Samoa Worm Sperm Spawns Annual Fiesta
for National Geographic News
|October 29, 2004|
It's nearly midnight on the Pacific island of Samoa. Several men are
pacing back and forth along the beach, staring at the ocean. One wades
into the water and lifts his Coleman lantern. Word spreads quickly:
The palolo are swarming.
Whole families grab homemade nets of mosquito netting or cheesecloth and wade into the sea. Men launch boats to scoop up the worms in deeper water. All around them palolo worms are thrashing in vast numbers, as thick as vermicelli soup. The water is milky with mucous.
Time is of the essenceit will all be over in a few short hours. Hardcore palolo connoisseurs grab the wriggling green-and-blue worms and swallow them raw on the spot. Most scoop them up in clumps and dump them into buckets.
The next day there's a celebrationa kind of Thanksgiving feast, Samoan style. The worms are fried in oil or baked into a loaf with coconut milk and onions. A new daily special shows up on local restaurant menus: palolo worm on toast. It's considered quite a delicacy.
What's a palolo worm? Any of more than a dozen species of segmented coral worm that shares certain distinguishing characteristics. In the South Pacific they are relatively well studied, because their annual risings are cause for local festivals.
What does the palolo worm taste like? "A little scratchy," said Kristian Fauchald, research zoologist and curator of worms at the Smithsonian Institution's National Museum of Natural History, in Washington, D.C. Others describe the flavor as a mix of seaweed and caviar. Fishy. Salty. Tart. Nutritious. It may be an acquired taste.
The palolo's curious behavior has attracted the attention of more than just hungry South Pacific islanders. The first biologists to describe the Samoan palolo scientifically, in the 19th century, made an interesting observation: The swarming worm has no head.
What biologists eventually discovered is that the swarming, writhing surface mass is not the actual worm itself, but rather its sperm and egg packets.
The palolo worm makes its home, according to Anja Schulze of the Smithsonian Marine Station, in the shallow reef, where it uses its sizeable jaws to dig itself a burrow in the limestone substrate. Most of the year it lives quietly, feeding on algae and microorganisms, small crustaceans, and even its own young.
As the time approaches for it to spawnwhich in Samoa usually happens in October or early Novemberthe palolo worm undergoes an extraordinary transformation. The organs in its posterior end, except those involved in reproduction, begin to degenerate.
Eventually these rear segments become little more than sacks engorged with either sperm or eggs. At exactly the right moment, Fauchald said, "the rear end starts some very heavy muscle contractions and eventually breaks off."
The liberated segments then start spiraling toward the surface. They float for up to an hour until the outer casings split open, spilling out their contents. Sperm fertilizes the floating eggs in a vast reproductive frenzy that happens just once a year and lasts only for a few hours.
But successful fertilization is not guaranteed. "There are several complicating factors," Fauchald said. "You must have an adequate sperm concentration. There must be enough mucous present to keep everything together, so that the spawning mass is not fragmented or washed apart. A storm would be a big problem." So would large quantities of predatory fish.
A few hungry islanders, by comparison, are the least of the worm's problems.
Once a successful swarming is over, the zygotesfertilized eggslive in the open water for only a few days before sinking to the bottom. There they burrow into the coral and grow into the next generation.
But what happens to the parent worms who so recently lost three quarters of their back end? "They don't necessarily die," Fauchald said. "Once the posterior has broken off, the anterior end promptly starts with wound-healing. They have to get their digestive tracts working fairly quickly, otherwise they won't be able to swallow." It takes about a week until they're fully healed, and then they start producing new segments to make up for the ones that were lost.
Timing Is Everything
Successful reproduction depends on getting all those packets to the surface at exactly the same time. But how does a worm that spends its life in a darkened burrow know when to release its sperm and eggs?
It's a question that interests the Samoans as well, and everyone has a favorite date.
Some say it happens three days after the new moon in October or November. Or a little after the last quarter of the first full moon in October.
Everyone agrees that the spawning follows the lunar cycle, and that it usually happens somewhere around the seventh night after the full moon that follows the autumnal equinox. If it's a weak showing, then a second rising can be expected in November.
To help find their way to the surface, the worms have a row of light-sensitive eyes along one side of their bodies. "Even on a cloudy night the surface will be lighter than the ground behind them," Fauchald said, "and that's enough to get them to the surface.
"Once the first worm goes, the presence of spawn in the water sets off all the others."
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