Sharks Terrorize Reef Fish In The Shallows, Changing When And Where They Eat Seaweeds

By Christie Wilcox | November 30, 2017 8:00 am
shark_fiji

A seascape of fear? New study suggests fear of sharks shapes ecosystems. Photo Credit: Narchuk/Shutterstock

It’s kind of incredible how our fears can shape our behaviors. When Jaws was released in 1975, it fundamentally changed how we interact with sharks. In the years that followed, we hunted these large marine predators more intensely, and came to view them as terrible monsters—attitudes scientists still fight to this day. But while our fears are largely unfounded, there are lots of species that have good reason to be wary of these awesome fish. Scientists have now discovered that such fear can ripple through the reef ecosystem, impacting community structure all the way down to seaweeds.

There’s no doubt that sharks can be a bit terrifying, especially if you’re a snack-sized fish. Scientists have long suspected that such fear can alter behavior. Just like people that are scared of sharks avoid beach vacations, preyed upon fish might try to avoid areas where sharks roam in the hopes of steering clear of those sharp, pointy teeth. And where the fish avoid, the species they eat proper, a marine version of ‘when the cat’s away, the mice will play.’ Thus by creating landscapes of fear—or, in this case, seascapes—sharks could shape entire ecosystems even if the amount of prey they actually consume is negligible.

Cascading effects have been shown for other predators. The mere sound of dogs barking can terrorize raccoons so much that they forget to eat. And when that happens, the myriad of species the raccoons hunt, from birds to crabs, flourish. But overall, demonstrations of the ‘landscapes of fear’ hypothesis are rare.

Not only do we not know how fear of sharks might shape marine habitats, our overall understanding of how sharks interact with other species is lacking. Despite our annual fin-fests and obsession with these fearsome fish, “we still only have a very basic understanding of their ecological roles in nature,” said Doug Rasher, a senior research scientist at Bigelow Laboratory, in a press release. So he and his colleagues decided to look a little closer, zeroing in on the impacts of sharks on shallow reef habitats off the coast of Fiji.

A diagram of the shallow lagoons studied. Figure 1 a and b from Rasher et al. 2017.

A diagram of the shallow lagoons studied. Figure 1 a and b from Rasher et al. 2017.

The well-lit, shallow lagoons of Fiji’s largest island, Viti Levu, are ideal habitat for tasty seaweeds like Turbinaria conoides, a favorite of herbivorous fish. Since the islanders established a no-take reserve protecting the fringing reef of Votua Village, Korolevu-i-wai, in 2002, the abundance of seaweeds has dropped dramatically, particularly in the more isolated back reefs, making room for corals to rebound. But not all areas of the lagoons are equally seaweed-free. The algae remain in the shallowest reef tops. Rasher and his colleagues wanted to understand why.

The research team put GoPros in the water to observe which fish were eating algae as well as when and where sharks were moving around the lagoons. They also surveyed for the presence of algae-eating fish during high and low tides, and to determine seaweed location and abundance. In addition, they calculated fish feeding rates on algae in shallow and deeper back reef areas during different tidal phases by deploying measured amounts of algae for the fish to snack on.

When they brought all that data together, a clear pattern emerged. The biggest predators like blacktip reef sharks (Carcharhinus melanopterus), whitetip reef sharks (Triaenodon obesus,) and tawny nurse sharks (Nebrius ferrugineus) only entered the back reefs when tides were high—the researchers estimated that on average, each 40 square meter section of backreef is trawled by 4 to 5 reef sharks and 1 jack during each high tide. And when that happened, the herbivorous fishes like unicornfishes (Naso lituratus and N. unicornis) pretty much stopped eating and disappeared, presumably steering clear of the meandering predators.

