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  • One of the reasons that I'm fascinated by the ocean

  • is that it's really an alien world on our own planet.

  • From our perspective,

  • sitting on the shoreline or even out on a boat,

  • we're given only the tiniest glimpses

  • at the real action that's happening

  • beneath the surface of the waves.

  • And even if you were able to go down there,

  • you wouldn't see very much

  • because light doesn't travel very far in the ocean.

  • So, to answer questions about how the ocean works,

  • in my research, we use sound.

  • We use sonars that send out pulses of sound

  • made up of a number of different frequencies, or pitches,

  • that are shown with different colors.

  • That sound bounces off things in the habitat

  • and comes back to us.

  • If it were to bounce off this dolphin,

  • the signal we got back

  • would look very much like the one we sent out

  • where all the colors are represented pretty evenly.

  • However, if we were to bounce

  • that same sound off of a squid,

  • which in this case is about the same size as that dolphin,

  • we'd instead only get the lowest frequencies back strongly,

  • shown here in the red.

  • And if we were to look at the prey of that squid,

  • the tiny little krill that they're eating,

  • we would instead only get the highest frequencies back.

  • And so by looking at this,

  • we can tell what kinds of animals are in the ocean,

  • we can look at how dense they are,

  • where they are distributed,

  • look at their interactions

  • and even their behavior

  • to start to study the ecology of the ocean.

  • When we do that, we come up with

  • something sort of surprising:

  • on average, there isn't very much food in the ocean.

  • So even in places which we think of as rich, the coasts,

  • we're talking about two parts of every million contain food.

  • So what does that mean?

  • Well, that means that in the volume of this theater,

  • there would be one tub of movie theater popcorn

  • available to be eaten.

  • But of course, it wouldn't be collected

  • for you neatly in this bucket.

  • Instead, you'd actually have to be swimming

  • through this entire volume Willy Wonka style,

  • picking off individual kernels of popcorn,

  • or perhaps if you were lucky,

  • getting a hold of a few small clumps.

  • But, of course, if you were in the ocean,

  • this popcorn wouldn't be sitting here

  • waiting for you to eat it.

  • It would, instead, be trying to avoid becoming your dinner.

  • So I want to know how do animals solve this challenge?

  • We're going to talk about animals in the Bering Sea.

  • This is where you may have see "Deadliest Catch" framed,

  • in the northernmost part of the Pacific Ocean.

  • We've been looking specifically at krill,

  • one of the most important food items in this habitat.

  • These half-inch long shrimp-like critters

  • are about the caloric equivalent

  • of a heavily buttered kernel of popcorn.

  • And they're eaten by everything

  • from birds and fur seals that pick them up one at a time

  • to large whales that engulf them in huge mouthfuls.

  • So I'm going to focus in the area

  • around three breeding colonies for birds and fur seals

  • in the southeastern Bering Sea.

  • And this is a map of that habitat

  • that we made making maps of food

  • the way we've always made maps of food.

  • This is how many krill are in this area of the ocean.

  • Red areas represent lots of krill

  • and purple basically none.

  • And you can see that around the northern two most islands,

  • which are highlighted with white circles

  • because they are so tiny,

  • it looks like there's a lot of food to be eaten.

  • And yet, the fur seals and birds on these islands

  • are crashing.

  • Their populations are declining

  • despite decades of protection.

  • And while on that southern island

  • at the very bottom of the screen

  • it doesn't look like there's anything to eat,

  • those populations are doing incredibly well.

  • So this left us with a dilemma.

  • Our observations of food don't make any sense

  • in the context of our observations of these animals.

  • So we started to think about how we could do this differently.

  • And this map shows not how many krill there are,

  • but how many clumps of krill there are,

  • how aggregated are they.

  • And what you get is a very different picture of the landscape.

  • Now that southern island looks

  • like a pretty good place to be,

  • and when we combine this

  • with other information about prey,

  • it starts to explain the population observations.

  • But we can also ask that question differently.

  • We can have the animals tell us what's important.

  • By tagging and tracking these animals

  • and looking at how they use this habitat,

  • we are able to say, "What matters to you?"

  • about the prey.

  • And what they've told us

  • is that how many krill there are really isn't important.

  • It is how closely spaced those krill are

  • because that's how they are able to make a living.

  • We see the same pattern

  • when we look in very different ocean,

  • further south in the Pacific,

  • in the warm waters around the Hawaiian islands.

  • So a very different habitat,

  • and yet the same story.

  • Under some conditions,

  • the physics and the nutrients, the fertilizer,

  • set up aggregations in the plants, the phytoplankton.

  • And when that happens,

  • these very dense aggregations of phytoplankton

  • attract their predators,

  • which themselves form very dense layers.

  • That changes the behavior and distribution

  • of their predators as well,

  • starting to set up how this entire ecosystem functions.

  • Finally, the predators that eat

  • these small fish, shrimp, and squid,

  • we're talking about two- to three-inch long prey here,

  • changes how they use their habitat

  • and how they forage.

  • And so we see changes in the spinner dolphins

  • that are related to the changes

  • we're seeing in the plant life.

  • And just by measuring the plants,

  • we can actually predict very well

  • what's going to happen in the top predator

  • three steps away in the food web.

  • But what's interesting is

  • that even the densest aggregations of their prey

  • aren't enough for spinner dolphins to make it.

  • It's a pretty tough life there in the ocean.

  • So these animals actually work together

  • to herd their prey into even denser aggregations,

  • starting with patches that they find in the first place.

  • And that's what you're going to see in this visualization.

  • We have a group of 20 dolphins,

  • you notice they're all set up in pairs,

  • that are working together

  • to basically bulldoze prey

  • to accumulate it on top of itself.

  • And once they do that,

  • they form a circle around that prey

  • to maintain that really dense patch

  • that is a couple thousand times higher density

  • than the background that they started with

  • before individual pairs of dolphins

  • start to take turns feeding

  • inside this circle of prey that they've created.

  • And so, this work is showing us

  • that animals can first give us the answers

  • that aggregation is critical to how they make their living.

  • And by looking more deeply at the ocean,

  • we're starting to understand our interactions with it

  • and finding more effective ways of conserving it.

  • Thank you.

One of the reasons that I'm fascinated by the ocean

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B1 TED-Ed krill prey ocean habitat popcorn

【TED-Ed】How giant sea creatures eat tiny sea creatures - Kelly Benoit-Bird

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    wikiHuang posted on 2013/12/04
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