MSCI
The cell wall of diatoms is called the frustule. silica
The cell wall of dinoflagellates is composed of cellulose and some species will form plate-like structures as their cell wall.
Manatees and dugongs are also known as sea cows (fig. 13.15); they are members of the order Sirenia and are thought by some to be the source of mermaid stories. Manatees and dugongs are the world's only herbivorous marine mammals. Manatees are found in the brackish coastal bays and waterways of the warm southern Atlantic coasts and in the Caribbean, and dugongs are found in the seas of Southeast Asia, Africa, and Australia. Like whales, they never leave the water.
Whales belong to the mammal group called cetaceans; see table 13.2 for information about representative whales. Some cetaceans are toothed, pursuing and catching their prey with their teeth and jaws (for example, the killer whale, the sperm whale, and the small whales known as dolphins and porpoises). These whales belong to the suborder Odontocetes. Other whales have mouths fitted with strainers of baleen, or whalebone, through which they filter seawater to capture krill and other plankton. The blue, finback, right, sei, gray, and humpback whales are baleen whales, members of the suborder Mysticetes. The mouths of toothed and baleen whales are compared in figure 13.16. The blue, finback, and right whales possess baleen and swim open-mouthed to engulf water and plankton. The tongue pushes the water through the baleen, and the krill are trapped. The sei whale swims with its mouth partly open and uses its tongue to remove the organisms trapped in the baleen. The humpbacks circle an area rich in krill and expel air to form a circular screen, or a net of bubbles. The krill bunch together toward the center of this net, and the whales pass through the dense cloud of krill and scoop them up. The gray whale feeds mainly on small bottom crustaceans and worms.
Some of this organic material will be exported to the deep ocean via the biological pump to form sediments, but the vast majority of the material is broken down by a process called remineralization, mediated by heterotrophic bacteria
When the organisms decompose, the nutrients are released back to seawater in this same ratio, leading to nutrient regeneration nutrient regeneration the release of nutrients from organic matter through biological activity by consumers or decomposers.
Receptors along the shark's sides are sensitive to touch, vibration, currents, sound, and pressure
Fish that live on or near the bottom are known as demersal fish.
The few specialized marine plants that do exist include sea grasses, which resemble grass but are actually part of the lily family, salt marsh plants such as cordgrasses and other salt-tolerant plants (halophytes), and mangroves, which are trees and shrubs adapted to living in tropical and subtropical coastal regions. All of these plants are bottom-dwelling and can only survive at the ocean margins. The primary distinction between sea grasses and halophytes is that sea grasses are permanently submerged by seawater and are therefore true marine plants.
Halophytes can tolerate exposure to seawater but cannot survive prolonged periods of submersion. Mangroves are essentially land plants that have developed mechanisms to tolerate salt water to some degree. Salt marshes replace mangroves at higher latitudes where cold winter temperatures limit the survival of the mangroves. Although confined to the ocean margins, these ecosystems serve as nursery grounds for many marine species, stabilize the coast, and provide an important source of primary production. Seaweeds, or macroalgae, are large, plantlike algae. Unlike true plants, they do not produce flowers or seeds, and they have relatively simple tissue structure.
The periwinkle snail Littorina is well adapted to an environment that is more dry than wet; it is an air-breather, and some species will drown if caught underwater. At low tide, snails withdraw into their shells to prevent moisture loss and seal themselves off from the air with a horny disk called an operculum. Limpets are able to use their single muscular foot to press themselves tightly to the rocks to prevent drying out.
Just below the zone of snails and limpets, the small acorn barnacles filter food from the seawater and are able to survive even though they are covered with water only briefly during the few days of the spring tides each month. Barnacles are crustaceans, related to crabs and lobsters but cemented firmly in place. They have been described as animals that lie on their backs and spend their lives kicking food into their mouths with their feet. In some areas, the rocky splash zone is the home of another crustacean, the large (3 to 4 cm, or 1 to 2 in) isopod Ligia.
Nanoplankton are between 2 and 20 microns in size. The picoplankton and nanoplankton dominate the plankton of open-ocean environments
Microplankton, or net plankton, range between 20 and 200 microns in size (fig. 12.2). The microplankton have been well studied over the years because it is relatively straightforward to capture and concentrate these organisms using a plankton net made of fine mesh that can be dragged through the water.
Extremophiles are microorganisms that thrive under conditions that would be fatal to other life-forms: extreme temperatures (hot and cold), high levels of acid or salt, no oxygen, no sunlight.
Some absorbed solar energy is lost as heat, and some is lost as fluorescence. Chlorophyll a fluorescence from individual phytoplankton cells can be viewed using a fluorescence-detecting microscope
About 80% of benthic animals belong to the epifauna, and live on or attached to rocky areas and firm sediments. Animals that live buried in the substrate belong to the infauna and are associated with soft sediments such as mud or sand.
Some animals of the sea floor are sessile, or attached to the sea floor, as adults (for example, barnacles, sea anemones, and oysters), whereas others are motile all their lives (for example, crabs, sea stars, and snails).
