Interactive effects of diet and temperature on the scope for growth of the scallop Argopecten purpuratus during reproductive conditioning

Effects of temperature, salinity, and food availability on shell growth rates of the Yesso scallop

Shell growth rates in relationship to seasonal changes of environmental factors were studied in a wild population of the Yesso scallop Mizuhopecten yessoensis inhabiting Amur Bay (Peter the Great Bay, Sea of Japan, Russia). It was found that food availability is not a limiting factor for the scallop growth in the study area. A phytoplankton biomass of 3.5-6.0 g m^-3 provided high scallop growth rates. The largest daily shell increments were observed with a phytoplankton biomass of about 6 g m^-3. With a decrease in the phytoplankton biomass to <2 g m^-3, as well as with an increase to >11 g m^-3, the daily shell increments reduced. It appeared that the main exogenous factors causing the seasonal variations in the scallop growth rates are the water temperature, which was too high in July and August (>18 °C) and too low in November-April (<4 °C), and the water salinity, which was too low (<30‰) for this stenohaline species in summer. The relationship of the daily shell increment in Yesso scallop with the water temperature can be described by a dome-shaped curve. The largest increments were observed at 8-16 °C. The dependence of the daily shell increments on the water salinity was also best described by a dome-shaped curve, showing the optimal range of 32.5-33.5‰. The revealed relationships, approximated by dome-shaped curves, evidently indicate that both insufficient and excessive effect of the factor negatively affects scallop growth. A suggestion was made to describe the result of the combined impact of several environmental factors on the daily shell increment as a multiplication of the functions of its dependence on each of the factors.

Scope for growth and dietary needs of Mediteranean Pinnids maintained in captivity

Background

The measurement of the energy available for growth (scope of growth, SFG) can be used in bivalves to make a long-term prediction in a short-term experiment of the condition of the individual. In order to tackle the best conditions for captive maintenance of Mediterranean Pinnids, a SFG study was conducted using Pinna rudis as a model species. Three diets were examined to test the viability of live microalgae and commercial products: i) a control diet using 100% of live microalgae based on the species Isochrysis galbana (t-ISO), ii) a 100% of commercial microalgae diet based on the product Shellfish Diet 1800®, and iii) a 50/50% mix diet of I. galbana (t-ISO) and Shellfish Diet 1800®.

Results

SFG results showed significant differences among diets in the physiological functions measured and suggested lower acceptability and digestibility of the commercial product. Negative SFG values were obtained for the commercial diet which indicates that it should be rejected for both Pinnid maintenance. The mixed diet showed improved physiological performance compared to the commercial diet, resulting in a higher SFG that had no significant differences with the control diet. However, in the long-term, the lower digestibility of the mixed diet compared to the control diet could lead to a deterioration of individuals’ conditions and should be considered cautiously.

Conclusions

This work represents the first case study of SFG in Pinna spp. and provides fundamental data on dietary needs for the critically endangered species, P. nobilis.

Contrasting responsiveness of four ecologically and economically important bivalves to simulated heat waves

Heat waves are expected to increase in duration and frequency, impacting coastal ecosystems, especially intertidal organisms living near their thermal tolerance limits. Sedentary infaunal species are limited to some extent in escapes from sudden temperature changes, rather modifications to their physiology and behaviour are expected. This may lead to strong ecological and economic impacts on commercial bivalve species, such as Venerupis corrugata, Ruditapes decussatus, the introduced Ruditapes philippinarum and Cerastoderma edule, the most relevant in NW Spain. We investigated lethal and sublethal effects of heat during low tide on these species in the laboratory. Summer temperatures experienced within field, shallow sediments at approximately 2 cm depth i.e. 20 °C (control), 27 °C, 32 °C, and 37 °C, were replicated during four consecutive days and the diffusion of heat at the burrowing depth of each species was estimated; temperature exposure was expressed as degree hours above 22 °C. After two days of tidal exposure, C. edule and V. corrugata suffered significant mortalities, and also the most dramatic decrease in scope for growth (SFG) as well as reduction in burrowing activity. After four days under stress, all species had negative SFG. On recovery, species showed compensation at longer exposures, particularly C. edule. These effects of temperature on mortality, growth potential and burrowing ability may increase the time to achieve commercial size and exposure to predation. Particularly, V. corrugata, with a center of distribution lower in the intertidal and subtidal, and C. edule, shallower in the sediment, may be the most affected. Clearly the intensity and frequency of heat waves will affect these key species in the intertidal sediment flats changing ecosystem functioning and fisheries management strategies.

