The marine environment is home to a beautiful variety of aquatic life. However, multiple marine species may present a hazard to humans via bite trauma, envenomation or even electrocution. This slideshow provides an overview of hazardous marine life and presents the basic treatment strategies for the care of victims.

Image courtesy of shutterstock | guentermanaus.

The great white shark (Carcharodon carcharias) is implicated in more attacks than any other species, while the bull shark (Carcharhinus leucas) and the tiger shark (Galeocerdo cuvier) are also responsible for a significant number of attacks worldwide. The oceanic whitetip (Carcharhinus longimanus) may be responsible for a significant number of attacks in the open ocean.

The United States is home to the most shark attacks annually, with most attacks occurring in Florida, Hawaii, California, and the Carolinas. Australia is home to the second most shark attacks and the most fatalities, with Queensland and New South Wales being the location of the majority of attacks.^[1]

Image courtesy of Alamy / Jeff Rotman.

Shark attacks can be broadly categorized into two main categories, provoked and unprovoked attacks.

• Hit-and-Run Attacks: The most common type, the shark most likely mistakes a human for normal prey and takes a single bite and then leaves the area.
• Bump-and-Bite Attacks: The shark circles and bumps the victim prior to biting.
• Sneak Attacks: Usually in deeper waters, the shark bites without warning, and then returns for further attacks.

The "bump-and-bite" and the "sneak attack" are not as common as the "hit-and-run" attack, but are more deadly and result in more significant injuries.

Sharks can generate a substantial bite force typically followed by tearing and torquing using their mass and musculature to rip apart flesh.

The image shows a Senegalese fisherman's thigh, forty years after a shark attack.

Images courtesy of Dreamstime (left) and Trape S. Shark attacks in Dakar and the Cap Vert Peninsula, Senegal: low incidence despite high occurrence of potentially dangerous species. PLoS One. 2008 Jan 30;3(1):e1495 (right).

All shark bites require immediate medical attention. On scene immediate pressure should be applied to the hemorrhaging wound. Tourniquets or application of pressure to pressure points should be considered if necessary. Wounds should be dressed in preparation of transporting the patient to definitive medical management. In the case of diminishing mental state, airway patency should be established and care should be taken to avoid hypothermia.

Upon arrival of EMS or at definitive medical care (typically an emergency department of a trauma center) large bore IV access should be obtained in order to provide immediate resuscitation. Establishment of a subglottic airway should be accomplished if necessary. Wounds should be explored for foreign bodies including shark teeth that may have broken off during the attack. The degree of vascular or nervous damage should be determined via detailed distal examination. Immediate control of hemorrhage may be difficult and a tourniquet may be required to prevent exsanguination. Large volume resuscitation and massive transfusion may also be required. Most victims of significant shark bites should be treated at trauma centers and tetanus vaccination and antibiotics as well as wound lavage should be provided.

Shown is a bull shark in the Bahamas and a shark tooth.

Images courtesy of Wikimedia Commons.

Even though the risk of a shark attack is minute, the following steps should be followed in order to further reduce the risk.^[3,4]

• Avoid the shark's favored hunting grounds. Sharks frequent drop-offs from shallow to deep water, troughs between submerged sand bars, and deep channels.
• Avoid the water if bleeding. Menstrual blood has not been shown to increase the risk of shark attack, but a shark in the vicinity can likely sense the blood.
• Avoid wearing or carrying shiny objects, such as jewelry or brightly contrasting colors. Some non-shark aquatic animals including barracudas are attracted to shiny objects as they may mimic the appearance of prey species.
• Spear fishing, fishing, and chumming the water will likely attract sharks.
• Erratic swimming or splashing at the surface may cause a shark to mistake a person for its natural prey.
• Agitated swimming movements by a shark, particularly if accompanied by a raised snout, lowered pectoral fins, and hump-backed posture, may indicate aggressiveness.
• Avoid swimming at dawn, dusk, and nighttime hours when many sharks actively feed.
• Swim in a group because sharks are more likely to attack if a person is isolated and alone.

Image courtesy of Sam Shlomo Spaeth, Medscape.

Marine envenomations are common among marine sport and recreation enthusiasts. Most envenomations are mild and self-limited, but several species of marine animals can cause significant morbidity and mortality. Among these are the cnidarians, cone shells, echinoderms, lionfish, stonefish, blue-ringed octopuses, and stingrays; each species produces a different clinical picture. Most of these species are found in exotic locations, but others may be found in the continental United States. The image shows a blue-ringed octopus in Australia.

Image courtesy of Wikimedia Commons / Jens Petersen.

Cnidaria envenomations are extremely common. This phylum contains the Portuguese man-of-war (class Hydrozoa),^[5] "true" and box jellyfish (respective classes: Scyphozoa and Cubozoa), fire and soft corals (respective classes Hydrozoa and Anthozoa), and sea anemones (class Anthozoa).^[6] Cnidaria toxins are located in stinging cells called nematocysts. The venom of each species is complex and unique, with some combination of catecholamines, histamines, hyaluronidases, fibrinolysins, kinins, phospholipases, and various hemolytic, cardiotoxic, and dermatonecrotic toxins.^[7] The box jellyfish is the deadliest of the cnidarians, with global reports of deaths from neuromuscular and respiratory paralysis, drowning, and cardiovascular collapse.^[7]

Shown is a box jellyfish (left) and envenomation caused by the Portuguese man-of-war (right).

