Endosymbiotic Symbiodinium clades occurrence and influence on coral growth and resilience during stress

Abstract

The endosymbionts of Symbiodiniaceae members establish an obligate relationship with most of the reef-building corals.Photosynthates of Symbiodiniaceae symbionts provide the maximum energy requirements of the host coral.Apart from the coral growth benefits, the mutual relationship extends to respond the environmental stress as well.Coral-endosymbiont mutualism is affected by various stress factors such as light, salinity, temperature, and eutrophication.However, the coral-algal symbionts adaptation to these rapid environmental changes is not much studied.Algal endosymbionts are classified into nine clades by genus level (major scleractinian corals - Clade A-D).These clades are named A to I with many subclades being presented in each clade that was identified based on the genetic marker ITS sequences, from which few are found tolerant to adverse conditions.This suggested that coral susceptibility or resistance to stress depends on the type of clade they harbor.Also, the prolonged environmental conditions may bring evolutionarily diverse clade lineages enabling corals to attain stress tolerance to temperature, UV, and high salinity.Thus, the present study may aid in understanding the coral-algal mutualistic adaptations under various stress conditions.