Taxonomic Distinctness Analysis between a Platform-Associated Community and a Coral Reef in the Southern Gulf of Mexico: A Proposal for Assessing Sessile Communities Associated with Offshore Oil Platforms

The ecological role regarding biological communities associated with Offshore Oil and Gas Platforms (OGP) remains controversial. New metrics are needed to analyze diversity on OGP and its relationship to the natural environment. We assessed taxonomic diversity of sessile communities on a Fixed Oil Tower (FOT) and compared it with natural reef systems using average taxonomic distinctness indices (Δ+) and variation (Λ+) in the southern Gulf of Mexico. As a first step, we assessed biodiversity through photographic analysis across 9 depth intervals (2–40 m). We employed a point abundance counting method to estimate the relative abundances (%). Sponges (Porifera) dominated the assemblage (54.08%), particularly at intermediate depths (5–30 m). Brown algae characterized shallow zones (2 m), while bryozoans prevailed in deeper areas (35–40 m). Species richness peaked at 15 and 25 m depths (S' = 53). Beta diversity analysis indicated that depth-driven species replacement was the primary mechanism structuring communities, creating distinct depth-specific assemblages. Gamma diversity estimates suggested 124 total species, with 115 observed. Taxonomic distinctness comparisons between FOT and Cayo Arcas Reef communities showed remarkably similar values (Δ+ = 76.13 vs. 78.49) across three taxa (Porifera, Cnidaria, Chordata), indicating comparable phylogenetic diversity despite structural differences. These findings suggest the FOT functions as an effective reef extension, supporting sponge-dominated communities analogous to natural systems. Our results demonstrate that taxonomic distinctness indices provide robust, scale-independent metrics for comparing artificial and natural marine communities. This study establishes the first comprehensive biodiversity baseline for OGP in the southern Gulf of Mexico.