Starfish, also known as sea stars, are captivating marine invertebrates that inhabit diverse marine environments worldwide. They are found in all oceans, from warm tropical zones to frigid polar regions, and from the intertidal zone down to abyssal depths. Their presence in various aquatic settings, including rocky shores, coral reefs, and sandy seafloors, highlights their adaptability. The appearance of starfish often sparks curiosity due to their distinctive shapes and surprising array of colors.
The Diverse Palette of Starfish
Starfish exhibit an astonishing spectrum of colors. Common shades include vibrant reds, oranges, yellows, browns, purples, and blues. Some species even display intricate mottled patterns. For example, the common starfish (Asterias rubens) is typically orange or brownish, but can also appear violet, with paler specimens found in deeper waters. The Pacific blood star often presents in bright orange or red, sometimes with purple variations.
Coloration varies significantly between different species and even within the same species, depending on factors like geographic location, diet, and life stage. The ochre sea star (Pisaster ochraceus), found along the North American Pacific coast, demonstrates this variability, appearing in purple, orange, or intermediate colors. While some ochre stars are predominantly purple, others can be orange or yellow based on food availability.
Biological Basis of Starfish Color
The vibrant colors of starfish are primarily due to pigments in their skin cells. Carotenoids, such as astaxanthin and mytiloxanthin, are key pigments responsible for these hues. These lipophilic compounds contribute to colors from pinks to oranges and reds. Astaxanthin, for instance, produces pink coloration.
Starfish acquire these pigments through their diet. They are opportunistic feeders, preying on various benthic invertebrates such as mollusks and crustaceans. When starfish consume organisms rich in carotenoids, like mussels, these pigments are absorbed and deposited in their tissues, influencing their coloration. For example, ochre stars consuming carotenoid-rich mussels often develop an orange hue, while those feeding primarily on barnacles, which lack these pigments, tend to be purple. Genetic factors also control the production, absorption, and deposition of these acquired pigments, contributing to species-specific color patterns.
Functional Significance of Color
The diverse coloration of starfish serves several important roles in their survival and interaction with the marine environment. One primary function is camouflage, allowing them to blend seamlessly with their surroundings, such as rocky seafloors, coral reefs, or sandy sediments, to evade predators. For instance, the mottled coloring of the Australian southern sand star helps it disappear into seagrass beds. Some starfish species also have irregular textures and bumps on their exoskeletons that aid in blending with craggy reef structures or rocky bottoms.
Another significant role is warning coloration, also known as aposematism. Bright, conspicuous colors can signal to potential predators that the starfish is toxic or unpalatable. The crown-of-thorns starfish, for example, displays prominent coloration and sharp spines, along with defensive chemicals, to deter threats. This visual warning system benefits both the starfish and the predator, as both avoid potential harm. Beyond defense, certain pigments offer protection against harmful ultraviolet (UV) radiation from sunlight, and starfish in deeper waters, where light penetration is limited, often exhibit paler colors compared to their shallow-water counterparts.