Salt marshes as nurseries for nekton: testing hypotheses on density, growth and survival through meta-analysis

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.