Showing posts with label Animal & Plant. Show all posts
Showing posts with label Animal & Plant. Show all posts

Monday, July 16, 2018

The Ocean Is A Strange Place After Dark

Moonlight triggers the world’s biggest orgy, strange creatures emerge from the depths, and waves glow blue. Some phenomena in the ocean can only be witnessed after dark.

1. Bioluminescence makes the sea shimmer

Dinoflagellates emit blue light when they’re disturbed
Dinoflagellates emit blue light when they’re disturbed, like at this bay on Vaadhoo Island in the Maldives (Credit: Naturepl.com/Doug Perrine)
You may have seen the pictures.

It’s night-time in an impossibly exotic location. Waves are breaking on the beach. The water is sparkling with electric blue lights.

The internet loves an image of a magical-looking bioluminescent bay. You may also have seen travel bloggers bemoaning the real event as not quite living up the hype.

Even if the latter is true, bioluminescence (in this case usually caused by planktonic organisms called dinoflagellates) is a pretty amazing natural phenomenon.

Dinoflagellates emit blue light when disturbed, which is why they can be seen sparkling over wave crests, around boats or when a hand or paddle runs through them.

These tiny creatures are the most common source of bioluminescence at the ocean’s surface.

So-called bioluminescent bays such as in Puerto Rico and Jamaica are among the best-known places to witness the glow. However, the ephemeral phenomenon can be found throughout the ocean where there are dense gatherings of dinoflagellates.

Sometimes dinoflagellates’ population increases rapidly causing blooms, which by day are coloured a less attractive red-brown, sometimes known as red tides. And some, but not all, of these red tides are poisonous.
These creatures provide the most common source of bioluminescence at the ocean’s surface
These tiny creatures provide the most common source of bioluminescence at the ocean’s surface (Credit: Naturepl.com/Martin Dohrn)
Even stranger and rarer than bioluminescent bays are “milky seas”, where continually glowing water stretches for as far as the eye can see.

Milky seas have only been seen a few hundred times since 1915, mainly concentrated around north-western Indian Ocean and near Java, Indonesia.

They are not caused by dinoflagellates, but are thought to be the result of “bioluminescent bacteria that have accumulated in large numbers near the surface”, explains to Dr Matt Davis, Assistant Professor of Biology, St. Cloud State University in the US, who specialises in bioluminescence.

Reports by sailors over the centuries have described milky seas as a nocturnal whitish glow like a field of snow, but scientists have had little chance to investigate the phenomenon first-hand.

In 2005, researchers analysing archived satellite images found that milky seas could be seen from space and that one satellite had captured images of a huge area of ocean that had displayed the strange glow for three consecutive nights a decade earlier.

2. Animals glow in the dark
Bobtail squid have a symbiotic relationship with bioluminescent bacteria
Bobtail squid have a symbiotic relationship with bioluminescent bacteria (Credit: Naturepl.com/Jurgen Freund)
Bioluminescence, the emission of visible light by an organism as the result of a natural chemical reaction, is common among marine life such as fishes, squid and molluscs. In the deep sea most species are bioluminescent, where it is the main source of light.

In shallower waters, most bioluminescent fish display their lights at night.

“Flashlight fishes have a specialized pouch under their eye that they can rotate to expose the light emitted from these bacteria, and they use this glow at night to hunt for food and communicate,” says Dr Matt Davis.
Flashlight fishes have a pouch under their eye used to expose bioluminescent bacteria
Flashlight fishes have a specialised pouch under their eye that use to expose bioluminescent bacteria (Credit: Matt Davis)
Ponyfish emit light from the bioluminescent bacteria housed in a pouch using transparent muscular shutters, to communicate, he explains.

Camouflage, defence and predation are among the variety of reasons fishes are thought to emit light.

For example, bobtail squid have an ingenious way of using lights. These nocturnal animals have a mutually beneficial relationship with luminescing bacteria that live in a mantel cavity on its underside. At night the squid control the intensity of this light to match the moonlight, and can reduce their silhouette to camouflage themselves from predators.

3. Moonlight triggers the planet’s biggest orgy
The biggest orgy on earth is triggered by moonlight [Credit: Naturepl.com/Jurgen Freund]
Mass spawning on the Great Barrier Reef is one of the extraordinary examples of synchronised behaviour on Earth (Credit: Naturepl.com/Jurgen Freund)
There is nothing more romantic than a moonlit night, especially if you are a coral on the Great Barrier Reef off Australia.

