Filter-feeding ethology of benthic invertebrates (ascidians). IV. Pumping rate,filtration rate,filtration efficiency

A combination of a direct and an indirect method has been used for the first time in the study of filter-feeding in benthic invertebrates. Experiments over 12 h periods under constant temperature, pH, light and feeding conditions have been carried out with 3 species of ascidians: Ciona intestinalis (Linné, 1767); Phallusia mammillata (Cuvier, 1815) and Styela plicata (Lesueur, 1823). In C. intestinalis and P. mammillata, no pumping rhythm has been found; the water flow was constant for 12 h, except for some brief accidental interruptions. In S. plicata, the particular rhythm of spontaneous periodical contractions recorded during the experiment were related to gamete emission. The speed of water flow, which was fairly constant during recording, varied considerably during the 12 h period; these variations were generally related to modifications in the diameter of the cloacal siphon. The average speeds, in cm sec^-1, lay between 5.7 and 9.5 for C. intestinalis, 5.2 and 19.4 for P. mammillata, and between 5.3 and 10.7 for S. plicata. Variations in the pumping-rate were small, oscillating around a mean value. In ml h^-1 g^-1 dry weight of organs these were 5,829 to 5,982 (mean=5,906) for C. intestinalis, 6,142 to 6,592 (mean=6,312) for P. mammillata, 1,0508 to 1,1505 (mean=1,0708) for S. plicata. Filtration was continuous without any particular rhythm; filtration rates in ml h^-1 g^-1 dry weight of organs varied between 4,244 and 4,418 (mean=4,331) for C. intestinalis, 4,620 and 4,960 (mean=4,779) for P. mammillata, 8,482 and 9,078 (mean=8,760) for S. plicata. The curves representing pumping and filtration were clearly parallel, indicating that filtration efficiency did not vary greatly during the course of an experiment; the rates obtained were 65 to 87% (mean=74%) for C. intestinalis, 66 to 88% (mean 76%) for P. mammillata, and 73 to 90% (mean=80%) for S. plicata. The slightly higher mean value in S. plicata is probably related to the higher complexity of the branchial apparatus of this species.     

Filter-feeding ethology of benthic invertebrates (Ascidians). III. Recording of water current in situ — Rate and rhythm of pumping

Water current in 4 species of ascidians (Ascidia mentula Müller, 1776; Phallusia mammillata Cuvier, 1815; Styela plicata (Lesueur, 1823) and Microcosmus sabatieri Roule, 1885) has been recorded for the first time in situ with hot film probes. The mathematical treatment of probe calibration has allowed the evaluation of the characteristics of currents (minimal, maximal and average velocities) and the calculation of pumping rates. The method utilized yields qualitative and quantitative results: Pumping is continuous, and no particular rhythm shows up in the curves obtained. The velocity of the current does not change in the course of a recording, but it can vary from one experiment to another in the same individual; these variations are related to the variability of the diameter of the cloacal siphon rather than to a change in the rhythm of the ciliary activity. The average velocities are 3.42 cm sec^-1 for A. mentula, 3.92 for P. mammillata, 3.30 for S. plicata and 3.79 for M. sabatieri. The pumping rates are fairly constant for the same individual. The means, expressed as ml x h^-1 x g^-1 organ dry weight are 3422 for A. mentula, 2070 for P. mammillata, 4892 for S. plicata and 3084 for M. sabatieri.This work was supported by the C.N.R.S. (L.A. No. 117) and C.N.E.X.O. (Convention No. 76/1497).     

