Loss of Top Predators Has More Far-Reaching Effects than Thought

[n2doc]

By Jenny Marder, PBS NewsHour


Sea otters eat sea urchins and sea urchins eat kelp. When sea otters are present, the coastal kelp forests maintain a healthy balance. But when the fur trade wiped out the otters in the Aleutian Islands in the 1990s, sea urchins grew wildly, devouring kelp, and the kelp forest collapsed, along with everything that depended on it. Fish populations declined. Bald eagles, which feed on fish, altered their food habits. Dwindled kelp supplies sucked up less carbon dioxide, and atmospheric carbon dioxide increased.

The animal that sits at the top of the food chain matters, and its loss has large, complex effects on the structure and function of its ecosystem, according to an article published on Thursday in the online issue of the journal, Science.

That the presence or loss of an ecosystem's top predator is linked to surges and crashes in the food chain is nothing new. The term for the phenomenon is "trophic cascade," and it's been applied to coastal sea otters, as well as the gray wolves in Yellowstone and the mountain lions in Zion National Park, to name just a few.

But what is new, authors of the paper say, is that this is ubiquitous across all ecosystems. "We see it on land, we see it on water, we see it in high latitudes, we see it in low latitudes," said James Estes, a research scientist at the Institute for Marine Sciences at the University of California, Santa Cruz and the paper's lead author. "We do not not see it anywhere."

more

http://www.scientificamerican.com/article.cfm?id=loss-of-top-predators-ecology-changes

[Orrex]

1. I totally thought that this was going to be about the Chris Hansen scandal

[cyberpj]

2. Unless the animal at the top of the food chain is called Man.

I would think the loss of that animal would greatly enhance the effects of Earth's ecosystem.

[BeFree]

3. Yep we are like the urchins

From OP: "...sea urchins grew wildly, devouring kelp, and the kelp forest collapsed"

[RC]

4. Will we learn a lesson from this?

No. Probably not even when it is too late.

[BeFree]

5. well

I am what you might call a knee jerk optimist. But sadly growing away, towards a word that rhymes, but starts with a 'P'.

I have longed for the day when my generation would take over. But it looks like that day may never come. We seem to be content with the bubbly baubles and obesity of over consumption.

Like with Fukushima and the subsequent turn away from nukes, we seem to have to be hit over the head with a clue by 4 before we begin to act correctly. Time, however, is not on our side.

[Nihil]

6. We need to invent an effective top predator to keep the human population down?

Yeah, a forward-looking culture that always considers the long-term effects
of their actions can certainly do that. The question is how soon?

(I was only wearing my Cyberdyne t-shirt yesterday too ...)

[jpak]

7. The literature on marine trophic cascades is frightening

Kingman Reef

(Nova) Scotia Shelf

Newfoundland

North Sea

Black Sea

Caspian Sea

Atlantic coast (cow-nosed ray explosion)

Alaska - NW Pacific

and on and on

The removal of top predators (sharks, cod and other large predatory fish - and urchin predators like large lobsters - and sea turtles: which consume jellyfish and reef sponges) and seagrass consumers (manatees, dugongs and green sea turtles) has resulted in profound changes in the structure and function of marine ecosystems - and produce alternate states that (may) inhibit recovery.

...and, there may trophic cascades in the ocean that may not be documented - how did the collapse of the Newfoundland cod fishery affect Architeuthis (giant squid) populations? How will overexploitation of Antarctic Toothfish affect Colossal Squid populations? How has the extirpation of baleen whales altered nutrient cycling in coastal environments (the so-called whale pump"). How will loss of sea ice influence the "krill iron pump" in Southern Ocean?

Overlay these changes on top of climate change (coral bleaching), introduction of invasive species, massive plastic pollution and coastal eutrophication and it is clear that we may/will transform our oceans into prokaryotic soups dominated by gelatinous zooplankton and invasives.

Do yourselves a favor and never do a Google Scholar search on "marine trophic cascades"

It ain't pretty