Abstract
Coral reefs are continuing to decline worldwide due to anthropogenic climate change. The study of the molecular diversity and biogeographical patterns of Symbiodiniaceae, is essential to understand the adaptive potential and resilience of coral–algal symbiosis. Next generation sequencing was used to analyze the Symbiodiniaceae rDNA internal transcribed spacer 2 marker genes from 178 reef-building coral samples in eight coral habitats across approximately 13° of latitude in the South China Sea (SCS). A total of three Symbiodiniaceae genera, Cladocopium, Durusdinium, and Gerakladium, as well as 31 dominant Symbiodiniaceae types, were identified. Symbiodiniaceae richness, diversity, and community composition varied according to latitude; intermediate and low latitude coral reefs (IR and LR) have higher Symbiodiniaceae richness and diversity than high latitude coral habitats (HC and HR). A PERMANOVA analysis found significant differences in the Symbiodiniaceae community composition in the SCS (F = 14.75, R2 = 0.20, p = 0.001 < 0.01). The major dominant Symbiodiniaceae types were C1 in the HC and the HR, C1/Cspc/C50/C15 and D1 in the IR, and C3u and C15 in the LR. Canonical correspondence analysis showed that the relative abundance of different Symbiodiniaceae types is affected by multiple environmental factors. Phylogenetic analysis indicated that the Symbiodiniaceae type Cladocopium, which shared common ancestors, shows similar environmental adaptability. Based on these results, we suggest that coral host species played a relatively small role in the identity of the dominant Symbiodiniaceae type. Therefore, the biogeographical patterns of Symbiodiniaceae may be mainly affected by environmental factors. Our research provides a comprehensive overview of the biogeography of Symbiodiniaceae in the SCS, where coral communities and reefs are widely distributed across different latitude regions and have variable environmental conditions. Our data will provide support for further study of the regional diversification of Symbiodiniaceae and the ecological resilience of the coral-Symbiodiniaceae symbioses.
Highlights
Coral reefs are the most diverse ecosystems in the oceans, and they provide habitats for at least 30% of marine organisms (Reakakudla et al, 1997)
We detected OTUs that belong to Symbiodinium, Breviolum, Cladocopium, Durusdinium, and Gerakladium, the relative abundance of ITS2 sequences and OTUs that belong to Symbiodinium or Breviolum are very low
Based on the results of ITS2 sequences and OTU analysis, we conservatively suggest that only three genera of Symbiodiniaceae, Cladocopium, Durusdinium, and Gerakladium, have symbiotic relationships with coral in the South China Sea (SCS)
Summary
Coral reefs are the most diverse ecosystems in the oceans, and they provide habitats for at least 30% of marine organisms (Reakakudla et al, 1997). The ability of reef-building corals to build reef structures depends on Symbiodiniaceae, which provides up to 95% of host respiratory demand (Falkowski et al, 1984; Muscatine et al, 1984) This special symbiotic relationship is threatened by anthropogenic climate change (Carpenter et al, 2008; Hughes et al, 2017; Langlais et al, 2017). The shuffling and switching of Symbiodiniaceae community composition does not seem to have saved more corals in the recent global bleaching event (Perry and Morgan, 2017; Hughes et al, 2018) This results from the fact that coral-Symbiodiniaceae symbioses are stable (Thornhill et al, 2006; Hume et al, 2015; Ziegler et al, 2017), which, does not eliminate the possibility of symbiont community composition change driven by SST and light stress (Silverstein et al, 2015; Boulotte et al, 2016). Orbicella faveolata, an endangered species from areas of the Caribbean Sea and Gulf of Mexico such as the Florida Keys (Florida, United States) (Manzello et al, 2018), retained some of the coral species that are vital for the heavily degraded coral reef ecosystem
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