The majority of animals living in the ocean spend their lives suspended in seawater; chapter 12 discussed the plankton— those (mostly small) organisms capable of vertical migration but at the mercy of horizontal currents. The nekton include approximately 5000 species— invertebrates and vertebrates—capable of swimming freely through the neritic and pelagic environments. The invertebrate group is quite small, including some large shrimp, crabs, and the mollusks. Fish have been phenomenally successful and dominate the nekton. And, while very popular, marine reptiles, birds, and mammals are also a small but very visible percentage of the nekton.
Some, particularly reptiles, birds, and mammals, spend part of their lives on land; to be considered "marine" they must spend at least 50% of their lives in the marine environment.
Tropical coral reefs are the most diverse and structurally complex of all marine communities. Coral reefs fringe one-sixth of the world's coastlines and provide habitat for tens of thousands of fish and other organisms.
ropical coral reefs account for somewhere between one-quarter and one-third of all marine species.
"The microbial loop" refers to the processes that convert DOM into biomass or inorganic nutrients that can be consumed by other organisms
A virus is a noncellular particle composed of genetic material surrounded by a protein coat.
There are more than 16,000 species of marine fishes, with the vast majority belonging to the class Osteichthyes (bony fish). More than three-quarters of the fish in the ocean live in coastal waters. Given the incredible diversity of bony fishes, it is perhaps not surprising that this group displays an incredible array of adaptations to various environments. Most fish are ectotherms, but there are exceptions; both the tuna and the mackerel shark family (which includes great white, mako, and salmon sharks) are capable of maintaining warmer core body temperatures than the surrounding seawater, making them endothermic, or warm-blooded. They accomplish this by minimizing heat loss through counter-current heat exchange (see chapter 12) and heat generated from muscular activity.
All bony fish possess gills (fig. 13.8) that allow exchange of oxygen and carbon dioxide with seawater (jawless fish have gill-like structures called gill pouches; sharks, skates, and rays have gills, but not gill covers). Most bony fish also possess a swim bladder to maintain buoyancy. Cartilaginous fish lack a swim bladder and must use the pectoral fins to provide lift, somewhat like the wings of an airplane (sharks) or bird wings (skates and rays). The swim bladder also provides the bony fish with extraordinary maneuverability; they can hover in the water or even swim backward, something cartilaginous fishes cannot do.
Among the most well-studied and widespread zooplankton types worldwide are small crustaceans (shrimplike animals), the copepods and euphausiids. They are found throughout the world's oceans, basically herbivores, and are able to consume more than half of there body weight each day.
Arrowworms, or chaetognaths (see fig. 12.12), are abundant in ocean waters from the surface to great depths. These macroscopic (2 to 3 cm, or 1 in), nearly transparent, voracious carnivores feed on other members of the zooplankton.
Blooms of phytoplankton occur when phytoplankton biomass increases more rapidly than can be balanced by loss processes such as sinking, death and grazing. Blooms commonly occur when growth conditions for the phytoplankton are favorable (sufficient nutrients and sunlight, for example), but zooplankton numbers are still low. Blooms can be detected as a rapid increase in chlorophyll a concentrations at a given site or a given depth.
Bacterioplankton have an enormous impact on biogeochemical cycles on our planet. They are directly involved in recycling nutrients, some can use nitrogen gas and they therefore influence nitrogen cycles, and they play important roles in the global carbon cycle.
While most of the phytoplankton in the ocean are harmless (indeed, they are the base of the food chain supporting all life!), a small subset can produce toxins, discolor the water, or otherwise negatively impact human and wildlife health. These organisms are collectively referred to as harmful algal blooms, or HABs.
Common members of marine phytoplankton are diatoms, dinoflagellates, coccolithophorids, cyanobacteria, and green algae.
Humans and their activities are among the greatest threats to the reefs. Reefs are damaged by careless sport divers trampling delicate corals and by boats grounding or dragging their anchors. Deforestation and development increase land runoff, carrying sediments, nutrients, and human and animal waste into coastal waters. Additional nutrients favor the growth of algae; the algae out-compete the corals for space, smothering the existing corals and preventing new coral colonies from starting.
Coral reefs are despoiled by shell collectors and mined for building materials. In French Polynesia, Thailand, and Sri Lanka, tons of coral are used as construction material each year. Low-lying coastal areas that lose their coral reefs have no protection against storm surges that accompany extreme weather events. This is particularly important to island nations in the Pacific.
Reef-building corals require warm, clear, shallow, clean water and a firm substrate to which they can attach. Because the water temperature must not go below 18°C and the optimal temperature is 23° to 25°C, their growth is restricted to tropical waters between 30°N and 30°S and away from cold-water currents.
Corals are colonial animals, and individual coral animals are called polyps
Where catching reef fish with a net is difficult, fishers may use sodium cyanide and explosives. Whether it is cyanide squirted into the water or explosives detonated in the water, the fish are temporarily stunned, making them easy to capture. These methods also kill many other reef organisms, including the reef-building organisms.
Deep-water corals, or "cold corals," lack zooxanthellae; they form large reefs at temperatures down to 4°C and at depths of up to 2000 meters.
Food webs complex of interacting food chains; all the feeding relations of a community taken together; includes production, consumption, decomposition, and the flow of energy.
Food Chain: examines the linear transfer of energy from one trophic level to the next.
