Starfish, also known as sea stars, are fascinating marine invertebrates recognized for their distinctive star-shaped bodies, typically featuring five or more arms radiating from a central disc. Found across all the world’s oceans, they inhabit diverse environments from shallow coastal waters to deep abyssal plains, thriving in both tropical and frigid polar regions. They possess a remarkable ability to regenerate lost or damaged limbs. This combination of widespread distribution and regenerative power contributes to their prevalence in marine ecosystems.
Decoding Starfish Activity Patterns
Starfish do not follow strict nocturnal or diurnal schedules; their activity is opportunistic, dictated by environmental factors. They remain continuously active, either moving or waiting for prey, and do not truly sleep. Their movements and foraging are primarily influenced by tidal cycles, prey availability, and water currents.
Some starfish species, like the crown-of-thorns starfish, are predominantly active at night. They hide in crevices or under coral during daylight to avoid predators and intense sunlight. As dusk approaches, they emerge to hunt coral, their preferred food source. This nocturnal strategy helps them avoid detection and competition.
Other starfish species are active during any tidal period, adapting their foraging to immediate food availability. Feeding rates can also be influenced by water temperature, with higher temperatures sometimes increasing predation. Many are opportunistic feeders, preying on benthic invertebrates, and speed up when detecting nearby prey. Some rely on water currents to forage, using the flow to locate chemical cues from prey.
How Starfish Sense Their World
Starfish perceive their environment through a sophisticated sensory system, despite lacking a centralized brain. Their nervous system, a decentralized network of a nerve ring and radial nerves, allows them to sense and react effectively. A key component is eye spots, or ocelli, located at the tip of each arm.
These ocelli are simple light-sensing structures, detecting changes in light intensity, shadows, and movement, rather than forming detailed images like human eyes. They are particularly sensitive to blue-green light, predominant in their underwater habitats. This vision aids navigation, obstacle avoidance, finding suitable environments, and identifying prey. Some research suggests it primarily helps them stay within preferred habitats, detecting when they move away from a reef.
Beyond light detection, starfish have a highly developed sense of chemoreception, like smell or taste. Their tube feet, on the underside of their arms, are sensitive to water chemicals, detecting cues from prey or predators. They can detect specific compounds, such as amino acids, from prey. This chemical sensing is a primary method for finding food; some species forage only when currents carry these signals. Additionally, starfish can sense touch, temperature, orientation, and gravity, enhancing their navigation and interaction with their marine world.