Ethologie alimentaire d'invertébrés benthiques filtreurs (ascidies). I. Dispositif expérimental. Taux de filtration et de digestion chez Phallusia mammillata

In a study on ascidian feeding ethology, rates of filtration and digestion of the unicellular algae Monchrysis lutheri by Phallusia mammillata (Cuvier, 1815) have been determined experimentally. All results were obtained under constant conditions of temperature, salinity, pH, light, and food, using 5 individuals in 9 experiments of 24 h each. The method of Winter (1969) has been modified by using an automatic system which enables constant food concentrations (±5%) to be maintained. Controls are made by a fluorometer. The rate of filtration is deduced from the quantity of culture food added each hour; this rate varies; a well defined rhythm is not observed, but alternating maxima and minima. The values obtained for, specimens of medium size (10 to 12 cm) vary from 3856 to 4730 ml/h and per gramme organic dry weight, the average being 4380 ml. The quantity of food actually converted by each ascidian, once it has passed the alimentary canal, is calculated from the amount of proteins present in food and faeces. Digestion rate varies from 4.65 to 5.75 mg of albumin equivalent/24 h and per gramme organic dry weight (mean 5.30 mg). The percentage food conversion (filtrated amount=100%) is high: 86 to 93%, with a mean of 90%.     

Ultrastructure of the vitelline coat in the ascidians Phallusia mammillata, Ascidia mentula and Ciona intestinalis : new aspects revealed by freeze-substitution and deep-etching

The microstructure of the vitelline coat (VC) of the three ascidian species Phallusia mammillata, Ascidia mentula and Ciona intestinalis was analyzed by transmission electron microscopy (TEM) using freeze-substitution and deep-etching. In addition, eggs were examined by light microscopy and prepared by conventional chemical fixation methods for TEM in order to illustrate the advantages of cryopreparation for the preservation of the VC ultrastructure. In conventionally fixed eggs of P. mammillata and A. mentula the VC appeared as a tripartite structure, consisting of a thin outer fibrous layer (OFL), a central dense layer (CDL) and a relatively wide inner fibrous layer (IFL). In C. intestinalis a sparse OFL is made up by fine tufts of filaments but an IFL is lacking. In all three species the test cells were located in the area between the inner VC boundary and the egg cell membrane. Using our modified freeze-substitution method a clear improvement in preservation of the VC matrix was obtained. In all three species the OFL as well as the IFL in P. mammillata and A. mentula appeared as extended fibrous meshworks. Furthermore, the area of the perivitelline space, empty after conventional TEM preparation, was found to be filled by an additional matrix, designated here as perivitelline fibrous matrix (PVFM). Quick-freeze/deep-etch/rotary-shadowing enabled us to confirm the overall architecture of the egg matrix and allowed a further detailed investigation of the VC fine structure in P. mammillata. Accordingly, the vitelline coat of P. mammillata and A. mentula is a multilayered matrix composed of four distinct subunits (OFL, CDL, IFL, PVFM), whereas in C. intestinalis an IFL is lacking. Received: 7 November 1996 / Accepted: 5 December 1996     

Co-ordinated rhythms of digestion,absorption and excretion in Mytilus edulis (Bivalvia: Mollusca)

Sequential alternation of extracellular digestion in the stomach and intracellular digestion in the diverticula appears widespread among bivalves. The present study documents some physiological consequences of such processes in Mytilus edulis L. collected during 1981 from Whitsand Bay, Cornwall, England. Pronounced temporal fluctuations in faecal deposition are described that relate, in terms of amplitude and period, to both sinusoidal rhythmicity established for ammonia excretion and changes in the morphology of digestive tubules. Although at least partially synchronised among replicate groups of mussels, these cycles bore no consistent relationship with exogenous influences. Hourly fluctuation in the net absorption efficiency for nitrogen, as evidenced by the mean percentage ±2 SE, measured over 24 h sampling periods, was considerable (16.0±53.7, 49.3±10.9 and 52.8±6.6 for mussels acclimated in March, June and October, respectively). This variation in absorption derived from an inverse relationship between the percentage nitrogen within faeces and the rate of faecal egestion. Accordingly, peaks of faecal deposition presumably represented the pulsed remnants of intracellular digestion. Co-ordinated rhythms of digestion, absorption and excretion were thus evident in M. edulis. These processes displayed seasonally dependent periodicities of approximately 8, 3 and 4 h in March, June and October, respectively. It was concluded that, at least for M. edulis, this previously unquantified rhythmicity of physiological processes warrants careful consideration during assays commonly undertaken in the complication of nutrient and energy budgets.     

