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← Expedition Reef for Educators | California Academy of Sciences

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Showing Revision 16 created 04/22/2019 by Marília Correia.

  1. (ambient noise)
  2. Coral reefs color our world.
  3. Their beauty captivates us. Their diversity astounds us.
  4. We build aquariums to house these treasures.
  5. But their greatest value lies in the natural world.
  6. ♪ (gentle music) ♪
  7. Here, near Devil's Point in the Philippines,
  8. we are immersed in one of Earth's most diverse ecosystems--
  9. a system that harnesses the power of the Sun
  10. through a unique collaboration between animals and algae.
  11. A system that supports thousands of species
  12. by making efficient use of often scarce nutrients.
  13. Hidden in these nooks and crannies, we find a multitude of organisms,
  14. in a complex web of connections.
  15. A moray eel gets a little help from its friends--
  16. a dental exam from cleaner shrimp and cleaner wrasse fish.
  17. They eat small parasites that can make the eel sick.
  18. A win-win, mutualistic relationship.
  19. Not all interactions turn out so well.
  20. A crown-of-thorns starfish devours coral,
  21. leaving bare white skeletons in its wake.
  22. A tiny Trapezia crab successfully defends its coral home
  23. from the much bigger creature.
  24. And a brightly-colored nudibranch
  25. dines on sponges growing on the reef.
  26. Its colors warn predators to stay away--
  27. chemicals ingested by the nudibranch make it poisonous.
  28. We observe these species and many more,
  29. but what we can't see are all the relationships
  30. that link them to one another.
  31. Most importantly, they take part in a food web,
  32. overlapping connections of producers and consumers,
  33. predators and prey.
  34. Humans take part in this food web, too.
  35. And coral reefs support more complex food webs
  36. than any other places on the planet.
  37. What makes these places special?
  38. We'll depart from the Philippines
  39. to explore where we find reefs around the globe.
  40. Although coral reefs support a quarter of ocean species,
  41. they cover far less than one percent of the oceans' area.
  42. Coral reefs thrive in the parts of the globe
  43. that receive the most sunlight.
  44. Earth's equator divides our planet
  45. into the northern and southern hemispheres,
  46. and a band around the equator-- the tropics--
  47. receives consistent sunlight throughout the year.
  48. Coral reefs line about a third of tropical coastlines.
  49. This part of our world takes in the most energy from our star,
  50. the Sun.
  51. That energy fuels coral reef food webs
  52. and supports the remarkable diversity of reef ecosystems.
  53. Coral reefs are the largest structures built by animals,
  54. and they take three basic forms:
  55. barrier reefs, fringing reefs, and atolls.
  56. Australia's Great Barrier Reef is the largest reef in the world.
  57. A barrier reef follows its shoreline,
  58. with lagoons separating the reef from the coast.
  59. Here in Curaçao, just off the coast of South America,
  60. we see a fringing reef, which grows directly from the shoreline,
  61. forming a border along the coast.
  62. And this is Ant Atoll in the western Pacific Ocean.
  63. An atoll forms when a volcanic island sinks beneath sea level,
  64. leaving behind a ring of coral.
  65. All these reefs are built by animals
  66. that harness the power of the Sun to make rock from water.
  67. This Philippine reef includes many species of living coral.
  68. Delicate soft corals are more common,
  69. but it's mostly the hard corals that construct reefs.
  70. And they've been doing that job for more than a hundred million years!
  71. To understand how corals build reefs, we need to see how they live.
  72. Each coral is actually made up
  73. of a colony of tiny animals called coral polyps.
  74. And like all animals, they eat.
  75. A polyp captures its prey.
  76. Similar to the sting of its relative, the jellyfish,
  77. the coral harpoons its meal
  78. with microscopic hooks released from its tentacle.
  79. The polyp then draws the copepod into its mouth to digest.
  80. These meals provide an important source of energy.
  81. But most of the coral's energy comes from someplace very different.
  82. We need to look more closely to find it.
  83. The inner layers of the polyp's tissue provide a home to algae
  84. called zooxanthellae.
  85. These algae give the coral its color,
  86. and more importantly, they harness light from the Sun
  87. through a process called photosynthesis.