One night a year in spring, the biggest orgy on earth is triggered by lunar light.

Over 130 coral species simultaneously release their eggs and sperm into the water during a window of just 30-60 minutes.

This mass spawning event might be the most extraordinary example of synchronised behaviour in the natural world.

When the gametes – eggs and sperm cells - are released they hover for a moment, forming a ghostly replica of the reef’s shape, before dispersing into an underwater blizzard as the sperm fertilise the eggs.

Dr Oren Levy, a marine biologist and ecologist and Professor of Life Sciences at Bar-Ilan University, Israel, has studied this extraordinary event.

“This is really fascinating phenomena…we know this event is going to happen a few nights after November's full moon each year, three to five [days] post full moon,” he says.

“[It is] always amazing, in particular I am so amazed how each of the coral species year after year spawn at the same hour of the night.”

He adds: ”Once it happens it is always so exciting to see how everything is becoming so live and synchronised. It is almost [a] spiritual event and you understand the power of nature in its best.”

Moonlight triggers the phenomenon by acting as a synchroniser or “alarm” probably with other environmental signals such as sunset timings, water temperature and tides to cue the time of the gamete [egg and sperm cells] release, explains Dr Levy.

He adds that corals seem to possess photoreceptors that detect the phases of the moon, which helps with the “fine tuning” of the gamete release.

4. Sharks and seals rely on celestial light
A great white shark hunting at night
Just when you think it's safe to go into the water... great white sharks hunt at night too (Credit: Naturepl.com/Chris & Monique Fallows)
For some seals, moonlit nights spell danger.

During winter months, the 60,000 cape fur seals on Sea Island in False Bay, South Africa run the gauntlet of being picked off by great white sharks patrolling the seas when they enter and exit the water.

One study in 2016 hypothesised seals swimming at night during a full moon are at more risk of being eaten by a shark since bright moonlight silhouetting them against the surface makes them an easy meal for predators lurking below.

However, most shark attacks on seals happen just after sunrise. Researchers behind the study, which measured shark attacks at dawn, were surprised to find seals were much less likely to be predated at this time of day if there was a full moon.

The researchers theorised that lunar illumination combined with emerging sunlight may decrease the stealth ability of the sharks and that the advantage switched from sharks to seals as night turned to day.

And seals may rely on another celestial feature to navigate - the stars.

Captive harbour seals (Phoca vitulina) are able to locate a single lodestar and steer by it, researchers have shown.

During a test using a simulated night sky, seals swam towards the brightest star and could orientate themselves when the stars were swivelled around.

In the wild, seals need to navigate the open ocean to find foraging grounds that may be separated by hundreds of kilometres.

Researcher Dr Bjorn Mauck said at the time: "Seals might learn the position of the stars relative to foraging grounds during dawn and dusk when they can see both the stars and landmarks at the coast."

5. Strange animals come to the surface every night
Humboldt squid are among the most striking creatures to surface every night
Humboldt squid are among the most striking creatures to surface every night (Credit: Naturepl.com/Franco Banfi)
Under the cover of darkness rarely seen creatures migrate to the ocean’s surface to feed.

The Humboldt squid, also known as the jumbo squid, is one of the most eye-catching marine animals you can see lurking in surface waters.
By day the squid lurk in the deep waters of the Eastern Pacific Ocean along the deep shelf that runs off the west coast of the Americas and every night they are one of the many ocean animals to migrate upwards to find dinner.

Vertical (or diel) migration - when ocean animals swim to the surface at dusk and disappear down again at dawn – is extremely common.

“What [Humbioldt squid are] doing largely is following their main food item, which is the so-called lantern fish,” explains Professor Paul Rodhouse, an Emeritus Fellow for the British Antarctic Survey (BAS) and former head of the organisation’s biological sciences division.

In turn, lantern fish follow vertically migrating zooplankton.

Since zooplankton are depended on by so many ocean animals, “the rest of the food chain will be following on after it,” says Prof Rodhouse.

“It is a huge movement of biomass every day,” says Prof Rodhouse. “More than a thousand metres. Some of the oceanic squid probably migrate over 1000m every day.”

He adds that almost all pelagic species (animals that live in the water column not near the bottom or shore) that can swim make the journey.

