Hobart

Seminar Abstract

Friday 18 December 2009, 11.30am (Tas time)
CSIRO Auditorium, Hobart

Anne-Elise Nieblas
QMS PhD Candidate
School of Zoology, University of Tasmania &
CSIRO Marine and Atmospheric Research
Hobart

Impacts of Climate Change on Regional Primary and Fisheries Productivity around Australia

Coastal upwelling regions account for 20% of global marine productivity; but upwelling ecosystems are vulnerable to climate change. This study examines the impacts of climate change on ecosystem productivity of a historically low-wind upwelling system. I investigate relationships between the physical environment, primary and fisheries productivity in an Australian upwelling ecosystem. These results provide insight into the vulnerability of the ecosystem to climate change to help inform an ecosystem approach to management.

This study investigates large-scale trophic control across a diverse suite of Australian marine bioregions. Bottom-up control is revealed, which indicates that changes in primary productivity will cascade throughout foodwebs. Though primary productivity is clearly important to ecosystem health, other oceanographic conditions are necessary for fisheries viability. I present a comparative analysis of key oceanographic characteristics of several productive Australian ecosystems to assess how enrichment, concentration, and retention mechanisms regulate successful fisheries recruitment.

These large-scale physics-to-biology relationships are then assessed at the regional scale for a particular productive ecosystem: the Bonney Upwelling. The Bonney Upwelling in southeastern Australia has classic enrichment, concentration, and retention features, but as it is a wind-driven system, it is vulnerable to climate change. The productivity of wind-driven upwelling systems depends on an “optimal environmental window” in which wind speed is strong enough to promote vertical mixing of nutrients that enhance productivity, but not so strong as to lead to deleterious turbulent mixing or pronounced advection that may reduce productivity. I find the Bonney Upwelling currently operates at low wind velocities (~4 m s^–1), and hence suboptimal productivity. Statistical models are developed that describe between 40%-50% of the phytoplankton biomass variance.

I then develop biophysical statistical models to describe relationships between regional and large-scale environmental drivers, primary productivity and catches of two commercial marine species to test the model methods and predictive skill. I examine two species with differing r- (arrow squid, Nototodarus gouldi) and K-selected (gummy shark, Mustelus antarcticus) life history traits. I find significant physics-to-“fish” relationships for these contrasting species that describe ~77% of arrow squid variance and ~50% of gummy shark variance. Arrow squid are closely related to the regional environment on a seasonal time scale, and gummy shark have closer links to large-scale climate drivers (El Niño-Southern Oscillation) at periods of up to 3 years.

Climate models are used to make projections of potential impacts of climate change on ecosystem productivity for two likely CO₂ emission scenarios (Special Report on Emissions Scenarios A1B, and A2). I find that the magnitude of the wind is not predicted to change; therefore the Bonney Upwelling is projected to remain a low-wind system. However, alongshore wind stress events are predicted to intensify and become more prevalent, especially in the upwelling season. This is due to the southward extension of the seasonal migration of the subtropical ridge. The “business-as-usual” emissions scenario (A2) predicts an extension of the upwelling season by one month, impacting intra-annual upwelling phases. Primary productivity is expected to increase linearly with wind stress, with potential shifts in seasonal peaks. Arrow squid catch rates are expected to increase due to higher upwelling and warming ocean temperature. Due to limitations of climate models, predictions for gummy shark populations were not assessed.

In this thesis, I apply ecological theory at large and regional scales to Australian marine ecosystems. I develop simple methods to describe complex environment-biology interactions. This thesis demonstrates the value of simple statistical models to investigate complex response to future change.

Seminar recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
To schedule a seminar, contact:
Clothilde Langlais, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5399
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 2265
Margaret Hazelwood, Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2971

Last updated 22/12/09