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increase toxicity, but were not measured in 2010. Concentrations of dioctyl sulfosuccinate (DOSS), a principal component of Corexit 9500, were measured in June
2011, 11 months after the spill stopped, and they were very low, because 35% of the
samples were below detection limits, and only one sample was as high as 84 ppb.
The effect ranges found here for PAH were consistent with sediment quality guidelines developed for shallow estuarine and marine waters.
Sediments from a total of 179 stations were measured for sediment toxicity
responses (Montagna and Arismendez 2019). Toxicity was assessed using the
Microtox® system, where reductions of fluorescence of the bioluminescent bacterium, Vibrio fischeri, indicate corresponding increases in toxicity. Toxic responses
were found as far away as 35 km from the spill site, and there were direct correlations between the presence of oil and biological and ecological effects of reduced
macrofauna abundance and diversity. The Corexit dispersants were also highly toxic
even when diluted 10,000 times, so a combination of dispersants and oil is responsible for the biological and ecological responses.
22.3.3 Soft-Bottom Habitats After DWH
In June 2011, 11 months after the well was capped, 32 stations from June 2010 were
resampled (Montagna et al. 2017). The design compared 20 stations from the combined moderate and severe impact zones to 12 stations in the reference zones. There
were no statistically significant differences in contaminant concentrations between
the impact and non-impact zones from 2010 to 2011, which indicates contaminants
persisted at the same levels after 1 year. Whereas meiofauna abundance and diversity exhibited some signs of recovery in 2011, there was evidence of persistent,
statistically significant impacts to both macrofauna and meiofauna community
structure. Macrofaunal taxa richness and diversity in 2011 were still 22.8% and
35.9% less, respectively, in the entire impact zone than in the surrounding nonimpact area, and meiofaunal richness was 28.5% less in the entire impact zone than
the surrounding area. The persistence of significant biodiversity losses and community structure change nearly 1 year after the wellhead was capped indicates that
full recovery had yet to have occurred in 2011.
The macrofauna community response was examined for the 2011 sampling
(Washburn et al. 2017). Richness, diversity, and evenness were severely impaired
within a radius of approximately 1 km around the DWH wellhead. However, lower
diversity than background was observed in several stations up to 29 km to the southwest of the wellhead. Abundance near the DWH wellhead increased in 2011 compared to 2010, and the highest abundances were found at stations within the 1 km
radius of the wellhead. The increase was caused mostly by high abundance of
opportunistic polychaetes of the family Dorvilleidae, genus Ophryotrocha. Diversity
did not change in the impact zone near the DWH wellhead, but there was an increase
of diversity at stations farther from the wellhead in the non-impact zone.
22 Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During…
increase toxicity, but were not measured in 2010. Concentrations of dioctyl sulfosuccinate (DOSS), a principal component of Corexit 9500, were measured in June
2011, 11 months after the spill stopped, and they were very low, because 35% of the
samples were below detection limits, and only one sample was as high as 84 ppb.
The effect ranges found here for PAH were consistent with sediment quality guidelines developed for shallow estuarine and marine waters.
Sediments from a total of 179 stations were measured for sediment toxicity
responses (Montagna and Arismendez 2019). Toxicity was assessed using the
Microtox® system, where reductions of fluorescence of the bioluminescent bacterium, Vibrio fischeri, indicate corresponding increases in toxicity. Toxic responses
were found as far away as 35 km from the spill site, and there were direct correlations between the presence of oil and biological and ecological effects of reduced
macrofauna abundance and diversity. The Corexit dispersants were also highly toxic
even when diluted 10,000 times, so a combination of dispersants and oil is responsible for the biological and ecological responses.
22.3.3 Soft-Bottom Habitats After DWH
In June 2011, 11 months after the well was capped, 32 stations from June 2010 were
resampled (Montagna et al. 2017). The design compared 20 stations from the combined moderate and severe impact zones to 12 stations in the reference zones. There
were no statistically significant differences in contaminant concentrations between
the impact and non-impact zones from 2010 to 2011, which indicates contaminants
persisted at the same levels after 1 year. Whereas meiofauna abundance and diversity exhibited some signs of recovery in 2011, there was evidence of persistent,
statistically significant impacts to both macrofauna and meiofauna community
structure. Macrofaunal taxa richness and diversity in 2011 were still 22.8% and
35.9% less, respectively, in the entire impact zone than in the surrounding nonimpact area, and meiofaunal richness was 28.5% less in the entire impact zone than
the surrounding area. The persistence of significant biodiversity losses and community structure change nearly 1 year after the wellhead was capped indicates that
full recovery had yet to have occurred in 2011.
The macrofauna community response was examined for the 2011 sampling
(Washburn et al. 2017). Richness, diversity, and evenness were severely impaired
within a radius of approximately 1 km around the DWH wellhead. However, lower
diversity than background was observed in several stations up to 29 km to the southwest of the wellhead. Abundance near the DWH wellhead increased in 2011 compared to 2010, and the highest abundances were found at stations within the 1 km
radius of the wellhead. The increase was caused mostly by high abundance of
opportunistic polychaetes of the family Dorvilleidae, genus Ophryotrocha. Diversity
did not change in the impact zone near the DWH wellhead, but there was an increase
of diversity at stations farther from the wellhead in the non-impact zone.
22 Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During…