Starfish, more precisely called sea stars, live in every ocean on Earth, from sun-warmed tide pools a few centimeters deep to the pitch-black abyssal plains several thousand meters below the surface. Their habitats share one baseline requirement: saltwater. Beyond that, the range is enormous. Roughly 1,900 known species occupy rocky shores, coral reefs, sandy seabeds, kelp forests, polar ice margins, deep-sea seamounts, and even sunken shipwrecks. Where any particular species turns up depends on temperature, salinity, depth, wave action, food supply, and what kind of surface it can cling to or burrow into.
Global Distribution and the Tropical Peak
If you mapped every known sea star species by location, the greatest concentration would sit in shallow tropical waters about 10 degrees north of the equator. From that peak, species numbers drop off steeply as you move toward the poles. At 60 degrees south latitude, roughly around the Antarctic Convergence, species richness is about 65 percent lower than the tropical maximum; at 60 degrees north, it is around 85 percent lower.1PubMed Central. Deep-sea-floor diversity in Asteroidea is shaped by competing processes across different latitudes and oceans That does not mean sea stars are rare at high latitudes. Some polar species exist in dense populations. It just means the variety of species thins out dramatically.
The pattern shifts with depth. That narrow burst of tropical diversity in shallow water broadens into wider bands of moderate diversity in the deep temperate zones between roughly 35 and 60 degrees latitude, in both hemispheres. So the deep seafloor has its own geography of sea star life, one that does not simply mirror what you see near the surface.1PubMed Central. Deep-sea-floor diversity in Asteroidea is shaped by competing processes across different latitudes and oceans
Rocky Intertidal Shores
The habitat most people picture when they think of sea stars is the rocky intertidal zone, the band of shore that gets submerged at high tide and exposed at low tide. This is a brutal environment. Animals living here face crashing waves, intense sun, temperature swings, and periodic drying. Sea stars cope by gripping rock with hundreds of tiny hydraulic tube feet, but the physical stress still shapes their bodies in visible ways.
The ochre sea star, Pisaster ochraceus, found along the Pacific coast of North America, actually changes its body proportions depending on wave exposure. On shores battered by heavy surf, these animals develop narrower arms, which cuts down on drag and lift from breaking waves. On sheltered shores, the same species grows fatter arms, possibly because the extra body mass helps resist overheating when the tide goes out, or because it provides more room for developing eggs and sperm.2Journal of Experimental Biology. Intertidal sea stars (Pisaster ochraceus) alter body shape in response to wave action This kind of physical flexibility lets a single species occupy microhabitats that look very different from each other within the same stretch of coastline.
Rocky intertidal zones are also where sea stars exert the most famous ecological effect. When Pisaster ochraceus is present, it preys heavily on mussels, preventing those fast-growing shellfish from monopolizing all the available space. Remove the sea star, and mussels can take over the lower intertidal within months, pushing out dozens of other species. The strength of this effect varies with wave exposure, prey abundance, and local conditions. At wave-exposed sites where mussel recruitment is high, sea stars are the main force keeping the community diverse. At sheltered, low-recruitment sites, other predators like whelks pick up some of the slack.3Ecological Monographs. The Keystone Species Concept: Variation in Interaction Strength in a Rocky Intertidal Habitat This is the research that originally gave biology the term “keystone species,” and it illustrates how tightly a sea star’s habitat and its ecological role are linked.
Coral Reefs
Tropical coral reefs support a different cast of sea stars, and the most consequential is the crown-of-thorns starfish, Acanthaster. This large, venomous, coral-eating species lives on reefs across the Indo-Pacific and can swing between two dramatically different population states. Under normal conditions, densities hover near zero to one individual per hectare, and their grazing causes little damage. During outbreaks, densities can spike to more than a thousand per hectare, and the result is mass coral death.4PubMed Central. Crown of thorns starfish life-history traits contribute to outbreaks, a continuing concern for coral reefs
Crown-of-thorns outbreaks rank among the most destructive natural disturbances on tropical reefs. They trigger a cascade: coral dies, algae move in, fish that depend on living coral decline, structural complexity collapses, and overall biodiversity drops.5PLOS ONE. Predator Crown-of-Thorns Starfish (Acanthaster planci) Outbreak, Mass Mortality of Corals, and Cascading Effects on Reef Fish and Benthic Communities The damage is not just about how much coral gets eaten, either. Crown-of-thorns feeding fragments the remaining coral patches, breaking larger continuous reef into smaller, more isolated pieces, especially at intermediate levels of coral cover.6Landscape Ecology. Crown-of-thorns starfish promote additional fine-grained habitat fragmentation in a coral reef ecosystem That fragmentation matters for coral recruitment and for the many small animals that rely on connected reef structure.