Age and growth variability of the yellow clam (Mesodesma mactroides) in two populations from Argentina: implications under climate change

Morphometric relationships and age and growth rates of the yellow clam (Mesodesma mactroides Reeve, 1854 = Amarilladesma mactroides (Reeve, 1854)) were compared in two populations from Argentina: Santa Teresita (36°32′00″S) and Mar del Plata (37°57′52″S). The Santa Teresita clams were heavier (shell, soft parts) than the Mar del Plata clams. Cross sections stained with Mutvei’s solution and acetate peels revealed an internal shell growth pattern of well-defined slow-growing translucent bands and alternating fast-growing opaque bands. Translucent bands (clusters) representing external rings were formed mostly during October in both sites, coinciding with gonadal maturation processes and spawning. Data confirm the annual formation of translucent bands in this species. Comparison of growth parameters showed a higher growth rate k and lower maximum age in Mar del Plata (8 years) than in Santa Teresita (9 years), which could be triggered by differences in salinity between localities due to the influence of the Rio de la Plata estuary, which is strongly linked to climate variability. Shell mass condition index and Oceanic Niño Index were negatively correlated, showing the influence of El Niño in shell properties of the species. Considering that events are becoming more intense and frequent, changes in growth rates and shell properties of Santa Teresita’s population could be expected to be more vulnerable under climate change.

Uptake and accumulation of cadmium, manganese and zinc by fisheries species: Trophic differences in sensitivity to environmental metal accumulation

Fishery targeted species living in estuaries face multiple anthropogenic pressures including habitat contamination. However, trace metal concentrations in aquatic organisms can be highly variable, making it difficult to interpret accumulation responses. Understanding sources for metal accumulation in these organisms and their biokinetics is important for management of local fisheries and ensuring safety and quality of consumed seafood, particularly in urbanised areas. In this study, we exposed Australian sand clams, school prawns and sand whiting to a combination of cadmium (Cd), manganese (Mn) and zinc (Zn) radioisotopes 1) dissolved in seawater, 2) adsorbed to suspended sediment particles and 3) in radiolabelled food. Sand clams were sensitive to Cd, Mn and Zn uptake and accumulation from all sources because of their filter feeding physiology. Mean Cd and Zn assimilation efficiencies (AE) were higher in clams fed benthic diatoms (51, 43, 63% for Cd, Mn and Zn, respectively) than clams fed an algal flagellate species (22, 32, 33% for Cd, Mn and Zn, respectively). Metal uptake by prawns from seawater was low, whereas assimilation from diet was high (67, 59, 64% mean AEs from Cd, Mn and Zn, respectively). Sand whiting did not accumulate metals from seawater, even after concentrations were increased. Assimilation from diet (labelled prawns) was also low for sand whiting, particularly for Cd and Zn (11, 26, 14% mean AEs from Cd, Mn and Zn, respectively). These results may help explain the persistence of sand whiting in contaminated estuaries. Suspended sediment exposures showed that prawns and fish are less likely than clams to be negatively affected by disturbance events such as floods, which can bring metals into estuaries. The findings of this study have implications for fisheries management, both for protection and remediation of important habitats, and to ensure safe standards for seafood consumption by humans.

Sand gapers' breath: Respiration of Mya arenaria (L. 1758) and its contribution to total oxygen utilization in sediments

To estimate the contribution of a Mya arenaria population to total oxygen utilization (TOU) at different temperatures, the respiration rate of M. arenaria was measured for a full size range at 5 and 15 °C. In this study we measured respiration rates in a closed system while the clams were burrowed in sandy sediment, resembling their natural habitat. Rates were measured over a sufficient time span (24 h) to average varying activity phases during the measurements. We calculated a size-dependent respiration rate for M. arenaria and its variation with temperature. Temperature strongly affects the total population respiration and the contribution of different size classes to respiration of the total M. arenaria population. M. arenaria was estimated to contribute up to 70% to the total oxygen utilization of benthic communities analyzed in this study very much depending on the size distribution of the bivalve population present. Given a specific size distribution, smaller individuals had a stronger influence on the total oxygen utilization at colder temperature, while the influence of larger individuals grew with warmer temperature. Even though sizes contribute differently, a significant relation between abundance and respiration could be drawn in most cases analyzed. However, this relation should not be used as a general rule, but when estimating a population's metabolism the size distribution within that population has to be regarded.

