Marine life ecology today and how climate change could affect it in the future.
Climate change effects on marine ecosystems report
Co-author of the Impacts of climate change on Australian marine life report, Dr Alistair Hobday, says climate change is likely to have important consequences for spawning patterns and productivity cycles in the ocean.
4 April 2007 | Updated 14 October 2011
Most international studies centred on change in the ocean take temperature increases into account. However, there is a suite of other variables that require consideration including:
changes to ocean chemistry (ie. acidification) impeding the ability of organisms to build shells
ocean circulation influencing population dynamics
change in cloud cover and sea ice affecting light supply to the ocean surface.
'The conspicuous roadblock to predicting the effects of climate change on marine life in the face of such uncertainties in Australia is the current lack of a strategic program that includes a combination of analysing or assessing and modelling potential impacts,' Dr Hobday says.
'Without this, we cannot progress far beyond the conclusion that climate impacts are occurring, and that some of those impacts might prove severe.'
Co-author Dr Tom Okey, says that although Australia has an extensive coastline and one of the largest fishing zones in the world, its coastal and mid-depth waters are considered to be low in productivity and fisheries are reliant on processes such as upwelling to provide nutrients.
Using computer simulations of possible change up to 2030, the scientists considered changes in temperature, ocean currents, winds, nutrient supply, rainfall and ocean chemistry.
Changes to ocean circulation in the western Pacific Ocean and Tasman Sea and an upward trend in water temperatures have led to environmental modification in south east Australia as the East Australian Current pushes further south carrying sub-tropical species into temperate waters.
'This is a region where climate models indicate rapid warming and a 50-year observation program has shown a water temperature increase of two degrees Celsius,' Dr Okey says.
'As a result, sub-tropical introductions to the Tasmanian east coast are already altering the habitat of a whole range of species, and introducing new species such as the sea urchin.'
He says the report generated three core findings:
- While ocean temperature has a significant influence on observed changes in Australia’s marine flora and fauna, it is the combined effects of multiple climate and oceanographic factors that will shape Australia’s marine life in the future.
- The ecological effects of non-climate related stress factors such as fisheries, coastal run-off and pollution which may reduce ecosystem resilience to climate change.
- Programs to measure change and modelling of climate change impacts will be crucial components of a strategic national assessment of climate change impacts so that management strategies can be developed.
Future climate questions
The Report identified six key questions that required addressing by future modelling and ocean and coastal monitoring programs:
- How will the distribution and abundance of marine species and communities alter with climate change? Changes have already been observed in some regions, for example in the south-east.
- Which marine species will be the best sentinels of climate change impacts? They could include corals and kelp, or species with key ecological roles such as phytoplankton.
- Within large marine regions such as the south-east, south west or northwest, where are the hotspots of change? Preliminary analyses suggest the Tasman Sea in the south-east and the east coast are examples of change hot-spots.
- How will productivity alter with climate change?
- How would reduction in non-climate related stress indicators increase ecosystem resilience to climate change?
- To what extent will marine climate change impacts affect socially and economically important uses of Australia’s marine ecosystems?
What constitutes an impact?
Scientists have reviewed the likely severity of impacts of Australian marine life, based on the expected responses of 13 groups of species to predicted changes in temperature, salinity, wind, chemistry, circulation and sea level.
Because of the lack of observations about changes in species, distribution and populations, and a view that responses in Australian waters will be similar to international influences, a mix of information is used to determine likely impacts based on four categories:
- Effects on distribution and stocks: species are generally expected to move southward with warming; species such as pteropods reliant on building shells are likely to decline in abundance.
- Effects on the timing of life cycle events: the timing of blooms and migrations are expected to occur earlier with warming.
- Effects on physiology and behaviour: environmental change will directly affect rates of metabolism, reproduction, development, photosynthesis and respiration.
- Effects on communities and productivity: this is dependent on the place of the species in relation to ecosystem functioning, for example the place of a species in the food chain.
Examples of species impacts
Longer term changes affecting just two key factors, ocean temperatures and nutrients will have a significant influence on marine biodiversity.
“Changes to ocean circulation in the western Pacific Ocean and Tasman Sea and an upward trend in water temperatures have led to environmental modification in south east Australia as the East Australian Current pushes further south carrying sub-tropical species into temperate waters. ”
In 2003, scientists projected that by 2070 the expected increases in Australian ocean temperatures would have a 35 per cent overall economic impact on Australian fisheries and that temperate Australian fisheries would be more vulnerable than tropical ones.
They projected that the economic impacts on Tasmanian, Victorian and West Australian fisheries would be 64 per cent, 40 per cent and 38 per cent respectively by 2070 – assuming that fishing effort is well-managed.
Coastal resource managers would face parallel climate change challenges in terms of maintaining watershed quality and the health and resilience of nearshore marine ecosystems. A 1996 New Caledonia study indicated that warmer and wetter climate, with increased rainfall and coastal run off, negatively affected the size of fish stocks. This could occur by increasing turbidity in the water, introducing nutrients from the land, decreasing light penetration to the seafloor and changing habitat and food resources.
Three of the 13 groups of marine life and habitats that were examined and the potential impacts on them are detailed here:
- Phytoplankton are microscopic plants inhabiting the illuminated surface layers of the ocean, comprise tens of thousands of different species. All underpin marine primary production and are the direct food source of small fish, prawns, and shoreline filter feeders, such as mussels and oysters. Phytoplankton also support the krill that the massive baleen whales feed upon and the squid and fish that large fish such as tunas depend on.
- Phytoplankton also play a central role in the global carbon, oxygen and nutrient cycles and produce half the oxygen on the planet.
- Changes in ocean temperature and circulation will push species southward on the east coast. Abundance is already changing and climate change is likely to alter the environmental conditions that affect the occurrence of toxic or harmful algal blooms that can accumulate in food webs.
- Warming may also cause changes in phytoplankton community composition and, for example, the productive south-eastern temperate phytoplankton region may shrink considerably in area.
- Tropical coral reefs are composed of corals containing microscopic algae that help provide food for the coral polyps that form the calcium carbonate skeleton of coral reefs. In Australia, coral reefs provide critical habitat for a diversity of fauna and flora, including over 400 species of corals, 4000 species of molluscs and 1500 species of fish. They are a significant platform for Australia’s tourism industry, generating around $5 billion a year. They also play a critical role in coastal protection and as a storehouse of genetic material
- Water quality is a primary short-term threat to coral reefs but now they face growing risks from climate change.
- Warming over the last 30 years has led to repeated coral bleaching events, with the reefs in NW Australia proving to be the most sensitive. As greenhouse emissions rise, ocean acidification may shift the balance from coral building to erosion thereby compromising the future of coral reefs.
- Changes in tropical storm activity, sea level rise and coastal run off – together with rising water temperatures and acidification – can reduce coral viability.
- Of the seven species of marine turtles, six are found in Australian waters and all are considered globally endangered. They nest on tropical and subtropical sandy beaches around Australia and all undertake extensive migrations except for the flatback turtle, which can be considered endemic.
- Climate change is likely to be a major threat to marine turtles given their life history characteristics, such as slow growth rate, and the potential influence of temperature on gender of embryos. Small increases in temperature may strongly bias the sex ratio of hatchlings towards females. Climate-induced changes in food resources will also have an affect.
- Climate-related increases in wave energy and storm events may erode nesting beaches and reduce egg survival rates. Alteration of peak timing of egg laying has already been observed in Florida for loggerhead turtles.
Downloadable image Marine life ecology today.
For more information Impacts of Climate Change on Australian Marine Life [external link].