Look For The Following Key Ideas In Chapter 15 • A community is a group of organisms that interact in a specific place. Pelagic organisms, those that live suspended in the water, compose one of the ocean’s largest communities. • Planktonic organisms drift or swim weakly, nektonic organisms actively swim. • The term plankton is not a collective natural category; it is a description of a lifestyle. Plankton is made up of many plantlike species and nearly every major group of animals. • The plantlike organisms that make up the phytoplankton are responsible for most of the ocean’s primary productivity. Of these, diatoms are the most productive and efficient. • Most primary productivity occurs above the continental shelves of the temperate zones and in the southern subpolar zones. • Important nektonic animals include cephalopods, shrimps, fishes, seabirds, and marine mammals. Each has continuously evolving suite of adaptations that allows it to meet the challenges of the marine environment.
Key Ideas Continued… • There are more species of fishes, and more individuals, than species and individuals of all other vertebrates combined. Fishes are divided into two major groups based on the material forming their skeletons. • Seabirds are indicators of oceanic productivity and are second only to marine mammals in consumption of large planktonic crustacea. There are four groups of seabirds: the gulls and the pelicans, and the even more pelagic tubenoses (albatrosses, petrels) and penguins. • Marine mammals, all of which evolved from land ancestors, share common adaptations for life in the ocean. There are three major groups of marine mammals: carnivorans, cetaceans, and sirenians.
Pelagic Communities Occupy the Open Ocean Pelagic communities. Representative plankton and nekton of the subtropical Atlantic Ocean. Note the relative magnification of organisms in the plankton community
Most Phytoplankton Are Photosynthetic Autotrophs What are the major types of phytoplankton? • Diatoms - the dominant and most productive of the photosynthetic plankton • Dinoflagellates - widely distributed single-celled phytoplankton; use flagella to move • Coccolithophores - small single celled autotrophs • Picoplankton - this category encompasses most other types of plankton, which are very small.
Plankton Size Determines Collection Method Pelagic organisms live suspended in seawater. They can be divided into two broad groups based on their lifestyle: The plankton drift or swim weakly, going where the ocean goes, unable to move consistently against waves or current flow. The nekton are pelagic organisms that actively swim. (right) The standard plankton net is made of fine mesh and has a mouth up to 1 meter (3.3 feet) in diameter. The net is towed behind a ship for a set distance. The number of organisms present in the water can be estimated if the trapped organisms are counted and the volume of sampled water is known.
Most Phytoplankton Are Photosynthetic Autotrophs The “official” food chain of larger planktonic organisms (green) contrasts with the “black market economy” of the microbial loop (red). Larger planktonic organisms are unable to separate the astonishingly small cyanobacteria and microscopic consumers from the water and so cannot utilize them as food.
Microbial loop vs “Official” food chain Microciliates microflagellates Zooplankton Cyanobacteria Phytoplankton Dissolved organic material; inorganic nutrients Fishes Decomposition, wastes Copepod Wastes, decomposition Diatom Dinoflagellate Prochlorococcus Synechococcus Stepped Art Fig. 13-4, p. 302
Phytoplankton Productivity Varies with Local Conditions Variation in the biomass of phytoplankton by season and latitude.
Bony Fishes Are the Most Abundant and Successful Fishes About 90% of all living fishes are contained within the osteichthyan order Teleostei, which contains the cod, tuna, halibut, goldfish, and other familiar species. (left) Some of the diversity exhibited by teleost (bony) fishes. These fishes are not all drawn to the same scale.
Fishes Are Successful Because of Unique Adaptations What are some problems posed by living in a marine environment? • Movement, shape and propulsion - fish must be able to move through water, which is 1,000 times denser and 100 times more viscous than air • Maintenance of level - fish tissue is usually denser than the surrounding water, so fish must have a system to keep from sinking • Gas exchange - the problem of extracting oxygen from water • Osmotic considerations - fish need a system to maintain proper salt levels in their bodies • Feeding and defense - competitive pressure among a large number of fish has caused a wide variety of feeding habits to evolve
Fishes Are Successful Because of Unique Adaptations Cutaway of a mackerel, showing the position of the gills (a). Broad arrows in (b) and (c) indicate the flow of water over the gill membranes of a single gill arch. Small arrows in (c) indicate the direction of blood flow through the capillaries of the gill filament in a direction opposite to that of the incoming water. This mechanism is called countercurrent flow.
Oxygen-enriched blood Oxygen-poor blood Gill arch Gill membrane Stepped Art Fig. 13-20, p. 314
Some Marine Birds Are the World’s Most Efficient Flyers Only 270 of the known species of birds qualify as seabirds. Seabirds have salt excreting glands to eliminate salt taken in with their food. There are four groups of seabirds: Tubenoses - this group includes the albatrosses and petrels Pelicans - this group includes relatives of the penguins that have webbed feet and throat pouches Gulls - these birds are found along the shore, where they scavenge for food. Penguins - these birds have lost the ability to fly, but are excellent swimmers
Marine Mammals Include the Largest Animals Ever to Have Lived on Earth What are the three groups of marine mammals? Cetacea – porpoises, dolphins and whales Carnivora - seals, sea lions, walruses and sea otters Sirenia – manatees and dugongs
Marine Mammals Include the Largest Animals Ever to Have Lived on Earth A few of the marine mammals of the Order Cetacea. Suborder Odontoceti (odontos = tooth) whales are known for being active predators who use teeth for feeding. The toothed whales search for food using echolocation, a biological equivalent to sonar.
Marine Mammals Include the Largest Animals Ever to Have Lived on Earth A few of the marine mammals of the Order Cetacea. Suborder Mysticeti (mystidos = unknowable) whales are known for having no teeth and instead use baleen for filter feeding.
Marine Mammals Include the Largest Animals Ever to Have Lived on Earth A plate of baleen and its position in the jaw of a baleen whale. For clarity, the illustration shows an area of the mouth cut away.
Chapter 15 Summary The organisms of the pelagic world drift or swim in the ocean. (Animals and plants are associated with the bottom are known as benthic organisms.) The organisms that drift in the ocean are known collectively as plankton. The plant-like organisms that comprise phytoplankton are responsible for most of the ocean's primary productivity. Phytoplankton -- and zooplankton, the small drifting or weakly-swimming animals that consume them -- are usually the first links in oceanic food webs. Plankton are most common along the coasts, in the upper sunlit layers of the temperate zone, in areas of equatorial upwelling, and in the southern subpolar ocean. Marine scientists have been inspired by the beauty and variety of plankton since first observing them under the microscope in the nineteenth century. Actively swimming animals comprise the nekton. Nektonic organisms include invertebrates (such as the squid, nautiluses, and shrimps), and vertebrates (such as fishes, reptiles, birds, and mammals). Each organism has a continuously evolving suite of adaptations that has brought it through the rigors of food finding, predator avoidance, salt balance, and temperature regulation -- all of the challenges of the marine environment -- time and time again.