Assessing the living and dead proportions of cold-water coral colonies: implications for deep-water Marine Protected Area monitoring in a changing ocean

Johanne Vad; Covadonga Orejas; Juan Moreno-Navas; Helen S Findlay; J Murray Roberts

doi:10.7717/peerj.3705

Assessing the living and dead proportions of cold-water coral colonies: implications for deep-water Marine Protected Area monitoring in a changing ocean

PeerJ. 2017 Oct 5:5:e3705. doi: 10.7717/peerj.3705. eCollection 2017.

Authors

Johanne Vad^{1

2}, Covadonga Orejas³, Juan Moreno-Navas⁴, Helen S Findlay⁵, J Murray Roberts^{2

6}

Affiliations

¹ School of Engineering Geoscience Infrastructure and Society, Heriot-Watt University, Edinburgh, United Kingdom.
² School of Geoscience, Grant Institute, University of Edinburgh, Edinburgh, United Kingdom.
³ Instituto Español de Oceanografía, Centro Oceanográfico de Baleares, Palma, Spain.
⁴ Physical Oceanography Research Group, Universidad de Málaga, Málaga, Spain.
⁵ Plymouth Marine Laboratory, Plymouth, UK.
⁶ Center for Marine Science, University of North Carolina at Wilmington, Wilmington, NC, United States of America.

Abstract

Coral growth patterns result from an interplay of coral biology and environmental conditions. In this study colony size and proportion of live and dead skeletons in the cold-water coral (CWC) Lophelia pertusa (Linnaeus, 1758) were measured using video footage from Remotely Operated Vehicle (ROV) transects conducted at the inshore Mingulay Reef Complex (MRC) and at the offshore PISCES site (Rockall Bank) in the NE Atlantic. The main goal of this paper was to explore the development of a simple method to quantify coral growth and its potential application as an assessment tool of the health of these remote habitats. Eighteen colonies were selected and whole colony and dead/living layer size were measured. Live to dead layer ratios for each colony were then determined and analysed. The age of each colony was estimated using previously published data. Our paper shows that: (1) two distinct morphotypes can be described: at the MRC, colonies displayed a 'cauliflower-shaped' morphotype whereas at the PISCES site, colonies presented a more flattened 'bush-shaped' morphotype; (2) living layer size was positively correlated with whole colony size; (3) live to dead layer ratio was negatively correlated to whole colony size; (4) live to dead layer ratio never exceeded 0.27. These results suggest that as a colony develops and its growth rate slows down, the proportion of living polyps in the colony decreases. Furthermore, at least 73% of L. pertusa colonies are composed of exposed dead coral skeleton, vulnerable to ocean acidification and the associated shallowing of the aragonite saturation horizon, with significant implications for future deep-sea reef framework integrity. The clear visual contrast between white/pale living and grey/dark dead portions of the colonies also gives a new way by which they can be visually monitored over time. The increased use of marine autonomous survey vehicles offers an important new platform from which such a surveying technique could be applied to monitor deep-water marine protected areas in the future.

Keywords: Cold-water corals; Colony size; Dead framework; Deep-water marine protected areas; Lophelia pertusa; Mingulay Reef Complex; Monitoring; Ocean acidification; PISCES site; Rockall bank.

Grants and funding

This paper is a contribution to the UK Ocean Acidification Research Programme (NE/H017305/1) to J. Murray Roberts; funded by the Natural Environment Research Council, the Department for Energy and Climate Change, and the Department for Environment, Food and Rural Affairs and the ATLAS project funded by the European Commission’s H2020 scheme through Grant Agreement 678760. Johanne Vad acknowledges support from the Natural Environment Research Council Centre for Doctoral Training in Oil & Gas (NEM00578X/1), through Heriot-Watt University (James Watt Scholarship scheme) and from the British Geological Survey (British University Funding Initiative). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.