5 to 5.4% surface irradiation. Their fluorescence intensity increased with depth below 10% surface irradiation. The prochlorophytes at a depth of 1% surface irradiation had ten times higher fluorescence than those at the surface layer. The total fluorescence intensity of the prochlorophytes accounted for 32 to 63% of the sum of the total fluorescence intensity of all fluorescing phytoplankton detected at subsurface chlorophyll maxima in the tropical area. These results suggest that distribution of the prochlorophytes is greatly affected by nitracline and by light intensity and that their chlorophyll is a major contributor to the subsurface chlorophyll maximum in the pelagic West Pacific Ocean.     

Phosphate uptake behavior of natural phytoplankton during exposure to solar ultraviolet radiation in a shallow coastal lagoon

The effect of solar UV radiation (UVR: 290–400 nm) on the ³²P-phosphate uptake rates of natural phytoplankton from a southern Atlantic Ocean coastal lagoon was studied during two consecutive summers at one station located in the marine-influenced area. Due to the shallowness of this lagoon and also to the generally high UV water transparency in this area, phytoplankton are exposed to high UV irradiances. The ³²P-phosphate uptake rates measured at several phosphate concentrations were inhibited up to 59.2% by UVR, although uptake stimulation was also observed in four of nine experiments (up to 28%). The effect of UVR on the apparent maximum velocity of ³²P-phosphate uptake (V _uptake) ranged from an inhibition of 49% to a stimulation of 31%. Although the highest inhibition values were associated with the maximum registered incident UV irradiance, a significant correlation between these two parameters was not observed. Changes in microalgal community structure were not related to the observed UV effect; however, a significant relationship was found between the inhibition of ³²P-phosphate uptake rates and V _uptake used as a proxy for phosphate deficiency. This relationship suggests that the phytoplankton phosphorus nutritional status modulates their sensitivity to UV exposure. Overall, our results suggest that solar UVR has the potential to affect phosphorus cycling.Communicated by O. Kinne, Oldendorf/Luhe     

Diel changes in gut-cell morphology and digestive activity of the marine copepod Acartia tonsa

Morphometric measurements of the gut cells of the marine calanoid copepod Acartia tonsa were made over a 24 h diel cycle to test the hypothesis that feeding rhythms in this copepod are limited by the cycles of blishter-like cells (B-cells) in the gut. Copepods were collected from Long Island Sound, New York, USA, in June 1991. Experimental treatments included low (1 g chlorophyll al^-1) and high (10 g chlorophyll al^-1) food concentrations. Copepods were fixed and embedded in Epon at six time intervals over the 24 h period, and semi-thin sections through the length of Midgut Zone II were analyzed for gut-cell area and vacuole area, with area measurements integrated to yield estimates of gut-cell volume and vacuole volume. Concurrent measurements of gut fluorescence, a measure of gut fullness, and digestive enzyme activities also were made. A diel cycle in gut fluorescence was observed, most notably in the low-food treatment, which exhibited a 3-fold increase in gut pigments. There was little consistent change in digestive enzyme activities over this time span. Gaps in the gut wall indicative of spent B-cells were observed in 17 of 39 copepods, with no trend over time or food treatment. Generally, only a single gap was seen in any one copepod. B-cells were vacuolated throughout the 24 h period. Morphometric analyses revealed a correlation between gut fluorescence and both maximum vacuole area and vacuole volume, as well as percent vacuolated cell volume, in the low-food treatment. The high-food treatment, which had a relatively smaller increase in gut fluorescence (1.5-fold) during the night cycle, showed no significant increase in vacuole size. B-cells appear to have a life-cycle greater than the diel feeding period, and while B-cell vacuoles respond to the ingested food during the diel cycle, production of B-cells does not appear to be a limiting factor in A. tonsa's feeding cycle.     

Behavior and growth ofMercenaria mercenaria during simulated storm events

Experiments were conducted in April–August 1989 on juvenileMercenaria mercenaria (L.) in an oscillatory water tunnel to simulate resuspension of bottom sediments by waves and to determine the effects of shortterm storm events on particle ingestion, pseudofeces production, and shell growth. Juveniles (mean length = 19.2 mm) were subjected to identical concentrations of algae in both low-flow, gentle waves (maximum velocity = 7 cm s^–1) and high-velocity storm waves (maximum velocity = 22 cm s^–1). Suspended sediment levels reached 193 mg 1^–1 at 1 cm above the bed during storms. Shell growth decreased by a maximum of 38% during the storm when levels of phytoplankton were high (average cell concentration = 43 × 10⁶ cells 1^–1), and by 18% when phytoplankton levels were low (av cell conc = 6 × 10⁶ cells 1^–1). Orientation of clam siphons was not related to flow direction. Significantly more pseudofeces were produced when the clams were subjected to increased sediment resuspension under waves, and in troughs of sand ripples. The size of sediment grains ingested did not vary significantly among the flow treatments. The decrease in shell growth during storms may be due to a reduction in filtration rate coupled with a decrease in net energy gained from filtration due to costs of pseudofeces production. The magnitude of the decrease seems to be related to concentration of algae, water temperature, age of clams and sediment transport mode (bed load or suspended load). Thus, the interpretation of growth increments must be made in the context of these environmental variables.     

