Sharks fear killer whales. How does this impact the ecosystems they share?
- A new study finds that sharks will flee areas they met orcas in for up to a year.
- Killer whales are known to eat sharks, but it is unknown if the sharks are fleeing because they know that too.
- The discovery will change our understanding of how marine ecosystems evolve.
The true apex predator<p>The study, titled "Killer whales redistribute white shark foraging pressure on seals," results from years of investigations into the movements and behavior of 165 tagged great white sharks, observations and records of killer whale movements, and information on seal populations off the coast of California. They also looked to previous descriptions of shark and whale interactions to give context to their findings.</p><p>The sharks immediately turned tail and fled in every time they crossed paths with orcas. They'd also stay away from that place long afterward. Only <em>one </em>observed shark dared venture back to where it had just encountered the whales, and it didn't stick around. Most of the sharks merely fled a bit further up the coastline, while others went much further out to sea to avoid the whales. </p>
Why are they doing this?<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="14ccb270e8cc6888b69118539a29b63b"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/B7GHCJXwLw8?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>Orcas have been known to eat great whites. The remains of the sharks are a grotesque sight to behold and are always missing their <a href="https://www.nationalgeographic.com/animals/2019/07/killer-whales-orcas-eat-great-white-sharks/#:~:text=By%20Emma%20Rigney&text=In%20October%201997%2C%20tourists%20in,killer%20whales%20eating%20white%20sharks." target="_blank">livers</a>, no matter how much else remains or is missing. If the orcas have discovered a source of Chianti to pair with them or not remains unknown at this <a href="https://youtu.be/bHoqL7DFevc?t=28" target="_blank">time</a>.</p><p>However, we don't currently know if the sharks are fleeing because they understand that risk, because they knew the orcas would fight them for the same food supply, because whales look big and scary to them, or some combination of the three.</p><p>Before this gets too frightening, there are no known cases of wild orcas killing <a href="https://en.wikipedia.org/wiki/Killer_whale_attack" target="_blank">humans</a>, and only a few examples of injuries being caused by these interactions. <a href="https://bigthink.com/surprising-science/orcas-and-stress" target="_blank">Orcas kept in tiny boxes</a> for long periods can be a bit more violent, but that's another story. </p>
A new study finds that starlet sea anemones have the unique ability to grow more tentacles when they've got more to eat.
- These anemones belong to the Cnidaria phylum that continues developing through its lifespan.
- The starlet sea anemone may grow as many as 24 tentacles, providing there's enough food.
- When deprived of the chance to reproduce, they also grow more tentacles.
Starlet sea anemone basics<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDM5Mzk3MS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0Njc2MDk0OX0.q_e2-_VyGcBaOoGM53Uu1XZPaaVxsPhsn7shaxVGu1c/img.jpg?width=980" id="ac056" class="rm-shortcode" data-rm-shortcode-id="200a59225bbce7ddda78d80a20fc267d" data-rm-shortcode-name="rebelmouse-image" alt="sea anemone" />
Credit: Smithsonian Environmental Research Center/Flickr<p>The <a href="https://en.wikipedia.org/wiki/Starlet_sea_anemone" target="_blank">starlet sea anemone</a>, or <em>Nematostella vectensis</em>, lives burrowed into the mud and silt of coastal salt marshes. Research suggests it's originally native to the east coast of North America, although it can also be found along the continent's west coast, around Nova Scotia, and in U.K. coastal marshes.</p><p>Being stationary creatures, starlet sea anemones have to reach out and grab nutrition floating by. Their natural diet is mainly copepods and midge larvae, though they're also perfectly happy eating brine shrimp in a laboratory setting. The anemones grab food with their tentacles whose cilia then wiggle the meal down to their mouths.</p><p>In the larval stage, the anemones have a quartet of tentacles, though they may develop up to 24 of them. A more typical amount is 16.</p><p>While the starlet sea anemone may grow larger in a lab setting, in the wild its clear, worm-like body typically extends from 10 to 19 millimeters (about three quarters of an inch) in length. Tentacles may add another 8 mm.</p><p>Members of the phylum to which the starlet sea anemone belongs, the <a href="https://en.wikipedia.org/wiki/Cnidaria" target="_blank"><em>Cnidaria</em></a> phylum, have the unique ability to grow new body parts throughout their lives in response to environmental influences. Among these influences are fluctuations in the amount of available food. Nonetheless, no other animal has yet been seen growing new appendages when they get extra sustenance.</p>
