Coral Reef Long-Term Monitoring at East and West Flower Garden Banks: 2024 Annual Report

This report summarizes fish and benthic community observations and water quality data collected from the coral reefs of East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB) in 2024, alongside 35 years of historical long-term monitoring data. EFGB and WFGB are part of the National Oceanic and Atmospheric Administration’s Flower Garden Banks National Marine Sanctuary (FGBNMS), located in the northwestern Gulf of America. The annual coral reef long-term monitoring program, initiated in 1989, is funded by FGBNMS and the Bureau of Ocean Energy Management, with support from the National Marine Sanctuary Foundation. In 2024, mean coral cover was 56%, estimated from random transect data within EFGB and WFGB one-hectare study sites. Coral cover at WFGB has increased significantly over time, while EFGB values have remained stable. The Orbicella spp. complex, listed as threatened under the Endangered Species Act, accounted for the majority of the coral cover within the study sites. Benthic composition across the coral reef differed significantly between the banks, largely due to differences in macroalgae and colonizable substrate cover. While mean macroalgae cover was 24% within the EFGB study site and 17% within the WFGB study site, macroalgae cover has increased significantly at both banks since 1998. The reef fish community was dominated in terms of relative abundance by the families Labridae (wrasses) and Pomacentridae (damselfishes). Biomass was evenly distributed between large and small individuals, and herbivores represented the greatest mean biomass at both banks, marking a notable shift from previous years when piscivores dominated total biomass. No non-native regal demoiselles were observed in 2024; however, they were observed on nearby artificial reef sites and Stetson Bank. A significant increase in reef-cap seawater temperature was detected at both banks from 1990 to 2024. In situ reef-depth temperature data indicated that EFGB approached, while WFGB exceeded, site-specific bleaching thresholds in 2024. Coral paling was first observed in July, with bleaching more pronounced later in the season. At WFGB, 10.3% of coral cover was bleached and 46.9% was pale by late September. The 2024 bleaching event followed a major bleaching event in 2023 and is the first instance of consecutive bleaching years recorded at FGBNMS. The Flower Garden Banks remains one of very few reefs in the Western Atlantic Ocean where coral reefs appear to have resisted degradation over the last several decades. Continued long-term monitoring will be essential for understanding the mechanisms underlying this apparent resistance and for supporting effective sanctuary management.

Key Words

benthic community, coral ecosystem, coral reef, fish community, long-term monitoring, Flower Garden Banks National Marine Sanctuary, Gulf of America, marine protected area, water quality, coral disease