Northern sea anemones

Language English

Onglets

Description

Distinguishing features

Northern sea anemones are remarkable for their wide morphological diversity, despite sharing a common biology. Typically, an anemone has a foot that anchors to a structure such as a rock, a pier piling, or even a shipwreck. This foot extends into a central column topped with numerous tentacles, which may be thick and fleshy or fine and delicate depending on the species.

The mouth is located at the center of the upper surface. Since it is the animal’s only opening, organic waste is expelled through it after digestion.

Their colors vary greatly from one species to another—many are white, orange, or even bright red!

In the St. Lawrence Estuary and Gulf, 11 species of sea anemones have been identified, belonging to 6 distinct families. Each family has its own characteristic features, which aid identification and reflect specific ecological adaptations.

Reproduction

Sea anemones display a remarkable diversity of reproductive strategies, both sexual and asexual.

All anemones are capable of sexual reproduction, which involves the mixing of genes, meaning each individual is either male or female.

Typically, at the end of summer, northern sea anemones release their reproductive cells (gametes) into the water, where external fertilization takes place. The fertilized egg develops into a planktonic larva, the planula, which drifts for about six months before settling on the seafloor and transforming into a young anemone.

Some species also reproduce asexually through different strategies:

Fission: The frilled anemone, for example, reproduces by longitudinal fission, splitting into two genetically identical clones, which allows for the rapid colonization of intertidal habitats (between the lowest and highest tides).
Fragmentation: In this strategy, a fragment of the body—often at the base of the foot—breaks off, drifts away, and regenerates into a complete new individual. This form of reproduction is more common in unstable or disturbed environments.
Budding: A bud forms on the adult, grows, and then detaches to become independent, creating clones. This type of reproduction occurs in at least one species of tropical anemone.

This reproductive diversity attracts great scientific interest. In marine ecology, it helps explain how disturbed habitats are recolonized after climate events such as hurricanes. In genetics, it provides insights into population structure, while in cell biology and medicine, it offers promising avenues for understanding tissue regeneration.

Diet

All sea anemones use their stinging tentacles to capture small prey such as crustaceans, zooplankton, worms, and occasionally small fish. Specialized cells on the tentacle surface inject venom that paralyzes the prey. Once caught, the prey is slowly guided toward the mouth at the center of the tentacle crown.

Inside, the tentacle delivers the food to a central cavity where digestion begins with the help of enzymes. Nutrients are absorbed by the internal tissues, while undigested material is expelled back through the mouth. This passive feeding strategy is highly effective for a stationary animal living in marine currents or tidal zones.

In some species, such as the rugose anemone, a facultative symbiosis occurs with photosynthetic unicellular algae called zoochlorellae. These algae live within the anemone’s tissues, benefiting from a stable environment and access to light. In return, they produce nutrients through photosynthesis, which the anemone can use.

Predators

Sea anemones have few predators because of their stinging cells. However, some nudibranchs (sea slugs), starfish, and fish can feed on them without being poisoned.

Planktonic larvae (planulae) are more vulnerable and may be eaten by zooplankton.

To defend themselves, anemones can contract and fold inward, taking on a compact shape that makes them resemble an ordinary pebble, helping them blend into their surroundings. A few species also secrete an irritating mucus that discourages certain attackers, especially invertebrates sensitive to chemical compounds.

Habitat

Northern sea anemones colonize the cold, salty waters of the St. Lawrence Estuary and Gulf. Along the Atlantic coast, they tolerate temperature variations ranging from 5 to 20 °C. Most species live at depths of less than 100 metres, although some are found at more than 300 metres.

In the intertidal zone, the rugose anemone is the only species that can withstand fluctuations in temperature, salinity, and air exposure. It settles on soft or shelly substrates and may form clonal aggregates, often in symbiosis with unicellular algae.

Moving into shallower subtidal waters, the silver spotted anemone and the northern red anemone both anchor themselves to exposed rocky bottoms, but with different depth preferences: the first is more common in dynamic, well-oxygenated areas, while the second is often found deeper, in more stable environments.

The frilled anemone occupies even deeper waters or areas subject to strong currents, where it attaches to hard substrates and captures suspended particles with its fine tentacles.

Finally, the swimming anemone—or spotted anemone—is notable for its ability to detach from the substrate and move short distances. This mobility allows it to colonize soft or mixed bottoms, often at depth, while avoiding direct competition with strictly sessile species.

Thus, although these anemones may coexist in the same geographic region, they are distributed across distinct ecological niches, which reduces overlap and supports a structured sharing of marine space.

Ecology, behaviour

A crucial aspect of anemone biology is competition for space. Because they are sessile animals (i.e., permanently attached to the substrate), they face constant rivalry with other seafloor organisms for access to areas favourable to feeding and light.

Anemones play an important role in benthic ecosystems (the ocean floor). They provide shelter for small crustaceans and fish, and help regulate zooplankton populations. Their ability to anchor firmly and retract quickly makes them resilient to disturbances. These may be caused by waves, tides, shifting substrates, burrowing animals, or even trampling.

French name

Anémones de mer nordiques

Scientific name

Various species

Phylum

Cnidaria (coelenterata)

Class

Anthozoa

Order

Actiniaria

Family

Actiniidae

Weight

3–15 cm in diameter

Status

At the Biodôme

At the Biodôme, you can see five species of anemones in the rocky shore zone of the Gulf of St. Lawrence. Here are a few features to help identify them:

Silver spotted anemone (Aulactinia stella) — Bright red body, tentacles with white spots, up to 5 cm in diameter.

Rugose anemone (Hormathia nodosa) — Small size (3 to 6 cm), often greenish, forms clonal colonies.

Frilled anemone (Metridium senile) — Large crown of fine, feathery tentacles, can reach 30 cm in height.

Swimming anemone (Stomphia coccinea) — Trunk marbled with red and white, 5 to 10 cm in diameter, occasionally mobile.

Northern red anemone (Urticina felina) — Large size (up to 15 cm in diameter), entirely red, less common.

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