Estuarine, Coastal and Shelf Science xxx (2012) 1e5 Contents lists available at SciVerse ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss Coral bleaching at Little Cayman, Cayman Islands 2009 Ruben J. van Hooidonk a,*, Derek P. Manzello a, Jessica Moye b, Marilyn E. Brandt c, James C. Hendee a, Croy McCoy d, Carrie Manfrino b,e a NOAA, Atlantic Oceanographic and Meteorological Laboratory (AOML), 4301 Rickenbacker Causeway, Miami, FL 33149, USA b Central Caribbean Marine Institute, PO Box 1461, Princeton, NJ 08542, USA c Center for Marine and Environmental Studies, University of the Virgin Islands, 2 John Brewer’s Bay, St. Thomas, VI 00802, USA d Department of Environment, Cayman Islands Environment Centre, PO Box 486, Grand Cayman KY1-1106, Cayman Islands e Kean University, Department of Geology and Meteorology, 1000 Morris Ave., Union, NJ 07083, USA article info abstract Article history: The global rise in sea temperature through anthropogenic climate change is affecting coral reef Received 16 August 2011 ecosystems through a phenomenon known as coral bleaching; that is, the whitening of corals due to the Accepted 19 April 2012 loss of the symbiotic zooxanthellae which impart corals with their characteristic vivid coloration. We Available online xxx describe aspects of the most prevalent episode of coral bleaching ever recorded at Little Cayman, Cayman Islands, during the fall of 2009. The most susceptible corals were found to be, in order, Siderastrea siderea, Keywords: Montastraea annularis, and Montastraea faveolata, while Diplora strigosa and Agaricia spp. were less so, bleaching yet still showed considerable bleaching prevalence and severity. Those found to be least susceptible were coral reefs climatic changes Porites porites, Porites astreoides, and Montastraea cavernosa. These observations and other reported e temperature tolerance observations of coral bleaching, together with 29 years (1982 2010) of satellite-derived sea surface Regional terms: temperatures, were used to optimize bleaching predictions at this location. To do this a Degree Heating British overseas territory Weeks (DHW) and Peirce Skill Score (PSS) analysis was employed to calculate a local bleaching threshold Cayman Islands above which bleaching was expected to occur. A threshold of 4.2 DHW had the highest skill, with a PSS of Little Cayman 0.70. The method outlined here could be applied to other regions to find the optimal bleaching threshold 19 410 000 N and improve bleaching predictions. 0 00 80 3 0 W Published by Elsevier Ltd. 1. Introduction The status of coral reefs in Little Cayman is well documented. The island has been included in the Atlantic and Gulf Rapid Reef Temperature is one of the most important environmental vari- Assessment (AGRRA, Manfrino et al., 2003), and the reefs have been ables limiting the distribution of reef-building corals (Dana, 1843; monitored most years since 1998, with coral bleaching reported in Vaughan, 1919), with most shallow-water tropical corals found Little Cayman previously in 1987, 1995, 1998, 2003, and 2005 within 18e30 C (reviewed in Kleypas et al. (1999)). Sustained high (Ghiold and Smith, 1990; Coelho and Manfrino, 2007; Eakin et al., temperature, however, causes large-scale coral bleaching, which is 2010). In 2002, 2004 and 2007 low levels (less than 5% of all the whitening of the coral animal host due to the loss of symbiotic colonies) of bleaching were reported. Prior to 2009, the most algae and/or a reduction in their photosynthetic pigments extensive bleaching occurred in 2005, but the prevalence (number (reviewed by Glynn (1993), and Brown (1997)). of affected colonies divided by total number of coral colonies) of Little Cayman, Cayman Islands is a 17 km by 1.6 km low-lying this event was surpassed in 2009 and remained high through the island in the Western Caribbean Sea with a shallow (9e20 m) spring of 2010. and narrow reef shelf that abruptly drops to great depths outside In July of 2009, parts of the Caribbean Sea began to experience the euphotic zone. The island has a small human population (<200 a positive anomaly above the maximum summertime temperature, full-time residents) and more than 50% of the nearshore waters are coincident with the development of an El Niño event (Bell et al., designated as a marine park or no-take zone, ensuring minimal 2009). direct anthropogenic stress. Coral bleaching has been predicted using various tools, such as a simple fixed threshold based on climatology (Hoegh-Guldberg, 1999), degree heating weeks (DHW) (Gleeson and Strong, 1995; Goreau and Hayes, 1994), and timeetemperature curves * Corresponding author. E-mail address: [email protected] (R.J. van Hooidonk). (Berkelmans, 2002). In this study we improve the DHW method by 0272-7714/$ e see front matter Published by Elsevier Ltd. doi:10.1016/j.ecss.2012.04.021 Please cite this article in press as: van Hooidonk, R.J., et al., Coral bleaching