Introduction to Plankton

So far I haven't been really talking much about my science in this blog, but It's because I want to introduce things slowly. Today I would like to start from the basics and introduce Plankton. So...what is it?

Several scientific terms are derived either from the Greek or Latin. The word plankton, for example, is from the Greek for "drifters". It is because those things that are called plankton are very small and therefore not strong enough to actively move against underwater currents. Although some can move up and down (vertically) in the water column, others cannot move at all and just....drift. 

There are different types of plankton, classified depending on their size but also depending on their functional groups. The latter means that plant, animals and bacteria that are considered "planktonic" have different names.

• Phytoplankton: unicellular plants (they are photosynthetic). Phyto is from the Greek for plant.
• Zooplankton: animals (they eat other zooplankton and phytoplankton). Zoo is from the Greek for animal.
• Ichthyoplankton: eggs and larvae of fish. They are temporary plankton, once they reach adulthood they become NEKTON - free swimming animals that move independent of water motion. Ichthyo is from the Greek for fish.
• Bacterioplankton: bacterias (they live everywhere!). 

Here a quick sketch to show you what I mean (not to scale!!!)

Plankton sketch (not to scale)

Plankton. From: http://www.duke.edu/web/nicholas/bio217/jrc25/impacts.html

The size classification is based on certain metric ranges and it can be independent of the type of plankton, like this:

Mega-plankton          20+ mm                    e.g. Jellyfish

Macro-plankton         2mm - 20mm          

Meso-plankton          0.2mm - 2mm           e.g. larger copepods

Micro-plankton         20µm - 200µm        e.g. most phytoplankton

Nano-plankton          2-20 µm                    

Pico-plankton            0.2-2 µm                e.g. bacteria & small phyto

Femto-plankton        < 0.2 µm                    e.g. viruses

PS: µm is called micro-metre

You can be a little more precise if you want and take it a step further combining the plankton type with the size, like this:

Meso-zoo-plankton

Pico-phyto-plankton

Not all the combinations can make sense thought! As you can see the  biodiversity in the world of plankton is enormous. My areas of interest are mesozooplankton and phytoplankton.

Why do we study plankton?

From http://www.sahfos.ac.uk/research/research-home.aspx

Plankton as indicators of the health of the oceans

At the base of the marine foodweb, the free floating plant life of the sea (phytoplankton) provide food for the animal plankton (zooplankton) which in turn provide food for many other marine organisms. The carrying capacity of marine ecosystems in terms of the size of fish resources and recruitment to individual stocks as well as the abundance of marine wildlife (e.g. seabirds and marine mammals) is highly dependent on variations in the abundance, timing and composition of the plankton.

These organisms also play a crucial role in climate change through the export of the important greenhouse gas CO2 to the deep ocean by carbon sequestration in what is known as the 'biological pump'. Without this process concentrations of CO2 would be much higher in the atmosphere and the climate of the world would be much warmer. Apart from playing a fundamental role in the earth's climate system and in marine foodwebs, plankton are also highly sensitive indicators of environmental change and provide essential information on the 'ecological health' of our seas.