Why are there so few fish in the Earth's oceans?

Feb 08, 2012
Image credit: Patrick Lyons

(PhysOrg.com) -- A Stony Brook University researcher has found that, contrary to popular belief, there are not plenty of fish in the sea.

In an article entitled “Why are there so few fish in the sea?,” published on-line this week in the Proceedings of the Royal Society B, John J. Wiens, Ph.D., an Associate Professor in the Department of Ecology and Evolution at Stony Brook University, addresses why the oceans contain only 15-25 percent of all of Earth's species even though they cover about 70 percent of Earth’s surface.

Dr. Wiens and student Greta Carrete Vega examined the evolutionary and ecological causes of the low species numbers of marine environments by studying the biodiversity of ray-finned fish, the most species rich group of marine vertebrates, containing 96 percent of all fish species. They performed analyses using evolutionary trees based on molecular data and fossils, and using a large database on the habitats of nearly all living fish species.

The study found a surprising difference in diversity between and saltwater habitats.

“There are more fish species in freshwater than in saltwater habitats, despite the much greater area and volume of the oceans,” he said, noting that freshwater environments occupy only about 2 percent of the Earth’s surface. “More remarkably, our results suggest that most marine fish alive today are descended from freshwater ancestors (even though fish and animals in general first evolved in the oceans).”

The authors hypothesized that extinctions in marine habitats, hundreds of millions of years ago, may help explain the low present-day diversity of .

“Our results suggest that ancient extinctions in the marine environment may have wiped out the earliest ray-finned fishes living in the oceans, that the oceans were then recolonized from freshwater habitats, and that most marine living today are descended from that recolonization (leaving less time for biodiversity to build up in the oceans),” he said. “This pattern of ancient extinction and more recent recolonization may help explain why the oceans are now so species-poor, even for fish.”

Explore further: Museum workers pronounce dobsonfly found in China, largest aquatic insect

More information: Paper online: rspb.royalsocietypublishing.or… 02/02/rspb.2012.0075

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verkle
1.3 / 5 (47) Feb 08, 2012
Confusing title. People would think just by the title that there are few fish in the ocean. But what the article says is that the number of species is lower than some scientists thought.

Why do the authors think that they have to bring in the uncredited thinking of evolution into this discussion. Some scientists should rather think out of that mold, and entertain other possibilies for the history of life.

AgentOfFate
4.1 / 5 (31) Feb 08, 2012
Confusing title...Why do the authors think that they have to bring in the uncredited thinking of evolution into this discussion. Some scientists should rather think out of that mold, and entertain other possibilies for the history of life.

There is no such thing as the uncredited thinking of evolution, just as there is no such thing as an uncredited scientific fact, its an oxymoron. Even if all of the bones and fossils at a scientist's disposal were not enough to convince him/her of evolution, the DNA and molecular evidence for evolution is astonishing in the sense that it is truly overwhelming in favor for the 'theory of evolution'--a title we only reluctantly, and at this point unnecessarily, use to describe the history of life on this planet.
kochevnik
3.6 / 5 (25) Feb 08, 2012
Some scientists should rather think out of that mold, and entertain other possibilies for the history of life.
Your christopathic sock puppets will be banned again, Heinrik. Kudos to the editors and moderators.
mrlewish
4.5 / 5 (18) Feb 08, 2012
I have a different theory. There are fewer species because their are fewer truly separate geographical areas in the oceans.. image how many land species their would be if there were just one continent that was a plain in which any type of animal could go anywhere. I suspect that there would be way fewer types.
that_guy
3.9 / 5 (15) Feb 08, 2012
Our results suggest that ancient extinctions in the marine environment may have wiped out the earliest ray-finned fishes living in the oceans


A common cause of speciation in animals comes from physical separation - for example, a freshwater fish species in one river separated from their cousins in another river.

In the ocean, there is no separation other than distance, for a fish that may range for thousands of miles over the years and can intermingle and breed with related populations.

I don't see how we need extinctions and calamity are needed when a simple, obvious, and logical argument based on current theory should suffice. Their job should be to disprove the most likely explanation before inventing new stories.
that_guy
3.8 / 5 (16) Feb 08, 2012
Why do the authors think that they have to bring in the uncredited thinking of evolution into this discussion. Some scientists should rather think out of that mold, and entertain other possibilies for the history of life.

This is a science site you retard. Until you learn what science is, perhaps you should go comment somewhere else.

