========================= Bleaching Report =========================== ************************************************************************ ******************* 2003 Bermuda bleaching event *********************** ************************************************************************ Report from: Helen Brylewska Samantha de Putron Graham Webster Matt Strong Bermuda Biological Station for Research Bermuda Date: 21 November 2003 "The following is a report of the bleaching event witnessed in Bermuda this summer. "Coral bleaching was witnessed this summer on the outer rim reefs and lagoonal patch reefs of Bermuda (32 20N, 65 50W). Surveys of 2 sites at each reef type were conducted by the Benthic Ecology Research Program of the Bermuda Biological Station for Research (BBSR) at the end of August/beginning of September (28/08/03 03/09/03) and again at the end of September/beginning of October (19/09/03 06/10/03), looking at the occurrence of bleaching and disease. The Rim Reef sites are at the edge of the Bermuda platform approximately 17 km from shore, at a depth of 2-8m. Inshore of the Rim Reef is the enclosed lagoon. The lagoonal patch reefs monitored in this study are approximately 9km from land, at a depth of 1-4m. Each survey consisted of 12 x 20m long 2 m wide transects. The surveys recorded the percentage cover as well as the occurrence of bleaching and disease of the primary reef building and most abundant coral species in Bermuda: Diploria labyrinthiformis, Diploria strigosa, Montastraea cavernosa, Montastraea franksii and Porites astreoides. The fire coral Millepora alcicornis was included as well as the gorgonians Pseudoplexaura porosa Gorgonia ventalina. General observational notes were made for other species, which are not included in this report. "Of all the coral colonies recorded on the initial survey, 21% were bleached at the rim reef sites and 19% were bleached at the lagoonal sites. Water temperatures were at a maximum and had remained so for longer periods of time than is typical (see below for temperature information). The second surveys, when water temperatures had decreased, showed a decrease in total bleaching to 13% at both sites. The fire coral, Millepora alcicornis was the coral species most affected by bleaching this summer, with 94% of the colonies being bleached to some degree on the rim reefs in early September. On the lagoonal reefs at this time, 77% of M. alcicornis colonies showed some sort of bleaching. Bleaching of M. alcicornis reduced to 70% occurrence on the rim reefs, and to 49% on the lagoonal reefs, one month later by the time of the second survey. In this species, the bleaching on the rim reefs was mainly composed of completely bleached (white) colonies or recently dead colonies (white skeleton with no fouling of algae). At the time of the initial survey 35% of the total M. alcicornis colonies on the rim reef were recently dead. This increased to 43% by the time of the second survey. On the lagoonal reefs, the majority of bleached M. alcicornis were classed as 'pale' or 'blotchy' and only 4% of the total colonies were initially recorded as recently dead. This reduced to 3% by the time of the follow up survey. A total of 60% of M. alcicornis colonies were classed as 'pale' or 'blotchy' initially; this reduced to 43% by the time of the second survey. Other colonies that were bleached at both sites were (in order of prevalence) Montastrea franksi, Diploria strigosa, M. cavernosa, D. labyrinthiformis and Porites asteroides. It should be noted that many Agaricia fragilis colonies were extensively bleached in areas on the outer rim reef, although this species was not included in these surveys. "Average temperature over the week in which the initial survey was performed (28/08/03 03/09/03) was 28.9 ºC at the rim reef and 29.5ºC at the lagoonal reefs. The maximum temperatures recorded from the sites were 30ºC at the rim reef, and 30.7ºC at the lagoonal patch reef. The average temperature during the week in which the second surveys were performed (19/09/03 06/10/03) was 26.7ºC at the rim reef and 26.9ºC at the lagoonal reefs. Bleaching was therefore more prevalent at the Rim Reef sites compared to the Lagoonal sites even though the temperature maximum was greater at the latter. This is similar to past observations in Bermuda (Cook et al., 1990: Coral Reefs 9:45-49; McKinney et al, 1998: BBSR unpublished data) and is understood to relate to a combination of increased turbidity in the lagoon reducing irradiance, and/or the prior thermal history at each site causing the adaptation (and therefore sensitivity) of the coral populations to local conditions. The incidence of disease was very low, with a total of only 1.5% of the rim reef colonies, and 0.1% of the lagoonal corals being diseased on the initial survey. Disease, however, increased slightly by the time of the second survey at both sites, to 1.9% at the rim reefs, and 0.9% at the lagoonal sites. The most commonly witnessed diseases on the scleractinians were a 'White Plague' type disease observed on Diploria labyrinthiformis, Diploria strigosa, Montastrea cavernosa, Montastrea franksi, and Porites asteroides on the rim reefs, and on all these colonies with the exception of Montastrea cavernosa on the lagoonal reefs. Black Band Disease was observed only on D. strigosa on the rim reefs, and on D. strigosa, M. cavernosa and M. franksi on the lagoonal reefs. Aspergillosis was observed on a low percentage of the sea fan Gorgonia ventalina (0% and 1.5% initially at the rim and lagoonal reefs respectively, and 10% and 1.2% at the rim and lagoonal reefs by the time of the second survey). We also collected data on the incidence of hyperplasmic tumours (seen in the Diploria species only) and fish biting (primarily of P. astreoides). Algal galls were sporadically seen on the sea rod Pseudoplexaura porosa." ======================================================================== NOAA's Coral Reef Watch Project NOAA/NESDIS 24 November 2003