Strong but declining coral recruitment rates in the region of Toliara, southwest Madagascar
Creators: name: BOTOSOAMANANTO, Radonirina Lebely
name: ZERAMBAY, Sarah
name: RANDRIANARIVO, Mahery
name: RAZAKANDRAINY, Andriamanjato
name: RATSIMBASAFIHERY, Pierro
name: GASIMANDOVA, Max
name: PENIN, Lucie
name: TODINANAHARY, Gildas
name: ADJEROUD, Mehdi
Publisher: name: Zenodo
Year: 2022
Subjects: Corals reefs
Scleractinian corals
recruitment
population regulation
Madagascar

description: Coral reefs provide crucial levels of biodiversity and ecosystem services, including foodprovision and coastal community protection against extreme weather disturbances. In thecontext of the ongoing degradation of coral reefs due to increased frequency and severity ofstressors, investigating the key processes involved in the replenishment and resilience of thecoral community is urgent for responsive management. One of these key processes is coralrecruitment, the addition of new individuals to the local population following settlement fromthe pelagic phase to the benthic early juvenile phase. We investigated the spatial and temporalvariation of coral recruitment rate and composition as well as the influence of benthic organismsusing a nested sampling design considering three distinct habitats (patch reefs, inner slopes, andouter slopes). The survey took place between 2018 and 2020 at ten stations located on these threehabitats. Overall, recruitment rates were high (ranging from 219.20 recruits. m-2 in 2018 to156.30 recruits. m-2 in 2020) compared to other reefs in the Western Indian Ocean, but declinedfrom 2018 to 2020. A high variation was observed among years, habitats and stations.Recruitment reveals a strong habitat association with higher recruitment in patch reef stations(187.06 recruits. m-2) and outer slope stations (156.99 recruits. m-2) compared to inner slopestations (108.04 recruits. m-2). However, decline in recruitment rates was observed among allhabitats. For the three surveyed years, Acroporidae (45.5%) and Pocilloporidae (45.0%) largelydominated recruit assemblages, followed by other taxa (3.6%), and Poritidae (1.9%). Thedensity of the three major families (Acroporidae, Pocilloporidae and Poritidae), declined overthe years, but remained higher in patch reefs and outer slope stations than in inner slope stations.A strong variation was also recorded among the three surfaces of the settlement tiles: Coralrecruits were mainly observed on the edge (60.0%) of the tiles, compared to the lower (24.4 %)and upper (15.5%) surfaces, which could be attributed to a strong negative effect of macroalgae,rubbles, and more surprisingly, Crustose Coralline Algae (CCA).This study highlights the high rates of coral recruitment in Madagascar compared to other SouthWestern Indian Ocean reefs, as well as high spatial and temporal heterogeneity in the rate andcomposition of coral recruitment. This spatio-temporal variability could be attributed tovariations in local environmental conditions. For example, the sharp decline documented duringthe three-year survey could be associated with the 2019 bleaching event that affected the cover,abundance, and fecundity of adult corals.