anglicky - Expedition Reef for Educators | California Academy of Sciences

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(ambient noise)

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Coral reefs color our world.

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Their beauty captivates us. Their diversity astounds us.

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We build aquariums to house these treasures.

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But their greatest value lies in the natural world.

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♪ (gentle music) ♪

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Here, near Devil's Point in the Philippines,

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we are immersed in one of Earth's most diverse ecosystems--

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a system that harnesses the power of the Sun

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through a unique collaboration between animals and algae.

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A system that supports thousands of species

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by making efficient use of often scarce nutrients.

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Hidden in these nooks and crannies, we find a multitude of organisms,

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in a complex web of connections.

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A moray eel gets a little help from its friends--

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a dental exam from cleaner shrimp and cleaner wrasse fish.

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They eat small parasites that can make the eel sick.

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A win-win, mutualistic relationship.

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Not all interactions turn out so well.

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A crown-of-thorns starfish devours coral,

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leaving bare white skeletons in its wake.

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A tiny Trapezia crab successfully defends its coral home

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from the much bigger creature.

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And a brightly-colored nudibranch

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dines on sponges growing on the reef.

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Its colors warn predators to stay away--

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chemicals ingested by the nudibranch make it poisonous.

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We observe these species and many more,

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but what we can't see are all the relationships

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that link them to one another.

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Most importantly, they take part in a food web,

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overlapping connections of producers and consumers,

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predators and prey.

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Humans take part in this food web, too.

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And coral reefs support more complex food webs

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than any other places on the planet.

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What makes these places special?

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We'll depart from the Philippines

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to explore where we find reefs around the globe.

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Although coral reefs support a quarter of ocean species,

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they cover far less than one percent of the oceans' area.

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Coral reefs thrive in the parts of the globe

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that receive the most sunlight.

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Earth's equator divides our planet

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into the northern and southern hemispheres,

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and a band around the equator-- the tropics--

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receives consistent sunlight throughout the year.

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Coral reefs line about a third of tropical coastlines.

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This part of our world takes in the most energy from our star,

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the Sun.

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That energy fuels coral reef food webs

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and supports the remarkable diversity of reef ecosystems.

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Coral reefs are the largest structures built by animals,

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and they take three basic forms:

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barrier reefs, fringing reefs, and atolls.

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Australia's Great Barrier Reef is the largest reef in the world.

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A barrier reef follows its shoreline,

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with lagoons separating the reef from the coast.

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Here in Curaçao, just off the coast of South America,

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we see a fringing reef, which grows directly from the shoreline,

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forming a border along the coast.

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And this is Ant Atoll in the western Pacific Ocean.

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An atoll forms when a volcanic island sinks beneath sea level,

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leaving behind a ring of coral.

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All these reefs are built by animals

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that harness the power of the Sun to make rock from water.

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This Philippine reef includes many species of living coral.

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Delicate soft corals are more common,

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but it's mostly the hard corals that construct reefs.

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And they've been doing that job for more than a hundred million years!

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To understand how corals build reefs, we need to see how they live.

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Each coral is actually made up

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of a colony of tiny animals called coral polyps.

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And like all animals, they eat.

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A polyp captures its prey.

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Similar to the sting of its relative, the jellyfish,

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the coral harpoons its meal

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with microscopic hooks released from its tentacle.

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The polyp then draws the copepod into its mouth to digest.

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These meals provide an important source of energy.

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But most of the coral's energy comes from someplace very different.

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We need to look more closely to find it.

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The inner layers of the polyp's tissue provide a home to algae

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called zooxanthellae.

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These algae give the coral its color,

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and more importantly, they harness light from the Sun

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through a process called photosynthesis.

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The algae that live inside the coral convert sunlight

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into energy-rich sugars and amino acids.

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Corals absorb up to 90 percent of that fuel!

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In exchange, the algae depend on waste from the polyps

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as a source of nutrients.

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This efficient recycling allows corals to thrive in tropical waters,

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where intense competition can make nutrients hard to come by.

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Let's look inside a polyp to see how it helps build a reef.

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It takes carbon from algae and seawater

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and turns it into calcium carbonate.

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When you breathe, you exhale carbon dioxide--

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all animals do, including corals.

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But their carbon combines with calcium from the ocean

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to create calcium carbonate.

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Corals use this chalky compound to build their skeletons.

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Hard coral polyps push away from the surface on which they reside,

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then fill the gaps with calcium carbonate.

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Repeating this process over and over,

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they help construct entire reefs.

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Corals can build a reef at a rate of several centimeters per year.

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Speeding up time allows us to watch the coral community grow,

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as individuals compete for resources on the reef.

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This slow, steady process can go on for a long time.

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Some reef structures are centuries old.

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Ocean currents and other factors can change the coral's shape.

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The same species can look quite different,

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depending on something as simple

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as how fast the surrounding water is moving.

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We call this attribute plasticity.

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Corals' flexible response to their environment

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helps them adapt to a changing world.

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And while we are most familiar

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with the colorful, shallow reefs we have visited so far,

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we know that reefs extend far below these sunny realms.

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Explorers from the California Academy of Sciences

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study these deep reefs in a region nicknamed the Twilight Zone.

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Unlike shallow reefs, corals here survive with little light.

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Without abundant solar energy, corals eat more, dining on tiny animals

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that take refuge at these depths to escape predators above.

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The plasticity of corals serves them well

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in this low-light environment.

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Some species have adapted pigments used as sunblock above,

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making them fluorescent at these depths.

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The pigments tune weak light to colors

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that algae can use for photosynthesis.

