Joëlle Robbe1, Magali Zbinden1, Franck Lartaud1
1Sorbonne Université, France
As their tropical analogues, cold-water colonial corals are engineer species that create complex habitats among the richest in deep-sea biodiversity (Rogers 1999). Although living in deeper waters than tropical corals (from 5 m to over 3,000 m depth), cold-water corals will soon face the cumulative threats of ocean warming and acidification (Foley et al. 2010). As their tropical counterparts, specific host-bacteria associations have been highlighted (Neulinger et al. 2008, Meistertzheim et al. 2016, Kellog et al. 2017). But due to the difficulty of deep-sea sampling, detailed knowledge of the ecology and physiology of cold-water corals is still lacking to forecast the response of the coral holobiont to climate change. Thus, we conducted an in-depth description of the coral holobiont, including growth and anatomy of the host to the localization and function of the associated bacteria. The study focused on the cold-water coral species Desmophylum pertusum present in the Lampaul canyon, Bay of Biscay (North-East Atlantic). In situ experiments using calcein staining and epifluorescence microscopy revealed particularly low polyp growth rates of D. pertusum in this canyon (2.9±1.3 mm/year) compared to the literature. A morphological description of different coral host tissues and the localization of the bacterial microbiome within these tissues, was carried out, using respectively histological stains and electron microscopy approaches. These approaches have enabled us to gain a better understanding of the tissues’ deep structure and the occurrence of bacteria within them. In order to study climate change-related effects on cold-water-corals, coral colonies were maintained in pressurized aquaria for 5 months, at +3°C and a reduced pH of 0.3 units, in line with the IPCC predictions for 2100 in the NE Atlantic. The effect of rising temperature and decrease in pH on skeletal growth and tissues’ structure has been studied using the same techniques as described above.
[The present work was supported by a grant (Project-ANR-20-CE02-0006) from French National Research Agency]
Biography
After obtaining a Bachelor’s degree in Biology and Ecology and a Master’s degree in Marine Sciences, Joëlle began her thesis on the effect of global change on the physiology and microbiome of cold-water corals in the Lampaul Canyon at Sorbonne Université. Particularly interested in deep-sea environments, she studies the diversity and functionality of bacterial communities present in coral tissues, their metabolic relationships, as well as the coral tissue morphology and and skeletal growth.