Corales

Hydrobiologia (2010) 655:99–108 DOI 10.1007/s10750-010-0407-4

PRIMARY RESEARCH PAPER

Assessing coral bleaching and recovery with a colour reference card in Watamu Marine Park, Kenya
Simone Montano • Davide Seveso • Paolo Galli David O. Obura
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Received: 30 July 2009 / Revised: 21 July 2010 / Accepted: 3 August 2010 / Published online: 17 August 2010 Ó Springer Science+Business MediaB.V. 2010

Abstract With this study we estimated the changes in colour, bleaching and mortality of coral colonies from February to December 2007, using the colour reference card method. The study was developed in the Watamu Marine Park lagoon (Kenya), bridging the local summer when seawater temperatures were highest and coral bleaching risk was at its maximum. Seven coral genera were selected, andtheir colour recorded using a colour reference card (Coral Watch card). Seven different scenarios of bleaching and mortality were observed, varying among the coral genera and between two species in the genus Pocillopora. Twenty percent of the colonies bleached, of which 50% died. Only 15% of the coral that did not bleach died. Branching genera had a higher bleaching incidence than massive andsub-massive genera. Pocillopora showed the highest bleaching susceptibility, followed by Acropora, and the highest level of mortality. Of the two species of Pocillopora considered in this study, P. eydouxi showed higher bleaching

and mortality levels, while P. verrucosa bleached less and experienced only partial mortality. Our results evidenced different patterns of coral bleaching and mortalitywhich were easily and clearly detected with the colour card method during both bleaching and a post-bleaching events. Keywords Coral bleaching Á Reference card Á Pocillopora Á Watamu Marine Park

Introduction Coral bleaching is characterised by the loss of dinoflagellate symbionts (genus Symbiodinium) and/or symbiont pigmentation (Hoegh-Guldberg & Smith, 1989; Brown, 1997) from the holobiont whichcauses colour loss/decrease in the coral colony, which can become paler to white. Colour bleaching is triggered by a number of stressful factors including the temperature increase of superficial waters (Jokiel & Coles, 1990; Brown, 1997). In the last two decades, frequency and severity of coral bleaching increased as water temperature increased, at rates that had never been detected before. Sincefurther increases in water temperature are expected, thus a dramatic impact on coral bleaching can be foreseen for the next 30–50 years (HoeghGuldberg, 1999; Hughes et al., 2003). Coral bleaching has several consequences for the organism, including reduced growth and reproduction,

Handling editor: P. Viaroli S. Montano (&) Á D. Seveso Á P. Galli Department of Biotechnologies and Biosciences,University of Milan-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy e-mail: simone.montano@unimib.it D. O. Obura CORDIO East Africa, 9 Kibaki Flats, Kenyatta Public Beach, P.O. BOX 10135, Mombasa 80101, Kenya

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Hydrobiologia (2010) 655:99–108

increased mortality (Brown, 1997) and ecological implications for the reef, including significant reductions in cover of susceptiblespecies, changes in community composition, decrease in species diversity and associated decrease in reef growth and habitat diversity (Glynn, 1993). Differential coral bleaching susceptibilities and post-bleaching colour change, survival or mortality have been observed, with variation among coral taxa, populations and even colonies on an individual reef (Coles & Brown, 2003). At the species level, oneof the clearest associations with these different susceptibilities is their growth rates, with branching and faster growing corals (e.g. acroporids and pocilloporids) being more severely affected by bleaching than massive and slower growing species, e.g. poritids and faviids, (Marshall & Baird, 2000; McClanahan et al., 2004; Obura, 2005a). Branching and susceptible species also show higher...