New James Cook University research shows the seagrass meadows of Trinity Inlet in Cairns Harbour have recovered after severe cyclones and flooding nearly wiped them out – but with a new mix of fish species.
Seagrasses are flowering plants that thrive in marine environments and form extensive meadows along the tropical Queensland coast.
"The seagrass meadows in Cairns are an extremely important ecosystem. They provide a fish nursery habitat for young fish and prawns, providing protection from predation and places to forage," JCU PhD candidate Darcy Philpott, who led the research, said.
A series of severe weather events between 2009 and 2011 – including major flooding and Cyclone Yasi – caused increased turbidity and prolonged poor water quality, contributing to widespread seagrass loss.
"Following those severe weather events, there was a 98% decline in intertidal seagrass meadow area, accompanied by dramatic declines in both fish abundance (84%) and species richness (73%)," Ms Philpott said.
Ms Philpott explained that even after the almost complete collapse in seagrass coverage following the flooding, both seagrass biomass and seagrass area had now bounced back to values seen prior to the flooding.
"We also saw a return in fish abundance and species richness – both the number of fish being caught and the number of different species present," she said.
However, when researchers examined the composition of the fish assemblage, they found that the recovered meadows supported a different mix of fish species.
"It wasn't simply a return to the same fish community that was there before," Ms Philpott said.
"Fish abundance and species richness have recovered strongly, but the community itself has reorganised and is recovering along a different trajectory."
The research, published in the journal Estuarine, Coastal and Shelf Science, used a 34-year dataset spanning 1991 - 2025, combining long-term fish surveys with records of seagrass condition. Surveys captured fish communities before the disturbance, following the major seagrass decline and during its subsequent recovery.
"You need long-term datasets like this to really understand how fish communities respond to major habitat disturbance and subsequent recovery," Dr Robert Coles – who was one of the study's co-authors and part of the original team that began surveying Cairns' seagrass meadows fish communities in the 1990s – said.
"Survey records spanning more than three decades are incredibly rare. By using consistent methods across that period, we've been able to directly compare the fish communities before the disturbance, after the seagrass loss and as the meadows recovered.
"Across those surveys we collected more than 11,000 individual animals representing 190 species, giving us a unique picture of how the fish community has changed over time."
Fish such as the Silver Javelin (Pomadasys argenteus) became more prevalent in the recovered meadows, while Pikey Bream (Acanthopagrus berda) were more abundant before the flooding.
"Our research shows that recovery is complicated … the habitat may recover and fish may return, but that doesn't necessarily mean you get exactly the same ecological community coming back," Ms Philpott said.
The research was supported through a scholarship from North Queensland Bulk Ports Corporation, with the findings helping to improve understanding of seagrass-associated fish communities in Queensland port environments.
