Acclimation of gametes to reduced salinity prior to spawning inLuidia clathrata (Echinodermata: Asteroidea)

AdultLuidia clathrata (Say) were held at salinities lower and higher (25 to 35) than environmental salinity (29) during gametogenesis and after sperm and primary oocytes were produced. The sperm and primary oocytes acclimated to the experimental salinities in both cases. Fertilization and development through gastrulation were not affected at the salinities at which the parents were held, but were affected at altered salinities. This indicates that intracellular osmoregulation can occur both during gametogenesis and after the stage of arrested activity has been reached. This is an important capacity forL. clathrata, which lives in estuaries with variable salinities.     

Responses of Leptasterias hexactis (Echinodermata: Asteroidea) to low salinity

The six-rayed starfish Leptasterias hexactis (Stimpson, 1862) is seasonally exposed to low salinities in southeastern Alaska. Individuals that were gradually exposed to reduced salinities in the laboratory had a 28-d TLm of 12.9 S. The activity of L. hexactis, as measured by its activity coefficient, varied directly with salinity. Individual feeding rates of the starfish on similarly exposed Mytilus edulis, measured daily for 21 d at salinities of 30, 20 and 15 S, also varied directly with salinity. The dry weight of mussel tissue consumed was 8.84, 8.49 and 0.58 mg ·starfish^-1·d^-1 at 20, 20 and 15 S. Expressed as percent of dry starfish weight, the daily feeding rate was 1.35, 0.76 and 0.10% at 30, 20 and 15 S. Absorption efficiency decreased from 64% at 30 S to 49% at 20 S, further reducing the energy available for metabolism. Growth, measured in terms of changes in total dry weight or dry weight of soft tissues, also varied directly with salinity. Although exposure to hyposmotic conditions did induce stress responses, as indicated by reductions in activity, feeding, absorption efficiency and growth rates, L. hexactis maintained positive growth for at least a 3-wk period in the laboratory at 20 S and 13°CC. The population of L. hexactis investigated must be considered euryhaline and brief periods of exposure to hyposmotic conditions should not limit its distribution.     

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

The feeding activity of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in 1978–1979 using various foods (natural particles, monospecific algal cultures, and artificial food) under different conditions of temperature and salinity. Experiments with Amphidinium sp. or Tetraselmis maculata as food showed that the ingestion rate increased with food concentration according to an asymptotic or a linear relationship. Although of slightly smaller size, T. maculata was ingested at a higher rate than Amphidinium sp. Large maximum daily rations (up to 150% of body carbon with Amphidinium sp. and up to 250% with T. maculata) were attained. These values, which greatly exceed those generally obtained with marine copepods, could result from adaptation of the feeding processes of this copepod to its very rich trophic environment. A significant correlation was demonstrated between ingestion rate and fecal pellet production using T. maculata as food. Therefore, daily fecal production was used as an index of feeding activity in experiments carried out with natural food, T. maculata cultures and artifical food (Tetramin). Increased temperature generally resulted in an activation of grazing and filtration rates and of fecal production at low temperatures (10° to 15°C), but a strong decrease was observed over 22°C. Differences of 10 S over or under the natural salinity level led to a decrease in fecal production, suggesting unachieved acclimatization to salinity variation due to a too short acclimation period before the experiments. Fecal pellet production was higher during the day than during the night. It depended also on the quality of food used: high values were obtained with T. maculata, Phaeodactylum tricornutum, Rhodomonas sp. and Chlamydomonas sp., low values with Chlorella sp. and Amphidinium sp., and medium values with natural food material. The assimilation rate (A) was calculated by Conover's methods. A significant negative correlation was obtained between A and the ash content of the food. High assimilation rates were attained with chlorophycean algae, while natural particulate food produced variable assimilation rates, depending on the amount of inorganic material present.

