Reef’s Nemo at increased risk of diseases due to suspended sediments

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Credit I. McLeod

A new research into Great Barrier Reef – specifically the effect of suspended sediments on clownfish larvae – has provided greater insight into the dangers suspended sediments and how they damage fish gills and subject fishes to increased rate of diseases.

Carried out by researchers from the ARC Centre of Excellence for Coral Reef Studies at James Cook University, the research confirms the adverse effects of sediment from coastal agriculture and industry development, such as the dredging for ports on fish populations.

Researchers say that fish gills are the first to come in direct contact with the environment and also the first line of defence against infection. This means that they are the organs that should be studied to evaluate the damage associated with sediment.

For the study, the researchers simulated sediment conditions frequently found on inshore reefs on the Great Barrier Reef, but they say the problem isn’t limited to Australian waters.

Coastal oceans affected by suspended sediment tend to overlap critical fish habitats and nurseries. The research highlights the need for the continued protection of these crucial habitats.

[Read: Group says Queensland’s Great Barrier Reef meets ‘in danger’ criteria]

Juvenile reef fish are often exposed to sediment as they swim in open waters before settling on a chosen reef. During this critical developmental stage they need great amounts of oxygen, but damage to their gills makes it hard for them to get it.

“The gills in sediment-exposed larval clownfish fish were congested, exhibiting twice as much mucous of what could be found in clean-water exposed fish,” says study lead author, PhD Student Sybille Hess.

“Sediment-exposed fish also increased the number of protective cells on their gills, presumably safeguarding the delicate tissue from the damage that sediment particles could cause.”

“Larval fish have very high growth rates. They’re swimming a lot, often over long distances. They have a very high metabolic rate and high-energy costs and need their gills to be working as efficiently as possible,” says co-author Dr Jodie Rummer.

[Read: Fishing significantly impacting make-up of fish population of the Great Barrier Reef]

The gills of affected fish were also found to harbor disease-causing bacteria.

“The presence of bacteria linked to fish disease on the gills of sediment-exposed fish suggests that exposure to, and accumulation of, sediment may trigger the development of fish diseases,” says co-author Dr Tracy Ainsworth.

[Read: Researchers propose roadmap to recovery for world’s coral reefs]

“This research underscores the necessity for future coastal developments to consider the adverse effects of sediment on fish and reef ecosystems,” adds Dr Wenger.