Deep-sea corals and coral-bioeroding foraminifera in the South China Sea

Coral reefs are shallow-water ecosystems that occur in tropical and subtropical seas. They feature very high biodiversity and primary productivity, as well as beautiful scenery. The species diversity and ecology of the coral reefs bordering Taiwan have been the focus of marine biology studies in the past several decades. However, the biodiversity of deep-sea corals in the seas surrounding Taiwan has not been investigated. From 2013 to 2016, we conducted field surveys on the species diversity and distribution of deep-sea corals in the South China Sea using R/V Ocean Researcher I. In total, 76 localities encompassing Dongsha Atoll, Macclesfield Shoal, and Spratly Island and located at depths ranging from -262 to -3732 m were surveyed. The approximately 8,000 specimens that were collected and examined include 190 species of deep-water scleractinian corals belonging to 15 families and 55 genera, including 1 new genus and 15 new species (Figure 1). Moreover, the species compositions of the coral communities found at the different localities vary widely, indicating that the species diversity of deep-sea corals in the South China Sea is high. Phylogenetic analysis based on two mitochondrial sequences (16S and 28S rRNA) reveals that several cryptic or new species may exist in our collections; thus, the species diversity is likely higher than expected. The high species diversity and the abundance of deep-sea corals found at several localities suggest that deep-sea reefs likely exist in the South China Sea. The calcium carbonate structures formed by deep-sea corals provide essential habitats that promote the survival of fish and invertebrates in marine ecosystems. Based on the high species diversity and the abundance and uniqueness of coral fauna, we propose designating the Dongsha continental shelf, Zhongsha Reef and An-Da Reef in the Spratly Islands as marine protected areas for the conservation of marine resources in the South China Sea.

Among the coral specimens, we found fifteen individuals of Hyrrokkin sarcophaga, a large commensal or parasitic foraminifer, on corals belonging to three species collected at depths ranging from -339 to -552 m. The study reporting this discovery was the first reported occurrence of a coral-bioeroding foraminifer in the Pacific Ocean [1]. H. sarcophaga is a large foraminifer that has tests of up to 7 mm in diameter and is mainly parasitic on deep-sea corals. It has previously been reported as occurring on hexacorals or octocorals at depths ranging from -200 to -500 m along the North Atlantic continental margin in polar to subtropical waters [2]; however, it had never previously been reported from the Indian or Pacific Oceans, even after several explorations. In our findings from the South China Sea, three new host corals, i.e., Madrepora occulata, Flabellum japonicum, and Caryophyllia diomedeae (Figure 2), were identified. The boring pattern produced by this large foraminifer characterized by a shallow groove of 0.55 ± 0.04 mm in diameter. Several whip-shaped extensions extend vertically from this groove into the substrate of the host and act as an anchor to enhance the attachment of the foraminifer. These findings extend our knowledge of the global distribution of H. sarcophaga, as well as its ecological affinities and host preferences.

Figure 1. Examples of deep-sea corals.

Figure 2. Deep-sea corals and coral-bioeroding foraminifera

References
1. Yu-Rong, Cheng and Chang-Feng Dai (2016). A bioeroding foraminifer, Hyrrokkin sarcophaga, on deepwater corals from the South China Sea. Coral Reefs, 35(3), 901-901. DOI:10.1007/s00338-016-1447-7.
2. Tomas Cedhagen (1994). Taxonomy and biology of Hyrrokkin sarcophaga gen. et sp. n.: a parasitic foraminiferan (Rosalinidae). Sarsia, 79(1), 65-82. DOI:10.1080/00364827.1994.10413549.

Professor Chang-Feng Dai
Institute of Oceanography
corallab@ntu.edu.tw

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Deep-sea corals and coral-bioeroding foraminifera in the South China Sea

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