Coral Bleaching

Large scale coral mortality in Barbados: a delayed response to the 2005 bleaching episode
H.A. Oxenford. R. Roach and A. Brathwaite Proceedings of the 11 th International Coral Reef Symposium, Ft. Lauderdale, Florida, 7-11 July 2008
Session number 16 ” Corals in Barbados suffered widespread bleaching during the high temperature event of 2005. Six reefs were monitored for one year (October 2005 – November 2006) to determine mortality impacts and rate of recovery from this bleaching event. Five 1 x 20 m band transects and five 20 m line transects were quantitatively surveyed at each site, every four months. Bleaching prevalence dropped from a mean of 71% of colonies in October 2005 to 38% in February, to 17% in June, before rising again to 25% in November 2006. Coral mortality remained low for five months (means: 3.8% colony surface dead; or 4.8% dead cover), but rose sharply after 10 months (means: 18.7% colony surface; or 25.9% cover), eventually declining after 15 months to near ambient levels (means: 2.0% colony surface; or 6.1% cover). Like other eastern Caribbean islands, recovery from bleached condition was slow and overall mortality impact was high on both deep and shallow reefs. In contrast were the delayed onset of mortality and low incidence of coral disease. High losses in live coral cover have significant economic implications for the island which derives a major proportion of its GDP from tourism, and relies heavily on healthy reefs for coastal protection.”

High Water Temperatures/Coral Bleaching
in Caribbean Summer-Fall 2023

From the August 2023 Caribbean Coral Reef Watch Bulletin

Dying coral reefs demand Caribbean takes new approaches
on, Oct 16, 2023 “Severe bleaching and the decline in the number of corals are posing a major threat to the Caribbean. At the start of summer, the Caribbean Institute for Meteorology and Hydrology (CIMH) declared the entire region was under coral bleaching watch or warning, due to the warmer temperatures. For the four-month period of June to September, CIMH predicted “there is high probability Coral Bleaching Heat Stress will reach and exceed Alert Levels One and Two for most of the Caribbean”…”We already have seen coral bleaching but we can expect if we get to 1.5 degrees Celsius that we will see a loss of 70 to 90 per cent of our corals. If we get to 2 degrees Celsius or higher, then 99 per cent of our coral is being lost and that is absolutely devastating and again affects the habitability of our islands,” said the IPCC vice chair…”Even if we adapt there are still going to be loss and damage to those impacts of climate change. Above 1.5 degrees Celsius, some natural solutions may no longer work – so things like planting mangroves, [and] coral reef restoration are not going to be feasible. So we are going to have to work on different ways…Senior climate change specialist of the IDB, Jennifer Doherty-Bigara, while speaking on climate change and poverty reduction supported Thomas’ sentiments. “Coral reefs are bleaching so fast in Barbados, that the solution they would have brought are no longer viable,” she told reporters.”Oct 12, 2023:
Coral Bleaching Alert
Barbados Fisheries Division, Oct 12, 2023 “Due to recent high water temperatures it is predicted that bleaching is likely to occur over the next few weeks.”

AGRRA Coral Bleaching Reports/Interactive Maps AGRRA refers to the The Atlantic and Gulf Rapid Reef Assessment Program.
There are two maps/datasets on Coral Bleaching. Both include observations from Barbados, with photographs.

AGRRA 2023 Coral Bleach Reports
“This map displays all available bleaching data for the current bleaching season (summer 2023). Date information is available in the pop up table for each survey. This map is currently being updated so be sure to check back for the latest information”. Currently there are reports posted for Folkestone Marine Reserve on Oct 6, 2023; and Bajan Queen & Reef, Sep 4, 2023.
All Coral bleach data combined (2017-2023)
“This map displays all available bleaching data from 2017 to present. Date information is available in the pop up table for each survey.”

Sep 2023:
Caribbean Coral Reef Watch Sep 2023
Significant and widespread coral bleaching and mortality expected over the following 2-3 months due to extensive and extreme heat stress across the region
All issues availale at

Largest, hottest, longest Caribbean bleaching: corals dying from extreme heat
By Tom Goreau Oct 14, 2023 on “The entire world is suffering record high temperatures, and the Caribbean is in the forefront of global warming… Decades of progress regenerating corals have been wiped out”

Caribbean sea coral bleaching 2023: Jamaica, Barbados, Belize
YouTube Video on Divingmore Channel

Tracking Coral Bleaching Events Globally Using Reef Check
YouTube Video, Coral Reef Alliance

