Interactions between stressors on coral reefs: analytical approaches, re-analysis of old data, and different conclusions

Recently, some of the older literature purported to demonstrate a positive interaction between solar radiation and thermal stress on the phenomenon of coral bleaching have been called into question (Dunne 2010). Dunne (2010) correctly points out important experimental design and analysis issues related to the interpretation of multi-factorial designs, and both positive and negative interactive effects, with emphasis on the point that once interactive effects are detected no interpretation of the main effects of a multi-factorial design is appropriate. Dunne (2010) presents a number of statistical analyses to address this issue that are valuable and deserve significant discussion. While Dunne (2010) was specifically addressing the issue of the misuse of the term synergy some of the analyses presented may have understated the presence of such interactions. Here, I conduct a re-analysis of specific datasets using another potentially useful approach that shows both positive and negative interactions during experiments on bleaching.