Charles E. Epifanio

Growth in bivalve molluscs: Nutritional effects of two or more species of algae in diets fed to the American oyster Crassostrea virginica (Gmelin) and the hard clam Mercenaria mercenaria (L.)

Abstract Each of 15 experimental groups of American oysters and hard clams was fed one of 15 diets composed of various mixtures of four species of algae ( Carteria chui, Isochrysis galbana, Platymonas suecica, Thalassiosira pseudonana ) for 6 weeks. Growth of hard and soft tissue was not correlated with gross chemical (protein, lipid, carbohydrate, ash) or amino acid composition of the diets but was instead related to the presence or absence of particular algal species in the diets. Growth was generally least in diets containing large proportions of C. chui and greatest in diets containing large amounts of I. galbana or T. pseudonana . Diets containing both I. galbana and T. pseudonana invariably supported greater growth than diets consisting solely of either species, indicating synergism in the relative food values of the species. P. suecica was a relatively poor food when used as the sole component of the diet, but its food value was markedly increased when fed in combination with either (or both) I. galbana or (and) T. pseudonana . Two contrasting hypotheses explaining this interaction are presented.

Dispersal and recruitment of blue crab larvae in Delaware Bay, U.S.A.

Abstract Results of a three-year survey of the occurrence of Callinectes sapidus larvae in the mouth of Delaware Bay indicated that stage I zoea larvae were most abundant insurface water as compared to mid-depths and near bottom. The major peak in abundance of stage I zoea larvae occurred in early August with a secondary peak in early September. Peaks in abundance of megalopae occurred five weeks after the respective peaks in zoeal abundance. Zoea stages II–VIII were not collected in the bay mouth. Results of sampling every 3 h over consecutive tidal cycles showed that stage I zoea larvae were most common in the water column on ebbing tidal currents. Megalopae were most common in the water column on flooding tidal currents, suggesting a tidally related, vertical migration. It was concluded that stage I zoea larvae are flushed from the estuary and undergo development on the continental shelf. Megalopae are then transported back to inshore waters by a combination of winds and currents and invade the estuary by means of migration into the water column on flooding tidal currents and migration to the bottom on ebbing tidal currents.

Seasonal abundance and vertical distribution of crab larvae in Delaware Bay

Larvae of 15 species or genera of crabs were collected and identified during a six month (May 26 to October 28, 1978) study in the mouth of Delaware Bay. Seasonal abundance and vertical distribution of each species were investigated. Most species studied had peak abundance in July and August except forCancer irroratus andOvalipes ocellatus which showed peak occurrence in May and June, respectively. Larvae of species strongly dependent on estuarine habitats, such asUca spp.,Pinnixa chaetopterana, andP. sayana, showed a tendency to congregate in near-bottom waters where net flow of water is landward, thus favoring retention within the estuary. Larvae ofOvalipes ocellatus, Cancer irroratus, andCallinectes sapidus were more common at the surface. This vertical distribution suggests that these larvae are flushed out of the estuary. The mechanisms of recruitment and replenishment of adult populations within the estuary would therefore depend on migration of megalopa and juveniles. *** DIRECT SUPPORT *** A01BY019 00006

Maximum ration of four algal diets for the oyster Crassostrea virginica Gmelin

Abstract The rate of removal of four species of alga from suspension by the oyster Crassostrea virginica was determined. The number of cells removed per hour depended upon the size of algal cells, but the total dry weight of algal material removed over 24 h was independent of size. Filtration rate was dependent upon the density of the algal suspension, and large quantities of pseudofeces were produced by oysters filtering algae from suspensions denser than 10 μg/ml. Oysters showed periods of high filtering activity and periods of relative quiescence during experimental trials of 24 h duration. Based on the periodic filtering activity of the oysters, a discontinuous feeding regime is proposed along with an equation predicting the maximum daily ration of oysters of various sizes.

Comparison of yeast and algal diets for bivalve molluscs

Abstract Four species of bivalve molluscs were fed diets consisting of varying proportions of the yeast Candida utilis and the diatom Thalassiosira pseudonana . Juvenile Argopecten irradians, Mercenaria mercenaria , and Mytilus edulis grew as fast or faster than controls when fed diets containing as much as 50% yeast. Growth of soft tissue in Crassostrea virginica , however, decreased with the amount of yeast in the diet. The relative food values of the different diets were not closely correlated with gross chemical composition or amino acid composition.