Influence of light and temperature on the photosynthetic rate of marine benthic diatoms

The influence of light and temperature on photosynthetic rate as measured by C¹⁴O₂-fixation of marine benthic diatoms was investigated, using both intact sediment samples (Marshall et al., 1973) and suspensions of diatoms harvested by a lenstissue technique (Eaton and Moss, 1966). After C¹⁴-incubation, sediment samples were filtered, burned in a sample oxidizer, and their activity determined in a liquid scintillation counter. Photosynthetic rate of mixed field populations is saturated by a light intensity of approximately 10,000 lux; at still higher light intensities no photoinhibition was found. In contrast to the mixed field populations, unialgal cultures of the benthic diatom Amphiprora alata Kütz. exhibited strong photoinhibition at higher light intensities (10,000 to 60,000 lux). Within a range of 4° to 20°C, the photosynthetic rate increased about 10%/C^o. No differences in photosynthetic pattern were observed between epipelic and epipsammic species.     

Influence of light and temperature on the growth rate of estuarine benthic diatoms in culture

Four species of estuarine benthic diatoms: Amphiprora c. f. paludosa W. Smith, Nitzschia c. f. dissipata (Kützing) Grunow, Navicula arenaria Donkin, and Nitzschia sigma (Kützing) W. Smith were grown in unialgal cultures. The growth rates of the diatoms were determined as the rate of increase of the chlorophyll a content of the cultures. The diatoms were cultured at different combinations of temperture, daylength, and quantum irradiance. The highest growth rates of Navicula arenaria occurred at 16° to 20°C; the other 3 species had their optimum at 25°C or higher. The small-celled species had higher growth rates at their optimum temperature, but at lower temperatures the growth rates of all 4 species became very similar. The minimum daily quantum irradiance that could effect light-saturated growth at 12° and 20°C ranged from 2.5 to 5.0 E.m^-2.day^-1. At 12°C, two species had their highest growth rates under an 8 h daily photoperiod. At 20°C, the three species tested all had highest growth rates under 16 h daily photoperiod. The growth response of the benthic diatoms is comparable to that of several cultures of planktonic diatoms, as described in the literature. The influence of temperature and quantum irradiance on the diatoms in the present investigation was comparable to the influence of temperature and light intensity on the ¹⁴C-fixation of marine benthic diatoms (Colijn and van Buurt, 1975).     

Influence of algal concentration and temperature on the filtration rate of Mytilus edulis

The filtration rates of Mytilus edilis (=galloprovincialis; 40 mm) were determined in relation to food concentration and temperature, using pure suspensions of the unicellular alga Platymonas suecica in concentrations ranging from 3x10⁵ cells/l to 1.5x10⁸ cells/l. The rate of filtration (ml/h/mussel) generally decreased as cell concentrations increased, and dropped to low values when concentrations above 5x10⁷ cells/l were supplied. The amount of water swept clear varied continuously, and noticeable differences in the filtration activity of M. edulis were observed over short time intervals (5 min). Fluctuations of filtered volumes per unit time were greater with lower than with higher concentrations of algae. The influence of temperature on filtration activity was highest between 5°–15°C and 25°–30°C. A temperature increase from 15° to 25°C resulted in only a slight increase in filtration rate. At 5° and 30°C, filtration dropped to very low values, namely 350 and 100 ml/h, respectively. The temperature coefficients for the filtration rates of M. edulis were determined as: Q₁₀ (5° to 15°C)=4.96; Q₁₀ (10° to 20°C)=1.22. The amount of algae cells ingested per mussel per hour is directly related to food concentration. The maximum number of cells filtered/mussel/h in an algal suspension of 70x10⁶ cells/l was 21.5x10⁵ cells/h. Cell concentrations of up to 40x10⁶ cells/l were swept clear without producing pseudofaeces. The critical cell density for M. edulis was reached at algal concentrations of 70 to 80x10⁶ cells/l. Above these concentrations no normal filtration activity was observed.     

