ArticlePublisher preview available
To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

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 (36–43°S, 136–141°E) 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 Niño–Southern Oscillation, Southern Annular Mode and Indian Ocean Dipole were cross-correlated with anomalous shelf and oceanic Chl-a at various lagged times (range = 15–0 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.
Content may be subject to copyright.
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
... Positive SAM conditions were associated with Lawrence Rocks Gannets being recovered closer to their banding site the following year. Positive SAM events have been linked to enhanced wind regimes that promote upwellings in south-eastern Australia (de Oliveira 2018), leading to later increases in primary productivity (Foo et al. 2021). Such conditions have been shown to produce delayed positive effects on the foraging efficiency of other marine predators in the region such as the Australian Fur Seal (Arctocephalus pusillus doriferus) (Speakman et al. 2020). ...
... In addition, positive current SOI was correlated to shorter recovery distances for Lawrence Rocks Gannets. This finding was unexpected as sustained positive SOI conditions are associated to La Niña events, characterised by higher sea surface temperatures, decreased upwelling activity and reduced local prey availability (Foo et al. 2021) which could be expected to lead to greater migration distances in older individuals. ...
... Indeed, the detrended BCI values were also positively influenced by current year SAM. Positive SAM phases are associated with weaker zonal winds in southern Australia (Marshall et al., 2018) and a stronger Bonney Upwelling during summer driven by more easterly winds (Foo et al., 2021). The increased marine productivity cascading into Bass Strait could then provide more favourable foraging conditions for AUFS (Middleton and Bye, 2007), potentially leading to increased body condition. ...
Article
Full-text available
The Australian fur seal (Arctocephalus pusillus doriferus, AUFS) population is still recovering from the over-exploitation of the commercial-sealing era (18th and 19th centuries). While the population is considered to be only < 47% of its pre-harvest size, it now represents the greatest resident marine predator biomass in the south-eastern Australian marine ecosystem. The region is experiencing rapid environmental change and, as a keystone predator species, the AUFS is an indicator of ecosystem health. In the present study, the body mass, standard length and body condition index (BCI) were analysed between 1997-2021 in adult female AUFS provisioning pups on Kanowna Island (northern Bass Strait), the third largest colony for the species. While substantial inter-annual fluctuations were observed, there was no temporal trend in standard length during the 23-year study period. In contrast, body mass and, consequently, BCI decreased significantly, suggesting the population is experiencing changing nutritional conditions. While these changes do not appear to be due to competition with commercial fisheries or population expansion, weak but significant negative relationships were observed between BCI and 1-year lagged sea surface temperature and summer zonal winds in the Bonney Upwelling region, and both current- and 2-year lagged Indian Ocean Dipole (IOD). These findings suggest the BCI of AUFS may continue to decline under predicted climate change conditions. While a lack of a concurrent decline in pup production could indicate a degree of nutritional tolerance or flexibility in energy allocation, further monitoring is required to assess decreases in reproductive parameters (e.g., birth mass, pre-weaning growth rates) or vital rates, which would be expected with continued nutritional stress.
Article
Animals typically reproduce at the time of year when environmental conditions and food availability are optimal. These may decline after the reproductive period; consequently, individuals that are no longer constrained by central-place foraging for offspring provisioning may leave the breeding area. For marine species, obtaining direct information about at-sea movements and distribution during the non-breeding period can be challenging, causing a lack of knowledge for this important part of the annual cycle. In the face of a changing environment, obtaining such information is essential for predicting potential consequences on population trajectories. Here we used light level geolocators to investigate the non-breeding movements, and intrinsic factors influencing them, of Australasian gannets Morus serrator from 2 colonies in northern Bass Strait, south-eastern Australia, in 2 consecutive years. Tracking data revealed that, while some gannets remained within their breeding season foraging range during the non-breeding period (n = 15), many individuals travelled widely along the southern Australia continental shelf, from Cape Leeuwin in the west to the eastern seaboard of the continent (n = 84). The continental shelf areas of western Tasmania and Bass Strait were the most frequented. Most individuals exhibited nomadic behaviour, with no overall pattern or synchronicity in their movements. Data suggested differences between sexes and years in the at-sea movements of individuals, potentially due to differences in foraging strategies and environmental conditions, respectively. However, the collection of long-term data and higher-resolution tracking data is required to investigate potential consequences on the species in a changing environment.
