Spatial analysis of cold-water coral and cold seep distributions in the Gulf of Mexico
The deep Gulf of Mexico is home to numerous cold seeps and cold-water coral communities that are found within close proximity to one another.1,2 The goal of this project was to characterize the fine-scale habitat changes that occur between these two distinct communities. The chemical environment produced by seepage from the seafloor alters the local water chemistry in was that can affect coral habitat suitability. The seep microbial community produces authigenic carbonate rocks that facilitate coral settlement, but only after the negative effects of seepage (toxic hydrogen sulfide, hydrocarbons, and lower dissolved oxygen) have declined or ceased.3
1. AUV Sentry was deployed at nine sites across the northern Gulf of Mexico, measuring water chemistry within 5m of the seafloor and taking downward-looking photos.
2. Photos were visually assessed and scored for presence or absence of the following:
- Seep organisms:
- Bacterial mats
- Seafloor substrate:
- Carbonate rocks
- The presence of carbonate rocks was significantly correlated with the presence of corals in all six dives tested (p < 0.001).
- Redox potential (an indicator of hydrogen sulfide) was negatively correlated with coral presence in three of six dives (p < 0.01) and fluorescence (an indicator of hydrocarbons) was negatively correlated in one dive (p < 0.01).
- Temperature and depth were also positively correlated with corals in four of six dives (p < 0.01) and salinity was negatively correlated in four of six dives (p < 0.01).
- Dissolved oxygen did not show a significant effect.
- At the three sites where both tubeworms and corals were present, a logistic regression showed carbonate rocks were significantly more likely to be occupied by corals if they were found further away from tubeworms within the survey area. (p < 0.001 for two of the three sites tested).
Dissolved oxygen was hypothesized to be a limiting factor for coral distributions, but it was not significantly correlated within these sites. This may be due to GoM cold-water corals living in lower oxygen conditions than conspecifics in other oceans.4,5
Local coral habitat is most constrained by the presence of hard substrate to settle on, and the chemical influence of seepage also showed the hypothesized negative correlation to coral distribution in most cases.
- Identify corals to genus level to examine taxa-specific trends, such as Callogorgia americana delta’s affinity for seeps.6
- Characterize the distributions of mobile fauna visible in photographs and their relationship to these habitats
1. Cordes, E. E., McGinley, M. P., Podowski, E. L., Becker, E. L., Lessard-Pilon, S., Viada, S. T., & Fisher, C. R. (2008). Coral communities of the deep Gulf of Mexico. Deep Sea Research Part I: Oceanographic Research Papers, 55(6), 777–787. http://doi.org/10.1016/j.dsr.2008.03.005
2.Cordes et al. (2009) Annual Review of Marine Science
3.Liebetrau et al. (2010) Marine Geology
4.Lunden et al. (2014) Frontiers in Marine Science
5.Georgian et al. (2016) Limnology and Oceanography
6.Quattrini et al. (2013) Molecular Ecology
This work would not have been possible without funding from the NSF Ocean Acidification program, the crew of the 2014 R/V Altantis cruise, and the scientific AUV Sentry team.