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    Zonation of the Marine Environment

Global Seafloor Topography

The abbyssal plains are not only flat plains but exhibit deep-sea mounts and long ridges of midoceanic ridges. The global topography of the sea floor became only known after special techniques of satellite measurements were made possible in the late 1990's.

Classification of the Marine Environment

  1. Classification by light
    • Photic and aphotic
    • Phytoplankton need light to photosynthesize and can only thrive in the photic zone
    • Zooplankton (animals) and bacteria do not need light and inhabit the oceans down to the deep-sea floor
  2. Classification by location
    • Water and sea floor divided into specific zones: benthic & pelagic
    • By water depth divided into coastal, neritic, oceanic
    • Each has distinct physical and chemical characteristics
    • Each supports different organisms
Inhabitants of Zones
  • Plankton (Pelagial)
    • Floaters and drifters, have to move with water currents
    • Plants and animals and protists and bacteria (free, attached); range from microscopic size to several meters in length (jellyfish)
    • Plants and photosynthetic cyanobacteria = phytoplankton Animals = zooplankton; bacteria = bacterioplankton
    • Also differentiation according to size: pico-, nano-, micro-, meso-, macro-, megaplankton.  Size does NOT separate plankton from nekton
  • Nekton (Pelagial)
    • Free swimmers, can overcome currents and move against them
    • Animals (large crustaceans, fish, mammals)
  • Benthos (Benthal)
    • Attached to, on, or in the sea floor
    • Plants and animals and protists and bacteria (range from microscopic size to several meters in length (kelps) 
Size Scale for Plankton

The discovery of very small (<2 µm) cyanobacteria as ubiquitous and abundant inhabitants of the oceans between 1979 and 1989 led to extending the size range of phytoplankton into the picoplankton size range. We know today that the picoplanktonic phytoplankton is a major component in all warm-water marine systems, and their discovery changed our perception of marine food webs substantially. Phytoplankton occurs in three size classes:
-- picoplankton: 0.2 - 2.0 µm
-- nanoplankton: 2 - 20 µm
-- microplankton: 20 - 200 µm

Living on the fast lane? 
r- and k- selection

r strategists
  • Opportunistic species

  • In variable or new environment
  • Small size, fast growth
  • Early mature, many reproduction cycles per season
  • Many offspring with high mortality rate and little care

  • High motility and dispersal

  • Life span short
  • Low competitive ability, thrive often in new environments
K - strategists
  • Equilibrium or capacity species
  • Stable environments

  • Large size, slow growth
  • Late mature, one or few repro- duction cycles per season
  • Few offspring with low mortal- ity and care taking of young
  • Low dispersal, territorial adults
  • Life span long
  • High competitive ability, out- compete r-strategists on long run