ACCESS NUMBER: 30660-19932 

STUDY TITLE: Characterization of Algal-Invertebrate Mats at CMI Study Platforms: 

Developing Survey Design and Quality Assurance for Artificial Substrate Studies 

REPORT TITLE: Characterization of Algal-Invertebrate Mats at Offshore Platforms and 

the Assessment of Methods for Artificial Substrate Studies 

CONTRACT NUMBER(S): 1435-0001-30660-19932 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA(S): Central Gulf of Mexico 

FISCAL YEAR(S) OF PROJECT FUNDING: 1996-2005 

COMPLETION DATE OF REPORT: June 2005 

COST(S): FY 1996 $232,000 CUMULATIVE PROJECT COST: $232,000 

PROJECT MANAGER(S): Robert S. Carney 

AFFILIATION: Louisiana State University 

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

70803 

PRINCIPAL INVESTIGATOR: Robert S. Carney 

KEY WORDS: Offshore platforms, artificial substrate studies, algal mats 

BACKGROUND: The “oil patch” of the northwest Gulf of Mexico is a unique marine 

system in several regards; possibly the most ecologically important aspect is the extent 

of introduced structure. From the late 1940’s to the present, oil and gas production has 

resulted in the installation of thousands of hard substrate islands from Mobile Bay 

westward and from coastal embayment to beyond the edge of the continental shelf. 

While it is possible to view this construction as an extension of natural hard bottom, it 

may be ecologically accurate to consider it a whole new habitat, a steel archipelago. It 

extends from bottom through the euphotic, tidal, and wave splash zones. Unlike natural 

seafloor hardgrounds, which can accrete shells and tests into bioherms, the 

predominantly vertical surfaces of platforms shed these same building components due 

to waves, predation, and gravity. As a result, the dynamics of platform biota are unlike 

natural systems. 

OBJECTIVES: The objectives of this effort include describing the invertebrate-algal 

communities at three oil platforms currently being investigated under other CMI studies 

and developing a more cost-effective and scientifically rigorous means of surveying 
ACCESS NUMBER: 30660-19932 

fouling communities that will be suitable for wider-area, longer-time studies, and be 

capable of supporting hypothesis testing. 

DESCRIPTION: The composition of biofouling communities on three offshore platforms 

in the Gulf of Mexico was examined. A platform in South Timbalier block 94 lay in 22m 

of water 40km from shore. A platform in Grand Isle block 94 lay in 60m of water 86km 

offshore. A platform in Green Canyon lease block 18 lay in 219m at 150km offshore 

near the edge of the continental shelf. The three platforms had been the site of 

previous fisheries-related investigations and offered an offshore gradient. Research 

operations were carried out from the platforms with Exxon and Mobil corporations 

hosting and providing logistical support. Field sampling was initiated in November 1995, 

and completed September 1997. Video surveying, high-resolution photography, surface 

scraping, and settling plates were employed to describe the biota and to evaluate the 

effectiveness of the methods. 

STUDY RESULTS: Combined, the methods showed that the inshore ST-54 platform 

biota conformed to a previously recognized inshore type dominated by barnacles with 

overgrowths of algae and hydroids. The more seaward platforms conformed to a 

previously recognized offshore type dominated by a mix of bivalves and larger 

barnacles overgrown by sponges, hydroids, and ectoprocts (bryozoans). No evidence 

could be found of a bluewater assemblage. Settling plates showed that new crust was 

forming at a slower rate at the most offshore platform, GC-18. 

A scenario was developed which viewed the biofouling crust as a system in equilibrium 

between accretionary growth and crust shedding. Loss of crust is a direct consequence 

of the vertical orientation of platform benthos and is an important factor distinguishing 

platforms from natural systems. Accretion of the crust is dependent on the passing 

ocean water for food and new larval settlement. Biotic interactions such as predation, 

competition, and bioerosion all contribute to crust loss directly or in concert with wave 

surge. The ecological scenario of an equilibrium system helps identify high priority 

research questions. 

Of the methods applied, all provided data and some degree of understanding. Video 

survey, however, proved a poor tool for obtaining quantitative data on species 

composition, but was very useful for planning and site characterization. The higher 

resolution of photography was better for quantitative data, the complexity of layered 

assemblages escaped documentation. Scrape samples were most informative but 

lacked consistent quantification. Settling plates produced important rate information, 

but the demands on dive time proved unrealistic given constraints of weather and 

conflicting platform operations. 

STUDY PRODUCT(S): Carney, R.S.. 2005. Characterization of Algal-Invertebrate Mats 

at Offshore Platforms and the Assessment of Methods for Artificial Substrate Studies. 

U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, 

New Orleans, LA. OCS Study MMS 2005-0038. 93 pp.