Images courtesy of Wikimedia Commons (left) and Medscape/ the Department of Dermatology, UTMB at Galveston, Texas (right).

Cnidaria envenomation may result in immediate allergic, immediate toxic, or delayed allergic responses, depending on the degree of envenomation and the patient's immunologic response. The most common presentation is a painful papular-urticarial eruption at the site of contact, often in a linear, streaklike distribution from the long tentacles (shown).^[7] Lesions may last for minutes to hours, with further progression to vesicular, hemorrhagic, or necrotizing lesions.

Image courtesy of Medscape/ the Department of Dermatology, UTMB at Galveston, Texas.

In Australia, where box jellyfish are prevalent, netting is used in the summer to enclose swimming areas for protection (shown). Treatment for most Cnidaria envenomations involves tentacle removal and inactivation of the nematocysts with vinegar or acetic acid.^[7] Local wound care to prevent secondary infection, oral antihistamines for pruritus, and topical anesthetics or corticosteroids may be used on a case-by-case basis.^[7] Antivenin also exists for box jellyfish stings.

Image courtesy of Wikimedia Commons / Colin Henein.

Conidae are a family of carnivorous cone shells with more than 500 members. They are prized by shell collectors for their bright colors and patterns. For these slow-moving organisms to hunt much faster prey, they have developed an extremely potent venom that they unleash from a chitinous barb attached to an extensible proboscis used like a harpoon.^[7,8] The attack itself is the fastest in the animal kingdom. The venom mixture is specific to each species, with rapidly acting paralytic and lethal oligopeptide toxins that target ion channels.^[7,8] Stings usually occur in the extremities of swimmers in shallow waters of the South Pacific. The image shown is of a Conus geographicus, which produces a potent conotoxin (cartoon representation of mu-conotoxin shown on inset) that is selective for the muscle-type acetylcholine receptor.

Images courtesy of Wikimedia Commons / Kerry Matz, National Institute of General Medical Services and Jawahar Swaminathan, European Bioinformatics Institute (inset).

Typical Conidae stings are followed by local numbness, paresthesias, and ischemia.^[8] Serious systemic envenomations may lead to nausea, cephalgia, paralysis, coma, disseminated intravascular coagulation, and respiratory failure within hours.^[8] Initial care with immersion of the affected body part in nonscalding hot water, compressive bandaging, and immobilization may help limit the disease course.^[7,8] No antivenin is available. Close monitoring for respiratory and cardiovascular complications is mandatory. It is important to ensure there is no retained tooth. Overall care is supportive in nature, and symptoms may take several weeks to resolve.^[7,8] The image shown is of a cone shell in Guam eating a small fish.

Image courtesy of Wikimedia Commons / David Burdick.

The phylum Echinodermata includes brittle stars (class Ophiuroidea), starfish (Asteroidea), sea urchins (Echinoidea), and sea cucumbers (Holothuroidea).^[9] Most echinoderms are poisonous, but only some species cause venomous injuries in humans. Starfish and sea urchins cause puncture wounds from their sharp spines (shown), and patients typically report incapacitating pain. There may be prolonged bleeding, ecchymosis, and soft-tissue swelling of the wound.^[9] Sea cucumbers may cause damage from contact with the toxin-containing body wall or from extruded threadlike organs from the anus, which may induce contact dermatitis. Ocular contact may lead to inflammation or even blindness. If ingested without proper preparation, sea cucumbers may be lethal.^[9]

Image courtesy of Jonathan Lai.

Systemic effects of echinoderm envenomation are protean and include nausea, vomiting, paresthesias, weakness, respiratory distress, and delirium.^[9] Retained spines may lead to granuloma formation. Treatment is largely supportive, with analgesia, wound exploration to remove foreign bodies, and direct pressure to control bleeding. No antivenin exists.^[9] People in shallow waters are at greatest risk for echinoderm envenomation, but envenomations in deep water have the greatest potential for complications, as the sudden illness may cause uncontrolled ascent, leading to barotrauma or drowning.

The image shown is a swollen right hand from the toxin introduced through a spiking by a crown-of-thorns starfish.

Image courtesy of Wikimedia Commons.

Lionfish and stonefish belong to the family Scorpaenidae (class Osteichthyes), known for their ability to envenomate by means of specialized spines.^[10,11] Stonefish have stout, powerful spines with highly developed venom glands and a potentially fatal sting.^[7,10,11] Lionfish have long, slender spines (inset) with small venom glands and a less potent sting.^[10,11] The venom toxicity is the result of antigenic, heat-labile proteins of high molecular weight. Lionfish envenomations are associated with pain and swelling. Stonefish envenomations cause immediate incapacitating pain which spreads to involve the entire limb and regional lymph nodes. Severe pain may last for 12 hours and diminishes over the course of several days to weeks.^[7,10,11]

Images courtesy of Wikimedia Commons / Christian Mehlführer and National Oceanic and Atmospheric Administration / Stephen Vives (inset).

