Chapter 17: The Open Sea

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