Abstract
Sea surface temperature (SST) was recorded hourly by an automatic data recorder in Reunion Island, at Pointe des Galets (21°55 S, 55°17 E) during 1993-2004. The data logger was installed on a beacon located at the port entrance exposed to the open sea. The SST measurements associated with auxiliary environmental data, such as wind stress, depict the main patterns of variability at various timescales for the marine climate of Reunion Island. The ’ten-year’ annual mean temperature is 25.7°C and the annual amplitude is 4.6°C. The highest monthly means are observed in February and March (28.0°C) and the lowest occur in September (23.4°C). The daily variation ranges from 0.25 to 0.74°C according to the season. In summer, the tropical cyclones are the major cause of short term variability, with sudden drops of SST than can exceed 2°C within a few hours. The annual cycle of SST is closely associated with that of wind stress, with a lagged response of about 2 months of SST to wind forcing. Throughout the ‘ten-year period’ covered by our dataset, the coldest years were 1993 and 2000, and the warmest were 2003 and 2004. A trend of increasing SST is suggested for the two major seasons, with a magnitude of 0.088°C/yr in summer and 0.052°C/yr in winter. Finally, the SST trend and variability depicted at our sampling site is shown to reflect the SST patterns of the whole south tropical Indian Ocean. Biological responses to SST variability are shown by coral bleaching events and the local tuna fishery. The major coral bleaching events recorded in Reunion in 1998, 2001, 2003 and 2004 occurred during episodes of intense and sustained anomalous high temperatures. The catch per unit effort (CPUE) of the local pelagic fishery was negatively correlated to SST anomalies with a decreasing trend of CPUE observed over the years, accompanied by an overall increase of SST. The SST observations made in Reunion Island, in a largely unsampled region of the Indian Ocean, show their relevance at a larger regional scale and their usefulness in monitoring changes of some biological components of the marine ecosystem. These examples highlight the need to maintain networks of automatic loggers worldwide at coastal stations.
Highlights
Long-term recording of sea surface temperature (SST) in fixed locations is one of the simplest methods used to observe changes in the marine environment
A variety of data are collected to address these problems at different scales in Reunion (Conand et al 2002; Turquet et al 2001, 2002), which include the decade-long temperature study presented in this paper
The presentation of the surface temperatures taken at a coastal station in close connection with the open sea, during the ten-year period 1993-2004, shows several points of interest
Summary
Long-term recording of sea surface temperature (SST) in fixed locations is one of the simplest methods used to observe changes in the marine environment. Coral bleaching is one of the major causes of worldwide reef degradation and since 1979 it has increased in intensity and frequency (Hoegh-Guldberg 1999) and understanding the processes controlling coral bleaching is a scientific priority (Sheppard 2003; Bellwood et al 2004). Discussion of this problem shows there is an urgent need for data from different origins to be analysed at several scales and with new methods (Wooldridge & Done 2004; Berkerlmans et al 2004).
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