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Northern sea stars (Asterias vulgaris) are avid predators and notable drivers of ecosystems within low intertidal habitats. The northern sea star is considered a keystone species in the North Atlantic and restricts the growth and distribution of the blue mussel, the species’ main competitor. Without northern sea stars, mussels outcompete all other organisms in lower intertidal and subtidal areas. Northern sea stars foster biodiversity by allowing other organisms, such as barnacles and seaweeds, to settle in areas that would else be occupied by mussel beds. Unlike many species of sea star, Northern sea stars can tolerate low salinity and brackish water. They are commonly found in rocky tide pools and other intertidal areas with sandy or stony bottoms. They are also often found in mussel beds, where prey is abundant. Of the about 2,000 species of sea star on Earth, five-armed stars, like the Northern sea star, are the most common. But some sea star species have 10, 20, or 40 arms. Northern sea stars vary in color from reds to browns, purples, and greens.

Photo and haiku: Samantha Oester