Nitrogen regeneration by the surf zone penaeid prawn Macropetasma africanus

Nitrogen excretion of individual Macropetasma africanus (Balss) from an exposed beach/surf zone in Algoa Bay, South Africa was monitored under laboratory and field conditions in relation to body mass, temperature and feeding during 1985. Excretion rate experiments were performed on starved prawns at 15°, 18°, 20° and 25°C, as well as on individuals fed on four different diets (mussel, fish, shrimp and natural diet) at 15° and 20°C. The ratios of the excreted compounds to total nitrogen excreted were similar for the four diets despite differences in their nitrogen content and in the amount of food consumed. At 15° and 20°C, ammonia excretion rates of fed individuals were four to seven times higher than in starved prawns. the excretion rates were not correlated with nitrogen content of diets. M. africanus recycles 1 557 g NH₄–N per metre strip per year or 1 832 g total nitrogen m^-1 yr^-1, which constitute 12 and 14%, respectively, of total phytoplankton requirements of the surf zone. This study indicates that large motile crustaceans, when abundant, can play an important role in nutrient recycling in turbulent marine environments.     

Effects of temperature on activity,food consumption rates,and gut passage times of seaweed-eating<Emphasis Type="Italic"> Tegula</Emphasis> species (Trochidae) from California

Previous feeding studies on herbivorous marine snails rarely have focused on temperature effects on food intake. If temperature affects food intake, ectothermic snails may experience difficulty obtaining sufficient nutritional resources, limiting their ability to sustain populations at suboptimal temperatures. We hypothesized that the feeding responses of Tegula species would correspond with temperatures characteristic of their geographic distributions. We determined activity, consumption rates, and gut passage times at 11°C, 15°C, 19°C, and 23°C for three Tegula species with distinct thermal distributions: T. brunnea (cold water), T. aureotincta (warm water), and individuals from warm- and cold-water populations of T. funebralis, a broadly distributed species. Activity and consumption rates of T. aureotincta increased with increasing temperature, but were highest for T. brunnea at 19°C, a temperature rarely achieved in habitats occupied by this species, and lowest at 11°C. Warm-water T. funebralis showed significantly lower activity and consumption rates at 11°C, whereas cold-water T. funebralis consumed food fastest at 15°C and were most active at 23°C. Temperature affected gut passage time only in T. aureotincta. These data suggest that temperature might influence the northern limit of T. aureotincta by affecting activity and food consumption rates. T. brunneas activity and ability to consume food were not hindered by warmer temperatures despite the present day restriction of this species to colder waters. Also, widely separated (>300 km) T. funebralis populations may be adapted to regional conditions based on the different temperature responses of northern and southern snails.Communicated by P.W. Sammarco, Chauvin     

Effect of temperature,salinity and food level on sexual and asexual reproduction in Brachionus plicatilis (Rotifera)

The reproductive response of sexual and asexual female Brachionus plicatilis (Muller) was examined over temperatures ranging from 20° to 40°C, salinities from 5 to 40 S, and food levels from 0.25 to 20 g Chlorella vulgaris dry-weight per ml. Reduced food levels, as well as temperature and salinity extremes, reduced reproduction of both sexual and asexual females, but did so differentially. Reproduction by sexual females was reduced to a greater extent at environmental extremes than asexual females. The broad, flat reproductive response curve of asexual females extended beyond the limits of the narrower, more sharply peaked curve of sexual females. Thus zones of exclusively asexual reproduction exist at environmental extremes where sexual reproduction is physiologically restricted. These results are corroborated by a comparison of the lifetime fecundity of individual sexual and asexual females over a 20°C temperature range. No differences in lifetime fecundity occurred between sexual and asexual females at 18° and 28°C. At 38°C, however, asexual female fecundity reached its highest level, while sexual female fecundity declined 15%. The appearance of sexual females in rotifer populations in the result of both inducible and repressible factors.     

