Impacts of human activities on cold-water sponges and the habitats they form in the North East Atlantic

Sponges are filter-feeders present in many aquatic environments, from rivers to abyssal plains. In the deep-sea, sponges can form dense aggregations (sponge grounds) which constitute important but vulnerable ecosystems. As human activities now take place in the deep-sea, the need to determine the resilience of sponge grounds to disturbances is essential. My PhD aimed at understanding the impacts of oil and gas activities on deepsea sponges and sponge grounds. First, a literature review on the known impacts of hydrocarbon production on sponge grounds is provided. Second, environmental data from industrial, academic and governmental sources were analysed to determine the impact of anthropogenic activities on sponge grounds. In a case study of the Faroe-Shetland channel, I showed that substrate characteristics and seawater temperature, modulated by anthropogenic activities, controlled the distribution of megafauna. Third, to determine the impacts of an oil spill on sponges, experiments exposing a shallow-water sponge model to crude oil and dispersant contaminated seawater or sediments were conducted. Through this experimental work, I showed that exposure to contaminants decreased the sponge filtering abilities. Furthermore, over 1000 genes, from the sponge and its associated microbes were detected as differentially expressed after exposure to contaminants. These effects were worsened by the addition of dispersant and their use within sponge grounds should therefore be avoided