Status of coral-Symbiodiniaceae research in Western Indian Ocean

Underpinning the success of coral reefs in nutrient poor marine environments is mutualism established between corals and members of the phylum Symbiodiniaceae. In recent decades, reef-building corals have been affected by multiple stressors including bleaching, which results largely from elevated sea surface temperature and exposure to excessive solar radiation, ultimately caused by global warming. Accumulating evidence demonstrates differential resistance to bleaching among coral-Symbiodiniaceae partnerships; encouraging studies on the diversity and phylogenetics of Symbiodiniaceae. Examination of the existing knowledge reveals insights into both longitudinal and latitudinal partitioning of members of Symbiodiniaceae at genus level, throughout the Western Indian Ocean (WIO). Contrary to expectations, due to decreasing sea surface temperature with latitude, this review has revealed an increase of polymorphic symbioses involving bleaching susceptible coral genera with latitude. This could partly explain the low impacts of bleaching episodes in the South Western Indian Ocean. In order to substantiate this, we suggest long term monitoring of coral-Symbiodiniaceae symbioses in the WIO region. Such monitoring should take advantage of genetic approaches that can decipher the fine scale diversity of Symbiodiniaceae in coral tissues within a changing climate.