Widespread Coral Bleaching at Enmedio Reef, Lobos–Tuxpan Reef System, Mexico (2024)

Resumen

Background: The Lobos-Tuxpan Reef System (LTRS) experienced a massive coral bleaching event in 2024. We documented the prevalence of bleaching in the Enmedio reef and analyzed data on sea surface temperature and Degree Heating Weeks (DHW) from a time series to determine the periods of greatest thermal stress. Objectives: To record coral bleaching on the Enmedio reef during 2024 on the leeward zone of the reef, an area with high abundance of massive corals. The thermal stress was analyzed based on the Nighttime Sea Surface Temperature (NSST). Methods: Sampling was performed on the leeward slope and in the western sector of the reef lagoon. Surveys were conducted by free diving along 50 × 2 m transects. Three transects were laid out west of the reef flat at a depth of 1 m, while four transects were established on the leeward slope at depths of 3 and 5 m. Coral colonies were identified to species level and classified as either healthy or bleached. Results: We recorded a 60.5% bleaching prevalence across nine coral species. The most susceptible species were Orbicella annularis (Ellis, 1786), Colpophyllia natans (Houttuyn, 1772), Pseudodiploria strigosa (Dana, 1846), and Millepora alcicornis (Linnaeus, 1758). Analysis of the time series revealed that the 2024 bleaching coincided with prolonged and intense thermal stress. Conclusions: The severity of bleaching can be directly attributed to a progressive accumulation of thermal stress, that reached level 3 (13.5 DHW) for the first time in 2024. These bleaching episodes occurred during the fourth global coral bleaching event (2023–2024) declared by NOAA, within the context of an increasing trend in the frequency of elevated temperatures affecting mid-latitude reefs (15–20° N), such as Enmedio Reef in the SALT.