Filter feeding marine animals living on the seafloor rely on the suspension of particles for food, and some species also utilise passing particles for the construction of dwelling tubes. However, the delicate balance between such animals and their environment can easily be disrupted by a variety of human actions. The extraction of aggregates for the construction industry, for example, results in significant disturbance through removal of substrate and the generation of sediment plumes through processing of the aggregate.  The latter can lead to local burial of habitats and smothering of animals.

So how do benthic animals respond to such environmental disturbances? To answer this we have designed and built special aquaria known as paddle Vortex Resuspension Tanks (pVORTs) to try to re-recreate typical conditions associated with dredging activities. Using these tanks we have been able to generate current flow and continuous suspension of sediment whilst subjecting animals to various burial durations and depths using different sediment fractions. So far our attentions have focused on the Ross worm (Sabellaria spinulosa, see figures 1 and 2), since this is an important reef-forming polychaete worm, and the mussel (Mytilus edulis), an important commercial species. Results so far suggest that both these species are tolerant of short term burial. Indeed some Sabellaria has been observed to continue growing its tubes whilst buried, probably in a bid for freedom, whilst some of the mussels have be able to just “climb” out of the burial chamber if the sediment is not too deep!

Fig 1 Sabellaria spinulosa clumps consisting of many individuals that have grown their sediment tubes in the pVoRTs. Tube growth rates can be up to 10 mm per day. These worms can form large aggregations under the right environmental conditions that result in extensive biogenic reefs (source: K S Last)

Fig 2 Two Sabellaria growing up the side of the aquarium in the lab. Notice the dark tentacles which are hollow and muscular and  are used to catch suspended particles for tube construction (source: V J Hendrick)

 Currently, little is known about how animals respond to increased sedimentation, their natural tolerance to it and their resulting behavioural responses. Hence this project, which is funded by the Marine Aggregate Levy Sustainability Fund (MALSF), is designed to supplement current understanding providing further insights into the impact of marine aggregate extraction. When our results are coupled to field data on burial from dredging, it will be possible to determine which species maybe most impacted, thus increasing the knowledge base on which to manage dredging operations.