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We examined the nursery role of salt marshes for transient nekton by searching the literature for data on density, growth, and survival of juvenile fishes and decapod crustaceans in marshes and using meta-analyses to test hypotheses. We analyzed density data from 32 studies conducted throughout the world. Based on fish density, habitat types could be ranked from highest to lowest as: seagrass > vegetated marsh edge, nonvegetated marsh, open water, macroalgae, oyster reefs > vegetated inner marsh. However, patterns of habitat use varied among the 29 fish species represented. For decapod crustaceans (seven species), habitat types were ranked: seagrass > vegetated marsh edge > nonvegetated marsh, vegetated inner marsh, open water, macroalgae > oyster reef. We identified only 5 comparative studies on transient nekton growth in salt marshes. Fish growth in nonvegetated salt marsh was not significantly different from growth in open water or in macroalgae beds but was significantly lower than in seagrass. Growth of decapod crustaceans was higher in vegetated marsh than in nonvegetated marsh. Nekton survival in salt marsh (11 studies analyzed) was higher than in open water, lower than in oyster reef/cobble and not significantly different from survival in seagrass. When density, growth and survival are all considered, the relative nursery value of salt marshes for nekton appears higher than open water but lower than seagrass. Vegetated marsh appears to have a higher nursery value than nonvegetated marsh; however, tidal dynamics and nekton movement among marsh components complicates these comparisons. The available data have a strong geographical bias; most studies originated in the northern Gulf of Mexico or on the Atlantic coast of the United States. This bias may be significant because there is some evidence that salt marsh nursery value is dependent on geography, salinity regimes and tidal amplitude.

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Climate has been linked to variation in marine fish abundance and distribution, but often the mechanistic processes are unknown. Atlantic croaker (Micropogonias undulatus) is a common species in estuarine and coastal areas of the mid-Atlantic and southeast coasts of the U.S. Previous studies have identified a correlation between Atlantic croaker abundance and winter temperatures in Chesapeake Bay, and have determined thermal tolerances of juveniles. Here we re-examine the hypothesis that winter temperature variability controls Atlantic croaker population dynamics. Abundance indices were analyzed at four life history stages from three regions along the east coast of the U.S. Correlations suggest that year-class strength is decoupled from larval supply and is determined by temperature-linked, overwinter survival of juveniles. Using a relation between air and water temperatures, estuarine water temperature was estimated from 1930 to 2002. Periods of high adult catch corresponded with warm winter water temperatures. Prior studies indicate that winter temperature along the east coast is related to the North Atlantic Oscillation (NAO); variability in catch is also correlated with the NAO, thereby demonstrating a link between Atlantic croaker dynamics, thermal limited overwinter survival, and the larger climate system of the North Atlantic. We hypothesize that the environment drives the largescale variability in Atlantic croaker abundance and distribution, but fishing and habitat loss decrease the resiliency of the population to periods of poor environmental conditions and subsequent weak year classes.

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We conducted a study to determine the trophic pathways leading to juvenile fish in 2 mesohaline tidal marshes bordering Delaware Bay. The relative roles of the major primary producers in supplying energy, ultimately, to the mummichog Fundulus heteroclitus were assessed by measuring the stable isotopic compositions of juveniles (21 to 56 mm total length, TL; most of which were young-of-the-year) and those of macrophyte vegetation, phytoplankton, and benthlc microalgae at each site. We collected samples of primary producers and F. heteroclitus, the dominant fish species in this and other marshes along the east coast of the USA, in June and August 1997, at 2 study sites (upstream and downstream) within Mad Horse Creek (a Spartina alterniflora-dominated site) and Alloway Creek (a Phragmites australis-dominated site), for a total of 4 study sites. Our results indicate that F. heteroclitus production is based on a mixture of primary producers, but the mixture depends on the relative abundance of macrophytes. In S. alterniflora-dominated marshes, C and S isotope ratios indicate that F. heteroclitus production is supported by S. alterniflora production (ca 39%, presumably via detritus), whde in P. australis-dominated marshes, secondary production is based upon P. australis (73%). To our knowledge, this finding provides the first evidence that P. australis may contribute to aquatic food webs in tidal marshes. Benthic microalgae also contribute to the food chain that leads to E heteroclitus in both marsh types, while phytoplankton may be of lesser importance. Benthic microalgal biomass was lower in the P. australis-dominated system, consistent with a greater effect of shading in P. australis-versus S. alterniflora-based creek systems. Based on the difference in nitrogen isotope values between F. heteroclitus and the primary producers, the trophic level of E heteroclitus appears to be similar in the 2 marsh types, despite the differing vegetation types. In summary, the relative roles of the primary producers in supplying energy to F. heteroclitus varies locally and, in particular, with respect to the type of marsh macrophyte vegetation.