1) Marine communities are classified by: a) proximity to shore, b) water depth (light), c) bottom type, d) wave energy
- highest classification is: pelagic (open water) vs benthic (bottom)
- pelagic zone is subdivided horizontally (neritic vs oceanic)
- pelagic zone also subdivided vertically based on light [photic (upper= euphotic, lower= disphotic) vs aphotic] or depth (epi-, meso-, bathy- and abysso-pelagic)
- benthic communities are often divided into hard bottom or soft bottom, and 'high' or 'low' energy based on wave action and currents
2) Members of the pelagic community are classified many ways
- highest level classification is based on control of movement: plankton (mostly passive) vs nekton (active swimmers)
- groups of plankton are subdivided by:
- source of energy (autotroph= phytoplankton, heterotroph= zooplankton),
- proportion of life that is pelagic (holoplankton vs meroplankton),
- overall body size [pico- (<2µm), nano- (2-20µm), micro- (20-200µm), meso- (0.2 - 20 mm), macro- (2-20 cm), & mega-plankton (>20 cm)
- the biomass distribution of plankton concentrates in 3 size peaks
3) Two important phytoplankters are diatoms and dinoflagellates
- diatoms: drift passively with currents; live inside nested, 2-part silicate shells and thus get smaller each subdivision!
- dinoflagellates can swim but are still at mercy of currents
4) Copepods (herbivores or carnivores): very significant zooplankton group
5) Other key zooplankters: protists (foraminifera, radiolaria), gelatinous forms (jellyfish, ctenophores, salps), crustacea (krill), chaetognaths (arrow worms)
6) Shallow plankton distribution is very heterogeneous even on a small scale, due to turbulent mixing at water surface (Langmuir circulation yields heterogeneity on a 10 - 50m scale)
7) Many megaplankton species exhibit pronounced vertical migration
- 'deep scattering layer' may shift vertically from 100 to 400m daily
- may yield significant transport of inorganic nutrients above the open-ocean thermocline