A deep-sea perspective on coral resilience in a changing world

The ocean is undergoing large scale physical, chemical and biological changes which are causing major ecosystem-scale shifts. The impact is clearly evident in shallow continental shelf waters easily accessible to local communities, the fishing industry, and scientists (e.g. increased coral reef bleaching, dwindling fish yields, blooms in nuisance algae and jellyfish). Changes in the deep sea are potentially as dramatic, with equally challenging long-term consequences (e.g. rising temperatures and lowering pH and oxygen levels) especially in the high latitudes. However, these changes are less visible to the general public and are chronically understudied given the logistical challenges of access to the deep sea. Even with increasing recognition of the intrinsic (e.g. biodiversity, blue carbon storage) and economic value (e.g. natural pharmaceuticals, heavy metal resources, fisheries nurseries) of the deep sea, there remain glaring gaps in our understanding of the resilience and vulnerability of the organisms which make up the major habitats of the deep. Particularly important in this regard are the extensive deep-sea habitats formed by calcifying corals. These corals can live for thousands of years and they form vast, diverse habitats in a surprisingly dynamic environment where food supply is controlled by falling particles from the surface and ever-changing currents. However, changes such as ocean acidification, food supply, and declining oxygen levels have the potential to reduce the ability of corals to produce their skeletons effectively. If corals were able to manipulate the composition of their skeletons to be more resilient to these changes, this would represent a key survival strategy in a rapidly changing world. Despite hints that some corals may have this ability, we do not know which taxa, or under what conditions, thus hampering effective marine conservation strategies.

In this project we intend to compare three habitat-forming coral taxa which exhibit contrasting modes of skeleton growth likely to dictate their vulnerability to external stress. Scleractinia calcify aragonite and are able to the modify seawater in which they grow so that they can live in low pH waters. Octocorals form their skeletons from calcite, which is more resistant to dissolution than aragonite. Stylasterids have the capacity to form from either aragonite or calcite, and as yet it is not known how they survive in low pH waters. Surprisingly, the phylogenetic tree for these corals is very poorly constrained, making it challenging to assess the relationships between the taxa or even to identify species. Using new genomic and geochemical data, together with a systematic examination of how and where corals grow in the modern ocean, we will be in a unique position to distinguish internal biological controls of coral biomineralization from external influences. We have exceptional access to deep-sea coral collections which will allow us to build the first phylogenomic framework for understanding mineralisation and susceptibility to external pressure in environmentally-critical, habitat-forming deep-sea corals. This will help us understand which deep-sea corals may be vulnerable to current and future climate change, and what environmental parameters are required for coral growth. These data will be used to better protect vulnerable marine ecosystems in the Southern Ocean via input to the Scientific Committee for Antarctic Research which provides objective and independent scientific advice to the Antarctic Treaty Consultative Meetings.