Odontaster validus

Lore & Background

Odontaster validus grows to about 10 cm in diameter, with a broad, thick, cushion-like disc creased by interambulacral grooves. Its surface is covered in small granulations in radial rows, and it has five short arms wide at the base and tapering sharply. The upper surface is plain red, the underside pink. It is the most common sea star in Antarctica, ranging from the Antarctic Peninsula to Bouvet Island, at depths down to 900 metres.

This species is an omnivorous scavenger, consuming carrion, detritus, seal faeces, red algae, bivalves, sponges, hydroids, other sea stars, sea urchins, and many other organisms. It aggregates on damaged mussel banks and injured sea stars. It is preyed upon by sea anemones and other sea stars. Ecologically, it controls the sea star Acodontaster conspicuus and the nudibranch Doris spp., which limit sponge growth.

Odontaster validus takes 3–6 years to reach maturity but may live for 100 years due to its cold-blooded nature and low metabolic rate in harsh Antarctic conditions. Oogenesis initiates from August to February, eggs mature over 18 months, and spawning occurs May to September. Larvae remain near the seabed for 2 months as bipinnaria, then become pelagic for up to 6 months as brachiolaria before settling and metamorphosing.

Reader's Guide

Odontaster validus is ecologically significant in Antarctic marine ecosystems because it consumes benthic larvae and exerts control over the sea star Acodontaster conspicuus and the nudibranch Doris spp., which themselves limit sponge growth that would otherwise dominate the seabed. Its role as a scavenger and predator helps maintain benthic community structure. Research shows it does not attack members of its own species, using chemoreceptors to identify conspecifics by odour; food-deprived individuals are attracted to odours of satiated same-species sea stars but not starved ones. This species is much less sensitive to higher water temperatures than its prey, many of which find temperatures above 3 °C lethal, raising implications for Antarctic marine environments under global warming. Fertilisation studies found that a sperm density of 105 sperm per millilitre is sufficient for high fertilisation rates—ten times the density needed by comparable temperate species—and sperm retain minimal fertilisation ability after 24 hours but have narrow tolerance to temperature variation.

Did You Know?

• Odontaster validus may live for up to 100 years.
• It can distinguish between odours of satiated and starved members of its own species.
• Its larvae remain pelagic for up to 6 months, allowing wide dispersal.
• It requires at least ten times the sperm density needed by comparable temperate sea stars for successful fertilisation.