A soft-bottom sublittoral mesocosm by the Oslofjord: Description, performance and examples of application

Controlled experiments and detailed studies of behaviour in the subtidal require diving, submersible vessels or instruments placed in situ. These methods often limit experimental design. Furthermore, experiments with toxic chemicals in the field may not be possible due to lack of dosage control, environmental consequences, and public welfare. Such problems can be overcome by the use of mesocosms. In this paper a soft-bottom mesocosm in the Oslofjord, Norway is described. The mesocosm consists of two indoor basins each with a surface area of 100 m2 and a maximum water depth of 1.7 m. Each basin is divided into three compartments. Soft-bottom sediment sections were collected in the field by a modified USNEL box-corer (0.25 m2). The sediment was transferred to boxes and brought into the mesocosm. The water level in the mesocosm can be lowered so that the sediment surfaces are easily accessible for sampling, manipulation, inspection, or measurements requiring equipment or techniques not compatible with field conditions. The performance of the mesocosm in terms of pore-water chemistry, bacterial production, sedimentation, animal recruitment and mortality are compared to field conditions. Examples of application of the system are given. It is concluded that the mesocosm provides unique experimental conditions for biological, chemical and physical experiments on subtidal soft-sediment communities.