Salp Counts, Tasman Sea off South Eastern NSW (Australia), 2008

Swarms of the salp, Thalia democratica, periodically occur off southeast Australia following the austral spring bloom of phytoplankton. This study aimed to determine the abundance and size/stage distribution of T. democratica and their relationship with copepods in three water types of the western Tasman Sea. Samples were taken from vertical net hauls along four cross-shelf transects spaced along 200 km of the New South Wales coast, from the East Australian Current (EAC) separation zone, around 32.5ºS to off Sydney (34ºS). Temperature-salinity signatures grouped stations into three distinct water types: inner shelf water, EAC, and upwelled water. Although common across all stations, T. democratica was significantly more abundant within inner shelf waters compared to both EAC and upwelled water. Analysis of population structure (aggregate buds, aggregate females, aggregate males, immature solitaries and mature solitaries) also identified higher proportions of reproductive aggregates and their offspring in inner shelf water. This salp population structure was significantly different in the EAC regions, characterised by a paucity of the solitary stages, higher temperatures and lower chlorophyll a concentrations. A weak negative correlation was identified between T. democratica and copepod abundance. In this study, the maximum abundance of T. democratica was twice the highest global recorded abundance and tenfold greater than maximum abundances sampled from the continental shelf and slope waters off southeast Australia during 1938-42.