Sampling Equipment and Methods Flashcards
(30 cards)
Bottles
Zoop samples can be obtained using water bottle samples, Niskin, Go-flow
Zoop removed by filter or by gravitational settlement
2-20L
Get fixed volume from known depth
wide zoop spectrum
Not representative of larger
Very susceptible to patchiness
Plankton pumps
Water pumped through mesh net and flowmeter to collect known value of water
Deck operated 80m or in situ with release (>1000m)
Ease of use
Known volume from known depth
Good representation, but active swimmers can avoid low suction pumps
Larger gelatinous species may get damaged
In Situ Plankton Pumps
Deployed in situ to known depth (1000sm)
Returns to surface via acoustic release
Autonomous time series sampling designs in shallow and deep sea
Used in hydrothermal vent larval dispersal studies
Good for short term time series studies.
Nets
Net design:
- filtration efficiency measures the volume of water passing through the net compared to theoretical volume passing through mouth in absence of the net.
- Factors that affect FE, and so vol of water sampled, measured using flowtometer:
a. Filtering area (open area ratio)
b. mesh size
c. towing speed
Nets, open area ratio
Open Area Ratio, ratio of the total open area of net, to the area of the net mouth
Ratio = a x B/A
- a = total area of net
- B = mesh porosity
- A = mouth area of net
If OAR <3 efficiency progressively declines to 30%
In absence of complicating factors efficiency is high in nets
>3, 85%
>5, 95%
Net mesh size porosity
Clogging of net by particulate material
Determines size spectrum of sample.
Particular material = suspended material (estuaries), plankton (bloom), POM
Nets, tow speed
if net speed too high, causes water to form static body in net
Mesh size and porosity dictates efficient towing speed
Small mesh size, samples smaller individuals but tow speed is slower, larger individuals may detect and swim off
Large mesh size can tow faster, smaller pass through or are damaged.
Increase tow speed
Individuals can detect nets, visually, pressure changes, turbulence, increased speed counters net avoidance.
But higher speeds reduce FE
Simple mouth reduction cone of non-porpus material reduces turbulence at mouth and slows flow in net to reduce backwash
High tow speeds can damage individuals, solutions, encase net in rigid body, gulf plankton samplers.
Internal flow reduction, jet net
Bongo nets
Based on a simple plankton net.
Each net has different mesh sizes.
Designed for vertical or oblique hauls.
Can have a closing mechanism
Nansen closing net
Messenger sent down cable to trigger the closing mechanism.
MOCNESS net
Multiple Opening Closing Net Environmental Systems Sampler
Used to assess vertical distribution in the open ocean to depths of 5000m
Midwater trawl nets
Rectangular, dragged along floor.
RMT 1 (1m2), for small plankton
RMT8 mouth for krill
RMT25 for fish
High speed samplers
Often used in fisheries surverys to collect ichthyoplankton
Advantages of nets
V efficient at sampling water column is used optimally
Can only sample size spectrum of mesh
Can only sample discrete sector of water column
Can be used with other sensors
Can identify and quantify samples.
Disadvantages of nets
Can only sample size spectrum determined by mesh
Can only sample discrete sector of water column
LT sampling procedure, time required to identify community structure and abundance
Cannot modify sampling programme in response to prior haul
Acoustics
Signal sent by transducer
On encountering an object denser than surrounding water, energy is reflected/scattered back toward source.
Nature of return signal informs on depth, size and type of object
Calibrated using object of known acoustic properties
Acoustic technical issues
Target strength depends on species size, shape, orientation, body type.
Behaviour of organisms living near bottom lost in large seabed echo.
Identify species and quantify to biomass
- measure TS of individual sp
- net hauls
- use different frequencies
Acoustics, different frequencies
Same object can provide different echo return at diff frequencies.
Once frequency response of object measured, identity derived from theory.
Acoustic applications
Monitoring of large scale distribution and biomass
Observing behaviour, DVM
Species interactions, whale/krill feeding.
Optical flow cytometers
Bench top, portable, submersible
Image 3um to 2mm size particles using 2x-20x objectives
Continuous imaging at 1-20fps
Automated ID and enumeration
Optical plankton counters
Laser OPC
Detects, sizes and counts individuals by measuring attenuance of a light beam.
Can determine the size of individual particles to 250um to 2cm
OPC towed or attached to moorings and other platforms
Generates silhouette image, can identify larger sp only
Optical methods
VPR, underwater video microscope system towed at 10kt
High-res digital video camera
Mesozoo (0.2-20mm) can be imaged at up to 60fps
Pros, high res, rapid, semi auto, concurrent environmental data.
Cons, identifucation to sp level under represent rare taxa
Optical image analysis of samples
Zoop samples digitised by ZooScan, processed by ZooProcess and PkID to detect, enumerate and classify
Advantages of optical methods
Efficient strategy, good correspondence between net haul samples and optical definition of community assemblage
Relatively wide size spectrum identified
Can only sample discrete sector of water column
Can use other sensors
ST sampling, detials of assemblage available immediately, can modify sampling.
No discrete sample for further analysis.
