Huang Hui's team, a researcher at the South China Sea Institute of Oceanography of the Chinese Academy of Sciences, made progress in the study of the plasticity of early symbiotic relationships of reef-building stony corals, revealing the early symbiotic establishment of reef-building stony coral larvae and the selectivity of corals to zooxanthellae under the influence of warming and acidification. The results were published in Frontiers in Microbiology and Coral Reefs.
The mutually beneficial symbiotic relationship between reef-building stony corals and zooxanthellae is a key support for coral reef ecosystems, but this symbiotic relationship is under threat of warming and acidification of seawater. Nearly 80% of reef-building stony corals do not contain zooxanthellae at the beginning of life, but instead acquire zooxanthellae from environmental water bodies and establish symbiosis at the larval stage, at which time coral larvae have the opportunity to choose the appropriate type of zooxanthellae according to the external environment to shape the physiological state of the symbiote to adapt to the specific environment. In the context of climate change and coral reef degradation, it is of great significance to study the effects of warming and acidification on the early symbiotic establishment process of corals, especially the plasticity of coral selection and early symbiotic relationships of cordyceps, which is of great significance for understanding and predicting coral larval replenishment and the environmental adaptability of coral larvae.
The study targeted two widespread reef-building stony corals in the Indo-Pacific region, the intermediate staghorn coral (Acropora intermedia) and the delicate flat-brained coral (Platygyra daedalea), which have different growth patterns and environmental stress sensitivity, the former being sensitive branching corals and the latter being tolerant clump corals. The researchers collected fertilized eggs from two coral species and bred them to the larval stage, and then reared them in a flow-through experimental culture system, and studied the early symbiotic establishment process and growth and development of the two coral larvae under the influence of warming (29 °C vs. 31 °C) and acidification (pH 8.1 vs. 7.8) by controlling seawater temperature and pH.
The study found that the warming will delay the early symbiotic establishment process of the two corals, and acidification has no obvious effect, but the response and sensitivity of different coral species are different, and the heating completely inhibits the successful establishment of early symbiosis of intermediate staghorn corals, and is not conducive to the asexual budding reproduction of juveniles; for delicate flat-brain corals, the warming significantly reduces the proportion of successful symbiosis in the larvae by 50%. In addition, the warming changes the selection preference of the intermediate staghorn coral larvae for zooxanthellae, under normal temperature conditions, the coral larvae mainly establish symbiosis with the zooxanthellae Caladocopium sp., and the larvae are more inclined to establish symbiosis with the heat-tolerant zooxanthellae Durasdiniumsp. after heating; the delicate flat-brain coral larvae prefer to establish symbiosis with the zooxanthogania Durusdiniumsp under acidification rather than heating. In addition, transcriptome analysis showed that the Genes associated with ribosomal synthesis and photosynthesis selected by the larvae of the intermediate staghorn coral larvae showed significant downregulation, indicating that although the zooxanthellae Durusdinium can enter the intermediate staghorn coral, it cannot multiply in large quantities under heating to establish a stable mutually beneficial symbiotic relationship. In summary, the influence of seawater warming on the early symbiotic establishment and growth and development of reef-building stony corals is much greater than that of acidification; compared with intermediate staghorn corals, the larvae of delicate flat-brained corals have stronger adaptability to climate change, suggesting that their larval replenishment process is less affected by climate change; the preferred selection of two corals on zooxanthellae under warming and acidification provides a new vision and idea for the academic community to understand the symbiotic relationship between corals and zooxanthellae under climatic conditions.
The research work has been jointly funded by the National Natural Science Foundation of China, the Guangdong Provincial Foundation of Basic and Applied Basic Research, and the Introduction of Major Projects by the Talent Team of the Guangdong Provincial Laboratory of Marine Science and Engineering (Guangzhou).
Figure 1. (Top) Middle staghorn coral Acropora intermedia and its larvae; (Bottom) Delicate flat-brained coral Platygyra daedalea and its larvae
Fig. 2.Composition of intermediate staghorn corals (left) and delicate flat-brain corals (right) larval xanthophylla under warming and acidification conditions and their differences in composition with adult xanthoellae
Source: South China Sea Institute of Oceanology, Chinese Academy of Sciences