Each winter in the Florida Big Bend Region millions of kilograms of fish and invertebrates migrate from their summer home in the seagrass beds to over-winter and/or spawn as far as 100 Km away on offshore reefs. We hypothesize that this egress constitutes a major flux of carbon and nutrients to offshore food webs. Furthermore, we hypothesize the timing of this egress contributes directly to the reproductive productivity of gag grouper (Mycteroperca microlepis) a highly valuable fisheries species that spawns in the late winter and early spring. We utilized stable isotopes (13C and 34S) as naturally occurring tracers to track this fluxed material from Florida Big Bend near-shore seagrass beds to the highly productive offshore reef fish communities.
Results/Conclusions Stable isotope values of fish muscle tissue collected from species occurring on offshore reefs at three depth stratums in the N.E. Gulf of Mexico (23m, 37m, and 49m) indicate that a significant amount of estuarine derived production is incorporated into the food webs at the shallowest (23m) sites. Species on the deeper sites appear to have a single source of pelagic primary production. However, isotope values of gag grouper captured at depths >30m indicate that estuarine production contributes 15-20 % to gag grouper biomass. Seasonal stable isotope values of gag grouper gonad tissue indicate that a significant portion of egg production is derived from estuarine sources. Our results confirm that estuarine-derived production is a significant food source for shallow water reef fish communities in the N.E. Gulf of Mexico and contributes directly to the reproductive productivity of gag grouper. Such large scale trophic linkages are virtually unstudied, but may be extremely important to maintaining community structure and ecosystem services, such as fisheries, particularly in temperate coastal zones.
