Jellyfish

Jellyfish are members of the phylum Cnidaria. Members of this structurally simple marine group possess one of two body forms. Sea anemones, sea whips, corals and hydroids are polyps growing attached to rocks or other hard surfaces of the sea. Jellyfish and the Portuguese man-of- war are free-swimming medusae. Both body forms display radial symmetry with body parts radiating from a central axis. This symmetry allows jellyfish to respond to food or danger from any direction.

Jellyfish occur in a wide variety of sizes, shapes and colors. Most are semi-transparent or glassy and bell-shaped, measuring less than an inch to over a foot across the bell, although some may reach 7 feet. The tentacles of some jellyfish can reach lengths greater than 100 feet. Regardless of their size or shape, most jellyfish are very fragile, often containing less than 5% solid organic matter.

Jellyfish inhabit every major oceanic area of the world and are capable of withstanding a wide range of temperatures and salinities. Most live in shallow coastal waters, but a few inhabit

Venom Apparatus
Jellyfish are equipped with a specialized venom apparatus (cnidoblast) for defense and feeding. A capsule (nematocyst) inside the cnidoblast contains a trigger and a stinging structure. The stinging structure varies according to species, but generally consists of a hollow coiled thread with barbs lining its surface. Nematocysts are concentrated on the tentacles or oral arms. A single tentacle can have hundreds or thousands of nematocysts embedded in the epidermis. Triggers of nematocysts are activated when contact is made with another object. Pressure within the nematocyst forces the stinging thread to rapidly uncoil. The thousands of nematocysts act as small harpoons, firing into prey, injecting paralyzing toxins. Stings usually paralyze or kill only small creatures but some jellyfish are harmful to humans. Jellyfish do not "attack" humans. Stings occur when swimmers or beachcombers come in contact with nematocysts. Severity of stings depends on the species of jellyfish, the penetrating power of the nematocyst, the thickness of exposed skin of the victim and the sensitivity of the victim to the venom. The majority of stings from jellyfish occur in tropical and warm temperate waters. Most species off the southeastern coast are capable of inflicting only mild stings resulting in minor discomfort.

Treatment of Sting
Primary first aid for any jellyfish sting should be to minimize the number of nematocysts discharging into the skin and to reduce the harmful effects of the venom. If stung by a jellyfish, the victim should carefully remove the tentacles that adhere to the skin by using sand, clothing, towels, seaweed or other available materials. As long as tentacles remain on the skin, they will continue to discharge venom.

A variety of substances have been used to reduce the effects of jellyfish stings. Meat tenderizer, sugar, vinegar, plant juices and sodium bicarbonate have all been used with varying degrees of success. Methylated spirits and other forms of alcohol formerly recommended for inhibiting stinging cells actually stimulate them and may increase pain and cause severe skin reactions. Picric acid and human urine also cause a discharge of nematocysts and should not be used. Victims of serious stings should make every effort to get out of the water as soon as possible to avoid drowning. If swelling and pain from more serious stings persists, prompt medical attention should be sought. Recovery periods can vary from several minutes to several weeks.

Prevention
Care should be taken when swimming in areas where dangerous jellies are known to exist or when an abundance of jellies of any type is present. Keep in mind that tentacles of some species may trail a great distance from the body of the organism and should be given lots of room. Stings, resulting from remnants of damaged tentacles, can occur in waters after heavy storms. Rubber skindiving suits offer protection against most contact.

Be careful when investigating jellyfish that have washed ashore. Although they may be dead, they may still be capable of inflicting stings. Remember to take precautions when removing tentacles after contact or additional stings may result.

Photographer: Florida Keys National Marine Sanctuary Staff
Credit: Florida Keys National Marine Sanctuary

Spotted Eagle Ray / Aetobatus narinari

Common Names: Spotted eagle ray, White-spotted eagle ray

Latin Name: Aetobatus narinari

Family: Myliobatidae

Identification: Very wide rhomboid disc. Prominent brow with flattened, pointed snout. Very long, whip like tail (often broken off part way). Dorsum black, bluish, or gray, covered with small white spots. In some individuals the white spots can be slightly larger with black centers. The species is apparently under review and may be divided in the future. Ventrum pale.

