L8 - Sampling Marine Monitoring Flashcards
Aim
Introduction to the methods used to sample marine organisms
Highlight the advantages and disadvantages of different sampling methods
What to consider when choosing a particular sampling method
References
Studying temperate marine environments, Kingsford & Battershill (desk copy)
Introduction
Objective: obtain an unbiased estimate of the number of organisms in a given area/volume (i.e. an estimate of the density).
Importance: fundamental to all studies
stock assessment
organism distribution
ecological interactions
environmental change
modelling energy transfer
Wide variety - function of habitat, target organism & logistical constraints
Quantitative methods
Give estimates of density
Widely used therefore analysis better understood
Qualitative
Generally ability to predcit how much area you’ve sampled is not that well known. Good for covering large areas and giving a rough estimate of abundance.
Area/volume sampled unknown
Increased sampled area
Analysis method do exist
Be aware of method limitations
- Over/under sampling certain groups?*
- What may be good somewhere for something may not work somewhere else for something else.*
Over/under sampling particular size classes
Sampling efficiency may vary in time/space
Shallow water benthos (< 30 m)
SCUBA
Epibenthic organisms
Video & cameras
Transects
Very useful for rocky shore habitats
Hydroplanes
Large area covered
Problem with position
Qualitative data
Shallow water benthos (< 30 m)
Cores/quadrats
Size & shape of sampling unit
Function of organism size/distribution
More 0’s than +’s too small
Too large - difficulties sampling, reduces number of replicates
Suction sampler
- The larger the sample the more work…*
- Maximise number of samples you take (cast your net far and wide)*
Working offshore very expensive
(more of the moon mapped than oceans surface)
ROVs
AUVs
Manned submersibles
Grab samplers
Box corer
corer delivers 10cm diametre intact sediment sample
Benthic dredges
Overfilling
Bouncing
Penetration depth
Escape
Semi-quantitative
Tow for a period of time do gather organisms
Sea state determines wether trawler sits on the benthos properly as it bounces in rough seas
Large bow wave generated by trawler displaces mobile species away from net area
Sometimes a big effort between samples to siv through material and identify organisms
Destructive?
Pelagic environment
Phytoplankton & zooplankton
Nets
Mesh size
Quantify volume samples
Net avoidance
Clogging
Predation
Bongo nets
MOCNESS
Multiple opening-closing nets
Net minders
Designed to open and close at different depths to attain samples from multiple depths, don’t work well in high seas state.
Very economic
Pelagic environment
Longhurst-Hardy plankton recorder
Pelagic environment
Trawls & seines
Stock assessments
Quantification
- Difficult
- Consistent methods
Depth
Speed
Time
- Size selective
- Non-visual
Sediment traps
Measure vertical fluxes
Swimmers
Aspect ratio & sampling efficiency
Resuspension
Carbon measuring
Left- simple, deployed at different depths
Right - sophisticated, deployed for up to several years.
rosette of sampling bottles to capture a time series of whats settling out, zooplankton can disturb samples
Case study:
Sample returned after one year empty as a fish blocked something?
Remote sensing
Acoustics
Sound waves & frequency
Non-destructive sampling
Requires calibration & data processing
Common in fish stock assessment
Towed sensors
Optical
Chemical
Remote sensing
1/2 a mil $
Remote sensing
Satellites
Synoptic view
Address large scale variability
Validation: case I & II waters
http://seawifs.gsfc.nasa.gov/SEAWIFS.html
Cant determine phytoplankton biomass based on colour wave lengths?
Surface layer data only
Intensity of colour = (red) high concentration
low concentration = (blue) low concentration
7 months to gather this data via ship
Satelite gives great real time data
Important for observing changes in ocean during global warming
Matching sampling to processes
