An investigation of nutrient transfer in a restored eelgrass, Zostera marina, meadow

The contribution of seagrass primary production to nutrient flow in temperate marine systems is widely debated. The purpose of this work was to ascertain whether Zostera marina (eelgrass) comprises a measurable fraction of consumer diets in recently restored Z. marina meadows in South Bay, Virginia. Dominant primary producers, consumers, and higher trophic level fish were collected from restored meadows and adjacent habitats devoid of Z. marina. Two methods were employed to identify the nutritional contributions from local primary producers. First, the stable isotope values of primary producers were compared with those of consumers within both site types. Stable isotope analysis gave little indication that consumers were consuming live Z. marina directly. However, significant differences were found between the isotope values of fish from the Z. marina meadows compared with the sites without Z. marina, suggesting that the base primary production sources differ between the two habitats. In particular, there was a strong deviation in consumer isotope values between the two sites in the late summer following a major macroalgal biomass crash. The second method employed involved monitoring the transfer of primary producer fatty acids to primary and higher level consumers. Two invertebrate species and one fish from Z. marina meadows contained small amounts of seagrass-specific fatty acid biomarkers. Relatively high levels of bacterial fatty acid markers were noted in all consumers. As bacteria are major arbiters of nutrient recycling in marine systems it is likely that bacteria mediate the transfer of Z. marina primary production to higher consumers via decomposition of detrital material. The decomposing matter then enters the local food web through detritivores.;This study has identified direct and indirect food-web related effects related to restoration of Z. marina to South Bay. The structural presence and seasonal persistence of Z. marina in South Bay has indirectly influenced overall primary production utilization by consumers. While the direct dietary importance of live tissue appears to be very limited, there are indications that a few species assimilate dietary fatty acids derived from Z. marina. Assimilation of additional Z. marina primary production is also likely via ingestion of detritus and associated microbiota.