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.

南半球春季浮游植物水华暴发后，海樽（salp）类物种民主海樽（Thalia democratica）的集群会周期性地出现在澳大利亚东南部近岸海域。本研究旨在探明塔斯曼海西部三种水团中民主海樽的丰度、体型/发育阶段分布特征，及其与桡足类（copepods）的相互关系。研究团队沿澳大利亚新南威尔士州沿岸200公里海域布设4条跨陆架断面，采样范围从约南纬32.5°的东澳大利亚流（East Australian Current, EAC）分离区延伸至悉尼近海（南纬34°），采样方式为垂直拖网。依据温盐特征，所有采样站位可划分为三种截然不同的水团：近岸陆架水、东澳大利亚流团以及上升流团。尽管民主海樽在所有站位均有分布，但其在近岸陆架水中的丰度显著高于东澳大利亚流团与上升流团。对种群结构（包括群体芽体、群体雌性个体、群体雄性个体、未成熟单体与成熟单体）的分析同样显示，近岸陆架水中具有更高比例的生殖群体及其子代个体。东澳大利亚流团海域的海樽种群结构则存在显著差异，其特征为单体阶段个体匮乏、水温更高且叶绿素a（chlorophyll a）浓度更低。研究发现民主海樽丰度与桡足类丰度之间存在微弱的负相关关系。本研究中测得的民主海樽最大丰度为全球已记录最高丰度的两倍，较1938-1942年间澳大利亚东南部近海陆架与坡地海域采样得到的最大丰度高出一个数量级。