Macrobenthic community structure and influence on denitrification capacity in soft sediments (Mobile Bay, Alabama, USA)

Abstract

Benthic macrofauna play important roles in coastal ecosystems through their impact on nutrient cycling and by serving as an important trophic link. This study investigated the influence of environmental stressors on macrofaunal community abundance, biomass and diversity and evaluated impacts of those benthic organisms on nutrient fluxes and denitrification capacity in Mobile Bay, a shallow subtropical estuary in the northern Gulf of Mexico. Between January and May 2016, 22 stations in the lower bay were sampled, and the distance from the sea and sediment characteristics were identified as the principal constraints for macrofaunal distribution and taxonomic composition. Higher diversity of macrofauna was found near the mouth of the bay, likely due to hydrological characteristics of the bay, in addition to distance from anthropogenic disturbances near coasts. Sediments comprised of 60−80% sand showed higher abundances, biomass and diversity compared to muddier or sandier sediments, potentially because these sediments were more stable. Although macrofaunal abundance, biomass and diversity differed across stations in the bay, we did not find a relationship between macrofaunal abundances or biomass and denitrification capacity. Both abundance and biomass of infauna were low in Mobile Bay (< 4000 ind. m −2 and < 5 g DW m −2 at most sites) compared to those in previous studies which showed a positive relationship between macrofaunal abundances and denitrification. The lack of the relation between macrofauna and denitrification suggests that a threshold of abundance, biomass and/or burrowing activity is necessary to increase bioturbation or irrigation to sufficient levels to affect denitrification.

In Search of a Field-Based Relationship Between Benthic Macrofauna and Biogeochemistry in a Modern Brackish Coastal Sea

“…However, we should not ignore this absence of correlations even if it does not meet the general expectation, and therefore we find reporting of these negative results here particularly important. For example, Jacquot et al (2018) also reported the lack of the relationship between macrofauna and denitrification they were aiming to find, and suggested that macrofaunal density and/or burrowing activity should be above some threshold to increase bioturbation or irrigation to sufficient levels to affect denitrification (see also Appendix 8).…”

Spatially and Temporally Variable Impacts of Hurricanes on Shallow Sediment Structure

“…River discharge into the bay peaks in late winter/early spring and reaches a minimum in late summer/early fall (Dzwonkowski et al., 2011; Stumpf et al., 1993). During high riverine inputs to Mobile Bay and/or periods of strong winds and waves, which resuspend the shallow (average depth: ∼3 m) sediments (mainly clays and silty clays; Jacquot et al., 2018), large amounts of muddy sediments are transported offshore through Main Pass in a surface plume, leading to annual sediment delivery of 1–2 × 10 6 t to the Alabama shelf (Dinnel et al., 1990). This sediment plume is usually deflected westward due to the predominant westward longshore current and the Coriolis effect (Cipriani & Stone, 2001).…”

Changing intra‐ and interspecific interactions across sedimentary and environmental stress gradients

“…The properties of coastal marine sediments are known to influence the structure and dynamics of benthic soft sediment ecosystem communities (Anderson, 2008; Ellis et al, 2015; Gray, 2002; Jacquot et al, 2018; Rhoads & Germano, 1982; Rowden et al, 2012). For example, sediment grain size often correlates with suspension and deposit feeder abundance, with deposit feeders more prevalent in depositional areas with muddy sediment where sediment organic matter concentrations are high enough to support their nutritional requirements (Peterson, 1991; Pratt et al, 2015; Probert, 1984).…”