Researchers increasingly suspect that the success of crown-of-thorns outbreaks is tied to the animal’s biology: extreme reproductive output, flexible larval diets, and the ability to grow quickly or slowly depending on conditions. Those traits may let them exploit situations created by human activity, like nutrient runoff that fuels plankton blooms for their larvae.4PubMed Central. Crown of thorns starfish life-history traits contribute to outbreaks, a continuing concern for coral reefs
The Deep Sea
Below the sunlit surface, sea stars colonize habitats most people never think about. The deep ocean is cold, dark, under crushing pressure, and food-poor, yet sea stars live there in meaningful numbers. Getting to these depths required evolutionary retooling. Genomic analysis of deep-sea lineages has found signs of natural selection acting on genes involved in energy metabolism, particularly in the enzyme complexes that drive cellular respiration. Mutations in those genes appear to help deep-sea species extract energy more efficiently under the extreme conditions of the abyss.7Scientific Reports. Mitogenomics provides new insights into the phylogenetic relationships and evolutionary history of deep-sea sea stars (Asteroidea)
Deep-sea sea stars often live on or around structures that concentrate food. On high-Arctic seamounts, for example, sea stars of the genus Tylaster have been found at high densities living among large sponges, where organic matter drifts and small invertebrates gather.8Scientific Reports. Habitat types and megabenthos composition from three sponge-dominated high-Arctic seamounts Sponge gardens, hydrothermal vents, cold seeps, and whale-fall communities all serve as oases on an otherwise sparse deep-sea floor, and sea stars show up at many of them.
Salinity and Why You Will Not Find Sea Stars in Fresh Water
One of the sharpest limits on sea star habitat is salinity. Sea stars cannot regulate the salt concentration of their body fluids the way fish or crabs can. Their internal fluid essentially matches the surrounding seawater. Drop the salinity, and water floods into their tissues, stressing or killing them. This is why no sea star species lives in fresh water and why their range in estuaries is very limited.
The common European sea star Asterias rubens illustrates this nicely. Populations from the North Sea tolerate salinity down to about 23 parts per thousand, while populations from the already-brackish Baltic Sea have adapted to survive at salinities as low as 8 parts per thousand. Even the Baltic populations cannot regulate their internal fluid, though; they simply tolerate a more dilute environment.9Journal of the Marine Biological Association of the United Kingdom. Salinity Tolerance and Permeability to Water of the Starfish Asterias Rubens L.
Salinity stress is not just a theoretical concern. Experiments on the New Zealand sea star Coscinasterias muricata showed that animals held at low salinity righted themselves about 47 percent more slowly than those in normal seawater, a functional measure of overall fitness. Temperature, by contrast, had no significant effect on that measure.10New Zealand Journal of Marine and Freshwater Research. Salinity has a greater effect on sea star righting time than temperature With climate change altering rainfall patterns and sending more frequent pulses of fresh water into coastal estuaries, salinity may become a bigger constraint on where sea stars can live.
