Utilization of natural and transplanted Texas salt marshes by fish and decapod crustaceans

Habitat utilization by fish and decapod crustaceans was compared among 3 transplanted and 3 natural Spartina alterniflora marshes on the Texas (USA) coast during spring 1986. Created marshes had been transplanted on dredged material and were approximately 2 to 5 yr old at the time of sampling. Although conclusions are limited to the spring season, the use of replicate marshes allowed us to test the null hypothesis that transplanted marshes on the Texas coast were equivalent to natural marshes. Mean values for stem density and above-ground biomass of S. alterniflora were consistently higher in the transplanted marshes, and the difference was statistically significant for stem density. Macro-organic matter (MOM) in the upper 5 cm of sediment was significantly lower in the transplanted marshes. Densities of polychaetes and amphipods within transplanted marshes were positively correlated with this MOM. Transplanted marshes had significantly lower densities of decapod Crustacea (primarily daggerblade grass shrimp Palaemonetes pugio and juvenile brown shrimp Penaeus aztecus) compared with natural marshes. This reduced utilization may have been a response to low densities of benthic food organisms, and densities of decapods were positively correlated with densities of prey in sediment cores. In contrast to the utilization pattern of decapods, densities of fish (dominated by the darter goby Gobionellus boleosoma and pinfish Lagodon rhomboides) were similar between natural and transplanted marshes. These small fish may rely on salt marshes more for protective cover than for enhanced food resources, and above-ground structure in the transplanted marshes may have adequately provided this function. Comparisons of functional equivalency between natural and transplanted salt marshes require adequate information on how salt marshes actually function for fish and decapod crustaceans. For example, the use of prey density as an indicator of food value in a marsh can be misleading unless trophic pathways are well understood and access to the marsh surface is considered.