Small (2-5 cm) greenish-colored body, often with pink-tipped tentacles; large rounded tubercles arranged in vertical rows on column, often covered in sand and shells; radiating lines in oral disc; can form dense aggregations.

These anemones can reproduce asexually or sexually; asexually by producing clones of themselves by longitudinal fission. All individuals in a group are members of a single clone, and are genetically identical to one another. Each clone is either male or female and all members produce either sperm or eggs.

Aggregating anemones are a major space occupier that competes with algae, mussels, and honeycomb tubeworms.

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

The low, shield-like, smooth shell of this abalone is dark blue, dark green, or almost black in color. Shell can reach lengths of 20 cm or more and contains a line of holes used for ventilation. Tentacles are black.

Natural predators of the abalone include octopuses, whelks, sea stars, fish, sea otters, and humans.

Abalone populations once occurred at a density of 60 to 80 individuals per square meter and dominated the intertidal in southern California. This species has experienced population decline due to overfishing, poaching, and disease (i.e., withering syndrome) throughout its range and has gone locally extinct in most locations south of Point Conception.

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

UCSC’s Pacific Coast Rocky Intertidal Monitoring: Haliotis cracherodii (Black Abalone)

For more information visit the NOAA Fisheries Species Directory for Black Abalone

Chitons are a basal group of mollusks. They are oval in shape and have 8 separate, overlapping calcareous plates. The plates are embedded in a tough muscular girdle. They can be many different colors and can be easily overlooked because they are often small and well camouflaged.

Like snails and limpets, chitons have a long tongue-like radula used for feeding. The radula has rows of strong, iron-capped teeth that scrape algae off of the rocks. Although they have no real “head” they have many tiny eyes in their shells.

Important grazers of algae in the intertidal.

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

Balanus glandula is moderate in size (~2 cm), white with a diamond-shaped operculum and more heavily ribbed walls. Chthamalus dalli/fissus is smaller (<1 cm), brownish with an oval shaped operculum, and smoother walls.

As adults, barnacles are hermaphrodites. They fertilize one another internally by means of a long penis. The eggs are brooded by the parent and released as nauplius larvae.

Competitors for space in the high and mid zone. Major prey for many intertidal species. Susceptible to high mortality from oil spills because oil can stick to high intertidal habitat.

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

UCSC’s Pacific Rocky Intertidal Monitoring: Chthamalus/Balanus (Acorn Barnalces)

Large, solitary anemone up to 25 cm in diameter (10 inches), same size as sunburst anemone or larger; olive-green to bluish green disc without radiating lines; small irregular tubercles arranged haphazardly on column gives this beautiful creature a velvet-like texture.

Stinging cells called cnidocytes are located within the tentacles of all anemones. These cells help the anemone to paralyze its prey; however, stinging cells of California anemones do not harm humans when touched, but those of some tropical species cause painful stings.

This is a northern species. Though it occurs from Alaska to northern Baja California, it is restricted to upwelling areas in the southern part of its range. Distribution of this species may shift farther north if global warming continues. Major space competitor and predator, associated with mussels.

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

Rocky intertidal hermit crabs in California are represented by the family Paguridae. They live in the abandoned shells of snails to protect their soft abdomens. Carapace grows to approximately 2 cm in length. P. hirsutiusculus, abundant in the mid zone, has white bands on walking legs, dark antennae with fine white bands, and a dark orange-brown body. P. samuelis is the most abundant hermit crab in the high zone of central and southern California. It has a hairy carapace and legs, blue bands on walking legs, and red antennae.

Hermit crabs can be choosey about the shells they live in.
P. hirsutiusculus prefers the shells of olive snails while P. samuelisprefers the shells of turban snails.

Important scavengers of dead plant and animal matter. Sensitive to pollution. Fun to count.

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

These marine solitary, polychaete worms form large aggregations of cemented sand-grain tubes. Tubes form masses up to 2 m in length and are positioned in a honeycomb arrangement, each tube with a flared rim. Though the group of tubes looks like a colony, each tube is the result of one individual worm settling near other worms and building its home. These worms are up to 5 cm in length and bear a crown of lavender tentacles.

This worms captures sand with its tentacles and transports the grains to an organ behind the mouth. Liquid cement is added to the sand for the construction of the walls of its tube.

Major space competitor, mid zone indicator.

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

Barnacle on dark, fleshy stalk; up to 8 cm in length; the top is covered with more than 5 white plates and surrounded by scales.

These barnacles are a main food source for Glaucous-winged Gulls. In Europe, humans harvest and eat another species of leaf barnacles.

Mid zone indicator; major space competitor with mussels.

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

UCSC’s Pacific Rocky Intertidal Monitoring: Pollicipes (Goose Barnacle)

Limpets are a group of gastropod mollusks with one uncoiled cone-shaped or flattened shell. Their muscular foot helps them cling to rocks. There are a handful ofLottia species that inhabit the rocky intertidal of California: the shield limpet (L. pelta), ribbed limpet (L. austrodigitalis/digitalis), rough limpet (L. scabra), file limpet (L. limatula), owl limpet (L. gigantea), and others. These limpets range from 12 mm to 10 cm in size. Shell color varies, though most are brownish and mottled and are well camouflaged.

Limpets often remain motionless during low tide during the day, but move about and forage at night, mainly during low tide. Some limpets will return after grazing to their own unique resting spot on the rock known as a “home site.” On soft rock, they chew out a depression in which their shells just fit, but on hard rock their shell grows to fit the rock.

Major grazers and prey for shorebirds.

