Valentin Lucet

Differential habitat use between two parrotfish grazers modulates the resilience of Caribbean coral reefs

Coral reefs in the Caribbean have been shown to undergo dramatic transitions from a coraldominated state to an algal-dominated state. Recovering from this change (resilience) is difficult since the crash of populations of urchin grazers Diadema antillarum in the Caribbean in 1983. This has led to two hypotheses regarding reef dynamics: phase shifts and alternative stable states. Models have emphasized the alternative stable states framework, with the first important model being that of Mumby and Hastings. This model has been subsequently modified to explicitly model grazing and fishing dynamics. Parrotfishes have become the most important grazers on those systems and have been shown to use their habitat differently. While some models have integrated some species interaction, the differential use of habitat and its implication for the resilience of reefs has been overlook. We contribute to filling this gap by modeling two grazers exhibiting differential habitat use. We show that differential habitat use lead to changes in the stability of the coral dominated state that can lead to the system exhibiting phase shift dynamics instead of the expected alternative state states dynamics. We also show that these changes can be asymmetric with regard to the species of fish considered and that consequently fish using different habitat might contribute differently to the resilience of the system. Finally, we propose further axes of the development for the present models of alternative stable states of Caribbean coral reefs.