Article
Full-text available
Coastal upwelling is important for marine ecosystems and the economy, because of its elevated primary and secondary productivity and large potential for fish catch. This study developed a scale-independent and semi-automatic image processing technique to map the upwelling areas along the 4500 km south-eastern coast of Australia from 14-year monthly MODIS Sea Surface Temperature (SST) data. The results show that there is significant spatial variability in the mapped upwelling areas, month to month, season to season and year to year. There is also strong temporal (month to month, seasonal and inter-annual) variability of the upwelling characteristics in area of influence, SST anomaly, chlorophyll-a concentrations and upwelling speed. This study identifies two prominent upwelling systems, the NSW system along the coast of New South Wales and the WVIC/SA system along the coast of western Victoria and adjacent South Australia. The NSW coastal upwelling system occurs more or less continuously from austral spring to autumn. The WVIC/SA coastal upwelling system is a seasonal upwelling system occurring in the austral summer. The NSW coastal upwelling system has a stronger upwelling intensity than the WVIC/SA system, in terms of area of influence, SST anomaly, chlorophyll-a concentrations and upwelling speed. We believe that the NSW coastal upwelling system, especially the northern and central parts, is mainly driven by the East Australian Current (EAC) and its eddies; while, the WVIC/SA coastal upwelling is a typical wind-driven system. In addition, the results indicate that the El Nino Southern Oscillation (ENSO) events are likely to have a low-to-moderate impact on both the NSW and the WVIC/SA coastal upwelling systems. The El Nino (La Nina) events tend to strengthen (weaken) upwelling intensity.
Article
Full-text available
The harbour seal (Phoca vitulina) population in Svalbard marks the northernmost limit of the species' range. This small population experiences environmental extremes in sea and air temperatures, sea ice cover and also in light regime for this normally temperate species. This study deployed Conductivity Temperature Depth Satellite Relay Data Loggers (CTD-SRDLs) on 30 adult and juvenile harbour seals in 2009 and 2010 to study their foraging behaviour across multiple seasons. A total of 189,104 dives and 16,640 CTD casts (mean depth 72 m ± 59) were recorded. Individuals dove to a mean depth of 41 m ± 24 with a maximum dive depth range of 24 - 403 m. Dives lasted on average 204 sec ± 120 with maximum durations ranging between 240 - 2,220 sec. Average daily depth and duration of dives, number of dives, time spent diving and dive time/surface time were influenced by date, while sex, age, sea-ice concentration and their interactions were not particularly influential. Dives were deeper (~150 m), longer (~480 sec), less numerous (~250 dives/day) and more pelagic during the winter/early spring compared to the fall and animals spent proportionally less time at the bottom of their dives during the winter. Influxes of warm saline water, corresponding to Atlantic Water characteristics, were observed intermittently at depths ~100 m during both winters in this study. The seasonal changes in diving behaviour were linked to average weekly wind stresses from the north or north-east, which induced upwelling events onto the shelf through offshore Ekman transport. During these events the shelf became flooded with AW from the West Spitsbergen Current, which presumably brought Atlantic fish species close to shore and within the seals' foraging depth-range. Predicted increased in the influx of AW in this region are likely going to favour the growth and geographic expansion of this harbour seal population in the future.
Article
Full-text available
Context Long-nosed (or New Zealand) fur seals breed on the southern coast of Australia, in New Zealand and on its subantarctic islands. They are recovering from over-harvesting that occurred in the early nineteenth century. Aims We estimated the rate of increase of the population at two colonies on Kangaroo Island, South Australia: Cape Gantheaume and Cape du Couedic. Methods From 1988–89 to 2013–14, pup abundance was estimated using a mark–resight procedure with multiple resights in large aggregations of pups and by direct counting in small aggregations. Key results At Cape Gantheaume, pup numbers increased by a factor of 10.7 from 457 to 5333 over 26 breeding seasons and the exponential rate of increase averaged 10.0% per annum (p.a.). Between 1988–89 and 1997–98, the population increased at 17.3% p.a., after which the increase was 7.2% p.a. At Cape du Couedic, pup numbers increased by a factor of 12.8 from 295 to 4070 over 21 breeding seasons at 11.4% p.a. Between 1988–89 and 1997–98, the increase averaged 14.2% p.a., after which it was 9.6% p.a. These increases have been accompanied by expansion in sub-colonies that existed in January 1989 and establishment of several new sub-colonies. Increases are likely to continue on Kangaroo Island. Conclusions There are few examples of increasing population levels for Australian native mammals and this is one of the best documented. It demonstrates that fur seal populations can recover from uncontrolled harvesting provided breeding habitat ashore is protected. Implications Fur seals interfere with fishers, disturb farmed tuna in aquaculture pens, and prey on little penguins.