Effects of temperature and body mass on metabolic rates of sprat, Sprattus sprattus L.

Sprat, Sprattus sprattus L., is a small schooling clupeid forming large stocks in several ecosystems. Despite its high trophodynamic impact, little is known about its energy consumption rates. As a central component of a bioenergetic budget, metabolic rates of sprat from 3.11 to 9.71 g wet weight (WW) were measured at nine different temperatures (T) ranging from 9 to 21°C using a computer-controlled intermittent-flow respirometer. Routine metabolism (R _R) was related to T (°C) and WW (g) by R _R = 0.074 WW^1.077 e^{0.080 T}. Standard metabolic rates (R _S) as calculated from the 10% percentiles of the repeated measurements were on average 12% lower and still influenced by continuous swimming activity: R _S = 0.069 WW^1.073 e^{0.078 T}. We interpret the deviation of the scaling exponent b from typically found exponents of b ~ 0.8 as a consequence of permanently elevated activity level. The high permanent swimming activities also indicated that the concept of standard metabolism may not be meaningful in schooling planktivorous fish. These results suggest that generally in bioenergetic models for clupeid schooling fish the activity multipliers should be chosen very conservatively.     

The ecophysiological complex of Bathyporeia pilosa and B. pelagica (Crustacea: Amphipoda). I. Respiration rates

The metabolic rates of high and low shore estuarine populations of Bathyporeia pilosa Lindström and an open coast population of B. pelagica (Bate) have been determined over a range of temperatures during January and February, and June and July, 1968. Changes in oxygen uptake have also been measured monthly at 15°C. During the winter, oxygen uptake was in the order: high shore B. pilosa>low shore B. pilosa>B. pelagica. During the summer, high shore B. pilosa and B. pelagica had similar metabolic rates, but both were significantly higher than low shore B. pilosa. Both populations of B. pilosa had lower metabolic rates in summer than in winter, whereas the metabolic rate of B. pelagica remained much the same. Seasonal changes in metabolic rate are closely correlated with reproductive cycles. The possible influences of environmental parameters are discussed.     

Physiological responses to fluctuation in temperature of salinity in invertebrates. Adaptations ofAlpheus viridari (Decapoda,Crustacea),Terebellides parva (Polychaeta) andGolfinigia cylindrata (Sipunculida) to the mangrove habitat

