Herbivory effects of sea urchin species on a coral reef (Bora-Bora, French Polynesia)

Stéphanie Krimou , Emma Gairin (1) , Laura Gautrand , Jérome Sowinski , Mila Trotier , Lana Minier (2) , Hugo Bischoff , Vincent Sturny (3) , Tehani Maueau , Viliame Waqalevu (4) , Fabio Bulleri (5) , Xavier Raick , Frédéric Bertucci (6, 7, 8) , David Lecchini (2, 4)

1 OIST - Okinawa Institute of Science and Technology Graduate University
2 CRIOBE - Centre de recherches insulaires et observatoire de l'environnement
3 Polynésienne des Eaux
4 LabEX CORAIL - Laboratoire d'Excellence CORAIL
5 University of Pisa - Università di Pisa
6 BOREA - Biologie des Organismes et Ecosystèmes Aquatiques
7 Université des Antilles (Pôle Guadeloupe)
8 UMR MARBEC - MARine Biodiversity Exploitation and Conservation - MARBEC

Macroalgae are becoming dominant on coral reefs worldwide, replacing corals as key habitat formers. Incrementing consumption rates by herbivores, such as sea urchins, has been identified as a viable strategy for promoting coral recovery. By means of a 28-day experiment, we assessed the grazing effects of the sea urchins, Tripneustes gratilla and Diadema setosum, on the macroalgal assemblages of shallow reefs at Bora-Bora (French Polynesia). In particular, each urchin species was either absent or maintained, using cages (n = 10), at a density of 5 individuals/m2. T. gratilla exerted stronger negative effects than D. setosum on all the examined macroalgae (i.e., Turbinaria ornata, Padina boryana, Halimeda spp, Dictyota spp). In addition, the grazing effects by T. gratilla on macroalgae emerged shortly after the start of the experiment, more rapidly than those of D. setosum. Despite an apparent lower food preference for T. ornata in D.setosum, all macroalgae were consumed by both species and the composition of the macroalgal assemblages (i.e., the proportion of each species) did not change after 28 days. Overall, our study suggests that herbivorous sea urchins, when at relatively high densities, could contribute to sustaining coral-dominance on coral reefs by keeping macroalgae under control.

Keywords: Macroalgae; Bora-Bora; Grazing; Herbivorous

Domains: Biodiversity and Ecology; Global Changes

Stéphanie Krimou, Emma Gairin, Laura Gautrand, Jérome Sowinski, Mila Trotier, et al.. Herbivory effects of sea urchin species on a coral reef (Bora-Bora, French Polynesia). Journal of Experimental Marine Biology and Ecology, 2023, 564, pp.151900. ⟨10.1016/j.jembe.2023.151900⟩. ⟨hal-04104170⟩