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Extremely high but localized pulses of coral recruitment in the southwestern lagoon of New Caledonia and implications for conservation

Mehdi Adjeroud*, Christophe Peignon, Camille Gauliard, Lucie Penin, Mohsen Kayal

*Corresponding author:

ABSTRACT: Recruitment processes largely drive spatial distributions, dynamics, and recovery potentials of marine communities. Determining scales of variation in recruitment rates and composition can help in understanding population replenishment mechanisms, while identifying recruitment hotspots is crucial for improving conservation strategies, particularly for threatened marine ecosystems such as coral reefs. We examined the spatial and interannual variability (2012 to 2014) of coral recruitment at multiple scales within and among reef habitats (14 stations) in the southwestern lagoon of New Caledonia. Recruit assemblages were characterized by high recruitment rates compared to other regions (overall mean of 34.9 recruits per settlement tile of 11 × 11 × 1 cm, corresponding to 1220.9 recruits m-2), and a strong dominance of Acroporidae. We found a marked spatial heterogeneity among habitats, but also an exceptionnally high interannual variation (100-fold), with extreme recruitment peaks (up to 13572.8 recruits m-2, with a maximum of 811 recruits on a single tile) recorded in 2014 at some fringing and mid-shelf reefs, the highest records ever reported to date. These encouraging results contrast with other reefs where recent declines in coral recruitment rates have been documented with major concerns for their resilience capacities. However, the marked spatio-temporal variability of coral recruitment complicates conservation strategies, as it makes it difficult to identify ‘recruitment hotspots’ as priority sites to protect for their potential capacity to boost the replenishment of local populations.