Over 45% of Australia’s coastal marine ecosystems have been damaged by extreme climate
Stating that the average recovery time for major species groups is 10 to 15 years, the researchers warn that habitat recovery is unlikely if the number of severe climate events increases
Severe climate events such as heatwaves and floods have damaged 45% of the marine ecosystems along Australia’s coastline. According to the researchers, the length of the coastline impacted by extreme climate events in the last decade is more than 8000 km, which is almost four times the length of coastline affected by the Gulf of Mexico oil spill, which had created a massive outcry. This includes impacts are irreversible, says the study published in the Frontiers in Marine Science.
“Australia has been impacted by an unprecedented number of extreme climate events (ECEs) since 2011, impacting more than 45% of the coastline. The Deepwater Horizon accident in the Gulf of Mexico caused a global outcry far larger than for any of the events documented here, yet it affected at most 2100 km of coast, with apparently short-lived impacts so far. In contrast, the length of coastline affected by the ECEs in the last decade described here is around 8000 km, nearly four times greater in extent and includes impacts that appear likely to be irreversible at least on decadal scales and possibly longer,” say the researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) - Australia's national science agency - in their findings.
What is the impact of extreme climate events?
Extreme climate events - such as heatwaves, droughts, and floods have been attributed to climate change and could have a significant ecosystem and evolutionary impacts because they provide little opportunity for organisms to acclimate or adapt.
“Extreme climate events, statistically rare or unusual climatic periods that alter ecosystem structure and/or function well outside normal variability are receiving increasing attention as drivers of change in ecological and evolutionary communities. ECEs are also associated with climate change, becoming more frequent and more intense. In coastal marine systems, heatwaves and floods could have a greater ecosystem and evolutionary impacts than the more
gradual effects of climate change,” says the team.
According to the researchers, half of the Australian coastal waters have experienced their warmest ever monthly temperatures since 2008, which reflects the increased extent, frequency, and magnitude of marine heatwaves. The duration and magnitude of these events are also extending, with warmer sea temperatures persisting for longer than previously recorded. In addition to extreme warming events, say the researchers, there is increasing consensus that climate change is also leading to extremes in other aspects of climate and weather, such as more severe storms.
Four major marine ecosystems have been adversely affected
The research team examined information on a series of such extreme climate events in Australia from 2011 to 2017 and the impact on marine habitat-forming organisms – corals, kelps, seagrasses, and mangroves. The CSIRO Oceans and Atmosphere research team studied events like the 2011 Western Australian marine heatwave, major cyclones like Cyclone Yasi, and back-to-back coral bleaching events in 2016 and 2017, to create a complete and bigger picture of the accumulated impact of extreme climate events.
They found that marine heatwaves, heavy rainfall from tropical storms, cyclones and droughts have all played a role in fundamentally changing Australia’s coral, kelp, mangrove and seagrass communities. For example, says the research team, coral reefs along thousands of kilometers of Australia’s west and east coasts were affected by four separate coral bleaching events between 2011 and 2017. Mortality of corals in Western Australia was as high as 90% in some places, shows analysis. In the north of the Great Barrier Reef (GBR), the average coral cover declined by around 50%. Coral habitats are home to over 83,000 animal and plant species and are susceptible to diminishing water quality, overfishing, construction, warming oceans and ocean acidification.
“Our research, for example, in developing new methods for restoring coral reefs, may be one way to help maintain ecosystems. We have developed industrial-scale methods to harvest coral spawn, grow it out in at-sea aquaculture systems and redistribute across damaged reefs. This is one example of a flexible and adaptable strategy that can be used to help reefs recover in the short term. But in the long-term, adaptation efforts will need to be coupled with efforts to reduce atmospheric greenhouse gases that drive climate change,” the team recommends.
Further, analysis of damage to mangrove forests - which support fish and fisheries in northern Australia as well as protect low-lying coastlines - shows that during the summer of 2015-16, over 1000 km of mangrove forest died around the Gulf of Carpentaria, which is home to one of Australia’s most valuable fisheries. “This has left the otherwise pristine ecosystem severely damaged,” says the study. Even the Kelp forests, which are critical marine habitats and sources of food, have suffered massive damage. “During the 2011 Western Australian marine heatwave several species of kelp became locally extinct depriving important fishery species of habitat, they are unlikely to recover in the foreseeable future,” the findings state.
The study shows that after the 2011 Queensland floods and seagrass loss, there was a marked rise in the number of turtle and dugongs found stranded, which has been linked to the decline in food availability.
“Coral bleaching occurred across much of northern Australia due to marine heatwaves affecting different regions in 2011, 2013, 2016, and 2017, while seagrass was impacted by anomalously high rainfall events in 2011 on both east and west tropical coasts. A marine heatwave off western Australia (WA) during the 2011 La Niña extended into temperate and subtropical regions, causing widespread mortality of kelp forests and seagrass communities at their northern distribution limits. Mangrove forests experienced high mortality during the 2016 El Niño across coastal areas of northern and north-WA due to severe water stress driven by drought and anomalously low mean sea levels. This series of ECEs reflects a variety of different events – marine heatwaves, intense rainfall from tropical storms, and drought,” says the study.
It adds, “Their repeated occurrence and wide extent are consistent with projections of increased frequency and intensity of ECEs and have broad implications elsewhere because similar trends are predicted globally.”
The researchers found that ongoing human-induced climate change, such as gradual increases of sea surface temperature, are worsened by extreme climate events, which leave most marine organisms and habitats unable to acclimatize or adapt in rapidly changing habitats.
“Our modeling indicates that the average recovery time for major species groups is around 10 to 15 years. If climate shocks happen more often than this, then ecosystems may never fully recover,” says the study.
Extreme events, say the researchers, are an emerging threat to marine ecosystems and will become more severe and extensive in the future. They highlight the urgent need for better seasonal prediction and mitigation strategies. “In developing adaptation strategies, we need to consider that ECEs can trigger fundamental shifts in ecosystems. Therefore, adaptive management strategies that maintain ecosystem resilience continue to be important. Adaptation strategies also need to be flexible and adaptive in response to the information revealed by monitoring and assessment. It is also likely that such strategies must include active restoration approaches,” says the study.