Egg survival,embryonic development,and larval characteristics of northern shrimp (<Emphasis Type="Italic">Pandalus borealis</Emphasis>) females subject to different temperature and feeding conditions

Laboratory experiments on ovigerous females of northern shrimp (Pandalus borealis) were used to assess the effects of temperature and food ration on female condition during incubation and examine how combined effects of temperature and female condition influenced egg survival, embryonic development, and larval characteristics. Ovigerous females were maintained at 2°C, 5°C, and 8°C and fed on a low (three times/week; 2–2.7% W/W) or high ration (five times/week at satiation). The increase in temperature accelerated the developmental time of the eggs but their survival at 8°C was reduced. Conversion efficiency of yolk reserves in developing embryos was significantly reduced at elevated temperatures and larvae hatching at 2°C and 5°C were significantly larger and heavier than those hatching at 8°C. The experimental design did not result in any effect of food ration on the energetic condition of females or on egg characteristics and their biochemical composition. However, lower energy reserves were observed for females held at 8°C.     

Effects of delayed feeding and temperature on the age of irreversible starvation and on the rates of growth and mortality of Pacific herring larvae

The time periods from exhausion of the yolk to the age of irreversible starvation for Pacific herring Clupea harengus pallasi larvae were 8.5, 7.0 and 6.0 d at 6°, 8° and 10°C, respectively. These periods are within the range perviously measured for Atlantic herring larvae and other temperature zone fish species; they are long compared to the periods for tropical species. The variation in the length of this period is due almost entirely to temperature; the natural logarithm of the time period from fertilization to irreversible starvation is highly correlated (r=0.91) with the mean rearing temperature for 25 species of pelagic marine fish larvae. The rates of growth and mortality, measured for 26 experimental populations of Pacific herring larvae reared at 6°, 8° and 10°C and ten ages of delayed first feeding, decreased and increased, respectively with increasing age of first feeding and increasing temperature. These rates, adjusted for the effects of rearing conditions, were compared with the rates for natural populations of herring larvae. Growth is generally faster in the sea than in experimental enclosures. Two of the eleven estimates of natural mortality rate were high enough to indicate possible catastrophic mass starvation. This is consistent with Hjort's critical period concept of year class formation and it suggests that mass starvation occurs in 18 to 36% of the natural populations of first feeding herring larvae.     

Long-Term observations on the moulting frequency of the shrimp Lysmata seticaudata

The effects of body-size and temperature on moulting frequency of the shrimp Lysmata seticaudata Risso were examined under controlled laboratory conditions. Shrimp ranging in weight from approximately 0.4 to 1.14 g and maintained at 17°C exhibited intermoult periods of similar duration (20 d). On the other hand, small individuals (0.23 g) held at the same temperature moulted on the average every 14.5 d. Over a temperature range from 8° to 20°C mean intermoult periods were inversely and linearly related to temperature; an increase of 1 C⁰ resulted in a decrease in the intermoult period of approximately 1.5 d. Although temperature acted to regulate the intermoult period of each shrimp in increments of whole days, it had little effect on the time of moulting within any 24 h period, since moulting occurred more than 93% of the time between 18.00 and 08.00 hrs. The night-time moulting pattern also tended to be most pronounced at lower temperatures (8° and 13°C) and in larger individuals. Possible factors controlling this phenomenon and its occurrence in other crustacean species are discussed.     

The respiratory metabolism of Tilapia mossambica (Teleostei)

In a series of experiments 174, 120 and 139 individuals of the teleost Tilapia mossambica (Peters), were acclimated to 30°C and to salinities of 0.4, 12.5 and 30.5, respectively. The effect of temperature and salinity upon oxygen consumption was studied by abruptly transferring fish of different wet weights to temperatures from 15° to 40°C at an average initial pO₂ of 250mm Hg. At each salinity, the proportionate response to temperature is size-independent. The metabolic rate increases as a function of temperature at 15° and 30°C but not at 40°C. Oxygen consumption is, however, salinity dependent; maximum rates are obtained at 12.5S. This salinity is isotonic in the 80 g fish and, to a lesser extent, in the 5 g fish. Reduction in osmotic load is suggested as the probable cause for a greater scope for activity and greater rate of oxygen consumption in 12.5 salinity.     

