Environmental heterogeneity contributes to population genetic diversity and spatial genetic structure of coral-algal symbiosis of Platygyra daedalea in the northern South China Sea

Abstract

Global climate change, human activities, and environmental pollution impact coral reefs worldwide. The South China Sea coral reefs have been severely degraded. Genetic diversity among populations of coral is important to implement appropriate protection and restoration measures. Platygyra daedalea, widely distributed in the South China Sea, is stress-resistant and forms a dominant species in some regions. Analyzing the genetic diversity of P. daedalea may provide clues to enhance the resistance of reef-building corals. In this study, we employed one nuclear DNA fragment (ITS) and sixteen microsatellite loci to investigate the genetic diversity of coral host and high-throughput sequencing to investigate on the Symbiodiniaceae types in P. daedalea. (1) The populations of P. daedalea and Symbiodiniaceae types in P. daedalea on Hainan and Xisha Islands were divided into three groups: northern to western Hainan Island, eastern to southern Hainan Island, and Xisha Islands. The ribotypes distribution of coral hosts and the Symbiodiniaceae community composition were strongly correlated with environmental factors in the three areas, especially phosphate concentration and diffuse attenuation. (2) Environmental heterogeneity significantly affected the genetic diversity of coral hosts and diversity of Symbiodiniaceae types, especially nutrient concentration, which significantly affected the diversity of coral-algal symbiosis of P.daedalea even if the seawater nutrient content was within the normal range of coral life. (3) Coral hosts with different genotypes may prefer different Symbiodiniaceae types. This study provides new insights into the changes in the genetic structure and diversity of reef-building corals in the Indo-Pacific region.