Nudibranchs in the Tidepools

Nudibranchs, also referred to as sea slugs, can frequently be spotted in the tidepools at Haystack Rock. There are many species of nudibranch, most having outstanding markings and colors. The nudibranch feed on bryozoans, hydroids and sponges and it's color can be changed by the food it eats.   The nudibranch has a pair of sensory projections on their head, called rhinophores, which allow them to smell and taste. Virtually all nudibranchs have some form of eyes but they are not well developed and in most cases are little more than a pigment spot in the head near the rhinophores.  The nudibranch breathes through gill projections which extract oxygen from the seawater. The Pacific Northwest has more than 200 species of nudibranchs.

The Opalescent Nudibranch (Hermissenda crassicornis) could be called 'showy'. It is found from Alaska to Baja, California and can grow to two inches in size. At Haystack Rock, it can be found in the sandy bottom of a tidepool. It is slender with numerous gills (called cerata) that are orange with white tips. There is typically an orange area of the back that is bordered in blue, although the colors may vary.

Opalescent Nudibranch 

Opalescent Nudibranch with aggregating anemone

The Rufus Tipped Nudibranch (Acanthodoris nanaimoensis), on the other hand, is not nearly as showy as the Opalescent. This nudibranch has a white or gray body that is covered with projections with yellow tips, except for the gills which have red tips. It lives in the low intertidal zone and typically grows to just over 1 inch long.

Rufus Tipped Nudibranch

 Other Recent Sightings at Haystack Rock

Pile Worm (Nereis vexillosa)

Ochre Sea Stars (Pisaster ochraceus)

Purple Shore Crab (Hemigrapsus nudus)

This weekend will be eventful one on the sands of Cannon Beach; the 51st Sandcastle Contest is Saturday, June 20th. On your way to the sand creations, make sure to make a stop at Haystack Rock and discover the inhabitants of the tidepools for yourself! HRAP Interpreters are on the beach every day at low tide and are happy to point out the tidepool dwellers and answer your questions!


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