Sea urchins are marine invertebrates. This article explores the diverse locations where sea urchins can be found across the world’s oceans.
Global Marine Distribution
Sea urchins are found in virtually all the world’s oceans. Their presence spans from the frigid polar regions to the warm tropical and subtropical waters. They inhabit the Atlantic, Pacific, Indian, Southern, and Arctic Oceans, demonstrating a remarkable adaptability to various climates. With about 950 known species, sea urchins are not confined to a single geographic area but are truly global. Their extensive distribution highlights their capacity to thrive in a broad spectrum of marine conditions across different latitudes.
Varied Ecosystem Habitats
Sea urchins occupy a diverse array of marine environments and ecosystems. They are commonly found clinging to rocks in rocky shores and intertidal zones, areas exposed to air during low tide where they seek refuge in crevices and under boulders. Some species, like the purple sea urchin, can even excavate pits in rock substrates for shelter.
Coral reefs are another significant habitat for sea urchins, where they hide in crevices during the day and emerge at night to feed on algae. Their grazing helps control macroalgae, which, if overgrown, can smother corals and negatively impact reef health.
Sea urchins also inhabit productive underwater landscapes such as kelp forests and seagrass beds, serving as grazers that influence these ecosystems. In kelp forests, they consume algae, including giant kelp, though overpopulation can lead to “urchin barrens” where kelp is severely depleted.
Beyond hard substrates, many sea urchin species are adapted to live on softer sandy and muddy seabeds. Irregular urchins, such as sand dollars and heart urchins, often burrow beneath the surface of sand or gravel. These burrowing species contribute to sediment aeration and nutrient cycling as they forage for organic matter.
Vertical Water Column Range
Sea urchins exhibit an impressive vertical distribution, inhabiting a vast range of depths in the ocean. They are present in shallow coastal waters, including the intertidal and subtidal zones, which extend from the low-tide line to about 200 meters deep. In these shallower areas, they are often found in high densities, particularly where wave action is less intense.
Their presence also extends into the deep-sea environments, adapting to conditions of high pressure, cold temperatures, and perpetual darkness. Species like Cidaris abyssicola can live several kilometers deep, and some, such as those in the family Pourtalesiidae, are found exclusively in the hadal zone, which includes the deepest ocean trenches, with some collected as deep as 6,850 meters. While not as abundant as some other echinoderms in the deepest parts, sea urchins have successfully colonized abyssal plains and can even be found near hydrothermal vents, adapting to unique chemical environments.