The snapping shrimpAlpheus viridari (Armstrong, 1949), the polychaeteTerebellides parva Solis-Weiss, Fauchald and Blankensteyn 1990, and the sipunculanGolfingia cylindrata (Keferstein, 1865) are commonly found in the same mangrove habitat, where they experience frequent, acute fluctuations in temperature and salinity. Ecological studies indicate a temporal variation, including occasional absence, in the distribution of bothG. cylindrata andT. parva; this fed us to examine the physiological adaptations of the three species (collected at Western Bay, Twin Cays, Belize in 1985, 1986 and 1988). Each was subjected to acute, repeated exposure to either control (35 S) and decreased (25 S) salinity or to control and increased (45 S) salinity. Ability to regulate water and ion content (g H₂O or mol g^-1 solute free dry wt) was examinedA. viridari behaved as a hyperosmotic conformer at decreased salinity but as an osmoconformer at increased salinity. Regardless of direction of salinity change,A. viridari regulated water content through change in Na⁺, K⁺, and Cl^– contents. In contrast,G. cylindrata behaved as an osmoconformer and did not demonstrate ability to regulate water content.T. parva behaved as an osmoconformer, showed incomplete regulation of water content via change in Na⁺, K⁺, and Cl^– contents but had limited survival following exposure to 45 S. Each species was also exposed to change in temperature. Species were subjected to acute, repeated exposure either to control (28°C) and decreased (21°C) temperature or to control and inereased (35°C) temperatureA. viridari regulated water and ion content under both experimental conditions. In contrast,T. parva did not regulate water and ion content under either experimental temperature.G. cylindrata did not regulate water and ion content during exposure to decreased temperature and did not survive exposure to increased temperature. ForA. viridari, weight specific oxygen uptake rates (mg O₂ g^-1 ash-free dry wt) were determined. Exposure to decreased salinity or to increased temperature resulted in a small sustained elevation in O₂ uptake. It is concluded that, unlikeA. viridari, T. parva andG. cylindrata are only marginally adapted to withstand the salinity and temperature stresses, respectively, of the mangrove habitat. The inability ofT. parva andG. cylindrata to fully adapt to extremes in the mangrove habitat could well explain the temporal variation seen in the distribution of these two species.Contribution number 380. Caribbean Coral Reef Ecosystems, National Museum of Natural History, Smithsonian Institution     

Physioecology of zooplankton. II. Effects of phytoplankton concentration,temperature, and body size on the development and molting rates of Calanus pacificus and Pseudocalanus sp.

Developmental time and stage duration for Calanus pacificus Brodsky and Pseudocalanus sp. and the rate of loss of body carbon by molting for C. pacificus were estimated for copepodite stages cultured under various combinations of phytoplankton concentration and temperature. Mean development time and stage duration for C. pacificus decreased hyperbolically with increasing food concentration, and the minimum time required for reaching a given stage decreased logarithmically with a logarithmic increase in temperature. Low temperature retarded the development of early stages proportionally more than that of late stages, and stage duration increased logarithmically with increasing body weight. Therefore, copepodite development was not isochronal. The rate of loss of body carbon by molting was small, ranging from 0.2 to 2% day^-1. This rate increased hyperbolically with food concentration and was linearly related to the growth rate. The critical food concentration for the rates of development and molting increased with temperature and stage of development, but these rates were less dependent on food concentration than the growth rate. The development rate of Pseudocalanus sp. was higher than that of C. pacificus, and was less influenced by changes in food concentration and temperature. It is postulated that the inverse relationship between temperature and body size results from a differential effect of temperature and body size on the rates of growth and development. That is, with increasing body size the growth rate tends to become temperature-independent, but the development rate remains proportional to temperature. Thus, copepodites growing at low temperature can experience a greater weight increment between molting periods than individuals growing at high temperature, because the growth rate is similar at all temperatures but stage duration is longer at low temperature.Contribution No. 1128 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA     

Influence of various concentrations of orthophosphate on the division rate of an estuarine benthic diatom,Navicula arenaria,in culture

A hydrolysis procedure along with a high-pressure liquid chromatographic procedure is given enabling simple and reliable thymine determinations in the nanogram range in different fractions of sea-water samples taken from three different locations in the Northern Adriatic Sea. The levels corresponded to 1–3 g DNA per liter. From total polyanionic thymine, which had been precipitated as the cetyltrimethylammonium salt, the highest percentage was linked to the particulate fraction, with a definite subsurface minimum at 10 to 15 m. There was a corresponding maximum of a high molecular non-particulate thymine-containing fraction at the corresponding depth. From the bottom at 30 m upwards to about 20 m, a low molecular thymine-containing material has been found. Remarkably these basic features were common to all three locations, one of which was supposed to be in clean water, one near a thickly settled, touristic area, and the other in front of a large river delta coming from industrial hinterland.     

Effect of temperature on permeability and drinking rates of the metanauplii of the brine shrimp Artemia sp.

