November 5, 2003
It used to be believed that red sea urchins lived to be only seven to 15 years of age, experts say. But the newest findings are based on the use of two completely different techniques of determining sea urchin ages - one biochemical and the other nuclear - that produced the same results. The studies show red sea urchins can have a vast lifespan surpassing that of virtually all terrestrial and most marine animal species, and seem to show almost no signs of senescence, or age-related dysfunction, right up until the day that something kills them.
"No animal lives forever, but these red sea urchins appear to be practically immortal," said Thomas Ebert, a marine zoologist at OSU. "They can die from attacks by predators, specific diseases or being harvested by fishermen. But even then they show very few signs of age. The evidence suggests that a 100-year-old red sea urchin is just as apt to live another year, or reproduce, as a 10-year-old sea urchin."
The more mature red sea urchins, in fact, appear to be the most prolific producers of sperm and eggs, and are perfectly capable of breeding even when incredibly old. There is no sea urchin version of menopause.
Some of the new studies on this species were done with funding support from the Pacific States Fishery Commission to gain more information about the species, its life cycle, biology, survival rate, growth patterns, and perhaps shed light on why the red sea urchin resource was declining in some areas.
This small marine animal, which is found in shallow Pacific Ocean coastal waters from Alaska to Baja California and also elsewhere in the world's oceans, lives by grazing quietly on marine plants and deterring most predators with its pointy spines. Historically, it had been considered a nuisance.
"In the U.S. in the 1960s, sea urchins were considered the scourge of the sea, a real menace," Ebert said. "They ate plants in kelp forests and people believed they were at least partly responsible for the decline of that marine ecosystem, so they tried to poison them, get rid of them however possible."
But in the 1970s a commercial fishery developed in the U.S. based on sea urchins, which were sold primarily to Japan where their sex organs were considered a delicacy. They brought high prices, and at one point in the 1990s were one of the most valuable marine resources in California.
Ebert did some early work on the red sea urchin, along with colleagues Steve Schroeter at the University of California, Santa Barbara, and John Dixon, of the California Coastal Commission. It quickly became apparent that sea urchins, among other things, grew a lot more slowly and lived a lot longer than had been believed. "Sea urchins live as male and females, and fertilization of eggs takes place while they float in the ocean," Ebert said. "The larvae then feed for a month or more before turning into tiny sea urchins."
The red sea urchin, in fact, does grow fairly quickly when it's young - at the age of two years, it can grow from two centimeters to four centimeters in one year, doubling its size. But even at that, it still takes at least 6-7 years before the sea urchin is of harvestable size, the scientists say, compared to the two years that had previously been believed.
By the time the sea urchin is a teenager, its growth slows dramatically. And at the age of 22, researchers found it grew each year from about 12 centimeters to only 12.1 centimeters. But somewhat remarkably, it appears to never really stop growing. It's just very, very slow.
"Some of the largest and we believe oldest red sea urchins up to 19 centimeters in size have been found in waters off British Columbia, between Vancouver Island and the mainland," Ebert said. "By our calculations they are probably 200 or more years old."
The first studies indicating these ages was done with tagging of individual sea urchins and injection with tetracycline, which becomes incorporated into the sea urchin skeleton and can be used to track the growth rates. The latest work, which was just published, used measures of carbon-14, which has increased in all living organisms following the atmospheric testing of atomic weapons in the 1950s.
"Radiocarbon testing in this type of situation provided a very strong and independent test of growth rates and ages," Ebert said. "Among other things, it confirmed that in older sea urchins there is a very steady, very consistent growth that's quite independent of ocean conditions or other variables, and once they near adult size our research indicates they do not have growth spurts. With this species, it's pretty simple. The bigger they are, the older they are."
The research was done with red sea urchins, Ebert said, but may be at least partly relevant to other sea urchin species.
The study suggests, among other things, that this invertebrate species has a fairly poor ability to survive various threats during the first year of life and reach reproductive age. Otherwise there would be a great many more sea urchins.
Older sea urchins can help
provide more young and therefore may play a key role in creating
a sustainable fishery, so a return to harvest policies that limits
harvest above a certain size might be prudent, the researchers
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