# Seychelles Lagoon Provides Corals with a Refuge from Bleaching

Authors: David Iluz; Razi Vago; Nanette E. Chadwick; Razi  Hoffman; Zvy Dubinsky
Journal: Research Letters in Ecology
 (2008)

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## Abstract

An extensive bleaching event in the summer of the year 1997-1998 affected most
reefs along East Africa's shores. In the aftermath of that episode, the reefs of Île
Alphonse in the Seychelles were examined and it was found that reefs along the seaward
slopes of the island lost >95% of their branching coral colonies, with considerably
higher survival of massive species. Île Alphonse features a nearly circular shallow
lagoon, with steep seaward slopes. Contrary to our expectations, mortality in the warmer
lagoon was far lower than of coral colonies on the surrounding slopes, bathed in deeper
and cooler waters. We suggest that corals in the lagoon were protected from UV radiation by
leachate stemming from seagrass leaves steeped in the lagoon. Our measurements in the
lagoon showed a strong attenuation of ultraviolet radiation, not observed in the waters outside
the lagoon, and laboratory examination confirmed that the strong UV absorption of
substances leached into seawater from decomposing leaves of the seagrassThalassodendron (=Cymodocea) testudinaceum. Our findings demonstrate
the synergism between elevated seawater temperature and UV radiation in triggering
bleaching on shallow reefs.


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*Source: 281038-2008-06-03.xml*