Asphyxiation by sedimentation? - a sponge's perspective

Abstract

Naturally occurring sedimentation is an important habitat-structuring factor. Increased sedimentation through anthropogenic actions can result in adverse effects to organisms and communities. With industrial activities moving further offshore, new habitats and organisms are affected. Particular in the North-East Atlantic, anthropogenic activities including oil and gas exploration and trawling have been recognised as major hazards to organisms that are sensitive to sedimentation. Sessile filter-feeders, such as sponges, provide vital functions to benthic habitats in many ecosystems and are believed to be adversely affected by turbid waters and settling particles. This project aimed to investigate the effects of sedimentation events from natural and anthropogenic sources on three different sponge species from contrasting habitats, Suberites ficus (shallow water, high sedimentation rates), Sycon ciliatum (shallow water, low sedimentation rates) and Phakellia ventilabrum (deep water, low sedimentation rates). The responses of the three species to increased concentrations of sediment were assessed on a physiological and a transcriptional level. Exposure to drill cuttings from oil exploration was investigated in Sycon ciliatum and Phakellia ventilabrum. It was shown that contrary to the expectations, respiration rates of all investigated sponges were not affected by sedimentation. However, on a molecular level the genes of the stress protein heat shock protein (hsp70) and the enzyme nitric oxide synthase (nos) were significantly regulated during exposure to sediment. Surprisingly, the expression pattern of hsp70 and nos was not consistent between the sponge species. Hsp70 transcription did not change in Suberites ficus, it was down-regulated in Sycon ciliatum and up-regulated in Phakellia ventilabrum. The expression of nos was down-regulated in Suberites ficus and up-regulated in Sycon ciliatum and Phakellia ventilabrum. Stress reaction seemed to be specific to each sponge species and might be dependent on the exposure to sedimentation that naturally occurs in their habitat.

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