The stable carbon isotope ratio of some components of an eelgrass, Zostera marina, bed

Abstract

Living and dead Zostera marina blades, plankton samples, sediments, and several animal components of an eelgrass bed near Beaufort, N.C. were collected and analyzed for ¹³C/¹²C ratios (δ ¹³C). The δ ¹³C values of producer and consumer organisms were compared in order to examine the possible origins of organic matter present in the consumers. Living and dead eelgrass blades displayed similar δ¹³C values,-12.2 and-10.6 per mil ‰ respectively, while the epiphytic community growing on the grass blades had a mean isotope ratio of-16.0‰. Animal components analyzed represented five major feeding-mode categories: invertebrates living on grass blades an presumably feeding on the epibiota (-15.1‰), deposit feeding invertebrates (-15.0‰), predatory and omnivorous invertebrates (-16.7‰), suspension and surface feeding invertebrates (-18.3‰) and omnivorous fish (-16.8‰). Organisms commonly found on the grass blades appeared to feed primarily on the epibiota growing on the blades. It is hypothesized that the epibiota derive some of their carbon from DOC released by the Zostera blade. The urchin, Lytechinus variegatus, and the brittle star, Ophioderma brevispinum, both deposit feeders, appeared to derive a major proportion of their carbon from eelgrass. With the exception of the shrimp, Alpheus heterochaelis, and the pipefish, Syngnathus floridae, the majority of other organisms analyzed appeared to be linked more directly to a plankton-carbon food chanin than to a seagrass-carbon system in this relatively young eelgrass bed.