Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops (Placopecten magellanicus)

On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton) food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized rates of scallop oxygen consumption (V _sO₂ , μmol O₂ g⁻¹ h⁻¹) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V _sO₂ and ammonium excretion (V _sNH⁺ ₄, μmol O₂ g⁻¹ h⁻¹) remained dependent on ambient temperature throughout the experiment. V _sNH⁺ ₄ Q₁₀ (2.77) was higher than V _sO₂ Q₁₀ (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism and a stressed state. At 10 °C, V _sO₂ and V _sNH⁺ ₄ in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction in scallop production could result. Received: 23 June 1998 / Accepted: 8 February 1999     

Lipid composition of eggs and adductor muscle in giant scallops (Placopecten magellanicus) from different habitats

Scallops (Placopecten magellanicus Gmelin) were collected during August 1989 from shallow water (10 m) and deep water (31 m) habitats at Sunnyside, Trinity Bay, Newfoundland, to compare the lipid composition of eggs and adductor muscle tissue. Less favorable food levels and lower temperature conditions associated with deeper water have previously been shown to produce slower growth and reduced fecundity in individuals from this habitat. Triacylglycerol reserves consistently accounted for 60% of the total lipids present in both groups. The total lipid content of the eggs and the composition of their triacylglycerol fatty acid pools were similar in shallow water and deep water scallops, indicating very little if any nutritional difference between the two groups. Relative to their counterparts from shallow water, individuals from deeper water contained higher proportions of docosahexaenoic acid [22:6(n-3)] in the egg phospholipids and higher levels of 24-methylenecholesterol (a phytosterol commonly found in diatoms) in the adductor muscle. Differences in fatty acid composition are interpreted as biochemical adjustments of cell membranes to increase membrane fluidity, thereby compensating for the lower temperatures prevailing at the greater depth.     

Settlement of larvae of the giant scallop,Placopecten magellanicus,in 9-m deep mesocosms as a function of temperature stratification,depth, food,and substratum

In January and February 1992 an experiment was conducted in a 10.5-m deep tank (diameter: 3.7 m, volume: 117 m³) to examine the effects of food distribution with respect to a stable thermocline, depth, and substratum type on the settlement and metamorphosis of larvae of the giant scallop, Placopecten magellanicus (Gmelin). Polyethylene tube bags (diameter: 0.60 m) were used to enclose 9-m deep columns of seawater which were then used as treatment replicates. A sharp thermocline (i.e. 7 to 11°C gradient) was created between a depth of 4.0 and 5.0 m. At the beginning of the experiment, one million 6-d old larvae were added to the surface of each tube. Two or three replicate tubes of each of four feeding treatments were established: (1) food (Isochrysis galbana) added to the top 1 m of the water column (top-fed, n=3); (2) food added to the bottom 1 m of the water column (bottom-fed, n=3); (3) food added throughout the water column (mixed, n=3); and (4) no food added (unfed, n=2). Settlement collectors were placed in two replicate tubes of each treatment at depths of 0.1, 4, 5, and 9 m and contained two different substrata, Polysiphonia lanosa (a red filamentous alga) and aquarium filter-wool as an algal mimic. Spat settlement in the different feeding treatments was a function of larval growth rate. Most spat were collected in the mixed tubes. Fewer individuals were collected in the top-fed treatment and fewer still in the bottom-fed treatment; minimal numbers of spat were found in the unfed tubes. Filter-wool collected more spat than P. lanosa, but this was evident only in the 4-m deep collectors in the mixed tubes. Most spat were found in the 0.1-m or 4-m deep collectors; generally few were located below the thermocline in collectors at 5 or 9 m. We suggest that, in areas of intense stable stratification, spat collection of the giant scallop may be enhanced by the placement of collectors with appropriate substratum material at or above the zone of stratification, rather than near the bottom. Furthermore, we propose that natural settlement may be increased in areas where a stratification layer intersects with the sea floor or where the layer is disrupted by turbulent mixing.Contribution to the programs of OPEN (Ocean Production Enhancement Network, one of the 15 Networks of Centres of Excellence supported by the Government of Canada) and GIROQ (Group Interuniversitaire de Recherches Océanographiques du Québec)     

Ontogenetic changes in the vertical distribution of giant scallop larvae,Placopecten magellanicus,in 9-m deep mesocosms as a function of light,food, and temperature stratification

