Coralline algae (Corallinophycideae) are calcifying red algae that are foundation species in euphotic marine habitats globally. In recent years, corallines have received increasing attention due to their vulnerability to global climate change, in particular ocean acidification and warming, and because of the range of ecological functions that coralline algae provide, including provisioning habitat, influencing settlement of invertebrate and other algal species, and stabilising reef structures. Many of the ecological roles corallines perform, as well as their responses to stressors, have been demonstrated to be species-specific. In order to understand the roles and responses of coralline algae, it is essential to be able to reliably distinguish individual species, which are frequently morphologically cryptic. The aim of this study was to document the diversity and distribution of coralline algae in the New Zealand region using DNA based phylogenetic methods, and examine this diversity in a broader global context, discussing the implications and direction for future coralline algal research. Using three independent species delimitation methods, a total of 122 species of coralline algae were identified across the New Zealand region with high diversity found both regionally and also when sampling at small local spatial scales. While high diversity identified using molecular methods mirrors recent global discoveries, what distinguishes the results reported here is the large number of taxa (115) that do not resolve with type material from any genus and/or species. The ability to consistently and accurately distinguish species, and the application of authoritative names, are essential to ensure reproducible science in all areas of research into ecologically important yet vulnerable coralline algae taxa.

Coralline algae perform important ecological roles in nearshore marine ecosystems globally by promoting the settlement of invertebrate larvae and enhancing biodiversity by creating habitat. However, these roles are severely threatened by global environmental changes. Most coralline algae are extremely difficult to identify, and DNA sequencing has revealed rampant inaccuracy of morpho-anatomical approaches to distinguish species, and even genera. If appropriate identification methods are not reported, or even used, we will be left with an uninterpretable body of literature where the species-specific biology of coralline algae cannot be validated. This will make it difficult to determine the impact a changing ocean may have on these ecologically important species. We reveal the magnitude of the issue in coralline algal research—both the identification methods used and the reporting of identification protocols. An analysis of 341 articles over the past decade revealed that only 7.6% used molecular methods, with over 70% not reporting any details of how species were identified. While many coralline algal taxonomists understand that the majority of species cannot be identified morphologically, this message has not disseminated to the ecological and physiological community. We provide a series of guidelines for conducting DNA-based identifications and strongly recommend the use of these methods over less informative morpho-anatomical techniques. Most importantly, the methods of identification should be adequately reported. Without following these guidelines, research on coralline algae runs the risk of collecting uninterpretable data, and conducting irreproducible science, slowing our ability to determine how these important species will respond to future ocean conditions.