Starfish, also known as sea stars, are familiar marine invertebrates belonging to the phylum Echinodermata. Most of the roughly 2,000 species are harmless, but a few specific varieties and certain types of human interaction can result in physical injury or chemical exposure. Understanding their biological structures and defensive mechanisms is key to safely appreciating them in their natural habitat.
Mechanisms of Injury
Starfish possess a rigid body structure composed of calcium carbonate plates, called ossicles, embedded in the skin. These ossicles create a rough, abrasive surface capable of causing minor cuts or abrasions if the animal is handled carelessly.
The primary risk comes from specialized structures designed for defense. Many species are covered in spines, which are calcified extensions of the skeletal ossicles that vary in size and sharpness. These spines can easily cause puncture wounds upon contact, leading to local pain and the risk of secondary bacterial infection. In dangerous species, the spines are often long, sharp, and fragile, frequently breaking off beneath the skin upon impact.
A less common mechanism involves pedicellariae, small pincer-like structures found on the skin of some echinoderms. Starfish use these structures to keep their body surface clean or for defense. Some starfish species also employ chemical defense by storing toxins in their tissues or on their spines.
Identifying High-Risk Species
The vast majority of starfish species pose little threat to humans beyond minor skin irritation. Only one group is widely recognized as a significant danger: the Crown-of-Thorns Starfish, primarily species within the genus Acanthaster. This easily identifiable group is responsible for almost all severe starfish-related injuries.
The Crown-of-Thorns Starfish (Acanthaster planci) is a large marine invertebrate found throughout the Indo-Pacific region, growing up to 80 centimeters in diameter. Its body is densely covered in numerous sharp, venom-coated spines, which give the animal its name. These long, brittle spines can pierce skin and footwear, delivering a painful envenomation.
The spines are covered in a toxic slime containing saponins, which cause intense, immediate pain, persistent bleeding, swelling, and systemic symptoms like nausea and vomiting. The toxins, known as asterosaponins, have been studied for their potential to cause liver damage, though this is rare in human cases. Since the spines are brittle, they often break off and remain embedded in the tissue, making removal difficult and prolonging symptoms.
Safe Interaction and Observation Guidelines
The most effective way to avoid injury is to maintain distance and observe marine animals without physical contact. Caution in shallow water is paramount, as most starfish injuries occur through accidental contact, such as stepping on the animal or careless handling. Always assume that any starfish, particularly those with noticeable spines, can cause a painful puncture wound.
In environments harboring high-risk species, wearing protective footwear is a highly effective preventative measure. Sturdy, thick-soled water shoes or diving boots prevent spines from penetrating the foot when wading or walking on submerged reefs. Divers and snorkelers should be mindful of their buoyancy and surroundings to prevent accidental contact with the sea floor or reef structure.
Never attempt to pick up or handle any starfish unless you are a trained professional or the species is known to be completely harmless. If a starfish must be moved, use a stick or tool to gently guide it, rather than bare hands. Starfish should never be removed from the water for extended periods, as this causes them significant stress and damage.
Even seemingly harmless or dead starfish still pose a risk of injury. The calcified ossicles and spines retain their sharpness after the animal dies, and stepping on a dry specimen on the beach can result in a painful cut or puncture.
Immediate Care for Injuries
If a puncture wound occurs from a starfish, immediate first aid focuses on neutralizing any venom and managing the wound. The affected area should be immersed in non-scalding hot water, maintaining a temperature between 110°F and 115°F (43°C–46°C). This heat helps to break down and inactivate the heat-labile venom, providing relief from immediate pain.
The limb should be soaked for 30 to 90 minutes and the process repeated if pain returns. After soaking, use tweezers to carefully remove any visible, superficial spine fragments from the wound. If spines are deeply embedded or near joints, nerves, or blood vessels, removal should be left to a healthcare professional to avoid further tissue damage.
The wound needs to be thoroughly scrubbed with soap and fresh water and then rinsed extensively. It should be left open and not covered with an occlusive dressing to reduce the risk of infection. Watch for signs of systemic reaction, such as weakness, severe nausea, or paralysis, which require immediate emergency medical attention. A tetanus booster is often recommended for deep puncture wounds.