Publisher Summary This chapter focuses on the rearing of bivalve mollusks. The rearing of larval and juvenile bivalves requires an adequate supply of sea water of proper salinity and free of substances that may interfere with their normal development. To condition mollusks for out-of-season spawning, it is necessary to keep them in running sea water at temperatures of 18°C to 20°C or sometimes higher. Warm sea water is also needed for rearing larvae and juveniles during the cold season. Conditioning of bivalves to develop mature gonads during the cold part of the year is relatively simple. It consists of placing mollusks, brought from their natural environment where water temperature may be near freezing, into somewhat warmer water, and then gradually increasing the temperature several degrees each day until the desired level is reached. Development of the egg of a bivalve is also discussed and the rearing of different species like Crassostrea virginica , Modiolus demissus , and Crassostrea gigas is reviewed.

Rearing of Bivalve Mollusks

CO2 emissions arising from the burning of fossil fuels have altered seawater chemistry far more rapidly than the Earth has previously experienced, and the rate and extent of this change are expected to affect shallow water marine organisms. The increased CO2 diffuses from the atmos- phere into ocean surface waters, resulting in increased partial pressure of CO2, and reduced (CO3 2- ) and pH. The CO2-driven ocean acidification leads to a decrease in calcium carbonate (CaCO3) satu- ration state in the ocean surface waters and has potential impacts on calcifiers. The present study focuses on the effects of ocean acidification on early developmental and reproductive stages of calci- fiers, both of which are believed to be the most vulnerable stages to environmental change within a life cycle. Laboratory experiments revealed that ocean acidification has negative impacts on the fer- tilization, cleavage, larva, settlement and reproductive stages of several marine calcifiers, including echinoderm, bivalve, coral and crustacean species. There appear to be significant ontogenetic impacts and species-specific differences in tolerance to the high CO2 levels. The conclusion is that future changes in ocean acidity will potentially impact the population size and dynamics, as well as the community structure of calcifiers, and will therefore have negative impacts on marine eco- systems. Further studies are needed to evaluate the potential impacts on non-calcifiers, as well as the synergistic impacts of ocean acidification and climate change. Studies should also focus on the adaptive capability of marine organisms, which will be crucial to the ability to forecast how marine organisms and ecosystems will respond to the world's oceans as they warm and acidify.

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Effects of CO2-driven ocean acidification on the early developmental stages of invertebrates

Over the next century, elevated quantities of atmospheric CO2 are expected to penetrate into the oceans, causing a reduction in pH (-0.3/-0.4 pH unit in the surface ocean) and in the concentration of carbonate ions (so-called ocean acidification). Of growing concern are the impacts that this will have on marine and estuarine organisms and ecosystems. Marine shelled molluscs, which colonized a large latitudinal gradient and can be found from intertidal to deep-sea habitats, are economically and ecologically important species providing essential

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Impacts of ocean acidification on marine shelled molluscs

Techniques for the induction of spawning of Mytilus edulis, the delay of spawning and the rearing of the larvae are described. The rate of growth of Mytilus larvae increased with increased temperature from 10–18° C, but from 13–18° C the growth was relatively temperature-independent. At temperatures higher than 18° C larvae from a littoral area grew at a slightly increased rate, but larvae from a sub-littoral area showed decline of the growth rate. There was a decline in the rate of growth during the life of a larvae at all temperatures. Cleavage and early development occurred from 8–18° C and increased with increased temperature. Isochrysis galbana and Monochrysis lutheri were good foods for Mytilus larvae. Growth rate increased with mcreased cell concentration to 100 cells Isochrvsis/µ litre and 2.0 µ litre packed cell volume of Monochrysis/litre. A mixture of these 2 species supported more rapid growth than either species indivldually. Larvae fed with Nannochloris atomus and Chlorella sp. grew...

Growth and the delay of metamorphosis of the larvae of Mytilus edulis (L.)

Planktonic marine invertebrate embryos and larvae lead transitory lives of great risk and grave uncertainty. Estimation of the magnitude of risk and mortality, however presents a formidable challenge. Three methods are currently in use to estimate levels of mortality among populations of marine invertebrate larvae: 1) theoretical models where rates of instantaneous mortality are correlated with other life history parameters, 2) estimation of mortality based on laboratory observations of predator-prey interactions and 3) analysis of relationships among gamete production, larval populations, and densities of post-larvae in the field. Theoretical exercises indicate that rates of larval mortality are correlated with duration of the planktonic period, and that differences in mortality rates may be offset by differences in egg size and fecundity. Results from laboratory investigations suggest that mortality rates change with larval size or age. Attempts to monitor cohorts of larvae in the plankton offe...

