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STUDY TITLE: New Invasive Marine Species Colonizing Energy Platforms in the

Northern Gulf of Mexico: Verification, and Examination of Spread.

REPORT TITLE: New Invasive Marine Species Colonizing Energy Platforms in the

Northern Gulf of Mexico: Verification, and Examination of Spread.

COOPERATIVE AGREEMENT NUMBER: M10AC20006

SPONSORING OCS REGION: Gulf of Mexico

APPLICABLE PLANNING AREA: Central

FISCAL YEARS OF PROJECT FUNDING: 2010-2014

COMPLETION DATE OF REPORT: January 2015

COSTS: $339,549.00

PROJECT MANAGER: Paul W. Sammarco

AFFILIATION: Louisiana State University, Coastal Marine Institute

ADDRESS: Coastal Marine Institute, Louisiana State University, Baton Rouge, LA 

PRINCIPAL INVESTIGATOR: Paul W. Sammarco

KEY WORDS: Platforms, Tubastraea micranthus, Tubastraea coccinea, invasive 

species, density, distribution, size, depth, Gulf of Mexico

BACKGROUND: Very few species of scleractinian corals have successfully invaded the 

Caribbean. A new one has emerged, found on an offshore platform south of the 

Mississippi River mouth. This Indo-Pacific coral is Tubastraea micranthus, and is closely 

related to T. coccinaea, which successfully invaded the Caribbean and Gulf of Mexico 

and has spread therein over the past 70 years. T. micranthus is new to the region and 

may have the potential to spread like its predecessor.

Accessibility is also important in determining whether an invasive species can be 

controlled. In the marine environment, depth limits accessibility.

Invasion success by an alien species into a new environment is not only dependent on 

rate of reproduction, growth rates, mortality rates, or the physical characteristics of the 

environment; it is also dependent upon the ability to successfully compete with native 

species for resources. For sessile, epibenthic marine species, one critical resource is 

space.

OBJECTIVES: We determined whether the populations of T. micranthus were 

spreading throughout the region and whether there was evidence of rapid population 

expansion. We also compared population density data with that of T. coccinea, a 

congeneric species. Fourteen energy platforms were assessed down to 138 m depth
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(max.) by remotely operated vehicle (ROV) using digital video. Colony densities in 

no./m

2 were determined for both species, and colony size for T. micranthus. Data were 

analyzed by platform and also with respect to geographic distribution.

We also assessed the depth distribution of two Indo-Pacific invasive coral species-T. 

micranthus and T. coccinea-on 15 energy platforms using ROVs.

We also examined the competitive abilities of these two invasive Indo-Pacific coral 

species, T. micranthus and T. coccinea, on 15 artificial reefs (offshore energy platforms) 

in the northern Gulf of Mexico, south of the Mississippi River. Underwater videos were 

taken using an ROV down to 183 m depth on the platforms, and still-capture photos 

were analyzed from them.

DESCRIPTION: The distribution and abundance of the invasive coral species T. 

micranthus and T. coccinea were assessed on 14 platforms in the central region of the 

Gulf of Mexico, south of the Mississippi River mouth.

SIGNIFICANT CONCLUSIONS AND STUDY RESULTS: T. micranthus densities were 

highest on GI-93C and on GI-116A, SW of the Mississippi River mouth, being 

significantly higher than most other platforms. Densities declined radially from there. 

Mean colony size was highest on MC-311A, at the head of the Mississippi Canyon, 

suggesting this to be the epicenter of colonization. This site is characterized by blue 

water instead of the turbid, lower salinity water of other sites. This suggests that T. 

micranthus may grow best under blue-water conditions. Size frequency distributions of

colonies for T. micranthus were skewed towards 1-200 cm

2

–sometimes >90% of the 

population, indicating populations are in an explosive growth phase. T. coccinea

densities were high (range: ~50-300/m

2

). Its populations were also centered SW of the

Mississippi River. T. micranthus is spreading through this region and the window for its 

potential eradication may be rapidly closing.

Pooled data indicated that T. micranthus extends to 138 m and probably deeper, while 

T. coccinea is generally limited to < 78 m. Average depths for T. micranthus were 

shallower west of the Mississippi River, in its plume, and deeper towards the east. 

Tubastraea coccinea exhibited a similar geographic depth-distribution pattern, but 

shallower and subtler. Broad geographic patterns were similar, whether using density or 

percent-cover data as the variable for analysis. When considering individual platforms, 

T. micranthus often reached the bottom and sometimes occurred at depths >66 m. 

Tubastraea coccinea were limited to shallow water on all platforms. Detailed depth 

distribution patterns varied significantly between analyses using density and percentcover as the variable for analysis, with density probably indicating colonization rates, 

and percent-cover colony growth. Depth limitation by T. coccinea may be associated 

with food availability rather than light since it is azooxanthellate.

Both species were involved widely in competition for space. T. micranthus was 

competitively superior (<90%) to all competitor species pooled, although frequency of 

competitive wins varied significantly between platforms. Success was highest in the NE 

part of the study area, characterized by blue water, and lowest in the SW area near the
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river plume, indicating that it may be better adapted to blue-water conditions. T. 

coccinea was also competitively superior to all competitors pooled, with little variability 

between platform populations and little spatial variation. The two congeneric coral 

species, when in competition with each other, were equal in their abilities for competitive 

success, although T. coccinea had a slight competitive advantage. T. coccinea’s

abilities appeared to peak in the SW part of the study area, suggesting that it may be 

better adapted to surviving in a more turbid, nutrient-rich environment. T. coccinea was 

found to be competitively superior to almost all its competitors, including the encrusting 

sponge Xestospongia sp. (with the commensal Parazoanthus catenularis), the light grey 

encrusting sponge Dictyonella finicularis, the black encrusting sponge Xestopongia 

carbonaria, the brown encrusting sponge Mycale carmigropila, and the red encrusting 

sponge Phorbas amaranthus. Both T. micranthus and T. coccinea are formidable 

competitors for space in the northern Gulf of Mexico.

STUDY PRODUCT: Sammarco, P. W. 2014. New Invasive Marine Species Colonizing 

Energy Platforms in the Northern Gulf of Mexico: Verification, and Examination of 

Spread. U.S. Dept. of the Interior, Bureau of Ocean Energy Management, Gulf of 

Mexico Region, OCS Study BOEM 2015-005. pp. 65