Variability in the phases of these climate phenomena change rainfall patterns, sea surface temperatures, surface winds and oceanic currents. These changes can influence the degree of vertical mixing through the water column and the relative location of cyclone events. Simultaneous fluctuations in the phases of these climatic phenomena, or particularly strong phases of each, can result in extreme changes in ocean processes and substantive impacts on the marine environment.

Sea surface temperatures are continuing to increase, with surface ocean warming during the 21st century occurring at approximately 7 times the rate observed during the 20th century. The frequency of extreme sea surface temperature events has increased. Rising summer ocean temperatures are increasing the extent of coral bleaching.

Climate change is also resulting in ocean acidification and changes to ocean currents. In response to changes in the marine environment associated with climate change, there have been significant shifts in the ranges of various invertebrates and fish.

Since 2011, there has been an increase in most forms of vessel activity in marine waters. As a result, risks associated with grounding of vessels, anchor scouring, accidents at sea in ecologically sensitive areas, vessel strike of marine animals, and introduction of foreign marine species to the Australian marine environment through the exchange of ballast water and biofouling are also likely to have risen, particularly those that are not currently managed across all forms of vessels. Improvements in the management of commercial vessels are resulting in mitigation and minimisation of some of the associated risks, but the outcomes of other risks remain unclear.

High, but variable, concentrations of land-sourced and ocean-sourced marine debris are found in all marine environments, with significant quantities of plastics reported in the digestive tracts of several species of marine vertebrates. Continued growth in plastics production and use is expected, despite initiatives banning the use of some plastic products and improved waste management processes. Thus, marine debris will continue to be a ubiquitous problem affecting marine animals and their environment.

Sources of high point-source anthropogenic noise are spatially variable, but generally regarded as either stable or decreasing. Increasing use of the marine environment is shifting anthropogenic contributions to marine soundscapes towards ongoing low-level noise, with uncertain long-term chronic impacts on the Australian marine environment.

Of those habitats, communities and species groups for which timeseries are available, many are in good condition or improving following historical impacts. Key indicators of marine health, such as primary productivity, trophic processes and algal blooms, are also mostly considered to be in good condition. Several habitats, communities and species groups are highly spatially and temporally variable, and determination of trends in these is difficult, particularly where timeseries are short.

Since 2011, 2 sea snakes, 2 seabirds, 2 sharks, 1 sawfish and 1 fish have been listed, and 2 fish species have been reclassified as critically endangered. Giant kelp forests across south-eastern Australia were the first marine community to be listed as a threatened ecological community. Australian populations of humpback whales have increased to the point that their current listing could now be reconsidered.

Efforts continue to be poorly coordinated across jurisdictions, although improvements have occurred in some sectors, such as fisheries and shipping. Coordination between sectors sharing common resources or using common regions remains lacking, resulting in inadequate accounting for all pressures and, in particular, cumulative pressures on the marine environment. As a result, many management plans do not currently support the development of resilience within marine ecosystems.

The use of formal risk assessments for managing marine resource use is patchy, resulting in variability in the prioritisation of limited resources and actions, associated processes in implementation, and addressing of cumulative impacts.

Although the overall status of the marine environment is good, some individual species and species groups remain in poor condition.

Despite improving management in several sectors, trends in many marine environmental resources and, in particular, many listed species are uncertain, and some populations continue to decrease in size. The lack of coordinated monitoring and management across sectors reduces Australia’s capacity to respond to new and increasing pressures and cumulative impacts.