That meant that the shallow reef tops received very little attention by the algae-eaters, as they could only be accessed when the reef sharks entered the shallows to feed. And in turn, those reef tops sported about 20 times the amount of seaweed. The researchers ruled out the possibility that these algae just do better on the reef tops for other reasons, like increased amounts of light, by comparing the growth rates of caged weeds in both areas. So the stark difference between the tops and deeper troughs in the backreef appears to be driven mostly by the fish’s fear of sharks.

A 2013 study in Shark Bay, Australia, had similar results, finding the risk of tiger shark predation affected the nature and abundance of seagrasses. Combined, they paint a much more interesting picture of the role sharks play in marine habitats. Their effects go far beyond what they consume directly, so their mere presence can “actually shape the way [an ecosystem] looks and functions,” explained Rasher.

On the practical side, these results suggest that we might be able to reduce our fishing impacts by taking this kind of thing into account. “Our example highlights the need to consider predator effects in ecosystem-based management,” the authors write in their conclusions. “With knowledge of predator movements and resultant herbivore migrations, resource managers could mitigate this negative human impact in similar ecosystems by regulating not only where but when herbivores are harvested.”

And ultimately, they underscore the need to better understand the ecological importance of sharks and other large predators. “Large apex predator sharks as well as the large mesopredator reef sharks studied here are now generally rare or absent on coral reefs exposed to heavy fishing pressure; thus, the effects we documented may already be extinguished from many places,” the authors write. “Despite these difficulties, we need to study Earth’s remaining wild places where predators still abound, and capitalize on chance events and variability in nature… Only then can we understand the ramifications of predator loss or recovery.”

 

Citation: Rasher et al. 2017. Cascading predator effects in a Fijian coral reef ecosystem. Scientific Reports 7, 15684. doi:10.1038/s41598-017-15679-w

CATEGORIZED UNDER: Ecology, More Science, select, Top Posts

Turd Tales: Did You Know You Can Sex A Turkey By Its Poo?

By Christie Wilcox | November 23, 2017 1:00 pm
Gobble gobble! Photo Credit: Michael Tatman/Shutterstock

Gobble gobble! My poops look a lot like yours! Photo Credit: Michael Tatman/Shutterstock

In the U.S., it’s Thanksgiving, which means today is all about the Turkey. So here’s a fun fact you may not have heard to chew on as you masticate your meal: you can tell a turkey’s sex by it’s poop. Read More

CATEGORIZED UNDER: More Science, select, Top Posts
MORE ABOUT: Thanksgiving, Turkeys

Crab Gloats After Winning To Discourage Rematches

By Christie Wilcox | November 7, 2017 8:00 am
After a win, mangrove crabs (Perisesarma eumolpe) will gloat to keep opponents from going for round two. Photo Credit: Marut Sayannikroth/Shutterstock

After a win, mangrove crabs (Perisesarma eumolpe) will gloat to keep opponents from going for round two. Photo Credit: Marut Sayannikroth/Shutterstock

From touchdown dances to victory laps, we all love to bask in the glory after a big win. So do mangrove crabs. After a fierce physical altercation, victorious male crabs sometimes stridulate, planting one claw into the ground and rubbing it vigorously with the other to both visibly and audibly revel in their triumph. But the purpose of this gloating was unclear, as little research has examined the consequences of such victory displays. Now, a new paper in Ethology may have an explanation: rejoicing discourages the losing crabs from attempting a rematch. Read More

CATEGORIZED UNDER: Ecology, More Science, select, Top Posts

From Longest Name to Loudest Sound, Scientists Catalog Over 100 Spider World Records

By Christie Wilcox | October 31, 2017 11:00 pm
C'mon, you're not really afraid of this cute little guy, are ya? Photo Credit: Plamuekwhan/Shutterstock

C’mon, you’re not really afraid of this cute little guy, are ya? Photo Credit: Plamuekwhan/Shutterstock

Few groups of animals are as feared as spiders. Doctors estimate at least 5% of people are arachnophobic, meaning they are terrified of the eight-legged critters. But such fear is largely misplaced. Of the nearly 47,000 species of spider on the planet, only 200 or so can actually bite through our tough skin and deliver venom that causes any kind of reaction. And of those, only a few are considered truly dangerous. Rather than fearing them, we should be in awe of just how incredibly diverse, successful, and unique these animals are.