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Scientists plunge up to five times deeper than a regular scuba diver

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to examine these rarely seen reefs.

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Every visit reveals new discoveries.

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These benthic ctenophores, for example.

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The small, sticky jellies cling to abandoned fishing lines,

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extending long, slender tentacles to grab prey and reel it in rapidly.

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Each expedition provides clues

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to conserving and restoring these ecosystems.

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Deep or shallow, these reefs inhabit one vast ocean.

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They are connected to each other by the geography of the ocean floor

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and the currents flowing through them.

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Corals migrate on ocean currents

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that carry eggs and larvae to new homes,

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enriching reefs along the way.

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Humanity, too, is connected to this underwater world.

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Just as corals depend on algae to survive, humans depend on reefs.

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Half a billion people rely on coral reefs for food and income.

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Many have learned to harvest the reefs' bounty sustainably

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in a way that supports healthy reef ecosystems.

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But reefs provide more than food. They also provide protection.

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Hurricanes, typhoons, and cyclones form over the tropical ocean,

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sometimes doing serious damage when they make landfall.

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In 2017, tropical cyclone Debbie struck northeast Australia,

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seen here in satellite images.

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Satellites have tracked tropical storms over many seasons,

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so we can speed up time to observe their movement.

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Bolder lines indicate more intense storms.

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Healthy reefs protect land from the damaging effects

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of these tropical storms.

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Here we see the Mesoamerican Barrier Reef,

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the largest coral reef in the Atlantic Ocean.

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When Hurricane Dean struck Mexico's Yucatán Peninsula in 2007,

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the reef helped shield the shoreline.

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Scientists created a computer simulation to understand how this works.

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Reefs dissipate waves' energy—

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reducing wave height and slowing the water

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before it crashes into shore.

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Worldwide, reefs protect hundreds of millions of people

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living in coastal communities.

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We need to ensure the health of coral reefs to reap their benefits.

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Here in the Caribbean,

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reefs have suffered from decades of overfishing,

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and humans continue to impact reefs around the globe.

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Development on land can create runoff into the ocean

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that smothers coral reefs.

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And pollutants such as plastic and pesticides

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can make the problems even worse.

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In addition to these local challenges, reefs face global threats.

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Rising sea temperatures and ocean acidification endanger reefs.

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Burning coal and oil and other fossil fuels

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introduces carbon dioxide into Earth's atmosphere,

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trapping heat and warming our planet-- including the oceans.

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The shallow waters of the Caribbean

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heat up more quickly than the ocean's depths,

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so reefs here experience the effects of warming more acutely.

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Let's visit Curaçao's fringing reef,

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where we can witness these effects firsthand

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and also learn what scientists are doing

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to help ensure reefs' survival.

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♪ (gentle music) ♪

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Shallow reefs are particularly sensitive to increasing temperatures.

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Warming water can cause coral bleaching

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when an entire colony of coral polyps loses its color.

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Let's visit an individual polyp to see how this happens.

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Too much light or heat causes the coral's algae

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to release chemicals that damage the host.

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The stressed coral expel their algae,

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sacrificing their primary energy source in doing so--

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much like an over-reactive immune system.

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Because corals lose their natural color when they lose their algae,

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we call this coral bleaching.

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Bleached corals are sick, but not dead.

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Algae can re-colonize bleached corals

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if conditions improve quickly enough.

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So bleached reefs can recover.

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And some corals seem resistant to bleaching altogether.

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These survivors-- whether it's the animals or their algae,

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or some combination of the two--

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could provide assistance to less resilient corals.

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But recovery takes time,

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a long time when slowed by ocean acidification--

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another by-product of excess carbon dioxide in our atmosphere.

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These colonies may take years or decades to recuperate,

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so we need to find ways to speed their recovery.

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Let's look at our coral reef ecosystem in a different way.

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Each species carries genetic code-- a molecular book of instructions

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that varies slightly from one individual to another.

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Some passages offer survival strategies for a changing world.

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When animals reproduce, they share these instructions,

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which can lead to more successful offspring.

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Each individual that disappears is a volume

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in the species' genetic library which is lost forever.

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This is why maintaining diversity within a species is important.

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To reproduce, corals release their genetic material

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into the surrounding water, typically at night.

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Because corals can't mingle to mate,

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they let the ocean currents do the matchmaking.

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A spawning event can occur at the same time

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among many species along a reef.

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Corals sense changes in daylight and water temperature--

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even the light of the full moon.

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These cue the corals to release bundles of sperm and eggs

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that float upward, drifting with the current.

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Fertilized eggs will develop into free-swimming larvae,

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which eventually settle onto a suitable surface and grow into polyps.

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Scientists are exploring methods to help corals reproduce

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perhaps a thousand times more successfully.

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They rescue fertilized eggs from predators,

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then rear the larvae in a lab before returning them to the wild.

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This teacup-sized pyramid is home to small coral colonies,

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each of which started off as a single, resilient polyp.

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The polyps will divide and grow,

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establishing a new home on the ocean floor.

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Much like encouraging new growth in a forest,

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scientists plan to introduce millions of resilient corals

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into overstressed reefs.

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We have visited only a few ecosystems enriched by corals.

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But in these places-- and many others--

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we hope to unlock the secrets to coral reefs' survival.

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Their survival means we benefit

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from their protection, from their bounty, and from their beauty.

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With our help,

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future generations of corals will continue to color our world.

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♪ (gentle music) ♪

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← Expedition Reef for Educators | California Academy of Sciences

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← Expedition Reef for Educators | California Academy of Sciences

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