Comparative life-history study on sympatric hyperiid amphipods (<Emphasis Type="Italic">Themisto pacifica</Emphasis> and <Emphasis Type="Italic">T</Emphasis>. <Emphasis Type="Italic">japonica</Emphasis>) in the Oyashio region,western North Pacific

Life-history features of the sympatric amphipods Themisto pacifica and T. japonica in the western North Pacific were analyzed based on seasonal field samples collected from July 1996 through July 1998, and data from laboratory rearing experiments. T. pacfica occurred throughout the year, with populations peaking from spring to summer. In contrast, T. japonica were rare from autumn to early winter, but became abundant in late winter to spring. Mature T. pacifica females and juveniles occurred together throughout the year, indicating year-round reproduction. Mature T. japonica females were observed only in spring, and juveniles occurred irregularly in small numbers, suggesting limited, early-spring reproduction in this study area. Size composition analysis of T. pacifica identified a total of eight cohorts over the 2 years of the study. Due to the smaller sample size and rarity of mature females (>9.6 mm) and males (>7.1 mm), cohort analyses of T. japonica were not comparable. Laboratory rearing of specimens at 2°C, 5°C, 8°C and 12°C revealed that a linear equation best expressed body length growth by T. pacifica, while a logistic equation best expressed body length growth by T. japoncia. Combining these laboratory-derived growth patterns with maturity sizes of wild specimens, the minimum and maximum generation times of females at a temperature range of 2–12°C were computed as 32 days (12°C) and 224 days (2°C), respectively, for T. pacifica, and 66 days (12°C) and 358 days (2°C), respectively, for T. japonica. The numbers of eggs or juveniles in females marsupia increased with female body length and ranged from 23 to 64 for T. pacifica and from 152 to 601 for T. japonica. Taking into account the number of mature female instars, lifetime fecundities were estimated as 342 eggs for T. pacifica and 1195 eggs for T. japonica. Possible mechanisms for the coexistence of these two amphipods in the Oyashio region are also discussed.Communicated by O. Kinne, Oldendorf/Luhe     

Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light,temperature and salinity

The influence of 49 combinations of salinity (10–40 S, at 5 S intervals) and temperature (0°–30°C, at 5C° intervals) on the maximum daily division rate (K) and 18 combinations of light intensity (six levels) and temperature (5°, 15°, and 25°C) on photosynthesis, cell division, and chlorophyll a was examined using two clones of Thalassiosira rotula Meunier isolated from the upwelling area of Baja California (clone C8) and from Narragansett Bay, Rhode Islands (clone A8). Physiological differences appear to characterize these to clones with regard to their temperature tolerance (C8 5°–30°C, A8 0°–25°C), maximum growth rate (C8 K=2.9, A8 K=2.4), chlorophyll a content, and in the rates of growth and photosynthesis in response to light intensity and temperature. Optimum salinity for both clones (25–30 S) was generally independent of temperature, while chlorophyll a content decreased with temperature. T. rotula is a cosmopolitan paractic species; experimental studies indicate that it is eurythermal and moderately euryhaline. Comparison of five additional Narragansett Bay isolates of T. rotula reveal minimal spacial or temporal variability in genetically determined physiological characteristics within this local population.     

Environmental information stored in otoliths: insights from stable isotopes

The present study compares the stable oxygen-and carbon-isotope ratios (¹⁸0:¹⁶O;¹³C:¹²C) in the otoliths of Atlantic cod,Gadus morhua, with those expected at equilibrium with seawater. Otoliths from juveniles reared for a 3 mo period under controlled conditions indicate that otoliths are formed in isotopic disequilibrium with seawater. This is probably due to positive metabolic fractionating of the heavier isotopes. This vital effect remains constant over the temperature range studied here (9 to 16°C) but may differ among other species. Our data indicate that the concentration of¹⁸O in calcium carbonate is inversely related to temperature and is described as ¹⁸O_a – _w – 3.79 – 0.200(T°C). The¹³C:¹²C ratios of otoliths and body tissues are related to the carbon ratio in the food source, although we found that the¹³C concentration is considerably higher in the otoliths relative te, the body tissues and the diet.     

