Impact of the Deepwater Horizon oil spill on a deep-water coral community in the Gulf of Mexico

Abstract

To assess the potential impact of the Deepwater Horizon oil spill on offshore ecosystems, 11 sites hosting deep-water coral communities were examined 3 to 4 mo after the well was capped. Healthy coral communities were observed at all sites >20 km from the Macondo well, including seven sites previously visited in September 2009, where the corals and communities appeared unchanged. However, at one site 11 km southwest of the Macondo well, coral colonies presented widespread signs of stress, including varying degrees of tissue loss, sclerite enlargement, excess mucous production, bleached commensal ophiuroids, and covering by brown flocculent material (floc). On the basis of these criteria the level of impact to individual colonies was ranked from 0 (least impact) to 4 (greatest impact). Of the 43 corals imaged at that site, 46% exhibited evidence of impact on more than half of the colony, whereas nearly a quarter of all of the corals showed impact to >90% of the colony. Additionally, 53% of these corals' ophiuroid associates displayed abnormal color and/or attachment posture. Analysis of hopanoid petroleum biomarkers isolated from the floc provides strong evidence that this material contained oil from the Macondo well. The presence of recently damaged and deceased corals beneath the path of a previously documented plume emanating from the Macondo well provides compelling evidence that the oil impacted deep-water ecosystems. Our findings underscore the unprecedented nature of the spill in terms of its magnitude, release at depth, and impact to deep-water ecosystems.

Fig. 1.

Healthy deep-water coral communities observed in November 2010 from various sites >20 km from the Macondo well (shown as a star on map). (A) Paramuricea sp. type E and Asteroschema sp. at 360 m depth in Garden Banks (GB) 299; (B) Paramuricea sp. type E and Asteroschema sp. at 440 m depth in Mississippi Canyon (MC) 751; (C) Paramuricea sp. type A and Eumunida picta at 530 m depth in Green Canyon (GC) 354; (D) Paramuricea sp. type E and Asteroschema sp., along with a brisingid basket star at 360 m depth in Viosca Knoll (VK) 906; (E) P. biscaya and A. clavigerum at 2,300 m depth in Desoto Canyon (DC) 673. Phylogenetic species identifications of corals and associated ophiuroids are given in Fig. S2.

Fig. 2.

Impacted corals at MC 294. Brown flocculent material and tissue loss is observed on the larger coral, A10, in November and December 2010. Although there is no evidence of recovery on A10, note that the tips of some branches that were living in November were still living in December (arrows). Coral A14 in the red box was the only colony showing apparent signs of recovery from coverage by the floc between visits.

Fig. 3.

Impact assessment for coral colonies (n = 43) where high-quality images could be obtained from at least the November or December 2010 cruise. The levels of impact are ranked according to the proportion of a coral exhibiting obvious tissue damage, bare skeleton above basal region, or covered by brown flocculation: rank 0 (0–1%), rank 1 (<10%), rank 2 (10–50%), rank 3 (50–90%), rank 4 (>90%). Numbers above bars are percentages of corals in a rating relative to all assessed colonies.