Temporal and spatial distribution of phytoplankton in waters of the Great Barrier Reef and Coral Sea

Phytoplankton were identified and relative abundance estimated in water samples collected between 1975 and 1977 in the central Great Barrier Reef and the Coral Sea.

Three reefs (John Brewer, Davies and Little Broadhurst) were sampled. Four stations were sampled within the lagoon of each reef and 4 stations sampled in the open waters outside each reef. John Brewer Reef was sampled once (February 1977) as was Little Broadhurst Reef (November/December 1976). Davies Reef was sampled three times (September 1976, December 1976 and March 1977).

Twenty stations, separated into two transects, were sampled in inter-reefal areas across the Great Barrier Reef and in the Coral Sea. Transect 1 (Stations 1-9) was sampled in April/May 1975 and Transect 2 (Stations 11-20) was sampled in June/July 1975. Each transect was sampled at times when there was no Trichodesmium bloom.

Three cross-shelf (inner-shelf) stations (21-23) were established and sampled approximately fortnightly. Stations 21 and 22 were sampled between December 1975 and November 1976. Station 23 was sampled between December 1976 and November 1977.

Five inshore stations located between Cape Bowling Green and John Brewer Reef were sampled at irregular intervals between December 1975 and May 1976. All samples were taken at a time when there was a marked Trichodesmium bloom.

Water samples were taken from approximately 1 m below the surface with 5 litre Niskin bottles. Subsamples of 500 ml were taken for phytoplankton species identification and immediately preserved with Lugol's solution made basic with sodium acetate. Aliquots of 100 ml of each sample were settled for approximately 3 days, and cell counts and examinations made by the inverted microscope method. In order to check that the samples were representative, collections were also made with a 20 um mesh net during 10 minute drifting trawls. Results were recorded in abundance categories for each species.