A brief survey of the ecology and biology of the Caspian Polyphemoidea

Not less than 25 autochthonous species of Polyphemoidea live in the Caspian Sea; 5 of these species also inhabit the Azov and Black Seas and 3 the Aral Sea, but none is found beyond the Pontoaralocaspian basin. A great degree of polymorphism and morphological variability characterizes this group. Most Caspian Polyphemoidea exist in salinities of 12 to 13, and cannot tolerate great changes in salinity; however, 3 or 4 species in the Pontoasov basin can live in quite fresh water and populate the river reservoirs; these species do not tolerate ocean salinities over 8 to 10. All species inhabit mainly the upper layers of the sea (0 to 50 m; Cercopagis and Polyphemus exiguus down to 75 to 100 m), but avoid shallows under 5 to 15 m depth. Polyphemoidea perform diurnal vertical migrations, accumulating in surface layers during the hours of darkness and descending at sunrise; they also descend during rough weather conditions. Abundance of Polyphemoidea is subject to great seasonal variation. Most species appear in spring when the water temperature has reached 10° to 15°C; maximum abundance occurs in summer at water temperatures of 5° to 20°C, and Polyphemoidea disappear in autumn from the whole Caspian Sea except for deep areas of the South Caspian Sea, where the temperature does not drop under 10°C. Reproduction of the Caspian Podonidae is distinguished by a strikingly high rate of parthenogenesis, which is accompanied by neoteny, i.e. the embryos mature before birth. Bisexual reproduction, on the other hand, is suppressed; males and gamogenetic females containing winter eggs do not occur in all species of Podonidae and only in some species of Cercopagidae, in these latter mainly as single specimens. The majority of Cercopagidae have no males, being completely acyclic. Parthenogenesis shows a clear diurnal rhythm; delivery of young begins only after midnight and ends before sunrise. All Polyphemoidea are predators; they catch mobile prey and suck out its contents; this prevents successful observation of details of their feeding habit. However, it has been proved that Evadne anonyx feed mainly on copepods (Eurytemora) and small podonids, and this is probably true also of Cercopagis, as both these species are more marked predators than Podonidae from the open seas (Evadne nordmanni and other forms). Many aspects of taxonomy (intraspecific forms) and biology (reproduction of acyclic species, feeding, behaviour and functional morphology) are obscure and require further investigation.     

Growth rate of the bathypelagic crustacean Gnathophausia ingens (Mysidacea: Lophogastridae). I. Dimensional growth and population structure

Gnathophausia ingens has 13 instars, each with a distinct range of sizes which does not overlap the sizes of adjacent instars. The intermolt interval, measured in the laboratory at 5.5°, 6.5° and 7.5°C, increases with increasing size and decreases with increasing temperature. At 5.5°C it varies from 166 days for the smallest individuals to 253 days for the oldest. The period of larval development in the marsupium of a female is estimated to be 530 days. The life span of females is estimated to be 2,950 days with the onset of reproduction at 2,400 days. It is sugquested that this species is semelparous. The population structure data suggest that there is low mortality through the first 7 instars, progressively higher mortality from Instar 8 through Instar 11, and slightly lower mortality in the remaining 2 instars. These life-history characteristics appear to be directed toward maximizing absolute fecundity (as opposed to time-specific fecundity) in a stable environment. These characteristics may have been selected for by low available food energy and made possible by the stability of the deep sea.     