Temperature, Ocean Warming, and Habitat Loss
While salinity may matter more than temperature in the short term for some species, rising ocean temperatures pose a serious long-term threat. A broad meta-analysis of warming effects on echinoderms (the group that includes sea stars, urchins, and sea cucumbers) found that sea stars are the most negatively affected class, with an overall performance decline of about 30 percent under elevated temperatures. Under warming scenarios projected for the end of this century, that impact deepened to roughly a 51 percent decline. Tropical species and juveniles were hit hardest.11PubMed Central. Impacts of ocean warming on echinoderms: A meta-analysis
Warming also interacts with other stressors. Low-oxygen conditions, which are becoming more common in warming seas, amplify the lethality of pollutants. In laboratory experiments, hypoxia significantly reduced survival time of Asterias rubens exposed to manganese, a common marine contaminant.12PubMed Central. Manganese Uptake and Lethality in the Sea Star Asterias rubens: Effect of Hypoxia As ocean warming drives the expansion of oxygen-depleted zones, some sea star habitats may become chemically hostile even before temperatures alone are lethal.
Sea Star Wasting Disease and the Reshaping of Habitats
Starting in 2013, a mass-mortality event called sea star wasting syndrome swept the Pacific coast of North America. Affected animals developed lesions, their arms fell off, and they essentially disintegrated. The disease killed billions of sunflower sea stars (Pycnopodia helianthoides) and devastated populations of several other species.13PubMed. Vibrio pectenicida strain FHCF-3 is a causative agent of sea star wasting disease A 2025 study identified a bacterial strain, Vibrio pectenicida, as a causative agent.13PubMed. Vibrio pectenicida strain FHCF-3 is a causative agent of sea star wasting disease
The ecological fallout reshaped entire habitats. With sunflower stars gone, sea urchin populations surged unchecked, and their grazing razed kelp forests up and down the coast.13PubMed. Vibrio pectenicida strain FHCF-3 is a causative agent of sea star wasting disease Kelp forests are among the most productive habitats in the ocean. Surveys in Washington state found that sea stars did not recover from the disease even years later, with several species, including sunflower stars, continuing to decline.14Marine Ecology Progress Series. Changes in kelp forest communities off Washington, USA, during and after the 2014-2016 marine heatwave and sea star wasting syndrome Subtidal monitoring confirmed dramatic population crashes across multiple species. Pycnopodia helianthoides densities dropped from 5.5 to 0.18 individuals per 100 square meters, while several less common species vanished entirely from surveys.15PLOS ONE. Devastating Transboundary Impacts of Sea Star Wasting Disease on Subtidal Asteroids
The wasting disease drove home how much surrounding habitats depend on sea stars being present. When a keystone predator disappears, the habitat itself transforms. Pisaster ochraceus, the intertidal species, is a keystone predator whose decline could cascade into major community-level changes across the rocky shore.16PubMed Central. Sea Star Wasting Disease in the Keystone Predator Pisaster ochraceus in Oregon: Insights into Differential Population Impacts, Recovery, Predation Rate, and Temperature Effects from Long-Term Research A habitat without its sea stars is not just missing one animal; it is a different kind of place.
Nursery Habitats for Juveniles
Adult sea stars and their young often live in very different places. Many sea star larvae drift in the plankton for weeks before settling, and where they land as tiny juveniles is not necessarily where they spend their adult lives. Research on the spiny sea star Marthasterias glacialis in Ireland found that juveniles as small as two millimeters across settled gregariously on shallow algae at depths of less than one to two meters, using the seaweed as a nursery habitat for a prolonged period before eventually migrating to the rocky substrates that adults prefer.17PubMed. The Waiting Stage, Prolonged Residency in Nursery Habitats by Juveniles of the Predatory Sea Star Marthasterias glacialis
This “waiting stage” matters for conservation. If the algal nurseries are damaged by pollution, sedimentation, or coastal development, juvenile recruitment could collapse even if adult habitat remains intact. Protecting sea star populations means protecting a chain of habitats, not just the reefs or rock faces where adults are visible.
Artificial Structures and Colonization
Sea stars are surprisingly quick to colonize human-made structures in the ocean. When the decommissioned warship HMS Scylla was sunk as an artificial reef off southwest England, Asterias rubens was among the early wave of settlers, appearing alongside barnacles, tube worms, sea urchins, and scallops within the first year.18Journal of the Marine Biological Association of the United Kingdom. Colonization of an artificial reef in south-west England—ex-HMS ‘Scylla’ Offshore wind turbine foundations, oil platform pilings, and breakwaters serve the same function, creating hard substrate where none existed before.
