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article imageTropical fish invasion destroying world's kelp forests

By Karen Graham     Jul 12, 2014 in Environment
A recently published study shows the migration of tropical fish as a result of warming ocean waters is creating a threat in the temperate waters they are invading. This migration has created a serious threat to kelp forests in these regions.
Most people think of kelp as being nothing more than sea grass. But kelp serves a greater function than just being a source of food and a protected habitat for marine animals. Kelp, and kelp forests are some of the most productive ecosystems on earth, and the impact of migrating tropical fish into the temperate zones where kelp flourishes was the reason for the study.
Kelp forest on high profile reef at Partridge Point  Cape Peninsula.
Photo taken: October 2010.
Kelp forest on high profile reef at Partridge Point, Cape Peninsula. Photo taken: October 2010.
Peter Southwood
Dr Adriana Verges, of the University of New South Wales, Australia, and lead author of the study published in the journal Proceedings of the Royal Society B said, "The tropicalisation of temperate marine areas is a new phenomenon of global significance that has arisen because of climate change." The study included researchers from Australia, the U.S., Spain, Singapore, the U.K. and Japan.
"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." Verges pointed out that some tropical species such as the unicorn-fish, parrot-fish, and rabbit-fish have already migrated into many temperate zones.
Some species of rabbitfish  or spinefoots  can  grow up to 21-inches in length. They have an unusual...
Some species of rabbitfish, or spinefoots can grow up to 21-inches in length. They have an unusual defense mechanism. The pelvic fins are formed into two spines with well-equipped venon sacs. Very painful, but generally not deadly to humans.
Uploaded by BS Thurner Hof
The study found that as the oceans have warmed, "hot spots" have subsequently developed in areas of the ocean where currents that carry warmer tropical waters to the poles are strengthening. With the Eastern Australia Current, for example, the researchers noted that waters southeast of the current are warming two to three times faster than the rate worldwide.
And it is not just Australia seeing this shift in temperatures. Japan, the east coast of the US, northern Brazil and southeastern Africa have also seen a change in water temperatures influenced by coastal currents that transport warm tropical waters. In Sidney Harbor, it is now common to see tropical fish during the summer months.
"In tropical regions, 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.
Case study: Southern Japan
In southern Japan, since the 1990s, more than 40 percent of the kelp and algae beds have been depleted, a phenomenon called isoyake in Japan. Rabbit-fish and parrot-fish are seen as the main culprits in this region. While these two particular fish have been seen in this area of the world for a considerable time, their numbers have increased dramatically as water temperatures have risen. Corals are now the main species dominating the region, and the changes in the ecosystem have resulted in the collapse of abalone fisheries.
While parrotfish are considered herbivores  they will also eat a wide variety of other organisms  in...
While parrotfish are considered herbivores, they will also eat a wide variety of other organisms, including coral. They generally reach 12-20 inches in length. Pictured here is a Turquoise parrotfish.
Nhobgood
Case study: Eastern Mediterranean Region
Tropical fish moved into this region after the opening of the Suez Canal. In the past few decades, there has been a rapid increase in the number of rabbit-fish. The resultant destruction of kilometers of kelp forests and algae beds has also led to a 40 percent decrease in the number of other marine inhabitants. As the rabbit-fish move westward, they will put other shallow marine ecosystems at risk.
Case study: The United States
Parrot-fish have increased over 20-fold in the Gulf of Mexico. These tropical fish are huge eaters, consuming sea grass at five times the rate of native marine herbivores. The number of plant-eating manatees and green turtles have also increased.
The report addresses an escalating environmental threat to one of the ocean's most valuable ecosystems. Not only are the kelp forests, algae beds and pastures of sea grasses being threatened, but the destruction of these valuable marine resources will have far-reaching effects, not only on shallow water marine and coastal marine habitats, but coastal erosion and the economies of the many people who depend on the sea for their livelihoods.
More about Tropical Fish, temperate waters, kelp forests, Mediterranean, Southern Japanese
 
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