Food Web Structure in a Chesapeake Bay Eelgrass Bed as Determined through Gut Contents and 13C and 15N Isotope Analysis
Changes in seagrass food-web structure can shift the competitive balance between seagrass and algae, and may alter the flow of energy from lower trophic levels to commercially important fish and crustaceans. Yet, trophic relationships in many seagrass systems remain poorly resolved. We estimated the food web linkages among small predators, invertebrate mesograzers, and primary producers in a Chesapeake Bay eelgrass (Zostera marina) bed by analyzing gut contents and stable C and N isotope ratios. Though trophic levels were relatively distinct, predators varied in the proportion of mesograzers consumed relative to alternative prey, and some mesograzers consumed macrophytes or exhibited intra-guild predation in addition to feeding on periphyton and detritus. These findings corroborate conclusions from lab and mesocosm studies that the ecological impacts of mesograzers vary widely among species, and they emphasize the need for taxonomic resolution and ecological information within seagrass epifaunal communities.
KeywordsMesograzer Diet Seagrass Stable isotope Omnivory Food web
We thank J. Paul Richardson, Rachael E. Blake, Romuald Lipcius, Paul Gerdes, and others for help and advice with field and lab work, and we thank David Harris and the staff of the UC Davis Stable Isotope Facility for invaluable sample processing services. This work was supported by grant #XXXXXX to J.E. Duffy. This is VIMS contribution #XXXX.
- Bobsien, I.C. 2006. The role of small fish species in eelgrass food webs of the Baltic Sea. Dissertation, Christian-Albrechts-Universität zu Kiel, GermanyGoogle Scholar
- Haahtela, I. 1984. A hypothesis of the decline of the bladder wrack (Fucus vesiculosus L.) in SW Finland in 1975–1981. Limnologica 15: 345–350.Google Scholar
- Jernakoff, P., A. Brearly, and J. Nielsen. 1996. Factors affecting grazer–epiphyte interactions in temperate seagrass meadows. Oceanography and Marine Biology: An Annual Review 34: 109–162.Google Scholar
- Kangas, P., H. Autio, G. Haellfors, H. Luther, A. Niemi, and H. Salemaa. 1982. A general model of the decline of Fucus vesiculosus at Tvaerminne, south coast of Finland in 1977–81. Acta Botanica Fennica 118: 1–27.Google Scholar
- Mansour, R.A. (1992). Foraging ecology of the blue crab, Callinectes sapidus Rathbun in lower Chesapeake Bay. Dissertation, Virginia Institute of Marine Science, College of William and Mary, VirginiaGoogle Scholar
- Nelson, W.G. 1980. A comparative study of amphipods in seagrasses from Florida to Nova Scotia. Bulletin of Marine Science 30: 80–89.Google Scholar
- Stoner, A.W., and B.A. Buchanan. 1990. Ontogeny and overlap in the diets of four tropical Callinectes species. Bulletin of Marine Science 46: 3–12.Google Scholar
- Tagatz, M.E. 1968. Biology of the blue crab, Callinectes sapidus Rathbun, in the St. Johns River, Florida. Fisheries Bulletin 67: 17–33.Google Scholar
- Virnstein, R.W. 1978. Predator caging experiments in soft sediments: caution advised. In Estuarine interactions, ed. M.L. Wiley, 261–273. New York: Academic.Google Scholar
- Williams, S.W., and K.L. Heck Jr. 2001. Seagrass communities. In Marine community ecology, ed. M. Bertness, S. Gaines, and M. Hay, 317–337. Sunderland: Sinauer.Google Scholar