The stable isotope compositions (C and N) of plants and animals of a marsh dominated by Spartina alterniflora in the Delaware Estuary were determined. The study focused on the juvenile stage of the Atlantic blue crab, Callinectes sapidus, and the importance of marsh-derived diets in supporting growth during this stage. Laboratory growth experiments and field data indicated that early juvenile blue crabs living in the Delaware Bay habitat fed primarily on zooplankton, while marsh-dwelling crabs, which were enriched in C relative to bay juveniles, utilized marsh-derived carbon for growth. In laboratory experiments, the degree to which juvenile blue crabs isotopically fractionated dietary nitrogen, as well as the growth rate, depended on the protein quality of the diet. The range of δC of amino acids in laboratory-reared crabs and their diets was almost 20‰, similar to the isotopic range of amino acids of other organisms. In laboratory studies, the δC of nonessential and essential amino acids in the diet were compared to those in juvenile crabs. Isotopic fractionation at the molecular level depended on diet quality and the crabs' physiological requirements. Comparison of whole-animal isotope data with individual amino acid C isotope measurements of wild juvenile blue crabs from the bay and marsh suggested a different source of total dietary carbon, yet a shared protein component, such as zooplankton.

No abstract

No abstract

No abstract

No abstract

No abstract

Weekly abundance of larval blue crabs CaUinectes sapidus was determined during late summer (1983 and 1984) at 15 stahons on the inner continental shelf within 50 km of Delaware Bay, USA. Simultaneous measurements of subtidal, surface flow were made at 5 current meter stations within the study area. During both years, larval abundance was greatest during early August when concentrations in excess of 100 zoeae m-3 were commonly observed. By the thud week in September, early zoeal stages had &sappeared from the water column, and zoeal abundances at all stations were less than 10 zoeae Results of the current meter measurements provide firm evidence of sustained northward flow of surface water on the inner shelf off Delaware Bay during late summer when C. sapidus larvae are common in the plankton. This northward flow occurs on time scales relevant to the rate of larval development of C. sapidus and may b e important in retaining zoeae near the parent estuary.

No abstract