Bleaching of the fire corals Millepora
William K. Fitt, Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 2012 9A Coral bleaching and climate change  “…Millepora complanata and M. alcicornis were among the first species to exhibit bleaching in the greater Caribbean during the 1973, 1982-3, 1987-88 El Niños ”

Response of Millepora alcicornis (Milleporina: Milleporidae) to two bleaching events at Puerto Morelos reef, Mexican Caribbean
Anastazia T. Banaszak et al. Rev. Biol. Trop., 51, Supl. 4: 57-66, 2003

Ecology, Biology and Genetics of Millepora Hydrocorals on Coral Reefs
Caroline E. Dubé et al., 2019.. FROM THE EDITED VOLUME Invertebrates – Ecophysiology and Management

Zooxanthellate hydrocorals are thought to be extremely sensitive to bleaching [130, 133] and can be threatened by future climate change. Millepora spp. have been reported to be among the first cnidarians to lose their zooxanthellae symbionts during widespread bleaching events [134] and they have suffered local or regional extinctions from bleaching in the Pacific [78, 85, 135]. Numerous investigations of bleaching events on Caribbean and Florida Keys reefs have reported bleaching of Millepora colonies [133, 136, 137, 138, 139], with M. alcicornis, a finely branched species, being the most severely affected reef corals. Such coral morphology has been described to be more susceptible to bleaching than encrusting and massive species [140]. Yet, bleached colonies of M. alcicornis remained alive during a bleaching event affecting a north-eastern Brazilian reef [133], which is in accordance with previous reports that Millepora species are also the first to recover from short-term bleaching [136, 137]. In the Maldives Archipelago (Indian Ocean), Millepora was reported to be the major reef-building coral in shallow reefs (7 m depth), producing some ‘Millepora zones’ [141]. Three species were well documented, the massive species M. cf. platyphylla [46, 142] and two branching ones, M. tenera [51, 143, 144] and M. latifolia [143]. However, many recent surveys of the Maldivian reefs have identified another pattern of distribution, where none to low abundances of Millepora species were recorded (1–2 depending on the species) [145, 146, 147, 148]. Gravier-Bonnet and Bourmaud [148] suggested that milleporids were extirpated from several Maldives atolls, following the 1997–1998 El-Nino Southern Oscillation event (ENSO). ENSO has induced a strong bleaching and massive coral mortality (of up to 90%) in the tropical Indian Ocean, including the Maldives [145, 149]. On the Great Barrier Reef, Millepora spp. were also the most susceptible taxa to the mass bleaching event of 1998, with 85% of mortality [130], while they showed no evidence of bleaching at Moorea, although scleractinian corals were severely bleached at this location [150]. During 2014–2017, the worst documented bleaching event observed [26, 27], M. cf. platyphylla showed no sign of bleaching at Moorea, although about 60% of scleractinian corals were bleached on the fore reefs (Figure 6A). Since February 2019, Moorea’s reefs are suffering from another mass bleaching event, with colonies of M. cf. platyphylla showing sign of bleaching and mortality (Figure 6B). Differential susceptibilities to this bleaching event were also observed between M. cf. platyphylla colonies (Figure 6C). Ongoing surveys will help quantifying bleaching susceptibility and mortality among coral taxa and locations, as well as between fire coral growth forms and genotypes (Dubé et al. in prep). Nevertheless, a previous study has shown that temperature is the primary factor related to bleaching in M. alcicornis, but that synergism with exposure to solar radiation may play a key role in hydrocoral bleaching [151]. Also, multifocal bleaching in hydrocorals, consisting of numerous scattered bleached spots, has been first described as a syndrome caused by an infectious disease affecting several colonies of M. dichotoma in the Red Sea [152]. 16S rRNA gene sequencing showed that affected tissues match sequences of bacteria belonging to Alphaproteobacteria and Bacteroidetes members previously associated with various diseases in scleractinian corals [153]. Yet the mechanisms of multifocal bleaching, its aetiology and mode of transmission remain unknown. Nevertheless, many studies have addressed the aetiology and effects of bleaching in Anthozoan species, wherein changes in the expression of genes and proteins were observed, and particularly heat shock proteins and transcription factors [154, 155, 156, 157, 158, 159]. A recent study demonstrated that bleached specimens of M. alcicornis in Mexican Caribbean undergo a moderate decrease in symbiont’s density and photosynthetic pigments, in addition to differential expression of 17 key proteins, such as calmodulin, actin and collagen often coupled with calcium homeostasis, exocytosis and cytoskeleton organization in Anthozoan species [139].