Examination of intertidal and nearshore benthic macroinvertebrates along two non-nourished Florida beaches

Abstract

Urban sandy beaches are often extensively modified by human activities such as nourishment projects. Such disturbances can significantly alter ecosystem structure, making it difficult to understand the “natural state”. Macrofaunal species are greatly influenced by direct sediment influx which may bury organisms that are unable to dig out quickly or relocate seaward. In this study we sampled the nearshore macrofaunal community in association to grain size on two beaches that are not directly nourished to help determine a “natural” state community. Macrofaunal samples were taken at four levels, two intertidal and two subtidal. Eighty overall samples were taken per beach. Cores were additionally taken at each level for geological analyses. The two beaches were found to differ both geologically (intertidally) and by macrofaunal community. Sediment grain size was highest in the intertidal levels at both beaches. Gulfstream Park’s intertidal zone possessed the largest grain-sized and most poorly sorted sediments. Gulfstream Park’s macrofaunal richness was greater at 17 taxa compared to MacArthur Beach State Park’s 5 taxa. From the 19 identified taxa 5 species constituted 83% of the macrofaunal community, with the isopod Ancinus depressus being the most common organism (32%). Community differences between the two beaches were attributed to greater sediment disturbance at Gulfstream Park. Macrofaunal species are important low-level consumers in coastal food webs. Changes to macrofaunal communities transmit to higher trophic levels and may potentially impact on human beach activities (e.g. fishing, nature watching).