A benthic mesocosm facility for maintaining soft-bottom sediments

Closed-circulation, water jacket-insulated laboratory basins (benthic mesocosms) of 1 m² surface area preserved the abundance and species composition of the principal benthic macrofauna of the 350-m-deep Laurentian Trough for periods exceeding a year. Abundance of meiofauna, and bacterial numbers and activity were also sustained. Although the overlying water was permitted to equilibrate with the atmosphere, oxygen penetration depths in the sediment stabilized at about twice the thickness of the in situ aerobic layer, while whole-sediment respiration rates remained within the range observed for freshly obtained sediment cores. Build-up of metabolic by-products in the overlying water was controlled by bi-monthly replacement of a third of the bottom water. The study demonstrated that close observation of organism behaviour and biogeochemical processes within deep coastal sediments can be carried out in laboratory mesocosms.