The study<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDM5NDAwOS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyOTMzMTcyMX0.aSMrGNPw3Hz_dAmy-PGe7sWHp-ePGZFhi4AT2M5zEfE/img.jpg?width=980" id="7f3ff" class="rm-shortcode" data-rm-shortcode-id="fb709c543b60912c99dc5ee9c2871d49" data-rm-shortcode-name="rebelmouse-image" />
Tentacles budding, or not, under different feeding conditions
Credit: Ikmi, et al./Nature Briefing<p>Observations of starlet sea anemones in his lab prompted lead author of the paper, <a href="https://www.embl.de/research/units/dev_biology/ikmi/members/index.php?s_personId=CP-60026325" target="_blank">Aissam Ikmi</a> of the European Molecular Biology Lab Heidelberg, to undertake the new research. He'd noticed what seemed to be an association between the amount of brine shrimp being consumed and the sprouting of new tentacles.</p><p>Ikmi and his team raised over 1,100 starlet sea anemone polyps to which they fed brine shrimp. Some of them began with 4 tentacles while the rest already had 16.</p><p>For over six months, the researchers varied the animals' food supply at cyclical intervals, feeding the anemones for a few days and then stopping for a few days.</p><p>The scientists tracked tentacle growth throughout the experiment, creating a spatio-temporal map that identified periods of tentacle growth in relation to feeding cycles.</p><p>They found that the anemones grew new tentacle pairs during feeding periods, and new tentacle production did indeed stop when their food supply was temporarily cut off. Tentacle-pair budding occurred at the same time as an anemone also doubled its body size.</p><p style="margin-left: 20px;">"When food was available, however, primary polyps grew and sequentially initiated new tentacles in a nutrient-dependent manner, arresting at specific tentacle stages in response to food depletion." — Ikmi, et al.</p>
Two ways to bud<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDM5NDA1NS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYwNjgzNDMzMX0.H7ATzKUDxJvdt1xKiaJe1oKG-foXqPWASin3nNm97gw/img.jpg?width=980" id="abca1" class="rm-shortcode" data-rm-shortcode-id="3ac439c1ad951d3a2aa2afa4b3a8a14b" data-rm-shortcode-name="rebelmouse-image" />
In this illustration from the paper, development from 4 to 12 tentacles is characterized by trans budding. Cis budding is present beginning with 16 tentacles.
Credit: Ikmi, et al./Nature Briefing<p>The team identified two budding modalities, they named "cis" and "trans." In both modes, pairs of tentacles were produced, budding either simultaneously or consecutively. In:</p><ul><li><em>Trans budding</em> — the two new tentacles budded on opposite sides of the anemone.</li><li><em>Cis budding</em> — the two new tentacles budded from within the same segment.</li></ul><div>The experiments also suggest that the starlet sea anemone appears to have ability to make good use of available energy dependent on its situation. Being prevented from spawning, for example, prompted the anemones to grow more tentacles, as if they were rechanneling the energy they'd have otherwise directed to reproduction.</div>
A new study bases its calculations on more than the great white shark.
- Previous estimates of the megalodon's size were based solely on its teeth compared to the star of "Jaws."
- The prehistoric monster is as closely related to other sharks.
- Imagine just a dorsal fin as tall as you are.
What’s different about this analysis<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzg3MjU5OS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYxNDc2MTQyNn0.K38h9qHeCM7jtYLA2Z25W7ZC9NiekmvL6CkQy82szzU/img.png?width=980" id="24ad8" class="rm-shortcode" data-rm-shortcode-id="fbc76e6dc6f82d299c7828a80272eede" data-rm-shortcode-name="rebelmouse-image" alt="megalodon compared to a school bus" />
The megalodon’s revised measurements<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMzg0OTAwMy9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNTM4MjA4M30.uArVFW_ithOZuZ1_oTKCg0y1-2Zue2VRD_C_j2KJVk4/img.jpg?width=980" id="98366" class="rm-shortcode" data-rm-shortcode-id="8caf88dda090ba04f0aac156e15b7a27" data-rm-shortcode-name="rebelmouse-image" alt="shark and diver illustration" />
Credit: Reconstruction by Oliver E. Demuth/Scientific Reports<p>The study proposes the following approximate measurements for a full-grown megalodon:</p><ul><li>Length: about 16 meters (52.5 feet). A full-size school bus is just 45 feet long</li><li>Head size: about 4.65 meters long (15.3 feet) </li><li>Dorsal fin: about 1.62 meters tall (5.3 feet). A person could stand on the back of a megalodon and be about as tall as the fin.</li><li>Tail fin: about 3.85 meters high (12.6 feet) </li></ul><p>Let's just hope this sucker is really extinct. </p>
According to international law, the seabed belongs to everyone.