Humboldt squid are among the most striking creatures to surface every night. Their ability to change colour and flash bright red when agitated has earned them the nickname “red devils”. Although much smaller than their cousin, the 13m-giant squid, they can reach a length of about 1.5m (almost 5ft). Highly aggressive predators, they capture prey with strong tentacles and suckers and tear into it with powerful beaks, and have reportedly occasionally attacked humans.

But even ferocious Humboldts are preyed upon by bigger predators such as billfish, swordfish and sharks.

“Of course what they are all doing [by being active at night] is avoiding predation by the top predators,” says Prof Rodhouse. "The big predators that are visual predators and which stay in the surface waters and see their prey.”

“So they’re all… reducing the risk of being preyed on by going down into deep, dark waters at night.”

at No comments:
Labels: , ,

Why Marine Animals Can’t Stop Eating Plastic

Plastic doesn’t just look like food, it smells, feels and even sounds like food.

In a recent interview about Blue Planet II, David Attenborough describes a sequence in which an albatross arrives at its nest to feed its young.

“And what comes out of the mouth?” he says. “Not fish, and not squid – which is what they mostly eat. Plastic.”

It is, as Attenborough says, heartbreaking. It’s also strange. Albatrosses forage over thousands of kilometres in search of their preferred prey, which they pluck from the water with ease. How can such capable birds be so easily fooled, and come back from their long voyages with nothing but a mouthful of plastic?

It’s small comfort to discover that albatrosses are not alone. At least 180 species of marine animals have been documented consuming plastic, from tiny plankton to gigantic whales. Plastic has been found inside the guts of a third of UK-caught fish, including species that we regularly consume as food. It has also been found in other mealtime favourites like musselsand lobsters. In short, animals of all shapes and sizes are eating plastic, and with 12.7 million tons of the stuff entering the oceans every year, there’s plenty to go around.

Even in the most remote areas of the open ocean, plastic flotsam can be found, with far-reaching consequences for marine life (Credit: BBC 2017)
Even in the most remote areas of the open ocean, plastic flotsam can be found, with far-reaching consequences for marine life (Credit: BBC 2017)

The prevalence of plastic consumption is partly a consequence of this sheer quantity. In zooplankton, for example, it corresponds with the concentration of tiny plastic particles in the water because their feeding appendages are designed to handle particles of a certain size. “If the particle falls into this size range it must be food,” says Moira Galbraith, a plankton ecologist at the Institute of Ocean Sciences, Canada.

Like zooplankton, the tentacled, cylindrical creatures known as sea cucumbers don’t seem too fussy about what they eat as they crawl around the ocean beds, scooping sediment into their mouths to extract edible matter. However, one analysis suggested that these bottom-dwellers can consume up to 138 times as much plastic as would be expected, given its distribution in the sediment.

For sea cucumbers, plastic particles may simply be larger and easier to grab with their feeding tentacles than more conventional food items, but in other species there are indications that plastic consumption is more than just a passive process. Many animals appear to be choosing this diet. To understand why animals find plastic so appealing, we need to appreciate how they perceive the world.

“Animals have very different sensory, perceptive abilities to us. In some cases they’re better and in some cases they’re worse, but in all cases they’re different,” says Matthew Savoca at the NOAA Southwest Fisheries Science Center in Monterey, California.

One explanation is that animals simply mistake plastic for familiar food items – plastic pellets, for example, are thought to resemble tasty fish eggs. But as humans we are biased by our own senses. To appreciate animals’ love of plastic, scientists must try to view the world as they do.
Many animals appear to be choosing a plastic diet (Credit: BBC 2017)
Many animals appear to be choosing a plastic diet (Credit: BBC 2017)
Humans are visual creatures, but when foraging many marine animals, including albatrosses, rely primarily on their sense of smell. Savoca and his colleagues have conducted experiments suggesting that some species of seabirds and fish are attracted to plastic by its odour. Specifically, they implicated dimethyl sulfide (DMS), a compound known to attract foraging birds, as the chemical cue emanating from plastic. Essentially, algae grows on floating plastic, and when that algae is eaten by krill – a major marine food source – it releases DMS, attracting birds and fish that then munch on the plastic instead of the krill they came for.

Even for vision, we can’t jump to conclusions when considering the appeal of plastic. Like humans, marine turtles rely primarily on their vision to search for food. However, they are also thought to possess the capacity to see UV light, making their vision quite different from our own.

