The response of a boreal deep-sea sponge holobiont to an acute crude oil exposure

Exploration and extraction of petroleum reserves in deep-sea marine ecosystems are ongoing activities world-wide and are continuously expanding with the identification of new reservoirs. Whilst a wealth of knowledge is known on the effects of oil spills on fish and other organisms in shallow water environments, the effects of subsurface oil spills (blowout events like the Deepwater Horizon) on deep-sea ecosystems have been less well studied. With exploration activities in deep-sea ecosystems predicted to increase, there are concerns regarding the accidental release of hydrocarbons into deep-sea ecosystems and the subsequent cascading effects on associated fauna. Sponges are abundant and ecologically valuable, known to be highly efficient filter feeders, contributing significantly to benthic pelagic coupling and providing habitat for a suite of organisms. However, sponges, which are sessile in nature, accumulate contaminants present in their ambient environments, making them vulnerable to oil spills. Surprisingly, the impacts of oil on deep-sea sponges remain unexplored, despite sponges being particularly dominant around oil and gas exploration locations in the Northern Atlantic. Here we present key findings from a mesocosm study, where we exposed the locally abundant deep-sea sponge Geodia barretti to three ecologically relevant oil concentrations for a duration of 8 days, followed by a recovery period of 30 days. A holistic approach to elucidate the effects of oil on G. barretti focused on measuring changes in physiology (respiration and filtration efficiencies), cellular stress (lysosomal membrane stability), and the structure of the sponge-associated microbiome using high-throughput sequencing of 16s rRNA gene amplicons. This study enhances our understanding of the vulnerability of deep-sea sponges to hydrocarbon exposure, providing useful data for managing risks associated with oil and gas exploration in the Northern Atlantic.