Marine Reptile Characteristics • Land vertebrates are called tetrapods because they have four limbs designed for locomotion on land. They have lungs and breathe air, and, except for amphibians, they have reproductive systems that are not tied to water. • Marine reptiles have scales to minimize water loss, their eggs have a leathery shell to prevent them from drying out, and they are poikilotherms and ectotherms. There are about 7000 species of reptiles.
Marine Reptile Characteristics • Poikilotherms are organisms that have a body temperature that varies with that of the environment. Ectotherms are organisms that lose metabolic heat to the environment without it affecting their body temperatures. Organisms that are poikilotherms and ectotherms commonly are called “cold-blooded.”
Sea Turtles • Sea turtles have an armor-like shell or carapace that is fused to their backbone. Unlike land turtles, sea turtles cannot retract their legs into their shells. Their legs are modified into flippers for swimming. There are only seven species of sea turtles in the world: the green turtles, the hawksbill turtle, the leatherback, the Ridleys, and the loggerhead.
Sea Turtle Reproduction • All female sea turtles return to land to lay their eggs. Many migrate very long distances (up to 1360 miles) to return to the beach where they were born. They probably do not breed every year. They lay 100 to 200 eggs in a nest that they excavate in soft sand. The eggs hatch after 2 or so months and the baby sea turtles immediately crawl to the water and swim away. Not much is known about what happens to the babies as they mature into adults. Mortality is very high.
Sea Turtle Endangerment • Sea turtle beaches have been developed as beaches, condos, and hotels, and the artificial lights that come with people are detrimental to both the females and the babies. Dogs, ghost crabs, raccoons, wild pigs, and people eat sea turtle eggs. The babies are easy prey for predators, both on land and in the water. Adult sea turtles are accidentally caught in fishing nets and drown. Ocean predators, including people, also eat them.
Marine Snakes • There are about 55 species of sea snakes and they are found in the tropical Indian and Pacific oceans. Their tails are paddle-shaped for swimming. They are completely marine; they mate in the ocean and give birth to live young. They are carnivores that are closely related to cobras, and they are venomous.
Marine Iguanas • Marine iguanas only occur on the Galapagos Islands, in the equatorial Pacific just off the coast of South America. These unique reptiles spend part of their time on land, resting, mating, and sunbathing. They live on rocky coastlines and feed in the coastal ocean, eating sea weeds. • BBC Video
Salt Water Crocs • Salt-water crocodiles live in mangrove swamps and estuaries in the eastern Indian Ocean, Australia, and some of the western Pacific islands. They are mostly coastal. They are very aggressive and will attack people. • BBC Video • Saltwater Croc vs. Great White
Marine Birds • Birds are homeotherms and endotherms, which allows them to live in a wide variety of habitats. Birds can fly, and their bodies are covered with waterproof feathers that also help insulate them. Birds have hollow, light bones that help them fly. The shells that cover bird eggs are harder and more resistant to water loss than are reptile eggs.
Homeotherms are organisms able to keep their body temperature more or less constant regardless of the temperature of the environment. Endotherms are organisms that retain some metabolic heat, which raises their body temperature.
Sea Bird Characteristics • Seabirds are birds that spend a significant part of their lives at sea and feed on marine organisms. Seabirds nest on land. Most breed in large colonies, mate as lifelong pairs, and take care of their young. Seabirds are related to several different groups of land birds, and they differ from each other with respect to their flying skills, feeding mechanisms, and ability to live away from land. Most are predators on fish, squid, and bottom invertebrates. They are found from pole to pole.
Types of Sea Birds • The five types of seabirds are the penguins, the tubenoses, the pelicans (and related birds), the gulls (and related birds), and the shore birds.
PENGUINS! • Penguins are flightless and their wings are modified to be flippers that help them “fly” underwater. They have dense bones, which reduce buoyancy and help them remain underwater. Penguins are very good swimmers, but are very clumsy on land. They generally are adapted for cold weather (both on land and in the water) and prey on fishes. Penguins are found only in the Southern Hemisphere or at the equator.
A penguin Dilemma • 2 volunteers are needed to voice the two penguins in the following video • A Penguin Dilemma • Serious BBC Video
Tubenose Birds • The tubenoses are a group of seabirds with tube-like nostrils and heavy beaks that usually curve at the beak. They have salt glands that help them get rid of excess salt. The salt glands empty into the nostrils, and as a result these birds often look like they have runny noses. Tubenoses include the albatross, the shearwaters, and the petrels. They are skillful and strong flyers and fishers that spend months at sea without landing. Their flights may take them thousands of miles at a stretch. They only return to land for reproduction.
