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  • Thanks to the Monterey Bay Aquarium for partnering with us

  • on this episode.

  • We hope you learn something crabulous!

  • [♪ INTRO]

  • This beach isn't normally red.

  • You are looking at tens of thousands of pelagic red crabs

  • that washed up on the shores of Monterey Bay.

  • They're also known as tuna crabs because tunas love to snack on them,

  • but these crimson creatures aren't really crabs.

  • They're a kind of squat lobstercrab relatives that look like

  • flattened lobsters with their long tails that curl under their bodies.

  • And they're kind of like little red weathermen,

  • because their presence on the beaches of California

  • indicates something unusual going on below the waves.

  • Normally, red crabs are mostly found in the waters off Baja California

  • — a Mexican state that borders the US state of California.

  • There, they dine on phytoplanktonthose tiny, microscopic marine algae

  • suspended in the water that we've talked about many times before

  • as well as any other edible bits they can find.

  • Once they're adults, they start to hang out near the bottom

  • in the benthic zone.

  • But the larvae, juveniles, and young adult crabs live in the

  • epipelagic zone, or upper part of the open oceanhence their name.

  • Of course, pelagic red crabs don't always stay in one spot.

  • And their movements have been pretty reliably linked

  • to ocean and climate patterns.

  • Sometimes, these movements are helpful to the crabs.

  • Like, they'll move with their food during certain stages of their lives.

  • Take a 2004 study in the journal Deep Sea Research Part II, for example.

  • Scientists recorded water temperatures and salinities

  • at different depths and locations along the Baja California coastline.

  • That let them map out ocean currents and areas of upwelling

  • where cooler, food-filled water gets pulled upward

  • to the warm ocean surface.

  • Scientists also used sonar and fishing nets to measure

  • how many red crabs there were.

  • And they found that there were more crabs

  • in areas of strong upwelling.

  • Turns out the pelagic red crabs were moving with the upwelling,

  • which makes sense since the plankton they eat

  • flourish in that nutrient-rich water.

  • It's also no coincidence that the lobsters' breeding season

  • is right around the time of the year that upwelling normally occurs,

  • since being able to get more food means healthier breeding adults.

  • But, the crabs don't get much of a say in where they end up.

  • The thing about spending quite a bit of your time floating around

  • in the top layer of ocean is that you can easily get carried away

  • literally carried away!

  • The crabs can swim.

  • Like, sort of.

  • They propel themselves backwards

  • by flapping their tails and tucking their legs into their bodies.

  • But they aren't great swimmers, especially when they're young.

  • So, they can get swept up in strong ocean currents which carry them

  • northwards to California and even as far north as Oregon.

  • And when this happens, hordes of them may wash up on shore.

  • You'll sometimes find red crabs covering entire beaches!

  • These mass strandings have been linked to large-scale climate events

  • like El Niño, where the permanent trade winds that flow

  • around the equator weaken, which causes warm currents

  • to flow from South America northward along the California coast.

  • For example, a study published in 2015 in Fisheries Science

  • examined the number of red crabs in their usual habitats off the coast

  • of Baja California six times between October 2004 and March 2007.

  • And they found that there were more crabs in the area during

  • cold water La Niña events and fewer during warm water El Niños

  • because the warm waters were carrying the crabs away from Mexico

  • and north toward California.

  • The upside of all this is that washed-up red crabs may be a nice

  • source of food for seagulls and other hungry predators during

  • El Niño events, when their usual fare tends to be more scarce.

  • But the crabs don't just signal El Niños.

  • They're also warning marine biologists and beachgoers alike

  • of our changing climate.

  • For example, a study published in 2019 in Scientific Reports

  • linked the distribution of red crabs with another kind

  • of ocean pattern: marine heatwaves.

  • In the winters of 2014 and 2016, areas of the northeast Pacific ocean

  • warmed to two to four degrees Celsius above normal for months on end,

  • creating what some people called the warm-water blob.

  • The blob wreaked havoc on ocean life, killing marine mammals and triggering harmful algal

  • blooms.

  • But it also meant that more than thirty-five species

  • of marine mammals, fish, seabirds and algae temporarily moved

  • or got carriednorthward.

  • That included pelagic red crabs who made it as far north as Newport, Oregon!

  • These northern shifts might not seem like a big deal now,

  • but scientists think marine heatwaves and other ocean warming events

  • are already more frequent than they used to be,

  • and are going to happen more often due to climate change.

  • That means coastal animal and plant communities will

  • likely look really different in the future.

  • And the red crabs show that changes are already happening,

  • as strandings are becoming more and more common.

  • The first recorded one was in 1859, then 1959, 1969, and 1983.

  • Then, there were a total of eight recorded strandings

  • between 2015 and 2017 alone.

  • In a way, these little red crustaceans are acting

  • as bellwethers for the ocean.

  • The impressive sight of millions of beached squat lobsters

  • is a clear signal that our ocean is being altered

  • one that's far more visceral than, say,

  • satellite images or temperature readings.

  • And by studying these little red drifters, scientists can gain

  • a better sense of how ocean habitats are changing

  • and what the effects of those changes will be.

  • Thanks again to the Monterey Bay Aquarium for partnering with us

  • on this episode of SciShow.

  • The Aquarium's mission is to inspire conservation of the ocean.

  • So give them a follow on their social media accounts, which are all

  • extremely worth it, visit their website at montereybayaquarium.org.

  • They shore would love to sea you!

  • [♪ OUTRO]

Thanks to the Monterey Bay Aquarium for partnering with us

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The Little Lobster That Reveals Climate

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    joey joey に公開 2021 年 05 月 11 日
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