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

Stanford’s SeaNet: Rocky Shore Limpets

Sea star typically has 5 arms, but rarely has from 4-7; aboral surface with many small white spines; average length is 14 cm; color yellow/orange or deep brown/purple.

Some prey can detect a scent from the ochre star and move away from the predator. This star has few predators including sea otters, gulls, and humans (for ornaments).

Important predators, vulnerable to parasitic castration, and overcollecting by humans.

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

This is the largest limpet in North America, reaching sizes up to 8 cm (3.5 inches) in length. The shell is oval and low in profile with the apex (highest point of the shell) positioned far forward. Shell surface often rough with raised brown areas relative to white areas. Tentacles and side of foot gray.

Owl limpets are hermaphrodites. They are born males and become females as they grow older and larger. The females have distinct grazing territories or “farms” that they clear by scraping rocks free of algae. This action creates space and promotes algal growth. Females are territorial and will dislodge small mussels, limpets and anemones from their territories by bulldozing them off the rock with the edge of their shell.

Humans eat owl limpets and preferentially take the largest limpets in a population for consumption. As a result, populations may become dominated by smaller males, skewing the gender ratio and decreasing reproduction.

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

UCSC’s Pacific Rocky Intertidal Monitoring: Lottia gigantea (Owl Limpet)

Pink acorn barnacles are large (3-5 cm), ribbed, and reddish-pink in color. They are usually found growing as solitary individuals rather than in groups.

This barnacle is an effective competitor for space in the low intertidal zone, and individuals may grow to a size large enough to exempt them from predation by many gastropods and sea stars. Some individuals may live as long as 10-15 years.

These barnacles are a southern species nearing their northern limit in the Monterey Bay National Marine Sanctuary (MBNMS). Their abundance in the MBNMS is expected to increase if global warming continues. This species might be sensitive to sewage pollution.

Dawson, M. N., Groberg, R. K., Stuart, Y. E. and Sanford, E. 2010. Population genetic analysis of a recent range expansion: mechanisms regulating the poleward range limit in the volcano barnacle Tetraclita rubescens. Molecular Ecology 19: 1585–1605. doi: 10.1111/j.1365-294X.2010.04588.x

Littler, M.M. and Murray and S.N. Murray 1975. Impact of sewage on the distribution, abundance, and community structure of rocky intertidal macro-organisms. Marine Biology 30:277-291.

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

UCSC’s Pacific Rocky Intertidal Monitoring: Tetraclita (Pink Barnacle)

The body and spines of this echinoderm are typically bright purple; juveniles are green; average body size is 5 cm in diameter; tube feet allow animals to cling to rocks.

Urchins can regenerate broken spines. This is the first species of sea urchin that has had its complete genome sequenced; it is a model animal for the study of development.

This species is harvested for food in California. In 2000, 20 million lbs of sea urchins were harvested, primarily for markets in Japan.

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

Stanford’s SeaNet: Phylum Echinodermata

Bivalve mollusk; shell up to 20 cm in length, black and bluish in color with coarse ribs.

Mussels are attached to hard substrate by secreting byssal threads at the base of the foot. Mussel beds provide important refuge and habitat for a variety of invertebrates and algae.

Competitive dominant; major space occupier in mid zone. Harvested extensively by humans for food (great steamed and dipped in garlic butter!), but can contain deadly poison.

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

UCSC’s Pacific Rocky Intertidal Monitoring: Mytilus (California mussel)

This anemone is distinguished by the sunburst pattern of radiating lines on oral disk; most are 10-15 cm (4-6 inches) in crown diameter, but can reach up to 25 cm (10 inches) in diameter. Tentacles usually with white blotches, rarely pink-tipped; can be confused with giant green anemones because they are similar in size, but are distinguished by lines on disc and tubercles in rows on column. More difficult to distinguish from aggregating anemone as main difference is mode of growth: clonal versus solitary; recent genetic studies revealed that the two are separate species that do not interbreed.

Closely related to the aggregating anemone, this species was given its own name only recently. Up until then it was known as a form of aggregating anemone that lived in the low intertidal in southern California and did not clone, remaining solitary. There is another solitary sea anemone that looks similar, the giant green anemone, that lives intertidally in the cooler waters of central and northern California but it lacks the conspicuous radiating lines on the oral disk.

This is a southern species near its northern limit in central California. Their abundance in central and northern California is expected to increase if global warming continues. Major space competitor and predator.

Biological Sciences: Santa Barbara City College

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

Pearse V. and Francis L. 2000. Anthopleura sola, new species, solitary sibling species to the aggregating sea anemone, A. elegantissima (Cnidaria: Anthozoa: Actiniaria: Actiniidae). Proc Biol Soc Washington 113: 596-608.

Shell is round, shaped like a turban, not pointed at the apex; can be dark purple, black, orange, or brown in color; usually up to 3 cm in diameter; often aggregates in groups.

Turban snails are preyed upon by sea otters, rock crabs and the ochre sea star; also collected by humans for food.

These are major grazers of algae in the intertidal. They are also harvested by people for food.

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

Whelks are a group of predatory snails. The shells can be lots of different colors; black, grey, orange, purple with stripes, gray with stripes; up to about 4 cm in length. Note that both ends of whelk shells are pointed.

Unicorn snails and dogwinkles spawn sporadically throughout the year in California most actively from November to March. Females deposit their eggs in yellow vase shaped capsules (as many as 300 capsules per cluster with average of 500 eggs per capsule).

These are major predators in the intertidal.

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