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Ocean Studies Introduction to Oceanography American Meteorological Society Chapter 10 Life in the Ocean © AMS Case in Point – For nearly 500 years the cod fishery was the basis of the economy of Newfoundland and other parts of Atlantic Canada. – Natural fluctuations in cod populations meant periods of low catches but fish stocks always recovered. – This changed after the middle of the 20th century when fishers began using huge factory trawlers to fish intensively for cod on the offshore banks, in waters beyond the limits of Canada’s national jurisdiction. • Some 40,000 people lost their jobs in Newfoundland where many small coastal villages depended entirely on the cod fishery for employment. © AMS Case in Point – Cod population declined, no sign of recovery, numbers continue to decrease • The ecosystem that formerly supported cod stocks was altered in such a way as to favor other fish and even lobsters in place of cod. • It is unclear if the fish stock and the ecosystem that sustained it for centuries can be restored. – The impact of the decline in cod stocks on the fishing industry in northwestern Europe is expected to be serious with the loss of many thousands of jobs and devastation of fishing communities—comparable to what happened earlier in Newfoundland. © AMS Life in the Ocean • Driving Question: – How have the large and diverse populations of marine organisms adapted to environmental conditions in the ocean? © AMS Life in the Ocean • In this chapter, we examine: – Various flora and fauna, marine habitats, and some of the ways marine organisms have adapted to the diverse environmental conditions in the ocean – Marine plant and animal life at the boundaries of the ocean including organisms living in the intertidal zone, wetlands and estuaries, the deep-sea floor, and coral reefs © AMS Marine Habitats – The ocean contains about 99.5% of Earth’s potentially inhabited living space. – Living organisms inhabit all parts of the ocean, even extreme environments such as Arctic and Antarctic sea ice and hydrothermal vents on the sea floor. • Including estuaries, coral reefs, polar oceans, and deep-sea trenches © AMS Marine Habitats • OCEANIC LIFE ZONES – Defines marine habitats in terms of distance from shore and depth – Open ocean waters constitute the pelagic zone. • Pelagic organisms include plankton (passive floaters or weak swimmers such as copepods, • larval fish, and jellyfish) and nekton (strong swimmers including most fish, squid, turtles, and marine mammals) – The environment of the sea floor at all depths is called the benthic zone. © AMS • Benthic organisms live either on the ocean bottom or within sediment deposits. • Include attached, burrowing, and mobile organisms, such as sea stars, crabs, worms, clams, sea cucumbers, sea anemones, urchins, snails, and barnacles Marine Habitats • OCEANIC LIFE ZONES – The area along the shore between high- and low-tide lines is the intertidal zone. • Home to ecosystems such as salt marshes and mangrove swamps – The area seaward from the shore, across the continental shelf, to the shelf break at a water depth of 120 to 200 m (390 to 650 ft) forms the neritic zone. • Commonly referred to as the coastal zone © AMS Marine Habitats Life zones in the ocean © AMS Marine Habitats • OCEANIC LIFE ZONES – Oceanic life zones are also defined in terms of nutrient supply and productivity. – Nutrient-poor waters having low primary production are described as oligotrophic. • Waters are exceptionally clear and appear luminous blue in sunlight due to the lack of organisms and suspended particles. – Nutrient-rich waters having high primary productivity are described as eutrophic • Excessive amounts of nutrients promotes an unusually abundant growth of phytoplankton (an algal bloom), which die, sink to the bottom, and deplete waters of dissolved oxygen as they decompose. © AMS Marine Habitats • PLANKTON IN THE PELAGIC ZONE – Phytoplankton are slightly denser than seawater and would gradually sink below the sunlit photic zone were it not for characteristics that counteract the tendency to sink. • Species have different shapes • This adaptation significantly slows sinking, especially in less dense, warm waters, and allows them to remain in the photic zone above the pycnocline. • The complex shapes and spiny structures of zooplanktonic organisms also increase their surface area to volume ratio, thereby adding to their buoyancy. – Some large planktonic animals have gelatinous bodies, consisting of 95% to 98% water, and are almost neutrally buoyant. © AMS Marine Habitats Although microscopic in size, diatoms can be beautiful and occur in a variety of shapes that provide them with © AMS buoyancy in the ocean. The bane of swimmers in the Chesapeake Bay, the stinging sea nettle, Chrysaora quiquecirrha. Marine Habitats • NEKTON IN THE PELAGIC ZONE – Larger, free-swimming pelagic animals, collectively called nekton, include fish of all sizes, squid, sea turtles, and marine mammals. – Many adaptations for buoyancy are found in nektonic organisms • Gas bladders – Many fishes have gas-filled swim bladders that control buoyancy and regulate the amount of gas in the bladder through a connection to the gut. © AMS – Most pelagic fish rely on active swimming to maintain their level in the ocean and obtain food. Life Strategies and Adaptations • VERTICAL MIGRATION – The photic zone is a dangerous place for marine organisms because predators can easily see them. – Many types of zooplankton avoid this threat by daily vertical migration. • Each day at dusk, they come to the surface zone to feed on phytoplankton. As daylight comes, they return to the relative safety of darker, deep waters. • Typically over a vertical distance of about 200 m (650 ft), require expenditure of enormous amounts of energy. • Vertical migration also plays a role in the carbon cycle in that carbon consumed by zooplankton feeding on phytoplankton near the surface at night is transported to deeper water as the animals respire during their return to depth at dawn. © AMS Life Strategies and Adaptations • LIGHT AND VISION – Near the ocean surface, light is abundant and predators have no problem locating prey. – The most common adaptation is adaptive coloration or camouflage where the animal’s color pattern closely matches its background substrate. • Many fish exhibit countershading, that is, their dorsal side (or back) is a dark color, making it difficult for predators above to see them against the dark, deep water. © AMS Life Strategies and Adaptations • LIGHT AND VISION – Marine animals that rely on sight to locate their prey in the dim light of the twilight zone have large, sensitive eyes. • The deeper in the twilight zone, the dimmer is the light, and the larger are the eyes of predators living there. – Below the twilight zone, in the greatest depths of the ocean, light is absent and vision is not useful for locating prey. • Many marine animals emit light, a phenomenon known as bioluminescence. © AMS Life Strategies and Adaptations • LIGHT AND VISION – Bioluminescence is mainly a marine phenomenon and is thought to have evolved a number of different times because it is a characteristic of a broad array of organisms. © AMS Bioluminescence is a property of a wide variety of marine organisms such as the jellyfish Aequorea aequorea pictured here. Life Strategies and Adaptations • LIGHT AND VISION – Marine animals use light emission to attract mates or prey, frighten or confuse predators, or to disguise themselves. – Short bursts of bioluminescent light apparently are especially effective at disorienting prey. © AMS Life Strategies and Adaptations • SOUND – Many marine animals have evolved ways of sensing the vibrations produced by other organisms moving through the water. – Seawater is essentially transparent to sound. – Many marine mammals, including whales, routinely communicate over great distances, even the width of an ocean basin. © AMS Life Strategies and Adaptations • FEEDING STRATEGIES – The general name for marine animals equipped with features that strain food particles out of large volumes of water is filter feeder. • Mostly eat food items trapped in their feeding structures; they are not selective – Some planktonic organisms, such as the planktonic snails called pteropods produce a large sticky net of mucus, which functions much like a spider web to trap small water-borne organisms and © AMS other food particles. This humpback whale feeds by straining water and trapping food in the baleen plates in its mouth Life at the Ocean’s Edge – After the pelagic zone, the next largest environment for marine life is the benthic zone, the sea floor at all depths, from the intertidal zone to the deep ocean. • Marine organisms that live in the benthic zone collectively are called benthos. – Three basic life strategies characterize the benthic zone: • Organisms may live attached to a firm surface – Seaweed, sea grasses, barnacles, mussels, clams, oysters, corals, and anemones • Construct burrows or tunnels or simply dig into sediment deposits • Move freely on the sea floor © AMS Life at the Ocean’s Edge • INTERTIDAL ZONE – The area along the shore between low and high-tide levels • Waves, winds, and tidal currents continually disturb the intertidal zone – Some intertidal zones feature extensive mud flats. • Often ideal habitats for submerged aquatic vegetation, salt marshes, and many forms of benthic animals – Seaweeds are important components of the intertidal zone and provide habitat for animals. © AMS Life at the Ocean’s Edge • INTERTIDAL ZONE – Animals are distributed in the intertidal zone according to their tolerance for drying and changes in temperature and salinity. – Highly mobile animals, such as crabs, move up and down with the changing water levels as the tide floods and ebbs. – Animals such as barnacles and mussels attach themselves to hard surfaces and can shut their shells completely, thereby retaining enough seawater inside to survive until they are covered again by the flood tide. © AMS Life at the Ocean’s Edge • INTERTIDAL ZONE – Tide pool: a volume of water left behind in a rock basin or other intertidal depression by an ebbing tide – Harbor species that have evolved to deal with wide fluctuations in environmental conditions; these organisms include certain algae, sea anemones, starfish, snails, small crustaceans, barnacles, mussels, and © AMS fish Life at the Ocean’s Edge • SEA GRASS BEDS AND SALT MARSHES – On mud flats and other soft-bottomed habitats the most important plants are sea grasses, also known as submerged aquatic vegetation (SAV). • These are angiosperms, flowering and seed bearing vascular plants with true roots. – Sea grass beds are highly productive with some rivaling the primary production of intensively developed agricultural land in the amount of carbon fixed. • Export large amounts of organic matter to nearby coastal waters © AMS Life at the Ocean’s Edge © AMS A sunlit sea grass meadow in the Florida Keys National Marine Sanctuary. Sea grasses are also known as submerged aquatic vegetation. Life at the Ocean’s Edge • SEA GRASS BEDS AND SALT MARSHES – Salt marshes commonly occur along sheltered shorelines and are ecologically similar to sea grass beds in estuaries. – Home to abundant marine life, and are refuges for waterfowl and other wildlife – Transition zones between marine and terrestrial ecosystems © AMS The edge of a salt marsh meeting oak and other higher ground flora on Daniel Island, SC Life at the Ocean’s Edge – Mangrove swamps: consist of tropical plant species including trees that grow in low marshy areas and can tolerate salt water flooding of their roots and lower stems – Compete successfully with local marsh grasses © AMS Red mangroves are common in Florida. Mangroves roots serve as critical habitat for many species and nutrient filters Life at the Ocean’s Edge • KELP FORESTS – Kelp forests grow where waters are cool and nutrient-rich. – Kelp includes various species of brown algae that grow to enormous size. – Strong waves easily destroy kelp beds and huge amounts of detached kelp wash onto beaches following storms. – Kelp forests support a rich community of animals that lives below its canopy © AMS Life at the Ocean’s Edge • CORAL REEFS – Carbonate-secreting colonial animals are the primary builders of coral-reef frameworks. – Open coral structures are bound together by layers of calcareous algae. – Grow along coastlines or cap extinct undersea volcanoes – Consist of thin veneers of living organisms growing on older layers of dead coral or volcanic rock – Corals are found in all ocean basins, but large reefs occur only in tropical waters, between about 30° N and 30° S. © AMS Life at the Ocean’s Edge © AMS The Great Barrier Reef extends for 2,000 kilometers along the northeastern coast of Australia. It is not a single reef, but a vast maze of reefs, passages, and coral cays Life at the Ocean’s Edge • CORAL REEFS – Most corals cannot tolerate prolonged exposure to either very low or high water temperatures or to large fluctuations in temperature. – Even small changes in sea surface temperatures— perhaps associated with large scale climate change— threaten coral reefs. – They also require clear water and are endangered by sediment runoff from land, oil spills, and other forms of water pollution. – Each type of coral animal builds a characteristic structure that is conspicuous on reef surfaces. © AMS Life at the Ocean’s Edge • CORAL REEFS – Individual coral animals, called polyps capture tiny plants and animals floating in the waters flowing over the reef. – Reef-building corals also obtain large amounts of energy from microscopic dinoflagellates called zooxanthellae living within the tissues of polyps. © AMS • Photosynthetic pigments in zooxanthellae are responsible for the bright color of corals. Coral polyps Life at the Ocean’s Edge • CORAL REEFS – Without zooxanthellae, corals cannot flourish. • Coral polyps have little pigmentation and appear nearly transparent on the coral’s white skeleton, a condition known as coral bleaching. • A rise in SST of one to two Celsius degrees (2 to 4 Fahrenheit degrees) is sufficient to cause temporary bleaching. – Atoll: A series of coral reefs surrounding a lagoon that remains after a volcanic island sinks beneath the waves or erodes away • Shaped like a ring or horseshoe and vary from 1 to 100 km (0.6 to 60 mi) across © AMS Life at the Ocean’s Edge Satellite image of an atoll in the western Pacific Ocean © AMS Life at the Ocean’s Edge • CORAL REEFS – Solitary corals and small coral reefs also live in cold, deep water along continental shelf breaks in some parts of the ocean (ahermatypic corals). • Cannot rely on zooxanthellae, so they depend exclusively on trapping food directly from the water using their stinging cells or nematocysts • Provide excellent habitats for deepwater fishes © AMS Life at the Ocean’s Edge Location of atolls and coral reefs in the world ocean. © AMS Life at the Ocean’s Edge Darkblotched rockfish nestled in the branches of a deep-sea gorgonian soft coral. © AMS Life at the Ocean’s Edge • BENTHIC FEEDING HABITS – Animals that live on or in soft-bottomed habitats—whether in the intertidal zone, shallow coastal areas, or in the deep sea— are divided into two categories. • Infauna inhabit sediment deposits. • Epifauna live on the sea floor. – Benthic animals living in muddy habitats require specialized breathing structures. © AMS Life at the Ocean’s Edge • LIFE ON THE DEEP-SEA FLOOR – Many unusual creatures live on the deep-sea floor. – Communities of specialized animals have evolved to live on the deep ocean bottom near hydrothermal vents. © AMS This delicate sea lily (crinoid), a