Zooplankton Abundance in Australasian Waters

Abstract

The seas surrounding Australia contain a relatively low zooplankton biomass, particularly in the open ocean. There is a region of higher biomass in an upwelling area between the north-west coast of Australia and Indonesia, and there are indications that there may be a shortlived spring increase in the southern Tasman Sea; otherwise, the biomass of zooplankton in the open ocean is no higher than in the Sargasso Sea. An examination of values for other parts of the world reveals that subtropical regions of the open ocean are characteristically poor in plankton.

The mean zooplankton biomass on the Australian continental shelf was estimated to be about 100 mg/m³ (exclusive of salp swarms), varying from 82 to 213 mg/m³ with the area and the year. The biomass in the upwelling area south of Java was of the same magnitude, but in most parts of the open ocean it was no greatsr than 50 mg/m³, and was usually less than 25 mg/m³. Salp swarms were found more commonly in the southern part of the area investigated, and constituted local concentrations of higher biomass. These swarms took place in sprlng and summer and led to a seasonal cycle in the biomass level on the shelf regions of the New South Wales south coast. An increased biomass was also observed off the north-west coast of Australia during the period of prevailing offshore winds. This was crustacean in character.