Mining the ocean floor for submerged minerals is a little-known, experimental industry.
In one of the ocean's most lifeless places, scientists discover and resuscitate ancient organisms.
- Seemingly dead microbes from 100 million years ago spring back to life.
- The microbes were buried deep beneath the Pacific's "Point Nemo."
- There's crushing pressure beneath the seabed, but these microbes apparently survived anyway.
There is a place in the South Pacific that's as far as you can get from land. This "oceanic pole of inaccessibility" lies beneath the South Pacific Gyre that covers 10 percent of Earth's ocean surface. It's so remote that spacecraft are regularly guided down into its waters at the end of their missions. Says NASA, "It's in the Pacific Ocean and is pretty much the farthest place from any human civilization you can find."
There's another reason, though, that this so-called "Point Nemo" isn't like anywhere else. It's an oceanic desert, about as devoid of standard marine life as any stretch of water can be. Nutrients from land can't reach it, and currents keep its waters isolated from the rest of the ocean. There's also an excess of ultraviolet light out there.
While there is some microbial life floating in the area, a team of scientists from Japan and the U.S. wanted to know if anything could possibly be living in the area's desolate seabed. What they found and retrieved were seemingly lifeless microbes trapped down there for 100 million years. It turns out that the tiny organisms are still alive after all this time —all they needed was food and oxygen.
"Our main question was whether life could exist in such a nutrient-limited environment, or if this was a lifeless zone," says study leader microbiologist Yuki Morono of the Japan Agency for Marine-Earth Science and Technology. "And we wanted to know how long the microbes could sustain their life in a near-absence of food." Apparently hundred of millions of years. Take that, tardigrades.
The research in published in the journal Nature Communications.
It's hardly a hospitable environment down there, and the weight of all that water above presses down hard on anything beneath it. Organisms trapped under this kind of pressure typically die and fossilize, given a million years or so. Still, for some reason, these microbes evaded that fate.
Co-author Steven D'Hondt, a geomicrobiologist from University of Rhode Island, says, "We knew that there was life in deep sediment near the continents where there's a lot of buried organic matter. But what we found was that life extends in the deep ocean from the seafloor all the way to the underlying rocky basement."
Morono (left) and D'Hondt (right) examining cores aboard JODIES Resolution.
Image source: IODP JRSO/University of Rhode Island
The microbes were brought up through 3.7 miles of water from the ocean bottom during the JOIDES Resolution drill ship's 2010 expedition to the Gyre. The researchers extracted samples from an array of sites and depths, including pelagic clay sediments as deep as 75 meters (246 feet) beneath the sea floor.
Examining the sediment cores on the ship, the researchers found small numbers of oxygen-consuming microbes in every sample from every depth. The samples were removed from the cores to see if their occupants could be resuscitated. They were given oxygen and their presumed food of choice, substrates of carbon and nitrogen, by syringe. The samples were then sealed in glass vials and incubated.
Growth of microbes after being fed carbon (top) and nitrogen (bottom)
Image source: Morono, et al
Vials were opened after 21 days, 6 weeks, and 18 months. Stunningly, up to 99 percent of the microbes were revived, even those from the deepest — and thus oldest — cores. Some had increased 10,000 times their number, consuming all of the carbon and nitrogen they'd been given.
The scientists could hardly believe what they were seeing. "At first I was skeptical, but we found that up to 99.1 % of the microbes in sediment deposited 101.5 million years ago were still alive and were ready to eat," recalls Morono.
A bottomless research opportunity
"It shows that there are no limits to life in the old sediment of the world's ocean," says D-Hondt. "In the oldest sediment we've drilled, with the least amount of food, there are still living organisms, and they can wake up, grow and multiply."
Some have suggested that the microbe may be more recent descendants of their 100-million-year-old ancestors, but D'Hondt says there isn't enough in the way of nutrients or energy down there to support cell division. That is, unless there's some other form of energy that has been overlooked, say, some form of radiation. "If they are not dividing at all, they are living for 100 million years, but that seems insane," he says.