Blue sea star (tan sea star) in Los Cabos

How to recognize it

A small central disc with five long, slender arms that are rounded like tubes and taper to the tips; the body is stiff, not floppy. The base color is grey, tan or brownish, sometimes strongly blue, with two brown stripes running the length of each arm and bluish spots between them. Along the top of each arm runs a main row of small, porous patches (papular areas), flanked by shorter rows on each side.

Biology

This sea star lives on rocky bottoms from the Gulf of California and the Pacific coast of Mexico south to Peru, including the Galápagos, from the shallows down to about 50 m. In a survey of rocky reefs from La Paz to Bahía de Los Ángeles, it was by far the most common sea star: 65% of all sea stars counted and present in 90% of transects, with up to about 11 per 50 m² around Loreto. That study classed it as a grazer that feeds on algae. It has been photographed at Cabo San Lucas and is regularly recorded at Cabo Pulmo.

Cold seems to hold it back in the north. A study comparing Loreto with Bahía de Los Ángeles, at the cold northern edge of its range, found it much more common at Loreto, and its activity and metabolism dropped in the low winter temperatures farther north. At Loreto, the population split by depth into a shallow group that was reproducing and a deeper group that was feeding.

Seeing them from the boat

This is a sea star to see while snorkeling or diving. Look on rocks and boulders in shallow water, from a few meters down; it is regularly recorded around Cabo San Lucas and the tourist corridor and at Cabo Pulmo.

Look, but leave it where it is. Mexico's sport fishing rules allow only fish to be taken, so sea stars can't be collected, and inside Cabo Pulmo National Park collecting wildlife needs a federal permit and visitors must keep 2.5 m from rock and coral formations.

Rules & conservation

Look, don't take: only fish may be taken under Mexico's sport fishing rules.

Don't confuse it with

The pyramid sea star (Pharia pyramidata), the second most common sea star on Gulf reefs, also has long arms but grows bigger (to about 30 cm) and is lavender to brown with yellow-green spots that leave a clear line down the middle of each arm. The blue sea star's two lengthwise brown stripes per arm are the quickest way to tell it apart.

Questions

By Max VargasTop Anglers, Cabo San Lucas · international judge at big game fishing world championships · reviewed October 2026

Sources

• Reef Life Survey: Phataria unifascialis
• SeaLifeBase: Phataria unifascialis
• Martín-Cao-Romero et al. 2017, redescription of Phataria unifascialis (Rev. Biol. Trop.)
• Reyes-Bonilla et al. 2005, sea star assemblages on Gulf of California rocky reefs (Rev. Biol. Trop.)
• Salazar & Reyes-Bonilla 1998, parasitism of Thyca callista on Phataria unifascialis (Rev. Biol. Trop.)
• Morgan 1992, effects of temperature on Phataria unifascialis in the Gulf of California (Loma Linda University thesis)
• Florent's Guide to the Tropical Reefs: tan starfish, Cabo San Lucas
• Reef Life Survey: pyramid sea star (Pharia pyramidata)
• iNaturalist research-grade observation near Cabo San Lucas (via GBIF)
• CONANP, Compendio del Programa de Manejo del Parque Nacional Cabo Pulmo
• NOM-017-PESC-1994, 2013 amendment (DOF)
• NOM-059-SEMARNAT-2010, 2019 update (DOF)

Top illustration: Top Anglers. Photos: iNaturalist contributors, credited on each photo.