Abstract
The continental shelf of the northwestern Gulf of Mexico harbors extensive reefs and banks that support diverse coral reefs and mesophotic communities. Mesophotic communities range in depth from 40 to 200 m and, in this region, foster some of the densest coral forests [aggregations of mesophotic octocoral, antipatharian, and branching stony coral communities] reported in published literature (10.23 ± 9.31 col/m2). The geologic features underlying the exposed substrates that harbor mesophotic communities are targeted for extensive hydrocarbon exploration and extraction, as they often contain oil and/or natural gas. The Bureau of Ocean Energy Management regulates offshore energy development in the United States and is tasked with protecting sensitive biological communities from impacts related to oil and gas activities. This study analyzed alpha and beta diversity of mesophotic coral forests on fourteen topographic banks in the northwestern Gulf of Mexico. The objective of the study was to examine differences in structure and community in relation to lease stipulations established by the Bureau of Ocean and Energy Management. It was determined that dense and diverse mesophotic coral forests and carbonate producers exist in present regulatory zones that prohibit oil and gas activities; however, the coral communities exist in higher densities, diversity, and richness in low relief substrates outside of these regulatory zones. Our findings suggest low relief hard substrates serve as important habitat for mesophotic coral forests; thus, we suggest the expansion of current stipulations should be considered to provide better protection to vulnerable coral communities on low relief features. Furthermore, additional studies to refine the relationship between low relief structures and biodiversity are needed to develop more meaningful habitat definitions to support resource management and improve resource protection in the future.
Highlights
In the Gulf of Mexico (GOM), mesophotic communities occur on many hard substrates between 40 and 200 m depth (Semmler et al, 2016)
From 2011 to 2013, remotely operated vehicle (ROV) surveys were conducted on selected hard substrates outside of Bureau of Ocean Energy Management (BOEM) designated No Activity Zones (NAZs) associated with the 14 targeted banks
The reefs and banks along the continental shelf of the northwestern GOM provide extensive habitats that support vulnerable mesophotic coral forests in densities greater than those documented to date in the Caribbean Sea (Slattery and Lesser, 2021), the North Atlantic Ocean, and the Mediterranean Sea (Cau et al, 2015; Chimienti et al, 2020)
Summary
In the Gulf of Mexico (GOM), mesophotic communities occur on many hard substrates between 40 and 200 m depth (Semmler et al, 2016). 70 m is predominantly composed of antipatharians [protected against international trade by the Convention on International Trade in Endangered Species (CITES)], octocorals, and few branching corals (Hickerson and Schmahl, 2005; Schmahl et al, 2008) These communities are considered vulnerable due to their susceptibility to bottom disturbing activities, including fishing, dredging, and hydrocarbon exploration, production, and decommissioning (Gass and Roberts, 2006; Lumsden et al, 2007; Reed et al, 2007; Heifetz et al, 2009; Yoklavich et al, 2018; Chimienti et al, 2019). Accidental discharges, spills, and dredging can introduce contaminants and pollutants into the water column that, depending on the specific chemicals and duration of the event, can cause patchy tissue death and non-acute general declines in coral condition (Esslemont et al, 2004; Erftemeijer et al, 2012; White et al, 2012; Hsing et al, 2013; Girard and Fisher, 2018)
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