But turning fear into fascination is no easy feat. Hopefully, a new paper in PeerJ can help. Stefano Mammola and his colleagues have meticulously summarized these octo-appendaged wonders, documenting dozens of incredible facets of their diverse anatomies, behaviors, and lifestyles. Read More

MORE ABOUT: PeerJ, Records, Spiders

Real Halloween Horrors: Corpse Cosplay by Zodarion Spiders

By Christie Wilcox | October 31, 2017 12:00 pm
An ant-hunting Zodarion maculatum spider. Photo by Antonio Pizarro via iNaturalist

An ant-hunting Zodarion maculatum spider. Photo by Antonio Pizarro via iNaturalist

Humans in North America only spend one night a year in costume with the hopes of feasting on tasty treats. For Zodarion spiders, that’s just called Tuesday. These clever mimics pretend to be ants to sneak close to their prey. And if in danger, they’ll use the corpse of their latest capture to complete the charade. Read More

CATEGORIZED UNDER: Evolution, More Science, select, Top Posts

The Mechanics of Dolphin Sex: All The Dirty Details You Need To Know

By Christie Wilcox | October 10, 2017 6:01 pm
It takes a lot of pressure to simulate an erection like this. Photo by Vladimir Wrangel

It takes a lot of pressure to recreate an erection like this. Photo by Vladimir Wrangel

Perhaps the hardest part about studying marine mammal reproductive anatomy using organs collected from deceased animals is that they can’t get an erection the easy way.

Reinflating human penises postmortem is a relatively trivial feat, says Diane Kelly, a research assistant professor at University of Massachusetts and penis inflation expert. Like most mammals, human penises are mostly fleshy, with lots of vascular space for blood to flow into to make the flaccid structure rigid with turgor pressure. But whale and dolphin penises are a lot tougher—quite literally. “It’s actually a real challenge to artificially inflate cetacean penises,” she told me. Yes, the size makes things difficult—it takes a lot more saline to fill a large penis than a small one—but it’s more than that. “They have what’s called a ‘fibroelastic’ penis,” she explained, which means their penile tissue contains “a lot of collagen, and it makes the penis, even when flaccid, very stiff and less extensible.”

Finding a way around this hard problem is a large part of why Dara Orbach and Patricia Brennan brought Kelly on to the project. The goal: make the first 3-D CT scans of simulated intercourse of any marine mammal species using real, post-mortem genitalia—scans that were just published in a paper in Proceedings of the Royal Society B. Read More

CATEGORIZED UNDER: Evolution, More Science, select, Top Posts

Whistling While They Work: Cooperative Laguna Dolphins Have A Unique Accent

By Christie Wilcox | September 30, 2017 10:40 pm
Fishermen working with a cooperative dolphin to enhance their catch. Photo Credit: Carolina Stratico

Fishermen working with a cooperative dolphin to enhance their catch. Photo Credit: Carolina Stratico

When the mullet migrate northward, the fishermen in Laguna, Brazil are waiting. They rise early and take their places in line, waist-deep in the water, tarrafa—a kind of circular throwing net—in hand. Without a word, the dolphins arrive, herding schools of mullet towards the fisher line. The fishers say that the dolphins are an essential part of their fishing; they wait to fish until their marine helpers to arrive, in some cases standing for an hour or more, calling to the animals: “let’s work”. The fishers work as a unit, trading out their spots in line as the dolphins fill their nets.