They are effective primary producers, exposing a large blade area to both the water and the Sun and thus taking advantage of the large surface/volume ratio of the blades. In the sea, the quality and quantity of light change with depth. On land and at the sea surface, algae receive the full spectrum of visible light. The green algae have the same chlorophyll pigments as land plants; they are able to absorb the same wavelengths of light and they are found in shallow water. Algae found at moderate depths have a brown pigment that is more efficient at trapping the shorter wavelengths. At maximum growing depths, the algae are red, for the red pigment can best absorb the remaining blue-green light. The characteristic pattern for seaweed growing on a rocky shore is the green algae in shallow water, then the brown algae, and the red algae at greater depths. Seaweeds provide food and shelter for many animals. They act in the sea much as forests and shrubs do on land.
Green algae are mostly freshwater organisms, but a small number occur in the sea, including Ulva, the sea lettuce, and Codium, known as dead man's fingers. Green algae are related to the land plants; they have the same green chlorophyll pigments as land plants and they also store starch as a food reserve. All brown algae are marine and range from simple microscopic chains of cells to the kelps, which are the largest of the algae. Kelps have more tissue structure than most algae but are much simpler than flowering land plants. The kelps have strong stipes and effective holdfasts that allow them to colonize rocky points in fast currents or heavy surf, a habitat favored by the sea palm, Postelsia. Other kelps grow with holdfasts well below the depth of wave action and float their blades at the surface supported by gas-filled floats; for example, the bull kelp, Nereocystis, is especially abundant along the Alaskan, British Columbian, and Washington coasts, and the great kelp, Macrocystis, is found along the California coast. Other species are found off Chile, New Zealand, northern Europe, and Japan. Storage products include the carbohydrates laminarin and mannitol but not starch. The red algae are almost exclusively marine; they are the most abundant and widespread of the large algae.
In recent years, there has been much debate on effects of human-generated noise on whale behavior. Sources of noise pollution in the ocean include military use of sonar, oil and gas exploration employing seismic air gun technology (which produce high intensity, low frequency bursts of sound), the gradual increase of ambient noise from tankers and other ships, coastal jet ski traffic, and even offshore wind farms used to develop alternative energy. The navy uses sonar, which can travel for miles underwater, to detect the presence of submarine and other potential underwater hazards. A number of years ago, fourteen beaked whales were found beached on islands in the Bahamas about thirty-six hours after navy vessels used sonar for training exercises, and the strandings were linked to the sonar.
In the 1700s and 1800s, whalers from the United States, Great Britain, and the Scandinavian and other northern European countries pursued the whales far from shore, hunting them for their oil and baleen.
In the dim, transitional mesopelagic layer, between 200 and 1000 m (660 and 3300 ft), the waters support vast schools of small, luminous fish. Fishes of the mesopelagic zone are small, with large mouths, hinged jaws, and needlelike teeth. The bristlemouths (Cyclothone) are believed to be the most common fish in the sea. Each of its species lives at a relatively fixed depth; the deeper-living species are black, and the shallower-living species are silvery to blend with the dim light. At this depth, the lanternfish has a worldwide distribution; some 200 species are distinguished by the pattern of light organs along their sides. They are a major item in the diet of tuna, squid, and porpoises. Stomias, a fish with a huge mouth, long, pointed teeth, and light organs along its sides, and the large-eyed hatchetfish prey on the great clouds of euphausiids and copepods found at the mesopelagic depth.
In the perpetually dark bathypelagic zone, there is little food; only about 5% of the food produced in the photic zone is available at these depths (fig. 13.11). Here, the fish are small, between 2 and 10 cm (1 and 5 in), and have no spines or scales but are fierce and monstrous in appearance. They are mostly black in color with small eyes, huge mouths, and expandable stomachs. They breathe slowly, and the tissues of their small bodies have a high water and low protein content. Floating at constant depth without using energy for swimming, these fish go for long periods between feedings by using their food for energy rather than for increased tissue production. Most have bioluminescent organs or photophores on their undersides that allow them to blend with any light from above. These photophores may show different patterns among species and between sexes; they may also identify predators and are used as lures to attract prey. Some species have large teeth that incline back toward the gullet so the prey cannot escape, and others have gaping mouths with jaws that unhinge to allow the catching and eating of fish larger than themselves.
Along exposed gravel and sand shores, waves produce an unstable benthic environment. Few algae can attach to the shifting substrate, and few grazing animals are found. Sands and muds deposited in coves and bays with reduced water motion provide a more stable habitat. Here, the size and shape of the sediment particles and the organic content of the sediment determine the porosity (the amount of space between particles) and quality of the environment.
Most sand and mud animals are detritus feeders. Most detritus is formed from plant and algal material that is degraded by bacteria and fungi. The sand dollar feeds on detritus particles found between sand grains. Clams, cockles, and some worms are filter feeders, feeding on the detritus and microscopic organisms suspended in the water. Other animals are deposit feeders that engulf the sediment and process it in their gut to extract organic matter in a manner similar to that of earthworms. These deposit feeders are usually found in muds or muddy sands that have a high organic content: for example, burrowing sea cucumbers and the lugworm Arenicola, which produces the coiled castings seen outside its burrow.
Production of organic material from inorganic nutrients using light energy is termed primary production. The total amount of organic material produced through photosynthesis is gross primary production.
