NEKTON USE OF VEGETATED MARSH HABITATS AT DIFFERENT STAGES OF TIDAL INUNDATION

Fishes and crustaceans are potentially important vectors for the trans fer of production from intertidal marshes to subtidal estuarine enviro nments. Because marsh habitats are accessible to nekton only when tida lly inundated, understanding variation in habitat use associated with the tidal cycle is crucial for estimating the magnitude of production transfers attributable to nekton populations. We compared species rich ness, abundance and size distributions of nekton on incoming, slack hi gh and ebbing stages of spring tides at 2 vegetated intertidal marsh s ites (25 and 90 m from the nearest tidal creek) on Sapelo Island, Geor gia, USA. The findings showed how use of an intertidal marsh by nekton varied on temporal and spatial scales pertinent to understanding salt marsh community and ecosystem dynamics. A total of 9627 individuals d istributed among 17 species of fishes and 4 species of decapod crustac eans were collected from 60 samples of 100 m2 each during June to Augu st 1991. The cyprinodontids Fundulus heteroclitus and F. luciae accoun ted for 90.2% of all fishes; caridean Palaemonetes pugio and penaeid P enaeus setiferus shrimps composed 99.8% of the decapod crustaceans. In general, nekton abundance and species richness were greatest at slack high tide. In contrast to the depth distribution patterns usually obs erved at low tide, most of the smaller size classes of nekton that use d the vegetated marsh at high tide were in the deeper site nearest the creek while larger size classes penetrated farther into the marsh int erior. The amount of intertidal marsh production transfered to subtida l estuarine habitats by different species of nekton may depend on how each responds, on balance, to the expanded foraging opportunity presen ted when the marsh floods and the risk of being stranded in the intert idal zone when the tide ebbs.