A submersible respirometer designed to measure the metabolism of benthic marine plants and invertebrates

The respirometer included: a data-logger (Li-1000, Li-Cor), secured within a pressure-resistant, waterproof, acrylic housing; different sets of transparent incubation chambers fitted within polarographic O₂ electrodes, containing built-in temperature sensors; and a spherical (4p) quantum sensor. Inlet and outlet teflon ball valves were fitted to the base of each incubation chamber and connected by Tygon hose to an external centrifugal pump, which flushed the chambers at regular intervals with fresh seawater. Incubations lasted a total of 24 h. The respirometer was used to investigate the primary production, at different depths, by the green alga Caulerpa taxifolia in the northern Mediterranean and by “micro-colonies” of the reef-building coral Stylophora pistillata in the northern Red Sea. These investigations indicated: (a) that C. taxifolin may satisfy a requirement at depths greater than 25-30 m near Monaco by uptake of organic carbon from substrata via its subterranean rhizoids; and (b) that S. pistillata comprises 3 different depth (light) adapted strains in the Gulf of Aqaba