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Ecological Techniques > Benthic Sampling > Flashcards

Benthic Sampling Flashcards

1
Q

What is benthic sampling?

A

Methods for sampling aquatic benthic fauna (macrofauna techniques)

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2
Q

What is the benthos?

A

The community of organisms that live on or near the seabed or on the bottom of freshwater bodies

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3
Q

What size are macrobenthos?

A

> 1mm
eg. Polychaetes, corals, crabs, lobsters

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4
Q

What size is meiobenthos?

A

0.1 - 1mm
eg. Nematodes, copepods, ostracods

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5
Q

What size is microbenthos?

A

<0.1mm
eg. Ciliates, diatoms, bacteria, Amoeba

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6
Q

What are the largest invertebrates called?

A

Not strictly defined in terms of size, often referred to as megabenthos

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7
Q

How can megabenthos and others be defined?

A

Usually defined operationally e.g. benthos that can be sampled using towed gear of a certain mesh size or recorded on seabed photographs e.g. Holothuroidea, Asteroidea, some Crustacea

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8
Q

What is the hyperbenthos?

A

Organisms that live just above the sediment

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9
Q

What is the epibenthos/epifauana?

A

Organisms that live on the substrate

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10
Q

What is the endobenthos/infauna?

A

Organisms that live in the substrate

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11
Q

What are two types of benthos sampling methods?

A

-Ex-situ sampling methods
-In-situ sampling methods

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12
Q

Describe ex-situ sampling methods

A

-A portion of the sediment and fauna are removed for latter processing and examination
-Trawls, dredges, cores, grabs, remotely operated vehicles (ROVs)

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13
Q

Describe in-situ sampling methods

A

-Benthos is directly observed
-Onshore observations, imaging, scuba observations

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14
Q

What is quantitative sampling?

A

-Sampling that produces data that can be measured numerically and transformed into usable statistics
eg. quadrats, cores can provide density estimates

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15
Q

What is qualitative sampling?

A

-Descriptive sampling, data can be observed but not measured explicitly
eg. some trawls/dredges

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16
Q

What is semi-quantitative sampling?

A

Eg. CPUE, some measure of numerical data

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17
Q

Describe intertidal sampling

A

-Relatively easy to access
-Must consider impact of tides on benthic fauna
-Often intertidal is sampled at a series of regular intervals from high to low water mark with replicates taken at each location eg. quadrats, small hand-hild cores (quantitative)

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18
Q

Describe the Riley Pushnet (Qualitative)

A

-Designed to sample benthic macrofauna (shrimp, juvenile flatfish) in shallow intertidal areas
-Light metal frame seated on two metal skies
-Net of 5-10mm mesh with finer mesh cod end
-Weighted footrope
-Tickler chain in front of mouth disturb organisms and drive them into net

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19
Q

What are some disadvantages of subtidal sampling?

A

-More expensive
-Requires shiptime
-Weather dependent

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20
Q

Describe trawls/dredges

A

-Skim over surface of the substrate
-Large swept area- suitable for rarer epifauna
-Selective sampling method- some organisms will escape
-Qualitative but can be used in a semi-quantitative fashion (CPUE)
eg. Beam, Agassiz, Otter Trawls

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21
Q

Describe beam trawls

A

-Used commercially to catch fish
-Mouth of net (12.5 mm mesh) held open by beam 1- 12m length
-Weighted chain ground rope lies behind upper mouth of net to prevent disturbed animals escaping
-Used on smaller vessesls

22
Q

Describe dredges

A

-Heavy metal frame designed for breaking off rock, scraping organisms off hard surfaces or collecting top layer of sediment
-Rectangular dredge/rock dredge

23
Q

Describe an anchor dredge

A

-Semi-quantitative sampling of firmly packed soft sediments
-Fitted with metal box that digs into sediment to depth of up to 25 cm
-Not towed behind boat- deployed from drifting vessel
-Takes a wedge shaped sample theoretically of equal area to the digging plate
-Easier to quantify than trawls and other dredges
-Several versions of this

24
Q

Describe the epibenthic sledge

A

-Metal frame with fine mesh net attached. Scrapes sediment collecting organisms from the surface
-May include open/closing devices and flowmeter and camera attachments
-Several nets may be used
-Often used to collect samples in the Deep-sea

25
Q

What effects and improves efficiency?

A

-Efficiency of trawls and dredges low
-Varies on nature of substrate, the ships system (length of warp, type of warp, speed of towing)
-Fitting of depressors, plates, tickler chains can improve efficiency
-Modern trawls employ depth and net sensors, fitted with cameras and ctd- semi-quantitative

26
Q

Describe grabs

A

-Used to take quantitative samples of infauna from top 15cm of the sediment
-Depth of bite can vary on how packed is sediment
-Cover a surface area of 0.1-0.2 m2, several replicate samples taken per station
-Suitable for quantitative determination of more common species- not good for rarer species
-Fast moving species can escape grab
-Can be supplemented with sledge/trawl samples, underwater video or diving

27
Q

Describe a Petersen grab

A

-Gauze-covered window allows water to escape when grab closes
-Lowering rope slackens when gear hits substrate, and release hook operates and buckets close together before grab leaves the bottom

28
Q

What disadvantages are there to Petersen grab?

