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Study Title: Evaluating the Importance of Shallow Water "Rigs" as Habitat for Newly Recruited ReefAssociated Fishes in the OCS Off Louisiana

Report Title: Use of small shallow water oil and gas as reef habitat for fishes and fouling biota

CONTRACT NUMBER: M12AC00015

SPONSORING OCS REGION: Gulf of Mexico

APPLICABLE PLANNING AREA(S): Central Gulf of Mexico

FISCAL YEAR(S) OF PROJECT FUNDING: 2012–2017

COMPLETION DATE OF REPORT: TBD

COSTS: $340,914

PROJECT MANAGER(S): Edward J. Chesney1, Donald Baltz2

AFFILIATION: 1Louisiana Universities Marine Consortium, 2Louisiana State University

ADDRESSES: 18124 Hwy 56, Chauvin, LA 70344; 2Department of Oceanography Coastal Sciences, 

School of the Coast and the Environment

PRINCIPAL INVESTIGATOR(S)*

: Edward Chesney1, Ryan Munnelly2, David Reeves2, Donald Baltz2

KEY WORDS: juvenile fishes, abundance, hydrography, hypoxia, small platform, reef associated fishes

BRIEF ABSTRACT: Coastal Louisiana has a huge network of oil and gas platforms, from inshore to 

deepwater. About 1/3 of all platforms in the Gulf of Mexico OCS are small, unpopulated, non-drilling 

platforms in <18 m of water. Platforms attract fishes and invertebrates. This project studied fish habitat in 

relation to species-specific responses to river-influenced hydrographic characteristics of Louisiana’s 

nearshore area (5–25 m water depth). To what degree do small, shallow water structures serve as 

important recruitment sites and habitat for juvenile reef-associated fishes in the coastal zone adjacent to 

Louisiana?

Survey cruises during summers 2013–2014 collected video and hydrographic data around hundreds of 

small platform in the nearshore coastal zone of the OCS, <18 m water depth from the LouisianaMississippi border to the Louisiana-Texas border. In 2015–2016, cruises focused on a set of small 

platforms in the Ship Shoal blocks in water depth from 7 to 35 m water depth; video and diver observation 

were used to compare fish assemblages, estimate grazing rates of select fishes, density of stone crabs,

and settling and growth rates of fouling organisms on and around small oil platforms, and how hypoxia 

affected small platforms as fish habitat on and off Ship Shoal, the growth and development rates of 

fouling organisms and grazing rates of fishes on fouling and fouling associated biota. Coast-wide studies 

observed 54 species of fishes associated with these small platforms in the nearshore zone. The 

assemblage(s) included juveniles of 29 species, indicating the importance of nearshore platforms as 

nursery habitat. Oxygen levels (both hypoxia and supersaturation) had significant impacts on the vertical 

distribution and behavior of the reef associated fishes around platforms. Platforms offer reef-like habitat 

features in the upper water column that appear to offer refugia for some reef-associated species during 

low oxygen events. The study found that the structures in the nearshore may be more important to 

platform-associated secondary production than platforms and other artificial reefs located in lower 

productivity areas of the coastal zone.

BACKGROUND: A distinctive feature of coastal Louisiana is the unrivaled network of oil and gas 

installations (platforms) extending from inshore waters to the deep Gulf of Mexico. Since 2007 there has 
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been a >38% reduction in platform numbers, with the highest removal rates occurring in shallow (< 18m) 

nearshore waters. Many fishes and invertebrates are attracted to platforms, including the newly recruited 

stages of snapper. This presented a unique opportunity to study highly valuable fish habitat in relation to 

the detailed species-specific responses to the river-influenced hydrographic characteristics of Louisiana’s 

nearshore zone (5–25 m water depth). Previous studies of fishes around oil platforms focused on a few 

relatively large platforms in water depths usually much deeper than 18 m. However, about one-third of all 

platforms in the OCS are small, unmanned and non-drilling platforms located in <18 m of water depth. 

OBJECTIVES: The primary research goal of this project was to determine the degree to which small 

shallow water structures serve as important recruitment sites and habitat for juvenile reef-associated 

fishes throughout the coastal zone adjacent to Louisiana. 

DESCRIPTION: These studies were completed in two distinct phases. On a series of survey cruises 

during the summers of 2013–2014, video and hydrographic data were collected around hundreds (~343) 

of small platform located in the nearshore coastal zone of the OCS. Of those locations sampled we were 

able to successfully analyze the video from 150 small platforms in <18 m water depth from the LouisianaMississippi border to the Louisiana-Texas border. We used the video drops and diver observations to 

estimate species composition and relative fish abundance as well as observe fish behaviors in relation to 

hydrographic conditions. From 2015–2016, we focused our studies on a set of small platforms in the Ship 

Shoal blocks in water depth from 7 to 35 m water depth, where we used video and diver observation to 

compared fish assemblages, estimate grazing rates of select fishes, density of stone crabs, and settling 

and growth rates of fouling organisms on and around small oil platforms.