Particle-Size-dependent maximum grazing rates for Temora longicornis fed natural particle assemblages

The hypothesis that lower retention efficiencies of filter-feeding copepods for small particles should result in different ingestion rate versus food concentration curves for different-sized foods was tested using Temora longicornis (Müller) fed natural phytoplankton. The copepods were fed different natural phytoplankton assemblages, which varied in their species and size distribution. Volume ingestion rates were an asymptotic function of food concentration, with maximum ingestion rates measured at food concentrations exceeding 5 to 10x 10⁶ m³ ml^-1, which were less than those occurring in the natural waters in which the copepods and phytoplankton were collected. Maximum volume ingestion rates increased linearly by a factor of 3.5, as the diameter of the particle forming the peak in the food size distribution increased fron 5 m (primarily microflagellates) to 30 m (mostly large diatoms). These results suggest that natural and pollutant-induced size reductions in natural phytoplankton could markedly decrease the volume of food consumed by filter-feeding copepods.Contribution No. 243 of the Marine Sciences Research Center     

Persistent blooms of surf diatoms along the Pacific coast,USA

Productivity was studied in two diatom species, Chaetoceros armatum T. West and Asterionella socialis Lewin and Norris, which form persistent dense blooms in the surf zone along the Pacific coast of Washington and Oregon, USA. Past observations have shown that surf-diatom standing stock usually declines in summer along with concentrations of nitrate and ammonium. Using the ¹⁴C method, photosynthetic rates in natural surf samples were measured monthly for one year (October 1981 through September 1982) at a study site on the Washington coast. Also measured were temperature, salinity, dissolved nutrients, particulate carbon and nitrogen (used as estimates of phytoplankton C and N), and chlorophyll a. Assimilation numbers (P _max) were higher in summer (5 to 8 g C g^-1 chl a h^-1) than in winter (3 to 4gC). Specific carbon incorporation rates (µ_max) showed no obvious seasonality, mostly falling within the range of 0.09 to 0.13 g C g^-1 C(POC) h^-1. The discrepancy between the seasonal trends for chlorophyll-specific and carbon-specific rates reflects a change in the carbon-to-chlorophyll ratio. Because of seasonal differences in daylength and light intensity, daily specific growth rates () are thought to be higher in summer than in winter. Neither ammonium enrichment assays nor particulate carbon-to-nitrogen ratios provided convincing evidence for nitrogen limitation during summer, and the observed changes in diatom abundance cannot be explained on this basis. Both the high diatom concentrations and their seasonal variations probably are due mainly to factors other than growth rates; two factors considered important are diatom flotation and seasonal changes in wind-driven water transport. C. armatum usually dominates the phytoplankton biomass in the surf zone, and evidence suggests that this species is strongly dominant in terms of primary production.Contribution No. 1391 of the School of Oceanography, University of Washington, Seattle, Washington, USA     

Fecundity studies on Acartia tonsa (Copepoda: Calanoida) in standardized culture

Acartia tonsa Dana longevity and egg production data were studied over a 4-year period under standardized culture conditions. Egg-laying patterns and daily rates were evaluated as bioassay tools for measuring the nutritional value of various copepod foods, as well as assessing other aspects of environmental quality. Altogether, 337 females were observed in various aspects of this work. Experiments were performed with newly matured females in loosely covered crystallizing dishes. Fresh water and a standard concentration of algae were supplied daily, and a running daily tally was kept of the eggs produced. The effects of male copepods on egg production were analyzed. Males were either removed after the first eggs were observed or they remained with the female throughout her life span. Daily egg-laying rates of this latter group of females appeared to be more stable, but abnormal embryo development occurred if the males were not removed after fertilization. Likewise, the results of females which were not mated were studied. Life spans were shorter and egg production rates were lower than those of contemporary mated females. Unmated females were subjectively observed to be less active than their mated counterparts. The effects of continuous and temporary starvation on egg-laying were also observed. Under both normal and starved conditions, males appeared to have shorter life spans than either mated or unmated females. During starvation there were no real differences between the life spans or egg productions of mated or unmated females. Non-nutritional particulate matter was evaluated as a food source. It was ingested by the females, but did nothing to prolong the egg-laying period. Finally, the three algal components of the standard ration were evaluated. Females produced equally well with a mixed diet or with Thalassiosira pseudonana (100 m³) or Chroomonas salina (140 m³), the two larger species of this diet, but when Isochrysis galbana (40 m³) was fed, females reacted as if in a starved situation.