Net primary production is the gain in organic matter from photosynthesis by phytoplankton minus the reduction in organic matter due to respiration by phytoplankton
The reefs are not formed exclusively from the calcium carbonate skeletons of the coral. Encrusting algae that produce an outer calcareous covering also contribute; so do the minute shells of foraminifera, the shells of bivalves, the calcareous tubes of polychaete worms, and the spines and plates of sea urchins.
Oceanographers, marine biologists, and all those who have enjoyed the experience of a tropical coral reef have become increasingly concerned with the health of these biologically rich but delicately balanced regions of the oceans. Coral bleaching episodes, in which corals expel their zooxanthellae, exposing the coral's white calcium carbonate skeleton, have occurred from time to time, but unless the episodes were especially severe, the corals regained their algae and recovered. Between 1876 and 1979, only three bleaching events occurred, but over sixty bleach events were documented between 1979 and 1990. In the last two decades, this bleaching has become more frequent and more severe, and not all reefs have recovered.
Sea stars of many colors and sizes make their home in the lower littoral zone; these slow-moving but voracious carnivores prey on shellfish, sea urchins, and limpets. Their mouths are on their undersides, at the center of their central disks, surrounded by strong arms that are equipped with hundreds of tiny suction cups, or tube feet. The tube feet are operated by a water-vascular system, a kind of hydraulic system that attaches the animal very firmly to a hard surface. In feeding, the tube feet attach to the shell of the intended prey and, by a combination of holding and pulling, open the shell sufficiently to insert the sea star's stomach, which can be extruded through its mouth; enzymes are released, and digestion begins. Shellfish sense the approach of a sea star by substances it liberates into the water, and some execute violent escape maneuvers. Scallops swim jerkily; clams and cockles jump away; even the slow-moving sea urchins and limpets move as rapidly as possible.
Octopuses are seen occasionally from shore on very low tides. These eight-armed carnivorous animals are soft-bodied mollusks. They feed on crabs and shellfish and live in caves or dens identifiable by the piles of waste shells outside. They are known for their ability to flash color changes and move gracefully and swiftly over the bottom and through the water. The world's largest octopus is found in the coastal waters of the eastern North Pacific. It commonly measures 2 to 3 m (10 to 16.5 ft) in diameter and weighs 20 kg (45 lb), but specimens in excess of 7 m (23 ft) and 45 kg (100 lb) have been observed. They are shy and nonaggressive, although they are curious and have been shown to have learning ability and memory.
Coastal waters: high levels of primary productivity, as a result of high- nutrient input
Open ocean gyres: low levels of primary productivity, as a result of low- nutrient input
Penguins (fig. 13.5 a) cannot fly. Their wings have been modified into flippers that allow them to swim underwater, using their feet for steering. All but one species of penguin live in the Southern Hemisphere, primarily in Antarctic and Subantarctic waters. They are adapted to life in the cold, with a thick layer of fat beneath their feathers. Penguins establish breeding colonies that for the Adélie penguins (Pygoscelis adeliae) may contain up to a million mating pairs. Emperor penguins (Aptenodytes forsteri) huddle together to keep warm; the male incubates the single laid egg on his feet against his body for over two months while the female returns to sea to hunt. Chicks are born in the spring when the plankton blooms. The Galapágos penguin (Spheniscus mendiculus) lives along the equator, far from Antarctica. This penguin is restricted to regions where cold water upwells.
Pelicans and cormorants are large fishing birds with big beaks. They are strong fliers found mostly in coastal areas, but some venture far out to sea. A pelican (fig. 13.5 b) has a particularly large beak from which hangs a pouch used in catching fish. White pelicans of North America (Pelecanus erythrorhynchos) fish in groups, herding small schools of fish into shallow water and then scooping them up in their large pouches. The Pacific's brown pelican (Pelecanus occidentalis) does a spectacular dive from up to 10 m (30 ft) above the water to capture its prey. Cormorants are black, long-bodied birds with snakelike necks and moderately long bills that are hooked at the tip. They settle on the water and dive from the surface, swimming primarily with their feet but also using their wings. Because they do not have the water-repellent feathers of other seabirds, cormorants must return to land periodically to dry out.
The Coral Reef Watch of the National Oceanic and Atmospheric Administration (NOAA) utilizes remote sensing and in situ tools to monitor and report on the physical environmental conditions of coral reefs. Although warm temperatures are a common cause for bleaching events, there are other triggers. For example, in January 2010 cold water temperatures in the Florida Keys caused a coral bleaching event when water temperatures dropped 6.7°C (20°F). Bleaching can also be triggered by other environmental stresses, including bacterial infection, drops in salinity, extreme light, and various toxins (see the Diving In box entitled "Undersea Ultraviolet Radiation").
Periodically, the population of the sea star Acanthaster, known as the crown of thorns, increases dramatically; this sea star feeds on the coral polyps. Fossil evidence points to outbreaks having occurred along the Great Barrier Reef for at least the last 8000 years. Why the Acanthaster population increases so rapidly is unknown, but evidence points to a correlation between rainy weather (low salinity) and runoff (increased nutrients), allowing large numbers of Acanthaster larvae to survive. The clearing of land for agriculture and the development of coastal areas may also be related. Concern also exists that the harvesting of the large conchs that prey on the sea star may upset the population balance. One outbreak began in 1995 and by 1997 was affecting 40% of the reef. Outbreaks in individual reefs can last one to five years; outbreaks throughout reef systems can last up to a decade or longer. It takes ten to fifteen years for reef areas to recover from an Acanthaster outbreak, but the opening up of areas on the reef by the sea star may also allow slower-growing coral species to expand.