  88. The algae that live inside the coral convert sunlight
  89. into energy-rich sugars and amino acids.
  90. Corals absorb up to 90 percent of that fuel!
  91. In exchange, the algae depend on waste from the polyps
  92. as a source of nutrients.
  93. This efficient recycling allows corals to thrive in tropical waters,
  94. where intense competition can make nutrients hard to come by.
  95. Let's look inside a polyp to see how it helps build a reef.
  96. It takes carbon from algae and seawater
  97. and turns it into calcium carbonate.
  98. When you breathe, you exhale carbon dioxide--
  99. all animals do, including corals.
  100. But their carbon combines with calcium from the ocean
  101. to create calcium carbonate.
  102. Corals use this chalky compound to build their skeletons.
  103. Hard coral polyps push away from the surface on which they reside,
  104. then fill the gaps with calcium carbonate.
  105. Repeating this process over and over,
  106. they help construct entire reefs.
  107. Corals can build a reef at a rate of several centimeters per year.
  108. Speeding up time allows us to watch the coral community grow,
  109. as individuals compete for resources on the reef.
  110. This slow, steady process can go on for a long time.
  111. Some reef structures are centuries old.
  112. Ocean currents and other factors can change the coral's shape.
  113. The same species can look quite different,
  114. depending on something as simple
  115. as how fast the surrounding water is moving.
  116. We call this attribute plasticity.
  117. Corals' flexible response to their environment
  118. helps them adapt to a changing world.
  119. And while we are most familiar
  120. with the colorful, shallow reefs we have visited so far,
  121. we know that reefs extend far below these sunny realms.
  122. Explorers from the California Academy of Sciences
  123. study these deep reefs in a region nicknamed the Twilight Zone.
  124. Unlike shallow reefs, corals here survive with little light.
  125. Without abundant solar energy, corals eat more, dining on tiny animals
  126. that take refuge at these depths to escape predators above.
  127. The plasticity of corals serves them well
  128. in this low-light environment.
  129. Some species have adapted pigments used as sunblock above,
  130. making them fluorescent at these depths.
  131. The pigments tune weak light to colors
  132. that algae can use for photosynthesis.
  133. Scientists plunge up to five times deeper than a regular scuba diver
  134. to examine these rarely seen reefs.
  135. Every visit reveals new discoveries.
  136. These benthic ctenophores, for example.
  137. The small, sticky jellies cling to abandoned fishing lines,
  138. extending long, slender tentacles to grab prey and reel it in rapidly.
  139. Each expedition provides clues
  140. to conserving and restoring these ecosystems.
  141. Deep or shallow, these reefs inhabit one vast ocean.
  142. They are connected to each other by the geography of the ocean floor
  143. and the currents flowing through them.
  144. Corals migrate on ocean currents
  145. that carry eggs and larvae to new homes,
  146. enriching reefs along the way.
  147. Humanity, too, is connected to this underwater world.
  148. Just as corals depend on algae to survive, humans depend on reefs.
  149. Half a billion people rely on coral reefs for food and income.
  150. Many have learned to harvest the reefs' bounty sustainably
  151. in a way that supports healthy reef ecosystems.
  152. But reefs provide more than food. They also provide protection.
  153. Hurricanes, typhoons, and cyclones form over the tropical ocean,
  154. sometimes doing serious damage when they make landfall.
  155. In 2017, tropical cyclone Debbie struck northeast Australia,
  156. seen here in satellite images.
  157. Satellites have tracked tropical storms over many seasons,
  158. so we can speed up time to observe their movement.
  159. Bolder lines indicate more intense storms.
  160. Healthy reefs protect land from the damaging effects
  161. of these tropical storms.
  162. Here we see the Mesoamerican Barrier Reef,
  163. the largest coral reef in the Atlantic Ocean.
  164. When Hurricane Dean struck Mexico's Yucatán Peninsula in 2007,
  165. the reef helped shield the shoreline.
  166. Scientists created a computer simulation to understand how this works.
  167. Reefs dissipate waves' energy—
  168. reducing wave height and slowing the water
  169. before it crashes into shore.
