Diffusion culture experiments using natural phytoplankton from the Great Barrier Reef

Seventeen experiments were carried out between April 1983 and June 1985 to measure in situ growth rates of phytoplankton communities and constituent species in mid- to outer-shelf waters of the central Great Barrier Reef. Growth rates of identifiable phytoplankton taxa, composite groups of phytoplankton (eg microflagellates) and size classes were calculated from changes in cell numbers or chlorophyll concentration occurring while size-fractionated natural phytoplankton assemblages were incubated in situ within diffusion chambers.

Growth experiments were carried out either in the lagoons of, or most commonly, in waters immediately adjacent to three reefs in the central GBR province, Myrmidon Reef, Rib Reef and Davies Reef. Myrmidon Reef was selected to typify conditions found on the outer shelf and in oceanic waters of the western Coral Sea. Located on a protrusion extending seaward from the continental shelfbreak, the sheltered northern side of Myrmidon Reef is exposed to oceanic waters in the southward flowing East Australian Current. Davies Reef and Rib Reef have mid- shelf locations and are surrounded by waters typifying the reef matrix and outer GBR lagoon. Sites at or near reefs for individual experiments were selected to enable safe deployment of diffusion chambers at depths corresponding to desired light penetration depths.

Water samples for dissolved nutrient, chlorophyll, phaeophytin, temperature and salinity analyses were collected daily from incubation depths at the mooring sites. At most deep water stations underwater light profiles were measured to determine irradiance levels at the depths of incubation.

The purpose of these experiments was to measure in situ growth rates of phytoplankton communities and constituent species in mid- to outer-shelf waters of the central Great Barrier Reef.