Decline in condition of gorgonian octocorals on mesophotic reefs in the northern Gulf of Mexico: before and after the Deepwater Horizon oil spill

Abstract

Hard-bottom 'mesophotic' reefs along the '40-fathom' (73 m) shelf edge in the northern Gulf of Mexico were investigated for potential effects of the Deepwater Horizon (DWH) oil spill from the Macondo well in April 2010. Alabama Alps Reef, Roughtongue Reef, and Yellowtail Reef were near the well, situated 60-88 m below floating oil discharged during the DWH spill for several weeks and subject to dispersant applications. In contrast, Coral Trees Reef and Madison Swanson South Reef were far from the DWH spill site and below the slick for less than a week or not at all, respectively. The reefs were surveyed by ROV in 2010, 2011, and 2014 and compared to similar surveys conducted one and two decades earlier.Large gorgonian octocorals were present at all sites in moderate abundance including Swiftia exserta, Hypnogorgia pendula, Thesea spp., and Placogorgia spp. The gorgonians were assessed for health and condition in a beforeafter-control-impact (BACI) research design using still images captured from ROV video transects. Injury was modeled as a categorical response to proximity and time using logistic regression. Condition of gorgonians at sites near Macondo well declined significantly post-spill. Before the spill, injury was observed for 4-9 % of large gorgonians. After the spill, injury was observed in 38-50 % of large gorgonians. Odds of injury for sites near Macondo were 10.8 times higher post-spill, but unchanged at far sites. The majority of marked injured colonies in 2011 declined further in condition by 2014. Marked healthy colonies generally remained healthy. Background stresses to corals, including fishing activity, fishing debris, and coral predation, were noted during surveys, but do not appear to account for the decline in condition at study sites near Macondo well.

Individual and Population Level Variation in the Reproductive Potential of Deep-Sea Corals From Different Regions Within the Gulf of Maine

“…However, the growth and formation of deep-sea coral habitat occurring on the time-scale of decades to millennia (Roark et al, 2009), in addition to their intricate morphologies make these organisms vulnerable to a multitude of disturbances. These disturbances range from bottom fishing activities (Koslow et al, 2000;Roberts and Hirshfield, 2004;Murillo et al, 2011), and oil and gas exploration and exploitation (Ramirez-Llodra et al, 2011;White et al, 2012;Fisher et al, 2014;DeLeo et al, 2016;Etnoyer et al, 2016), to more protracted disturbances including increases in ocean stratification, temperature and acidification due to climate change (Roberts et al, 2006;Lumsden et al, 2007;Hofmann et al, 2010;Mercier and Hamel, 2011;Maier et al, 2012;Lunden et al, 2014;Hennige et al, 2015;Soetaert et al, 2016). In response, and to better understand the rate at which recovery and subsequent biogenic habitat formation occurs, it is necessary to investigate the reproductive biology, growth, and relationships therein of deep-sea corals at both the individual and population level.…”

Environmental effects of the Deepwater Horizon oil spill: A review

“…At least four well-known MCEs are documented in the northeastern and eastern parts of NGOM; the Flower Garden Banks National Marine Sanctuary off the coast of TX, the Pinnacles Trend area off AL, the FL Middle Ground reef system, and the Pulley Ridge reef east of the FL Keys(Locker et al, 2010). The reefs in Pinnacles Trend were situated below oil-slicks for several weeks and, in addition, dispersants were added to oil slicks in this area Etnoyer et al (2015a;. found evidence that the oil spill caused injury to at least four species of gorgonian octocoral sea-fans in the Pinnacles Trend area, in the form of eroded polyps, discoloration, bare branches, overgrowth, missing branches, and broken branches.…”

Theme section on mesophotic coral ecosystems: advances in knowledge and future perspectives

“…Using a ROV, Etnoyer et al (2016) recorded the decline in condition of sea fans (Octocorallia, Alcyonacea) on lower MCEs (60-90 m depth) in the northern Gulf of Mexico before and after the Deepwater Horizon oil spill. They present clear evidence of direct injury and decline in the health of sea fans at sites situated below the surface slick.…”