Marine Envenomations: Invertebrates

Many marine invertebrates are equipped with toxin-based defense or prey-capture systems. Some of the most potent natural toxins are produced by marine invertebrates. Divers and snorkelers may be envenomed via contact with these creatures during a dive or when entering or exiting the water. While many envenomations result only in irritation and mild pain, serious immediate reactions and complications may occur. This article describes envenomations by invertebrates other than jellyfish; jellyfish stings merit a column all their own.
Like the venoms of marine vertebrates, marine-invertebrate venoms are often mixtures of compounds. Venom may induce tissue damage, systemic syndromes or even death via disruption of normal nervous system function or toxic effects on various types of cells and blood vessels. Marine- invertebrate toxins perform ideally within a narrow temperature range, so irrigation with hot (but not scalding) water can inactivate many of them. Foreign material, including small spines, should be removed to reduce the total amount of toxin delivered and, in some cases, the likelihood of infection.

Most of the symptoms associated with envenomation are due to toxic effects of the venom, but allergic reactions have been observed. Anaphylaxis is a potentially life-threatening allergic reaction that may involve difficulty breathing, low blood pressure and other severe symptoms. Treatment includes administering epinephrine, an antihistamine such as diphenhydramine (Benadryl), oxygen and corticosteroids. (Note: Epinephrine and corticosteroids must be prescribed by a physician and should be administered only by trained individuals.) Anyone suspected of having a serious reaction, whether a direct effect of the venom or an allergic response to it, should be treated immediately by a physician.
Starfish are common bottom-dwelling animals, and contact by divers is usually accidental. The crown-of-thorns starfish is a species with particularly potent venom. The thornlike spines on the starfish's surface are sufficiently sharp and stout to pierce a thick wetsuit. The spines release a toxin that can cause significant stinging pain as well as systemic symptoms such as nausea and vomiting.

Immediately immerse starfish puncture wounds in hot water to tolerance (generally about 113°F). A rescuer should test the temperature to avoid scalding the injured person. If the spines can be easily grasped without fragmentation, they should be removed and the wounds then washed with soap and water. Wounds should not be closed but may be dressed and bandaged. Puncture wounds are especially prone to infection, so treating physicians will consider antibiotic therapy, particularly if damage to deeper tissues is suspected or if the victim has an impaired immune system.

Sea urchin punctures may be treated similarly, although it is often difficult to achieve thorough removal of all spine fragments. The long, thin and brittle spines are likely to break off inside wounds, making identification and extraction challenging. Purple or black discoloration of the skin at the puncture site does not necessarily mean that a fragment is still embedded in the tissue. This "tattoo" may result from dye that has rubbed off the surface of the spine. If the discoloration persists after 24-48 hours, a retained spine fragment should be suspected. Spines or fragments penetrating deeply into tissues or joints should be removed by a physician.

Cone snails and blue-ringed octopuses are mollusks with potentially deadly venom.

Cone snails can be found in tropical waters worldwide but are most common in the Indo-Pacific region. Their shells have a variety of colors and patterns and may be attractive to divers; stings usually occur during attempts to handle or collect them. Cone snails are carnivorous and use their venom to catch worms, mollusks and small fish. They deliver venom to immobilize prey using a "harpoon," which in larger species is capable of piercing a wetsuit glove.

The venom from certain species is highly toxic and may cause serious illness or even death in humans. However, most cone snail stings are about as severe as a bee sting. Larger species may cause more significant symptoms, including intense localized pain, numbness and tingling, swelling and possibly vomiting. Onset of symptoms may be delayed for a few hours. Severe cases may involve muscle paralysis, changes in vision and breathing failure.

If the sting occurs on an arm or leg, a pressure-immobilization bandage should be applied. Place a thick, two- or three-inch square cloth or gauze pad directly over the sting. Hold this dressing firmly in place by applying an elastic bandage around the dressing and the limb. Wrap tightly enough to press the dressing into the skin but not so tight as to impair arterial circulation. Check for normal sensation and color in the fingers or toes to ensure that circulation is adequate. Continue wrapping the bandage around the entire limb, and apply a splint to keep the limb immobilized. Check the fingers or toes frequently on the way to the hospital to make sure that swelling has not impaired circulation.
Most octopus bites are uncomplicated injuries requiring wound care and vigilance for signs of infection. However, some species employ potent toxins capable of causing severe symptoms and even death. Blue-ringed octopus species inhabit shallow and tidal waters in the Indo-Pacific region. Although they are relatively small, one of their toxins, tetrodotoxin, is among the most lethal venom components in the animal kingdom. Tetrodotoxin is a neurotoxin that causes systemic symptoms including muscular weakness, paralysis and eventually respiratory arrest. Onset of symptoms may occur within minutes after a bite.

If a bite from a blue-ringed octopus occurs on an arm or leg, apply the pressure-immobilization technique described for cone snail envenomations. Victims of blue-ringed octopus bites may experience paralysis and difficulty breathing; rescuers should be prepared to provide supplemental oxygen and prolonged rescue breathing, which might save the victim's life. Despite progressive and complete paralysis, victims may remain conscious. Definitive care by a qualified physician is critical.

Marine-invertebrate envenomations are frequently painful, and some species have the potential to cause serious symptoms, even death. Care must be exercised while sharing the environment with these creatures. In the event of a significant envenomation, careful employment of the techniques described, an effective emergency plan and knowledge of local medical resources may be lifesaving.

© Alert Diver — Spring 2011