Article
Full-text available
Marine predator populations are sensitive to temporal variation in prey availability, but prey dynamics are often difficult to quantify. Long-term measures of offspring growth is a useful performance attribute to gauge the potential demographic direction for such predator populations, especially where other metrics (e.g., population size estimates) are lacking. Subantarctic fur seal (Arctocephalus tropicalis) females are central place foragers during a protracted lactation period, and their foraging success determines the growth and vitality of their offspring. Using data spanning over 2 decades, we assessed geographic and temporal variation in growth rates and weaning mass of subantarctic fur seal pups at 2 of the species' principal populations (Gough and Marion islands) and identified environmental conditions that may, through assumed bottom-up mechanisms, affect body mass at weaning. While Marion Island pups grew at an average rate of between 0.040 and 0.067 kg/day early in lactation (comparable to conspecific growth at Amsterdam Island), the mean growth rate at Gough Island (approximately 0.030 kg/day) was lower than the growth rate represented by the bottom 5% of the body mass distribution at Marion Island. Notwithstanding substantial interannual variability, we found support for a negative trend in weaning mass at both populations, suggesting a rise in limiting factors that is hypothesized to relate to concurrent local population size increases. Weaning mass tended to be higher when sea surface temperatures were warmer (with a stronger positive effect at Gough Island) and during positive phases of the Southern Oscillation Index (La Niña events), with a stronger positive effect in males. Given the low weaning mass of Gough Island fur seal pups, continued population growth here seems unlikely. While density-dependent regulation appears to have increased in strength at Marion Island, terminating rapid population growth, current weaning weights remain above the physiological limits of growth in subantarctic fur seals.
Article
Full-text available
The strong La Niña of 2010–2011 provided an opportunity to investigate the ecological impacts of El Niño-Southern Oscillation on coastal plankton communities using the nine national reference stations around Australia. Based on remote sensing and across the entire Australian region 2011 (La Niña) was only modestly different from 2010 (El Niño) with the average temperature declining 0.2%, surface chlorophyll a up 3% and modelled primary production down 14%. Other changes included a poleward shift in Prochlorococcus and Synechococcus. Along the east coast, there was a reduction in salinity, increase in nutrients, Chlorophytes and Prasinophytes (taxa with chlorophyll b, neoxanthin and prasinoxanthin). The southwest region had a rise in the proportion of 19-hexoyloxyfucoxanthin; possibly coccolithophorids in eddies of the Leeuwin Current and along the sub-tropical front. Pennate diatoms increased, Ceratium spp. decreased and Scrippsiella spp. increased in 2011. Zooplankton biomass declined significantly in 2011. There was a reduction in the abundance of Calocalanus pavo and Temora turbinata and increases in Clausocalanus farrani, Oncaea scottodicarloi and Macrosetella gracilis in 2011. The changes in the plankton community during the strong La Niña of 2011 suggest that this climatic oscillation exacerbates the tropicalization of Australia.
Article
Full-text available
During the breeding season, seabirds adopt a central place foraging strategy and are restricted in their foraging range by the fasting ability of their partner/chick and the cost of commuting between the prey resources and the nest. Because of the spatial and temporal variability of marine ecosystems, individuals must adapt their behaviour to increase foraging success within these constraints. The at-sea movements, foraging behaviour and effort of the Australasian gannet (Morus serrator) was determined over three sequential breeding seasons of apparent differing prey abundance to investigate how the species adapts to inter-annual fluctuations in food availability. GPS and tri-axial accelerometer data loggers were used to compare the degree of annual variation within two stages of breeding (incubation and chick rearing) at a small gannet colony situated between two larger, nearby colonies. Interestingly, neither males nor females increased the total distance travelled or duration of foraging trip in any breeding stage (P>0.05 in all cases) despite apparent low prey availability. However, consistently within each breeding stage, mean vectorial dynamic body acceleration (an index of energy expenditure) was greater in years of poorer breeding success (increased by a factor of three to eight), suggesting birds were working harder within their range. Additionally, both males and females increased the proportion of a foraging trip spent foraging in a poorer year across both breeding stages. Individuals from this colony may be limited in their ability to extend their range in years of low prey availability due to competition from conspecifics in nearby colonies and, consequently, increase foraging effort within this restricted foraging area.
