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Reef fish are extra placid round islands infested with invasive rats



Round rat-infested tropical islands within the Indian Ocean, jewel damselfish change their behaviour as a result of the algae they eat is much less nutritious


5 January 2023

Jewel damselfish round rat-infested islands defend territory much less aggressively

Dr Rachel Gunn/Lancaster College

Invasive rat populations on tropical islands have lengthy been recognized to pose a severe risk to seabirds, because of their voracious urge for food for eggs and chicks. Now we’re studying that they alter the behaviour of fish across the islands too.

Within the Chagos Islands within the Indian Ocean, invasive black rats arrived with Western settlers within the 1700s and may now be discovered on roughly 34 of the 55 islands of the archipelago. On infested islands, populations of seabirds corresponding to boobies, frigatebirds, noddies and shearwaters have been decimated.

Fewer birds imply much less chook droppings. This in flip means a fall in nitrogen and phosphorus within the waters across the islands, which assist the expansion of algae round coral reefs.

Earlier analysis has revealed that round rat-infested islands within the Chagos archipelago, the algae are much less nutrient-dense. Now, Rachel Gunn, then at Lancaster College, UK, and her colleagues have proven that this variation in nutrient flows immediately impacts the behaviour of reef fish.

Jewel damselfish (Plectroglyphidodon lacrymatus) are herbivorous fish that aggressively guard patches of turf algae that develop on coral reefs and “farm” them by hunting down the algae they don’t eat.

Gunn and her colleagues positioned Go-Professional cameras underwater in 60 completely different areas across the Chagos archipelago, recording and analysing footage of the damselfish defending their territories to guage their ranges of aggression. A digicam arrange above the water was used to map the dimensions of damselfish territories.

Round rat-infested islands, the fish farmed bigger patches as a result of the algae have been much less nutritious, and so they have been additionally much less aggressive, says Gunn.

“Aggression and territory defence is a really high-energy behaviour, so it requires a high level of nutrients in order for that behaviour to be carried out,” says Gunn. It doesn’t make sense for the fish to aggressively defend a bigger territory with decrease worth. “It just isn’t worth investing that extra energy in being aggressive,” she says.

Jewel damselfish have been the best species to review, given their abundance within the water and daring behaviours. However the lack of vitamins may be affecting the behaviour of different species, says Gunn.

It’s but another excuse to press forward with the eradication of invasive rats on tropical islands, says Gunn. Eradicating rats would deliver again seabirds, restoring nutrient flows into the reefs and giving the resident fish an opportunity to revert to their naturally aggressive behaviours.

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