Sampling marine ecosystems

Question 1

How much of the Earth’s surface is covered by seawater?

Answer 1

~70%

Question 2

What is the average depth of the oceans?

Answer 2

3.7km

Question 3

What is the neritic province?

Answer 3

Coastal above continental shelf

Question 4

What is the oceanic province?

Answer 4

offshore, beyond continental edge

Question 5

What methods can be used to measure the inter-tidal area of the neritic province?

Answer 5

1. Remote sensing
   - satelite data
   - high and low altitude recording (aerial photographs)
   - ground level observations (camera and video)
2. Transect and quadrats to measure the health of the shore.
   - sampling units (quadrats) may be random over the whole shore or in distinct bands or distnaces (transect)kLinear or belt transects.

Question 6

What methods can be used to estimate population abundance of the inter-tidal neritic province?

Answer 6

• Mark and recapture
• Removal sampling
• Using ‘signs’

Question 7

What methods can be used to estimate population abundance AND distribution of the inter-tidal neritic province?

Answer 7

• Grid (systematic) sampling

- Simple random

Question 8

What are some of the limitations when studying the inter-tidal neritic province and what preparations can be done to get around these?

Answer 8

Tides are a limitation so consulting admirality charts for tidal range and times is important when carrying out a study.

There is variation and patchiness in this habitat with biological cycles such as seasons and larvae.

Preperation can include reconnaissance, pilot study, ACFOR scales

A – The species observed is “Abundant” within the given area.

C – The species observed is “Common” within the given area.

F – The species observed is “Frequent” within the given area.

O – The species observed is “Occasional” within the given area

R – The species observed is “Rare” within the given area

Question 9

What methods can be used to measure the nekton in the sub-tidal area of the neritic province?

Answer 9

1. Mid-water trawls
   - locate fish with sonar
   - Opening and closing trawls
2. Long-line
   - baited hooks
   - floats to keep lines near surface
3. Drift nets
   - Very long vertical curtains
   - mono-filament, nets catch on fish gill covers

Question 10

What methods can be used to measure the benthos in the sub-tidal area of the neritic province with soft sediment?

Answer 10

1. Dredge
   - digs and removes the top few centimetres of sediment
2. Corer (quantitative)
   - small tube or metal box is pushed into the sediment, remove as whole sample
3. Grab (quantitative)
   - Grabs a set surface area - sediment not always intact

Question 11

What methods can be used to measure the benthos in the sub-tidal area of the neritic province with hard sediment?

Answer 11

1. Trawl
   - scapes along sediment surface.

a) Agassix trawl
- simple net bag with metal oblong mouth, dragged over sediment surface.
- easy to deploy

b) Beam trawl (for commericial, inverts and fish)
- Beam on top of mouth, runners on bottom sides.
- ground rope and tickler chains from bottom of mouth
- net, cone shaped, often tied cod-end.

c) Otter trawl (common or fishing)
- large, no frame around mouth.
- net held open by “Otter boards”
- big heavy metal boards make noise as they’re dragged along.
- head rope has floats and the ground rope has big bobbins - “rock hoppers”

2. SCUBA

a) Manta tow
- diver is towed behind boat ~ 2 knot and makes observations and then communicates this at de-brief sessions.
- This is good for large distances, rapid simple assessment but no detail and no control by diver.

b) Diver propulsion vehicle
- followed by boat, some control over areas surveyed.
- little detail recorded but can stop and debrief.

c) Free observer
- this technique is widely used. Hands are available to make notes by using a water proof slate and pencil.
- This method is cheap, covers a small area but in detail.
- Diver can take photographs, videos, examine permanent stations.
- survey quadrats along transects eg. reef edge
- can mark and tag organisms

Question 12

What are the main issues with trying to sample the oceanic deep sea?

Answer 12

Depth, cold, dark, pressure, oxygen, time and difficulty in deployment.

Question 13

What methods are used for sampling the oceanic deep sea?

Answer 13

1. Manned submersibles
   - ‘Alvin’ 1964 could descend to 3,000m so could study mid-oceanic ridges.

• more recently ‘Johnson Sea Link’
• A perspex bowl on front allows easy viewing with a range of gadgets such as; corers, suction, arms, video, cameras, lights, water collection, thrusters.
• Problem is it can only be deployed from large research vessels and only during calm weather.

2. Un-manned submersibles
   - ‘Auto-sub’ NERC or deploy remote operated vehicle (ROV)
   - operated by crew on board boat.
   - can monitor - video photographs
   - can do simple tasks using arms.
3. Sledges
   - Towed behind boat. Has TV, cameras record sea bed for mapping.