Article
An analysis is presented of hydrographic and nutrient data collected over three years for the Kangaroo Island upwelling region, Lincoln Shelf, South Australia, to determine the signature of upwelled water, depth of upwelling and the source water mass being brought onto the shelf. Strong upwelling seasons were recorded during the 2007–2008 and 2009–2010 summers, while the summer of 2008–2009 had only one weak upwelling event. Strong upwelling events during February and March 2008 and February and March 2010 recorded temperatures and salinities as low as 10.4 °C and 34.85, and NOx and phosphate concentrations as high as 13.35 and 0.94 μmol/L, respectively, at 105 m on the shelf. Upwelled water properties matched slope water properties between 240 and 370 m, indicating water can be upwelled over depths of 200 m or more. Upwelling from these depths sources South Australian Basin Central Water of Southern Ocean origin, which is transported west along the slope by the Flinders Current System. New results for nutrients show average values of NOx and phosphate during months of strong upwelling to be 6.1 times and 4.6 times greater, respectively, than during winter months, and that upwelled water can have nutrient concentrations up to 90 times higher than those in summer surface waters. Strong relationships between temperature and nutrients on the slope can help estimate nutrient concentrations supplied to the shelf during upwelling events. Upwelled water was also low in silicate, a signature of Southern Ocean water masses, which has implications for phytoplankton community structure and diatom abundance on the shelf.
Article
We used a suite of physical, chemical and biological datasets to assess the influence of upwelling/downwelling on enrichment and primary productivity in shelf waters of the eastern Great Australian Bight at seasonal and event scales. Results showed that the length of an upwelling season did not dictate its intensity or productivity, and that long seasons were not necessarily the most intense or productive. At the event scale, temperature and salinity were found to be better indicators of enrichment of shelf waters than wind stress, with temperatures < 15 °C and salinities < 35.6 psu associated with elevated concentrations of NOx (> 2 µm) and bursts of primary productivity (up to ∼ 700 mg C m⁻² d⁻¹). A key finding of this study was the importance of differentiating between upwelling events and enrichment events. The former occurred in the early upwelling season (November-December) and were demonstrated by periods of positive wind stress. The latter only occurred in the late upwelling season (January – April), and saw water with temperatures < 15 °C and salinities < 35.6 psu drawn onto the shelf and into the euphotic zone where it was available for primary producers. We used this information to develop a conceptual model which describes five different meteorological/oceanographic scenarios that occur in the eastern GAB, and their potential influence on enrichment and primary productivity, and hypothesise that total ecosystem productivity depends on the combination of these scenarios that occurs in the region in a given season/year. It is our contention that the early upwelling season represents a preconditioning period that plays a critical role in characterising late season enrichment events, and drives overall seasonal productivity.
Article
We estimated mixed layer gross and net community production on a total of 20 crossings in the Australian sector of the Southern Ocean during the summer half-years (October to March) of 2007–2010. These estimates were calculated from measurements of O2/Ar ratios and triple isotope compositions of O2 in~250 seawater samples collected underway. For comparison purposes, we also measured the seasonal drawdown of mixed layer NO3- and SiO2 concentrations during 2006–2007 and 2007–2008. Across all samples, average values of gross and net O2 production (measured by O2/Ar and O2 isotopes), were about 86±90 and 18±17 mmol O2 m−2 day−1, respectively. Gross production was highest at the Subtropical Front (up to ~230 mmol O2 m−2 day−1), and decreased southward (to ~10 near the southern boundary of the Antarctic Circumpolar Current). In contrast, net community production showed little meridional variation. Net and gross O2 production increased throughout the spring-to-fall period, although most SiO2 drawdown occurred in December. Consistent with satellite chlorophyll estimates, we saw no evidence for an intense spring bloom (e.g. as has been observed in the North Atlantic). Volumetric net and gross O2 production in the mixed layer, normalized to chlorophyll, increased (with considerable scatter) with average irradiance in the mixed layer. These relationships provide a basis for estimating production from Argo float data and properties observed by satellite.