Wet biomass of the main mesoplankton groups in the Guaymas Basin (Gulf of California) measured in October 1990

Plankton above the vent fields of the Guaymas Basin was studied over the entire water column with the use of the MIR deep-sea manned submersible and BR plankton nets. Our studies confirmed that there is a certain increase in zooplankton biomass in the near-bottom layers. A reason for this phenomenon is not clear, but it may be related either to concentration of food particles precipitating from highly-productive surface waters, or to the effect of changes in concentration of dissolved oxygen or to the influence of hydrothermal production. This paper also deals with influence of the oxygen minimum layer at depth of 450-800 m on plankton.