Molecular diversity of reef-associated crustose coralline algae (Corallinophycidae, Rhodophyta) of the Spermonde Archipelago, Indonesia

Although important consolidators and settlement inducers of organisms such as corals, echinoderms, and molluscs on coral reefs, crustose coralline algae (CCA) have been some of the least studied organisms in the megadiverse Coral Triangle in the tropical Indo-Pacific Ocean. CCA were sampled from reefs across different ecological zones of the Spermonde Archipelago within the Coral Triangle through diver collections along 10 X 1 m transects on coral reefs and deployment of Autonomous Reef Monitoring Structures (ARMS). Using DNA sequences of psbA, COI-5P, and rbcL barcodes, we re-assessed the diversity of the reef-associated CCA of this region, previously studied only using morpho-anatomy. Species delimitation methods resulted in 63 molecular operational taxonomic units (OTUs) representing 11 genera from three orders. This tripled the species richness previously reported, with cryptic diversity observed in all genera except Porolithon (order Corallinales) and Melyvonnea, (order Hapalidiales) represented by one OTU each. Distinct communities of CCA OTUs were recorded from reef surveys and the ARMS collections that targeted the external and internal reef environments, respectively. Thirty-five OTUs appeared to be endemic to the Spermonde Archipelago. The rich phylogenetic diversity exhibited in the Spermonde Archipelago, as in studies on other Pacific areas, revealed that a significant amount of biodiversity has been overlooked in Indo-Pacific reefs, especially in the Coral Triangle. These findings emphasize the need for more research before losses are incurred due to their vulnerability to climatic and anthropogenic threats.