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Chapter 16

Continental Shelves and Neritic Zone. Chapter 16. Key Concepts. The number and kinds of benthic organisms on continental shelves are influenced by sediment characteristics. Hard-bottom communities are dominated by epibenthic organisms.

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Chapter 16

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  1. Continental Shelves and Neritic Zone Chapter 16

  2. Key Concepts • The number and kinds of benthic organisms on continental shelves are influenced by sediment characteristics. • Hard-bottom communities are dominated by epibenthic organisms. • In areas north and south of the tropics, kelps (a type of brown algae) dominate the subtidal zone where the water is cold and the sediments are hard.

  3. Key Concepts • Kelps are important primary producers and provide habitats for many animals. • Soft-bottom communities are dominated by suspension feeders and deposit feeders. • The distribution of organisms in benthic communities of the continental shelf is patchy.

  4. Key Concepts • The neritic zone is the water column that lies above the continental shelves. • The neritic zone receives high levels of nutrient input from rivers, coastal runoff, and upwellings. • The neritic zone supports enormous amounts of phytoplankton. • The high productivity of coastal seas supports large numbers of fishes, birds, and marine mammals.

  5. Continental Shelves • Average 67 km (40 miles) wide • Descend gradually from shore to depths of 130 m (430 feet) • at this point, bottom may become steep slope or shear drop-off • Rivers carry large amounts of sediment to coastal seas, providing nutrients that settle on the shelves or are dissolved in the seawater • Plenty of sunlight

  6. Benthic Communities • Role of sediments • epifauna are adapted to bottoms composed of coarse sediments (where currents on the bottom are strong) • epifauna—animals that live on surface sediments • infauna and interstitial animals are adapted to bottoms of fine sediments (where currents are weak) • infauna—animals that burrow in the sediments • interstitial animals—animals that live in the spaces between sediment particles

  7. Benthic Communities • Hard-bottom communities • hard-bottom habitat = large sediments that cannot be pushed apart (e.g. rocks) • many sessile organisms • epibenthic organisms—organisms that live on the surface of the bottom sediments • characterized by patchiness—uneven distribution of benthic organisms • sunlight exposure • landslides and shifting sediments

  8. Benthic Communities • Kelp communities • kelp beds • may be underwater forest with canopy and understory; kelp may be distanced or dense

  9. Benthic Communities • Kelp communities • kelp life cycles • spores germinate with sufficient light • microscopic form establishes itself only if it is not over-consumed by herbivores • stipes grow upward and spread out into a canopy • mature kelps constantly grow and erode

  10. Benthic Communities • Kelp communities (continued) • kelp community • kelps provide food, shelter or both • kelps may increase usable habitat • many filter feeders and some herbivores rely on kelp forests

  11. Benthic Communities • Kelp communities (continued) • impact of sea urchins on kelp communities • kelps are a favorite food of sea urchins • sea urchins are usually held in check by wave action and predators • decline in predators (e.g. otters) can lead to urchin population explosion and mass destruction of kelp forests

  12. Benthic Communities • Soft-bottom communities • patchiness in soft-bottom communities • changes in sediment distribution • bottom currents • larval settlement • soft-bottom food chains • detritus is primary source of food • suspension feeders eat detritus and plankton • deposit feeders eat detritus and its bacteria • these inactive animals are eaten by more active predatory species

  13. Benthic Communities • Soft-bottom communities (continued) • succession in soft-bottom communities • disturbance of sediments by erosion or landslides removes or kills many animals • disturbance exposes deeper, anoxic sediments • larvae arrive and recolonize • surface dwellers like polychaete worms feed on organic material and aerate the sediments • increased oxygen allows other animals to move in

  14. Neritic Zone • Food chains in the neritic zone • phytoplankton growth is supported by nutrients from freshwater runoff from land • zooplankton feed on phytoplankton • most abundant are copepods (crustaceans) • benthic filter feeders eat phytoplankton • small fish eat zooplankton • large fish eat filter feeders • fewer trophic levels than in the open sea

  15. Neritic Zone • Productivity in the neritic zone • areas of upwelling, where nutrients are brought from the ocean floor to the surface where plankton live, are the most productive • Other roles of plankton in coastal seas • many animals spend some part of their lives as members of plankton • having planktonic larvae allows sessile organisms to disperse to new areas

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