Dead man’s fingers point towards new species: A taxonomic revision of Alcyonium aurantiacum with statistical discrimination methods and a survey of integrative taxonomy in Octocorallia
Octocorals are a diverse group of sessile, colonial, filter-feeding anthozoan cnidarians, which form significant components of benthic marine communities worldwide. Globally, the most critical hurdle to the effective management of octocorals in the face of increasing anthropogenic pressure is the poor state of their species-level taxonomy, which hinders understanding of their biodiversity. New Zealand’s octocoral assemblage is among the most diverse of any country and is characterised by high levels of endemism, yet over half of its octocoral species remain undescribed. While progress is being made, this has focussed almost exclusively on protected deep-sea gorgonian octocorals.
Unprotected coastal soft corals are less studied in New Zealand. This includes the endemic Alcyonium aurantiacum Quoy and Gaimard, 1833. Multiple, morphologically diverse forms have been attributed to this species. Here, the taxonomic status of A. aurantiacum is reviewed, and its phylogenetic relationships are examined using molecular data (nuclear 28S and mitochondrial MutS genes), which is compared to morphology in an integrative approach. As a result, evidence for two new, endemic genera and ten new species is presented. Alcyonium aurantiacum is referred to Kotatea gen. n. (as K. aurantiaca comb. n.), which contains seven additional new species. A second genus, Ushanaia gen. n., contains three new species.
Of the new taxa described herein, K. aurantiaca and K. lobata sp. n. are the most commonly encountered and widespread, yet little is known regarding their biology. Both species co-occur in their natural habitat, could not be differentiated genetically with the tools used here, and can be difficult to distinguish without microscopic sclerite examinations. To facilitate the identification of these two similar species by non-taxonomists, a statistical model was developed that can discriminate them with up to 90% accuracy using easily obtainable measurements of gross colony morphology. Relationships between colony morphology and depth are also examined.
Considering the difficulties associated with species discrimination among octocorals, a literature survey was conducted to review the use of integrative taxonomy in this group since the start of the 21st century, focusing particularly on morpho-molecular data comparisons. This revealed that, while description rates at family, genus, and species levels over the last twenty-one years rank among the highest ever, integrative techniques have been applied unevenly across taxonomic groups and geographic regions and overall remain a minority compared to taxonomic research based solely on morphology. Implementation of the integrative approach is increasing, however, as are the per-annum number of taxonomic publications and the total pool of authors associated with these publications.
It is hoped that the research presented herein can contribute to ongoing global efforts of revising octocoral systematics and that the examination of integrative practices in octocoral taxonomy will serve as a baseline against which future taxonomic progress can be compared and promoted. For New Zealand specifically, elucidating the taxonomy and variability of these endemic taxa will enable aspects such as their contribution to ecosystem functioning and management needs to be examined accurately for the first time, which in turn may lead to their recognition as organisms worthy of legal protection.