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A photo of a Stoplight parrotfish in the Caribbean.

This spotlight parrot fish (Sparisoma viride) was spotted grazing on coral near the island of Bonaire in the Caribbean.

Photograph by age fotostock Spain, S.L. via Alamy

Doug Struck

for National Geographic

Published July 25, 2014

Marine ecologist Adriana Vergés emerged from a scuba dive in Tosa Bay off the coast of southern Japan last week and was amazed at what she'd seen: A once lush kelp forest had been stripped bare and replaced by coral.

The bay is hundreds of miles north of the tropics, but now "it feels like a tropical place," said Vergés, a lecturer at New South Wales University in Australia.

The undersea world is on the move. Climate change is propelling fish and other ocean life into what used to be cooler waters, and researchers are scrambling to understand what effect that is having on their new neighborhoods. They are finding that the repercussions of the migration of tropical fish, in particular, are often devastating. Invading tropical species are stripping kelp forests in Japan, Australia, and the eastern Mediterranean and chowing down on sea grass in the northern Gulf of Mexico and Atlantic seaboard.

"The faunas are mixing, and nobody can see what the outcome will be," said Ken Heck, a marine scientist at the University of South Alabama in Mobile. But the consequences of that mixing are already trickling up the food chain.

Voracious Eaters

Sea grass beds and kelp forests are often known as the sea's nurseries because they have nooks and crannies filled with nutrients that feed and protect fish larvae and juveniles. The kelp and sea grass, however, are being replaced with other warm-water species such as coral that follow the arrival of tropical fish, said Vergés.

Vergés and her colleagues recently documented how tropical fish, which are normally a beneficial companion to coral beds, can devastate a kelp forest. Their study appeared July 9 in the Proceedings of the Royal Society B.

Many tropical fish species are "browsers" or "scrapers" that clean coral of algae and plants that could otherwise choke the reefs. But when the herbivorous fish move toward more temperate waters, they often find a bountiful harvest of kelp or sea grass to feed their voracious appetites.

Once a tropical fish species arrives in a new area, it can quickly mow down vegetation and algae and destroy the lush habitat that protects other species. For instance, "parrotfish are capable of eating a lot of sea grass per individual," said marine scientist Joel Fodrie of the University of North Carolina at Chapel Hill.

Tropical rabbitfish have been swimming in the Mediterranean Sea since 1869 when they slipped in through the newly opened Suez Canal from the Red Sea. But the warming of the Mediterranean has allowed their numbers to explode in recent decades, and the fish have deforested hundreds of miles of kelp there, Vergés said.

The shrimp, crab, and other species that often spend the first year of their lives hiding from predators in the protection of the grasses disappear when their cover is gone, leaving a void for the creatures that depend on them. The loss of vegetation can completely change the community of species that live there, Vergés said. "If you dive in a kelp forest, you find a very different fish community than if you dive in a coral-dominated area."

The removal of a kelp forest or sea grass bed can have devastating effects not only on native plants and animals, but also on commercial fisheries. In southern Japan, for example, the arrival of rabbitfish and parrot fish destroyed as much as 40 percent of the kelp forests there. These lush areas were once thick with abalone and spiny lobster, which supported a famed fishery. But when the kelp disappeared, so did the abalone and spiny lobster, and the fishery plummeted.

A photo of a Blue Headed Wrasse on coral.
Bluehead wrasse, native to the Caribbean and Gulf of Mexico, dart among coral.
Photograph by Michael Patrick O'Neill, Alamy

Fish on the Move

In the northern Gulf of Mexico, Heck started seeing unusual species several years ago as he pulled specimens from the water near the Dauphin Island Sea Lab south of Mobile.

"It wasn't just one or two. There were many. It got me thinking, this is something different," Heck said.

Working in the Gulf, Heck and Fodrie netted 128,000 fish in 2006 and 2007 and compared the numbers of tropical fish in their trawl nets with records from the 1970s. They found a 22-fold increase in emerald parrot fish—a coral cleaner common in the Caribbean and the waters off Latin America—and new arrivals of snapper, grouper, butterfly fish, and surgeonfish, among others, they reported in Global Change Biology in 2009. Green sea turtles and manatees have also found northern Gulf waters increasingly comfortable, Heck said.

Heck and Fodrie are updating their research and said they expect to find large changes in the food webs of the Gulf as coral moves into areas overgrazed by tropical fish, and as the crabs and shellfish that depend on the sea grass dwindle.

