Long-Term Monitoring at East and West Flower Garden Banks: 2023 Annual Report

This report summarizes fish and benthic community observations and water quality data collected from East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB) in 2023, along with 34 years of historical 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 Mexico. The annual long-term monitoring program began in 1989 and is funded by FGBNMS and the Bureau of Ocean Energy Management, with support from the National Marine Sanctuary Foundation. In 2023, mean coral cover, estimated from random transect data within EFGB and WFGB one-hectare study sites, was 55%. Mean macroalgae cover was 31% within the EFGB study site and 29% within the WFGB study site. Since 1989, mean coral cover has increased significantly at WFGB and remained stable at EFGB. Mean macroalgae cover has increased significantly at both banks since 1998. This is the second year that data from reef-wide stratified random photo transects were include in the report in addition to data from the study sites on each bank. Mean benthic cover in reef-wide random transects was similar to that in study site random transects; however, more data are needed for a trend analysis. Mean coral cover within repetitive photostations has increased significantly since 1989 at both banks. The Orbicella spp. complex, listed as threatened under the Endangered Species Act, accounted for the majority of the coral cover within the study sites. The reef fish community was comprised primarily of 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. One manta ray and two lionfish were observed. No non-native regal demoiselles were observed in 2023; however, they were observed in Stetson Bank surveys and on nearby artificial reef sites. During 2023, water temperatures at reef depth exceeded 30 °C for 53 days at EFGB, surpassing the local threshold for coral bleaching (33 days). At WFGB, temperatures exceeded 30 °C for 31 days, surpassing the local threshold for coral bleaching (22.3 days). By late September, coral bleaching affected an average of 28.06% of reef-wide coral cover at EFGB and 5.61% of reef-wide coral cover at WFGB, with paling affecting an average of 50.64% and 17.09% of coral cover, respectively. A significant increase in seawater temperature was detected at both banks from 1990 to 2023. The Flower Garden Banks remains one of very few reefs in the Western Atlantic Ocean where resources have resisted degradation over the last several decades. Maintaining successful stewardship will require continuing the strong links between sanctuary management and long-term monitoring.

Key Words

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