Pelagic Autotrophs - Phytoplankton Fun Times Flashcards
What size do most pelagic autotrophs have? And what is the famous exception?
Most pelagic autotrophs, that is photosynthesizing organisms, are unicellular algae known as phytoplankton.
A famous exception is the Sargassum weed in the subtropical gyre of the north Atlantic, the Sargasso sea.
What is the range in cell diameter of phytoplankton? What are the sizes of other microscopic things?
From 1 mikrometer to 70 mikrometer.
Most algal cells in the sea are in the lower end of that range.
Typical bacteria are 1 mikrometer.
A red blood cell is 7 mikrometers.
An object of 50 mikrometers are just visible to the naked eye if contrast is high.
Plankton size:
Femtoplankton
<0.2 mikrometer
Viruses
Plankton size:
Picoplankton
0.2-2 mikrometer
Bacteria, very small eukaryotes
Plankton size:
2-20 mikrometer
Nanoplankton
Diatoms, dinoflagellates, protozoa
Plankton size:
20-200 mikrometer
Microplankton
Diatoms, dinoflagellates, protozoa, copepod nauplii
Plankton size:
0.2-20 mm
Mesoplankton
Mostly zooplankton
Plankton size:
2-20 cm
Makroplankton
Who proposed the plankton size prefixes that people usually use?
Sieburth et al 1978
Why are pelagic autotrophs so small?
They are small in order to provide a large surface area relative to their biomass in order to absorb nutrients like nitrate, phosphate and iron from extremely dilute solutions.
What is the importance of having a small size?
It is to provide a large relative surface toward which diffusion can move nutrients. It is the rate of diffusion that is limiting at low concentrations.
Boundary layer close to the cell is large compared to cell size, viscosity dominates and the impact of turbulence is small. Thus effectively, the water next to a cell exchanges only slowly and although sinking and turbulence can increase nutrient availability at a distance from the cell supply is effectively limited to molecular diffusion.
The diffusive flux of a dissolved solute such as nitrate toward an absorbing surface area is given by what law?
Fick’s law:
Flux (amount arriving/time) = - A * D (dC/dx)
A = surface area D = substance specific diffusion coefficient dC/dx = the gradient of concentration (amount/volume) away from the surface (hence the minus).
What systems have small oceanic plankton changed to require less iron?
Photosynthetic and oxidative metabolism
How rapid can many phytoplankton cells reproduce? And why is it important that they do so?
One or more times a day. Important because pelagic grazers typically eat the entire cell and they therefore have to reproduce quickly to maintain a phytoplankton stock.
If grazers are few and conditions (light, nutrients, temperature) are good then stocks can grow exponentially. Known as an algal bloom.
