MEPS 194:103-112 (2000)  -  doi:10.3354/meps194103

Carbon and nitrogen sources for juvenile blue crabs Callinectes sapidus in coastal wetlands

A. I. Dittel 1,*, C. E. Epifanio1, S. M. Schwalm1, M. S. Fantle2,**, M. L. Fogel2

1University of Delaware, College of Marine Studies,700 Pilottown Road, Lewes, Delaware 19958, USA
2Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA
*E-mail: **Present address: Dept. of Earth Sciences, University of Cal-ifornia at Berkeley, Berkeley, California, USA

ABSTRACT: We used a combination of field and laboratory techniques to examine the relative importance of food webs based on marsh detritus, benthic algae, or phytoplankton in supporting growth of the blue crab Callinectes sapidus. We conducted a laboratory experiment to compare the growth of newly metamorphosed juveniles fed natural diets from potential settlement habitats such as marshes. The experimental diets consisted of zooplankton, Uca pugnax and Littoraria irrorata tissue, a mixture of plant detritus and associated meiofauna and detritus only. Crabs fed the zooplankton diet showed the fastest growth and reached a mean dry weight of 32.4 mg, from an initial dry weight of 0.8 mg, during a 3 wk period. Based on the isotopic composition, juvenile crabs obtain carbon and nitrogen from various food sources. For example, crabs fed zooplankton obtained their nutrition from phytoplankton-derived organic matter, consistent with zooplankton feeding on phytoplankton. The mean δ13C values for juveniles fed detritus and detritus-plus-meiofauna were considerably lighter (δ13C = -19 o/oo), than that of their respective diets ( δ13C = -16 o/oo), suggesting that crabs were selectively ingesting prey items that obtain their nutrition from an isotopically lighter carbon source like phytoplankton. Conversely, crabs fed U. pugnax or L. irrorata had isotopic ratios (δ13C = -16 to -14 o/oo) consistent with these species feeding on isotopically heavier marsh grass carbon. Isotopic ratios of crabs collected in the field appeared to corroborate the experiment and suggest that either Spartina alterniflora detritus or benthic algae-based food webs supported juvenile crab growth in marsh environments, whereas phytoplankton-based food webs dominate habitats more closely associated with the main estuary.

KEY WORDS: Callinectes sapidus · Juveniles · Growth · Stable isotopes · Carbon and nitrogen · Salt marsh · Food web

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