S2: Sampling and Experimental Approaches (combined)

What determines the sampling methods we use? 

• Questions that the study will address

• Nature and patchiness of target species and/or habitat

• Practical considerations e.g. site and habitat type

• Economic considerations (expensive)

• Previous adopted practice

• Benthic size

Benthic size classification for Nanobenthos: Shallow water v.s. Deep sea

(microflora & fauna)

< 63 μm (shallow water) and < 43 μm (deep sea)

Benthic size classification for Meiofauna: Shallow water v.s. Deep sea

63 – 500 μm (shallow water) v.s. 43 – 300 μm (deep sea)

Benthic size classification for Macrofauna: Shallow water v.s. Deep sea

500 μm – 3 cm (shallow water) v.s. 300 μm – 3 cm (deep sea)

Benthic size classification for Megafauna

• > 3 cm

• Identifiable in seafloor images

What are the four stages of benthic gear deployment?

1. Preparation of the gear before deployment

2. Deployment

3. Processing of the sample between deployments

4. Post-deployment processing of samples

At water depths typical of the shelf,

How long does it typically take to obtain a single grab sample?

Almost 1 hour

(compared to around 20 mins at 30m water depth under calm conditions)

Macrofaunal sampling techniques: Trawls types

1. Beam, otter

→ -Larger mesh; larger fauna

• Including more benthic fish

2. Agassiz/ Blake

Shrimp

Macrofaunal sampling techniques: Trawls positives and negatives

• Qualitative

• Wide coverage

• For Epifauna ~ live at the surface of the sediment

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• Low efficiency

• Preliminary survey use

Macrofaunal sampling techniques: Fishing dredges

• Scallop dredge

• Oyster dredge

Macrofaunal sampling techniques: Fishing dredges positives and negatives

• Qualitative

• Wide coverage

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

• Designed for hard substrates

• Low efficiency

• Preliminary survey use

Macrofaunal sampling techniques: Bottom sleds type

Epibenthic sleds

Macrofaunal sampling techniques: Bottom sleds positives and negatives

Semi-quantitative

Reduced coverage

Epifauna & benthopelagic taxa ~ living just above the sediment

Low efficiency & contamination

Macrofaunal sampling techniques: Bottom sleds main feature and modifications

Heavy frame enclosing the net

Some modified designs, e.g. tickler chains, open and closing mechanisms or flow meter

Macrofaunal sampling techniques: Grabs types

• Van Veen grab

• Smith-McIntyre grab

• Day grab

• Hamon grab

Macrofaunal sampling techniques: Grabs positives and negatives

(Semi-)Quantitative

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

Limited coverage

Macrofaunal sampling techniques: Grabs efficiency

Depends on the depth of burrowing

Grabs penetrate < 10 cm (max 15 cm)

Bow wave effect

What is the 'bow wave effect' in the context of grabs and box samplers?

Effect associated with descent

where the pressure wave can remove surficial sediments and fauna before the sampler makes contact.

Macrofaunal sampling techniques: Box samplers type

Box core

Macrofaunal sampling techniques: Box samplers features

Quantitative

Infauna

Limited coverage

Macrofaunal sampling techniques: Box samplers efficiency +/- compared to standard grab for quantitative sampling

Reliable & collects a relatively deep, large, undisturbed sample

that retains SWI & supernatant water

Large & expensive

Macrofaunal sampling techniques: Corers & Multiple Corers types

• Hand-held corers

• Multiple corer (including Megacorer)

Macrofaunal sampling techniques: Corers & Multiple Corers features

Quantitative

Limited coverage

Infauna

Macrofaunal sampling techniques: Corers & Multiple Corers efficiency +/-

Similar to a Box corer

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

What prevents sediment and water loss in a Craib corer?

A ball closure mechanism and hydraulically dampened penetration into the sediment.

What determines the efficiency of the 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

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

• Previous adopted practice

How sampler choose what benthic sampling gear to use?

Sampler choice depends on survey requirements, working conditions and availability of suitable gear

Why are trawls used despite being qualitative and having low efficiency?

Useful for identifying rare species or those with a patchy distribution by covering wide areas quickly.

Why is the use of multicorers sometimes cautioned against in experimental design?

A risk of pseudoreplication if all cores from a single deployment are treated as independent replicates.

For macrofauna processing, what is the standard mesh size of the final sieve?

Typically 500 μm

after an initial wash through a coarse sieve of 5 mm5mm or 1 cm1cm.

Which chemicals are used to preserve faunal returns after sediment removal?

Reserved in either 70% industrial methylated spirit (IMS) or 4% formaldehyde

What is the purpose of adding a 1% Rose Bengal stain to faunal samples?

Aids in the visual location of fauna during the sorting stage.

Megafaunal sampling techniques: Optical imaging techniques

Megafaunal sampling techniques: Optical imaging techniques

Megafaunal sampling techniques: Carrier platforms

Megafaunal sampling techniques: Carrier platforms

Megafaunal sampling techniques: Carrier platforms

Sediment profile as advanced through the transect (with SPI)

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

Benthic sample processing - what causes results to differ

• Size of mesh selected matters

• Timing of sampling is important

Variability & variation in benthic populations

Genetic differences between animals

Environmental effects

Different types of organism

- M or F, species, age etc.

Sampling & experimental errors

What five key factors determine the sampling methods used by benthic ecologists?

Economic considerations, previously adopted practice, questions to be addressed by the study, nature and scale of patchiness of substrate and/or biology, and practical considerations such as site and habitat type.

Megafaunal: What was the original purpose of Sediment Profile Imaging (SPI) developed by Don Rhoads?

To understand invertebrate-sediment relations below the sediment-water interface (SWI).

Megafanual: What are the physical limitations of using a Sediment Profile Imaging (SPI) camera?

It is limited to soft-to-medium sediments and requires calmer weather conditions for deployment.

Megafaunal: How do Autonomous Underwater Vehicles (AUVs) navigate to complete biological surveys?

They follow pre-programmed routes, often using a 'mow the lawn' pattern, to cover an area without operator intervention.

Megafaunal: Define the three-dimensional rotation axes used in AUV assessment.

Yaw (rotation about a vertical axis)

Pitch (nose up/down about a transverse axis)

Roll (rotation about a longitudinal axis).

What are four biological and environmental factors that cause benthic patchiness?

Disturbance (natural and anthropogenic)

recruitment

predation

competition

What is the difference between spatial and temporal replication in benthic studies?

Spatial replication: predicts abundance based on factors like sediment type

Temporal replication: focuses on seasonal patterns and disturbance over time.

How can a researcher determine if the number of samples taken is representative of the parent population?

By conducting a preliminary assessment and calculating a running mean or a collectors curve.

What is Stratified sampling in benthic ecology?

A strategy used when the parent population is made up of subsets (strata) of known size.

What are the common consequences of a poor experimental survey design?

Large but useless data sets, wasted time and money, unanswered research questions, and unwieldy statistical analysis.

What is an Agassiz trawl specifically designed to do?

It is designed to skim over the surface of the seafloor to selectively sample decapod crustaceans, echinoderms, gastropods, and fish.

What is the 'ISIS' in the context of deep-sea carrier platforms?

It is a Remotely Operated Vehicle (ROV) capable of operating at depths of $6500\,m$ .