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The reproduction of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in winter and spring 1978, under various temperature and salinity conditions, using Chlorella sp. and Amphidinium sp. as food. Maximum numbers of successive eggs sacs (9), eggs per sac (39.3) and total egg production per female (311) were recorded for the witner generation, only 4.8, 34.8 and 109, respectively, for the spring generation. In contrast, the number of eggs per female per day was highest (11.3) in the spring generation, which displayed a more rapid reproductive cycle. Despite strong individual variations in the rhythm of egg sac production and in abundance of eggs per sac, egg production was generally higher during the first third of adult life, attaining a maximum after production of the second or the third egg sac. The continuous presence of the males was necessary to assure complete fertilization of eggs throughout the whole life of adult females. Hatching rate displayed high individual variability, in particular for the spring generation, which had lower average hatching rates (between 0 and 26%, depending on salinity or temperature) than the winter generation (14 to 64%). These differences may be related to the ability of E. velox to produce resting eggs during spring, allowing the species to maintain itself in a temporary water milieu. Temperature significantly affected longevity and daily egg production of females; presence or absence of males did not affect these parameters. An increase in salinity from 20 to 30%. reduced longevity, number of egg sacs, and daily egg production in the winter generation, but not in the spring generation. The specific daily production of females during their adult life was calculated from the egg production:biomass ratio of females, in carbon units. In the winter generation, this ratio increased between 10° and 15°C compared to ratios between 15° and 20°C; the opposite was observed for the spring generation. The seasonal differences in the effects of temperature and salinity on reproduction could indicate an adaptation mechanism to the strongly thermal and haline seasonal fluctuations which characterize the habitat of Ex. velox (brackish waters, drying-up in summer). Larval mortality was high, except at 20%. S for the spring generation. The sex-ratio of the offspring was unaffected by variations in breeding conditions. Hatching time and development time of larvae could be described by two Blehrádek equations displaying close b and () coefficients. We calculated the energy balance of adult females from data obtained in a previous study on feeding and respiration in E. velox, and this is discussed in context with the egg production results. Net growth efficiency varied with algal concentration according to an asymptotic curve, reaching a maximum of 0.43 with Tetraselmis maculata as food or 0.53 with Amphidinium sp. Actual egg production rate obtained in the present study was in good agreement with that calculated by the difference between assimilated food and respiration expenses.     

Effect of temperature and food on the heart beat,ventilation rate and oxygen uptake of Mytilus edulis

The heart beat, ventilation rate and oxygen uptake of Mytilus edulis L. were measured simultaneously, in response to changes in temperature and food level. There was no thermal acclimation of heart-beat frequency or amplitude to temperatures from 5° to 25°C. Oxygen consumption and ventilation rate acclimated to 10°, 15° and 20°C, but not to 25°C. Starvation reduced the rate of oxygen uptake and heart-beat frequency to a standard level and, in response to food, the ventilation rate and oxygen consumption immediately increased to an active level. Feeding was maintained after the initiation of active metabolism, and during the following 10 days the heart-beat frequency gradually increased to the level characteristic of fed individuals. There was no direct correlation between the rate of oxygen consumption and heart rate, and an apparent absence of a close nervous coupling between ventilation rate and heart rate in M. edulis.     

Effects of acute changes in temperature and salinity on the oxygen uptake of larvae of herring (Clupea harengus) and plaice (Pleuronectes platessa)

Routine oxygen uptake (QO₂) by yolk-sac and firstfeeding larvae of herring (Clupea harengus L.) and plaice (Pleuronectes platessa L.) was studied after acute change of temperature (8°, 13°, 18°C) and salinity (5, 12.7, 32, 40). In both species, QO₂ (l mg^-1 dry wt h^-1) of both larval stages increased with increasing temperature. Salinity effect on QO₂ varied: for yolk-sac larvae of both species a lower QO₂ was found at lower combined salinities (5 and 12.7); for feeding larvae a lower QO₂ was observed at 12.7 for both species, possibly due to the relatively smaller size of larvae used at this salinity. For both species, oxygen uptake increased as larvae grew and weight regression coefficients were between 0.74 and 1.33. At 32 S, no difference was found in oxygen consumption between species as a function of temperature.Based on a dissertation submitted in partial fulfillment of the requirements for the degree of Master of Science at the University of Stirling, Stirling, Scotland. The work was performed at the Dunstaffnage Marine Research Laboratory, Oban, Scotland     

Temperature,salinity and ultraviolet irradiation effects on the growth of strains of Nitzschia ovalis

Three strains of Nitzschia ovalis Arnott grew at temperatures from 15°–36°C and at salinities from 5–40 S Optimum growth occurred at combinations of 25°, 27.5° and 30°C and 25, 30 and 35S. This estuarine benthic diatom tolerates wide salinity and temperature conditions while demonstrating resistance to ultraviolet irradiation at 350 nm.     