On examination, patients who encounter lionfish or stonefish will classically have one or more puncture wounds with surrounding cyanotic tissue, as shown in this patient who suffered a stonefish envenomation.^[7,10,11] Edema, erythema, and warmth may involve the entire limb, with subsequent vesicle formation, skin sloughing, and hypesthesia. Nausea, weakness, dyspnea, and hypotension may also occur. Treatment is largely supportive, including analgesia, immobilization, wound debridement, and hot water immersion of the affected limb(s). Monitor for respiratory and cardiovascular complications.^[7,10,11] Stonefish antivenin is available for intravenous or intramuscular administration.

Image courtesy of John Williamson, MD and Surf Lifesaving Queensland.

Octopuses are generally harmless except for the blue-ringed octopus (Hapalochlaena maculosa) (shown), found in the Indo-Pacific, particularly southern Australia.^[7,11,12] Octopus venom is a tetrodotoxin stored in the salivary glands and delivered by means of biting. The toxin blocks voltage-gated fast sodium channels, which impedes peripheral nerve conduction and can lead to flaccid paralysis and death from respiratory failure.^[7,11,12] Nausea, emesis, miosis, diabetes insipidus, and depressed cortical activity may also develop.^[12] Treatment is largely supportive, including immobilization, wound compression, and cardiopulmonary support.^[7,12] Closely monitor for respiratory failure; be prepared to administer rescue breathing. No antivenin or antidote is available. Experimental animal models have shown some success reversing tetrodotoxins with neostigmine, edrophonium, or 4-aminopyridine.^[12] Envenomation typically lasts 4-10 hours.

Image courtesy of Wikimedia Commons.

Stingrays (class Chondrichthyes) are bottom-dwelling cartilaginous fish that are not aggressive towards humans but frequently cause accidental injuries. The stingray tail has barbed stingers and 2 venom-containing grooves encased in an integumentary sheath.^[11,12] The tail may cause traumatic wounds (eg, penetrating injuries, evisceration wounds).^[13] More commonly, the tail may be thrust into the victim, producing a puncture wound (shown) or laceration into which toxin is injected. This causes immediate intense pain. Systemic symptoms, including syncope, nausea, vomiting, diarrhea, diaphoresis, muscle cramps, fasciculations, abdominal pain, seizures, and hypotension, may also develop.^[11,13]

Image courtesy of Wikimedia Commons.

Stingray barbs often detach and remain within the victim, as shown. The affected body part should be immediately immersed in very hot, nonscalding water.^[11,13] The toxin is a heat-sensitive protein which breaks down rapidly when heated. Careful wound exploration is needed to rule out a retained stinger, and plain x-rays are typically helpful to localized retained spines. Unless the wound is life threatening (eg, lacerations of major blood vessels or organs), treatment is otherwise supportive, and most patients recover quickly in the next 24-48 hours. Some patients may need surgical removal of a deeply embedded barb; others may require more aggressive management (eg, fluid resuscitation, blood transfusions).^[11,13] Of note, Steve Irwin, the wildlife television personality, died from a stingray barb that pierced his heart.

Image courtesy of John L. Meade, MD.

Sea snakes are members of the subfamily Hydrophiinae, venomous elapid snakes, who breathe air and have no gills. They are usually identifiable by their paddle shaped tail, which improves swimming ability.^[14] Sea snakes are generally gentle, and bites are not common and are usually provoked. They inhabit warm coastal waters in the tropics. The venom of these snakes is some of the most potent of any snake species. Nearly 80% of bites fail to produce any significant envenomation.^[14] The fangs, however are fragile and frequently break off and become lodged in the soft tissues. The toxins are mainly neurotoxins and myotoxins and peripheral paralysis and myonecrosis are frequently signs of envenomation. Symptoms may be generalized and typically occur within several hours of envenomation. Progressive paralysis of facial muscles leading to ptosis and respiratory musculature, including the diaphragm can lead to hypoventilation and eventually death. Myoglobinuria can result and impaired renal function and severe hyperkalemia can be noted.

The image shows a blue-lipped sea krait in Thailand.

Image courtesy of Wikimedia Commons / Jon Hanson.

To treat sea snake bites, apply pressure immobilization of the bitten extremity as quickly as possible because it may impede venom spread.

The bandage should be as tight as would be applied to a sprained ankle. An extremity splint completes the immobilization.^[14] Antivenom administration is indicated for any patient with signs of envenomation. Indications for antivenom use include shock, respiratory distress or failure, generalized myalgias, trismus, moderate-to-severe pain with passive movement of extremities, myoglobinuria, elevated creatine kinase level (>600 IU/l), altered level of consciousness, hyperkalemia, or leukocytosis. Administer antivenom as soon as possible and it can be administered up to 36 hours after envenomation.^[15]

Image courtesy of Medscape.