Sea Strawberry

Gersemia rubiformis

A colonial soft coral, it has thick, soft, red-pink lobes in which the polyps live. Individual polyps have eight tentacles. The polyps form thick clusters on the lobe tips. Colonies form pink, erect structures with several branches off a central stalk. They are normally five to 15 centimetres high but can be up to 25 centimetres. When inflated, branches are thick, swollen, and semi-transparent. When disturbed, the colony contracts to form a tough cauliflower-like lump that is only a few centimetres high.

Authority

Ehrenberg, 1834

Classification Details

Phylum: Cnidaria (Cnidarians); Class: Anthozoa (sea anemones, corals, and sea fans); Subclass: Octocorallia (octocorals); Order: Alcyonacea (soft corals).

Habitat

Widespread, boreal-arctic species found in both Pacific and Atlantic Oceans. Present in almost all Arctic seas but also reported from as far south as California. Often found in rock and boulder habitats, as colonies need a hard substrate for attachment. Often found on small stones or shell fragments in high-current areas. Sublittoral, to depths greater than 2 000 metres.

Diet

Suspension feeder, feeding on zooplankton. Each polyp in the colony has eight tentacles at its end, with delicate branches to catch plankton in the water. Prey is stunned by stinging cells (nematocysts) that are on the tentacles. Unlike many other corals, Gersemia do not have the symbiotic photosynthesizing organisms called zooxanthellae.

Reproduction

Sexes are separate, growing as male or female colonies. They reproduce asexually through vegetative budding. They also reproduce sexually through external fertilization of eggs by sperm. Fertilized eggs produce ciliated planula larvae. These can disperse widely, although many of them settle near the parent. Their lifespan is unknown.

Fun Facts

Large aggregations of sea strawberries are known as strawberry grounds. They are an important habitat for lobsters and juvenile basket stars.

Young basket stars (genus Gorgoncephalus) are often found attached to sea strawberries. This association allows them to feed and grow without harming the coral. Very young basket stars may even live inside the polyps.

References

Williams GC and Lundsten L (2009) The nephtheid soft coral genus Gersemia Marenzeller, 1878, with the description of a new species from the north east Pacific and a review of two additional species (Octocorallia: Alcyonacea). Zoologische Mededelingen 83,1067–1081.

Itken K, Bluhm B and Blanchard A (2012) Sea Raspberry: Gersemia rubiformis. In: Arctic Ocean Diversity http://www.arcodiv.org/seabottom/cnidaria/Gersemia_rubiformis.html Accessed online 20 January 2020.