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The Isopods of the Pacific Northwest

Isopods, Fish, Vancouver Island, BC Coastal Region, Pacific Northwest
Isopods, Photo By Bud Logan

The ligia occidentalis has a flat, mottled dark grayish green segmented body, 12 legs, a short forked tail and two long searching antennae. As you can see in the photos, these antennae are almost as long as their bodies, which is about an 2.5 cm. This marine creature is a member of the isopod family. You can find these isopods in inter tidal areas along beaches in the pacific northwest, including here on Vancouver Island, B.C.

The ligia occidentalis uses gills to breath which are located in the rear end and even though it spends most of the time out of the water, it has to make its way back to the water to breath on a regularly basis.

It feeds at night on different kinds of organic matter that it scavenges from rocks and pilings. It will spend the daylight hours hiding under rocks. It is eaten itself by seabirds and other small creatures that are able to catch it, it has the ability to run quite fast.

The females emit a pheromone to attract males, the males then produce a package of sperm to fertilize the female’s eggs. The female can produce an egg case with up to 100 embryos in it. The average lifespan of these isopods is about a year but they can reproduce as many as eight times during their life.

Beach isopods are scavengers, nibbling on whatever recently died on the rocky shore. At low tide, they swarm over the beach looking for the recent dead. Isopods can be found under rocks or clinging to the holdfasts, stalks or blades of seaweed at high tide.  They are also sometimes found in mussel beds.

Isopods have a myriad of different predators that include foraging shore birds and fish.

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