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

     

Effect of reduced salinity on adenylate energy charge in three estuarine molluscs

The value of adenylate energy charge as a biological indicator of the severity of departure from normal environmental conditions was examined in the gastropod Pyrazus ebeninus (Bruguière, 1792) and the bivalves Anadara trapezia (Deshayes, 1840) and Saccostrea commercialis (Iredale and Roughley, 1933). Mean energy charge for each species decreased by 17% or more when salinity was reduced from 35 to 10. Changes with reduced salinity were also found in the concentrations of individual adenylates and several adenylate ratios other than energy charge. Energy charge was calculated from the relative concentrations of adenosine 5-tri-, di- and monophosphate (ATP, ADP, AMP) in the columellar muscle of P. ebeninus and in the adductor muscle of A. trapezia and S. commercialis. Mean energy charge values for individuals in the low-salinity condition (10) were 0.61 for P. ebeninus, 0. 69 for A. trapezia and 0.53 for S. commercialis, compared with mean energy charge values in the control individuals (35 S) of 0.85 to 0.87 for P. ebeninus, 0.84 to 0.85 for A. trapezia and 0.64 to 0.76 for S. commercialis. The decrease in energy charge occurred within 24 h; no further change was found with exposure to low salinity for 48 h (A. trapezia) or no further change was found with exposure to low salinity for 48 h (A. trapezia) or 20 h (P. ebeninus, S. commercialis). Total adenylate concentrations (ATP+ADP+AMP) differed between the three species, with mean values (kg^-1 wet weight) of 5.0 mmol in P. ebeninus, 3.4 mmol in A. trapezia and 3.0 mmol in S. commercialis. No trends with time were found in total adenylate concentrations in any species. The changes in energy charge that occurred were not consistent with the differing sensitivity of the three species to reduced salinity, and do not support the use of energy charge as an absolute measure of stress in molluscs generally.     

Respiration,pumping activity and heart rate in Ciona intestinalis exposed to fluctuating salinities

Specimens of Ciona intestinalis L. were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and the changes in pumping activity and oxygen sonsumption monitored. Heart rate was monitored under steady state conditions using a new in vivo method, and pumping activity was monitored as spontaneous squirting by use of a pressure transducer. Oxygen consumption was also monitored under steady state conditions and under conditions of declining oxygen tension. It was found that during periods of regular beating the mean heart rate for 5 ascidians was 13.2 beats min^-1 for the branchial pacemaker and 32.6 beats min^-1 for the visceral pacemaker. Regular periods of beating lasted for approximately 1 min, followed by periods of irregular activity prior to heart beat reversal. The heart beat became irregular and reversal occurred sporadically when the ascidians were exposed to dilute seawater. The ascidians showed a pumping rate of 14 squirts per hour in full-strength seawater. This rate declined during decreasing salinity and ceased entirely when the external seawater concentration reached approximately 60% seawater (100%=32% S). During periods of decreased salinity, the siphons were tightly closed and oxygen consumption was zero. The rate of oxygen consumption by C. intestinalis decreased during decreasing salinities and there was no evidence of an oxygen debt. Oxygen consumption under steady state conditions varied with body weight according to the following: oxygen consuption =0.515 W ^0.831 (where W is body weight). The rate of oxygen consumption was found to be dependent on the external oxygen tension.     

Effects of salinity fluctuations on the respiration rate of the southern oyster drill Thais haemastoma and the blue crab Callinectes sapidus