"People are seeing these fish all over the world" in unexpected places, Heck said. "I don't think there's any question that the movement of many tropical species is related to the warming of coastal waters."

Warming Waters

Climate change has warmed the ocean surface by an average of a little more than one degree Celsius in the past century, but the warming has not been uniform. Currents have created "hot spots" in temperate oceans, where temperatures have risen two to three times more than the global average, according to Vergés. In those hot spots, tropical species have been able to move in after the minimum temperature in winter has reached a tolerable level.

Fodrie said the research in the Gulf found the minimum temperature on the coolest days in the winter had inched up by as much as 3 degrees Celsius, an open invitation for fish that like warmer water. "That's huge," Fodrie said. "When you do the geographic comparison, it's like moving from the northern Gulf down to Miami." That has let species more common off Miami, for example—such as snappers, groupers, and parrot fish-become established in the northern Gulf of Mexico and up the Atlantic seaboard.

Florida's famous stone crabs have been found in the Carolinas, and the Chesapeake's blue crabs have been seen as far north as New York, Fodrie said. He has seen colorful tropical species, such as angelfish and damselfish, off the Carolinas. Plants, too, are on the march: Black mangroves are growing miles farther north along the Florida coast than they were a decade or so ago, Fodrie said.

Devastation doesn't always follow when tropical species move poleward. Some fish and other plants and animals in more temperate waters are moving, as well—when they can.

"In the Gulf of Mexico, they can't do that," Heck said. "The North American continent is in the way. These native species really don't have anywhere to go."

Species on land and in the oceans have always moved around, but now climate change is increasing the speed of this movement, Vergés said. "There's no doubt. The magnitude of the change is so large that it's very obvious."

Regions are losing and gaining species, but the overall result is a decline in biodiversity. "It's a fascinating phenomenon that is happening right now," Vergés said. "It's alarming, as well. But as a scientist, I'm focusing on the exciting."

Follow Doug Struck on Twitter.

33 comments
Cj Mendoza
Cj Mendoza

Why worry about global warming? Everyone knows about it and yet nothing is done. Everyone just enjoy your family and friends and live life to the fullest and stop crying about it! What is done is done:-) 

Tanmay Sharma
Tanmay Sharma

Now, after knowing all that, its time to act to protect those biodiversity.

Aaron Heller
Aaron Heller

Chicken little sky is falling story. I suppose those worried about climate change have explanation for ice lingering on Great Lakes into July of 2014 and greatest extant of antarctic ice ever recordeded and mild summer in Midwest and northeast this year. Chicken little sky is falling false prophets looking for excuse to raise taxes. In maryland we now pay a rain tax, that's insane!

pamela letstalkaboutcorsica
pamela letstalkaboutcorsica

I'd focus on the alarming - and of course there will be food changes, one thing leads to another and so forth .. it's not reassuring at all

Garrett Van Cleef
Garrett Van Cleef

it's a good thing this global warming thing is a lie, otherwise I might be  very concerned about it!

Ralph Pemberton
Ralph Pemberton

Sounds almost like the Mexican/American border crisis.

Elie Morisse
Elie Morisse

Why stick "Climate change" into the title when the warming of the concerned waters was caused by currents? Then scientific journalists (not thinking about NatGeo specifically) will write contemptuous articles about people dubious about climate change, while you're clearly not great examples of basic logic and sticking to the facts yourselves.

An interesting news ruined by slapping nonsense and uncalled controversy into it, too bad.

walter gillis
walter gillis

Eric,  if you ever spent any time in the ocean you would be aware of the changes in water temperature, even in short distances, up to 5 degrees.  There is no change in ocean temperature that can be documented.  As for polar caps,  when ice melts it takes up less volume.  so if the arctic  would start to melt,  sea levels would lower.

Eric Paul
Eric Paul

What's worse is the overall water quality of the world's oceans are deteriorating.  I've seen the destruction of coral reefs with my own eyes.  The amount of chemicals and organic compounds we're pouring into our natural bodies of water are astounding and atrocious.  Overpopulation will ultimately stall and negate ANY progress we make technologically or culturally with the way we treat our environment/economy.  Until we solve the problem of too many people on the planet, we'll continue to see environmental destruction and "humanitarian crisis" around the globe!  And politicians will NEVER admit to this being a problem...it's the Gorilla in the room they'd rather completely ignore and deny out of fear it will completely destroy their political careers and giant checks they receive from corporations.  "Sorry kids, no more trips around the world this year because daddy thought with his heart/head and not with his wallet" - says no politican ever!

walter gillis
walter gillis

Whoever  wrote this should be institutionalized.

