Could warming waters expand coral reefs and tropical fish populations along the WA coast?
QUESTION
Hi there, recreational fisher here and avid life long SCUBA diver. I wanted to ask about the hotter than normal waters off the WA coast this year. My (limited) understanding of the coral reefs around Rottnest is that they are (almost but not quite) the southern most coral reefs in the world (and by that, I presume are also further away from the equator than Northern hemisphere coral reefs too) and that the reason for that was b/c of the oddity that is the warm Leeuwin current running down the WA coast. I understand that climate change and hotter waters off the coast of QLD are wreaking havoc on the GBR. But I assume that is not the case this far South? If this warming of WA waters is a sign of things to come, does this mean we could expect to have more plentiful coral reefs off the southern WA coast and that they may start forming further south? Would this be a generally good thing for increasing the number and types of fish life off our coast? Would placing FAD type concrete structures closer to shore encourage the growth of coral reefs, create new dive sites and encourage more fish life? Even without warming of the seas, would placing concrete FAD type structures say 250-500m off shore see an increase in fish populations and more coral reefs forming? Thanks in advance for your reply. Cheers.
ANSWER 1
Written response:
Thanks for your question – I am an experienced fisheries scientist, not a coral expert but will answer you as best that I can.
Yes 2025 was warmest SST year on record in WA (previously was 2024). Marine heatwave conditions in February-March in the northwest caused significant bleaching to many of our key coral reefs including Ningaloo (and Scott Reef). And yes, coral at Rottnest and adjacent sites such as in Cockburn Sound are our southern most reefs. Your comparison between impact of warmer waters on west and east coast is correct – GBR lies at lower latitude than Rottnest and therefore is more at risk to marine heatwave conditions being pushed south by Eastern Australian Current (equivalent of our Leeuwin Current).
There is potential for coral reef building further south in WA under increasing ocean temperatures into the future however other climate change factors e.g. rising sea levels and acidification will play a role. We have been seeing a topicalisation of our fish communities off WA coast for sometime, with tropical species being observed further south – see Redmap (www.redmap.org) and Busselton Underwater Observatory. Placing low relief structures at appropriate depths to encourage coral settlement (from Rottnest or Abrolhos where Rottnest coral first came from) and encourage settlement of coral reef fishes have potential. While there has been substantial investment in coral reef restoration on the GBR, much less has been done in the west.
Currently research coordinated by WA Marine Research Institution (WAMSI) and involving DBAC, AIMS and CSIRO is working on growing live coral to restore damaged reefs at Ningaloo. If you want more details suggest that you contact Dr Luke Twomey at WAMSI (wamsi.org.au).
Answered by:
Dr Gary Jackson
ANSWER 2
Written response:
Thanks for your question. You are right, the Leeuwin (and other poleward flowing currents, like the Kuroshio current in Japan) enables corals and coral reefs to be found further south/north than in other places. In WA, our research shows that climate change is indeed supporting the expansion of corals (e.g. the staghorn corals you may have seen in Rottnest appeared in the late 1990s), but that often comes at the cost of “cooler-water” or temperate species such as the forests of golden kelp. Australian kelp forests are amongst the most biodiverse in the world and support Australia’s most valuable fisheries (rock lobster and abalone), so there is a lot to lose as well. While some coral species may be able to migrate further south, temperate species may “fall of the continent” as they run out of suitable habitat to migrate to. This is concerning as around 70% of Australian temperate reef species are found nowhere else on Earth and may thus disappear forever, compared to just 3% of tropical species. Importantly, corals (and associated communities) that have expanded south may not be necessarily safe from the impacts of climate change, as they have also showed evidence of bleaching from warm and even cool temperatures.
Answered by:
