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Tropical Warm Water Reef Fish Extending Range to Temperate Regions

In their newfound homes, tropical fish are overgrazing temperate macro algae.

By John B. Virata | July 17, 2014

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Algae is the bane of my reef tanks, but did you know that warming of the world’s oceans due to climate change is creating warm water currents that take tropical herbivorous reef fish to temperate regions where they are eating temperate seaweeds and macro algae? 


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Scientists have published a paper last month that details the havoc the warm water fish have wrought upon temperate regions in the journal Royal Society B. 

    "The tropicalization of temperate marine areas is a new phenomenon of global significance that has arisen because of climate change,” says study lead author, Dr. Adriana Vergés, from the University of New South Wales.


Masked Spinefoot (Siganus puellus). Photo by Leonard Low/Wikipedia

 "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.”

According to the paper, "The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts” herbivorous fish have been found in areas that are typically cooler than their native waters, and have been feasting on abundant seaweeds and algaes of those areas. 

This migration is caused by what the scientists call poleward flowing boundary currents that create warm areas in places that were previously cooler in ocean temperature. These warm waters enable tropical warm water herbivorous reef fish to flourish due to the abundance of temperate macro algae. The scientists say that this phenomenon is occurring off the coast of Japan as well as in the Mediterranean and other temperate regions throughout the world’s oceans. 

AsianScientist reports that the Eastern Australian Current has caused waters southeast of Australia to warm at two to here times the global average, and because of this, tropical reef fish are now a common sight in temperate Sydney Harbor during warm months. Conversely in Japan, more than 40 percent of the country’s kelp and algal beds have disappeared in the last 20 years, with two tropical herbivorous fish, rabbitfish and parrotfish to be the main grazers of the Japanese nori. AsianScientist says that though the two species have been found in Japan for a long time, the grazing rates of these species has increased due to the increase in ocean temperatures. These changes have also been attributed to the collapse of the abalone fishery in Japan. Abalone are dependent on marine algae to survive.  


John B. Virata has been keeping fish since he was 10 years old.  He currently keeps an 80 gallon cichlid tank, a 20 gallon freshwater community tank and a 29 gallon BioCube with a Percula clown, a huge blue green chromis, and a firefish all in his kitchen, and a 55 gallon FOWLR tank with a pair of Ocellaris clowns, two blue green chromis, a six line wrasse, a peppermint shrimp, assorted algae and a few aiptasia anemones in his living room. Follow him on Twitter @johnvirata  

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