L2 Sampling, Methodology and experimental approaches

What determines the sampling methods we use

Nature and patchiness of target species and/or habitat

Practical considerations

Questions that the study will address

Economic considerations

Pervious adopted practice

What are the benthic size classifications

Nanobenthos (microflora & fauna) - < 63 μm (shallow water) - < 43 μm (deep sea)

Meiofauna - 63 – 500 μm (shallow water) - 43 – 300 μm (deep sea)

Macrofauna - 500 μm – 3 cm (shallow water) - 300 μm – 3 cm (deep sea)

Megafauna - > 3 cm

What are some generalisations of trawls

- Qualitative

- Wide coverage

- Epifauna ~ live at surface of the sediment

- Low efficiency

- Preliminary survey use

Beam & Otter trawls

- Larger mesh; larger fauna

- Including more benthic fish

What are some generalisations of Fishing dredges

Scallop dredge or Oyster dredge Some generalisations:

- Qualitative

- Wide coverage

- Epifauna (and rock) ~ live at surface of the sediment

- Designed for hard substrates

- Low efficiency

- Preliminary survey use

What are some generalisations for bottom sleds

Epibenthic sleds Some generalisations:

- Semi-quantitative

- Reduced coverage

- Epifauna & benthopelagic taxa ~ living just above the sediment

- Heavy frame enclosing the net

- Some modified designs, e.g. tickler chains, open and closing mechanisms or flow meter- Low efficiency & contamination

What are some generalisations of grabs

- (Semi-)Quantitative

- Limited coverage

- Sessile & discretely sessile epifauna & infauna (living in sediment) to the depth excavated

- Efficiency depends on depth of burrowing

- Grabs penetrate < 10 cm (max 15 cm)

- Bow wave effect

What are some generalisations of a box corer

- Quantitative

- Limited coverage

- Infauna

- Similar to a Box corer

- Less of a bow wave effect compared to traditional Box corer and grabs

What determines the efficiency of benthic sampling gear

Digging characteristics of the sampler

- depth of penetration, volume of sediment & degree of disturbance

Efficiency of capture

- representative picture of density & distribution

Technical characteristics

- ease of manipulation, weight, ease of access to sample, safety and mechanical reliability Sampler choice depends on survey requirements, working conditions and availability of suitable gear

What is optical imaging techniques

- Underwater video & camera systems

- Surveys, ID & enumeration, behaviour, and evaluation and performance of samplers

what are some generalisations of optical imaging techniques

- Quantitative

- Wide coverage

- Epifauna ~ live at surface of the sediment

- Efficient

what are some examples of carrier platforms

Yoyo camera system, Manned-submersible, ROV ISIS, scuba and autosub7000

How does benthic sampling differ in the deep sea

Time consuming

- Requires special skills and failure rates can be high

Gear is larger & heavier than equivalent apparatus

- Excessive winch wire needed

Specific problems

- Replicated sampling

- Lower faunal densities & body size

What are some generalisations of benthic sample processing

- Size of mesh selected matters

- Timing of sampling is important

- Depends on the question

What is experimental or survey design essential to

-Provide a robust and testable dataset allowing powerful testing

-Save time and money

-Ensure that the data collected can actually answer the questions that are asked

-Make the data analysis and testing as straightforward as possible

What does a poor experimental survey design lead to

-Large but potentially useless data sets offering low power

-Wasted time and money

-Initial research questions remaining unanswered

-Unwieldy and complex statistical analysis which relies on estimates of statistical powers