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Sea Urchins
Sea urchins play an important ecological role as grazers of
marine algae. When their predators such as
sea otters are absent, urchins can become very numerous.
In these situations, the seabed is stripped bare of marine
algae creating what is known as urchin barrens.
Three commonly encountered sea urchins along the Pacific coast
are the purple sea urchin Strongylocentrotus purpuratus,
red sea urchin S. franciscanus, and green sea urchin
S. droebachiensis. Purple sea urchins prefer high wave and
current-washed shores to a depth of 65 meters. In areas with
particularly high wave action, the urchin sometimes carves out
a depression in the rock to shelter it from the force of the
waves. There it relies on catching bits of algae drifting by
as food. Red sea urchins are the giants among sea urchins with
some individual attaining 30 cm in diameter. They live from
the intertidal to 125 meters depth. The green sea urchin is
found widely in sheltered locations away from surge.
References
Lamb, A and BP Hanby. 2005. Marine Life of the
Pacific
Northwest. Harbour Publishing, Madeira Park, BC.
Red
& Purple
Urchins
Photo Courtesy Rick Harbo
Marine Visions Ltd
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