Examples of Tubenoses • Albatross Mating Dance • Shearwater Behavior
Mammal Characteristics • Marine mammals are in the Class Mammalia, and, like birds, are endotherms and homeotherms. They have hair, give birth to live young, and nurse their young. Pregnant females nourish their unborn babies through a placenta, a membrane that connects the embryo to the womb. Like other mammals, marine mammals have large brains relative to their body sizes. Additionally, like other mammals but unlike fishes, they breathe air.
Groups of Marine Mammals • The four groups of marine mammals are the 1) seals, sea lions, and walruses; 2) sea otters and polar bears; 3) manatees and dugongs, and 4) whales, dolphins, and porpoises. Seals, sea lions, and walruses are in the Order Pinnipedia, which are closely related to the Order Carnivora, with its cats, dogs, bears, and their kin. Sea otters and polar bears are in the Order Carnivora. Manatees and dugongs are in the Order Sirenia and are closely related to elephants and their relatives. Whales, dolphins, and porpoises are in the Order Cetacea and are distantly related to animals such as cattle, sheep, pigs, and hippos.
Pinnipedia • The Order Pinnipedia includes the seals, sea lions, and walruses. They are streamlined and have paddle-shaped flippers for swimming. They rest and breed on land. Pinnipeds are predators that eat mostly fishes and squid and mostly live in cold water. They have a thick layer of fat called blubber just under their skin that helps keep them warm, serves as a food reserve, and aids in buoyancy. Pinnipeds also have bristly, thick hair to help keep them warm.
Seals • Seals are pinnipeds with rear flippers that do not move forward well and which do not rotate backwards—this limits their mobility while on land. In the sea, they swim with powerful strokes of their rear flippers. On land, they pull themselves forward using their front flippers. There are 19 species of seals.
Conservation • Seals have been hunted for their blubber, skin, and meat for centuries and longer. Overhunting in the 20th century led to precipitous declines in some seal populations—many species are endangered or threatened. The Marine Mammal Protection Act of 1972 protects all marine mammals, including seals, and restricts the sale of all products in the United States.
Sea Lions • Sea lions are pinnipeds that are similar to seals in terms of their distribution and life styles. Sea lions include the fur seals (which aren’t really seals!), and there are 14 species. They have the following characteristics: they have external ears, they can rotate their rear flippers forward and backwards (which means they can move around on all four limbs on land), and their front flippers can rotate forward and backwards (allowing them to prop themselves up on land). Sea lions exhibit sexual dimorphism—the males are much larger than the females.
Sea Lion Conservation • Sea lions have been hunted for their blubber, skin, and meat for centuries and longer. Overhunting in the 20th century led to precipitous declines in some sea lion populations—many species are endangered or threatened. The Marine Mammal Protection Act of 1972 protects all marine mammals, including sea lions, and restricts the sale of all products in the United States.
Walruses • The walrus is a large pinniped with a pair of large tusks that protrude downwards from the mouth and that are used for defense. Unlike the other Pinnipeds, it feeds mostly on bottom-dwelling marine invertebrates.
Sea Otters • Sea otters are the smallest marine mammals and, unlike other marine mammals, lack a layer of blubber. Instead, sea otters have dense fur that traps air as insulation. Sea otters spend all of their time in the water; they live, breed, feed, etc. there. They feed on many different types of invertebrates, including sea urchins, abalone, mussels, and crabs.
Sea Otter Conservation • Sea otters were hunted to near extinction because of their thick, soft fur. International protection in 1911 helped re-establish the severely decimated populations. However, recently, populations are again in decline, due most likely to changes in their ecosystem due to pollution and overfishing. Sea otters are a threatened species.
Polar Bears • Polar bears are semi-aquatic marine mammals that spend a lot of time on drifting ice in the Arctic. They are carnivores, feeding mostly on seals. Their populations have been declining due to habitat loss—warmer climates near the poles is melting the ice upon which they depend.
Sirenia • The Order Sirenia includes the manatees and the dugong. They are the only vegetarians among the marine mammals and feed on sea grasses and submerged vegetation. They have a pair of front flippers but instead of rear flippers, they have a paddle-shaped horizontal tail. Manatees live in the Atlantic Ocean in tropical and subtropical waters. The dugong lives on the east coast of Africa to some of the Pacific islands
Sirenia • People hunted sirenians for food, skin, and their oil-rich blubber. Because they reproduce slowly and because their habitat (the coastal ocean) has been altered and destroyed by human development, sirenians are in danger of extinction. Several species are already extinct; the four remaining species are all endangered.
