Closed-circulation, water jacket-insulated laboratory basins (benthic
mesocosms) of 1 m(2) surface area preserved the abundance and species
composition of the principal benthic macrofauna of the 350-m-deep Laur
entian Trough for periods exceeding a year. Abundance of meiofauna, an
d bacterial numbers and activity were also sustained. Although the ove
rlying water was permitted to equilibrate with the atmosphere, oxygen
penetration depths in the sediment stabilized at about twice the thick
ness of the in situ aerobic layer, while whole-sediment respiration ra
tes remained within the range observed for freshly obtained sediment c
ores. Build-up of metabolic by-products in the overlying water was con
trolled by bi-monthly replacement of a third of the bottom water. The
study demonstrated that close observation of organism behaviour and bi
ogeochemical processes within deep coastal sediments can be carried ou
t in laboratory mesocosms.