The only well supported theories for how speciation occurs are natural selection and evolution. Until another theory is proven better, or evolution et al proven wrong, logical or smart scientists and biologists are going to use and quote these theories unless they have a reason to specify otherwise.
Callippo
3.4 / 5 (11) Feb 08, 2012
A common cause of speciation in animals comes from physical separation
Right. Another explanation may be, the marine watter is untasty and noble fishes avoid it. But IMO the main reason could be, the depth of oceans provides lower evolutionary pressure with compare to freshwater environment, which is shallow and its conditions are changing rapidly. For example, you cannot find parthenogenetic primitive fishes with full cartilaginous skeleton like the sharks widespread in fresh water - so it's all about speed of evolution and speciation in particular.
Shootist
2 / 5 (27) Feb 08, 2012
Why are there so few fish in the Earth's oceans?


Bush's fault.
encoded
3.9 / 5 (8) Feb 08, 2012
neutron repulsion strikes again!!!!
I mean... yeah the oceans are a relatively undifferentiated environment. Over millions of years DNA spreads in every direction and a kind of genetic monopoly takes shape.
StarGazer2011
1.8 / 5 (20) Feb 08, 2012
Mr_Lewish, Callippo and That_Guy:
Awesome comments, you should email the scientist, much simpler explanation. Lower selective pressure due to relatively stable environment (Callippo) plus lack of isolation (That_Guy) plus fewer niches to exploit in relatively homogenous environment (Mr_Lewish).
Telekinetic
2 / 5 (24) Feb 08, 2012
Friend: Suzie dumped me for another guy.
Telekinetic: Ahh, don't sweat it. There are plenty of other fish in the ..., in the- LAKE!
Estevan57
2.3 / 5 (27) Feb 08, 2012
No parthenogenetic primitive fishes with full cartilaginous skeleton like the sharks widespread in fresh water? What about eels and lampreys?
Deesky
4.6 / 5 (10) Feb 08, 2012
A common cause of speciation in animals comes from physical separation

True.

In the ocean, there is no separation other than distance, for a fish that may range for thousands of miles

True to a point. Not all fish endlessly roam the oceans. Most fish species live in localized environments, such as estuaries and reef systems. There are shallow water environments and deep (and ultra deep) water environments. There are environments that range widely in temperature, salinity and nutrient content. It isn't all just one big, er, fishbowl.

Another source of speciation is food availability and specialization, sexual selection, predation and of course all the above mentioned environment variations.

I would think that researchers knowledgeable in this field would have taken all these factors into account before making their conclusions.
Skyking211
3.7 / 5 (6) Feb 08, 2012
Thanks to all for defending the sciences against the garbage that is creation. My take on ID: What intelligence designs multiple life forms which live by terrorizing and rending other living species to pieces in order to eat and survive? Intelligent design would be more likely if we were all air ferns. Real life is extremely intense and evolution describes the process to a T. No more of this other nonsense, please.

I agree that fresh water from small ponds to large lakes offer the seperation needed to diversify. Evolutionary changes are driven by necessity as the recent lizard transplantation experiment shows. The oceans have likely been too stable to drive change. If it ain't broke why evolve.

Mike_Massen
1.3 / 5 (14) Feb 09, 2012
@verkle
Please try, try to understand:-
Science is "The disciplined acquisition of knowledge".

What other "..history of life." is there that has any discipline attached to it - pray tell, actually don't pray, please just articulate ?

You come across as a creationist with a fixed position.

Science is a dynamic & with a successful discipline, creationism is an uncredited (& arbitrary) belief with no discipline at all !
Evolution has periods of slow & of rapid change that may appear to be like creation, in a sense it is but, not from any anthropomorphic deity, nature is the master craftsman stimulated by many sources of mutation over very LONG periods.

Sadly all the creationists I have met over the course of 35 years rely on a book written at a time when there was no discipline. People then attached significance to the authority of a book when 99% of people couldn't read or write, its plainly evident Moses wrote it in concert with others over many decades & collated even older ideas.
ThanderMAX
3 / 5 (2) Feb 09, 2012
They have not checked the ocean in 15th century or the like.

It might be due to overfishing by humans.
Skyking211
5 / 5 (1) Feb 09, 2012
Using the overfishing hypothesis from our recent pact I would expect to see an extinct Atlantic Cod as this was about ray-finned species. Whaling and sealing also pushed species to the brink.
antialias_physorg
3.7 / 5 (6) Feb 09, 2012
Why are there so few fish in the Earth's oceans?

Maybe because the energy available isn't as big in the oceans as on land?

