On the “hidden” phytoplankton blooms on Australia's southern shelves

Abstract

AbstractPhytoplankton blooms on Australia's southern shelves are revisited using satellite‐derived monthly data of chlorophyll a concentrations for the period 2003–2015. It is known that the region hosts a seasonal coastal upwelling system that develops in austral summer (January–March) with chlorophyll a concentrations of >2 mg/m3. While this summer upwelling is spatially limited to a few hot spots, here we show that widespread phytoplankton blooms of moderate (~1 mg/m3) chlorophyll a concentrations develop during autumn and early winter on most of Australia's extensive southern shelves—from the vast shelves of the Great Australian Bight (GAB) in the west to Bass Strait in the east. This surprising finding disproves the widespread belief that shelf waters of the GAB are generally oligotrophic and may explain the relatively high abundance of both forage fish (sardines) and upper trophic‐level predators (e.g., tuna and whales) in the region.