Polychaete Annelid Dynamics in the Northern Gulf of Mexico, From Shallow Water to the Deep-Sea

Polychaete annelids dominated the macrobenthos in sediments located 5 to 9 km from the Deep Water Horizon (DWH) Oil Spill site five months after the event. Numbers of species, abundance, and biodiversity indices in the polychaete taxa were significantly lower than pre-spill values from similar depths in the eastern Gulf of Mexico (GoM). Both non-selective and selective deposit feeders were the most frequent feeding guilds, but their abundances were significantly lower. An increase in the number of carnivorous Sigalionidae may be a response to an accumulation of petroleum hydrocarbons on the sediment. The concentration of oil in the sediments was low and the source of the oil remains equivocal. Multivariate analyses illustrated the differences between communities near the DWH and those from prior studies in similar deep GoM habitats. In summary, Deep Water Horizon oil spill appears to have had a measurable impact on the polychaetes.

A time series of benthic samples from 2004 to 2012 has been utilized to assess the influence of hypoxia on the mean sizes (wet weight) of polychaeteannelid worms.While the mean body size over the entire study was 3.99?4.66 mg wet weight per individual, the mean ranged from 2.97?2.87 mg during consistently hypoxic conditions (< 2 mg/L)to a high of 7.13?7.60 mg (p < 0.01)under oxic conditions (> 2 mg/L). The decline in size was due to the elimination of large species under hypoxic conditions, not a reduction in size within species. At 'severe' levels of hypoxia (< 1 mg/L), the smallest species also declined in abundance, whereas the ubiquitous ?medium sized? Paraprionospio pinnata flourished.

The infaunal benthos of the upper continental slope, a transition zone between the dynamic continental shelf and the deep sea, has been sampled in 1983-85 and then again in 2000-02 at nine locations. The polychaete annelid worms, the dominant taxon within the samples, exhibited remarkable stability in abundance, diversity, depth-related zonation, and species composition (> 35% similarity in species) over that period. At 7 of the 9 locations, single appearances of several dominant species resulted in the 1983-85 samples being more abundant but less diverse than the 2000-02 survey.