Temporal variability in tropical lagoon sponges from Mauritius (Western Indian Ocean)

Abstract

Coastal lagoons are subjected to complex abiotic interactions which result to strong spatio-temporal variability of lagoon-inhabiting communities. Sponges are important components of coastal lagoons, yet their temporal variability is poorly understood. Here, we investigated the temporal variability in local distribution area (LDA), abundance (number of patches) and percentage cover of three lagoon-inhabiting sponge species: Neopetrosia chaliniformis, Amphimedon navalis and Spheciospongia vagabunda from Mauritius (Western Indian Ocean), over a 6- to 8-year period (depending on species). The correlations between two known drivers of sponge temporal patterns, sea surface temperature (SST) and chlorophyll a (Chl a) concentration, were also explored. After the survey, the total LDA and percentage cover of N. chaliniformis decreased by 40.2% and 14.6%, respectively, whereas total LDA and percentage cover of S. vagabunda increased by 135.1% and 23.3%, respectively. No significant changes were seen in the total LDA and percentage cover of A. navalis. While the abundance of N. chaliniformis and A. navalis declined over the study period, the abundance of S. vagabunda increased. SST and Chl a concentration were significantly correlated with temporal changes in abundance of all species, although correlations were species-specific. However, no significant correlations were seen between the environmental parameters and changes in sponge percentage cover, except between SST and N. chaliniformis percentage cover. Our results demonstrate that lagoon sponges show species-specific patterns in temporal variability and, while some species may potentially become locally extinct over the next few decades, if trends continue other species may become more abundant or may remain stable.