To understand how thermal stratification and food abundance affects the vertical distribution of giant scallop larvae Placopecten magellanicus (Gmelin), a mesocosm study was conducted in January and February 1992. The position of larvae was followed over 55 d in replicated 9-m deep tanks in relation to a sharp thermocline and the presence or absence of phytoplankton. Growth and vertical position of larvae were monitored in separate treatments which included phytoplankton added above the thermocline, below the thermocline, throughout the mesocosm, or absent from the mesocosm. Changes in the vertical position of larvae over time were quantified with a new, profiling, video-optical instrument capable of semi-automatically identifying, counting and sizing larvae. The strong diurnal migration of scallop larvae resulted in aggregations at two interfaces: the air/water interface during the night, and at the thermocline during the day. At times, the concentration of larvae within cm of the surface was > 100 times that in the remaining water column. The formation of bioconvective cells of swimming larvae at the air/water interface allowed larval aggregations to persist throughout the period of darkness. Regardless of the distribution of food, larvae remained above the thermocline during most of the experiment. Therefore, only in those treatments where food was also present above the thermocline was larval growth relatively high. Larger larvae penetrated the thermocline only after reaching a shell length of about 200 m; thus larval size, rather than chronological age, was more important in describing their vertical distribution. The rapid increase in kinematic viscosity with decreasing water temperature at the thermocline may retard the movement of larvae and contribute to aggregation at this interface. The influence of larval size on their vertical distribution, and the resulting potential for horizontal transport to settlement sites, points to the importance of persistent hydrographic features as critical factors contributing to settlement variance in scallops.     

Relation of spawning of the giant scallop,Placopecten magellanicus,to temperature fluctuations during downwelling events

We examined the relation of spawning to biological and physical factors for the scallop Placopecten magellanicus (Gmelin, 1791) over 8 yr (1984 to 1991) in the Baie des Chaleurs, southwestern Gulf of St. Lawrence, Canada. Spawning was always abrupt and occurred between July and mid-September. It did not appear to be related to the abundance of phytoplankton or particulate organic carbon and nitrogen in the water. It further showed no relationship to lunar or tidal phascs or to current velocity. Spawning consistently occurred during the summer temperature maximum, but did not coincide with any critical temperature or cumulative temperature threshold. All but one of the 33 spawning events, for which temperature data were recorded, were associated with temperature changes; 25 of these were sharp temperature increases and 7 were during strong temperature fluctuations when the mean temperature was 9 to 14°C. Both types of temperature changes were caused by downwelling of warm surface water. The delay by about 1 d in time of spawning between sites coincided with the rate at which downwelling events propagated into the bay. Virtually all of the spawning events resulted in gametes being ejected into warm water masses where conditions are likely to favour larval development.     

Recruitment,growth and production of giant scallops (Placopecten magellanicus) along an environmental gradient in Baie des Chaleurs,eastern Canada

We measured population structure, growth and production of four beds of the giant scallop Placopecten magellanicus (Gmelin, 1791) in Baie des Chaleurs, southwestern Gulf of St. Lawrence, Canada in July 1992. Differences in the relative strength of the younger cohorts in each of the four beds, indicated marked differences in recruitment and/or survival in individual years over distances of 10 to 40 km. Part of this variability appeared to be related to environmental conditions prevailing during and after spawning. The growth rate of small individuals (<50 mm) was correlated with the gradient of increased temperature and food availability going up the bay. In all beds, both total production and reproductive effort increased with increasing age and then leveled off. Somatic production reached a maximum after 7 to 10 yr and then decreased for older scallops. Reproductive effort (percentage of production dedicated to reproduction) increased monotonically with age and, for any given age, followed the increase in temperature and food availability going from the mouth into Baie des Chaleurs. Marked differences in the contribution of different beds to the total reproductive output for Baie des Chaleurs are inferred from inter-bed differences in the lipid content of the oocytes, in the proportion of non-reproductive juveniles, and in individual reproductive output.     