The word plankton comes from the Greek planktos, meaning to wander. In general, plankton are small organisms, commonly less than a few millimeters in size. Their small size means that they tend to be moved by currents from place to place while suspended in seawater.
Phytoplankton use solar energy (sunlight) to generate oxygen and the organic food that fuels most of the rest of life in the seas. Phytoplankton form the base of most food webs. Cyanobacteria are the only bacterial members of the phytoplankton. All other phytoplankton are eukaryotic . Zooplankton are composed of unicellular as well as multicellular organisms. In general, zooplankton consume other organisms. Many juvenile stages of non-planktonic adults are also members of the zooplankton. Bacteria are not members of the zooplankton. Zooplankton contain the largest members of the plankton. For example, some jellyfish are huge, trailing 15 m (50 ft) tentacles. The bacterioplankton are composed of members of the domains Bacteria and Archaea. Bacterioplankton commonly rely upon inorganic and organic compounds that are dissolved in the seawater.
The polar bear (Ursus maritimus) is the top predator in the Arctic (fig. 13.14). They are long-lived (up to twenty-five years) carnivores with dense fur and blubber for insulation. They live only in the Northern Hemisphere and in a region where winter temperatures can be as low as -46°C (-50°F); they maintain a body temperature of 37°C (98.6°F). Polar bears actually have more problems with overheating than with getting too cold. Adult males weigh 250 to 800 kg (550 to 1700 lbs) and females weigh 100 to 300 kg (200 to 700 lbs). They feed primarily on ringed seals. They hunt seals by waiting for them to emerge from the openings in the ice that the seals make so they can breathe or climb out to rest. The polar bear may wait hours for the seal to emerge. Polar bears also feed on the carcasses of dead whales or walruses.
Polar bears travel long distances over the ice, 30 km (19 mi) or more each day. They are also strong swimmers, swimming continuously for 100 km (62 mi). They have partially webbed feet to aid swimming. Polar bears commonly breed in April. The males spend the winter on the pack ice; pregnant females dig large dens either on the mainland or on sea ice to spend the winter. They commonly give birth to two cubs in December or January. In spring, mother and cubs migrate to the coast near the open sea. Cubs remain with their mother for at least two years. The world's total population of polar bears is estimated at 20,000 to 25,000. They are found in the United States, Canada, Greenland, Norway (Svalbard Islands), and Russia. The primary threat to polar bears is the decrease in sea ice coverage that is occurring. These bears are completely dependent on sea ice for all aspects of their lives.
Terns (fig. 13.5 c) and gulls are members of the fourth group of seabirds and are found all over the world except in the South Pacific between South America and Australia. Gulls are strong flyers and will eat anything; they forage over beach and open water. The terns are small, graceful birds with slender bills and forked tails. The Arctic tern (Sterna paradiseae) breeds in the Arctic and each winter migrates south of the Antarctic Circle, a round trip of 35,000 km (20,000 mi).
Puffins, murres, and auks are heavy-bodied, short-winged, short-legged diving birds.
Fish are found at all depths and in all the oceans. Their distribution patterns are determined directly or indirectly by their dependency on the ocean's primary producers. Fish are concentrated in upwelling areas, shallow coastal areas, and estuaries. There are three major groups of fish: jawless fishes, which include hagfish and lampreys; cartilaginous fishes, which include sharks, rays, skates, and ratfish; and bony fishes, which include the great majority of fishes.
Schooling has evolved independently in the majority of fish species; almost 80% of the more than 30,000 freshwater and marine fish species exhibit this behavior at some point during their life cycle, including predatory fish such as tuna and sharks. Schools may consist of a few fish in a small area, or they may cover several square kilometers; for example, herring in the North Sea have been seen in schools 15 km long and 5 km wide (9 × 3 mi). Why has schooling evolved so many times? There are several benefits. First, it reduces individual encounters with predators and may also confuse predators, making it more difficult to target individuals. Schooling may also enhance foraging success by making it more difficult for prey to evade the school. Fish may also save energy when swimming together, similar to drafting used by automobile drivers and bicyclists. Schooling also presumably increases reproduction success by maintaining a population in a constrained region. Usually fish in a school are of the same species and are similar in size. Schooling fish keep their relationships to one another constant as the school moves and changes direction.
. Sea otters inhabit coastal areas, taking shellfish and other foods from the bottom in relatively shallow waters. Sea otters are the smallest marine mammals. An average male sea otter that weighs about 36 kg (80 lb) will consume almost 9 kg (20 lb) of food each day, about 20% to 25% of his body weight. This food intake allows sea otters to maintain a metabolic rate almost 2.5 times higher than terrestrial mammals of the same size. That amount of food consumption would be comparable to a 120 lb human consuming 30 lb of food each day without gaining weight! They depend on their thick fur, which traps air to keep them warm; unlike other marine mammals, they do not have an insulating layer of blubber or fat. Sea otters spend almost all of their time in the water, where they breed and give birth. Sea otters live in and around kelp beds, where they often use rocks to help them break open huge quantities of sea urchins, mussels, abalone, and crabs that they consume for food. They often float on their backs and use their bodies as a table to work on while they eat.
