Sanctuary Integrated Monitoring Network
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Species Database

Aplysia californica - California seahare

California seahare image

Geographic range:

Oregon to central Mexico

Key features:

Dorsal flaps separate, deep red, and can ink.

Similar species:

Aplysia vaccaria -- Black seahare


bay (rocky shore), bay (sandy shore), exposed rocky shore, kelp forest, protected rocky shore

Primary common name:

California seahare

General grouping:

Nudibranchs or sea slugs

ITIS code:


Geographic Range

Range Description:

Found in Japan and El Salvador. Occurs from Yaquina Bay, Oregon down through the Gulf of California and to Guaymas, Mexico.

Intertidal Height

Lowest intertidal height:

meters OR feet

Highest intertidal height:

meters OR feet

Intertidal height notes:

Can be found in the low intertidal, especially in tide pools.

Subtidal Depth Range

Minimum depth:

0 meters OR 0 feet

Maximum depth:

18 meters OR 59 feet

Subtidal depth notes:

Usually found in shallow depths (<10 m).


bay (rocky shore), bay (sandy shore), exposed rocky shore, kelp forest, protected rocky shore

Habitat notes:

Usually found in areas with abundant algae, although they can occur in adjacent sandy areas. Since sandy habitats lack algae for the seahares to consume, it is more likely these individuals were displaced by wave action and will attempt to return to the rocky reef and more suitable habitat.


Relative abundance:

Common in southern California. Rare in central California until 2011. Since 2011 or so, California seahares have become more commonplace. In particular, warm water years in 2014 and 2015 saw these animals become relatively common at shallow depths in Monterey and Carmel bays.

Species Description

General description:

The California seahare is a very large 'sea slug.' It has prominent rhinophores (tube-like projections at the anterior) that resemble rabbit ears, hence the common name seahare. Like many gastropods, it has a large foot, a rounded body akin to a tapered balloon, two dorsal flap-like projections (parapodia), and at the tip of the anterior below and in front of the rhinophores are two cephalic projections. The color is usually a pale red on the background and there are white and black speckles and lines, sometimes forming a reticulated pattern. Between the parapodia (which are not joined posteriorly) is an exhalant siphon.

Distinctive features:

Parapodia (dorsal, flap-liek projections derived from the foot) are not joined at the posterior (whereas they are joined for the congener A. vaccaria). Usually a deep red color, almost appearing a drab black, as adults, but pale red as juveniles. If disturbed, will exude a purple-red ink.


Up tp 40 cm in length.
Can weigh up to several kilograms.

Natural History

General natural history:

Seahares can be conspicuous members of the kelp forest community. They are important grazers, can attain large size, and then after spawning senesce. Although this species has been studied extensively, most of that work relates to laboratory studies, and use of the animal to investigate nervous system control, since the nerve cells are so large. Locomotion and neurological control of behavior have been extensively researched, but in terms of ecological impacts in the field, much less work has been completed.

California seahares are simultaneous hermaphrodites, having both male and female sex organs at the same time. They cannot self fertilize, so must find a mate to reproduce. Often mating aggregations form with 3 to 15 individuals, each slug serving as either a male, a female, or both at the same time.

Shortly after mating, or apparently sometimes during mating, individuals will begin laying eggs that are contained within a long, yellow, spaghetti-like string. Each string may contain millions of fertilized eggs. Different individuals will lay egg masses on top existing egg masses. This is likely an effort to spread the risk of mortality to the developing larvae, as this is essentially the most vulnerable stage of the life cycle.

Hatched veligers swim for 5 to 6 weeks before settling and metamorphosing on red algae, one of their preferred dietary items. Juveniles double their weight every 10 days for 3 months. Individuals are sexually mature about 120 days after hatching (i.e. emerging from the egg capsule). The life span is a year or less, which is amazingly short for such a large animal, but common to other mollusks. High egg production, short generation lengths, and local oceanic conditions lead to high variation in population densities from year to year.


There are very few predators of juveniles and adults, although in southern CA giant green anemones Anthopleura xanthogrammica have been observed feeding on them. Seahares do respond to contact by some sea stars and Navanax.


Seahares feed on algae. The color of the animal can be a reflection of its diet. Individuals fed only a diet of brown algae were no longer able to exude purple-red ink. The color of the ink is derived from a red pigment (phycoerythrin) in the consumed red algae.

Feeding behavior


Feeding behavior notes:

Seahares have very good chemosensory abilities, and essentially 'taste' the water, following chemical cues towards algae. They use there cephalic tentacles/podial extensions to grab algae, then use a radula to rasp off tissue.

May - October


Seahares aggregate in mating clusters and lay egg masses, which appear as white or yellow, spaghetti-like strings. See our Photo Library for example images.
Click on an image below to view a larger version in the SIMoN Photo Library. You will also be able to view important information on each photo such as photographer, date, caption and more.
Behrens, D.W. and A. Hermosillo. 2005. Eastern Pacific nudibranchs: a guide to the Opisthobranchs from Alaska to central America. Sea Challengers. 137 p.
Carlton, J.T. 2007.
The Light and Smith Manual, 4th edition
Intertidal Invertebrates from Central California to Oregon
University of California Press. 1001 p.

Morris, R.H., D.P Abbott, and E.C. Haderlie. 1980. Intertidal Invertebrates of California. Stanford University Press, Stanford, California. 690 p.