Abstract
The blue coral, Heliopora coerulea, is a reef-building octocoral that prefers shallow water and exhibits optimal growth at a temperature close to that which causes bleaching in scleractinian corals. To better understand the molecular mechanisms underlying its biology and ecology, we generated a reference transcriptome for H. coerulea using next-generation sequencing. Metatranscriptome assembly yielded 90,817 sequences of which 71% (64,610) could be annotated by comparison to public databases. The assembly included transcript sequences from both the coral host and its symbionts, which are related to the thermotolerant C3-Gulf ITS2 type Symbiodinium. Analysis of the blue coral transcriptome revealed enrichment of genes involved in stress response, including heat-shock proteins and antioxidants, as well as genes participating in signal transduction and stimulus response. Furthermore, the blue coral possesses homologs of biomineralization genes found in other corals and may use a biomineralization strategy similar to that of scleractinians to build its massive aragonite skeleton. These findings thus offer insights into the ecology of H. coerulea and suggest gene networks that may govern its interactions with its environment.
Highlights
Octocorals are the most diverse coral group and can be found in various marine environments, including shallow tropical reefs, deep seamounts, and submarine canyons[1]
The blue coral is a holobiont consisting of a cnidarian host and endosymbiotic dinoflagellates of the genus Symbiodinium
The blue coral, H. coerulea, is unique among octocorals for its ability to produce a massive skeleton of crystalline aragonite
Summary
Octocorals are the most diverse coral group and can be found in various marine environments, including shallow tropical reefs, deep seamounts, and submarine canyons[1] They reportedly exhibit greater resistance and resilience to environmental perturbations, to thermal stress, compared to scleractinians[2,3,4]. H. coerulea is found in equatorial waters between 25°N and 25°S in the Indo-Western Pacific region, Red Sea, American Samoa, southern Japan, and Australia It is uncommon throughout its range, it is the dominant species on some reefs[10]. In recent years, heat stress due to global warming and increasing intensity of El Niño Southern Oscillation (ENSO) events have worsened the bleaching of hard corals worldwide Such recurrent disturbances have caused mass die-offs of many hard coral species, reducing their abundance and total cover[12]. A shift in the dominant taxa from branching scleractinian corals to H. coerulea have been observed on reefs in Ishigaki island, Okinawa, Japan and Bolinao, Pangasinan, Philippines[15,16]
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