Crustaceans get the spotlight at Birch Aquarium lecture in La Jolla
By Zoe Kleinfeld
Oh, isn’t it fab to be a young crab? They molt off young age to acquire new sage, and brave brackish waves in La Jolla’s dark caves. Crustaceans spelunk with abandon and punk! But if one might have thunk local shellfish surreptitious, there’s more to a shrimp than being delicious. So read on about prawn, and learn something new! See below for an exposé that is long overdue.
Our local ecological reserve is host to countless crustaceans — barnacles, shrimp, crabs and spiny lobsters. Compared to the relative dearth of diversity of local human citizens, La Jolla’s crustaceans constitute an incredibly varied group of arthropods.
Just in terms of size, they can range from fractions of an inch to several feet long. And they live just about anywhere — deep in the briny sea, grass marshlands, even on land!
Jennifer Taylor — an assistant professor at the Scripps Institution of Oceanography — dipped into this vast realm of crustaceans in the latest of a series of public colloquiums at Birch Aquarium on June 9. Her presentation considered the evolution and biomechanics of crustacean’s exoskeleton, and illuminated how crabs grow into their new shells.
Crustaceans are unique in that they have an exoskeleton, or an exterior skeletal body. The body is comprised of a four-layer cuticle, which is arranged in a specific shape that forms a “helicoid pattern,” not unlike the structure of DNA. Such configuration is generally uniform among crustaceans and gives them an exceptionally strong and lightweight outer shell that adapts to different functions — including support, motion, weaponry and communication.
Crustaceans shed their exoskeletons on a regular basis in a process that has been recognized as the most gruesome weight-loss fad ever. In the initial stages of the practice, the molting crustacean assumes a temporary dormant state while its underlying skin cells separate from the exterior shell. During this resting period, the animal secretes fluids to expedite the transformative process; the old skeleton cracks at pre-formed suture levels and water seeps in. Once enough water has built up, the newly molted crab can wriggle free of its former self.
In fact, everything (even the gut lining!) is molted when a crab sheds its skeleton for growth. Akin to any major body-transformation, the new version of the animal is delicate. Before a freshly molted crab’s new shell has hardened through calcification, the animal is entirely soft and flimsy.
In response to their fragile condition, crustaceans use water pressure to replace the hardness of the shell. By inflating their body with fluid, crustaceans create a pseudo-armor against which they can contract their muscles. This temporary system is comparable to a water balloon because the animal can change shape, but resists compression. In this way, every time the crab contracts any muscle — claw, or otherwise — the inner fluid acts as a stiff element against the body wall.
A similar phenomenon occurs in land-bound crabs. Yet in lieu of water, these animals inflate their gut with air — like blowing up an internal balloon.
Beside our crabby counterpart’s striking presence, the animals are also a very important commercial species (see: local restaurants, California rolls, etc.), and have biomechanical lesson for us humans to boot. At this point, crustaceans’ strong and lightweight exoskeleton structure has led to modification in armory, helmets, plane and car shells.
If this news was of your amuse — and you want to hear more about our local seashore — then go to the Birch for other talks on research! July 14, sharks are the topic.
— If You Go: Doors open at 6:30 p.m., lecture begins at 7 p.m., Monday, July 14, 2300 Expedition Way, La Jolla. Admission: $8, students/educators $5, free for members. (858) 534-7336. aquarium.ucsd.edu
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