member of the phylum that includes starfish, can orient toward the current to increase food capture. © AMS Tube worms at a hydrothermal vent on the floor of the Pacific Ocean. Discovery of such organisms launched a new avenue of inquiry into our understanding of biological processes operating in the deep ocean (especially chemosynthesis). Marine Animals • FISHES – Fish are cold blooded and hence are as warm or cold as the surrounding water. – Inhabit all parts of the ocean and possess special adaptations for buoyancy, swimming, and life in the dimly lit twilight zone as well as the greatest depths of the ocean – May be herbivorous, carnivorous, or omnivorous – Two major groups of fishes: elasmobranchs (or cartilaginous fishes) and teleosts (or bony fishes) • Elasmobranchs or cartilaginous fishes include sharks, skates, and rays and are considered to be more primitive. © AMS Marine Animals • FISHES – Their skeletons lack true bones and consist entirely of cartilage. – There are over 800 species of cartilaginous fishes. – Reproductive strategies favor survival of their young. © AMS Marine Animals • FISHES – Teleosts (or bony fishes) have bony skeletons, scales, and a flap covering their gills. – Most have a swim bladder, a gas-filled structure that can be inflated or deflated enabling the fish to adjust its buoyancy with changes in water depth. – Fishes living on or near the ocean bottom are called demersal fishes and many of them are commercially important, such as cod, halibut, haddock, and sole. – Flatfishes are demersal fishes that have a special coloration that camouflages them against the ocean bottom. © AMS Marine Animals • FISHES – Many environmental factors influence the reproductive success of bony fishes. • Anadromous fishes spend most of their lives in cold regions of the ocean, returning to the same river to breed when they are sexually mature. • Catadromous fishes are not as well known as anadromous fishes; they breed in the open ocean, but spend their adult lives in fresh water. – Many species of fish reduce predation by swimming together as organized groups, keeping a certain distance between one another. • This so-called schooling behavior is particularly advantageous in the open ocean where hiding places are few and far between. © AMS Marine Animals Note the two eyes on one side of the head of this flounder photographed at an ocean depth of more than 2600 m (8600 ft) off the North Carolina coast © AMS School of northern anchovies. Schooling is a behavioral adaptation of teleosts that may offer protection from predators. Marine Animals • MARINE MAMMALS – Warm blooded, air breathing animals that bear live young, which they nurse • Include whales, dolphins, seals, walrus, sea lions, and polar bears – The largest marine mammals, baleen whales, live primarily in the open ocean where they filter zooplankton from the water as they swim slowly with their mouths open. – Polar bears are unique to the Arctic and are the region’s largest land predator. • Inhabit the waters and coastal areas of Alaska, northern Canada, northern Russia, Greenland, and Norway © AMS Marine Animals • MARINE MAMMALS – Pinnipeds, named for their distinctive swimming flippers, include seals, sea lions, and walruses. • Many of them inhabit coastal waters. • Come ashore to breed, give birth, and rear their young © AMS Marine Animals • MARINE REPTILES – The few reptiles that live in the ocean fall into three groups, the best known being sea turtles. • All sea turtles live in the ocean, but come ashore to lay their eggs. • Only a few hatchlings survive to adulthood. © AMS Marine Animals • MARINE REPTILES – Sea snakes are rare, occurring only in the tropical Pacific and Indian Oceans, usually around reefs. • Sea snakes are reptiles and must come to the surface to breathe. • Some species of sea snakes go ashore to reproduce and lay eggs; others mate and bear live young without leaving the sea. – Marine iguanas are herbivores, feeding mostly on seaweeds in the intertidal zone. • Occur only in the Galápagos Islands in the equatorial Pacific Ocean • Having evolved from land lizards, they need a special adaptation to deal with the large amount of salt water they swallow while feeding. © AMS Marine Animals • SEA BIRDS – Carnivorous predators that occupy a high trophic level in marine food webs – No seabird can stay at sea for its entire life • All of them must come ashore to breed and lay eggs on a solid surface – Where fishing grounds are exceptionally productive, seabirds establish huge colonies on rocky shores and cliffs, especially during their breeding season. © AMS Marine Animals Brown pelican in breeding colors © AMS Although ungainly on land, the flightless penguin is an expert swimmer. Shown here are Gentoo Penguins (Pygoscelis papua), largest of the “bush-tail” penguins. They live on Antarctic islands as well as the Antarctic Peninsula Conclusions – Marine plants and animals have evolved many specialized adaptations involving buoyancy, feeding, reproduction, and protection from predators – Marine plants and animals are distributed nonuniformly in the ocean; their distribution is controlled primarily by environmental factors such as water temperature, salinity, light, and availability of food © AMS