The influence of temperature stress on the physiology of the Atlantic surfclam, Spisula solidissima

Atlantic surfclam populations have significantly declined in state and federal waters from the south shore of Long Island, New York to the Delmarva Peninsula since the early 2000s. Previous studies have demonstrated that surfclams in this geographic range show signs of physiological stress, suggested to be a result of increasing ocean temperatures. In this study, we examined the effect of 2 temperature regimes (19 °C and 23 °C) on surfclam physiology. These temperatures were chosen because they represent maximal (23 °C) and minimal (19 °C) temperatures prevailing in New York clamming areas during summer. Results demonstrated enhanced energy metabolism and significant reductions in filtration rate, scope for growth, and immune functions in clams exposed to the warmer temperature treatment. Although net energy gains remained positive in both treatments under our experimental conditions, the findings suggest that temperature stress is involved in the recent observations of surfclams in poor condition. The impact of elevated temperatures on phytoplankton quantity/quality and other environmental variables in combination with the direct impact on surfclam filtration and metabolic rates could lead to a negative energy balance. While some uncertainties remain about population-scale impacts of overall warming trends, we fear that future increases in temperature may lead to the collapse of the Atlantic surfclam between New York and Virginia, especially within inshore regions.

Effects of temperature and salinity on metabolic rate of the Asiatic clam Corbicula fluminea (Müller, 1774)

The effects of temperature and salinity on the metabolism of the Asiatic clam Corbicula fluminea (mollusca, Lamellibranchia) were studied experimentally. Firstly, three indexes of basal metabolism (oxygen consumption rate, OCR; ammonia excretion rate, AER; and CO₂ emission rate, CER), patterns of diurnal rhythm and O: N ratios were measured for three size ranges (large: h = 25.54 ± 1.96 mm, medium: h = 22.07 ± 1.33 mm and small: h = 17.70 ± 1.43 mm) at two salinities (0.3‰ and 1.8‰). The results showed that: (1) three indexes decreased with increasing body size. (2) no significant difference was found between two salinities for the O: N ratios of the small and large size, but a significant difference was found for the medium-sized one; (3) however, there were similar and distinct diurnal rhythms of metabolic rate at two salinities over a 24 hour period in three size C. fluminea.

OCR, AER, CER, O: N ratios and Q10 (temperature coefficient) of small-sized C. fluminea were measured across five water temperatures (4, 11, 18, 25 and 32°C) and two salinities (0.3‰ and 1.8‰) in the following experiments. Our results of the small C. fluminea were as follows: there was no significant difference in the O: N ratios among the five temperatures and two salinity treatments; and no significant difference of three indexes between both salinity levels were observed at same temperature controlled; and three indexes increased significantly with increasing temperature from 4°C to 25°C, while no significant difference was observed in the 25-32°C range; and the highest Q₁₀ coefficients (Q₁₀ = 1.825 at salinity of 0.3‰ and Q₁₀ = 1.683 at salinity of 1.8‰) were observed at the 18-25°C temperature increase, and the low values were found in the 4-11°C, 11-18°C and 25-32°C interval. It indicates that there is not a synergetic effect of our temperature and salinity on the metabolic rate of small C. fluminea, and a temperature of 18-25°C may represent an optimum adequate metabolic temperature range. For the purposes of ecological monitoring and restoration, small individuals of C. fluminea planted are more likely to survive than larger ones.

Filtration rate, assimilation and assimilation efficiency in Crassostrea virginica (Gmelin) fed with Tetraselmis suecica under cadmium exposure

