Watchable Wildlife: Sea Slugs
by Bob Garrison
Outdoor California - November 19, 1997
What do butterflies and slugs have in common? Well on land, not much. But take a trip to California's estuaries, bays or rocky coastline and you will be amazed at the delicate beauty of the over 130 species of sea slugs found along the Pacific shores. Found in every color of the rainbow, sea slugs have names that match their looks. Imagine what the Spanish shawl, white knight, clown nudibranch, crimson dorid, or speckled sea lemon must look like. Sea slugs even seem to flutter as ocean currents sweep over their soft, fragile bodies.
Sea slugs, like their land relatives, are closely related to snails. They all travel slowly on one foot, but most slugs lack a shell to protect their soft bodies. As a result, sea slugs have developed many ways to avoid being eaten. Some use mottled colors to hide against the rocks and kelp. Others use bright colors to announce they taste bad. If attacked, some sea slugs can swim away, shoot purple ink, or jettison the gills on their back much like a lizard loses its tail.
Most of these delicate animals are carnivores. Each species specializes in a different type of prey, from sponges and barnacles to other sea slugs. Many have cutting jaws and file-like rows of teeth called radula to scrape away flesh. The largest of the sea slugs is a vegetarian. The sea hare, named for two projections that look like rabbit ears, is over 12 inches long and feeds on algae in many bays and estuaries.
Although sea slugs are quite common, most are less than two inches in length and often hide beneath rocky ledges, under kelp or in the muddy bottoms of bays. They tend to be solitary and pair up only to breed. Sea slugs are hermaphroditic, maintaining both male and female organs in one animal. When two sea slugs mate, both are fertilized. Each one produces an egg mass which is unique in size, shape and color to that species. Some sea slugs produce up to a million eggs, others only a few.
TIPS for Viewing Sea Slugs
- Pick up a Field Guide -- if you are serious about identifying sea slugs, pick up Pacific Coast Nudibranchs by David W. Behrens. This guide contains color photos of over 150 species of sea slugs.
- View at Low Tide -- plan your trip to coincide with the lowest possible tides, generally those that occur near the times of a full or new moon. Pick up a tide chart at a sporting goods store and look for minus tides for the best viewing opportunities.
- Search in Deep Pools -- sea slugs are fragile and seek deep, sheltered tide pools with rock overhangs or mats of kelp.
- Look, Don't Touch -- gently push aside floating seaweed to look beneath, but leave the sea slugs and other animals alone.
- Tread Lightly -- stay out of the pools and carefully place each footstep to avoid stepping on sea life. Animals that can withstand crashing waves are easily crushed underfoot.
- Search Eel Grass and Algae Beds in Bays and Estuaries -- murky water can make viewing difficult. Look for quiet water rich with plant life.
Where to Watch Sea Slugs
Follow wildlife viewing road signs or check the California Wildlife Viewing Guide for directions to the following areas:
North Coast
- Patrick's Point State Park
- Shelter Cove/Lost Coast Wilderness
- MacKerricher State Park
- Salt Point State Park
Central Coast
- Elkhorn Slough National Estuarine Research Reserve
- Fitzgerald Marine Reserve
- Point Lobos State Reserve
- Montana de Oro State Park
South Coast
- Channel Islands National Park
- Bolsa Chica Ecological Reserve
- Crystal Cove State Park
- Cabrillo National Monument