Phytoplankton pigments, species and light climate in a complex warm-core eddy of the East Australian Current

Abstract

The complex warm-core eddy system Marion, documented by Cresswell and Legeckis (1986, Deep-Sea Research, 33, 1527–1562) from July 1980 to February 1982, was examined for phytoplankton species and pigments in autumn (April–May) 1981. During this period phytoplankton biomass (60–80 mg Chl α m −2) was higher at the eddy centre and western margin,than at other stations inside and outside the eddy (20–40 mg Chl α m −2). Nanoplankton plus picoplankton accounted for 60–70% of the chlorophyll at the eddy centre and western margin, and as much as 90% at some of the non-enriched stations. Light-penetration profiles (400–750 nm) distinguished eddy water with its increased phytoplankton biomass from tropical Coral Sea water from which the eddy was derived. Thin-layer chromatographic pigment analyses defined most algal types, confirmed the dominance of diatoms at high biomass sites and distinguished between pigments from living phytoplankton and dettrital material. High proportions of detrital pigments were found in an “old” submerged eddy system. Eddy centre and eddy margin enrichment processes resulted in blooms of the diatoms Nitzshia and Rhizosolenia, similar to those in the previously studied Eddy F ( Jeffrey and Hallegraeff, 1980a, Marine Ecology Progress Series, 3, 285–294). Species differences between Eddy Mario and surrounding waters were minor, with 110 out of a total of 160 species present both inside and outside the eddy. Tropical flora (e.g. Trichodesmium erythraeum, Richelia intracellularis and Scyphosphaera apsteinii) were found throughout the area as a result of flooding by water of tropical origin.