Abstract
Ostreobium sp. (Bryopsidales, Ulvophyceae) is a major microboring alga involved in tropical reef dissolution, with a proposed symbiotic lifestyle in living corals. However, its diversity and colonization dynamics in host’s early life stages remained unknown. Here, we mapped microborer distribution and abundance in skeletons of the branching coral Pocillopora damicornis from the onset of calcification in primary polyps (7 days) to budding juvenile colonies (1 and 3 months) growing on carbonate and non-carbonate substrates pre-colonized by natural biofilms, and compared them to adult colonies (in aquarium settings). Primary polyps were surprisingly already colonized by microboring filaments and their level of invasion depended on the nature of settlement substrate and the extent of its pre-colonization by microborers. Growth of early coral recruits was unaffected even when microborers were in close vicinity to the polyp tissue. In addition to morphotype observations, chloroplast-encoded rbcL gene sequence analyses revealed nine new Ostreobium clades (OTU99%) in Pocillopora coral. Recruits and adults shared one dominant rbcL clade, undetected in larvae, but also present in aquarium seawater, carbonate and non-carbonate settlement substrates, and in corals from reef settings. Our results show a substratum-dependent colonization by Ostreobium clades, and indicate horizontal transmission of Ostreobium-coral associations.
Highlights
Reef-building scleractinian corals are associated with complex microbial communities, distributed in the mucus, tissue and skeletal compartments[1]
We aim to study the microborer colonization process of coral recruits and to address the following questions: (i) At what developmental stage does the colonization of coral skeleton by microborers take place, and how fast does it spread? (ii) What are the sources and reservoirs of colonizing microborers? (iii) Does the dominant Ostreobium clade depend on the site origin of the host and does it change in the course of the coral development?
We present a pilot study of colonization dynamics by microborers of early life stages of the coral Pocillopora damicornis type beta[20,21]
Summary
Reef-building scleractinian corals are associated with complex microbial communities, distributed in the mucus, tissue and skeletal compartments[1]. Marcelino and Verbruggen (2016)[3] determined that the tufA Ostreobium clade includes more than 80 taxonomic units at the near-species level They combined tufA with ribosomal RNA gene markers (nuclear 18S rDNA, and plastid 16S and 23S rDNA) and suggested that Ostreobidineae form a complex that has evolved over the last 500 million years. None of these studies, investigated the possible relationship between the developmental stages of the coral host and the Ostreobium clade diversity, and the colonization dynamics of microborers in corals remained unclear.
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