Qamar Schuyler at The University of Queensland, Australia, has got into turtles’ heads by modelling their visual capabilities and then measuring the visual characteristics of plastics as turtles see them. She has also examined the stomach contents of deceased turtles to get a sense of their preferred plastics. Her conclusion is that while young turtles are relatively indiscriminate, older turtles preferentially target soft, translucent plastic. Schuyler thinks her results confirm a long-held idea that turtles mistake plastic bags for delicious jellyfish.

Colour is also thought to factor into plastic consumption, although preference varies between species. Young turtles prefer white plastic, while Schuyler and her colleagues found that seabirds called shearwaters opt for red plastic.

Every year, around 8 million metric tons of plastic waste enters the ocean (Credit: BBC 2017)
Every year, around 8 million metric tons of plastic waste enters the ocean (Credit: BBC 2017)

Besides sight and smell, there are other senses animals use to find food. Many marine animals hunt by echolocation, notably toothed whales and dolphins. Echolocation is known to be incredibly sensitive, and yet dozens of sperm whales and other toothed whales have been found dead with stomachs full of plastic bags, car parts and other human detritus. Savoca says it’s likely their echolocation misidentifies these objects as food.

“There’s this misconception that these animals are dumb and just eat plastic because it is around them, but that is not true,” says Savoca. The tragedy is that all these animals are highly accomplished hunters and foragers, possessing senses honed by millennia of evolution to target what is often a very narrow range of prey items. “Plastics have really only been around for a tiny fraction of that time,” says Schuyler. In that time, they have somehow found themselves into the category marked ‘food’.


Because plastic has something for everyone. It doesn’t just look like food, it smells, feels and even sounds like food. Our rubbish comes in such a range of shapes, sizes and colours that it appeals to a similarly diverse array of animals, and this is the problem. Schuyler recalls someone asking, “why don't we make all the plastics blue?”, seeing as experiments suggest this colour is less popular among turtles. But other studies have shown that for other species the opposite is true.

So if there is no ‘one size fits all’ solution, no aspect of plastic that we can easily change to prevent animals from eating it, then what can we take from our foray into the minds of plastic-eaters? Savoca hopes that tragic stories like Attenborough’s albatross will help to turn the consumer tide against disposable plastics and encourage people to empathise with these animals. Ultimately this will help to cut off the supply of junk food pouring into the oceans.

at No comments:
Labels:

Here’s Why Your Cat Loves Crawling Into Small Spaces



Sure, your cat might come off like an aloof, self-possessed loner, but he’s also proof that you don’t need to be affectionate to share a bond — and if nothing else, the two of you are bound by the fact that, like you, your cat has his own deeply weird, unshakable habits.

One of which, you may have noticed, is likely an affinity for small spaces. “As a panelist on Animal Planet’s “America’s Cutest Pets” series,” veterinarian Nicholas Dodman recently recalled in the Washington Post, he “was asked to watch video after video of cats climbing into cardboard boxes, suitcases, sinks, plastic storage bins, cupboards and even wide-necked flower vases.” You can see it for yourself with #CatSquare, a social-media phenomenon that boils down to this: Make a square on the floor with tape and your cat will definitely go hang out in it.


But that’s not even a real space! you say. It’s a metaphorical representation of a space! This is true. But as Dodman, author of Pets on the Couch: Neurotic Dogs, Compulsive Cats, Anxious Birds, and the New Science of Animal Psychiatry, explained in the Post, cats aren’t picky: More than anything, they crave the security of borders, no matter what form those borders take. “Instead of being exposed to the clamor and possible danger of wide-open spaces,” he wrote, “cats prefer to huddle in smaller, more clearly delineated areas”:

When young, they used to snuggle with their mom and litter mates, feeling the warmth and soothing contact. Think of it as a kind of swaddling behavior. The close contact with the box’s interior, we believe, releases endorphins — nature’s own morphinelike substances — causing pleasure and reducing stress … Seeking small spaces is part of cats’ behavioral repertoire, and such spaces are generally good.

So attached are cats to their nooks and crannies, in fact, that researchhas shown that giving boxes to shelter cats helps them to de-stress and adjust more easily to their new surroundings. Think of it like a spatial security blanket. And for the box-deprived cat, there’s always the option to relax with a little cat wine — just another way for you and your pet to have something in common.

at No comments:
Labels:
Subscribe to: Posts (Atom)