Log Transcript

This is Genevieve Johnson speaking to you from the Odyssey in Greece.

Sponges (Phylum porifera) first appeared in the sea over half a billion years ago and are the oldest living group of multicellular organisms on earth. While often referred to as 'primitive' or 'simple', they are in fact highly evolved organisms that have diversified into an estimated 5,000 to 9,000 species; although scientists believe these are probably conservative estimates. While having a comparatively straightforward body plan, sponges can live for 200 years or more exhibiting an astonishing array of growth forms. They range in size, shape and color from thin encrusting sheets to magnificent vases the size of a barrel or sofa, huge balls and giant lettuces. They are found at all latitudes of the marine environment from the intertidal zone to the deepest ocean trenches and in a variety of fresh water habitats, but are most abundant on the coral reefs of the tropics.

The biology of sponges is relatively unknown. They lack muscles, nerves and organs, have no digestive cavity or mouth and biological interactions within the sponge occur at the cellular level. A minute network of hard crystalline structures called spicules, flexible fibers and sometimes sand provides skeletal support, while collagen and spongen (protein) fibers produce the classic soft 'spongy' skeleton typical of many sponges.

Sponges are sedentary filter feeders structured to form a network of inhalant and exhalent canals. The inhalant canals originate as small pores on the outer surface leading inward and utilizing flagella to pump water through the body in one direction Ð creating a vacuum that sucks water through the sponge. Water carried through the animal is filtered of food particles, bacteria and oxygen and is expelled through the exhalent pores. Sponges can pump 4-5 times their volume of water in 1 minute. A sponge the size of a basketball can filter thousands of liters each day. Sponges remove about 90% of the bacteria from the water passing through them, making them the water purifiers in their respective habitats.

Sponges often form complex associations with other organisms, providing homes for a huge variety of animals including crabs, shrimps, sea stars, worms, barnacles, cucumbers and other sponges. Some residents earn their keep by grooming the sponge and keeping it clear of debris and parasites which could otherwise clog or kill the sponge. A multitude of microbes also live within the canals, between and even inside the cells. Scientists can only guess at the possible reasons for these relationships.

Sponges must compete with a host of other bottom dwelling invertebrates for space, particularly other sponges. 'Chemical warfare' is the most popular offensive strategy in deterring others that may try to attach or grow to close. Not surprisingly, scientists are researching what are some of nature's most toxic chemicals as potential sources of new pharmaceutical compounds. So far, several toxins are shown to demonstrate activity that may be effective in treating diseases such as arthritis, heart disease and even AIDS.

Homer first raved about the absorbent properties of sponges in 'The Odyssey' almost 3,000 years ago. However, today, sponges are in trouble. Commercial collection for 'bath sponges' means they have practically disappeared from the Eastern Mediterranean. In Greece, sponges are a $100 million-a-year industry. The Greek island of Kalymnos near Rhodes (Rodos) in the southern Aegean is the global headquarters for the sponge industry.

Divers armed with a knife and a netted pouch collect the sponges. When first brought to the surface, the coating of slime and jelly is smashed out of the sponge, usually by stomping on it with bare feet. The sponge is washed and bathed in seawater for several hours, then stomped on again. The process continues until only the soft skeleton remains. The sponge is clipped of its ragged edges and shaped ready for sale.

A sponge shop in Rodos. By selecting sponges for your bathroom that are grown in captivity you will help support sustainable sponge industries and protect threatened populations.

Photo : Chris Johnson

In almost every souvenir and tourist shop in the towns of ports the Odyssey visits, the crew sees sponges for sale on stands along docks and harbors.

For the 2004 Olympic Games in Athens, organizers ensured that more than 10,000 sponges be available as gifts for important guests in addition to the tens of thousands currently sold on the streets all over Greece. However, there are not enough Greek sponges to go around. Due to Olympic demand a new treaty negotiated with Libya allows Greece to access one of the largest known luxury sponge reserves in the world.

The Aegean Sea is no longer rich in sponges and the homegrown Greek sponge is now largely a myth. In fact, the majority of sponges for sale in Greece are removed from the reefs of the Caribbean, the Philippines, the Gulf of Mexico and the Bahamas. If the trends of the past few decades continue, divers will be lucky take more than a ton of sponges from the Aegean and little more from the rest of the Mediterranean. In addition to the over-harvest, an unknown bacterial infection is ravaging the remaining sponges causing them to disintegrate leaving scientists baffled by the cause.

Some sponges reproduce sexually with individuals releasing either eggs or sperm into the water synchronously, a phenomenon triggered by lunar cycles. However, many sponges reproduce asexually through a variety of methods including 'budding' and 'fragmentation'. This means that with many species, an individual can be cut into pieces and each will grow as a separate animal. This phenomenon forms the basis of efforts to establish sustainable and commercially valuable 'bath sponge' aquaculture industries. Selected species grown and farmed in captivity can double in size every few months and are used for harvest and to re-seed wild populations.

The demand for sponges in Greece employs thousands of people, but also puts lives at risk by continuing wild collection. Some call sponge diving "the most dangerous business on earth". Some divers make up to four dives a day to over 180 feet or 60 meters. Experienced recreational divers are advised to dive no deeper than 130 feet or 40 meters. Not surprisingly, the bends have a close and tragic historical association with the business.

Next time you are traveling or enter a shop and purchase a sponge for your bathroom, be sure to establish where it came from before buying it. Was it cultivated or taken from dwindling wild populations? Selecting your bath sponge wisely will help support sustainable sponge industries for years to come and protect threatened populations.

Links:

• What did the crew report on one year ago in Sri Lanka?
  Two years ago in the Seychelles?
  Three years ago in Australia?
  Four years ago crossing the Pacific Ocean -
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Log written by Genevieve Johnson.