Gill function and particle transport in Placopecten magellanicus (Mollusca: Bivalvia) as revealed using video endoscopy

The technique of endoscopic video observation was used to study feeding processes of Placopecten magellanicus (Gmelin), collected from Bull Arm, Newfoundland in August 1991 and 1992, under near-natural feeding conditions. The fate of captured particles depended on the extent of ingestive or handling capacity saturation. Under low (1 to 10 particles l^-1) to medium (10 to 20 particles l^-1) particle concentrations, most particles were incorporated in continuous anteriorly directed slurries in the dorsal ciliated tracts of the gill arch and dorsal bends. As particle concentration or exposure time to the lower particle concentrations increased, four endogenous mechanisms of ingestion volume control were increasingly observed: (1) rejection of dense mucus-particle masses from the principal filament troughs onto the ventrally beating cilia and associated currents of the ordinary filament plicae, counter to and below the incoming pallial current maintained by the principal filament cilia; (2) intermittent stopping of the anteriorward flow in the dorsal ciliated tracts; (3) reduction or cessation of input from the principal filaments to the dorsal ciliated tracts; (4) detachment of the dorsal bends from the mantle to establish a shunt from the infrabranchial to the suprabranchial cavity. Chemical and histochemical tests of purified fluid withdrawn from the dorsal ciliated tracts indicate that mucus is present at all particle concentrations. Mucus therefore participates both in normal feeding and in ingestion volume control on the bivalve gill, although different mechanisms, and types of mucus, effect transport of material in the dorsal (feeding) and ventral (cleaning) ciliated tracts.     

Postingestive selection in the sea scallop (Placopecten magellanicus) on the basis of chemical properties of particles

Suspension-feeding bivalves are adapted to use a highly variable mixture of particles by sorting them before and after ingestion. Postingestive sorting in bivalves has been confirmed for several bivalve species, but few studies have attempted to isolate the factors influencing postingestive selection among different particles presented simultaneously. The ability of the sea scallop, Placopecten magellanicus (Gmelin), to sort a mixture of organic (¹⁴C-labeled dinoflagellates, Prorocentrum minimum) and inorganic (⁵¹Cr-labeled beads, diameter 16-18 µm) particles of similar size and shape within the stomach was examined. The study was carried out in August 1997 using scallops collected near Deer Island, New Brunswick, Canada. Sorting of the two particle types was measured by dissecting the scallops at intervals after feeding and comparing the ¹⁴C:⁵¹Cr ratios within the stomach, digestive gland, and feces. The ¹⁴C:⁵¹Cr ratio in the stomach decreased over time, indicating that sea scallops were sorting organic from inorganic particles. The ability of P. magellanicus to sort particles solely on the basis of chemical properties was tested in a second study by presenting them with a mixture of protein-coated and uncoated beads of two different colors. This study was carried out in February 2000 using scallops collected near Maces Bay, New Brunswick, Canada. Gut retention times of the two types of beads were measured using flow cytometry. Scallops retained protein-coated beads in the gut longer than uncoated beads, indicating postingestive selection by chemical properties. This study provides the first evidence for simultaneous postingestive sorting by bivalves of particles based solely on chemical properties. This would potentially enable P. magellanicus to preferentially retain particles of higher food quality longer than those of poor quality, thereby enhancing digestive efficiency.     

Influence of temperature and food availability on the ecological energetics of the giant scallop Placopecten magellanicus

Scallops (Placopecten magellanicus) were collected in 1981–1983 from two water depths at a location in Newfoundland, Canada, where temperature and food conditions associated with shallower water have been shown to be more favourable for somatic growth and gamete production. To gain insight into the seasonal energy balance for this species, metabolic and clearance rates were measured monthly under ambient temperature conditions and natural seston levels. Stereological techniques were used to determine the gamete volume fraction in the gonad in order to establish the annual reporductive cycle. The less favourable conditions associated with deeper water were relfected in reduced rates of gamete development, but the diameter of spawned eggs and the timing of spawning appeared unaffected by poorer conditions in the natural environment. Estimates of scope for growth were low or negative during the winter, but consistently high during the spring bloom, corresponding to a period of rapid gamete maturation. Somatic weight declined in both populations as gamete development proceeded but increased again during periods of low gametogenic activity, suggesting a close relationship between energy available for growth and the reproductive cycle. Oxygen uptake and clearance rate varied seasonally in relation to ambient temperature and food conditions, all of which appeared to be interrelated in a complex fashion with the energy demands of gametogenesis.     