Respiration rates of Thais haemastoma and Callinectes sapidus were determined as a function of salinity with a flow-through respirometer at 20°C. Respiration rates were measured at 10, 20 and 30 S for acclimated animals. The effects of 10-5-10, 20-10-20, 30-10-30 and 10-30-10 S semidiurnal cycles (12 h) of fluctuating salinity on the rate of respiration of the oyster drill were studied. During each cycle, salinity was changed from the acclimation salinity over a 4 h interval, held at that salinity for 2 h, returned to the acclimation salinity over 4 h and held at that salinity for 2 h. The effects of diurnal (24.8 h) salinity cycles on respiration in the oyster drill and blue crab were also studied. Salinity was changed from the acclimation salinity over a 10.4 h interval, held at that salinity for 2 h, then returned to the acclimation salinity over 10.4 h and held at that salinity for 2 h. The respiration rate of 30 S acclimated oyster drills (679 l O₂ g dry weight^–1 h^–1) was significantly higher than for individuals acclimated to 10 S (534 l O₂ g dry weight^–1 h^–1). Blue crab respiration was 170 l O₂ g dry weight^–1 h^–1 at 30 S, and was significantly higher at 10 and 20 S than at 30 S. With the exception of the 20-10-20 S semidiurnal cycle, the respiration rate of oyster drills declined as salinity fluctuated in either direction from the acclimation salinity and increased as ambient salinity returned to the acclimation salinity. Semidiurnal cycles (12 h) of fluctuating salinity produced greater changes in the respiration rate of snails than analogous diurnal cycles (24.8 h). A 10-30-10 S pattern of fluctuation caused a greater percentage reduction in the steady state respiration rate of oyster drills than the 30-10-30 S pattern. The respiration rate of blue crabs varied inversely with fluctuating salinity. Relatively minor changes occurred in blue crab respiration rate with fluctuating salinity. Blue crab respiration rate characteristically dropped during the initial phase of declining salinity at a rate directly proportional to the rate of salinity decrease, perhaps representing a metabolic adjustment period by the blue crabs. The respiratory response of T. haemastoma to salinity is consistent with its incomplete volume regulation, while the response of C. sapidus is compatible with its ability to regulate extracellular fluid osmotic and ionic composition.     

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.     

An energy budget for individual barnacles (Balanus glandula)

An annual energy budget was constructed for individual adult barnacles (Balanus glandula Darwin) for the first year after settlement. The production of body tissue, egg, shell, aquatic and aerial respiration, molting and faecal production was determined and consumption was derived from the summation of these budget items. To provide an estimation of the accuracy of the budget equation, energy budgets were constructed for three small groups of barnacles (n=40) kept under laboratory conditions, in which the budget items, including consumption, were determined independently. The results of the laboratory energy budgets indicated that consumption values derived from the summation methods for the three groups of barnacles were 7.4% higher and 16.2 and 15.6% lower than those determined by actual feeding experiments. The average consumption, assimilation and production of individual barnacles were estimated to be 699.5, 647.3 and 159.6 cal year^–1, respectively. B. glandula has an exceptionally high assimilation efficiency (92.5% from the annual budget and 99.3% from the laboratory budgets) but a low gross production efficiency (22.8%) and net production efficiency (24.7%). A very large proportion of energy (67.4%) was lost in respiration. The second most important budget item was egg production (12.3%); followed in decreasing order by: shell production (6.6%)> production of body tissue (3.9%)>molting (2.3%).This paper was presented at the 58th Annual Meeting of the American Society of Limnology and Oceanography, San Francisco, 1977, and received the Award for Excellence for the best student paper.     

Levels of intracellular free amino acids used for salinity tolerance by oysters (Crassostrea virginica) are altered by protozoan (Perkinsus marinus) parasitism

Free amino acid (FAA) levels were measured from May through October 1991 in gill tissues of two groups of juvenile oysters (Crassostrea virginica Gmelin), one transferred from a low salinity field site (8) to a field site of high salinity (20) and high Perkinsus marinus (Mackin, Owen, and Collier) prevalence, the other kept at the low salinity field site. Within 24 h, glycine levels in the oysters transferred to high salinity increased 8-fold, taurine concentrations doubled and the total FAA pool rose from 150 mol g^–1 dry wt to 400 mol g^–1 dry wt. Taurine levels reached a plateau within 20 d after transfer to high salinity and remained at that level until P. marinus infections were detected 85 d after transfer. Taurine and glycine levels declined by 40% in the high salinity population as infection intensity increased between 70 and 105 d. Total FAA declined by approximately 33% over this period. The oysters kept at low salinity were not infected and continued to grow while the infected high salinity oysters showed no increase in shell length after Day 85. FAA levels in the low salinity group remained relatively constant throughout the experiment except for an initial rise triggered by an increase in ambient salinity from 8 to 12. The results suggest that salinity tolerance mechanisms in C. virginica may be impaired by P. marinus infection.     

