Beautiful but a threat: Tropical fish invasion destroys kelp forests

Jul 08, 2014
An eyestripe surgeonfish, one of the tropical species shifting its distribution towards temperate waters. Credit: Credit: Adriana Verges

The migration of tropical fish as a result of ocean warming poses a serious threat to the temperate areas they invade, because they overgraze on kelp forests and seagrass meadows, a new study concludes.

The harmful impact of is most evident in southern Japanese waters and the eastern Mediterranean, where there have been dramatic declines in kelps.

There is also emerging evidence in Australia and the US that the spread of tropical fish towards the poles is causing damage in the areas they enter.

"The tropicalisation of temperate marine areas is a new phenomenon of global significance that has arisen because of climate change," says study lead author, Dr Adriana Verges, of UNSW Australia.

"Increases in the number of plant-eating tropical fish can profoundly alter ecosystems and lead to barren reefs, affecting the biodiversity of these regions, with significant economic and management impacts."

The study is published in the journal Proceedings of the Royal Society B.

As the oceans have warmed and the climate has changed, hotspots are developing in regions where the currents that transport warm tropical waters towards the poles are strengthening.

Increased flow of the East Australian Current, for example, has meant waters south-east of the continent are warming at two to three times the global average. Tropical fish are now common in Sydney Harbour during the summer months.

Japan, the east coast of the US, northern Brazil and south eastern Africa are also strongly influenced by coastal currents that transport warm tropical waters.

A school of tropical plant-eating fish including various species that are shifting their distribution towards temperate waters. Credit: Adriana Verges

"In , a wide diversity of plant-eating fish perform the vital role of keeping reefs free of large seaweeds, allowing corals to flourish. But when they intrude into temperate waters they pose a significant threat to these habitats. They can directly overgraze algal forests as well as prevent the recovery of algae that have been damaged for other reasons," says Dr Verges.

Tropical fish expanding their ranges into temperate areas include unicornfish, parrotfish, and rabbitfish.

The study authors include researchers from Australia, the US, Spain, Singapore, the UK and Japan.

Case studies:

Southern Japan:

More than 40 per cent of the kelp and algal beds have disappeared since the 1990s, a phenomenon known in Japan as isoyake. Tropical species including rabbitfish and parrotfish appear to be mainly responsible.

Although these fish have been present for a long time, their annual grazing rates have increased dramatically as ocean temperatures in winter have risen. Corals now dominate the ecosystem in many locations. The changes have led to the collapse of the abalone fishery.

Eastern Mediterranean:

Tropical fish moved into the eastern Mediterranean from the Red Sea after the opening of the Suez Canal. In recent decades, rabbitfish numbers have increased, resulting in hundreds of kilometres of deforested areas and a 40 per cent decrease in the variety of marine species.

As the Mediterranean warms the rabbitfish are expanding their range westward, putting other shallow ecosystems at risk.

US:

There has been a more than 20-fold increase in the number of parrotfish in the Gulf of Mexico – a species which consumes seagrass at five times the rate of native grazers. The number of plant-eating green turtles and manatees has also increased.

Australia:

In Western Australia, emerging evidence suggests that increases in the number of tropical fish are preventing the recovery of kelp forest damaged by a heat wave in 2011.

In eastern Australia, kelp has disappeared from numerous reefs in the past 5 years and Dr Verges' research suggests intense grazing by tropical fish on the kelp preceded this.

Explore further: Ancient reefs preserved tropical marine biodiversity

More information: The tropicalisation of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts, rspb.royalsocietypublishing.or… .1098/rspb.2014.0846

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User comments : 7

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GuruShabu
1 / 5 (4) Jul 08, 2014
Pure BS!
Tropical fish and the "doomed" corals have been there for millions of years and have experienced temperature variations greater than what the article suggests.
Vietvet
3.7 / 5 (3) Jul 08, 2014
Pure BS!
Tropical fish and the "doomed" corals have been there for millions of years and have experienced temperature variations greater than what the article suggests.


Try reading the article again.
GuruShabu
1 / 5 (4) Jul 08, 2014
Pure BS!
Tropical fish and the "doomed" corals have been there for millions of years and have experienced temperature variations greater than what the article suggests.


Try reading the article again.

I've c tied the "doomed corrals" because years ago this site has publicised a number of papers "predicting" a devastation (as usual) on corals because of AGW.
The cose of my contempt remains the same: AGW or more recently Climate Change are created by certain opportunistic people to get money.
However, there is not a single truth on the claims.
In sum, BS.
Vietvet
3.7 / 5 (3) Jul 09, 2014
Pure BS!
Tropical fish and the "doomed" corals have been there for millions of years and have experienced temperature variations greater than what the article suggests.


Try reading the article again.

I've c tied the "doomed corrals" because years ago this site has publicised a number of papers "predicting" a devastation (as usual) on corals because of AGW.
The cose of my contempt remains the same: AGW or more recently Climate Change are created by certain opportunistic people to get money.
However, there is not a single truth on the claims.
In sum, BS.


The article is about the destruction of kelp forests and sea grasses not corals. That destruction has already happened, is continuing, and will get worse.
Captain Stumpy
4 / 5 (4) Jul 09, 2014
The cose of my contempt remains the same: AGW or more recently Climate Change are created by certain opportunistic people to get money.
However, there is not a single truth on the claims.
In sum, BS.
@gurushamu
well then today is your lucky day, Thermodynamics posted earlier:
http://dialogueso...nge.html

the entry requirements are simple:
be 18 or over
prove, via the scientific method, that man-made global climate change is not occurring;

now is YOUR CHANCE to prove that you are correct, win $30,000 and get fame and bragging rights to rub our nose in it!
all you have to do is prove AGW wrong via the scientific method... simple, according to your posts to date... so you should be able to, right?
better hurry, though...as it says on the page: Entries do not have to be original, they only need to be first
(and antigorical, rygg, ubavontuba as well as others have all been told already)

SO PROVE IT
Dr_toad
Jul 09, 2014
This comment has been removed by a moderator.
Porgie
3 / 5 (2) Jul 13, 2014
San Onofre has been sucking in and grinding up kelp for dozens of years not to mention all the dead sea otters. SO this can't be any more serious.
GuruShabu
1 / 5 (2) Jul 14, 2014
Repeated BS...the planet is going to die, the corals are going to bleach, the kelps desapear and we are all doomed to be suffocated by CO2...
Call a the corrupt Al Gore and Leonardo di Caprio, and all hollywoodies to teach us how to make a horror movie (for sure they all get $$$ for that)

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