Benthic Sample Processing Flashcards
What’s a benthos sample
Usually a volume of sediment from which organisms must be extracted.
What’s the initial treatment of benthos sample
Bottom sampler placed on metal lined sieve table or hopper
Vol sediment may be measured to assess efficiency of sampling
Allows sample to be washed through sieve w/out loss of material
May include mechanical shaker
Advantage to hopper designs
Efficient processing of samples
Disadvantages to hopper designs
Potentially damaging to fauna of water pressure too high
How much samples be treated
Life of fresh samples extended by cooling - freezing gel in insulated boxes
Samples must be :
- treated with fixative to harden and coagulate tissues
- treated with preservative to prevent rotting and decay
What’s the most common fixing and preservative reagent
Formaldehyde
Sold as a 40% solution mixed with water known as formalin
- 10% formalin 4% formaldehyde
What concentration is formaldehyde used at
4-5% - best dissolved in water from the sampling area
Should be buffered to pH 8 to prevent dissolution of calcium carbonate structures
Advantages of formaldehyde
Cheap
Long lasting
Preserves pigmentation/colouration
Disadvantages of formaldehyde
Toxic - protective measure must be taken to avoid human exposure to fines and liquid
Can make tissues hard and brittle. Addition of propylene phenoxetal and propylene glycerol can address this
Alternatives to formaldehyde
Dowicil 100 or Kohrsolin
- Formaldehyde containing chems
- doesn’t give off fumes
- expensive not widely used
- Reluctance to use alternative preservative because results may not be comparable with older time series.
How are samples usually preserved
After initial fixation of tissue sample maybe transferred to another preservative.
Usually 70% ethanol
How are macrofauna sorted
Larger organisms sorted by hand
May be divided into fractions by passing through a fine sieve with water and agitation
How are benthic macrofauna identified
Taxonomic identification using keys.
Computer based interactive keys
Advantages of computer based interactive keys
Character can be used and values changes in any order
Correct identification made in spite of errors
ID errors easier to find
More than one value can be entered for a feature where the user is unsure.
Application of benthic surveys
Marine benthos - important component of ecosystem.
- food webs
- commercial fisheries
Taxonomic studies - new species
Benthic habitats can support high biodiversity, provides reliable indicator of habitat quality
