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  • Coming up next on Jonathan Bird's Blue World, Jonathan explores the biology of sponges,

  • and you might be surprised at what he finds!

  • Hi, I'm Jonathan Bird and welcome to my world!

  • When people think of a sponge, they usually imagine something like this: a cleaning sponge

  • for washing the dishesor for washing the car. Cleaning sponges are synthetic these

  • days, but they used to come from the ocean.

  • Back in the days before we had synthetic sponges for housework, cleaning sponges did come from

  • the ocean. They were harvested by hard-hat divers walking along the ocean floor in heavy

  • weighted boots with a rake-like tool to pluck the sponges off the bottom. It was a dangerous

  • and difficult job.

  • Bagfuls of sponges were lifted to the boat above. Immediately, the crew set to work cleaning

  • the sponges. Then they were hung to air dry. After days or weeks at sea, when the boat

  • was full of sponges, they were taken to shore, where they were auctioned to the highest bidder.

  • Finally they were trimmed, sorted and sold to the public.

  • Natural sponges are still harvested in nearly the same way today, but the synthetic sponge

  • has spared the lives of countless ocean sponges!

  • While an ocean sponge looks something like a weird plant, it's actually an animal.

  • In fact, sponges are among the simplest multi-cellular animals on Earth. They live on the bottom

  • of the ocean, attached to a surface and never moving because they can't walk or swim. Some

  • are quite colorful, while others are drab. They also come in all shapes and sizes. There

  • are tube sponges, vase sponges, barrel sponges, rope sponges, encrusting sponges and many

  • other types. Sponges live from the frigid waters of the arctic and Antarctic, to the

  • tropics. On many coral reefs, sponges dominate the sea floor and the drop off.

  • One of the most common sponges on coral reefs is the barrel sponge. Barrel sponges grow

  • to epic proportions, getting larger than a person!

  • Although sponges can't walk or swim, they can feed. They do it by filtering tiny plankton

  • from the water.

  • A sponge is covered with small pores, called ostia, which lead to a system of internal

  • canals and eventually out to one or more larger holes, called oscula. Within the canals of

  • the sponge, chambers are lined with specialized cells called choanocytes, or collar cells.

  • The collar cells have a sticky, funnel shaped collar and a hairlike whip, called a flagellum.

  • The collar cells serve two purposes. First, they beat their flagella back and forth like

  • fans to move water through the sponge. The water brings in nutrients and oxygen, while

  • it carries out waste and carbon dioxide. Second, the sticky collars of the collar cells pick

  • up tiny bits of planktonic food brought in with the water.

  • Sponges are very effective filter feeders, since they are able to capture and eat particles

  • as small as bacteria as well as much larger particles. They might not look like they are

  • doing much, but a simple demonstration shows how effectively sponges can pump water.

  • On a reef in the Caribbean, I make a dive with a syringe filled with a non-toxic dye

  • called fluorescein. By squirting it around the base of some sponges, we can observe how

  • the water is moving by watching what the dye does.

  • Within only seconds, the dye is pumped through the sponges along with the water. As you can

  • see, a sponge is a pretty good water pump, and also a good strainer. Any plankton that

  • goes in with the water, won't come back out through the osculum.

  • Tube sponges are even more spectacular to observe. They pump the dye so furiously that

  • they look like a collection of miniature smoke stacks!

  • The ultimate test is a hefty barrel sponge! What will a big monster like this do? It takes

  • a few seconds for the dye to work its way through the spongebut then it pours out

  • like smoke from a chimney. That's pretty good pumping from those tiny little collar cells!

  • Since sponges can't get together to reproduce, they spawn in a way similar to coral. The

  • sperm is released into the water column by the male sponge and finds its way to the female

  • sponges, where fertilization occurs internally. Eventually, the planktonic larvae are released

  • from the female sponge and float around in the water column as plankton for only a few

  • days. They then settle down and start growing.

  • Sponges don't have many predators. There is not much nutritional value in a sponge and

  • they're hard to digest. Hence, very few animals can eat sponges. But something was clearly

  • eating this sponge! A sea turtle is the culprit. Sea turtles are one of the principal predators

  • of sponges, along with a few species of fish and some invertebrates like nudibranchs.

  • Sponges might not be very exciting and they certainly don't have much personality, but

  • they're an ancient animal that has been living in the oceans for at least half a billion

  • years! They can't crawl around, or swim, but they are very good at reproducing and feeding

  • themselves by pumping water. So, chances are, sponges will continue to populate the oceans

  • longer than people will populate the Earth.

Coming up next on Jonathan Bird's Blue World, Jonathan explores the biology of sponges,

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ジョナサン・バードの青い世界海綿!? (Jonathan Bird's Blue World: Sponges!)

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    張凱堯 に公開 2021 年 01 月 14 日
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