But while the humans are united, the dolphin community is divided. Only some of the population cooperate with fishers in this manner. Scientists discovered that the ones that work with people form their own cohesive social network, separate from the other dolphins in the area. “The cooperative fishery appears to have influenced the structuring of this bottlenose dolphin population into social communities,” explain Bianca Romeu and her colleagues at Brazil’s Universidade Federal de Santa Catarina in a new paper this month in the journal Ethology. Their latest work reveals the depth of this rift: the cooperative dolphins don’t just behave differently, they communicate differently, too.

Read More

An Unprecedented Number Of Species Have Crossed The Pacific On Tsunami-Liberated Plastic Debris

By Christie Wilcox | September 28, 2017 1:00 pm
These Asian amur sea stars (Asterias amurensis) were found ~5,000 miles from home on the Oregon coast. Image provided by Oregon State University

These Asian amur sea stars (Asterias amurensis) were found ~5,000 miles from home on the Oregon coast.
Image provided by Oregon State University

March 11, 2011, 2:46 PM, 45 miles east of Tōhoku, Japan. Fifteen miles beneath the waves, a magnitude-9 megathrust earthquake strikes. The Pacific and Eurasian tectonic plates suddenly shift, shaking the surrounding crust for six minutes and creating a tidal wave almost 40 meters high, which races towards the coast of Japan. In the hours that follow, it claims at least 15,894 lives, with thousands more unaccounted for. More than a million buildings are damaged or destroyed, causing nearly $200 billion in damages.

The remnants of those buildings and all sorts of debris liberated by the moving waters have since spread the tsunami’s legacy far beyond the site of impact. As a new study in the journal Science explains, thanks to objects set adrift by the tsunami’s waves, more than two hundred and eighty species have been found on the wrong side of the ocean.

How did hundreds of animals hitch rides across such vast distances? Well, to paraphrase the slogan from America’s Plastics Makers, plastics made it possible. Read More

CATEGORIZED UNDER: Ecology, More Science, select, Top Posts

Birds of a Feather Hunt Better Together

By Christie Wilcox | September 26, 2017 6:01 pm
le there's no I in TEAM, each penguin benefits from hunting together. Photo credit Sergey Uryadnikov

While there’s no I in TEAM, each penguin benefits from hunting together. Photo credit Sergey Uryadnikov

They say that many hands make light work. Well, for African penguins, many beaks make for bountiful hunts, according to a new study in Royal Society Open Science. The results suggest that dwindling populations may have greater consequences than previously realized.

African penguins (Spheniscus demersus), or “jackass” penguins after their donkey-like calls, are currently endangered. Found only on the southern tip of Africa, populations of these flightless birds have dropped from an estimated 4 to 5 million in 1800 to a mere 50,000 or so animals today. Their situation is considered so dire that, if the penguins do not begin to rebound soon, it’s predicted they’ll go extinct in about a decade. Read More

CATEGORIZED UNDER: Ecology, More Science, select, Top Posts

Tiny Bat Shrugs Off Stings From Deadly Scorpion

By Christie Wilcox | August 31, 2017 1:46 am
These tough bats can tussle with the deadliest scorpions in North America and win. Photo by Connor Long

These tough bats can tussle with the deadliest scorpions in North America and win.
Photo by Connor Long

Pallid bats (Antrozous pallidus) are quirky little creatures, the sole species in their genus. Their long ears, which can equal half their body length, make them look quintessentially batty, but unlike most of their night hunting relatives, they prefer to tackle ground-dwelling dinners—a strategy called “gleaning.” Pallid bats glean as much as half their body weight in prey every night, and their diet includes a wide range of crunchy little critters, including crickets, praying mantis, and beetles.

It is their taste for scorpions, though, that is particularly intriguing, and piqued the curiosity of scientists. It was unknown whether the bats have a trick for catching scorpions that keeps them from being stung, or whether they are resistant to the animals’ agonizing toxins. In a new PlosONE paper, researchers show it’s the latter: the bats’ laissez-faire attitude towards venom stems from an invulnerability to scorpion neurotoxins due to alterations in the voltage-gated sodium channels that the toxins target. Read More

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