Comparative effects of diets consisting of one or two algal species upon assimilation efficiencies and growth of juvenile oysters, Crassostrea virginica (Gmelin)

Abstract Juvenile oysters, Crassostrea virginica , were fed one of six diets consisting of three species of algae fed singly or in two-species combinations. Dietary components were Isochrysis galbana (Diet I), Platymonas suecica (Diet P), and Thalassiosira pseudonana (Diet T). High (Diet TI), intermediate (Diets T, I, PT, PI), and low (Diet P) growth responses were observed. Intermediate and low growth responses were explained in terms of differing levels of ingestion and assimilation. The high growth response with Diet TI was not explained by measured values of ingestion and assimilation.

The estuarine character of the Gulf of Nicoya, an embayment on the Pacific coast of Central America

Hydrography and exchange processes in a tropical estuary, the Gulf of Nicoya, Costa Rica, are described from data collected in 1979 and 1980. The measurements and analyses were made in both the dry season and wet season and include temperature, salinity, and density at twenty locations in the gulf and currents (over a semi-diurnal tidal cycle) at five locations. These new results enlarge on the early study by Peterson (1958). Circulation in the lower gulf shows a marked east-west asymmetry due to the predominant runoff along its eastern shore from Rio Barranca and Tarcoles. The freshened surface water from the upper gulf combines with the runoff from these rivers and flows southward along the eastern side of the lower gulf. This flow is compensated by a northward flow of more saline water on the western side at all depths and on the eastern side along the bottom. The boundary between the southward and northward surface flow is marked by a strong salinity front in the rainy season. There is a rapid increase in tidal energy density toward the shoaling northern reaches of the lower gulf, between San Lucas Island and Puntarenas Peninsula. Enhanced mixing must accompany this increase, and direct measurements in the constriction between San Lucas and Puntaneras show that tidal mixing is dominant in transporting salt into the upper gulf against the freshwater runoff.

Abundance of brachyuran larvae in a small coastal inlet over six consecutive tidal cycles

Brachyuran larvae were sampled every two hours at two depths in Indian River Inlet over six consecutive tidal cycles. Larvae from seven taxa were collected. Three taxa were identified at the level of species. Pinnixa spp. and Uca spp. zoeae were most common at the surface on ebbing tides and were apparently exported to coastal shelf waters. Uca spp. and Callinectes sapidus megalopae were common near the bottom on flooding tides. This would promote retention in the estuary and is consistent with previous reports in the literature. Ovalipes ocellatus, Cancer irroratus and Libinia spp. were most common on flooding tides. This suggests that a pool of these larvae existed in adjacent coastal waters, and that these larvae were carried into the inlet on flooding tides.

A comparison of Phaeodactylum tricornutum and Thalassiosira pseudonana as foods for the oyster, Crassostrea virginica

Abstract Juvenile oysters, Crassostrea virginica, were fed diets consisting of varying proportions of the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. Growth of the oysters over a 5-week period was inversely proportional to the amount of P. tricornutum in the diet. Analysis of the diatoms showed similar amounts of protein and lipid in the two species, while P. tricornutum was higher in carbohydrate and T. pseudonana higher in ash. P. tricornutum lacked the essential amino acid tryptophan, but this deficiency has been reported for other diatom species that are good foods for bivalves.

Predation on mud crab megalopae, Panopeus herbstii H. Milne Edwards: effect of habitat complexity, predator species and postlarval densities

Abstract Laboratory experiments were conducted to evaluate the magnitude of predation on megalopae of the Atlantic mud crab, Panopeus herbstii H. Milne Edwards, in four simulated habitats (salt marsh bottom, shell bottom, seaweed patch and sand bottom). Predators included juvenile blue crabs (Callinectes sapidus Rathbun), common killifish (Fundulus heteroclitus (L.)) and grass shrimp (Paleomonetes pugio Holthius). Experiments were run at two different densities of megalopae. Two-way analysis of variance revealed significant effects of predator type and substratum. Proportional mortality was lowest on shell bottom, and blue crabs were the least effective predators, regardless of habitat. Additionally, proportional mortality was lower at low megalopal densities than at high megalopal densities. Decreased predation at low megalopal abundance may afford density-dependent modulation of mud crab populations.