Sea otters are considered keystone predators in kelp forests. A keystone predator, or keystone species keystone predator (or keystone species) an organism that plays a crucial role in an ecosystem, such as maintaining species diversity. , is an organism that plays a crucial role in an ecosystem, such as maintaining species diversity. An important food source for sea otters is the sea urchins that graze on kelp. If the numbers of sea otters decline, the numbers of sea urchins increase. Increased numbers of sea urchins impact the ability of kelp forests to grow. Kelp forests serve as nurseries for small fish and other animals and a reduced density of kelp reduces the size of fish nurseries.
Sea turtles can be distinguished from land turtles because sea turtles can not retract their heads into their shells and because their front limbs have been modified into flippers for swimming. Six of seven species of sea turtle are found in U.S. and Caribbean waters, including the green (Chelonia mydas), hawksbill (Eretmochelys imbricate), loggerhead (Caretta caretta), Kemp's ridley (Lepidochelys kempii), olive ridley (L. olivacea), and leatherback turtle (Dermochelys coriacea). The flatback sea turtle (Natator depressus) lives exclusively in Australian coastal waters.
Sea turtle population numbers are being dramatically reduced due to pollution, habitat degradation, and the demand for turtle products. Turtle eggs and turtle meat are prized throughout the Pacific, and turtle nests are raided by poachers. Sea turtle eggs incubate for up to a few months, during which time they are vulnerable to harvesting by humans, dogs, rats, or other carnivores.
Seals and sea lions belong to the pinnipeds, or "feather-footed" animals, so named for their four characteristic flippers. Representative pinnipeds are shown in figures 13.12 and 13.13. Both seals and sea lions spend most of their time at sea, hunting for fish and squid, but need to rest and breed on land. To stay warm, they have hair and blubber, although not nearly as much blubber as whales.
Seals are divided into true seals and eared seals. True seals have small ear holes and their rear flippers cannot be moved forward. Therefore, they do not get around well on land but move quickly through the water. Common true seals include the harbor seal (Phoca vitulina), the harp seal (Pagophilus groenlandicus), the Weddell (Leptonychotes weddellii) and leopard (Hydrurga leptonyx) seals of the Antarctic, and the northern elephant seal (Mirounga angustirostris), whose males can reach 3 tons. Common eared seals include the California sea lion (Zalophus californianus) and the northern fur seal (Callorhinus ursinus), once almost hunted to extinction for their fur. Eared seals have external ears and they can move their rear flippers forward so they can move quickly on land and can rear up into a partially erect position.
Seaweeds are members of a large group called algae. Photosynthetic autotrophs were introduced in chapter 11, and the unicellular planktonic algae were included in chapter 12. Here we consider the role of seaweeds and marine plants as part of the benthic community. Algae are distinguished from plants by body form, reproduction, accessory pigments, and storage products. Algae have simple tissues; they do not produce flowers or seeds (but some do produce planktonic spores), and they do not have roots (table 14.1).
Seaweeds are benthic organisms; they grow attached to rocks, shells, or any solid object. Seaweeds are attached by a basal organ known as a holdfast that anchors the seaweed firmly to a solid base or substrate. The holdfast is not a root; it does not absorb water or nutrients. Above the holdfast is a stemlike portion known as the stipe. The stipe may be so short that it is barely identifiable, or it may be up to 35 m (115 ft) in length. It acts as a flexible connection between the holdfast and the blades, the alga's photosynthetic organs. Seaweed blades are thin and are bathed on all sides by water.
Sharks, skates, and rays belong to the class Chondrichthyes, or cartilagenous fish. Unlike most fishes, most sharks bear live young. They also differ from other fish by their skeletons of cartilage rather than bone and by their toothlike scales. Shark scales have a covering of dentine similar to that on the teeth of vertebrates, and they are extremely abrasive; sharkskin has been used as a sandpaper and polishing material. The shark's teeth are modified scales; they are replaced rapidly if lost, and they occur in as many as seven overlapping rows. Sharks are actively aware of their environment through good eyesight; excellent senses of smell, hearing, and mechanical reception; and electrical sense.
Sharks see well under dim-light conditions. They have the ability to sense chemicals in their environment through smell, taste, a general chemical sense, and unique pit-organs distributed over their bodies. These pit-organs contain clusters of sensory cells resembling taste buds. The shark's sense of smell is acute; it has a pair of nasal sacs located in front of its mouth, and when water flows into the sacs as the shark swims, it passes over a series of thin folds with many receptor cells. Sharks are most sensitive to chemicals associated with their feeding, and all are able to detect such chemicals in amounts as dilute as one part per billion.
Many sharks are swift and active predators, attacking quickly and efficiently, using their rows of serrated teeth to remove massive amounts of tissue or whole limbs and body portions. They also play an important role as scavengers and, like wolves and the large cats on land, eliminate the diseased and aged animals. Sharks can and do attack humans, although the reasons for these attacks and the periodic frenzied feeding observed in groups of sharks are not understood. A human swimming inefficiently at the surface may look like a struggling, ailing animal and be attacked; a diver swimming completely submerged may appear as a more natural part of the environment and be ignored. Worldwide, there are only fifty to seventy confirmed shark attacks and five to fifteen fatalities annually.