A

-Rope may slacken momentarily as ship rolls- grab closes prematurely
-Grab may not penetrate sufficiently into sediment
-Closure may be incomplete leading to loss of sediment from grab

29
Q

Describe the van veen grab

A

-Long arms give better leverage for closing
-Lowering rope slackens when gear hits substrate, release hook operates and buckets close together before grab leaves the bottom

30
Q

Describe the day grab

A

-Pressure plates are pushed upwards on hitting substrates, releasing transverse beam so that hooks holding the buckets are released

31
Q

Describe shipek sediment sampler

A

-Single semi-circular scoop activated by powerful springs
-Small sampling area: 0.04 m2; mainly used to take sediment samples

32
Q

Describe corers

A

-Quantitative sampling method
-Length of plastic or metal tube pushed into sediment
-Often deployed by divers
-Bung inserted in tube to retain contents

33
Q

Describe box samplers and corers

A

-Deploys corer into sample
-Cutting arm released to close bottom of tube
-Samples area 20 x 30 cm down to 45cm depth
-Weighs 750kg
-Modified designs allow multiple cores to be taken
-Provide deep and relatively undisturbed sediment sample sample- suitable for deep sea use
-Requires large vessel and calm conditions

34
Q

What can the box corer be used to do?

A

-Suitable for deep-sea sampling
-Can be used to profile the sediment

35
Q

Describe suction samplers

A

-Pump attached to wide coring tube (36cm diameter, 30cm long)
-Coring tube is inverted once it is lifted off the bottom retaining sample
-Some designs are operated underwater by divers
-Suction samplers often attached to ROVs for sampling individual organisms (targeted)

36
Q

What effects the choice of sampler

A

-Requirements of survey
target organisms, spatial coverage etc.
-Quantitative/qualitative sampling
-Working conditions – weather, vessel size power etc.
-Availability of suitable gear

37
Q

What are some alternative sampling methods

A

-Some species are not readily taken by conventional sampling methods (trawls, dredges, grabs, corers)
-Too sparsely distributed to be recorded in limited sampling area
-Live in habitats inaccessible to conventional gear eg. reefs

38
Q

Describe various imaging techniques

A

-Video - hand operated and remote options
Go-pros attached to sleds/ trawls
Non - invasive, used to assess Zebra mussels in lake Michigan
-Collected continuous footage from 500 m long quadrats

39
Q

Describe Remotely Operated Vehicles (ROVs)

A

-Tethered/ Untethered
-Video/ still footage
-Sampling arms/tubes
-Auto Hold

40
Q

Describe the imaging technique Sediment profile imagery (SPI)

A

-Inverted periscope penetrates sediment and photographs profiles of sediments
-Can be interfaced with a computerised measuring system
- Cost-effective survey method
-Used for monitoring environmental status

41
Q

What is an example of indirect detection?

A

Fish stomach contents useful for detecting organisms not available to trawls and dredges
-Must consider selective feeding of fish and differential rates of digestion

42
Q

Describe artificial substrates

A

-Synthetic structures used to collect settling organisms
-Advantages
-Can be used to sample difficult areas
-Passive collection method
-Confounding effects of habitat differences are minimized by providing a standardized microhabitat
-Sampling variability is decreased due to a reduction in microhabitat patchiness

43
Q

What are disadvantages of artificial substrates?

A

-Must be deployed and recovered - two sampling trips
-Prone to loss, natural damage or vandalism
-Substrate material will influence the composition and structure of the community
-Orientation and length of exposure of the substrate will influence the composition and structure of the community

44
Q

How can hidden organisms be collected?

A

-Organisms that hide in rock crevices, weeds etc
-Can be removed using
-Explosives, anesthetics
-Electrofishing
-Baited/ light traps

45
Q

Summary of trawls

A

-Qualitative / semi-quantitative. Suitable for epifauna on mud/sand substrates. Can be used from small vessel

46
Q

Summary of dredges

A

General use on all bottom types. Qualitative (anchor dredge design semi-quantitative)

47
Q

Summary of grabs

A

-Suitable for muds/sands
-Quantitative (although bite depth and shape can very with substrate)
-For shallow infauna
-Suitable for small vessels

48
Q

Summary of box corer

A

Heavy, needs large vessel
-Good depth penetrations
-Quantitative
-Mud/sand

49
Q

Summary of remote suction sampler (Knudsen)

A

-Can collect known area by great depth within core
-Large amount to sort, to diving depth only, very good for finding what other methods miss and to calibrate other techniques

50
Q

Summary of cameras: remote and in-situ

A

See only surface species or marks, need to be able to identify from film

51
Q

Summary of sediment profile imagery

A

see cross section of bottom, can get much data, but not many species

Ecological Techniques (7 decks)

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