Starfish, or sea stars, are marine invertebrates known for their distinct star-like shapes. They inhabit diverse underwater environments globally, from shallow coastal areas to the deep ocean floor.
Marine Environments
Starfish are exclusively marine animals, living only in saltwater ecosystems. They are found in all the world’s oceans, including the Atlantic, Pacific, Indian, Arctic, and the Mediterranean Sea. They inhabit a broad range of depths, from shallow coastal waters like the intertidal zone to abyssal depths reaching up to 6,000 meters (20,000 feet).
Specific Ocean Habitats
Tide pools and rocky shores are common habitats, where starfish like the ochre sea star cling to rocks. These areas experience fluctuating water levels and wave action, requiring starfish to adapt to periods of exposure to air and sun. They use their tube feet to attach firmly to surfaces, preventing them from being swept away or drying out.
Coral reefs provide vibrant homes for many starfish species. Some, like the blue Linckia starfish, reside on living coral reefs and in lagoons, often at depths between 1 and 20 meters. The crown-of-thorns starfish, a well-known coral predator, also inhabits these warm, tropical waters.
Sandy and muddy seafloors are also important habitats for various starfish. Some species are adapted to burrow into these soft sediments, searching for food. For instance, sand-sifting starfish require a deep layer of soft substrate to forage.
Kelp forests, underwater “forests” of large algae, offer shelter and food. Starfish are found within these productive ecosystems, often preying on other invertebrates like sea urchins. Certain starfish species, such as the sunflower sea star, help maintain kelp forest health by controlling urchin populations.
The deep sea represents another habitat for starfish, with many species adapted to extreme pressure and the absence of light. Over 1,200 species of brittle stars, closely related to starfish, are found in waters deeper than 200 meters, with some reaching abyssal depths. Deep-sea starfish can have adaptations such as well-developed eyes despite the dark conditions, indicating diverse visual ecologies.
What Influences Where Starfish Live
Several environmental factors determine where starfish can live and thrive. Salinity, the salt content of the water, is a primary factor, as starfish are exclusively marine and cannot survive in freshwater. Their bodies maintain an internal salt concentration similar to seawater, and exposure to freshwater causes their cells to swell and rupture. While most require oceanic salinity, some species show tolerance to a range of salinities, adapting to local conditions in areas like the White Sea.
Temperature is another environmental influence, with different species tolerating varying ranges. Some starfish prefer warm tropical seas, while others are adapted to the cold waters of polar regions or the deep sea. For instance, the crown-of-thorns starfish thrives in tropical waters, with metabolic rates increasing between 26°C and 30°C. However, temperatures that are too high can cause thermal stress and negatively impact their survival and regeneration abilities.
The type of seafloor, or substrate, also influences starfish distribution. Starfish are primarily benthic animals, meaning they live on the seabed, and their tube feet are adapted for movement and gripping specific surfaces. Some species prefer rocky areas where they can anchor themselves, while others are found on sandy or muddy bottoms where they might burrow or sift for food.
Food availability plays a role in determining where starfish are found. As many starfish are predators, their presence is often tied to the abundance of their preferred prey, such as shellfish, crustaceans, or detritus. Studies show that the distribution and size of certain starfish species can decrease with depth, correlating with a reduction in their primary food sources.
Water depth and pressure are also significant factors. Starfish inhabit depths ranging from the intertidal zone to over 6,000 meters. Species living in the deep sea have adaptations to withstand immense pressure, often using their water vascular system to facilitate movement and feeding in such environments. These adaptations allow them to colonize a wide vertical range within the ocean.