Diversity and composition of macrobenthic community associated with sandy shoals of the Louisiana continental shelf

Abstract

Along the Louisiana, USA continental shelf, sandy shoals are shallow, possibly oxygen-rich ''islands'' surrounded by deeper muddy deposits prone to hypoxia. Shoals also contain significant quantities of fine sand that may be mined in the future for coastal restoration. The ecological role of shoals remains poorly understood and we hypothesized that shoals provide critical habitat for benthic invertebrates. Using Ship Shoal as a model system, we assessed the diversity and structure of macrobenthic assemblages and how community structure varies with season and environmental parameters. High biomass (averaging 26.7 g m -2 ) and high diversity (161 species) of macrobenthos was found in 2006. Polychaetes (45%-72 species) and crustaceans comprised most of the species (28%-46 species); spionids and amphipods dominated the polychaete and crustacean groups respectively, both in terms of number of species and abundances. Sharp decreases in diversity, abundance and biomass occurred from spring to autumn. Species diversity and total abundance significantly increased with decreasing sediment grain size and increasing bottom water dissolved oxygen. Across seasons, mole crabs Albunea paretii and amphioxus Branchiostoma floridae typified the community and contributed most of the biomass. The polychaetes Nephtys simoni, Neanthes micromma, Dispio uncinata, Mediomastus californiensis and Magelona sp. A, the amphipod Acanthohautorius sp. A and the burrowing shrimp Ogyrides alphaerostris also contributed to variation in community composition. Cluster analyses quantified seasonal variation, mainly based on sharp decreases in abundance, as well as spatial differences in species composition oriented along both eastwest and north-south gradients. Variation in benthic assemblages was correlated with

Spatial variation in basal resources supporting benthic food webs revealed for the inner continental shelf

“…Recent surveys on SS revealed a high biomass (averaging 37.3 g m 22 ), and high diversity (161 taxa) of macrobenthos (Dubois et al 2009), primarily spionid polychaetes and haustoriid amphipods. In the fine, silty sediments characteristic of off-shoal areas of the seasonally hypoxic Louisiana shelf, polychaetes dominate the benthic macroinfauna but mollusks, echinoderms, and crustaceans are also abundant in most areas (Baustian and Rabalais 2009).…”

“…In the fine, silty sediments characteristic of off-shoal areas of the seasonally hypoxic Louisiana shelf, polychaetes dominate the benthic macroinfauna but mollusks, echinoderms, and crustaceans are also abundant in most areas (Baustian and Rabalais 2009). Both on and off-shoal, the macroinfauna assemblage is dominated by surface deposit-feeders, with subsurface deposit-feeders and suspension-feeders being comparatively less common (Baustian and Rabalais 2009;Dubois et al 2009). …”

Relationships of benthic amphipod communities with environmental variables in the shallow waters of the Dardanelles

“…Irregular bottom topography in coastal waters has been known to affect coastal hydrodynamics and bottom boundary layer dynamics (Dubois et al 2009). Dubois et al (2009) reported 161 bethic species in the sandy shoals of Louisiana (the southern United States) and said that the species' abundances were steady.…”

“…Dubois et al (2009) reported 161 bethic species in the sandy shoals of Louisiana (the southern United States) and said that the species' abundances were steady. Meanwhile, they recorded a large rate of decline in amphipod diversity in the periods of spring, summer, and autumn.…”

“…Zonation of macrobenthic assemblages is directly affected by the sediment structure and several changes that are related to sediment characteristics could negatively influence the structure of a benthic community (Dubois et al 2009). The effects of hydrodynamic characteristics such as currents and waves are also significant in determining the community structure of the benthic environment (Seiderer & Newell 1999;Desroy et al 2007).…”