Life in the Pelagic: An introduction to the Plankton Size classifications and terminology
• Classification of planktonic organisms is generally based upon size – rather than function (most methods involve filtration which distinguishes organisms based upon size rather than species).
• This can be problematic because in the plankton, trophic position is not always determined by size (size ratios between predator and prey are not constant). Abundance of living organisms
Organism and size Typical abundance
Bacterioplankton (~1um) 105 to 107 per ml
Nanoflagellates (1-10um) 102 to 104 per ml
Protizoan plankton (20-50um) 10 to 102 per ml
Phytoplankton (20-200um) 10 to 104 per ml
Humans (2m) 6x106 in Washington State Bacterioplankton in Aquatic Systems
• Found in all natural waters • Non-pathogenic! • Small (≤1µm) yet abundant (>106 cells ml-1) • Comparable in biomass to phytoplankton • Fundamental in nutrient & carbon cycling • Drive water quality parameters (i.e. anoxia, nutrient availability) • Extremely diverse
10 µm (DAPI stained slide of bacterioplankton from Chesapeake Bay) Femtoplankton (0.02 – 0.2 µm)
Bacteriophage •Diverse and ubiquitous viral community in the marine environment
•Significant role suspected (certainly impact bacteria and may also impact primary production and higher trophic levels, viruses suspected in some marine mammal beachings).
•Viruses may be important agents in demise of some phytoplankton blooms (e.g., Trichodesmium)
•Viruses are important agents for DOM release and nutrient cycling
0.1um Picoplankton (0.2 – 2 µm)
Bacteria Archaea •Very important role in marine food webs, •Distinct RNA especially degradation and recycling •Early evolutionary separation •Ubiquitous in ocean (~106 / ml) •Favoring extreme environments •Various forms (motile, rods, spiral, coccoid) •Recently discovered in ocean Picoplankton (0.2 – 2 µm)
Vertical distribution of Bacteria and Archaea cell abundance at HOTS (Karner et al 2001). • Opposite patterns of distribution • Archaea are ubiquitous, but biogeochemical significance is poorly understood More on Picoplankton (0.2 – 2 µm)
Cyanobacteria – “blue-green algae”
Photosynthetic bacteria e.g. Synechococcus spp. • Up to 106/ml in euphotic zone • In both coastal and oceanic waters • In temperate and tropical oceans • Can play major role in primary production, especially open ocean
Prochlorophytes
•Prochlorococcus marinus •Abundant at base of the euphotic zone in open ocean (106 / ml) •Ubiquitous distribution •Can play a major role in primary production, especially in the open ocean •Different strains have been identified that live in different depths in the water column and have different metabolic capabilities particularly with respect to what forms of nutrients they can use, i.e., NH4 vs. NO3.
Note: Prochlorococcus is currently believed to be the most abundant form of plant life on earth.
2µm Nanoplankton (2 – 20 µm)
Mostly small eukaryotic phytoplankton
Dominate more oligotrophic open ocean environments
dinoflagellates small centric diatom
small pennate diatom
coccolithophorid Microphytoplankton (20 – 200 µm)
Large eukaryotic phytoplankton
Prominent in productive coastal / upwelling zones
Heterosigma
large dinoflagellates
chain-forming diatoms
centric diatom Microzooplankton (2 – 200 µm)
These are heterotrophic and mixotrophic protozoans
•Large group and taxonomically diverse • ciliates • dinoflagellates • hete