Size: Wing span to 200cm. Max 250cm. Nose to tail (when complete) max 500cm.

Habitat: Cruises reef faces and sand flats (where it feeds). Also open ocean. Intertidal to 24m.

Abundance: Commonly seen in Florida and Caribbean.

Distribution: On the Atlantic coast from Virginia to Brazil. Circumtropical.

Behavior: Known to school in some areas. It feeds by scooping its flattened snout through the sand. Preys mainly on mollusks.

Reproduction: Ovoviviparous.

Reaction to divers: Generally shy and hard to approach. The best way I have found to get close to these rays is to sneak up on them from behind when feeding

Photography: Playa Santa Maria / Los Cabos Corredor / Alberto Misrachi

Hammerhead Shark / Sphyrna zygaena

GENERAL DESCRIPTION
The great hammerhead shark has a wide, thick head with the eyes at the margins. The head is indented at the center of the "hammer," which is almost rectangular in shape. This shark is gray-brown above with an off-white belly. The first dorsal fin (the large fin on the top of the shark that most people associate with sharks) is very large and pointed.

TEETH
Teeth are triangular with extremely serrated edges.

SIZE
The average great hammerhead shark is up to 11.5 feet (3.5 m) long. The largest reported was 20 feet (6 m) long. These large sharks average about over 500 pounds (230 kg) but can weigh as much as 1,000 pounds (450 kg).

DIET AND FEEDING HABITS
The great hammerhead is a fierce predator with a good sense of smell that helps it find its prey. The great hammerhead eats fish, including rays, and other sharks, squid, octopuses, and crustaceans. The great hammerhead has been known to be cannibalistic.

Stingrays seem to be a particular favorite of the great hammerhead. It kills the ray by using its "hammer" to pin the stingray down while it takes bites from the ray's wings.

HAMMERHEAD SHARK ATTACKS
Many of the hammerheads are harmless to people, but a few species, like the great hammerhead, can be very dangerous.

HABITAT
The great hammerhead swims in warm and relatively warm water along the coastlines. They live over the continental shelves and the adjacent drop-off (the upper part of the mesopelagic zone) to depths of about 260 feet (80 m). DISTRIBUTION
The great hammerhead is found in tropical and sub-tropical waters worldwide.

MIGRATION
The great hammerhead migrates seasonally to cooler waters during the summer.

REPRODUCTION
The great hammerheads are viviparous, giving birth to live young. The 20-40 pups are about 27 inches (70 cm) long at birth.

Photography: Gordo Banks / San Jose del Cabo / Alberto Misrachi

California Sea Lion / Zalophus califonianus

The California sea lion is a type of seal that lives in cool waters off the rocky coast of western North America. This marine mammal makes a roaring noise (hence its name), barks, and honks. Sea lions are fast swimmers, going up to 25 mph (40 kph) in short bursts. They are also very fast on land, "walking" with all four flippers.
These intelligent and social animals congregate in large groups on land (called colonies) and smaller groups in the water (called rafts). Breeding areas are called rookeries. (Classification: Suborder Pinnipedia, Family Otariidae, Subfamily Otariinae, Genus Zalophus, Species californianus)

Anatomy: The California sea lion has a thick layer of blubber (fat), short, thick fur that is dark brown to buff-colored, and a dog-like head. Males (called bulls) are darker and bigger than females. Males also have a thick furry mane around the neck. Bulls weigh up to 850 pounds (380 kg) and are up to 8 feet (2.5 m) long. Females weigh up to 250 pounds (115 kg) and are up to 6.5 feet (2 m) long. The whiskers (called vibrissae) help the seal's sense of touch. The nostrils are closed in the resting state. The sea lion has small external ears and a good sense of hearing. It also has keen eyesight but no color vision.

