In-situ measurement of photosynthetic oxygen production in the water column.

A novel hardware device is described to determine photosynthetic and respiratory oxygen uptake and release, respectively, in organisms in their natural habitat even under the rough conditions of their marine environment. Both macroalgae and phytoplankton can be utilized and oxygen exchange can be determined in solar radiation. The chamber can be used at or above the water surface or can be lowered into the water column. The data of oxygen concentration, irradiance and temperature are constantly monitored by a laptop computer and stored in disk files. The experimental data measured in some macroalgae as well as in phytoplankton indicate that the irradiance window for positive net photosynthetic oxygen production is fairly limited under natural conditions; at too low irradiances respiration exceeds photosynthesis and at too high irradiances photosynthesis is shut down by photoinhibition, at least in species not adapted to unattenuated solar radiation.