Urban Land-Use Effects on Resident Saltmarsh Fish in the Gulf of Mexico

Abstract

Salt marshes are valuable ecosystems and provide a number of important services, including providing habitat for fish. Urban land-use has been shown to alter salt marshes through changes in the hydrology, sedimentation, and vegetation, but little is known about how urban land-use near salt marshes impacts fish. In this study I compared resident fish in urban and reference salt marshes in tidal creeks of Alabama and west-Florida. Reference creeks had very little surrounding development (<3.0 houses km shoreline-1) while urban creeks had ≥30.0 houses km shoreline-1. Fish were sampled seasonally for one year along salt marsh edges using baited minnow traps and results were used to characterize fish communities. In addition two common salt marsh resident fish, Fundulus grandis and Poecilia latipinna, were evaluated to determine the impacts of urban land-use on fish condition through Liver Somatic Index (LSI), caloric density, and tissue concentration of metal contaminants. To help interpret fish data, marshes also had various habitat attributes assessed including: plant species composition and biomass, sediment contaminants, slope, salinity, and temperature. Fish abundance and length-weight regressions were compared for common species in addition to characterizing fish communities at both urban and reference marshes. Fish communities varied with season, but reference creek communities were consistently dominated by Fundulus grandis. Urban creeks had higher abundance of other species including Poecilia latipinna, Fundulus confluentus, Gambusia holbrooki, and Adinia xenica. Length-weight relationships showed that F. confluentus, A. xenica, C. variegatus, and F. confluentus were larger at urban marshes, while G. holbrooki was smaller. Based on the results of a nonmetric multidimensional scaling (NMDS) ordination and a Poisson generalized linear model, urban and reference fish assemblages were significantly correlated with salinity, slope, and sediment contaminants. Condition measures showed F. grandis had lower LSI and caloric density at urban salt marshes compared to reference. However, P. latipinna did not have significantly different condition measures at urban salt marshes compared to reference. Both species showed seasonal patterns related to conditional measures that were likely related to reproduction and annual fattening cycles. Except for zinc, no significant differences were detected in metal concentration between urban and reference F. grandis and many metals associated with urban runoff (Cd, Cr, Pb) were below detection levels for fish from both creek types. Differences in fish condition, fish size and fish community at urban marshes are likely a result of an altered salinity regime and other habitat alterations.