First in-situ monitoring of sponge response and recovery to an industrial sedimentation event.

Assessment of risks to seabed habitats from industrial activities is based on the resilience and potential for recovery. Increased sedimentation, a key impact of many offshore industries, results in burial and smothering of benthic organisms. Sponges are particularly vulnerable to increases in suspended and deposited sediment, but response and recovery have not been observed in-situ. We quantified the impact of sedimentation from offshore hydrocarbon drilling over ∼5 days on a lamellate demosponge, and its recovery in-situ over ∼40 days using hourly time-lapse photographs with measurements of backscatter (a proxy of suspended sediment) and current speed. Sediment accumulated on the sponge then cleared largely gradually but occasionally sharply, though it did not return to the initial state. This partial recovery likely involved a combination of active and passive removal. We discuss the use of in-situ observing, which is critical to monitoring impacts in remote habitats, and need for calibration to laboratory conditions.