Variation of Nursery Habitat Quality in a River-Dominated Estuary: A Diet Study of an Estuarine-Dependent Fish

The value of estuaries as nursery habitat for juvenile fishes depends on their connection with coastal watersheds that provide nutrients, freshwater, and other materials essential to the productivity of these ecosystems.  This connectivity is of particular importance for river-dominated estuaries, such as Apalachicola Bay, which is one of the most productive estuaries in the northern hemisphere.  Apalachicola Bay experiences considerable spatial and temporal variation in hydrography and flow of alluvial materials due to both natural processes and anthropogenic activities in the watershed.  Variation in nutrient and fresh water inputs to the Bay may alter the foraging value of these habitats for juvenile estuarine-dependent fishes.  Using juvenile spot as a model species, I am testing the hypothesis that spatial and temporal variation in diet composition and foraging success within Apalachicola Bay is related to seasonal variation in river flow and associated environmental conditions.  The diets of over 300 juvenile spot (9 – 210 mm standard length) sampled monthly in 2009 and 2010 from 12 locations throughout Apalachicola Bay were included in this analysis.  Stomach fullness was quantified and contents were identified to the lowest possible taxonomic level, counted, and the volume of each prey category estimated.  The relative importance and percent frequency of occurrence of individual prey items was then calculated.  Prey items of juvenile spot included harpacticoid and calanoid copepods, ostracods, small bivalves, nematodes, amphipods, and polychaetes.  Freshwater chironomid larvae and detrital material were important dietary components during the spring, high flow season.  An index of feeding intensity and the relative importance of different prey groups will be compared among regions of Apalachicola Bay that differ in the degree of riverine influence to test the hypothesis that foraging dynamics of juvenile spot vary in relation to river flow. Continued diet and future analyses of stable isotopes and nutritional condition over two years will contribute to a better understanding of how riverine inputs influence the foraging ecology of juvenile spot during their residency in estuarine nursery habitats.