Multiple stress effects on deep-sea sponges

Sponge grounds are benthic ecosystems dominated and densely populated by sponges. Sponges grounds are widespread throughout deep-sea habitats in the North Atlantic where they are usually dominated by only a few different species. These sponges play a crucial role in the function of benthic deep-sea habitats by providing habitat for several invertebrates and fish species and by nutrient cycling. As of now, little research effort has been addressed to sponge grounds in deep-sea environments. While we hardly understand these ecosystems and their importance for benthic-pelagic-coupling processes, they are already facing anthropogenic induced environmental changes and disturbances. Climate change, causing global ocean warming and acidification, is rapidly altering marine habitats. Organisms have to cope with these changes on an evolutionary short time scale. In addition, benthic habitats in the North Atlantic face increasing bottom-trawl fishing activities and offshore drilling for fossil hydrocarbons. The influence of these changes on the highly abundant deep-water sponges is yet unknown. This project aims at assessing the biological performances (growth-, respiration- and pumping-rates) of the two deep-water key-species Geodia barretti (Bowerbank, 1858) and Vazella pourtalesi (Schmidt, 1870) under different environmental conditions. By using a multifactorial approach we will show how North Atlantic sponge grounds may respond to future changes in their environment. First, individuals of the two target species will be long-term exposed to different seawater pH and temperature regimes including those reflecting predicted conditions for the year 2100. Second, the sponges will be exposed to suspended sediments to evaluate how long-term acclimatized individuals cope with this additional stressor, which simulates the resuspension of sediments by fishing or exploitation activities. As deep-water sponges often thrive within the vicinity of oil seepages, we will also test the hypothesis that sponges metabolize certain fossil hydrocarbon compounds. This study will be the first to examine how these potential metabolic pathways might influence the potential of sponges to cope with changing environmental conditions. Multifactorial ex situ experiments on the effects of the different stressors on physiological performances of the two sponges species allows an identification and quantification of the individual and cumulative impacts of climatic drivers and local interactions on the functioning of deep-water sponges. The project will be embedded in the European project SponGES, which aims to close knowledge gaps about the valuable sponge ecosystems in the North Atlantic.