Protected coral connectivity in New Zealand

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Summary 

The management and conservation of deep-sea coral communities requires an understanding of the extent to which separate coral populations can exchange motile larvae or gametes. This connectivity underpins a population’s genetic diversity, which in turn influences adaptive resilience to natural and anthropogenic stresses, including recovery from benthic disturbances such as deep-sea mining and fishing. Knowledge of the dispersal potential of black coral populations is limited however, as is our understanding of the delimitation of what constitutes a genetically and geographically distinct population. This project sought to examine population delimitation and connectivity of a single black coral species – Bathypathes patula – by building upon the preliminary results of a previous study, including an increased sample size and testing novel genetic markers for resolution of genetic variation.

DNA barcoding was used to successfully determine the relationships of 77 specimens of B. patula housed within the NIWA Invertebrate Collection, using a combination of five genetic markers. Four markers were adapted from previous studies, but one was newly developed for this project and shows promise for distinguishing black coral populations and species. However, our results indicated that, in reality, the tested specimens belonged to a cryptic complex of at least five different genera- not a single species - and no obvious subdivision of these genera into species or populations was discernible from over 2000 base pairs of DNA sequence data. We suggest that this complex warrants a reconsideration of past estimates of anthropogenic effects on B. patula, and allowances for hidden diversity should be made during management considerations for black coral species.

Although a population genetic analysis could not be achieved due to multiple species being present in our sample, the hidden taxa uncovered in this study increases our knowledge of black coral diversity in New Zealand and greatly expands the known distribution of one of the cryptic taxa – Telopathes tasmaniensis - to include locations across the Exclusive Economic Zone.

The co-occurrence of B. patula and T. tasmaniensis was also examined and it was found their geographic and bathymetric distributions to largely coincide. This presents additional difficulty in distinguishing these and other cryptic species, since it appears that gross similarities in their morphology make genetic barcoding the most reliable tool for telling them apart. However, given that we were not able to reliably discriminate multiple species within any of the cryptic genera we sampled, the use of higher-resolution genetic techniques is advisable for future efforts to document species diversity and population connectivity among black corals. While it remains prohibitively expensive for routine identification, genomic approaches comprise the most effective methods for resolving population-level differences for black corals, including connectivity analysis. Given recent reductions in per-sample costs, the ability to resolve relationships at a wide range of taxonomic levels, and amenability to the use of older collections material, we recommend that future attempts to measure the connectivity of black coral populations should employ Ultra-Conserved Elements or RADseq – both are contemporary methods that have shown much promise among related groups of deep-sea corals.

Publication details

Bilewitch, J.P. and Tracey, D. 2020. Protected coral connectivity in New Zealand. Final Report for project POP2018-06 prepared by NIWA for the Conservation Services Programme, Department of Conservation. DOC19306-POP201806.32 p.