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- Fifty years of changes in reef flat habitats of the Grand Récif of Toliara (SW Madagascar) and the impact of gleaning doi link

Auteur(s): Andrefouet Serge, Guillaume Mireille M. M., Delval A, Rasoamanendrika F, Blanchot J., Bruggemann J. H.

(Article) Publié: Coral Reefs, vol. p.In press (2013)


Ref HAL: hal-00807803_v1
DOI: 10.1007/s00338-013-1026-0
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Résumé:

The Grand Récif of Toliara (GRT) in Madagascar is a large (33 km2) barrier reef system of the SW Indian Ocean that had been well investigated in the 1960s and early 1970s. A massive degradation of the reef has been reported since at least the early 1980s, just a few years after research activities ceased in the area. Examination of historical aerial photographs and modern high-resolution remote sensing images confirms a continuous loss of coral habitat on GRT outer reef flats between 1962 and 2011, with an average loss of 65 % and a range of 37-79 % loss during this 50-year period. The usual suspects of coral community declines (cyclones, bleaching and sedimentation) may have contributed to the demise of the GRT. However, an independent study (Salimo 1997) suggests that the chronic pressure of fisherman gleaning on reef flats with destructive tools is the main driver of the observed changes. Salimo's reported level of frequentation (6.8 fishermen per day and per km−2) and rates of destruction per fisherman (7.7 m2 of coral habitat h−1) yield a cumulated overall loss in agreement with the image-based rates of habitat loss. The GRT is unlikely to recover because this chronic stress is unlikely to decrease in the near future. Indeed, the GRT daily provides subsistence fishery resources for local Vezo people and to agriculturalist or pastoralist ethnic groups who have turned to exploiting coastal resources due to increasing aridity and dwindling agricultural and livestock production