Comparison of benthic macroinvertebrate assemblages associated with salt marshes in low and high salinity areas of Galveston Bay

Abstract

Two study areas in Galveston Bay, Texas were chosen to assess the species composition and abundance of benthic macroinvertebrates in salt marshes that are utilized by juvenile brown shrimp. The objectives of the study were to compare the benthic macroinvertebrate assemblages in a low salinity area, Trinity River Delta, with those in a high salinity area, West Bay, and to compare the benthic invertebrate community between the vegetated and non-vegetated habitats of the salt marshes in those areas. Benthic invertebrate samples were collected from about one meter on either side of the marsh-open water interface. Measurements of salinity, dissolved oxygen, water temperature, and sediment pore salinity were also obtained. Analyses on the physical parameters and the benthos using one year of data were completed. Benthic invertebrates were more abundant at West Bay than at Trinity River Delta. Polychaetes dominated at West Bay whereas oligochaetes dominated at Trinity River Delta. Arthropods and molluscs were additional major taxonomic groups of macroinvertebrates observed at either area. At Trinity River Delta, most arthropods were insect larvae and pupae, and at West Bay, most arthropods were amphipods and trails, although insect larvae in the marsh were also observed. Differences in benthic invertebrate densities between the vegetated and non-vegetated habitats varied among the taxonomic levels analyzed. In both study areas, oligochaetes were more abundant in the vegetated habitat than in the non-vegetated habitat, but polychaetes were observed to have the opposite trend. This trend in the polychaetes was similar for nereidids at Trinity River Delta and spionids but not capitellids at West Bay. For the arthropods, insects at Trinity River Delta and amphipods and tabards at West Bay were more abundant in the vegetated habitat than in the understated habitat most of the year. Differences in the densities of molluscs in the vegetated and non-vegetated habitats were variable over time. Relationships between salinity and benthic invertebrates in vegetated or non-vegetated habitat appeared nonexistent. The species composition between the low and high salinity areas were compared with other studies. Several factors may have contributed to the observations of the vegetated and non-vegetated habitats.