Skates and rays (fig. 13.7) are flattened, sharklike fish that live near the sea floor; there are some 450 to 550 species of skates and rays. They move by undulating their large side fins, which gives them the appearance of flying through the water. Their five pairs of gill slits are on the underside of their bodies, not along their sides. The large manta rays are plankton feeders, but most rays and skates are carnivorous, eating fish but preferring crustaceans, mollusks, and other benthic organisms. Their tails are usually thin and whiplike, and in the case of stingrays, carry a poisonous barb at the base. Some skates and a few rays have shock-producing electric organs that can deliver shocks of up to 200 volts; these are located along the side of the tail in skates and on the wings of the rays. Their purpose appears to be mainly defensive. Like the sharks, most rays bear their young live. Skates enclose the fertilized eggs in a leathery capsule called a sea purse or mermaid's purse that is ejected into the sea and from which the young emerge in a few months.
Dinoflagellates assume a wide variety of shapes (figs. 12.7, 12.8). One of the more intriguing aspects of dinoflagellates is that some species are autotrophic and possess pigments necessary for photosynthesis (fig. 12.7a and b); some species are heterotrophic (fig. 12.7c and d) and are incapable of photosynthesis; and some species are both autotrophic and heterotrophic, or mixotrophic, depending on food availability. The capacity to feed heterotrophically, either exclusively or as a supplement to photosynthesis, means that dinoflagellates are often found in low-nutrient environments, including those of the open ocean.
The cell wall of dinoflagellates is composed of cellulose, and some species from plate like structures on their cell walls.
Clear, shallow water is required by the reef-building coral, because within the tissues of the polyps are masses of single-celled dinoflagellate algae called zooxanthellae that require light for photosynthesis and therefore are limited to the photic zone. Polyps and zooxanthellae have a symbiotic relationship, in which the coral provides the algal cells with a protected environment, carbon dioxide, and nitrogen and phosphorus nutrients, and the algal cells photosynthesize, returning oxygen and removing waste. Symbiosis is a close ecological relationship between organisms of two different species. The zooxanthellae supply the corals with substantial amounts of their photosynthetic products; some coral species receive as much as 60% of their nutrition from the algae. Zooxanthellae also enhance the ability of the coral to extract the calcium carbonate from the seawater and increase the growth of their calcareous skeletons. The degree of interdependence between zooxanthellae and coral is thought to vary from species to species. The polyps feed actively at night, extending their tentacles to feed on zooplankton, but during the day, their tentacles are contracted, exposing the outer layer of cells containing zooxanthellae to the sunlight.
The corals require a firm base to which they can cement their skeletons. The classic reef types of the tropical sea—fringing reefs and barrier reefs—are attached to existing islands or landmasses. Atolls are attached to submerged seamounts. (For a review of reef formation around a seamount, see chapter 3.) Corals are slow-growing organisms; some species grow less than 1 cm (0.4 in) in a year, and others add up to 5 cm (2 in) a year. The same corals may be found in different shapes and sizes, depending on the depth and wave action. Environmental conditions vary over a reef, forming both horizontal and vertical zonation patterns that are the product of wave action and water depth, as shown in figure 14.17. On the sheltered (or lagoon) side of the reef, the shallow reef flat is covered with a large variety of branched corals and other organisms. Fine coral particles broken off from the reef top produce sand, which fills the sheltered lagoon floor. On the reef's windward side, the reef's highest point, or reef crest, may be exposed at low tide and is pounded by the breaking waves of the surf zone. Here, the more massive rounded corals grow.
The zonation of benthic forms varies with local conditions; zones are generally narrow where the beach is steep and the tidal range is small, while zones are wide in areas where the beach is flat and the range of tides is large.
The deeper the tide pool and the greater the volume of water, the more stable the environment during isolation by the receding tide. The larger the tide pool, the more slowly it will change temperature, salinity, pH, and the carbon dioxide-oxygen balance.
A few flowering plants with true roots, stems, and leaves have made a home in the sea. Seagrasses grow, often completely submerged, in patches along muddy beaches, where they help to stabilize the sediments. Eelgrass, with its strap-shaped leaves, is found on mud and sand in the quiet waters of bays and estuaries along the Pacific and Atlantic coasts, and turtle grass is common along the Gulf Coast. Surf grass flourishes in more turbulent areas exposed to waves and tidal action.
The distribution of the algae and animals is governed by their ability to cope with the stresses that accompany exposure, turbulence, and loss of water, as well as food web dynamics. Biologists have noted that patterns form as the algae and animals sort themselves out over the intertidal zone. This grouping is called zonation; vertical zonation, or intertidal zonation, is shown in figure 14.7.
Seabirds swim at the sea surface and underwater; they use their webbed feet, their wings, or a combination of wings and feet. They float by using fat deposits in combination with light bones and air sacs developed for flight. Most seabirds have feathers waterproofed by an oily secretion called preen, and the air trapped under their feathers helps keep the birds afloat, insulates their bodies, and prevents heat loss. When diving, the birds reduce their buoyancy by exhaling the air from their lungs and air sacs and pulling in their feathers close to their bodies to squeeze out the trapped air. The underwater swimmers such as cormorants and penguins have thicker, solid bones, and penguins have no air sacs.
