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Life on the Continental Shelf

013. Life on the Continental Shelf. Continental Shelf : shallow submerged extension of the continent. THE CONTINENTAL SHELVES. Average width – 75 km, narrower in areas with strong current; Average slope – 0 o 07’; Average depth flattest portion– 60 m;

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Life on the Continental Shelf

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  1. 013 Life on the Continental Shelf

  2. Continental Shelf: • shallow submerged extension of the continent

  3. THE CONTINENTAL SHELVES • Average width – 75 km, narrower in areas with strong current; • Average slope – 0o07’; • Average depth flattest portion– 60 m; • Average depth where greatest change of slope – 130 m; • Hills of 20 m or more and depression of 20 m or more

  4. slope continental shelf rise abyssal plain abyssal hills ridge transform fault

  5. Photic 100m (low tide to shelf break)) (Tidal zone)

  6. SUBTIDAL ECOSYSTEM • Marine areas that are never exposed during low tide i.e. always submerged. • Also known as the sublitoral zone

  7. SUBTIDAL ABIOTIC FACTORS • rich innutrients (brought in from river discharges), i.e., sediment runoff) Nile River Delta Mississippi Delta

  8. SUBTIDAL ABIOTIC FACTORS • Influenced by sedimentation processes (especially shallow areas) - lithogenic sediments (physical and chemical weathering of rocks (turbidities, volcanic ash, red clay)) - biogenic sediments (shells and skeletons of marine organisms)

  9. SUBTIDAL ORGANISMS Pelagic • Plankton (suspended in water column) • Nekton (able to swim against current) Benthic (on/in bottom sediment) • Demersal • Epifauna • Infauna

  10. Distribution of marine life Pelagic Benthic

  11. SUBTIDAL COMMUNITIES • Soft-bottom Subtidal Communities • Hard-bottom Subtidal Communities

  12. SOFT-BOTTOM SUBTIDAL COMMUNITIES Made up of : • Muddy substrate • Sandy substrate

  13. SOFT-BOTTOM SUBTIDAL COMMUNITIES Influenced by: 1. Particle size distribution 2. Sediment stability 3. light 4. salinity 5. temperature

  14. CHARACTERISTICS OF SOFT-BOTTOM SUBTIDAL COMMUNITIES • Type of dominant substrate i.e. sand, mud etc. • Mainly infauna, some epifauna and almost no sessile organisms

  15. SOFT-BOTTOM SUBTIDAL ORGANISMS 1. infauna • Benthic organisms that bury themselves in the sediment 2. epifauna • Organisms that inhabit the surface of the bottom sediment No. of subtidal sp. > intertidal (more stable, no desiccation) Distribution of organisms influenced by particle size (mud or sand)

  16. Infauna

  17. Epifauna

  18. Soft-bottom subtidal communities Epibionts

  19. Soft-bottom subtidal communities • Infauna:  • live within the sediment, mostly soft bottom;  • mostly clams and worms (polychaetes)  • burrow tubes for food scavenging and oxygen supply • Primary producers: algae, mostly benthic diatoms and dinoflagellates • cyanobacteria mats on mudflats • mud more productive than sand • macro- and meiobenthos, often detrivores, living of deposits from seagrasses and marshes • birds important grazers

  20. Soft-bottom subtidal communities

  21. Soft-bottom subtidal communities Examples of meiofauna in sand

  22. Soft bottom subtidal communities • 32,000 polychaetes in sand/m2 • vs • 50-500 earth worms in soil/m2 • Ecological Role: • clean sediments • aerate soil

  23. Carnivore feeders • Fish, crabs and birds Hawaiian Stilt

  24. Herbivore feeders

  25. Deposit-feeders

  26. Suspension-feeders

  27. HARD-BOTTOM SUBTIDAL COMMUNITIES • Rocky shore • Coral reefs • Most important organisms are the sea weeds (able to settle on rocks/hard substrate

  28. PRODUCERS • Most important communities - seaweeds • Strong competition • Amount of light influence distribution of seaweeds • Seaweeds found in these areas have higher chlorophyll concentration

  29. grazers • Invertebrates that move slowly: sea urchin, limpets, chitons, abalone • Algal defense against predators - By having food that are not tasty - Fast regeneration - Calcification (formation of calcium)

  30. Hard-bottom subtidal communities Generalized food web Detritus

  31. Hard-bottom subtidal communities Examples of N. Atlantic Kelp

  32. Hard-bottom subtidal communities Geographic Distribution of Kelp

  33. Air sack holdfast

  34. Recap • Muddy shores • Deposition of silt by tide or river • Temperate: intertidal- mud flat communities • subtidal- muddy bottom or seagrass communities • Tropic: intertidal- mangroves • subtidal- muddy bottom or seagrass communities • Sandy shores • Deposition of sand by wave action • Temperate: intertidal- beach communities • subtidal- muddy bottom or seagrass communities • Tropic: intertidal- beach communities • subtidal- sandy bottom or seagrass communities • Rocky shores • Little deposition • Temperate: intertidal- barnacles, seaweeds, mussels • subtidal- kelp beds or forests • Tropic: intertidal- algae and corals • subtidal- coral reefs

  35. Inquiry • What is the sublittoral zone? • What is meiofauna (infauna)? • How do organisms survive living in a soft bottom community? • What food source are soft-bottom communities are based on? • Why don’t we see anemones and sea slugs in the high tide zone?

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