Coral bleaching and recovery from 2016 to 2017 at East and West Flower Garden Banks, Gulf of Mexico

Abstract

East Flower Garden Bank (EFGB) and West Flower Garden Bank (WFGB), part of Flower Garden Banks National Marine Sanctuary (FGBNMS) in the northwestern Gulf of Mexico, support tropical coral reefs that exhibit over 50% living coral cover. These reefs have been monitored annually since 1989, and in 2016 were exposed to higher than normal seawater temperatures leading to a severe bleaching event. Corals at EFGB and WFGB showed no signs of bleaching until September 2016, occurring later in the year compared to other reefs in the Caribbean region. Coral bleaching and subsequent recovery at each bank were documented through a time series of repetitive photographs within previously established long-term monitoring stations. Preceding the event, mean live coral cover within monitoring stations was collectively 64 ± 2%. Prior to signs of bleaching from July to September 2016, seawater temperatures on the reef were above 30°C for a total of 36 d at EFGB and 21 d at WFGB. By October 2016, 67 ± 5% of the coral cover within EFGB monitoring stations and 25 ± 3% within WFGB monitoring stations exhibited signs of bleaching or paling stress, with dissimilarities in the amount of bleaching most likely due to significant differences in thermal profiles between banks. Significantly increasing long-term trends for daily mean seawater temperature indicate that temperatures on the banks have become warmer over time, and calculated bleaching threshold curves suggest that more than 50 d above 29.5°C would initiate a bleaching year at EFGB and WFGB. Even though recovery within monitoring stations at both banks was documented with no significant declines in mean coral cover from 2016 to 2017 (64% and 62%, respectively), it is likely FGBNMS will be subject to additional and more frequent bleaching events in the future as ocean temperatures continue to rise.

The 2014–2017 global-scale coral bleaching event: insights and impacts

“…In some cases, local conditions like upwelling (Riegl et al 2019) or high turbidity (Morgan et al 2017;Teixeira et al 2019) may help corals survive, while local growth of fleshy algae may increase bleaching susceptibility (Smith et al 2019). In others, reefs may be predominated by a few species that are resilient to bleaching and recover well (Johnston et al 2019) but may have reduced reproductive output or success (Fisch et al 2019;Hughes et al 2019b). Repeated years of heat stress may result in less bleaching during later events (Harrison et al 2018;Fisch et al 2019;Hughes et al 2019a) or may overwhelm reefs to the point that their persistence is in question (Riegl et al 2018;Raymundo et al 2019).…”

Transcriptomic plasticity of mesophotic corals among natural populations and transplants ofMontastraea cavernosain the Gulf of Mexico and Belize

“…Depth was a significant factor for all environmental metrics, but site was only a significant factor affecting PAR metrics (Kruskal‐Wallis: all significant p < 0.002; Table ). During September 2016 (just prior to and during the 12 month timepoint), sea surface temperatures were >30°C, corresponding to a coral bleaching event observed at WFGB and EFGB (Johnston et al., 2019). All of the shallow controls and transplants at both sites exhibited some level of visible bleaching.…”

“…Perhaps the most interesting, yet unexpected, outcome of the transplant experiment was the opportunity to examine responses of transplanted corals following a thermal stress event. Previous monitoring efforts at WFGB and EFGB have demonstrated that temperatures of 29.5°C or greater for >50 days can cause bleaching events (Johnston et al., 2019). Mean daily temperatures at the shallower sites remained >30°C for at least 80 days through the 12 month timepoint (Figure ), resulting in widespread coral bleaching observed at the shallower depth zones of both WFGB and EFGB.…”

The Future of Reef Ecosystems in the Gulf of Mexico: Insights From Coupled Climate Model Simulations and Ancient Hot-House Reefs

“…• Mean annual SST: an upper temperature limit for coral bleaching in the Pacific has been reported as 28.1 • C, but more recent work shows an increasing bleaching threshold of 28.7 • C (Sully et al, 2019). In the GoM, reported bleaching thresholds are higher, approaching 30-31 • C. Wilkinson and Souter (2008) found corals bleached in the Caribbean when SST reached 31 • C and were sustained; Florida Keys and Flower Garden Banks reefs bleach when SST reached 30-31 • C (Johnston et al, 2019b) or 29.5 • C if temperatures were sustained for 50 days (Johnston et al, 2019a). We consider mean annual SSTs approaching 30 • C as high risk for coral bleaching in the GoM.…”

“…At present, there is strong evidence that GoM reefs have experienced thermal stress since 1878 (Kuffner et al, 2015) with recent bleaching events in 2016/2017 (Johnston et al, 2019a). In situ SST records show a 0.8 • C increase over the last century in the Florida Keys, where corals have declined especially in the later part of the twentieth century.…”