2 METHODOLOGY & EXPERIMENTAL APPROACHES Flashcards
What determines sampling methods used? (5 things)
- Nature & patchiness of target species and/or habitat
- Practical considerations
- Questions that the study will address
- Economic considerations
- Previous adopted practice
If a study required an undisturbed section of the sediment profile, what would be ruled out/preferred as a sampling device?
- Rule out towed dredges
- Sediment grabs are possibility
- Corer would be preferred sampling device
What is the 4 stage process of deployment of gear (especially when sea conditions/weather are inclement)?
- Preparation of gear prior to deployment
- Deployment
- Processing of samples between deployments
- Post-deployment processing of the samples
What factors influence the time taken to deploy?
- deeper water = longer
- bad weather = longer
- tiredness
Need plan B bc unlikely to be given extra time on active research cruises.
What sampling gear is deployed for benthic habitats?
Beam trawl: consists of net & heavy metal frame with skids. Skids slide across seafloor, dragging ground rope & net behind during fishing. Wide coverage & designed to sample demersal fish & benthic invert species. Pelagic fish close to seafloor also may be caught.
Multiple corer: designed to sample SESSILE & DISCRETELY SESSILE sediment infauna. Larger versions = v expensive & need large vessel & calm conditions. Takes 4 cores of rel. deep, large & undisturbed sediment samples. Include sediment-water interface & overlying supernatant water.
Van Veen Grab: collects surficial sediment samples & captures SESSILE & DISCRETELY SESSILE epifauna & infauna to depth of sediment excavated. Depth excavated depends on sediment type & amount of weight applied to grab frame. Efficiency of sampling depends on burrowing depth of target benthic taxa. Most grabs penetrate <10cm into sediment, but most fauna within top 5-1cm.
Why is sampling in intertidal areas sometimes limited, even though access is easier?
Tidal restrictions apply
Transit across mud flat can be difficult w heavy equipment and samples
What are the 4 size classifications of fauna?
Microfauna
- < 63µm (shallow water), < 43µm (deep sea)
Meiofauna
- 53-500µm (shallow water, 43-300µm (deep sea)
Macrofauna
- 500µm-3cm (shallow water), 300µm-3cm (deep sea)
Megafauna
- >3cm (identifiable in seafloor images)
Lifestyle of organisms depend on size, especially with regards to how they interact with their environment. What is the difference between the lifestyle of micro/meio sized animals and macro/mega organisms with regards to sediment habitat/movement?
- Micro and meio sized animals associated with INDIVIDUAL MINERAL GRAINS of the sediment, living ON PARTICLES (micro) or IN BETWEEN them (meio)
- Macro and mega organisms MOVE OR MANIPULATE MINERAL GRAINS & either live ABOVE or ON the sediment, or WITHIN THE SEDIMENT PROFILE
What is the different sampling equipment for benthic fauna?
Trawls & dredges Bottom sledges Grabs Box samplers/box corers Corers & multiple cores
What are trawls used for? What are their advantages/limitations?
- Useful for collecting epifaunal organisms, esp rare ones or ones with patchy distribution
- Hard subtrates
- Cover wide areas in short time period
- Deployed in most weather conditions
- Good for collecting epifaunal organisms
- Not quantitative as impossible to know how much of seafloor been sampled
- Low sampling efficiency; long deployment
- Limited penetration into seafloor thus not designed for sediment collection
What are bottom sledges designed for? What are their advantages/disadvantages?
- Designed to sample epifauna & water immediately above the seafloor
- Semi quantitative
- Good for sampling epifauna and suprabenthic organisms
- Can be advantage over v uneven substrates
- Reduced coverage
- Low efficiency
- Requires experienced pilot and good sea conditions
What are grabs designed for? What are their advantages/disadvantages?
- Most common method for obtaining macrofauna inhabiting sediment
- Soft to medium hard sediment
- Quantitative
- Leave significant elements of the fauna e.g. mobile epifauna and deeper dwelling macrofauna
What are box corers designed for? What are their advantages/disadvantages?
- Used in shelf and deep sea, sometimes shallower coastal
- Return rel undisturbed large samples
- Excellent for obtaining intact microbial, meiofaunal communities & undisturbed biogeochem profiles
- Retains sediment-water interface and overlying water
- Large size & weight so difficult to operate
- Physically demanding for deployment
- Can only be used in calmer conditions
- Limited spatial coverage
- Expensive
What are corers & multiple corers designed for? What are their advantages/disadvantages?
- Drive tube into sediment profile to retrieve intact column of sediment
- Reliable
- Return undisturbed samples of sediment profile
- Lightweight corers easy to operate and can be deployed from rel small boats
- Limited diameter samples
- Multicorers may not be suitable for some studies due to pseudoreplication
How are faunal samples processed, e.g. for macrofaunal returns from a grab or core?
- Washed through coarse sieve to remove debris
- Washed through 500µm mesh sieve
- Faunal returns and residue rinsed into container and immediately preserved using e.g. formaldehyde
- 1% Rose Bengal stain can be added for visual location of fauna at sorting stage
- Minimum storage of 3 months to stabilise biomass
- Fauna sorted under low mag. into broad groupings (molluscs, polychaetes, crustacea, etc)
- More thorough analysis under high mag using keys
- For biomass, fauna blotted dry on absorbent paper to remove excess liquid prior to wet weighing
- Liquid retaining fauna are punctured and drained
