Crude Oil in the Deep: Investigating the Responses of a Deep-Sea Sponge Holobiont to Hydrocarbon Exposure

The deep-sea is increasingly considered for extraction of petroleum reserves as offshore oil and gas development is expanding with the identification of new reservoirs. This raises considerable concerns about accidental releases of hydrocarbons into deep-sea ecosystems and the subsequent cascading effects on associated fauna. Sponges are abundant and ecologically valuable in these ecosystems. They are known to be efficient filter feeders, contributing to benthic-pelagic coupling and providing a habitat for a suit of organisms. Surprisingly, there is a dearth of studies on the impacts of oil pollution on sponges. Using a mesocosm setup, we investigated the responses of a deep-sea sponge from the Northern Atlantic, Geodia barretti, exposed to three ecologically-relevant oil concentrations for a duration of 8 days, followed by a recovery period of 30 days. Changes in physiology and cellular stress were assessed through respiration rates and lysosomal membrane stability, respectively. The structure of the sponge associated microbiome was investigated using high-throughput sequencing of 16s rRNA gene amplicons. Acute crude oil exposure did not induce strong sub-lethal stress effects in G. barretti. Respiration showed varying patterns of both increased and decreased rates, with no significant effect from the treatments, while lysosomes were significantly impacted by oil, displaying destabilization of lysosomal membranes. After the recovery period, sponges were observed to return to their initial physiological and cellular pre-experimental state. Sponge microbiome however, showed no significant changes with either treatment or exposure time. Such studies are essential to advance our understanding of the vulnerability and resilience of deep-sea sponges to hydrocarbon exposure, providing useful data for managing risks associated with oil and gas exploration in the Northern Atlantic.