Nutrition and grazing behavior of the green turtle Chelonia mydas

The apparent digestibility coefficients for 4 size classes of the green turtle Chelonia mydas feeding on the seagrass Thalassia testudinum were measured in Union Creek, Great Inagua, Bahamas, from September 1975 to August 1976. The values ranged from 32.6 to 73.9% for organic matter; from 21.5 to 70.7% for energy; from 71.5 to 93.7% for cellulose; from 40.3 to 90.8% for hemicellulose; and from 14.4 to 56.6% for protein. Digestive efficiency increased with increases in water temperature and body size. There was no seasonal variation in the nutrient composition of T. testudinum blades. Grazing on T. testudinum may be limited by its low quality as a forage, a result of its high fiber content and possible low protein availability. Turtles did not graze at random over the extensive beds of T. testudinum, but maintained grazing plots of young leaves by consistent recropping. They thus consumed a more digestible forage-higher in protein and lower in lignin-than the ungrazed, older leaves of T. testudinum. The selectivity of green turtles for either a seagrass or algal diet may reflect the specificity of their intestinal microflora.     

Effects of temperature and salinity acclimation of adults on larval survival,physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea)

Larval survival and developmental rates of Lytechinus variegatus (Lamarck) were determined as a function of temperature and salinity in two experiments by: (1) directly transferring fertilized eggs to 35, 30, 27.5, 25, 20, 15, and 10S seawater at 18 and 23°C, and (2) acclimation of adult sea urchins to the conditions described above for 1 to 4 wk prior to spawning. Developmental rates and percent survival of larvae prior to metamorphosis decreased at salinities below 35 (Q₁₀ values for metamorphosis=0.380 to 0.384). Temperature and salinity significantly (P<0.05) affected metabolic rates of L. variegatus plutei. These results show that L. variegatus larvae are stenohaline when compared to larvae of other echinoderm species. LC₅₀ values (S), developmental rates, and survival to metamorphosis indicate that acclimation of adult sea urchins to lower salinity prior to spawing and fertilization does not enhance development or survival of embryos exposed to low salinity.     

Effects of salinity and bromine on zygotes and embryos of Fucus vesiculosus from the Baltic Sea

Zygotes and young embryos derived from Fucus vesiculosus collected in the archipelgo of Stockholm in 1990, growing at a salinity of 6 to 7 S, were cultured under different salinity conditions and in media of different bromine concentrations. Optimum salinity was 10 to 12 S for germination (rhizoid initiation) while apical hair formation showed a broader tolerance curve with an optimum at 8 to 14 S. Bromine caused inhibition of early development of F. vesiculosus. At 6 salinity a 50% reduction in germination took place at 10.0 mM Br and at 1.25 mM Br only 4.7% of the embryos developed apical hairs, as compared to 32.7% in the control. Bromine toxicity decreased at higher salinities. The results indicate that F. vesiculosus in the Baltic Sea has diverged from its Atlantic progenitors and to some extent acclimated to low salinity. Still, the salinity in the normal environment of the tested population is lower than optimum, leading to a lower degree of germination of zygotes, a lower growth rate of young embryos and probably also a higher sensitivity to additional stress factors such as chemical pollution.     

