̽��ֱ�� of Cambridge - reef

Buying time: can science save the Great Barrier Reef?

sc604 — Wed, 16 Oct 2024 04:18:14 +0000

If we don’t stop global temperatures – both on land and at sea – from rising, the Great Barrier Reef could become a coral graveyard. A team of scientists has decided to do something about it.

Colour-morphing reef fish is a 'wolf in sheep's clothing'

fpjl2 — Thu, 19 Mar 2015 15:45:31 +0000

A new study has shown that the dottyback, a small predatory reef fish, can change the colour of its body to imitate a variety of other reef fish species, allowing the dottyback to sneak up undetected and eat their young.

̽��ֱ��dottyback also uses its colour-changing abilities to hide from larger predators by colour-matching to the background of its habitat - disappearing into the scenery.

̽��ֱ��research, published today in the journal Current Biology, reveals a sophisticated new example of 'mimicry': disguising as a different species to gain evolutionary advantage.

While using mimicry to hunt or hide from other species is commonplace in nature - from cuckoos to butterflies - scientists point out that if the same physical deception is encountered too frequently, species on the receiving end become more vigilant and develop tactics to mitigate the mimics.

̽��ֱ��dottyback, however, is able to colour-morph depending on the particular colour of the surrounding species it is currently hunting: different types of damselfish being a popular target.

Scientists say that this flexibility of physical mimicry makes it much harder for the dottyback's prey to develop detection strategies and avoid getting eaten.

"By changing colour to imitate local damselfish communities, dottybacks are able to overcome the predator avoidance behaviour in the juvenile fish they hunt," said Dr William Feeney, co-author of the study from the ̽��ֱ�� of Cambridge's Department of Zoology.

" ̽��ֱ��dottyback behaviour is comparable to the 'wolf in sheep's clothing' scenario from Aesop's Fables, where distinguishing the predator from the harmless 'flock' becomes increasingly difficult when they look alike - allowing the dottyback to creep up on unsuspecting juvenile damselfish," Feeney said.

Dottybacks are generally solitary and highly territorial predators of around eight centimetres in length, commonly found in Indo-Pacific coral reefs.

While dottybacks can vary their colouration from pink to grey, the researchers focused on two colour 'morphs' - yellow and brown - that both occur on the reefs surrounding Lizard Island, off the coast of north-east Australia. This is because the area has populations of both yellow and brown damselfish, and habitat consisting of live coral and dead coral 'rubble'.

̽��ֱ��scientists built their own simulated reef outcrops comprising both live coral and rubble, and stocked them with either yellow or brown damselfish. When released into reefs with damselfish of the opposite colour, scientists found the dottybacks would change from yellow to brown or vice versa over the course of approximately two weeks.

Anatomical study of dottyback skin cells revealed that while the level of 'chromatophores' - pigment-containing cells that reflect light - remain constant, the ratio of yellow pigment cells to black pigment cells shifts to move the dottyback from yellow to brown or back again.

̽��ֱ��team conducted lab experiments with adult and juvenile damselfish to test whether this colour change affects dottyback hunting success. They found that once the dottyback matched the colour of the damselfish, they were up to three times more successful at capturing juvenile damselfish.

̽��ֱ��scientists also found that the dottyback use their colour-morphing powers to blend into the coral of their habitats to hide from their own predators, such as the coral trout - a predator they share with damselfish, who have also adapted to match the colour of their environment.

̽��ֱ��scientists measured the strike rates of coral trout when exposed to images of different colours of dottyback against different habitats. ̽��ֱ��coral trout had trouble picking out the fish when the colour matched the habitat.

"While the dottybacks change colour to aggressively mimic damselfish, they may also gain a secondary benefit: a reduced risk of being eaten themselves. Damselfish have evolved to blend into their environment, so, by imitating the damselfish, they also colour-match the habitat - making it harder for coral trout to see them," said Feeney.

"This is the first time that an animal has been found to be able to morph between different guises in order to deceive different species, making the dottyback a pretty crafty little fish"

Inset image: dottyback eyeing up damselfish prey, credit Christopher E Mirbach

̽��ֱ��dottyback changes its colour to match surrounding damselfish species, enabling it to counter the defences of its damselfish prey by disguising itself as a harmless part of their community, then swoop in to hunt their young.