Cetaceans (whales) • The largest group of marine mammals is the Order Cetacea, which includes the whales, dolphins, and porpoise. Of all the marine mammals, the cetaceans are most fully adapted to an aquatic life style. They spend their entire lives in the water, have very stream-lined bodies, and superficially resemble fish.
Why do these mammals look like fish? • Convergent evolution describes different, usually “very” un-related species that have similar structures because they have similar life styles. Cetaceans are mammals; fish are fish—definitely not closely related. They superficially resemble one another—stream-lined bodies, pectoral fins/flippers, dorsal fins, etc.—because their bodies are well adapted to swimming and life in the ocean.
Cetacean Anatomy • Cetaceans have a pair of front flippers. The muscular tail ends in a pair of fin-like, horizontal flukes. There is a dorsal fin, towards the end of the body. The nostrils are on top of the head and form a single or double holed opening called the blowhole. The blowhole is using for both inhaling and exhaling when the animal is at the surface.
Groups of Cetaceans • The two groups are the toothless, filter-feeding whales and the toothed, carnivorous whales (which includes the dolphins and porpoises).
Baleen Whales • The toothless whales are also known as the baleen whales. There are 13 species of baleen whales, and they are among the largest animals that have ever lived on earth. They were once common in the oceans, but hunting for their meat and blubber has decimated many of their populations. Baleen whales have two blowholes (compared to the toothed whales, which only have one blowhole).
Baleen Whales • The baleen whales have rows of flexible, fibrous plates called baleen that hang from their upper jaws. The inner edge of each baleen plate is made up of hair-like bristles that form a dense mat on the roof of the mouth. The baleen plates are made up of keratin, the same material that makes up our fingernails and hair. The baleen whales filter feed by gulping mouthfuls of water and then squeezing the water out through the bristles. Any food that is left behind sticks to the bristles and the whale licks it off with is tongue and then swallows it.
Toothed Whales • There are approximately 80 species of toothed whales. Their teeth are adapted to catch fish, squid, and other prey—they don’t chew their prey; they swallow it whole. The toothed whales have a single blowhole opening, unlike the baleen whales, which have two blowholes. The toothed whales include the dolphins, porpoises, and the non-baleen whales.
Adaptations for diving • A feature that helps the cetaceans swim and dive more effectively is having the blowhole on top of the head, which helps them to inhale and exhale very efficiently and quickly at the surface.To help them remain underwater for long periods of time without running out of oxygen for respiration, marine mammals breathe very efficiently and are able to put large amounts of oxygen into their bloodstreams. They have more blood cells that carry oxygen and have more muscle cells that store oxygen.Marine mammals are able to reduce their oxygen consumption while diving. They typically reduce their metabolism and heart rates and reduce blood flow to their extremities (while maintaining blood flow to essential organs like the brain).
Echolocation • Echolocation is a sensory system based on hearing that most toothed whales (dolphins and porpoises) and some pinnipeds and baleen whales use to find prey and to orient to their surrounding.
Echolocation • Cetaceans echolocate by emitting a series of clicks, squeaks, and whistles as air is forced through passages in the head while the blowhole is closed. These noises are focused and directed outward by the melon, a fatty structure on the forehead (the melon gives toothed whales their characteristic rounded foreheads). The echo of the noises (which bounce off objects around the cetacean) is received primarily by the lower jaw, which transmits the echoes to the two very sensitive inner ears. The echoes are interpreted by the brain, which forms a mental “picture” of the surroundings.
Communication • Vocalizations are the sounds that animals make to communicate with each other (echolocation is NOT a type of vocalization). Sea lions and fur seals bark and whimper; seals grunt, whistle, and chirp. Cetaceans use low-frequency sounds such as grunts, barks, squeaks, chirps, and even “moos” to communicate with each other. Perhaps the most well known cetacean vocalization is the song of the humpback whale, which may last for 1/2 hour or longer.
Communication • Marine mammals vocalize for many reasons. Pinnipeds vocalizations are especially important in maintaining territories and in recognition between mother and pup. Cetaceans vocalize during social and sexual encounters. Vocalization allows individuals to identify one another and communicate information about food sources, predators, and alarm. Male humpback whales “sing” to attract females and to advertise their readiness to mate.