Life needs energy. Energy comes primarily from the sun. In all food chains the bottom rung are solar energy using organisms (almost*).
So the volume of the oceans doesn't help, as the energy is delivered by area.

Though oceans do have a low albedo (i.e. take up more energy than land does per square meter) the energy gets diluted over the volume much more quickly than on land (energy seeps slower into a solid than a liquid). Organsims need not only energy. They also need an energy GRADIENT to work on in order to sustain life. A large, homogeneous energy content in the oceans isn't favorable for life. The bottom rung of the food chain works only in the upper layer, where the gradient is large.

*Exceptions are environments like black smokers or bacteria living off radioactive decay deep underground.
MarkyMark
1.8 / 5 (5) Feb 09, 2012


In the ocean, there is no separation other than distance, for a fish that may range for thousands of miles

True to a point. Not all fish endlessly roam the oceans. Most fish species live in localized environments, such as estuaries and reef systems. There are shallow water environments and deep (and ultra deep) water environments.

not that i disagree with your basic points i would like to add that fish eggs and Fry have been known to spread around quite far due to watercurrents and mini habitats creted via for example Driftwood.

Of course most if not all such life would likely die due to gradual changes in conditions such as Specific Gravity and Salinity, and of course being very young. However despite these challenges dont forget my point would die a quick death the less time such life had. In a world that ( Ahem!) was "created" 6000 years ago ad apposed to one that had millions of years for a slow spread.

Just an idea!
baudrunner
2 / 5 (12) Feb 09, 2012
I agree with mrlewish. The oceans ar a huge environment, and logically, the opportunities for genetic diversification are much more prevalent in more confined environments. It's simple.
Sinister1811
1.4 / 5 (19) Feb 09, 2012
And they've always told me that there are plenty more fish in the sea.. Not likely.
Skyking211
not rated yet Feb 09, 2012
A non arguable evolutionary trait would be a genus of fish which thrives on the plastics in the mid ocean gyres.

I think that it would be a symbiotic relationship with bacteria in the gut metabolising the various types mixed together, as this stuff has no nutritional value as we know it
But then humans have the same type of digestive process.
Plenty of material there, now we wait to see if evolution occurs before everything dies.

kaasinees
1 / 5 (6) Feb 09, 2012
because not all parts of the ocean have enough oxygen and other nutrition content, also with depleting rivers this nutrition content becomes lower means less life means less oxygen in ocean means more less life. if that makes any sense.
Skyking211
1 / 5 (1) Feb 09, 2012
Back to the old standby: Life, as we know it!
that_guy
3 / 5 (2) Feb 09, 2012
Not all fish endlessly roam the oceans.... It isn't all just one big, er, fishbowl.

Another source of speciation is food availability and specialization, sexual selection, predation and of course all the above mentioned environment variations.

I would think that researchers knowledgeable in this field would have taken all these factors into account before making their conclusions.

I think you bring up some good points, but they kind of back up what I'm saying - Estuaries and reefs are where we find the most diversity - and are most susceptible to river like evolutionary pressure. From how the article is written, I don't believe that estuaries are included as ocean.

Obviously the ocean is not devoid of diversity, just substantially because some of the pressure for speciation is lower.

Science papers are overturned all the time because of incorrect conclusions, missed factors, etc. I highly respect science, but I hold no scientist on a pedestal.
Husky
not rated yet Feb 12, 2012
because the ocean is like soap television and the rivers are like packet radio thats why
Koen
1 / 5 (7) Feb 12, 2012
claustrophobic fish species mutate slower ... and the salty seawater raises blood pressure and stress which lowers reproduction rates
Mike_Massen
1.4 / 5 (10) Feb 24, 2012
Skyking211 offered this observation
A non arguable evolutionary trait would be a genus of fish which thrives on the plastics in the mid ocean gyres.


Skyking211 went on the make a rather staggering claim:-
... as this stuff has no nutritional value as we know it
Actually there is nutritional value, eg melamine has amines just like amino acids & other plastics & their color/fixative/uv protect maybe likewise have some value albeit narrow.

Some 20 years back Warfarin (rat poison) was found to be losing effectiveness, a test conducted on rats over several generations in an evolution trial resulted in the ability to place a rat by itself in a cage with only water and Warfarin and it would put on weight!

I would love to find that documentary, dont know if it was pbs or horizon or national geographic or in UK etc - it does seem to prove selection pressure leads to evolution, I hope the creationists haven't created a black hole for it :-(

Send me pm please if found ??
Mike