Phytoplankton blooms on the western shelf of Tasmania: evidence of a highly productive ecosystem

J Kämpf

doi:10.5194/os-11-1-2015

Abstract

Abstract. Satellite-derived chlorophyll a data using the standard NASA-OC3 (ocean colour) algorithm are strongly biased by coloured dissolved organic matter and suspended sediment of river discharges, which is a particular problem for the western Tasmanian shelf. This work reconstructs phytoplankton blooms in the study region using a quadratic regression between OC3 data and chlorophyll fluorescence based on the fluorescence line height (FLH) data. This regression is derived from satellite data of the nearby Bonney upwelling region, which is devoid of river influences. To this end, analyses of 10 years of MODIS-aqua satellite data reveal the existence of a highly productive ecosystem on the western Tasmanian shelf. The region normally experiences two phytoplankton blooms per annum. The first bloom occurs during late austral summer months as a consequence of upwelling-favourable coastal winds. Hence, the western Tasmanian shelf forms a previously unknown upwelling centre of the regional upwelling system, known as Great South Australian Coastal Upwelling System. The second phytoplankton bloom is a classical spring bloom also developing in the adjacent Tasman Sea. The author postulates that this region forms another important biological hot spot for the regional marine ecosystem.

Highlights

Physical processes that enrich the euphotic zone with nutrients are principal agents of coastal phytoplankton blooms
Averages of phytoplankton-related parameters were constructed from the satellite data of predefined target areas as the average of 10 pixel data of the highest values for Sea-viewing Wide Field-of-view Sensors (SeaWiFS), and 50 pixels of the highest values for MODIS-aqua; this corresponds to combined areas of 810 and 800 km2, respectively
Chlorophyll a levels on the western Tasmanian shelf attained values of ∼ 3 mg m−3, the same order of magnitude as those observed in the upwelling centre along the Bonney coast (Fig. 3a)

Summary

Introduction

Physical processes that enrich the euphotic zone with nutrients are principal agents of coastal phytoplankton blooms. This upwelling system, referred to as the Great South Australian Coastal Upwelling System, consists of three upwelling centres (Fig. 1): the long-known Bonney upwelling (Rochford, 1977; Lewis, 1981; Schahinger, 1987; Griffin et al, 1997) along the so-called Bonney coast, and an upwelling centre off the southern tip of the Eyre Peninsula (Kämpf et al, 2004) The latter region plays a vital role in the life cycles of sardine (Sardinops sagax), anchovy (Engraulis australis), and southern bluefin tuna (Thunnus maccoyii) (Ward et al, 2006). Another smaller upwelling centre develops occasionally off the southwest coast of Kangaroo Island (see Kämpf et al, 2004)

Methods

Results

Conclusion