Coral Gardens Reef, Belize: An Acropora spp. refugium under threat in a warming world

Abstract

Live coral cover has declined precipitously on Caribbean reefs in recent decades. Acropora cervicornis coral has been particularly decimated, and few Western Atlantic Acropora spp. refugia remain. Coral Gardens, Belize, was identified in 2020 as a long-term refugium for this species. This study assesses changes in live A. cervicornis coral abundance over time at Coral Gardens to monitor the stability of A. cervicornis corals, and to explore potential threats to this important refugium. Live coral cover was documented annually from 2012–2019 along five permanent transects. In situ sea-surface temperature data were collected at Coral Gardens throughout the study period and compared with calibrated satellite data to calculate Maximum Monthly Mean (MMM) temperatures and Degree Heating Weeks (DHW). Data on bathymetry, sediment, substrate, herbivore abundance, and macroalgal abundance were collected in 2014 and 2019 to assess potential threats to Coral Gardens. Live coral cover declined at all five transect sites over the study period. The greatest loss of live coral occurred between 2016 and 2017, coincident with the earliest and highest maximum average temperatures recorded at the study site, and the passage of a hurricane in 2016. Structural storm damage was not observed at Coral Gardens, though live coral cover declined after the passage of the storm. Uranium-thorium (230Th) dating of 26 dead in situ fragments of A. cervicornis collected in 2015 from Coral Gardens revealed no correlation between coral mortality and tropical storms and hurricanes in the recent past. Our data suggest that several other common drivers for coral decline (i.e. herbivory, predation, sedimentation, pH) may likely be ruled out for Coral Gardens. At the end of the study period, Coral Gardens satisfied most criteria for refugium status. However, the early onset, higher mean, and longer duration of above-average temperatures, as well as intermittent temperature anomalies likely played a critical role in the stability of this refugium. We suggest that temperature stress in 2016 and perhaps 2015 may have increased coral tissue vulnerability at Coral Gardens to a passing hurricane, threatening the status of this unique refugium.

A Ten-Year Record Shows Warming Inside the Belize Barrier Reef Lagoon

“…Our in situ data were higher than the SST data overall except for the summer months July, August, and September when satellite SSTs were lower than in situ measurements. Comparative results from other studies found that SSTs were lower than in situ temperatures [12,13]. The key point is that the satellite data do not match temperature data at the depths where corals are growing.…”

“…This study revealed increasing lagoon water temperatures over the course of 10 years. It adds a point of comparison for other sites in Belize (e.g., [3,8,12,13,16,19]) and elsewhere in the Western Caribbean region (e.g., [5]). Temperatures were more variable and higher inside the lagoon than at the nearby reef crest of Carrie Bow Cay).…”

“…The Belize Reef system, and especially its huge lagoon, have unique marine ecological habitats that support a regional fauna, with many species being adapted to this particular environment. Oceanographic conditions in this region should be monitored and the reefanimal populations carefully surveyed to assess changes in fisheries and the coral reefs (e.g., as nicely exemplified by [12,19]).…”