Diet: Sea lions are carnivores (meat-eaters); they eat fish, squid, octopi, crabs, clams, and lobsters. Seals don't chew their food. They swallow it in large chunks. They can crush the shells of crustaceans and mollusks with their flat back teeth.

Predators: Sea lions are hunted by killer whales (orcas) and some sharks.

Photography: North Wall / Cabo San Lucas / Carlos Aboyo

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Whale Shark / Rhincodon Typus

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WHALE SHARK
Rhincodon typus
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GENERAL DESCRIPTION
The whale shark is a the biggest shark and the biggest fish. It is NOT a whale. It has a huge mouth which can be up to 4 feet (1.4 m) wide. Its mouth is at the very front of its head (not on the underside of the head like in most sharks). It has a wide, flat head, a rounded snout, small eyes, 5 very large gill slits, 2 dorsal fins (on its back) and 2 pectoral fins (on its sides). The spiracle (a vestigial first gill slit used for breathing when the shark is resting on the sea floor) is located just behind the shark's eye. Its tail has a top fin much larger than the lower fin.
The whale shark has distinctive light-yellow markings (random stripes and dots) on its very thick dark gray skin. Its skin is up to 4 inches (10 cm) thick. There are three prominent ridges running along each side of the shark's body.
This enormous shark is a filter feeder and sieves enormous amounts of plankton to eat through its gills as it swims.
SIZE
The whale shark is up to 46 feet (14 m), weighing up to 15 tons. The average size is 25 feet (7.6 m) long It is the largest fish in the world. Females are larger than males (like most sharks).

TEETH
Whale sharks have about 3,000 very tiny teeth but they are of little use. Whale sharks are filter feeders who sieve their tiny food through their large gills.
DIET AND FEEDING HABITS
The whale shark is a filter feeder that sieves small animals from the water. As it swims with its mouth open, it sucks masses of water filled with prey into its mouth and through spongy tissue between its 5 large gill arches. After closing its mouth, the shark uses gills rakers that filter the nourishment from the water. Anything that doesn't pass through the gills is eaten. Gill rakers are bristly structures (the thousands of bristles are about 4 inches or 10 cm long) in the shark's mouth that trap the small organisms which the shark then swallows. The water is expelled through the sharks 5 pairs of gill slits. The prey includes plankton, krill, small fish, and squid. The shark can process over 1500 gallons (6000 liters) of water each hour.
SOCIAL GROUPS
Whale sharks are solitary creatures. Groups of whale sharks have only rarely been seen.
HABITAT
Whale sharks live in warm water (near the equator) both along the coast and in the open seas. They spend most of their time near the surface.
DISTRIBUTION
Whale sharks are found worldwide in the warm oceans from the equator to about ±30-40° latitude. They are not, however, found in the Mediterranean Sea.
SWIMMING
Whale sharks are slow swimmers, going no more than 3 mph (5 kph). They swim by moving their entire bodies from side to side (not just their tails, like some other sharks do).
REPRODUCTION
The Whale shark was long thought to be oviparous (an egg 14 inches (36 cm) long was found in the Gulf of Mexico in 1953; this would be the largest egg in the world). Recently, pregnant females have been found containing hundreds of pups, so, Whale sharks are viviparous, giving birth to live young. Newborns are over 2 feet (60 cm) long.
Whale sharks are sexually mature at 30 years old. This is the age at which they are able to mate and reproduce.
WHALE SHARK ATTACKS
Whale sharks are harmless to people and usually indifferent to divers.
LIFE SPAN
It has been estimated that whale sharks may live up to 100 - 150 years.
Photography: Islotes / La Paz / Carlos Aboyo

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Life begins with a sunset at the sea of cortez.
Photography: Cabo San Lucas / Alberto Misrachi