Feeding ecology of a size-structured predator population,the South American sun-star Heliaster helianthus

Patterns of feeding in a population of Heliaster helianthus (Lamarck), a common and dominant species of starfish indigenous to the Pacific South American coast, were investigated in an intertidal habitat in central Peru from October 1986 to April 1987. The H. helianthus population comprised individuals of 3.5 to 30.2 cm body size (diameter) with two modal size classes. The number of rays ranged between 18 and 40, and individuals with 31 to 33 rays accounted for ca. 42% of the total population. There was a higher rate of increase in ray number with body size amongst small individuals(<13.0 cm diam). H. helianthus is capable of feeding on more than one prey item at a time (average of 5.6 to 13.2 prey items handled, with several predators observed to hold >100), and both the number of prey individuals captured and the total prey biomass were significantly correlated with predator size. Amongst a total of 1132 feeding observations, the largest number of predators (an average of 85.4% of those feeding) were preying on the mussel Semimytilus algosus whilst another mussel, Perumytilus purpuratus, ranked second with 21,9% of predators feeding. The proportion of S. algosus in the diet increased from 65.4% in the smallest predator size-group (10.9 cm diam) to 91.2% in the largest (19.0 cm). In contrast, P. purpuratus and barnacles were more highly represented in the diet of small H. helianthus. The smallest size-group (10.9 cm) had low dietary overlap with larger sizes and less specialized prey utilization. Two geographically separated populations of H. helianthus in Peru and Chile showed contrasting patterns of prey utilization. S. algosus and P. purpuratus comprised 85.5 and 6.5% by number in the diet of the Peruvian population, respectively, whilst corresponding figures for the Chilean population were 8.3 and 60.5%, with barnacles attaining a higher share (22.6%). However, the total number of prey individuals per feeding predator was almost the same in Peru and Chile, with 10.0 and 10.7 individuals, respectively. H. helianthus individuals of different sizes occupy slightly different microhabitats within the intertidal area, which, coupled with differential spatial distribution of prey species, results in the predator population being able to utilize a wide range of resources.     

Growth rate and reproductive differences in a widespread estuarine harpacticoid copepod (Scottolana canadensis)

We demonstrate the presence of significant genetically based differentiation in growth rate (g dry weight d^-1) and reproductive traits (percent reproductive females and mean clutch size g dry weight^-1) among females of an harpacticoid copepod (Crustacea),Scottolana canadensis (Willey), taken from a broad range of latitudes and reared in the laboratory under the same conditions. As temperature increases (15°–25° C), the growth rate of southern-derived copepods continues to increase, while that of northern-derived copepods levels off or decreases. Southern-derivedS. canadensis also have a higher percentage of reproducing females at high temperature (25°C) when rations (cells ml^-1) are reduced, while northern-derived females are at an advantage at low temperature (15°C). Both life-history traits indicate local adaptation to maximize scope for growth and reproduction at prevailing temperatures. The data support our hypothesis that evolution has occurred to maximize feeding minus metabolic energy expended, and that this maximization requires changes in feeding efficiency with differing temperatures.     

Intake and coversion of food in the fish Limanda limanda exposed to different temperatures

In the flat fish Limanda limanda L., feeding rate and conversion efficiency were studied as functions of body weight, sex, temperature and food quality. When offered herring meat at 13 °C (series I), females (live weights 1 to 150 g) consume more food than males; the magnitude of this difference is body weight-dependent. With increasing wieght, both females and males consume less food per unit body weight per day. Variations in daily ration are considerable; the range of deviation from mean feeding rate is about 60% for males and 40% for females. The range of deviation does not vary significantly among females and males of different body weights. At the same temperature level (13 °C; series II), females consume almost the same, or even less, cod meat than males. Among individuals of series I and II, there is a little difference in the feeding rate; however, herring-fed individuals obtain about 2 times more energy than cod-fed individuals. Each gram wet weight of herring meat yields 2001, each gram cod meat 1137, calories. Small individuals completely cease to feed at 3°C; they feed little at 8 °C. Larger females consume maximum amounts at 8 °C. Small individuals consume maximum amounts at higher temperatures. Thus, with increasing body weight (age), the temperature for maximum feeding shifts downwards. Feeding with cod or herring meat results in considerable changes in composition and calorific content of L. Limanda. The magnitude of these changes depends both on temperature and food quality. Food conversion efficiency values of herring-fed individuals are about 1 1/2 times higher than of cod-fed individuals. In series I and II, females are more efficient converters than males. In individuals weighing more than 50 g, conversion efficiency decreases in the order: 8°, 13°, 18° C; in smaller individuals this order is 13°, 18°, 8 °C. Conversion rate is about 2 to 5 times faster in individuals fed herring meat than those receiving cod meat. Conversion rate decreases in the order 13°, 8°, 18 °C in males, and in the order 18°, 13°, 8 °C in females; females of more than 80 g are exceptional in that they reach the maximum at 8 °C. From the data on food intake and food conversion, the biologically useful energy available for metabolism has been calculated for each test individual kept at 13° and 18 °C. At these temperature levels, the weight exponents are about 0.6; the a value or metabolic level for the 18 °C series is about 2 times higher than that at 13 °C. Thus, temperature affects metabolic rate but not the exponential value. The exponential value for the body weight-metabolism relation at 13 °C is for dab fed herring meat 0.9; the a value amounts to about half that for dab fed cod meat. Food quality, unlike temperature, alters not only the exponential value but also metabolic rate.     

