Cold-water corals from the deep-sea to the TV: development of shelf-edge mounds, assessment of anthropogenic stressors and geochemical parameters, and impacts of science communication

Abstract

Cold-water corals (CWCs) are the hidden reef-builders of the deep ocean. They are out of sight, yet they perform important functions for marine ecosystems, play a role in stabilising climate change, and hold clues to study past climates. CWC reefs form biodiversity hotspots used as habitat and shelter for over 1,300 species of fishes and invertebrates; these biodiversity hotspots are especially important as nurseries for many juvenile fish species and macro-organisms. As CWCs form their skeleton, they passively record chemical information which reflects local environmental conditions, increasing their use as palaeoceanographic archives. The ocean is becoming warmer and increasingly acidic due to elevated concentrations of atmospheric and oceanic carbon dioxide, causing coral skeletons to become more fragile, and leaving CWC frameworks more at risk from breakage in strong deep ocean currents. It has been reported that dead coral frameworks are just as important as live corals, as they provide a base for coral reef formation in the deep sea. Destruction of CWCs would have a negative impact on marine biodiversity and deep-sea ecosystems as a whole; a reduction in biomass of these three-dimensional structures could result in a lessening of carbon cycling and a loss of these ecosystem engineers in the deep ocean. As important as CWCs are, they are still relatively poorly understood by the scientific community and undervalued by society.

This thesis aims to investigate the development of CWCs and environmental parameters (i.e. ocean acidification, rising seawater temperatures, geochemical proxies) associated with coral skeletons. Samples analysed in this study were obtained from three locations in the eastern boundary of the North Atlantic. For Chapter 2, two cores were collected from a previous research expedition in the Macnas Mounds, an area along the Irish shelf-edge margin at roughly 370 m water depth. Radiocarbon dating and particle size analysis from these cores describe an environment that was once a thriving coral community. Previously thought to be sand dunes along the outer edge of the Porcupine Bank Canyon, radiocarbon dating constrains these coral mounds to 7.11 (?0.03) to 0.61 (?0.02) ky BP. Multibeam echosounder data and seafloor images from a more recent cruise assisted in confirming the past existence of these coral communities and provided novel data that assisted in the publication of this research.

Coral samples from the Nakken Reef (200-220 m water depth) were collected during a Norwegian research expedition to be analysed as part of the ?FATE of cold-water corals?drivers of ecosystem change? project. Following the completion of this project, unused dead coral fragments were obtained for collaborative research for Chapter 3 of this thesis. This study invited an interdisciplinary aspect, partnering with researchers in the School of Engineering at Trinity College Dublin. Nanoindentation methodology normally used for human bone analysis was applied to dead coral skeletons exposed to various seawater temperature and increased carbon dioxide treatments to assess the effects on skeletal structure. This analysis determined that these stressors significantly impacted skeletal properties, resulting in possible breakage and decreased stability of coral mound development.

Chapter 4 provides preliminary data of CWC geochemical concentrations for Mg, Sr, and U and the potential for palaeoenvironmental proxies. As Sr and U are directly related in aragonite, a Sr-U thermometer has been successful as a seawater temperature proxy for tropical corals. However, more research is needed to determine the validity of the Sr-U thermometer in CWCs as other factors may influence the elemental concentrations. A comparison of Mg-U is analysed to support published literature that the two concentrations are inversely related. Although this research is not new in terms of methodologies, preliminary results indicate further need to validate certain elemental pairings in CWCs as effective geochemical proxies due to impacts from environmental parameters. Future research objectives and possibilities are discussed in Chapter 6.

The desire to communicate science to the public is lacking, and there is an unprecedented need for scientists to be good communicators. It is imperative to demonstrate positive perspectives in research so that we can advance studies and continue learning. Throughout my PhD, I used science communication (Sci Comm) and public engagement to disseminate my CWC research and educate the public on the importance of these ecosystem engineers. Chapter 5 demonstrates how this involvement transformed the way I view science and have realised the critical need for understandable explanations of scientific research so the public feel engaged and involved. Participating in Sci Comm has enhanced my professional development skills in creative and non-scientific ways, such as the use of character-driven figurines. Through television, over 113,000 people tuned in to watch an episode of 10 Things to Know About where I discussed Ireland?s CWCs and my PhD research. From social media, a research collaboration was formed that resulted in critical data for the publication of Chapter 2. During a research expedition, the learner-led approach to Sci Comm resulted in over 100,000 engagements via Twitter/X, and greatly increased public knowledge of what a working research vessel is like. A culmination of these points above suggest that PhD programmes should require some form of Sci Comm or public engagement in their curricula through a combination of formal training and hands-on experience.