Natural mortality of marine invertebrate larvae

Rapid progress in studies of the morphology, physiology and ecological requirements of lamellibranch larvae, as well as other forms, can be achieved only if these organisms are easily available for study. This is seldom so in the case of lamellibranchs because the majority have a breeding period of comparatively brief duration lasting only a few months (Lebour, 1938; Thorson, 1946). During this period the larvae can be collected in plankton tows but, unfortunately, the early stages of many lamellibranchs are so alike in size and appearance that it is often impossible to distinguish with any degree of certainty the larvae of different species, or even genera. Thus, unless these larvae can be grown to metamorphosis their specific identity may remain in doubt. It is preferable, therefore, to work with larvae raised in the laboratory from fertilized eggs because in that case their identity cannot be questioned. In obtaining material for morphological and physiological studies of larvae the advantages of the direct method, i.e., the method of raising larvae in the laboratory, over the indirect method of collecting them in plankton and often only guessing their identity, are clear. However, because lamellibranch larvae are small, and because their free-swimming period is relatively long, they are difficult to culture. As a result, with the exception of a few successful attempts, mostly confined to commercially important species, such as oysters and mussels, few lamellibranchs have been grown in laboratories past the early veliger stage (Thorson, 1946). Therefore, the need for a simple but reliable method for culturing them is, of course, obvious. It is hoped that the simple but efficient method described in this article for conditioning the hard shell clam, V. mercenaria, to spawn out of season and for culturing its larvae will be applicable to many other species of lamellibranchs permitting their successful cultivation in the laboratory, where their morphological features and various aspects of behavior can be studied under controlled conditions. Realizing the importance of having a good supply of larvae for studies of the life history of Venus mercenaria, Belding (1912) tried to raise them in the laboratory. He was not successful because most of the larvae in his cultures died either before they reached the straight hinge veliger stage or soon afterwards. Belding concluded that there was no practical method for raising hard shell clams to the setting stage because of the small size and delicate nature of the eggs. Several years later, nevertheless, Wells (1927) succeeded in growing clam larvae to the setting stage. Wells, however, was mostly interested in oysters and did not continue the clam work.

Conditioning; mercenaria for spawning in winter and breeding its larvae in the laboratory.

1. The pH range for normal embryonic development of oysters was 6.75 to 8.75, and for clams, 7.00 to 8.75.2. More than 68% of the larvae of both clams and oysters survived at pH 6.25 to 8.75. The lower pH limit for survival of oyster larvae was 6.00 and for clam larvae, 6.25.3. The pH range for normal growth was 6.75 to 8.50 for clam larvae and 6.75 to 8.75 for oyster larvae. The rate of growth of both species dropped rapidly at pH levels below 6.75.4. The optimum pH for growth was 7.50 to 8.00 for clam larvae and 8.25 to 8.50 for oyster larvae.5. At pH 9.00 to 9.50 the percentage of eggs that developed normally, the percentage of larvae that survived, and the percentage increase in mean length of both species decreased rapidly.

THE pH TOLERANCE OF EMBRYOS AND LARVAE OF MERCENARIA MERCENARIA AND CRASSOSTREA VIRGINICA

1. Some clam eggs developed normally in concentrations of 4.0 g./l. of clay, precipitated chalk or finely ground Fuller's earth, although the percentage developing normally decreased as the concentration of these suspended materials increased.2. In silt concentrations below 0.75 g./l. the percentage of clam eggs developing normally was not significantly different from that in control cultures but decreased progressively in successively higher concentrations.3. None of the clam eggs developed normally in silt concentrations of 3.0 or 4.0 g./l.4. Larvae resulting from clam eggs developing in high concentrations of each of the suspended materials were reared to metamorphosis after being returned to normal sea water at 48 hours.5. Clam larvae were unable to grow in concentrations of clay, chalk or Fuller's earth as high as those at which some eggs developed.6. The highest concentration of chalk was 0.25 g./l. and 0.5 g./l. was the highest concentration of clay and Fuller's earth at which clam larvae showed an...

Effects of turbidity-producing materials in sea water on eggs and larvae of the clam (venus (mercenaria) mercenaria)

1. None of the 13 species of marine bacteria tested to date was utilized as food by oyster larvae.2. Five species of flagellates, Dicrateria inornata, Chromulina pleiades, Isochrysis galbana, Hemiselmis rufescens and Pyramimonas grossii, were utilized as food by oyster larvae, while another, an unclassified chrysomonad, in addition to the three flagellates previously reported, was not.3. Chlorella sp. was not utilized as food by young oyster larvae but was utilized during later larval stages.4. None of the combinations of foods tried gave any evidence of providing a more balanced diet or more rapid larval growth than could be obtained by feeding equivalent quantities of a single food. The effects of all foods tested, including Chlorella, are additive.5. When equal numbers of cells are fed, different species of flagellates induce different rates of growth of oyster larvae.6. Species of flagellates also differ in the number of cells needed to induce the maximum rate of growth of oyster larvae.7. The maximum...

Harry C. Davis

Papers

Rearing of Bivalve Mollusks

Conditioning; mercenaria for spawning in winter and breeding its larvae in the laboratory.

THE pH TOLERANCE OF EMBRYOS AND LARVAE OF MERCENARIA MERCENARIA AND CRASSOSTREA VIRGINICA

Effects of turbidity-producing materials in sea water on eggs and larvae of the clam (venus (mercenaria) mercenaria)

On food and feeding of larvae of the american oyster, c. virginica