The 2025-26 Australian summer continued the pattern of significant marine heatwave activity along the East Australian Current. Sea surface temperatures across substantial stretches of the New South Wales and southern Queensland coast tracked well above the long-term averages, with multiple discrete heatwave events that exceeded category 3 (severe) thresholds at the offshore monitoring sites.

The ecological implications continue to be the substantive concern. The 2025-26 summer is not an outlier — it sits in a multi-year pattern of warmer ocean conditions that the long-term observational record makes clear is the new normal rather than an exceptional period.

The temperature picture

The East Australian Current has been one of the most-studied marine heatwave systems in the world, with continuous observational records from coastal monitoring stations and offshore moorings that allow careful tracking of conditions year-on-year. The 2025-26 summer ocean temperatures from these stations show several discrete heatwave events through December, January, and February, with regional peaks that exceeded historical baselines by 2 to 4 degrees Celsius at the surface.

The depth-stratified data tells a more nuanced story. The warming penetrates meaningfully below the surface in some periods and remains a near-surface phenomenon in others. The thermocline behaviour during the 2025-26 events was variable, which has implications for the depth-stratified ecological effects.

The fisheries implications

The commercial fisheries operating along the EAC reported variable catch outcomes through the 2025-26 season. Some species that have been shifting their range southward in response to long-term warming continued the pattern; specific reports from fishing operators in northern NSW and southern Queensland note ongoing changes in species composition that have become familiar over the last decade.

The longer-term implications for fisheries management in the EAC system are an active research and policy area. The shifting species distributions affect quota frameworks, fishing community economics, and ecological understanding of food web dynamics. The CSIRO Oceans and Atmosphere, the relevant state fisheries departments, and several university marine biology groups are tracking the changes.

The reef ecosystem implications

The Great Barrier Reef sits in the warmer northern end of the EAC system and experiences related but distinct warming patterns. The 2025-26 summer saw additional bleaching events on parts of the GBR, continuing the pattern of recurring bleaching pressure that has affected reef ecosystems since the late 1990s. The current cumulative impact of repeated bleaching events on reef community composition is significant, and the recovery dynamics between events are an active research area.

The southern reef ecosystems — including the Solitary Islands and the smaller subtropical reef communities further south — have also experienced warming-related impacts. These ecosystems were historically buffered by cooler conditions and the changing temperature regime has produced visible community shifts in 2025-26.

The coastal habitat picture

Kelp forest ecosystems along the southern NSW and Tasmanian coast continue to face pressure from the warming EAC system. The long-term decline of the giant kelp ecosystems in eastern Tasmania has been one of the more visible and well-documented Australian marine ecosystem changes. The 2025-26 conditions added to that pressure.

The seagrass and estuarine ecosystems along the coast have experienced more localised heatwave impacts, often interacting with rainfall and runoff patterns from individual catchments to produce specific local effects.

The research and monitoring infrastructure

The Australian marine science infrastructure for tracking and understanding these changes remains strong. The IMOS network of moorings, the satellite-based sea surface temperature observations, the research vessel campaigns, and the long-running monitoring programs at various reef and coastal sites produce a continuous data record.

The research effort to understand the ecological responses, to track species range shifts, to understand the human community and economic implications, and to inform management responses is substantial but stretched. The funding picture for marine research in Australia in 2026 is mixed — some specific programs are well-resourced, others are operating on tighter budgets than the work warrants.

The management response

The management response to the changing marine climate continues to evolve. The Marine Protected Area network plays a role in providing reference sites and supporting some ecosystem resilience. The fisheries management frameworks are adapting to shifting species distributions, though the policy and regulatory adjustment is generally slower than the ecological change. Coastal management at the state and local level is starting to incorporate climate change considerations more systematically.

The longer arc

The 2025-26 summer fits within a longer arc of change in the Australian marine environment that has been clearly documented since the late 20th century. The pace of change is fast in ecological terms. The management and research responses are adapting. The communities — fishing, tourism, coastal — that depend on these ecosystems are facing a future that will not look like the past.

The work of understanding, monitoring, and responding to these changes continues. The ocean conservation community remains focused on the practical work of protecting ecosystem function under changing conditions, recognising that the climate driver is global but the local conservation work is what determines what survives the transition.