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Shelf–oceanic dynamics of surface environmental
parameters in the Kangaroo Island–Bonney Coast region
Dahlia Foo
A
,
D
,Clive McMahon
B
,Mark Hindell
A
and Simon Goldsworthy
C
A
Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade,
Battery Point, Tas. 7004, Australia.
B
Sydney Institute of Marine Science, 19 Chowder Bay Road, Mosman 2088 NSW, Australia.
C
South Australian Research and Development Institute (Aquatic Sciences), 2 Hamra Avenue,
West Beach, SA 5024, Australia.
D
Corresponding author. Email: dahlia.foo@utas.edu.au
Abstract. The shelf and oceanic waters of the Kangaroo Island–Bonney Coast region are important foraging habitats for
top marine predators in the ecosystem; however, the dynamics between the two distinct water types have not been
investigated. This study examined the spatial and temporal variability of oceanographic parameters in the southern waters
of Australia (36–438S, 136–1418E) associated with the Bonney Upwelling (shelf) and subtropical front (STF; oceanic).
Using satellite data from 1997 to 2016, we found that productive oceanic waters were associated with the STF and eddy
activity; they were generally furthest from the shelf break in spring–summer (upwelling season on the shelf) and closest to
the shelf break in winter–autumn (downwelling season on the shelf). Inter-annual variabilities of chlorophyll-a
concentration (Chl-a), sea-surface temperature and sea surface-height anomaly were generally higher in summer than
in winter for both shelf and oceanic waters. El Nin
˜o–Southern Oscillation, Southern Annular Mode and Indian Ocean
Dipole were cross-correlated with anomalous shelf and oceanic Chl-aat various lagged times (range ¼15–0 months). This
study provides a regional perspective of the spatial and temporal oceanographic variability in southern Australian waters,
which may help with understanding apex-predator ecology in the ecosystem.
Keywords: ecology, marine mammals, oceanography, pelagic zone.
Received 4 April 2020, accepted 15 October 2020, published online 26 November 2020
Introduction
The World’s continental shelves, slope edges and mesoscale oce-
anic features, such as eddies and fronts, are important sources of
food for top marine predators (Bost et al. 2009;Rogers et al. 2015).
As the aquatic environment is highly dynamic, the productivity of
these features vary seasonally (Behrenfeld et al. 2001;Bender et al.
2016) and inter-annually (Demarcq et al. 2003;Legaard and
Thomas 2007). This variability in the productivity of the local
environment may influence the distribution and abundance of mid-
trophic species, the foraging success of marine predators (Blanchet
et al. 2015) and, ultimately, their fitness (Oosthuizen et al. 2016).
For example, little penguins from south-eastern Australia increase
their foraging effort with lower sea-surface temperature in the local
region (Berlincourt and Arnould 2015). Several species of seals
concentrate foraging in areas with a greater sea surface-
temperature variability, a potential proxy for long-term produc-
tivity (Bradshaw et al. 2004). Therefore, understanding how
environmental conditions change at various temporal scales is an
important step in understanding how the physical and biological
processes underpin the prey base that supports marine predators.
The Bonney Upwelling is one of the most prominent and
predictable upwelling centres in south-eastern Australia and it is
part of the eastern Great Australian Bight (GAB) ecosystem
(Fig. 1,2). The Bonney Upwelling and other upwelling centres
in the eastern GAB are important drivers of phytoplankton
growth, feeding marine animals in the region (Butler et al.
2002). Several marine species in the region, such as seabirds
(Angel et al. 2015;Berlincourt and Arnould 2015), fishes
(Rogers et al. 2015), whales (Butler et al. 2002) and seals
(Page et al. 2006;Lowther and Goldsworthy 2011), are known
to feed at or near the Bonney Upwelling area; it is also a
productive fishing ground for rock lobster (Butler et al. 2002;
Goldsworthy et al. 2013).
The Bonney Upwelling occurs on the narrow shelves of the
Bonney Coast where its seasonal upwelling cycle begins in the
austral summer and extends to late autumn (November–April).
Enhanced primary production from upwelling is greatest in
March (Nieblas et al. 2009). The Bonney Upwelling is predomi-
nantly a wind-driven system (Butler et al. 2002) where the
upwelling season is characterised by westward shelf currents,
and south-easterly coastal winds along the Bonney Coast (Robe,
South Australia to Portland, Victoria; Fig. 2a;Middleton and Bye
2007). Thus, the Bonney Upwelling plume usually extends north-
west towards the local waters south of Kangaroo Island.
CSIRO PUBLISHING
Marine and Freshwater Research, 2021, 72, 679–692
https://doi.org/10.1071/MF20100
Journal compilation ÓCSIRO 2021 www.publish.csiro.au/journals/mfr