The response of sea scallop (Placopecten magellanicus) veligers to a weak thermocline in 9-m deep mesocosms

We examined the vertical distributions of scallop (Placopecten magellanicus) veligers in deep (0.6 m diameter, 9.5 m deep) polyethylene mesocosms from December 1991 to January 1992. In the mesocosms temperature stratification varied from 0 to 1.5 °C. Profiles of vertical distribution revealed several repeated patterns. Peaks in veliger numbers often appeared at the water surface and just above the thermocline. Higher density patches were seen below the surface peaks, and revealed the presence of bio-convective cells. Distribution away from these discontinuities was usually even. Distribution of veligers was affected by thermoclines above 1.0 °C. Responses to thermoclines varied with larval age and time of day, and 28 to 30 d veligers passed in both directions through a 1.5 °C thermocline. We conclude that larval behaviour is a major determinant of whether veligers pass through a thermocline. Kinematic viscosity may play a role in perception of temperature changes. Two potential consequences of such behaviour are (1) remaining in more productive upper water layers, where feeding opportunities are enhanced, and (2) increased horizontal transport in the region of the thermocline, which may enhance recruitment. Received: 15 May 1996 / Accepted: 11 May 2000     

Exfoliation of epithelial cells by the scallop Placopecten magellanicus : seasonal variation and the effects of elevated water temperatures

Previous studies have shown that large numbers of ciliated and nonciliated epithelial cells (diam.: 6 to 15 μm) are released by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in Newfoundland when water temperatures are at a maximum and gonads are well developed. Such exfoliation of cells could be a response to stresses associated with elevated water temperatures and/or spawning activity. In the present study an electronic particle counter/sizer was used to further investigate the factors that influence exfoliation of epithelial cells by juvenile and adult scallops throughout the year. We observed release of epithelial cells from juveniles, and from adults collected in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers of cells may be a consequence of cellular turnover and normal physiological function. Adult scallops were monitored in a second experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 °C on the frequency (proportion) and rate of cellular exfoliation. Only at the highest experimental temperature (21.0 °C) were exfoliation rates significantly higher than rates recorded at 8.5 or 14.7 °C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops were exposed to 14.7 and then to 21.0 °C for a total of 8 d. Received: 21 August 1996 / Accepted: 13 September 1996     

Small-scale spatial and temporal genetic structure of the Atlantic sea scallop (Placopecten magellanicus) in the inshore Gulf of Maine revealed using AFLPs

Despite long planktonic durations, many species of broadcast spawning invertebrates exhibit genetic structure at small spatial and temporal scales. Amplified fragment length polymorphisms were used to assess genetic variation in the sea scallop, Placopecten magellanicus, among four inshore and one offshore location in the Gulf of Maine and temporal genetic variation among age classes of sea scallops at one site. Our results indicated that genetic structure for P. magellanicus exists on smaller spatial scales (tens to hundreds of kilometers) than expected given the 40-day planktonic larval period. In addition, genetic differences among age classes may be influenced by inter-annual differences in larval supply or reproductive success. Future genetic studies should sample multiple age classes prior to comparison among locations.     

Growth and lipid composition of scallop juveniles, Placopecten magellanicus, fed the flagellate Isochrysis galbana with varying lipid composition and the diatom Chaetoceros muelleri

The effect of feeding the flagellate Isochrysis galbana (Parke; clone T-Iso) of modified lipid composition on the growth and lipid composition of juvenile scallops [Placopecten magellanicus (Gmelin)] was investigated in the spring of 1993. I. galbana grown in 85-liter cage culture turbidostats under conditions of nitrogen limitation had a significantly higher total lipid content than when grown under nutrient-replete conditions. This was due mainly to a doubling in the amount of less unsaturated triacylglycerol in the cells. The concentrations of methyl and ethyl ketones were also greater in nitrogen-limited cells. Diets of nitrogen-limited I. galbana and nutrient-replete I. galbana grown in continuous and semi-continuous cultures were compared. Scallop juveniles were batch fed daily, and measurements of ingestion were determined. Samples of juveniles were removed periodically for determination of organic weight. The juveniles did not grow when fed nitrogen-limited or nutrient-replete I. galbana alone; however, when each diet was supplemented with 20% of the diatom Chaetoceros muelleri (Lemm.), there was a significant increase in growth in the juveniles receiving the nitrogen-limited I. galbana compared with juveniles on other diets. In comparison with I. galbana,  C. muelleri provided a rich source of carbohydrates and the essential fatty acid 20:4ω6. This study shows the importance of providing optimal dietary levels of ω3 and ω6 polyunsaturated fatty acids, as well as less unsaturated fatty acids and carbohydrates. Received: 29 September 1997 / Accepted: 2 October 1998     

Growth of sea bass,Dicentrarchus labrax,larval and juvenile stages and their otoliths under quasi-steady temperature conditions

