Researchers Amy Johnson and Olaf Ellers are studying how sea urchins (and echinoderms in general) can grow. Somehow, they can do it without having to shed their shells or skeletal plates.
They discovered that as urchins grow, the collagenous tissue inside, outside, and between their skeletal plates softens. The shell inflates like a balloon. The collagen stretches and expands gaps between the plates from the inside, while containing them from the outside. Eventually, the tissue between the plates is reabsorbed and is replaced by hard shell. This mechanism is similar to the growth of a vertebrate skull. 
Scientists want to use this information to make “sea farms” of sea urchins possible. Only two experimental hatcheries are in use right now: a commercial one in Lubec, Maine, and another developed by the University of New Hampshire. If they are successful, they could “seed” areas overharvested for sea urchins to restore their populations. (Sea urchins are a delicacy in Japan. In 1993, 30 to 40 million pounds were harvested.)
They are still looking into what makes sea urchins reproduce, grow, and thrive. This research is complicated by the fact that it takes sea urchins six years to reach sexual maturity.
Right now they aren’t sure yet if sea urchin sea farms would be economically viable.
 Bowdoin Researchers Seek Methods to Spur Sea Urchin Growth
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