We observed an increase in crude mineral content in Acropora intermedia embryos during the planula-larval stage, suggesting that mineralization may start before settlement. Samples from different developmental stages, including eggs, planulae, and metamorphosed polyps, were analyzed for crude ash content using a muffle furnace. Our results indicate significant differences between stages, supporting the possibility of early mineralization, aligning with findings of Akiva et al. (2018) on larval-stage mineralization in corals.

The scleractinian family Astrocoeniidae includes three genera. Palauastrea and Stylocoeniella are widely distributed throughout the Indo-Pacific region, while species of the genus Stephanocoenia (star corals) are found only in the Atlantic. Although Astrocoeniidae is considered to be phylogenetically most closely related to Pocilloporidae, their molecular phylogenetic position remains unclear. Here we report complete mitochondrial genomes of Palaustrea ramosa and Stylocoeniella guentheri. We also compared mitochondrial genomic structure between Astrocoeniidae (P. ramosa and S. guentheri) and Pocilloporidae. This study provides evidence of the phylogenetic structure and taxonomic relationships within Astrocoeniidae.

Coral reefs possess the highest biodiversity of all marine ecosystems and zooxanthellate scleractinian corals, the keystone organisms of these reefs, are in crisis due to climate change and anthropogenic activities. Future reef conservation requires comprehensive understanding of the present status of scleractinian taxa in each region. Environmental DNA metabarcoding (eDNA-M) is a method to meet such requirements. Still, it requires optimized primers for PCR amplification of eDNA and complete genomic sequence information for bioinformatic analyses. Coral reefs of Japan reportedly host 85 scleractinian genera. Our previous study developed a primer set that can be used to amplify scleractinian mitochondrial 12S rDNA for eDNA-M analysis. However, at present, the NCBI nucleotide database contains only ~60 genera with available 12S rDNA sequences, indicating that nearly 25 genera that should be detected by this system have no sequence information. To overcome this problem and to establish a nearly complete eDNA-M system for generic level detection of Japanese scleractinians, we collected 22 scleractinian genera and sequenced their mitochondrial genomes. In addition, species of another 12 genera were re-sequenced to avoid sequence differences caused by geographic variation. Incorporation of these data into a newly constructed informatic pipeline resulted in an eDNA-M system that can detect 83 of the 85 genera. This provides a tool for comprehensive, generic level detection of scleractinian corals in Japanese waters.