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Chapter 17: The Open Sea

Chapter 17: The Open Sea. 300 million cubic miles Limited amounts of nutrients Restricts numbers of primary producers Supports few large animals. Regions of the Open Sea. Based on physical characteristics of the water and life forms in them Vertical zonation

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Chapter 17: The Open Sea

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  1. Chapter 17:The Open Sea

  2. 300 million cubic miles • Limited amounts of nutrients • Restricts numbers of primary producers • Supports few large animals

  3. Regions of the Open Sea • Based on physical characteristics of the water and life forms in them • Vertical zonation • Depends on depth that light penetrates to support photosynthesis

  4. Photic zone • Receives sunlight • Corresponds to the epipelagic zone • Location of pelagic animals in upper 200m of ocean • Aphotic zone • Extends to ocean bottom • Light disappears (total darkness)

  5. Life in the Open Ocean • 2 groups: plankton and nekton • Classification of plankton • Taxonomic groups • Seston: particles suspended in the sea • Consists of tripton (mineral particles, dead, organisms, decaying organic matter) and plankton • Phytoplankton • Zooplankton • Bacterioplankton (archaea and eubacteria) • Virioplankton(free viruses)

  6. Functional groups • Akinetic: do not move at all • Kinetic: move by flagella, jet propulsion, body undulation, or appendages • Size • Macroplankton: visible to the naked eye (>1mm) • Microplankton: could be caught with plankton nets • Nanoplankton (centrifuge plankton) • Pass through plankton nets • Concentrated best through centrifugation • Femtoplankton and picoplankton (viruses and smallest prokaryotes) • Mesoplankton and megaplankton (animal plankton  larval fish)

  7. Life history • Holoplankton • Planktonic throughout their lives • Ex: microbes, invertebrates • Meroplankton • Benthic as adults but plankton as larvae • Spatial distribution • Neritic plankton (presence of meroplankton) • Neuston • Live close to water’s surface • Use surface tension of water to remain at or near surface • Pleuston • Break the surface of water • Can be buoyed by gas bladders or bubbles

  8. Patchiness in the Open Sea • Patches: localized aggregations • Factors that contribute to their formation: • Areas of upwelling • Variations in sea-surface conditions • Vertical mixing of water • Downwelling events • Meeting waters of different densities • Grazing by zooplankton • Micropatchiness • Microbes attach to organic matter particles to form marine snow

  9. Plankton migrations • Zooplankton • Daily migrations from the surface down to 1 mile • Densely packed  form a deep scattering layer • Can give a false sonar reading

  10. Megaplankton • Most are animals • Cnidarian zooplankton: moon jellyfish, lion’s mane, Pelagianoctiluca • Molluscan zooplankton: sea butterflies, purple sea snail, Glaucus (nudibranch) • Urochordates: salps, larvaceans

  11. Nekton • Active swimmers • Invertebrates: squid • Fish: billfish, tuna, ocean sunfish, sharks, manta rays • Birds: penguins • Mammals: whales

  12. Survival in the Open Sea • Adaptations for staying afloat: • Swimming • Flagella, cilia, jet propulsion • Appendages: legs, antennae, paired limbs • Body undulation: side-to-side horizontally or vertically

  13. Reduce sinking rates • Increase friction • Decrease volume • Flatten body • Increase body length • Buoyancy • Storage of oils • Increase water content of body • Exchange of ions • Use gas spaces

  14. Avoiding predation • Camouflage • Countershading • Dark dorsal surfaces with light ventral surfaces • Hard to see from above and below • Some species are almost transparent • Form colonies • Helps to capture prey, digest food, maintain colony, provide floatation, or reproduce

  15. Ecology of the Open Sea • Pelagic ecosystem • Inhabitants live in the water column • Few seaweeds; no vascular plants • Get nutrients from the surrounding seawater

  16. Surface water receives large amounts of light but no nutrients from the land • Low levels of nitrogen and phosphorus needed to support phytoplankton • Water above the deep-sea floor has higher levels of nutrients but not enough light to make them productive • Little mixing of deep high-nutrient water with low-nutrient water at surface

  17. Tropical water • Low level of nutrients • Permanent layers separated by a thermocline • Warmer, less-dense layer of water on top of colder, denser water • Prevents exchange of nutrients

  18. Food webs in open sea • Base formed by phytoplankton and heterotrophic bacteria • Provide food for herbivores • Release photosynthetic products into surrounding seawater as dissolved organic matter (DOM) • Heterotrophic bacteria rapidly recycles DOM in open sea • Bacteria can form a bacterial loop • Returns nutrients rapidly to phytoplankton in water easily depleted of critical nutrients • Metabolize some of the DOM and return it as an inorganic form

  19. Virioplankton • Most abundant plankton in the ocean • Lysis of bacterioplankton and phytoplankton by viruses releases DOM directly • Produces particulate organic matter (POM) • Disrupts bacterial loop

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