This is the first time that an animal has been found to be able to morph between different guises in order to deceive different species, making the dottyback a pretty crafty little fish

William Feeney

Justin Marshall

Brown Vs Yellow Dottyback

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Researchers appeal for new regulations to save coral reefs from live fish trade

bjb42 — Fri, 04 Aug 2006 00:00:00 +0000

Twenty of the world's leading marine scientists, including a team from the Department of Zoology, ̽��ֱ�� of Cambridge, have called for action by governments to halt the unsustainable plunder of the world's ocean resources.

For decades tropical coral reefs have battled for survival against a complex array of threats including pollution, coral bleaching triggered by rising sea temperatures and over-fishing.

In particular, the health of the reefs is being compromised by the live reef fish trade, a serious threat that has prompted scientists to call for tighter regulations on the exploitation of reef resources which are particularly important to developing tropical nations.

̽��ֱ��scientists say there is now sufficient evidence to conclude that reforming markets, which have dramatically expanded as a result of global trade liberalization, is an important strategy for controlling roving bandits.

̽��ֱ��live fish trade is an increasing pressure on coral reef resources, both in terms of magnitude and geographical spread. ̽��ֱ��combination of destructive harvesting methods and over-harvesting of large, predatory fish reef fish have devastating effects.

Being able to choose a huge fish to eat from a tank is a big pull in luxury seafood restaurants. Fish such as the Napoleon wrasse, a giant reef fish that commonly reaches 2 m in length and lives for more than 30 years, are top of the menu and especially vulnerable.

But once on the plate, the absence of an important part of the food chain means the coral reef hierarchy is in turmoil. ̽��ֱ��coral-eating crown-of-thorns starfish is likely to thrive in these situations, particularly when the corals are already stressed by a multitude of other impacts including global warming.

According to the 2004 Status of the Coral Reefs of the World report, coral reefs are in serious decline due largely to human activities; an estimated 20% of the world's reefs have been effectively destroyed with no immediate prospects of recovery, 24% are under imminent risk of collapse and 26% are under longer term threat of collapse.

̽��ֱ��scientists argue in their letters that multilevel action, from local to international, is needed to establish institutions that are able to learn from experiences with roving bandits, develop decision-making skills in an environment of uncertainty and complexity, and respond quickly to shifts in demand from global markets.

"Due to the high international demand for live fish, these roving bandits deplete coral reef stocks before local institutions have time to implement laws to regulate the poaching."

" ̽��ֱ��bandits take advantage of porous world trade policy and ineffective fisheries management to sell their plunder," says Dr Helen Scales, from the Department of Zoology, ̽��ֱ�� of Cambridge.

By analysing the mass of live fish imported into Hong Kong from various source nations across the Indo-Pacific region, Dr. Andrea Manica and his team from the Department of Zoology, ̽��ֱ�� of Cambridge have tracked the fisheries trade radiating out from Hong Kong, the hub for international trade in live reef fish.

They have also demonstrated the accelerating pace of the boom and bust pattern of exploitation, a characteristic dynamic of unregulated high-value commodity markets.

̽��ֱ��trade has spread from Hong Kong at an accelerating pace, starting at 100 km per year from its coast in the 1970s, to reach over 400 km per year in the 1990s.

However, the scientists say the strongest argument for balancing international trade and local needs is the social inequity that arises from the export of the dwindling coral reef resources of developing tropical nations.

"Once those resources are destroyed and forgotten, it is the local people who bear the costs of reduced options for future development," they warn.

̽��ֱ��letters will be published in Science on Friday the 4th August.

Researchers are calling for tighter controls on the live reef fish trade, a growing threat to coral reefs, in letters to the international journal Science.

̽��ֱ��bandits take advantage of porous world trade policy and ineffective fisheries management to sell their plunder.

Dr Helen Scales

USFWS Pacific from Flickr

Coral Reef at Palmyra Atoll National Wildlife Refuge

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

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