Habitat use, secondary production, and trophic export by salt marsh nekton in shallow waters

I used 1.75 m&\sp2& drop rings and throw rings to sample communities of nekton at high and low tides in contiguous salt marshes, unvegetated flats, and seagrass beds (Ruppia maritima) of lower Chesapeake Bay. Thirty-two species of nekton were captured between June and October 1995, with a mean overall abundance of 28.6 inds m&\sp{lcub}-2{rcub}& and a mean biomass of 3.8 g m&\sp{lcub}-2{rcub}& (dry weight, dw). Blue crabs, Callinectes sapidus, were the biomass dominants and used seagrass and marsh edge habitats extensively from recruitment to maturity. Palaemonetes shrimp were the most abundant nekton; patterns of allopatry and apparent sympatry were found among the three species present. Menidia menidia used the marsh surface at night. Behavioral patterns for marsh residents Fundulus heteroclitus, F. majalis, Lucania parva, Gobiosoma bosc, and P. intermedius differed from patterns reported elsewhere. This suggests behavioral flexibility in habitat use between regions. Seagrass and marsh edges supported a large biomass of nekton. Secondary production on the marsh surface was estimated at 7.4-8.0 gdw m&\rm\sp{lcub}-2{rcub}150\ d\sp{lcub}-1{rcub}& (28.4-30.7 gww m&\rm\sp{lcub}-2{rcub}150\ d\sp{lcub}-1{rcub}&) between June and October 1995 (150 days). Gut contents of predators were examined, and a mathematical model was constructed to estimate consumption and export by nekton. Predation on invertebrates was highest in marsh edge areas, at 44.2 gdw m&\rm\sp{lcub}-2{rcub}150\ d\sp{lcub}-1{rcub}& removed; predation at the edge by transients (export) was 28.0 gdw m&\rm\sp{lcub}-2{rcub} 150\ d\sp{lcub}-1{rcub}.& The value of marsh edge was clearly linked to both vegetated and unvegetated components as refuge and feeding. Predation in the entire marsh was approximately 13 gdw m&\rm\sp{lcub}-2{rcub} 150\ d\sp{lcub}-1{rcub},& and transient export was 5.6 gdw m&\rm\sp{lcub}-2{rcub} 150\ d\sp{lcub}-1{rcub}.& Most export from marsh interior habitats was via blue crab predation on Uca and Sesarma. Predation in unvegetated areas was 13.3-17.0 gdw m&\rm\sp{lcub}-2{rcub} 150\ d\sp{lcub}-1{rcub};& export was 8.0-11.7 gdw m&\rm\sp{lcub}-2{rcub}150\ d\sp{lcub}-1{rcub}.& The unvegetated intertidal was an important resource for nekton due to lengthy inundation and abundant polychaete prey. The trophic contribution of each habitat was significant. Marsh, unvegetated, and seagrass habitats function together in this area to provide feeding and refuge for intertidal nekton