Paul Lassiter
Paul Lassiter

It would be logical to assume that as the water temperature changes, the kelp and such will migrate. We know fish and animals migrate and being so, it is likely that plant life will as well. 


The planet has gone through this at least once before and came out fine, this planet is alive and knows what it is doing. We should be more concerned with how we can evolve and adapt to the changes as they occur. This is assuming that Mankind can survive the changes that will occur.


It is arrogant of mankind to even assume that we can have any effect on the planet. In reality all we can effect is our own place on the planet. Chances are very good that the planet will be alive and well, long after our extinction.    

Eric Paul
Eric Paul

@Aaron Heller - Are you serious?  And here we thought that every square inch of real estate looked like Mars already.  Thank god for Aaron Heller - the genius who debunked a scientific fact, all by his little self!  Next he's going to take on the theory of gravity while using his Spongebob Squarepants birthday balloons filled with helium as supporting evidence.

John Hartshorn
John Hartshorn

@Aaron Heller You really don't get it, do you? These sorts of changes are leading to impoverished ecosystems that are then more vulnerable to every change that comes later. We are at the top of a web of life which is showing severe signs of strain. Stop obsessing about the climate wars and pay attention. When all you can worry about are your taxes going up you are showing a deep impoverishment of the imagination.

Alec Sevins
Alec Sevins

@Garrett Van Cleef Yes, and you can also breathe easy knowing man-made smog is a lie. Trees cause most smog, per good ol' Reagan. AGW and smog of course have no connection, other than both being hoaxes.

Chris Crawford
Chris Crawford

@Elie Morisse On what evidence do you base your claim that the warming is caused by currents? We have lots of data showing that the oceans are warming due to AGW. Do you have some other data?

Alec Sevins
Alec Sevins

@walter gillis Come on, don't pull stuff out of a hat and pass it off as truth. Ocean temperatures most definitely have been rising, and are well documented. Your "5 degrees" is a random generalization, even though some areas will obviously get warmer than others. You really think opinions from random swimmers vs. global thermometers determine ocean temperatures?


Your claim about Arctic ice shows a lack of education. Floating ice displaces an equal amount of water, so the effect is null when it melts (it doesn't "lower" the ocean level). But land-based core ice on Greenland and Antarctica will raise sea levels because it has been out of ocean circulation for many centuries.

Chris Crawford
Chris Crawford

@walter gillis Um, Mr. Gills, it's a basic principle of physics that, when ice floating in water melts, it has no effect on the level of the water. It has to do with the displacement of water. 

Moreover, there's a big difference between local, temporary changes in water temperature and long-term changes. 

Alec Sevins
Alec Sevins

@Eric Paul Eric Paul, eh? Are you sure you're not Paul Ehrlich, who was wrong in '68 with certain dire predictions, therefore will always be wrong about overpopulation? After all, the Earth is infinitely large, as any good growthist economist will tell you. We could easily fit 20 billion people on Earth and feed them with algae and Soylent Green. Sure, wilderness and other species will be wiped out in the process, but it's all about the people aka God's children.


(sarcasm)

Samuele Rosa
Samuele Rosa

@Paul Lassiter Exactly. Adapting would be the most mature thing we could ever do. Personally I'm very excited about this; our planet's flora and fauna have gone through countless of mutations/extinctions before we even existed.

Zen Galacticore
Zen Galacticore

@Paul Lassiter We already know that plant -life migrates with changes in climatic temperature (and other factors).


It has been extensively documented, i.e., land plants migrating either to higher altitudes, or, more long-term, higher latitudes, due to a warming world. So of course it stands to reason that marine plants also migrate due to changing conditions.


And to say that it is arrogant that we can assume that we can have, "any effect on the planet" is an incredibly ignorant thing to say. It is incredibly selfish to say that we can effect only, "our own place on the planet."


If we, in our collective actions cause the global ecosystem to unravel, if we ourselves are in fact the cause of the current Sixth Extinction, then we effect the "place" of every living thing in that ecosystem.


One can argue that extinctions, even mass extinctions, "are only 'natural'". Well, nuclear fusion is, "only natural" too, it happens everyday as the Sun shines and all over the known Universe. So, why don't we and the Russians go ahead and detonate our 20,000 plus hydrogen bombs? After all, it's only natural.


