Polychaetes exhibit diverse feeding strategies and diets, with some species possessing hardened teeth or jaws of varying complexity. Species in the order Eunicida have complex, rigid, articulated jaws consisting of multiple pairs of maxillae and a pair of mandibles. While all Eunicida possess this general jaw structure, several characteristics of the jaws vary considerably among families. These differences, described for fossilized and extant species' jaws, have been used to infer evolutionary relationships. Little has been done, however, to relate jaw functional morphology and feeding behavior to diet. To explore these relationships, we compared the jaw kinematics and morphology of two distantly related eunicidan taxa with superficially similar jaw structures: Diopatra spp. (Onuphidae), predominantly herbivorous and tube dwelling, and Lumbrineris spp. (Lumbrineridae), a burrowing carnivore. Jaw kinematics were observed by filming individuals biting in a number of orientations. Some differences in jaw structure and kinematics between Diopatra spp. and Lumbrineris spp. can be interpreted to be consistent with their differences in diet. Relating jaw morphology to diet would improve understanding of early annelid communities by linking fossil teeth (scolecodonts) to the ecological roles of extant species with similar morphologies.

Anthropogenic disturbances such as oil spills can cause mortality in benthic infaunal communities, reducing diversity and abundance and impeding sediment ecosystem functions. Sublethal effects of oil exposure have received less attention, however. We conducted a mesocosm experiment exposing 2 infaunal taxa, the polychaete Owenia fusiformis and the brittle star Hemipholis elongata, to sublethal concentrations of the water-accommodated fraction (WAF) of oil. We evaluated the effects of WAF on animal behavior, bioturbation, and sediment oxygen demand (SOD) in infaunal assemblages of both mixed and single species. WAF exposure did not affect O. fusiformis feeding behavior, nor did it influence bioturbation. Compared to O. fusiformis, the brittle star H. elongata mixed more surface sediments to greater depths and to a greater extent horizontally. Bioturbation in mesocosms with both taxa was consistent with predictions from monocultures for substitutive densities, but lower than predicted for additive densities. This indicates that taxa interacted (negatively) only at higher densities. SOD was higher in oiled than unoiled treatments initially (at 1-3 d), but this difference disappeared after the first sampling, consistent with a decrease in total petroleum hydrocarbons in the WAF treatment over the same time period. Higher SOD in WAF-exposed faunal treatments than sediments with no fauna suggested that faunal activities may enhance microbial degradation of hydrocarbons. These findings suggest that exposure to WAF stimulated microbial metabolism in the first few days of the experiment, but did not affect macrofaunal behavior/function, nor have lasting effects on sediment ecosystem functions.

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.