at Little Cayman, Cayman Islands 2009, Estuarine, Coastal and Shelf Science (2012), doi:10.1016/j.ecss.2012.04.021 2 R.J. van Hooidonk et al. / Estuarine, Coastal and Shelf Science xxx (2012) 1e5 establishing a local threshold based on observational evidence; this 2.3. Degree heating weeks can dramatically increase skill of the predictive method (van Hooidonk and Huber, 2009). DHWs were calculated from OISST V2 data for the period We describe the 2009 bleaching event and highlight the response 1982e2010. The DHW method is an accumulative stress index of various coral species. Satellite-derived sea surface temperature based on the sum of the positive anomalies above the maximum (SST) data were used to quantify thermal anomalies expressed in summertime temperature of the previous 12 weeks (Gleeson and DHWs at Little Cayman for the past 29 years (1982e2010). By Strong, 1995; Goreau and Hayes, 1994). The maximum monthly combining the hind-cast with observations of bleaching, a refined, summertime temperature was defined as the warmest month in site-specific thermal threshold in DHWs was established. the 1971e2000 OISST climatology. The method used is similar to previous published work (Donner et al., 2007; van Hooidonk and Huber, 2009). 2. Methods The skill of the DHW technique was assessed using the Peirce Skill Score (PSS, Peirce, 1884), a quantitative score often used in 2.1. Environmental data meteorology and other fields. This score has been applied successfully to predictions of bleaching in the past and allows for The National Oceanic and Atmospheric Administration (NOAA) a quantitative improvement in bleaching prediction, or comparison Optimum Interpolation Sea Surface Temperature version 2 (OISST) between techniques (van Hooidonk and Huber, 2009). This score is data were utilized for temperature analysis. This multi-source defined as the hit rate minus the false alarm rate. Where the hit rate record combines ship and buoy data, together with satellite data is the number of correct predictions of bleaching divided by the from the Advanced Very High Resolution Radiometer (AVHRR) total number of bleaching events, and the false alarm rate is the instrument (Reynolds et al., 2002). OISST data are recorded weekly number of incorrectly predicted bleaching events divided by the at a 1 by 1 resolution. This product has been produced and total number of non-bleaching events (Jolliffe and Stephenson, archived since 1982 and is freely available at: http://www.esrl.noaa. 2003). The score ranges from À1, indicating all predictions or gov/psd/data/gridded/data.noaa.oisst.v2.html. A climatology has hind-casts were wrong, to 1, representative of all predictions being been constructed for this dataset based on the 1971e2000 SST correct. Constant or random predictions score 0. To calculate a skill analysis data utilizing the methodology outlined in Reynolds and score, a hind-cast of bleaching was made. This was done by Smith (1995) and Smith and Reynolds (1998). In situ sea temper- comparing DHW data from 1982 to 2010 to bleaching episodes ature was recorded every 12 min with Hobo data loggers (Onset observed in those years. Bleaching reports were collected from the Corp.) deployed in Bloody Bay Marine Park from February 2008 to literature (Ghiold and Smith, 1990; Coelho and Manfrino, 2007; October 2009. Since July 2009 a Coral Reef Early Warning System Eakin et al., 2010) and reefbase.org. We classified a bleaching year (CREWS: Hendee et al., 2006) station has measured oceanographic as that in which bleaching prevalence was greater than 5% (1987, and meteorological data on the north fringing reef near Bloody Bay 1995, 1998, 2003, 2005, 2009). Years without any recorded obser- Marine Park. These data were used to ground truth the OISST data vations were assumed to be non-bleaching years. in this study. 3. Results 2.2. Bleaching observations and surveys 3.1. Sea surface temperatures In October 2009 bleaching extent was quantified at two sites In situ data from the CREWS station and the HOBO loggers in (Sailfin Reef and Grundy’s Garden) using three randomly placed Bloody Bay Marine Park show very similar patterns to the OISST 10 m transects per site. Sailfin and Grundy’s garden are spur and data (Fig. 1). When data from both in situ sources were averaged to groove reefs at approximately 10 m depth. For each transect, all coral colonies that intersected with the transect line were identi- fied to species. The centimeters of living coral cover directly under the line, not the area of the entire colony, was quantified and assessed for bleaching (complete visual absence of pigment) or paling (visually lighter shade of pigment than what was considered normal). These sites and an additional three locations (Nancy’s Cup O’Tea, Rock Bottom and Snapshot) were resurveyed using four to six randomly placed transects per site in March, May, and June 2010 to monitor recovery from bleaching.