Reporting on the current state and recent trends of the biological and ecological components of Australia’s marine environment is highly variable across Australia’s marine estate, and is often inadequate for robust assessment. There are few coordinated, sustained monitoring programs at the national level for the marine environment, and most monitoring is restricted to fisheries assessments and short-term programs in localised regions. Reporting also varies in terms of spatial and temporal coverage, parameters measured, methods used and key indicators. This results in varying certainty in the state and trends reported for the state of the environment (SoE) assessment.
Generally, habitats and communities in the Temperate East and the South-east marine regions have been subject to higher historical impacts, such as bottom-trawling impacts on shelf and slope communities, than those in other regions. The condition of habitats and communities in the Great Barrier Reef to the end of 2015 is considered to range from poor and deteriorating (corals) to good and stable (macroalgae, offshore banks and shoals). Large canopy-forming seaweeds are still prevalent in many locations around Australia, but increased water temperatures and range extension by the sea urchin Centrostephanus rodgersii in south-eastern Australia have led to the loss and overgrazing of kelp beds in temperate rocky reefs, resulting in a poor and deteriorating state and trend for this habitat. Giant kelp forests of south-eastern Australia were the first marine community to be listed as a threatened ecological community under the Environment Protection and Biodiversity Conservation Act 1999 in 2012.
Most species groups assessed are regarded to be in good condition overall, although information is lacking to assess the condition or trend of many species and species groups because they are not regularly monitored, if at all. Trends are stable or improving for most fish species, except inner shelf reef species, which are highly spatially variable—some are in good condition and stable, whereas others are in poor condition and deteriorating. Shelf demersal and benthopelagic fish species, while in poor condition, are considered as generally improving, with a few exceptions. Some species have improved from past declines (e.g. long-nosed fur seals, southern Great Barrier Reef green turtles, humpback whales, the eastern stock of orange roughy), and others are currently stable (e.g. mesopelagic and epipelagic fish species, shy albatross). Some species have declined because of cumulative impacts associated with high mortality from bycatch within fisheries, impacts associated with coastal nesting/breeding sites and climate change (e.g. flesh-footed shearwater, Australian sea lion, north Queensland hawksbill turtle, some demersal shark species).
Overall, the state of components of the marine environment identified in SoE 2011 as providing biophysical and ecological indicators of marine health shows the marine environment to be in good condition in 2016, although several indicators are highly spatially and temporally variable, and determining trends is difficult. Overall, on a national scale, water column turbidity in open-water environments has decreased; this is largely the result of improved wastewater treatment, reduced nutrient inputs, and improved management of agricultural practices and associated run-off. Observed reductions in primary and secondary productivity are considered to be associated with reduced nutrient supply because of ocean warming. Changes to ocean currents have affected connectivity within marine ecosystems, as observed through shifts in species distributions, especially in south-eastern Australia. There has been trophic (food chain) restructuring of some ecosystems as a result of commercial and recreational fishing, pollution, introduction of foreign species, and habitat modification. Some of these impacts are irreversible, but the effects are generally unknown. Introduced species, blooms and infestations of jellyfish and algae, diseases, and animal kills appear to be stable, whereas trends in crown-of-thorns starfish outbreaks are unclear.