The relationship between somatic growth and growth of otoliths of sea bass larvae, postlarvae and juveniles under relatively steady temperature conditions was studied. Larvae were incubated at the constant ambient temperature of 13.5°C, whereas postlarvae and juveniles were reared at a comparatively steady temperature ranging from 18.6 to 20.4°C, with a mean of 19.67°C. The patterns of both somatic and otolith growth were found to be similar. Differentiated data on larvae length and otolith diameters indicated three periods of change in their growth rates. Since temperature was kept relatively steady during the experiment, and larvae fed ad libitum, these periods could be attributed with relative certainty to intrinsic changes which occur during stage-specific periods of growth. The third period of change in both growth rates indicates a specific phase of growth during metamorphosis. The changes in growth rates, as well as the raw time series of the growth of both larval lengths and otolith diameters, may be described by higher order polynomials with a high degree of probability levels. A non-linear relationship between body length and otolith diameters was established, indicating positive allometric growth of otoliths. It was also observed that the coefficient of allometric growth changed at the time estimated for the end of metamorphosis. Thus, a non-linear relationship and changes in the coefficients of allometry should be borne in mind when back-calculating somatic growth from the growth of otoliths.     

Uptake and effects of copper and cadmium in the gonad of the scallop Placopecten magellanicus: concurrent metal exposure

Sea scallops Placopecten magellanicus in early gametogenesis from the southern shelf of Hudson Canyon, New Jersey, USA, were exposed in late winter 1984 to sublethal levels of Cu and Cd in a flowing seawater system at the NMFS Milford Laboratory. Exposure was to copper (10 and 20 gl^-1: low-Cu and high-Cu groups) or to a combination of copper and equimolar cadmium (10g Cu+17.7 g Cdl^-1: low-Cu/Cd group) for eight weeks, with sampling at 2-wk intervals. Copper had a strongly inhibitory effect on gamete production and maturation, which in some respects was partially moderated in the presence of cadmium in the female gonad only. Total gamete weight per scallop doubled in control individuals but dropped by 60% in both high-metal exposure groups over the 8-wk exposure period, with a smaller, temporary decrease in the low-Cu group. Cadmium did not add to the inhibition by copper of gamete development in the low-Cu/Cd group, but there was no partial recovery at 8 wk, as was seen in female scallops exposed to low-Cu alone. Gonadal RNA, higher in the females, decreased proportionately more in that sex than in the males of the metal exposure groups. Conversely, DNA levels were higher in the male than in the female gonad, and decreased sharply in all metal-exposed males. Gonadal protein concentration also dropped in all metal-exposed scallops with time and degree of metal exposure. Copper uptake in the gonad increased with time and metal exposure concentration, and cadmium increased in the low-Cu/Cd group with time. In contrast, manganese decreased significantly in the gonads of Cu-exposed scallops, especially in the high-Cu group. In the low-Cu/Cd group, manganese concentrations stabilized after an initial sharp drop at 2 wk in the low-Cu/Cd group, then rose at 6 and 8 wk. We ascribe this phenomenon to the induction by cadmium of metal-binding proteins (Fowler and Megginson 1986). In both sexes, gonadal magnesium concentrations did not change with increasing tissue burdens of copper and cadmium, but instead rose initially in proportion to the degree of metal exposure, homeostasis being maintained thereafter.     

Allozyme and physiological variation in the scallop Placopecten magellanicus and a general model for the effects of heterozygosity on fitness in marine molluscs

Heterozygosity and growth rate have been correlated in many molluscs, although the phenomenon is not universal. Enhanced growth of heterozygous molluscs has been attributed to lower energetic requirements for basal metabolism. We have investigated heterozygote deficiency, and the correlation between single-locus and multiple-locus heterozygosity and phenotype in juveniles of the scallop Placopecten magellanicus (Gmelin). Six samples were collected between 22 November 1984 and 11 December 1985 at Passamaquoddy Bay, New Brunswick, Canada. On average, heterozygote deficiency was small, although somewhat higher at the octopine dehydrogenase (Odh) locus, and decreased with age. No correlation was observed between genotype and growth rate. This result and published records indicate that allozyme heterozygosity of pectinids does not influence growth to the same degree as in other bivalves. However, we have observed in P. magellanicus a correlation between allozyme heterozygosity and octopine accumulation, a trait that relates to functional anaerobiosis, and may be related to the scallop's scope for movement. We combine these results and results from the literature into a model that relates the hypothesis of associative overdominance (at the population genetics level) with the hypothesis of energetic efficiency (at the physiological level). The model assumes that energy savings attributed to heterozygosity are used to maximize fitness. In freely moving molluscs this results in enhanced activity (such as searching for prey or swimming away from a predator), and in sessile molluscs either in enhanced somatic growth in juveniles or gonadal growth in adults.     

