Appendix B: Coral Taxonomy

Coral taxonomy is challenging given tremendous variation in morphology and the lack of reliable field traits for many taxa. Coralite structure is often used as a diagnostic tool, but requires bleaching and microscopic examination. Using coralite structure, we identified the Porites reefs that we surveyed as P. lobata. For our field experiments, we did not examine corallite structure (because we did not want to sacrifice the corals). In a previous study in Moorea, but at a different site, Edmunds (2009) inspected 20 juvenile Porites colonies and based on corallite structure determined they were a mix of P. lobata and P. lutea.

However, in a detailed molecular phylogenetic analysis of Porites, Forsman et al (2009) showed that corals with the same gross morphology and coralite structure and identified as the same “species” could be deeply divergent. Similarly, they showed that different species might be more closely related than individuals from the same species: e.g., their “Clade I” included seven “species” (and three corallite morphologies) with little apparent phylogenetic structure to the classically defined groups. P. lobata samples were contained in this clade as well as a very divergent group (their Clade IV), the latter of which consisted of P. lobata and P. lutea from Samoa. Similar taxonomic challenges exist for Montipora and Pocilllopora (e.g., Bergsma 2009), although Porites rus seems to be well resolved (Forsman et al. 2009).

Based on gross morphology, we tentatively identified the four focal species we used in the field experiments as Porites lobata, P. rus, Pocillopora verrucosa, and Montipora floweri. Although these identifications may be in error, and may consist of closely related species, our experiment should be robust to any variation within a taxonomic variation within a “species” because individuals were randomly assigned to treatment groups. Thus, taxonomic variation would add to the noise but not introduce bias. Because our results were all strongly significant, any underlying variability was relatively minor (and did not affect our interpretations). To clearly distinguish “species” in the main text, but to avoid any undue assertion about species names, we refer to these four groups as Porites lobata, P. rus, Pocillopora, and Montipora, respectively.

Bergsma, GS. 2009. Tube-dwelling coral symbionts induce significant morphological change in Montipora. Symbiosis 49:143-150.