Biological and physical factors influencing invertebrate community structure of natural and planted seagrass beds

Various biological and physical factors have been hypothesized to explain the benthic community structure of seagrass habitats. An opportunity was presented to evaluate some of these factors in natural and created seagrass beds in Galveston Bay, Texas. The experimental design for these created seagrass beds permitted an evaluation of effects from water depth, planting density, and distance to edge on benthic community composition. Following the initial planting benthic core samples were collected for 16 months to assess the development of the invertebrate community. Sandflats adjacent to the planted sites and a natural seagrass bed were used for comparison.;Organisms were enumerated and identified to species when possible which yielded 164 species or taxonomic groups. Annelids were the dominant organisms in both planted and natural beds and defined most of the trends observed in the final analyses. After 16 months species richness and abundance within the planted seagrass beds increased relative to adjacent sands, however, epibenthic and infaunal densities and species composition did not reflect those of the natural seagrass bed. The highest planting densities, 0.25 m centers, contained the greatest number of individuals and species. Numbers of individuals and species were negatively affected by water depth, and distance to edge of the planted sites had no effect. Shallow water and 0.25 m centers had the highest abundance of organisms, whereas deeper water and 1.00 m centers had the lowest when water depth and planting density interactions were considered.;Variability in the number of individuals and species of new recruits is considered an important contribution to variability within the adult community of some benthic systems. Benthic communities in seagrass habitats had greater diversity, higher abundances, and different assemblages of organisms when compared to adjacent sandflats. Settlement traps were utilized to test the hypothesis that larval supply equally affects benthic community structure in two habitats. Traps were set in the sediments of a seagrass bed and sandflats with twice-weekly sample collections from February through April 1996. Analysis indicated that larval supply did have an effect on the adult community of some taxa, but hydrodynamic processes may have masked relationships for many others.