Demographic shifts in stony coral populations in a remote reef system in the Southern Gulf of Mexico during the 2023-2024 marine heat wave

We evaluated shifts in coverage and colony size structure distribution of scleractinian corals at a remote reef system in the Southern Gulf of Mexico during the 2023–2024 marine heatwave. Permanent parcels established at three reef sites (9–20 m depth) were surveyed in the summer of 2023 and 2024 using underwater digital photogrammetry. The obtained orthomosaics were analysed in Geographical Information Systems (GIS) to estimate species richness, area of live tissue cover (m ² ), and colony partial mortality. Probability density curves based on log10-transformed colony area measurements were constructed, and skewness and kurtosis estimated. Colony size classes for each species were categorised I small, medium, and large based on observed size ranges quartiles. Non-parametric statistical tests were used to identify significant changes (p < 0.05) over time. The temperature data showed that the DHW values reached 19.3°C-weeks during the study period. The coral community comprised 13 taxa, dominated by reef building corals. Live coral tissue decreased by 4.7% over time. Colpophyllia natans , Orbicella annularis , O. faveolata , and O. franksi lost coverage and presented changes in population size structure, characterised by the loss of large colony sizes and an increase in small colonies. Montastraea Cavernosa and Diploria labyrinthiformis , showed a shift in the size distribution, with no coverage changes. Pseudodiploria strigosa , Siderastrea siderea , and Porites astreoides were tolerant to thermal stress. Partial mortality remained relatively stable, except for D. labyrinthiformis . Coral populations showed differential responses to unprecedented thermal stress, underscoring the need for conservation strategies, even in regions with low anthropogenic disturbance.