The eyesight of seabirds is highly developed. Their senses of hearing and smell are less developed, and their least developed sense is taste; they have few taste buds and swallow quickly. They drink seawater or obtain water from their food. Excess salt is concentrated by a gland over each eye, and a salty solution drips down or is blown out through their nasal passages. To conserve water, the birds reduce and concentrate their urine, forming uric acid, a nearly nontoxic white paste that is mixed with feces and excreted.
Picoplankton are less than 2 to 3 microns in size.Picoplankton are composed of phytoplankton, unicellular zooplankton, and bacterioplankton.
The most abundant phytoplankton in the world's oceans is a group of cyanobacteria known as Prochlorococcus. These organisms are less than 1 micron in size. The extent of diversity of this group of organisms is only just beginning to be uncovered. Within the last few years, there has been an explosion of new information about the diversity of the picoplankton because of the new ability to identify organisms based on their DNA sequences.
The concept of iron limitation was championed by John Martin (1935-1993), who argued that high nitrate (or nutrient), low chlorophyll a (HNLC) regions of the equatorial Pacific, subarctic Pacific, and Southern Ocean exhibited low phytoplankton standing stock because of low iron concentrations
The process of generating organic carbon from carbon dioxide is commonly referred to as carbon fixation.
There are four general related groups, or orders, of seabirds: (1) albatrosses, petrels, fulmars, and shearwaters; (2) penguins; (3) pelicans, cormorants, boobies, and frigate birds; and (4) gulls, terns, and alcids.
The wandering albatross (Diomedea exulans) of the southern oceans is the most truly oceanic of marine birds with the largest wing spread of all birds, 3.5 m (11 ft). These great white birds with black-tipped wings spend four to five years at sea before returning to their nesting sites. The smaller, North Pacific, black-footed albatross (Phoebastria nigripes) is a pelagic scavenger, searching the sea surface for edible refuse, including scraps from ships and fishing boats. The smallest of the oceanic birds, Wilson's petrel (Oceanites oceanicus), is a swallowlike bird that breeds in Antarctica and flies 16,000 km (10,000 mi) along the Gulf Stream to Labrador during the Southern Hemisphere winter, returning to the Southern Hemisphere for the austral summer, another 16,000 km.
CDOM is very effective at limiting the penetration of UVA and UVB because it strongly absorbs solar radiation in the UV wavelengths. The presence of CDOM can be easily observed by noting the green to brown coloration of the water as opposed to a blue ocean color in waters with little CDOM. CDOM is not one particular organic molecule, but rather a heterogeneous pool of dissolved organic compounds. Further, it should not be confused with suspended phytoplankton or detrital particles that may also appear to have color (and can also absorb UV). There are numerous sources of CDOM in coastal waters, including decaying vegetation such as mangrove leaf litter, sea grasses, and phytoplankton blooms.
There are three different categories of symbiosis. In commensalism, one partner benefits from the relationship and the other is unaffected. For example, barnacles that live on whales benefit from movement through the water, but the whale is thought to be unaffected. In mutualism, both partners benefit from the relationship (fig. 14.22). The hydrothermal vent worm Riftia and its symbiotic chemosynthetic bacteria that provide organic matter, the angler fish and its symbiotic bacteria that provide light, and the close association between coral polyps and zooxanthallae that provide the corals with the organic matter necessary for growth are all examples of mutualism. In each case, the host provides waste products to the symbiont (used as food by the symbiont), as well as a sheltered habitat. In exchange, the symbiotic partner provides a benefit to the host. In parasitism, one partner lives at the expense of the other. Parasites obtain food and shelter by damaging, but not killing, the hosts. For example, parasitic worms are found in most fish.
The carbon-14 method is extremely sensitive, allowing it to be used in even the most oligotrophic waters.
This is known as the Redfield ratio after the researcher who first reported the observation. It is often defined as molar quantities of 106:16:1 (C:N:P).
Foraminifera and radiolarians are microscopic, single-celled, amoeba-like protozoans
True jellyfish, or sea jellies, come from another and unrelated group of animals, the Coelenterata, also called Cnidaria. Another group of unusual jellyfish are colonial organisms, including the Portuguese man-of-war, Physalia, and the small by-the-wind-sailor, Velella. Both are collections of individual but specialized animals. Some gather food, reproduce, or protect the colony with stinging cells, and others form a float.
Primary producers, primary consumers, and secondary consumers represent different steps in the transfer of carbon and nutrients, and each step represents a different trophic level.
Why are there fewer apex predators than primary producers represented in a trophic pyramid? Trophic efficiency is observed whereby only 10% of the energy is transferred from one level to the next.
Holoplankton organisms living their entire life cycle in the floating (planktonic) state. Meroplankton spend only a portion of their lives as plankton.
Zooplankton control the biomass of primary producers in the ocean by: their short life spans lead to rapid liberation of nutrients that can be used for growth by primary producers, they consume large quantities of primary producers. Zooplankton reproduce sexually.
