Rapid respiratory responses of the deep-water sponge Geodia barretti exposed to suspended sediments

Sponges often dominate deep-water benthic faunal communities and can comprise up to 90% of the benthic biomass. Due to the large amount of water that they filter daily, sponges are an important link between benthic and pelagic ecosystems. Across the Tromso-flaket, Barents Sea, Norway, there are high biomasses of deep-water sponges. This area is also an important fishing ground, with fishing activity in some areas >27000 trawl hours yr(-1). Bottom trawling suspends large quantities of sediment into the water column, with measured concentrations up to 500 mg l(-1). This is the first study on the effects of suspended sediment exposure on deep-water sponges. In a laboratory experiment, Geodia barretti (Bowerbank 1858) (Class: Demospongiae) was exposed to 5 different sediment concentrations (0, 10, 50, 100 and 500 mg l(-1)). Respiration rates were measured before, during and after the exposure period. The results demonstrate that G. barretti physiologically shuts down when exposed to concentrations of 100 mg l(-1) (86% reduction in respiration), with thresholds of responses occurring between 10 to 50 mg l(-1). However, rapid recovery to initial respiration levels directly after the exposure indicates that G. barretti can cope with a single short exposure to elevated sediment concentrations. Given the high bottom-trawling frequency in Tromso-flaket, sponges may be frequently exposed to suspended sediments. Therefore, it is important that further investigations on the effects of suspended sediments on filter feeding organisms focus on the effects of repeated and long-term suspended sediment exposures to evaluate the overall ecological impacts.