Fish populations could be significantly damaged by the dredging of seabed sediment, with new research finding that larvae development is hindered by murky water.
The study, conducted at James Cook University, raises fresh concerns over dredging work to expand several ports located near the Great Barrier Reef.
Researchers studied the larval development of clownfish in tanks at the university. The fish larvae were subjected to varying degrees of sediment – from 15 milligrams per litre up to 45 milligrams per litre – to see how the silt affected their progress.
The research discovered that larvae raised in even only slightly increased sediment took far longer to develop into juvenile fish. The development time increased from around 11 days to up to 22 days – doubling the time the fish took to reach juvenile status.
“I was surprised to see how sensitive fish were, I expected them to be more hardy,” Dr Amelia Wenger, who led the study, told Guardian Australia. “Even at low levels, the response to sediment is pretty negative.
“At the higher levels of sediment, we started to see changes in their growth rates, too. Fish use smell and taste and we know sediment can affect their ability to find habitat and forage. The sediment is disrupting their ability to pick up chemical and visual stimuli.”
This prolonged development is risky for fish because they are in open water during their larval phase, exposing themselves to the threat of being eaten by predators. Once they become juveniles, they head to coral reefs, which provide shelter and safety.
“By doubling the development time, you would most likely see greater mortality of these fish,” Wenger said. “These guys are the newest generation of fish, you need that constant input of new generations so you’d probably see widespread detrimental effects.”
Professor Geoff Jones, co-author of the study, said: “We don’t know if all fish are going to be as sensitive to sediment as clownfish, but if you don’t get new recruits into a population then you won’t have any new ones to replace the adults when they die off.
“This early development is a crucial stage for fish recruitment and population viability.”
Sediment is deposited into the sea via rivers, with flooding events increasing the load that is carried into the sea. Human activity can also contribute towards this, with the digging up of the seabed, known as dredging, to allow ships to access ports creating plumes of sediment in the water.
Last year, the federal government approved the dredging of 5m tonnes of sediment to expand the Abbot Point port, near Bowen. While the sediment will now be dumped on land, rather than within the Great Barrier Reef marine park as was originally planned, activists and some scientists have warned the very action of dredging will create extra silt in the water.
Further dredging projects are also taking place at Townsville and Cairns, with the latter development aimed at providing access to cruise ships to allow patrons to frequent Cairns’ gambling attractions.
In July, research was released that showed that coral disease can be doubled if dredging activity occurs near reefs.
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