The class Asteroidea, commonly known as sea stars, exhibits significant chromatic diversity across its more than 1,800 known species. These creatures belong to the phylum Echinodermata and display coloration that is a dynamic biological feature. Pigmentation varies widely based on species, habitat, and diet, and serves several important biological functions related to survival and metabolism.
The Vast Spectrum of Sea Star Colors
Sea stars display a palette covering nearly the entire visible spectrum, ranging from monochromatic shades to complex, multi-hued patterns. Common colors include brilliant reds, deep blues, vibrant oranges, purples, yellows, and greens, often appearing highly saturated. The blue sea star (Linckia laevigata) is known for its cobalt or sapphire blue, though some individuals may be purple or greenish-blue.
Other species, such as the ochre star (Pisaster ochraceus), display color polymorphism, including deep purple, reddish-brown, and yellowish-orange morphs even within the same population. The sunflower sea star (Pycnopodia helianthoides) can exhibit a mix of yellow, orange, and purple across its multiple arms. Coloration often includes intricate patterns, such as mottling, spotting, or contrasting bands and stripes that break up the animal’s outline.
Why Sea Star Colors Matter for Survival
The specific coloration of a sea star serves one of two contrasting biological purposes: concealment or advertisement. For many species, mottled or subdued colors provide crypsis, or camouflage. This allows them to blend into the seafloor, rocky substrates, or coral reefs, acting as a primary defense mechanism against predators such as birds, fish, and sea otters.
Conversely, brightly colored sea stars use aposematism, or warning coloration, to advertise their unpalatability or toxicity. Highly visible colors, such as high-contrast red, orange, and purple, signal to predators that the sea star is not a profitable meal. Many echinoderms contain saponins, which are distasteful or mildly toxic compounds. The visual signal helps predators learn to avoid these pigmented individuals, benefiting both the predator and the sea star.
How Diet and Environment Influence Pigmentation
The production of diverse colors is often directly linked to the sea star’s diet, especially for warmer hues. Red, orange, and yellow pigments are derived from carotenoids, which the sea star sequesters from consumed organisms like algae, sponges, and mussels. Since sea stars cannot synthesize these compounds, the availability of carotenoid-rich prey directly influences the intensity of their coloration.
Environmental stressors also drive the development of specific pigments. For example, the blue coloration in the shallow-dwelling Linckia laevigata is created by a blue carotenoprotein pigment that acts as a powerful antioxidant. This pigment helps the sea star manage oxidative damage caused by high levels of sunlight, UV radiation, and elevated temperatures in intertidal habitats. While diet and environment influence specific shades, the underlying genetic makeup determines the range of colors a species can produce.