Feeding energetics and metabolism in demersal fish species from Antarctic,temperate and tropical environments

The energetics of feeding has been investigated in demersal fish with similar sedentary lifestyles from the Antarctic (Notothenia neglecta Nybelin), North Sea (Myoxocephalus scorpius L.) and Indian Ocean (Cirrhitichys bleekeri Bleeker). In general, the metabolic rates of fasting individuals were positively correlated with adaptation temperature: values for a standard 100 g fish (mg O₂/h) were 3.3 for N. neglecta at around 0 °C, 2.7 for winter-acclimatized M. scorpius at 5 °C, 4.3 for summer-acclimatized M. scorpius at 15 °C, and 7.0 for C. bleekeri at 25 °C. In all species, following a single satiating meal, oxygen consumption increased to a peak of 2 to 3.5 times the fasting values. Maximum rates of oxygen consumption after feeding were several-fold higher in the warm-than in the cold-water species. After controlling for the effects of body mass and energy intake by analysis of covariance, the duration of the increase in metabolic rate, referred to as specific dynamic action (SDA), was found to be 3 to 4 times shorter in the warm- than in the cold-water fish, ranging from 57 h in C. bleekeri to 208 h in N. neglecta. In contrast, the SDA was not significantly different in the various species, corresponding to 15 to 23% of the energy ingested. Seasonal influences on metabolism and feeding were also studied in N. neglecta acclimated to simulated winter (-1.0 to-0.5 °C; 3 h light:21 h dark) or summer (0 to 0.9 °C; 21 h light:3 h dark) conditions. The metabolic rates of fasting and fed individuals, and the characteristics of the SDA were found to be independent of acclimation conditions. This suggests that N. neglecta is capable of processing food at similar rates throughout the year. Energy stores and enzyme activities were measured in the swimming muscles and liver of fish fed ad libitum. Summer-acclimated fish had higher concentrations of liver triglyceride stores and elevated activities of some enzymes of intermediary metabolism relative to winter-acclimated fish. The observed changes in intermdiary metabolism are probably related to annual cycles of growth and reproduction. It is suggested that the low aerobic scope for physiological performance in Antarctic fish may necessitate the seasonal switching of energy allocation between growth and reproduction.     

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.     

Laboratory spawning and rearing of a marine fish,the silverside Menidia menidia menidia