Routine oxygen consumption of Mugil cephalus,Liza dumerili and L. richardsoni at Different temperatures and salinities

Oxygen consumption studies were undertaken with 3 mullet species to determine b, the exponent of w, as well as a, as indices of metabolic rate in the equation M=aw ^bwhere M=metabolic rate, a=the intensity of metabolism, W=body weight, and b=the exponent of w. This was done under 5 experimental temperatures (13°, 18°, 23°, 28°, 33°C) for Mugil cephalus and Liza dumerili at 1 and at 35 S, and for L. richardsoni at 35S only. Mean b values were approximately 0.85. The a values depended on temperature, and increased according to Van't Hoff's law except for L. dumerili (1 S) and L. richardsoni (35 S) for a temperature increase from 23° to 28°C. It was found that handling had a profound influence on metabolic rate and led to considerably increased consumption rates during the first 8 h after introduction into the respiration chambers. Fasting in L. dumerili resulted in a total drop of 27% in oxygen consumption over a period of 6 days, of which 10% occurred over the first 24 h. Oxygen consumption displayed diurnal rhythms during the 6 day period, with lowest consumption rates at midday and midnight and highest just after sunrise and sunset.     

Distribution of the cladoceran Podon polyphemoides in the Chesapeake Bay

The distribution of the cladoceran Podon polyphemoides (Leuckart) in the Chesapeake Bay (USA) estuarine system was determined by a quantitative pump sampling method, and the patterns of abundance were correlated with temperature and salinity distributions. The species was seasonally recurrent, with distinct population maxima in the central portion of the bay. Population densities in excess of 60,000 podonids/m³ have been recorded. The podonids first appeared in the spring in the shallow tributaries, when water temperatures near the bottom reached 6°C. The vernal populations disappeared when summer temperatures exceeded 27°C, but reappeared in the fall as the water cooled. The species was euryhaline and eurythermal in its distribution, but the greatest concentrations were attained within relatively narrow zones of temperatures between 11^o and 26°C, and salinities between 8 and 18. The production of males, sexual females and sexual eggs occurred both in the spring and the fall between the thermal limits of 11^o and 17°C.     

Feeding of laboratory-reared larvae of the sea bream Archosargus rhomboidalis (Sparidae)

Feeding by larvae of the sea bream Archosargus rhomboidalis (Linnaeus) was investigated from late September, 1972 to early May, 1973 using laboratory-reared larvae. Fertilized eggs were collected from plankton tows in Biscayne Bay, and the larvae were reared on zooplankton also collected in plankton nets. Techniques were developed to estimate feeding rate, food selection, gross growth efficiency, and daily ration. Daily estimates of these were obtained through 16 days after hatching at rearing temperatures of 23°, 26°, and 29°C. Feeding rate increased exponentially as the larvae grew, and increased as temperature was raised. At 23°C larvae began feeding on Day 3, at 26° and 29°C larvae began feeding on Day 2. Feeding rates at initiation of feeding and on Day 16 were, respectively: 23°C, 7.16 food organisms per larva per hour (flh) and 53.78 flh; 26°C, 7.90 flh and 168.80 flh; 29°C, 17.62 flh and 142.07 flh. Sea bream larvae selected food organisms by size. At initiation of feeding they selected organisms less than 100 m in width. As larvae grew they selected larger organisms and rejected smaller ones. The major food (more than85% of the organisms ingested) was copepod nauplii, copepodites, and copepod adults. Minor food items were barnacle nauplii, tintinnids, invertebrate eggs, and polychaete larvae. Mean values for gross growth efficiency of sea bream larvae ranged from 30.6% at 23°C to 23.9% at 29°C. Mean values for daily ration, expressed as a percentage of larval weight, ranged from 84% at 23°C to 151% at 29°C and tended to decline as the larvae grew.This paper is a contribution from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, 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.