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  • As the sun rises over a quiet coral reef, one animal breaks the morning silence.

  • Named for their vibrant scales and beak-like teeth,

  • these parrotfish are devouring a particularly crunchy breakfast: rocks.

  • It may not be immediately clear why any creature would take bites

  • out of the seafloor.

  • But the diet of these flashy foragers actually plays a key role

  • in defending the coral reef's complex ecosystem.

  • Massive coral reefs begin with tiny coral larvae,

  • which settle on the seafloor's hard surfaces

  • and metamorphasize into coral polyps.

  • Over time, these polyps generate rock-like skeletons

  • made of calcium carbonate.

  • Together, colonies of polyps produce large three-dimensional structures,

  • which form the basis of an underwater metropolis.

  • These coral complexes are full of nooks and crannies

  • that house and protect countless life forms.

  • Even though coral reefs occupy less than one percent of the ocean floor,

  • these dense ecosystems are home to more than twenty-five percent of marine life.

  • Many fish use corals as shelters for sleeping and to hide from large predators

  • between their trips foraging for seaweed.

  • As the primary food source for many of the reef's fish and invertebrates,

  • seaweed is vital to this ecosystem.

  • But in high densities, seaweed can become problematic,

  • and even lethal to corals.

  • Seaweed grows on the same hard open surfaces that coral larvae rely on,

  • and their growth prevents new coral from settling and expanding.

  • These competitors have also evolved a variety of ways to kill existing corals,

  • including smothering and abrasion.

  • Some seaweed species even engage in chemical warfare

  • synthesizing compounds that destroy coral on contact.

  • This is where parrotfish come in.

  • Like many reef fish, these colorful creatures eat seaweed.

  • But unlike their neighbors,

  • parrotfish can completely remove even the tiniest scraps of seaweed

  • from the ocean floor.

  • Their so-called beak is actually a mosaic of tightly-packed teeth

  • which can scrape and grind rock,

  • allowing them to consume every bit of seaweed covering a stony surface.

  • This helps parrotfish reach seaweed other fish can't consume,

  • while simultaneously clearing out open space for new corals

  • to settle and existing colonies to expand.

  • Eating rocks is just one way parrotfish help manage seaweed.

  • Through a dynamic system of social networks,

  • parrotfish can convey information to other coral dwelling fish.

  • Each fish's presence and simple routine behaviors produce sensory information

  • that nearby fish can see, hear, or smell.

  • They can even detect changes in water pressure produced by their neighbors

  • using a special sensory organ.

  • All these factors can inform the behavior of nearby fish.

  • For example, a fish safely entering an open feeding ground

  • and not getting attacked means it's safe to forage.

  • Conversely, a fish rapidly leaving a location can provide an early warning

  • that a threat is approaching.

  • By simply trying to stay alive,

  • these reef fish can incidentally help their neighbors survive

  • and more of these fish means less seaweed.

  • Unfortunately, human activities over the last several decades

  • have disrupted almost every part of this complex system.

  • In many coral reefs, overfishing has reduced the number of parrotfish,

  • as well as other seaweed eaters, such as surgeonfish and rabbitfish.

  • This has led to unchecked seaweed growth,

  • which threatens to degrade entire coral reefs.

  • The parrotfish that remain live in much smaller communities.

  • Their reduced numbers can weaken their social network,

  • making surviving fish more timid and less effective at controlling seaweed.

  • Today, climate change and pollution are lowering coral's natural defenses

  • while contributing to runaway seaweed growth

  • leaving reef ecosystems more fragile than ever.

  • Our reefs are vitally important to both marine and human life.

  • Their unparalleled biodiversity offers unique opportunities for ecotourism,

  • sustainable fishing, and scientific research,

  • while their rocky structures guard coastlines from waves and storm surges.

  • Fortunately, continued research into reef species

  • like the quirky and critical parrotfish can inform new strategies

  • for preserving these essential ecosystems.

As the sun rises over a quiet coral reef, one animal breaks the morning silence.

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B2 coral seaweed parrotfish fish reef seafloor

The big-beaked, rock-munching fish that protect coral reefs - Mike Gil

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    林宜悉 posted on 2020/10/25
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