Benthos, plankton, macrophytes - who's who in an aquatic ecosystem
In limnology and water assessment, words keep coming up: plankton, benthos, macrophytes, periphyton. They sound scholarly, but they simply mean groups of organisms divided according to where and how they live in the water. This short guide sorts out who is who - and why it matters for quality indicators.
Plankton - suspended in the water column
Organisms floating in the water, carried by its movement:
- phytoplankton - microscopic algae (including cyanobacteria); their biomass is described by chlorophyll-a, and an excess means blooms,
- zooplankton - tiny animals (e.g. rotifers, planktonic crustaceans) feeding on phytoplankton.
Benthos - life on the bottom
Organisms bound to the bottom. In water assessment the key ones are the benthic macroinvertebrates (insect larvae, molluscs, crustaceans), which are an excellent bioindicator - see bioindication with macroinvertebrates.
Periphyton - coatings on substrates
A thin layer of algae and micro-organisms growing on stones, plants and other surfaces. It includes, among others, diatoms (phytobenthos), used in the assessment of rivers.
Macrophytes - aquatic plants
Larger plants: submerged, with floating leaves, and emergent. Their composition and cover are a biological indicator of status - see mapping macrophytes.
Nekton - active swimmers
Organisms that move independently of the current - above all fish (ichthyofauna), also an element of status assessment (fish monitoring).
What this division is for
Because different groups respond differently to conditions and reflect them on different time scales - which is why the assessment of ecological status relies on several of them at once (see elements of assessment).
In practice
Biological data is usually lists of species and abundances - which can also be kept systematically. In LimnoLog you record them as custom indicators, alongside physico-chemical measurements, in a single project.
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