Growth rates, densities, and distribution of Lophelia pertusa on artificial structures in the Gulf of Mexico.
Open Access
- Author:
- Larcom, Elizabeth Ansley
- Graduate Program:
- Biology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- February 11, 2013
- Committee Members:
- Charles Raymond Fisher Jr., Thesis Advisor/Co-Advisor
- Keywords:
- Lophelia pertusa
growth rates
artificial structures
Gulf of Mexico
oil rigs
ship wrecks
image analysis
depth distribution - Abstract:
- Using industry inspection video and ROV imaging, we examined Lophelia pertusa (Linnaeus 1758) on 10 artificial structures of known ages (9 to 103 years) in the northern Gulf of Mexico (GoM). Five different types deep-water hydrocarbon installations with depths ranging from 320 to 995 m, and three shipwrecks with depths ranging from approximately 530 to 615 m were examined. Density, depth ranges, and growth rates of L. pertusa colonies were calculated from video and image analysis. L. pertusa colonies were present on all structures examined. Minimum calculated growth rates for the largest colonies ranged from 0.32 to 3.23 cm/year on the different structures. Colony density varied with structure type, age, and depth, with of the highest density between 503-518 m on the single structure that spanned the entire depth range of occurrence of L. pertusa. L. pertusa on thinner and deeper, hydrocarbon structure types (spar and tension leg platforms) appear to have higher colonization rates as the support higher densities in less time. However, on average, colonies have slower growth rates on these structures than colonies on more massive, shallower hydrocarbon structure types (compliant and solid platforms). In general, the calculated minimum growth rates were higher on the hydrocarbon installations than on the shipwrecks, which were substantially older. A continuum of colony sizes was documented on all installations, suggesting multiple settlement events. L. pertusa thickets were observed on the oldest structures with most structural components covered by colonies of L. pertusa. The shallowest depth of L. pertusa observed was at 201 m and the deepest at 801 m, considerably expanding the known depth range of the species in the northern GoM. Brown, orange, and mottled morphotypes were documented for the first time in the GoM. All energy platforms examined for this study were colonized by L. pertusa and it is likely that most artificial surfaces in appropriate depths in the GoM will be as well.