1) Marine communities are classified by: a) proximity to bottom, b) proximity to shore, c) light levels or depth, and d) bottom type and water motion
- 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 (at mercy of currents) vs nekton (active swimmers)
- groups of plankton are subdivided by:
- source of energy (autotroph= phytoplankton, heterotroph= zooplankton),
- fraction of life that is planktonic (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) Three important unicellular phytoplankton groups are:
- 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
- coccolithophores (green algae): passive drifters, intricate calcareous skeleton
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) Some zooplankton 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