Adult silversides, Menidia menidia menidia (Linnaeus), were collected in early March, 1974 and maintained in 3 recirculating seawater tanks in the laboratory. Respective groups were fed Moore-Clark Fry Fine at 3, 7 and 10% of their body weight per day. The photoperiod (light intensity approximately 2000 lux) was increased in increments of 10 min/day from 12 h light to 14 h light. The water temperature was increased by 1C°/day from the ambient collection temperature, 14°C, to 22°C. Twenty-four days after beginning laboratory conditioning, fish in each tank were stripped. There was a significant increase (², =0.05) in the number of ripe males at all three feeding levels, compared to an initial field-collected group that was checked at the beginning of the conditioning period. Females also showed significant increases in ripeness at the 7 and 10% but not at the 3% feeding level. The gonadal indices (gonad weight expressed as percentage of body weight) of both sexes were significantly greater than those measured for the initial field-collected group, but did not differ from those of adults collected from the field at the time laboratory conditioning was terminated. Techniques for maintaining eggs from field-ripened adults in the laboratory have been developed, and the effect of salinity on the percentage emergence of larvae determined. The highest emergence rate of larvae was 61% when eggs were maintained at 30 S. Emergence was 56% at 20 S and 47% at 10 S. The effect of delayed feeding on survival and growth of larvae was determined at 20 and 30 S and 25°C. Survival and growth was best for larvae fed Artemia sp. nauplii immediately after emergence at 30 S.Contribution No. 252, Gulf Breeze Environmental Research Laboratory.Associate Laboratory of the National Environmental Research Center, Corvallis, Oregon, USA.     

The filtration rate of Mytilus edulis and its dependence on algal concentration,measured by a continuous automatic recording apparatus

A new apparatus for long-term, continuous automatic measurements of filtration rates in suspension-feeding organisms is described. As the concentration of algae in the experimental medium is diminished by the filter-feeding activity of the experimental animals, algal suspension is automatically added, thus keeping the algal concentration constant. In this way, accurate determinations of filtration rates in relation to particle concentration are made possible. For determination of filtration rates in the common mussel Mytilus edulis L., individuals of different body size (shell length 8.5 to 56.5 mm) were used. Within the range of 10x10⁶ to 40x10⁶ cells of Dunaliella marina/l, mussels of the same body size filter-out approximately the same amount of algae at high or low concentrations. A low algal concentration is counterbalanced by a corresponding higher filtration rate. Within the range of body size (W=dry weight of tissues) and algal concentrations used, the filtration rate (F) follows the general allometric equation F=a·W ^b, where a and b are constants at specific experimental conditions. At a temperature of 12 °C, the values obtained for a are 2410 at a concentration of 20x10⁶, and 1313 at a concentration of 40x10⁶ Dunaliella cells/l; correspondingly, the filtration rates of a mussel of 1 g dry-tissue weight are 2410 ml/h and 1313 ml/h. b, the slope of the regression line (0.73 to 0.74), is independent of algal concentration. However, examination of all known measurements reveals that, most probably, the general allometric equation is an oversimplification; in large individuals there is a more pronounced decrease in filtration rate. The relationship between filtration rate, body size of mussels, and algal concentrations used is discussed.This work was made possible through a research grant from the Deutsche Forschungsgemeinschaft in connection with the program Litoralforschung — Abwässer in Küstennähe.     

Effect of temperature on specific dynamic action in the common octopus,<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> (Cephalopoda)

Feeding causes an increase of metabolic rate, which initially escalates rapidly, reaches a peak value and then gradually declines to the pre-feeding rate. This phenomenon, termed specific dynamic action (SDA), reflects the energy requirements of the behavioral, physiological and biochemical processes that constitute feeding. The effect of temperature on SDA of the common octopus, Octopus vulgaris, was evaluated, by measuring the temporal pattern of the oxygen consumption rates of octopuses, after feeding, at two constant temperatures, 20°C and 28°C. At 20°C, the relative increase in the oxygen consumption rate after feeding (relative SDA) was significantly greater than at 28°C. The peak of the relative SDA occurred 1 h after feeding, and it was 64% at 20°C and 42% at 28°C. However, the SDA absolute peak, SDA duration (9.5 h) and SDA magnitude (the integrated postprandial increase in oxygen uptake) did not differ significantly between the two temperatures, indicating that the energetic cost of feeding was the same at both temperatures. The SDA response in O. vulgaris was much faster than it was in polar species, which have extended SDA responses due to low temperatures, and was also relatively fast in relation to the response in other temperate species, which is probably connected to the remarkably high growth rates of the species. A possible explanation of the observed summer migration of large octopuses from shallow to deeper areas is given, based on the effect of temperature on the energetic requirements of octopuses.