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Marine

Estuaries within south eastern Australia are experiencing sea surface temperatures increasing at a rate of approximately four times the global average. This has potentially significant consequences for marine and estuarine species. Temperate locations and cool water species are the most likely to be negatively impacted by increasing water temperature. Increased temperatures may exceed the optimal temperature range of certain species, particularly those with limited thermal ranges.

The warming of the oceans has already resulted in southward range extensions of seaweed, phytoplankton, zooplankton and pelagic fish. The macroalgae of Australia’s south coast have retreated 10–50 km south per decade on both sides of the continent. Macroalgae support much of the diversity of marine life and changes to its distribution have devastating impacts on a huge range of species and marine communities.

Increasing water temperatures also impact on marine mammals and birds. The ranges of species are likely to move south. Breeding may also be affected for example, little penguins are expected to have increased breeding success in the short term. Although as temperatures continue to rise, success will decline and colonies will be at increasing risk of death due to extreme heat effects and fire.

A summary of predicted physicochemical changes in western Victoria’s marine environment is presented in the table below: 

 

Summary of predicted physicochemical changes in Victoria’s marine environment

 

The most important current driver of change in marine systems for south eastern Australia is the southern extension of the East Australian Current and the associated warming of the ocean. These changes have resulted in range extension of many marine species. In some cases these provide new opportunities, such as the potential for a snapper fishery to develop in Tasmania. However, they also have potential negative consequences. One pressing challenge is the range extension of the sea urchin Centrostephanous rodgersii which has resulted in substantial degradation of kelp beds in some areas and is currently a threat to the rock lobster fishery of Tasmania’s east coast.

An additional threat associated directly with increasing atmospheric carbon dioxide is ocean acidification. When carbon dioxide dissolves in the ocean, carbonic acid is formed leading to higher acidity. This increased acidity raises the metabolic energy required for marine organisms to lay down a calcium carbonate shell, resulting in thinner, lighter shells. This in turn can lead to substantial effects on the food chain and marine ecological systems. The effects of acidification are most pronounced in colder waters and a large scientific effort is underway to establish the rate of change in southern ocean systems and potential impacts of these changes. Reduced calcification has been observed in Southern Ocean zooplankton suggesting that ocean acidification is already impacting the biological system. Ocean acidification will negatively impact coastal and marine species, particularly temperate invertebrates such as sea urchins, many of which are ‘keystone species’. The outcome of such impacts may result in ecosystem-wide consequences.

The impacts of climate change on marine systems are severe and potentially catastrophic if tipping points are reached in terms of ocean warming and acidification. Adaptation will not be possible for the majority of species. However, if warming can be mitigated, adaptation can be supported through the protection and enhancement of land-based systems that influence the marine environment.

There is increasing evidence that land-based management decisions (e.g. dam construction or removal, deforestation, green infrastructure to limit runoff, shoreline hardening, and urban development) will be significant and important interactions affecting adaptation in marine and coastal systems. What happens on the land influences the ocean; reducing the impacts of land management will help to build the adaptive capacity of marine systems.