Bleaching

El Niño Southern Oscillation (ENSO) events are known to bring high sea surface temperatures and in turn cause coral bleaching. The Fall 2015 ENSO event has had record breaking temperatures and has been severely detrimental to Pacific coral reef ecosystems. To gauge the effect this ENSO event would have on the Caribbean, this study looked at the frequency and severity of bleaching and paling, during this ENSO event. The bleaching was measured along a 2 m wide by 10 m long transect. Coral colonies along the transect were observed once a week for four weeks and the water temperature was recorded hourly. At the end of data collection, the overall number of corals experiencing bleaching was recorded and the percent difference in paling and bleaching from week to week was measured. At the end of the four weeks it was found that 60 out of 192 coral colonies were experiencing some form of bleaching. By the fourth week there was no significant increase in bleaching, and paling had significantly increased until week four. This trend followed the decrease of water temperature from week one to week three with signs of coral recovery, but there was also evidence of water temperature starting to increase again by week four.. This study shows the resilience of Bonairean reefs and that this ENSO event may have a lesser affect on the Caribbean coral reefs compared to the Pacific.

This student research was retrieved from Physis: Journal of Marine Science XVIII (Fall 2015)19: 47-52 from CIEE Bonaire.

In 2004, as part of a GEF funded project entitled “Coral Reef Targeted Research and Capacity Building” (CRTR), to assess the current status and future of these important communities, six groups of researchers looked at different aspects of the dynamics and degradation of coral reefs worldwide (i.e. Coral diseases, bleaching, connectivity, remote sensing. One of these groups, the Coral Disease Working Group (CDWG), assessed the number, prevalence, distribution, impacts and host range of coral diseases and their spatial and temporal variability in the wider Caribbean.

Curacao was selected as one of six localities spread over the Caribbean, and one of two southern localities. Results presented here represent our preliminary approach and surveys in Curacao. Surveys were done in permanently marked transects using the CARICOMP sampling protocol. Overall, coral diseases in these sites had, on average, a relatively low prevalence (5.74 ± 3.7%) at the community level (all colonies from all species included). Curacao was the second country with higher disease prevalence of the 6 countries visited across the Caribbean during the Summer-Fall of 2005, the weight of this prevalence coming from one of the two sites surveyed on the island. The most common diseases observed were dark spots syndrome (DSS), white plague type II (WP-II) and secondary infections by ciliates. Noteworthy was the lack of bleaching in these two reef localities and in general, in the Netherland Antilles when most of the eastern, northern and western were suffering the worst bleaching event on record for the Caribbean. Bleached colonies were only mild paling patterns and the overall prevalence was below 1.0 %. Octocoral diseases were almost two times more prevalent (9.6 ± 16.9%) than coral diseases in Curacao.

Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m. Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent photo quadrats. About 20 zoo- xanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies in deep reefs over the last 30 years. In deep reefs, non- agaricid species are decreasing but agaricid domination will be interrupted by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in the deep-reef environ- ment with extremely low temperatures possibly related to deep-reef bleaching.