SIGNIFICANT CONCLUSIONS: Small oil platforms located in the nearshore zone off Louisiana appear to 

be important habitat for fishes, especially juvenile reef associated fishes such as young-of-the-year (YOY) 

red and lane snapper, gray trigger fish, gag grouper and many species that occur around these platforms 

as juveniles. Distribution and abundance of these fishes appear to be driven by the complex and diverse 

patterns of hydrography off Louisiana. Because these platforms are located in high productivity areas of 

the coast and some species, such as sheepshead, triggerfish, black drum and stone crabs, were 

observed to graze the barnacles and infauna that reside on the structures, the structures in the nearshore 

may be more important to platform-associated secondary production than platforms and other artificial 

reefs located in lower productivity areas of the coastal zone.

STUDY RESULTS: Coast-wide studies observed 54 species of fishes that were associated with these 

small platforms in the nearshore zone. The assemblage(s) included juveniles of 29 species, indicating the 

importance of nearshore platforms as diverse nursery habitat. Juvenile red snapper were observed at 

many of these platforms (~42% in 2013 and 57% in 2014), often in large number, during the late summer 

when YOY recruitment peaks. Other important reef fish such as YOY lane snapper, mangrove snapper 

and gag grouper were also observed frequently at nearshore platforms. We were able to subdivide the 

coastal zone into three regions based upon broad-scale interactions between freshwater input and the 

bathymetry that drives major distinctions in interregional hydrography and fish assemblages. Co-occurring 

within this expansive artificial reef network we observed that oxygen levels (both hypoxia and 

supersaturation) had significant impacts on the vertical distribution and behavior of the reef associated 

fishes we observed around platforms. Platforms offer reef-like habitat features in the upper water column 

that appear to offer refugia for some reef-associated species during low oxygen events. Significant 

intraregional differences in physicochemical features were related to the presence of hypoxia and the 

distribution of sandy shoals, and platform complexity. Eleven species accounted for most of the fish 

assemblage dissimilarities, composing ~93% of all fishes observed. Habitat suitability indices for these 11 

species provided information about habitat selection across horizontal and vertical physicochemical 

gradients throughout the coastal zone, and within hypoxic and well-oxygenated stratified water columns. 

East Bay, near the outlet of the Mississippi River, exhibited less hypoxia and a distinct fauna that included 

four adult goliath grouper (Epinephelus itajara). This endangered fish was observed during spawning 

season (summer), suggesting that East Bay might support a spawning aggregation.

In summers of 2015–2016 studies focused on small platforms in the area of Ship Shoal blocks off central 

Louisiana. These studies focused on how hypoxia affected small platforms as fish habitat on and off Ship 
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Shoal, the growth and development rates of fouling organisms and grazing rates of fishes on fouling and 

fouling associated biota. Results of cross shelf hydrographic factor analysis showed that the river’s 

influence, bottom oxygen depletion and bottom salinity, and temperature gradient were the principal 

factors driving environmental variation in the Ship Shoal area during 2016. There was no clear effect of 

hypoxia on the relative abundances of reef-associated fishes suggesting that fishes stay at platforms 

during low oxygen event. There were 29 fish species identified in this area with Atlantic spadefish, 

sheepshead, gray snapper, blue runner, and Atlantic bumper observed at ~73% of sites comprising ~96% 

of all fishes. Amphibalanus spp. was the dominant barnacle on platforms in this area, comprising 93.2% 

of all newly settled barnacles. There were significant inter-annual differences in the settlement and growth 

rates of barnacles fouling small platforms. Barnacle settlement rates were generally higher at shoreward 

platforms and closer to the surface. Observations of fish grazing showed that grazing on platforms was 

dominated by sheepshead in this area although a variety of other fishes such as spadefish, gray snapper, 

and black drum were also observed grazing prey living on platforms. Diet studies of sheepshead and 

stone crabs showed a strong dependence on platform derived primary and secondary production.

STUDY PRODUCT(S): 

Reeves D. 2015. Oil and gas platforms on Ship Shoal, Northern Gulf of Mexico, as habitat for reefassociated organisms [thesis]. Baton Rouge: Louisiana State University.

Munnelly RT. 2016. Fishes associated with oil and gas platforms in Louisiana’s river-influenced nearshore 

waters [thesis].Baton Rouge: Louisiana State University.

DB Reeves, RT Munnelly, EJ Chesney, DM Baltz, BD Marx. 2017. Stone crab Menippe spp. populations 

on Louisiana's nearshore oil and gas platforms: Higher density and size at maturity on a sand shoal. 

Trans Am Fish Soc.146(3):371–383.

DB Reeves, EJ Chesney, RT Munnelly, DM Baltz, BD Marx. 2017. Abundance and distribution of reefassociated fishes around small oil and gas platforms in the Northern Gulf of Mexico’s hypoxic zone. 

Estuaries Coasts. 41(7):1835–1847.

DB Reeves, EJ Chesney, RT Munnelly, DM Baltz. 2018. Barnacle settlement and growth at oil and gas 

platforms in the northern Gulf of Mexico. Mar Ecol Prog Ser. 590: 131–143.

DB Reeves 2018. The influence of river discharge on fishes and invertebrates associated with small oil 

and gas platforms in nearshore Louisiana [dissertation]. Baton Rouge: Louisiana State University.

* P.I.’s affiliation may be different than that listed for Project Manager(s).

MAP SHOWING AREA OF STUDY (Figure 4 of Report OCS Study BOEM 2019-077)
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Figure 4. Regions (West, Central, East) of distinctly different hydrography based on all 

hydrographic data collected in 2013 and 2014. (n=343)