Crassostrea virginica is an epibentic filter-feeding bivalve of economical importance in coastal lagoons of the Gulf of Mexico, locations with increasing inputs of heavy metals such as cadmium that have become environmental stressors. In this study, feeding and assimilation of the species were evaluated as physiological indicators of cadmium exposure. For this purpose, the filtration rate (FR), food assimilation (A) and assimilation efficiency (AE) of oysters from the Mandinga Lagoon, Veracruz, Mexico, were examined under sublethal and environmentally realistic cadmium concentrations (95 and 170 micro gCd L(-1)). Semi-static, 12-day bioassays were conducted with organisms placed into individual chambers and fed daily with Tetraselmis suecica. FR was calculated by measuring the depletion in algal density. Caloric contents of food and feces produced were also obtained. Condition Index (CI) and morphometric parameters were evaluated at the beginning and at the end of the assay. Total cadmium concentrations were quantified in water and tissue, and the metal bioconcentration factor (BCF) was calculated. Cadmium exposure significantly reduced FR in oysters (mean value: 0.64 L h(-1) and 0.44 L h(-1)) from control values (1.17 L h(-1)). Extreme values among results demonstrate the existence of a high FR (over 4 L h(-1)) mainly in control oysters, and this was associated with a better physiological condition; a low FR (under 2.5 L h(-1)) indicated metabolic stress as a consequence of Cd exposure. A and AE were significantly modified due to cadmium external levels, and time of exposure. FR and A were linearly related, and both decreased as metal BCF increased. Cadmium bioaccumulation was linearly related with external metal levels. The physiological deterioration of native C. virginica from Mandinga Lagoon was reflected in the alteration of FR, A and AE due to cadmium exposure in concentrations considered sublethal, lowering the feeding and assimilation capability of the organisms. The weight loss and mortality recorded in the oysters exposed to the highest metal concentration, was the final consequence of the overall adverse effect of cadmium exposure.

Dynamics of biochemical components, lipid classes and energy values on gonadal development of R. philippinarum associated with the temperature and ingestion rate

This study evaluates the effect of temperature, coupled with ingestion rate, on the dynamics of biochemical components and lipid classes in R. philippinarum. The data are discussed with regard to sexual development and energy balance. Experimental protocol developed in the present study used two groups of the clam R. philippinarum: L (temperatures of 14 degrees C and 18 degrees C) and H (temperatures of 18 degrees C and 22 degrees C). The intra-group ingestion level was similar, although the ingestion level of the clams in the group H was 2.4 times higher than group L. We observed that R. philippinarum conditioned at 18 degrees C (18L) shows higher protein content, furthermore an important loss of organic weight was observed after 48 days. In such a situation, the clams use their own reserves (carbohydrates and glycogen) for sexual development while in situations without food stress (positive energy balance) and low temperature (14 degrees C) an accumulation of reserves is produced. Strikingly dissimilar behaviour in biochemical composition was observed for the 18H and 22H treatments, both with a positive energy balance. Despite similar protein content, the highest levels of carbohydrates were observed at the lower temperature (18 degrees C). Glycogen was also higher for the 18 degrees C treatment, although the differences were significant only in the males. Although the total lipids in R. philippinarum showed no significant differences in any treatment, they became apparent and related to sex when considering the individual lipid classes. There was no variation in lipid classes in the males between the 14L and 22H treatments despite the large disparity in the degree of sexual development. However, in the females significant differences in lipid classes (phospholipids, triglycerides) were observed. The results of this study show that a positive energy balance permits R. philippinarum gonadal development and accumulation of reserves both in low and high temperature conditions. In low temperature situations, gonadal development is slower and the energy reserves are accumulated in the form of carbohydrates. When the clams are conditioned at high temperatures, gonadal development is fast and complete, carbohydrates are consumed and lipids are accumulated.

Effect of diet and temperature upon muscle metabolic capacities and biochemical composition of gonad and muscle in Argopecten purpuratus Lamarck 1819

Recently spawned Argopecten purpuratus broodstock were conditioned at two temperatures and fed three different diets (microalgae, microalgae mixed with lipids and microalgae mixed with carbohydrates) to examine changes in the biochemical composition of gonad and muscle as well as muscle metabolic capacities. During one experiment, scallops were fed at 3% of their dry mass per day whereas during a second experiment, they were fed at 6% of their dry mass per day. During both experiments, total gonadal levels of lipids and protein increased markedly during conditioning with the two mixed diets at 16 degrees C. These increases were less pronounced at 20 degrees C. Carbohydrate gonadal levels only increased during the second experiment at both temperatures and with the three diets. Of the major biochemical components of the adductor muscle, carbohydrate levels changed most during conditioning. Whereas muscle protein levels increased slightly with gonadal maturation, carbohydrate levels dropped considerably. Despite the marked drop in the levels of glycolytic substrates, only the activities of octopine dehydrogenase in the adductor muscle of the scallops conditioned at 16 degrees C consistently decreased. Muscle levels of glycogen phosphorylase were higher in mature than in recently spawned (control) scallops, suggesting a role in the transfer of glucose equivalents from the adductor muscle to other tissues.