Feeding patterns of salt marsh fishes

Salt marshes are widely recognized as faunal nurseries but feeding studies of salt marsh fishes have often focused on a single species (Fundulus heteroclitus). To accurately assess the feeding habits of salt marsh fishes, fish must be sampled after feeding inside the marsh and after feeding in the outer estuary because fish exit the marsh during outgoing tides and reenter with incoming tides. Three species (Fundulus heteroclitus, Fundulus majalis, Menidia menidia) were consistently collected with a fyke net and were subjected to intraspecific comparisons of diets between the salt marsh and the outer estuary using the modified form of Morisita's index. Fundulus majalis consumed gastropods (Hydrobia sp., Littorina spp.) frequently in the marsh and rarely outside the marsh. The bivalve (Gemma gemma) was consumed in both environments. Molluscs numerically dominated the diet across all sampling seasons and years.{09}During fall, non-molluscan prey were almost excluded from the marsh diet and this led to a diet shift between the salt marsh and the outer estuary. Fundulus heteroclitus is known to feed actively during high tide periods and a higher proportion of empty guts at the end of low tides in this study reflects this pattern. Its diet is not dominated by a few prey taxa. For Fundulus heteroclitus, diet shifting between the marsh and the outer estuary appears to be related to its highly diversified diet. Diet overlap measures for Menidia menidia are seasonally influenced. Copepods numerically dominate the prey count during spring, early summer, and fall in the marsh and in the outer estuary. Diet shifting occurs in July when additional zooplanktivorous, nektonic and benthic prey are consumed. Consumption of seasonally available brachyuran megalops, ostracods and harpacticoids by smaller Fundulus majalis does not always lead to a measurable ontogenetic diet shift between size ranges from the same sample. Diet diversification in Fundulus heteroclitus increases with fish size and diet shifts between size ranges are measurable. Ontogenetic diet differentiation in Menidia menidia was minimal in spring and fall when copepods dominated the diets. A shift occurs in July, as smaller Menidia menidia continue to consume copepods while larger fish consume megalops.