Factors affecting the community composition of epibenthic and infaunal invertebrates of newly planted seagrass beds

Epibenthic and infaunal organisms represent an important link between macrofauna and the seagrass beds they utilize. Consequently, benthic organisms should be taken into account when assessing the structural and functional equivalency of planted beds in relation to natural seagrass beds. Three Halodule wrightii beds were planted during May 1994 in western Galveston Bay, Texas. The experimental design allowed for evaluation of the effects of relative water depth, planting density, and distance to edge on benthic community composition. Bare sand adjacent to the planted sites and a natural seagrass bed 15 km southwest of the planted sites were used for comparison. Monthly cores 10 cm (id) by 5 cm deep were taken over a 16 month period after beds were planted. Organisms were enumerated and identified to species when possible which yielded 164 species or taxonomic groups. Annelids (Classes Polychaeta and Oligochaeta) were the dominant organisms in both planted and natural beds and defined most of the trends observed in the final analysis. Although species richness and abundance within the planted seagrass beds increased relative to adjacent sands, epibenthic and infaunal community densities and species composition did not reflect those of the naturally occurring seagrass bed even after 16 months. Of the three seagrass planting densities (0.25, 0.50, 1.00 m centers), 0.25 m centers contained the highest numbers of individuals and species. Distance to the edge of the planted sites had no effect on benthic community composition. Numbers of individuals and species were negatively related to water depth. When water depth and planting density interactions were considered, shallow water with 0.25 m centers had the highest abundance of organisms, whereas deeper water with 1.00 m centers had the lowest (difference between shallow and deep = 15-20 cm). Given the best circumstances, it will probably take the benthic community of a planted seagrass bed at least 2-3 years to compare with that of a naturally occurring bed. Maturation of the planted seagrass, as well as the benthic community, could be enhanced with a suitable planting design which takes into account planting density and water depth