Role of biochemical energy reserves in the metamorphosis and early juvenile development of the oyster Ostrea chilensis

Metamorphosis in the Chilean oyster Ostrea chilensis was complete 36 h after release of the larvae, when 100% of the individuals showed edge growth of the dissoconch. The size of the larval shell did not change during metamorphosis, although the total dry weight of the larva decreased considerably. During this period, when the gill ciliature was undeveloped and the oyster therefore unable to feed, energy demands were met by biochemical reserves retained from the larval phase. Proteins contributed the largest quantity of energy to the metamorphosing oyster, 69.3% of the total expended, whereas lipids supplied 24.3% and carbohydrates only 6.4%. The process of metamorphosis consumed 64.5% of the energy reserves held by the pediveliger at the time of release. When metamorphosis was complete, growth began and tissue reserves were replenished, protein and carbohydrate accumulating rapidly early in the juvenile stage. Received: 26 December 1997 / Accepted: 8 July 1998     

Some effects of temperature on the growth and metabolic rate of juvenile blue crabs,Callinectes sapidus,in the laboratory

Juvenile blue crabs, Callinectes sapidus Rathbun, were grown in the laboratory at different temperatures, and metabolic-rate determinations were made. Growth is shown to be dependent upon temperature. Crabs kept at high temperatures (34° and 27°C) grow faster than those kept at lower temperatures (13°, 15°, and 20°C). Increase in size per molt is less at higher temperatures than at lower ones. Mortality is directly proportional to temperature between 13° and 34°C and is very high during ecdysis at elevated temperatures. Metabolic rate increases with temperature, but various degrees of acclimation are seen after 4 weeks exposure. No acclimation of general activity to temperature was found. The findings are applied theoretically to crabs living in the region of heated discharge canals of electrical generators: the motile blue crab could extend its growing season without decreasing size at maturity by active selection of thermal surroundings.In part based on a thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science at the University of Florida, USA.     

Ultrastructural and biochemical studies of intracellular metal-binding patterns in kidney tubule cells of the scallop Placopecten magellanicus following prolonged exposure to cadmium or copper

Sea scallops Placopecten magellanicus, which had been trawl-collected in late November, 1982 off the Rhode Island, USA coast, were exposed to 20 g of Cd or Cu per liter for a period of seven weeks in a flowing seawater system. Metal analyses of kidneys from both groups indicated uptake of both metals, although the tissue concentrations of Cd declined markedly in the Cu-treated scallops. The ultrastructural appearance of tubule cells of kidneys from Cd-exposed scallops was indistinguishable from controls. In contrast, tubule cells from scallops exposed to Cu showed marked cellular degeneration with loss of concretions. These ultrastructural changes were associated with significant reductions in renal isocitrate dehydrogenase activity in the Cu-treated scallops. Elemental analyses conducted on the kidney concretions and on the cytosolic metal-binding proteins of Cd-exposed scallops showed a 6-to 7-fold increase in Cd content of both these metalsequestering compartments, with concomitant changes in Zn, Mn, and Cu content. Loss of the concretions from Cu-treated scallops precluded analysis of this compartment, but Cu sequestration within cytosolic metal-binding proteins was associated with marked reductions of Zn and Cd from these proteins, suggesting disruption of this cellular mechanism for control of divalent metal cations. These findings support the hypothesis that toxic metal perturbation of normal homeostatic mechanisms that control divalent metal cation bioavailability is important factor in mediating cell injury from these agents.     

Cellular and ultrastructural changes in the endoderm of the temperate sea anemone Anemonia viridis as a result of increased temperature

Exposure of the temperate sea anemone Anemonia viridis Forskål to increased seawater temperature (from 16 to 26°C) reduced the lysosomal latency of coelenterate tissues. Lysosomes in the mesenterial filaments of anemones were destabilised by increased temperature, with greater destabilisation in heat-shocked symbiotic anemones than in heat-shocked aposymbiotic anemones in the early stages of the experiment. Lysosomal enzyme activity in zooxanthellae from heat-shocked symbiotic anemones was associated with the algal membranes and the cytoplasm of degenerate algal cells. While the relationship between host coelenterate and symbiotic alga may confer many benefits under normal conditions, comparison of the responses of symbiotic and aposymbiotic anemones to heat shock suggests that there may be disadvantages for symbiotic anemones under stress.