Diffusional permeabilities and drinking rates of 24 h-old Artemia sp. metanauplii incubated at 20 °C were studied at five temperatures: 15, 20, 25, 30, and 35 °C over a period of 6 h. Departures from the incubation temperature resulted in changes in both permeability and drinking rates which both reached their highest values at 35 °C. Metanaupliar permeability and drinking were more elevated than previously reported for adults.     

Influence of pH, salt concentration and temperature on the growth of Aeromonas hydrophila

The influence of environmental factors on the growth of Aeromonas hydrophila was investigated Four isolates (AH 37, AH 79, AH 86 and AH 100) were exposed to various environmental factors such as pH, salt concentration and temperature in laboratory condition. All the four isolates showed more or less similar growth at pH 7.0, 8.0 and 9.0 at 30 degrees C and 5 degrees C. At pH 5.0, 6.0 and 10.0, the log number of cells was found to be lesser than that of pH 7.0, 8.0 and 9.0 at both 30 degrees C and 5 degrees C. The results of the influence of salt concentration on the growth of Aeromonas hydrophila revealed that NaCl concentration of 0.5%, 1.0% and 2.0% favored the growth of this organism at both 30 degrees C and 5 degrees C. Increase in the salt concentration resulted in the growth of the decrease of this organism. Three percentages and 4% salt concentration moderately supported the growth of the organisms in the medium whereas at 5.0% NaCl concentration, there was no growth. Moderate growth of A. hydrophila at 5 degrees C is an interesting observation. The ability to grow at salt concentration between 0.5%, 4.0% under acidic and alkaline conditions pose a problem in the preservation of seafoods. These criteria may account for modified preservation techniques.     

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.     

Comparative species richness,composition, and abundance of invertebrates in Caribbean seagrass (Thalassia testudinum) meadows (Panamá)

The results of a year-long study in which epibenthic invertebrates were collected monthly from seagrass (Thalassia testudinum) meadows along the Caribbean coast of Panamá and the Panamá Canal Zone are described in this paper. Differences in species composition and abundance among sites were primarily due to the proximity of surrounding habitats, especially coral reefs, which contain a number of species that utilize the seagrass meadows. In contrast to many previous characterizations of tropical marine habitats, important seasonal fluctuations in both species number and abundance took place at each of the sites. Data on breeding activity among several species of decapod crustaceans indicate year-round reproduction, although considerable seasonal differences occur in the percentage of ovigerous females. These interspecific differences in observed reproductive output may be explained by differences in life-cycle length, a factor not often considered in discussions of seasonal breeding patterns in tropical marine invertebrates. Overall species composition was qualitatively similar to that reported in comparable studies of tropical and subtropical seagrass meadows elsewhere, although caridean shrimp and xanthid orab species were reduced in number and total abundance were much lower than in previous studies.     

Influence of temperature changes on oxygen uptake and ammonia and phosphate excretion,in relation to body size and weight,in Oikopleura dioica (Appendicularia)

The relationship between the rates of oxygen consumption, ammonia and phosphate excretion of a pelagic tunicate, the larvacean Oikopleura dioica Fol, 1872 were assessed as a function of size, dry weight and ash-free dry weight at 15°, 20° and 24°C. O. dioica has higher respiration and excretion rates than copepods of similar weight, but the weight exponent of the allometric power function: Y=aX ^b is similar to that of other poikilotherms. Temperatures above 20°C have a depressing effect on respiration and ammonia excretion. 90% of the variance in metabolic rates is explainable by body mass and temperatures Q₁₀ values for oxygen consumption, ammonia and phosphate excretion, respectively, are 2.45, 1.86 and 1.75 between 15° and 20°C, and 3.75, 2.90 and 3.60 between 20° and 24°C. Metabolic quotients (O:N, O:P, N:P) indicate a protein-oriented diet. The results of this study suggest weak metabolic regulation in O. dioica, an energetic strategy which allows an immediate response to favourable changes in feeding conditions.     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.