  170. Worldwide, reefs protect hundreds of millions of people
  171. living in coastal communities.
  172. We need to ensure the health of coral reefs to reap their benefits.
  173. Here in the Caribbean,
  174. reefs have suffered from decades of overfishing,
  175. and humans continue to impact reefs around the globe.
  176. Development on land can create runoff into the ocean
  177. that smothers coral reefs.
  178. And pollutants such as plastic and pesticides
  179. can make the problems even worse.
  180. In addition to these local challenges, reefs face global threats.
  181. Rising sea temperatures and ocean acidification endanger reefs.
  182. Burning coal and oil and other fossil fuels
  183. introduces carbon dioxide into Earth's atmosphere,
  184. trapping heat and warming our planet-- including the oceans.
  185. The shallow waters of the Caribbean
  186. heat up more quickly than the ocean's depths,
  187. so reefs here experience the effects of warming more acutely.
  188. Let's visit Curaçao's fringing reef,
  189. where we can witness these effects firsthand
  190. and also learn what scientists are doing
  191. to help ensure reefs' survival.
  192. ♪ (gentle music) ♪
  193. Shallow reefs are particularly sensitive to increasing temperatures.
  194. Warming water can cause coral bleaching
  195. when an entire colony of coral polyps loses its color.
  196. Let's visit an individual polyp to see how this happens.
  197. Too much light or heat causes the coral's algae
  198. to release chemicals that damage the host.
  199. The stressed coral expel their algae,
  200. sacrificing their primary energy source in doing so--
  201. much like an over-reactive immune system.
  202. Because corals lose their natural color when they lose their algae,
  203. we call this coral bleaching.
  204. Bleached corals are sick, but not dead.
  205. Algae can re-colonize bleached corals
  206. if conditions improve quickly enough.
  207. So bleached reefs can recover.
  208. And some corals seem resistant to bleaching altogether.
  209. These survivors-- whether it's the animals or their algae,
  210. or some combination of the two--
  211. could provide assistance to less resilient corals.
  212. But recovery takes time,
  213. a long time when slowed by ocean acidification--
  214. another by-product of excess carbon dioxide in our atmosphere.
  215. These colonies may take years or decades to recuperate,
  216. so we need to find ways to speed their recovery.
  217. Let's look at our coral reef ecosystem in a different way.
  218. Each species carries genetic code-- a molecular book of instructions
  219. that varies slightly from one individual to another.
  220. Some passages offer survival strategies for a changing world.
  221. When animals reproduce, they share these instructions,
  222. which can lead to more successful offspring.
  223. Each individual that disappears is a volume
  224. in the species' genetic library which is lost forever.
  225. This is why maintaining diversity within a species is important.
  226. To reproduce, corals release their genetic material
  227. into the surrounding water, typically at night.
  228. Because corals can't mingle to mate,
  229. they let the ocean currents do the matchmaking.
  230. A spawning event can occur at the same time
  231. among many species along a reef.
  232. Corals sense changes in daylight and water temperature--
  233. even the light of the full moon.
  234. These cue the corals to release bundles of sperm and eggs
  235. that float upward, drifting with the current.
  236. Fertilized eggs will develop into free-swimming larvae,
  237. which eventually settle onto a suitable surface and grow into polyps.
  238. Scientists are exploring methods to help corals reproduce
  239. perhaps a thousand times more successfully.
  240. They rescue fertilized eggs from predators,
  241. then rear the larvae in a lab before returning them to the wild.
  242. This teacup-sized pyramid is home to small coral colonies,
  243. each of which started off as a single, resilient polyp.
  244. The polyps will divide and grow,
  245. establishing a new home on the ocean floor.
  246. Much like encouraging new growth in a forest,
  247. scientists plan to introduce millions of resilient corals
  248. into overstressed reefs.
  249. We have visited only a few ecosystems enriched by corals.
  250. But in these places-- and many others--
  251. we hope to unlock the secrets to coral reefs' survival.
  252. Their survival means we benefit
  253. from their protection, from their bounty, and from their beauty.
  254. With our help,
  255. future generations of corals will continue to color our world.
  256. ♪ (gentle music) ♪