Developing Management Practices for Ecosystem Resilience: Functional group analysis of the degraded Grand Recif of Toliara, Madagascar

The Grand Récif of Toliara (GRT) (Fig. 1) ranks among the largest tropical coral reefs in the world and is of great importance for human populations in South-West Madagascar. Early studies recognized this ecosystem as an important regional reservoir of marine biodiversity. Severe degradation of the GRT has been reported since the mid 1980s, with concerns for the sustainability of this ecosystem as a marine resource base.

The MASMA-GRT program aimed to develop recommendations for reef management, through an analysis of the capacity of the GRT to restore itself to a pre-existing state that was described in considerable detail by French scientists in the 1960‟s and 70s. The salient changes since these early descriptions are the almost total disappearance of corals from shallow reef parts, their place being taken by foliose and canopy-forming macroalgae, and the decline of fish stocks. The program’s analysis of resilience capacity focuses on the functioning of the three key compartments (corals, benthic macroalgae and herbivores) in a context of human disturbance and climate change.
The program was developed in response to call for collaboration from the Institut Halieutique et des Sciences Marines (IH.SM) of the University of Toliara. Because the IH.SM is facing a major challenge of replacing their retiring staff, capacity building through the training Malagasy PhD students was an integral part of the program from its first conception. These students were to play a major role in collecting field data on reef state and the ecology of key functional groups.
The first two years of the MASMA-GRT project coincided with another research program (ICAR-GRT) coordinated by Robert Arfi of the French Institut de Recherche pour le Développement (IRD) analysing the impacts of changing land use on the quality and trophic fluxes in the coastal waters bathing the GRT. This provided a window of opportunity to advance the program’s understanding of the (dis)functioning of the GRT through multidisciplinary research.
Thus, a collaborative program between the University of Réunion, the MNHN, IH.SM and the IRD was set up, with external collaborations that could bring in further expertise.

Initially the program comprised three phases:
1) Assess the current state of the GRT and compare this to the historical data to quantify the loss of biodiversity, the areas that remained stable, and conversely the areas of erosion of functional redundancy of coral and fish assemblages;
2) Describe the responses of reef organisms, representative of critical functional groups (corals, benthic macroalgae and herbivores) to altered environmental conditions and biotic interactions; emphasis will be placed on identifying agents that control macroalgal biomass (nutrients, herbivore stocks);
3) Produce a Bayesian reef state model of the GRT to predict outcomes of different management scenarios based on inherent resilience capacity and formulate specific management practices aiming to preserve and increase this capacity.

1. Maina J., de Moel H., Zinke J., Vermaat J.E., Grove G., Bruggemann J.H., Guillaume M.M.M., Mertz R., Madin J. Linking coral river runoff proxies with hydrology and land-use in Madagascar catchments. (in prep.)
2. Rodier M., Arfi R., Chevalier C., Blanchot J., Montel Y., Rougier G. (2011). Local and large scale factors affecting hydrography and plankton variability in the Toliara coral lagoon (Madagascar, Indian Ocean). Bull. Mar. Sci. (in press)