And the planet has suffered through more mass extinctions than just, "once before". I'm assuming you're referring to the Cretaceous/Paleogene extinction that wiped out the dinosaurs and 90% of the other living things on this planet 65 Million years ago. Well guess what? It took millions of years for the biosphere to fully recover from that event.


There was the Permian/Triassic  Extinction 250 Million years ago, and in addition to the Cretaceous, there are three other known mass extinctions. You comment on the Nat' Geo board, do you ever actually read the magazine?

Forrest Evans
Forrest Evans

@Chris Crawford @Elie Morisse We never hear about what model you used to determine the data.  What was left out to make it convenient to spout out another wave of climate change doom and gloom.  How many versions of your "evidence" do you have?  Does it take into account the "natural" shifting of the poles or do you just plant them where you want them to be and when your data is finally supports run with that model.  

Elie Morisse
Elie Morisse

@Chris Crawford No more than what's written above us:

« Climate change has warmed the ocean surface by an average of a little more than one degree Celsius in the past century, but the warming has not been uniform. Currents have created "hot spots" in temperate oceans, where temperatures have risen two to three times more than the global average, according to Vergés. In those hot spots, tropical species have been able to move in after the minimum temperature in winter has reached a tolerable level. »

Currents cause temperature to rise in some areas and drop in others, regardless of how the global average performs.

Sorry for overreacting though, the abstract of the original article does say "current-induced climate change" but doesn't make any connection to global warming, so the journalist shouldn't either but may have misinterpreted.

Eric Paul
Eric Paul

@Alec Sevins  Paul Ehrlich - LOL.  Although I completely agree with his "population bomb" theory, he was overzealous with his predictions...but it was probably intentional to try and fuel the debate.

Jake Williams
Jake Williams

@Zen Galacticore Why call someone "ignorant and selfish"? 

"And to say that it is arrogant that we can assume that we can have, "any effect on the planet" is an incredibly ignorant thing to say. It is incredibly selfish to say that we can effect only, "our own place on the planet.""

Alec Sevins
Alec Sevins

@Forrest Evans @Chris Crawford @Elie Morisse What species do you think causes smog all over the world where said species exists in dense populations?


I find it fascinating that there aren't more "smog deniers." It's probably because smog is visible and can't be wished away. If CO2 was colored, more of you would probably get a clue. Look up a YT video called "CO2-ink demonstration" for some insight into what a "trace gas" really means.

Chris Crawford
Chris Crawford

@Forrest Evans @Chris Crawford @Elie Morisse There are many models used for climate change. The most popular is called CMIP5, but it is used with a great many variable input parameters, generating a great many possible scenarios. 

You're welcome to your belief that scientists are engaged in a massive conspiracy to deceive the world, and if so, you might want to seek similarly inclined minds among the evolution deniers, the flat earthers, the 9/11 conspiracy theorists, the UFO fans, and of course the "moon landings were filmed in a studio" people. I'm sure that you'll be very much at home among these people.

Alec Sevins
Alec Sevins

@Elie Morisse @Chris Crawford If you're going to cherry-pick, don't post quotes that debunk your intent. The non-uniformity is caused by currents. Climate change causes the general warming. Read that first sentence!


Actually, your post is a real-time example of how the denial machine chooses its words and ignores context. Thank you on that count.

Chris Crawford
Chris Crawford

@Elie Morisse @Chris Crawford There are some aspects of your reply that bother me. Yes, currents can lead to areas of higher-than-average temperatures and areas of lower-than-average temperatures. But the average is rising. We have documented many examples of poleward migration of terrestrial species; we would certainly expect the oceans to be no different in this regard. Hence, while currents can create localized hot and cool spots, the general trend of ocean warming continues everywhere.

What really confuses me is your last sentence, in which you seem to differentiate between global warming and climate change. While climate change is the preferred term, in actual usage the two are synonymous. Do I misunderstand your meaning?

Jake Williams
Jake Williams

@Zen Galacticore Perhaps what you meant to say was..., I disagree? Here is why I disagree. But, I do respect your opinion, friend.

Yeah, right.

Eric Paul
Eric Paul

@Jake Williams @Zen Galacticore - He may have been a bit abrasive, but his point is solid.  People comment on here with such certainty and arrogance about a subject that they completely misunderstand.   Sometimes this happens because people don't care to "know better", they only care to spew opinions that fit their personal beliefs/agendas, often religious in origin.  Which could be the case with the original post...especially considering anyone with above a 5th grade education should know better.

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