Whether these artificial habitats are ecologically equivalent to natural reefs is debatable. They do attract sea stars and the invertebrate prey sea stars feed on, but they also introduce novel connectivity between previously isolated populations. For a native species, that can be neutral or even beneficial. For an invasive one, it can accelerate spread. Asterias amurensis, a northern Pacific sea star that has invaded southeastern Australian waters, thrives on soft sediment habitats where it has been associated with changes in bottom-dwelling communities. However, teasing apart the effects of the sea star itself from the effects of different sediment types is tricky; one study cautioned that differences in community composition between areas with and without the invasive star may reflect underlying physical habitat variation rather than predation impact alone.
Polar Habitats
Despite the low species diversity at high latitudes mentioned earlier, polar waters support thriving sea star populations. Antarctic species like Odontaster validus are common in shallow bays around the continent, living at temperatures that hover near or below freezing year-round. Their metabolisms run slowly, growth is sluggish, and lifespans tend to be long. Arctic sea stars, though fewer in species, occupy a range of depths and substrates, from shallow gravel beds to sponge-covered seamounts hundreds of meters deep.8Scientific Reports. Habitat types and megabenthos composition from three sponge-dominated high-Arctic seamounts
Polar habitats face their own set of pressures. Warming is happening faster at high latitudes than in the tropics, and the meta-analysis finding of severe performance decline in asteroids under projected warming scenarios applies here too. Ice retreat also opens new habitat that was previously scoured by glaciers, creating colonization opportunities for some species while eliminating the stable cold conditions others depend on.
What Makes a Good Sea Star Habitat
Across this enormous range of environments, a few features consistently define a suitable habitat for sea stars:
- Full-strength seawater: Most species need salinity above roughly 25 parts per thousand, and even brackish-tolerant populations are limited to about 8 parts per thousand at the extreme low end.
- Some form of substrate: Sea stars need something to move across and anchor to, whether that is rock, coral rubble, sand, mud, or a steel hull. Species that live on soft sediment typically have different arm morphologies and locomotion strategies than those on hard rock.
- Adequate oxygen: Low-oxygen conditions stress or kill sea stars, especially when combined with pollutants. Expanding dead zones are a genuine threat to populations in enclosed or semi-enclosed seas.
- Food supply: Different species need different prey, but the common thread is access to invertebrates. Mussels, barnacles, sponges, corals, detritus, and other echinoderms all appear on various sea star menus. Habitats with high prey density support denser sea star populations.
Temperature tolerance varies wildly among species, so it is not a universal threshold the way salinity is. A tropical crown-of-thorns starfish and an Antarctic Odontaster occupy opposite ends of the thermal spectrum, each perfectly suited to conditions that would kill the other. What matters for any individual population is whether warming or cooling is pushing conditions beyond that species’ evolved range.
Shifting Ranges and Uncertain Futures
Sea star habitats are not static. As ocean temperatures climb and salinity regimes shift with changing rainfall, the geographic boundaries of many populations are moving. Species at the warm edge of their range may contract poleward, while polar species face shrinking thermal refugia. Meanwhile, episodic catastrophes like sea star wasting disease can empty a habitat of its dominant species in a single season, and recovery can take years or may not happen at all within monitoring timescales.14Marine Ecology Progress Series. Changes in kelp forest communities off Washington, USA, during and after the 2014-2016 marine heatwave and sea star wasting syndrome The loss of kelp forest habitat triggered by the sunflower star die-off is a vivid example of how the disappearance of one habitat resident can eliminate the habitat itself for countless other organisms.
For reefs, the interplay between crown-of-thorns outbreaks, bleaching events, and storm damage means that coral habitats face compounding threats, and the sea stars that live among them, both the reef-builders’ predators and the small detritivores that clean up after them, are tangled in the same web of stress. Understanding where sea stars live is not just a matter of cataloging addresses. It is a window into the health, connectivity, and resilience of the marine ecosystems they hold together.