Trophic relationships of juvenile blue crabs (Callinectes sapidus) in estuarine habitats |
| |
Authors: | Ana I Dittel Charles E Epifanio Marilyn L Fogel |
| |
Institution: | (1) College of Marine Studies, University of Delaware, Lewes, DE 19958, USA;(2) Carnegie Institution of Washington, Washington, DC 20015, USA |
| |
Abstract: | Salt marshes and shallow-water macroalgal beds are known to provide nursery habitat for many species of fish and invertebrates.
The role of these habitats as refuge from predation is well established, but the degree to which indigenous primary production
within the nursery provides food for growth and development of estuarine species remains unresolved. In this study, we tested
the hypothesis that juvenile blue crabs depend on indigenous primary production, directly or indirectly, during their entire
stay within the nursery. To test this hypothesis, we conducted isotopic studies and stomach content analyses of juveniles
from habitats near the mouth of Delaware Bay and from an adjacent lagoonal estuary (ca. 39.5° N, 75.1° W). Primary producers,
marsh detritus, various life-history stages of blue crabs and potential prey species were sampled in the main estuary and
in an adjacent marsh during the summer and early fall of two consecutive years. Newly settled juveniles (<15 mm carapace width)
from the marsh were about 1.8‰ lighter in carbon (−17.2‰) relative to larger juveniles from the marsh (15–30 mm carapace width)
and appeared to have retained a carbon isotopic signature indicative of the phytoplankton-based food web associated with larval
stages. However, the signature of juveniles changed as a function of size. Large juveniles and crabs >60 mm were enriched
in δ13C (−14.7 ± 0.1‰) compared to small crabs, suggesting a gradual shift in diet from a planktonic to a detritus-based food web
with increasing size. As with crabs from Delaware Bay, the δ13C signature of juvenile crabs sampled from macroalgal beds in the lagoonal estuary (Rehoboth Bay) changed as a function of
size. Also, δ13C ratios of crabs varied among the various species of macroalgae. The δ15N composition of primary producers in the marsh and main estuary also was reflected in the δ15N values of crabs and other benthic consumers in the respective habitats. Results of stomach-content analysis in this study
were consistent with isotope data. Observed changes in prey preferences were related to changes in size of juvenile crabs
and also differed among habitats. Gut content analyses of the three size classes of juveniles in macroalgal beds from Rehoboth
Bay indicated that the crabs depend heavily on various amphipod species that occur on the seaweeds. These amphipods graze
directly on the macroalgae and are among the most abundant invertebrates in the macroalgal beds. This implies a direct trophic
relationship between the juvenile crabs and the macroalgae. In summary, our study provides strong evidence that the value
of nursery areas such as salt marshes and macroalgal beds goes beyond that of providing refuge from predation, and that species
using these nurseries (e.g. juvenile blue crabs) are ultimately dependent on primary production originating in benthic plants
indigenous to the nursery. |
| |
Keywords: | stable isotopes carbon and nitrogen sources food webs blue crab juveniles |
本文献已被 SpringerLink 等数据库收录! |
|