Abstract Bacteria, fungi and green algae are common inhabitants of coral skeletons. Their diversity is poorly characterized because they are difficult to identify with microscopy or environmental sequencing, as common metabarcoding markers have low phylogenetic resolution and miss a large portion of the biodiversity. We used a cost-effective protocol and a combination of markers ( tuf A, 16S rDNA, 18S rDNA and 23S rDNA) to characterize the microbiome of 132 coral skeleton samples. We identified a wide range of prokaryotic and eukaryotic organisms, many never reported in corals before. We additionally investigated the phylogenetic diversity of the green algae—the most abundant eukaryotic member of this community, for which previous literature recognizes only a handful of endolithic species. We found more than 120 taxonomic units (near species level), including six family-level lineages mostly new to science. The results suggest that the existence of lineages with an endolithic lifestyle predates the existence of modern scleractinian corals by ca . 250my and that this particular niche was independently invaded by over 20 lineages in green algae evolution. These results highlight the potential of the multi-marker approach to assist in species discovery and, when combined with a phylogenetic framework, clarify the evolutionary origins of host-microbiota associations.

PAPUA NIUGINI

ATIMO VATAE

The green algal genus Ostreobium is an important symbiont of corals, playing roles in reef decalcification and providing photosynthates to the coral during bleaching events. A chloroplast genome of a cultured strain of Ostreobium was available, but low taxon sampling and Ostreobium 's early‐branching nature left doubt about its phylogenetic position. Here, we generate and describe chloroplast genomes from four Ostreobium strains as well as Avrainvillea mazei and Neomeris sp., strategically sampled early‐branching lineages in the Bryopsidales and Dasycladales respectively. At 80,584 bp, the chloroplast genome of Ostreobium sp. HV 05042 is the most compact yet found in the Ulvophyceae. The Avrainvillea chloroplast genome is ~94 kbp and contains introns in inf A and cys T that have nearly complete sequence identity except for an open reading frame (ORF) in inf A that is not present in cys T. In line with other bryopsidalean species, it also contains regions with possibly bacteria‐derived ORF s. The Neomeris data did not assemble into a canonical circular chloroplast genome but a large number of contigs containing fragments of chloroplast genes and showing evidence of long introns and intergenic regions, and the Neomeris chloroplast genome size was estimated to exceed 1.87 Mb. Chloroplast phylogenomics and 18S nr DNA data showed strong support for the Ostreobium lineage being sister to the remaining Bryopsidales. There were differences in branch support when outgroups were varied, but the overall support for the placement of Ostreobium was strong. These results permitted us to validate two suborders and introduce a third, the Ostreobineae.

KAVIENG 2014

Aim: Historical processes that shaped current diversity patterns of seaweeds remain poorly understood. Using Dictyotales, a globally distributed order of brown seaweeds as a model, we test if historical biogeographical and diversification patterns are comparable across clades. Dictyotales contain some 22 genera, three of which, Dictyota, Lobophora and Padina, are exceptionally diverse. Specifically, we test whether the evolutionary processes that produced the latitudinal diversity patterns in these clades are in line with the tropical conservatism, out-of-the-tropics or diversification rate hypotheses.

KAVIENG 2014, PAPUA NIUGINI