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Commercial and recreational marine fisheries

Red Sea Urchin Biology

General biology:

Red sea urchins are of separate sexes (diecious), which broadcast spawn (emit gametes into the water column simultaneously). This method of reproduction is rarely successful. Sea urchins must be in close proximity, be in perfect sync, then resultant larvae is at the whim of prevailing ocean currents.  New larvae stays in the water column for 6-8 weeks, where larvae lands is critical and depends on 1) direction of ocean currents and 2) larval behavior. Sea urchin larvae must settle on appropriate adult habitat in order to survive. In Oregon, these rocky, vegetated habitats are rare, therefore new larvae rarely lands on these and recruitment is rare.

What do you do if you rarely succeed in reproducing? You try a lot! Red sea urchins can live more than 100 years, and typically mature at 5-7 years. In this way, each sea urchin has many attempt to reproduce. Key management such are marine reserves allow the persistence of high density aggregations to further increase these chances.

The red sea urchin fishery targets urchins with ripe gonads, typically produced by good feeding. Red sea urchins are primarily herbivores, most often feeding on drifting bull kelp. If kelp is not available, sea urchins may eat whatever may be growing on rocks, often indiscriminately. If no food is available, sea urchins may also eat nothing or very little and simply not grow.

sea urchins in kelp bed

Two large red sea urchins with a small purple sea urchin in front, kelp in background.


Pentamerous symmetry:

Sea urchins are echinoderms (meaning spiny-skinned), closely related to sand dollars, sea stars, and sea cucumbers. Like those echinoderms, sea urchins have pentamerous (or pentaradial) symmetry, meaning “divided in five parts”, which is easily seen when looking at a sea urchin test. This type of symmetry can be found in many places in nature including in many flowers and even apples.

Urchin sand dollar blood star orange sea cucumber apple
A pentagon shape can be seen on the underside of a sea urchin test Five sided symmetry is obvious on the top of a Eccentric sand dollar, Dendraster excentricus. In sea stars, pentamerous symmetry is obvious in the fact that many have five arms, as in this blood star, Henricia leviuscula In the orange sea cucumber, Cucumaria miniata, five rows of tube feet show off their pentamerous symmetry An apple, also featuring pentamerous symetry.


Scott Groth- Marine Resources Program, Charleston
Phone:(541) 888-5515




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