Ageing Deep-Sea Black Coral Bathypathes patula

Peter Marriott,Stewart J Fallon,Helen Bostock,Helen Bostock,Nicholas Hitt,Dianne Margaret Tracey

doi:10.3389/fmars.2020.00479

Abstract

Deep-sea corals are a highly diverse group of marine organisms, several of which are characterised by slow growth and extreme longevity up to thousands of years. Due to their fragile forms, skeletal composition, and location, they are vulnerable to various anthropogenic threats, with some groups expected to have little to no ability to recover. Within the New Zealand region an understanding of age and growth parameters and recovery potential for some deep-sea coral fauna is being developed, but a limited understanding remains for some of the key Antipatharian black coral fauna. Ten individual colonies of the black coral species Bathypathes patula were sourced from the National Institute of Water and Atmospheric Research Invertebrate Collection for the purposes of this age estimation study. Corals were selected based on their size, completeness of the colony (whole colony from base to tip), and the regional water mass within which they grew. Coral samples from the Chatham Rise, east of New Zealand, and the Bay of Plenty, north-eastern New Zealand, were selected as the water masses for these two regions are reasonably well understood. Thin section preparations of the main stem of the 10 specimens of B. patula were observed with compound microscopes. Two interpretation protocols were used to describe the zone structures observed, both the coarse wide zones and the thin fine zones, and counts were then made of these structures. Four of the specimens were also sampled for radiocarbon assay. The radiocarbon isotope (14C) age data results were used to independently verify if either of the developed zone counting protocols reflected annual periodicity. Neither method was verified, indicating zone counting protocols could not be used to generate reliable age estimates for B. patula. Twenty radiocarbon assays from four specimens were used to derive the age and growth rate estimates presented here. The radiocarbon results from this work show B. patula to be a long-lived species, attaining ages in excess of 385 years, with linear growth rates of 5.2-9.6 mm/yr, and radial growth rates ranging from 11.1 to 35.7 mm/yr. The delicate nature of these organisms along with their longevity and slow growth rates means a low resilience and low recoverability from anthropogenic activities such as fishing and mining.

Highlights

Deep-sea corals are a highly diverse group of marine organisms, and the New Zealand region is a hotspot for deep-sea corals (Sánchez and Rowden, 2006; Cairns et al, 2009)
Radial growth of the branches in B. patula was reasonably regular, there was no marked bias in the zone deposition forming thicker zones on any particular side of the branch, which has previously been observed in other black coral species
The radii used for the growth rate calculations was a mean of the minimum and maximum radii observed in the prepared sections, meaning reported radial growth rates will be a mean radial growth rate for the coral

Summary

Introduction

Deep-sea corals are a highly diverse group of marine organisms, and the New Zealand region is a hotspot for deep-sea corals (Sánchez and Rowden, 2006; Cairns et al, 2009). Several studies have investigated the effects of bottom trawling on deep-sea macro-invertebrate assemblages (including coral) in the South Pacific region (Althaus et al, 2009; Clark and Rowden, 2009; Clark et al, 2010, 2019; Williams et al, 2010; Anderson et al, 2014) These have demonstrated appreciable impacts from bottom trawling on slow growing and fragile deep-sea coral colonies and communities with little to no ability to recover. The age and growth rate for this coral have not been previously studied in this region The selection of this species was based on the risk assessment priority list (Clark et al, 2014) and the literature review (Tracey et al, 2018), coupled with availability of samples (location and total numbers), and other complementary black coral research being undertaken in New Zealand (Hitt et al, 2020)

Methods

Results

Discussion

Conclusion