Soft Sediment Ecosystems

Question 1

Name the three classifications of the benthos (position) and briefly describe them.

Answer 1

1. Epibenthic (surface of sediment on the bottom of the sea)
2. Infauna (animals burrowing into marine or freshwater sediment)
3. Interstitial fauna (situated between the cellular components of an organ or structure)

Question 2

Name and briefly describe the four classifications of the benthos (size)

Answer 2

1. Megabenthos
2. Macrofauna > 500 micr. -e.g. bivalves, sponges -move thorugh sedmiment -bioturbators
3. Meiofauna 63- 500 micr. -e.g. nematodes, copepods -Move through gaps between grains
4. Microfauna <63 micr. -e.g. bacteria -Associated with sediment grains -Not sampled with sieves

Question 3

What are characteristics of deposit-feeders?

Answer 3

• Feed mainly on bacteria associated with the sediments
• Affect sediment biogeochemistry
• Surface or sub-surface

Question 4

Give an example for a head down deposit feeder

Answer 4

Arenicola marina

Question 5

What are characteristics of suspension feeders?

Answer 5

• feed on particles in the water column
• Active and passive modes
  e. g. parchment worm, sepula, bivalve

Question 6

How is the grain size in a physical environment measured?

Answer 6

• Sieves
• Optically
• Fines

Question 7

What controls the structure of a community in a physical environment regarding grain size?

Answer 7

• Mobility
• Feeding mode
• Bacterial processes

Question 8

How is the benthic boundry layer (BBL) defined?

Answer 8

1. Outer layer

2. Logarithmic Layer

• Fully turbulent
• Rapid and intense mixing

3. Viscous layer

• weak turbulance
• vertical mixing = molecular diffusion

4. Diffusive sub-layer

• no turbulance
• mixing by molecular diffusion

Question 9

What controls the Benthic Boundary Layer (BBL)?

Answer 9

• Dissolved nutrient fluxes
• Oxygen availability
• Paricle dynamics

Question 10

Why does erosion increase with decreasing grain size?

Answer 10

Increased surface area and elcetro static charge of smaller grains increase erosion

Question 11

Describe the aerobic diffusion of Oxygen in soft sediment (what curve?)

Answer 11

Question 12

Why is the benthic biomass of coastal waters so much higher than ocean waters?

Answer 12

• higher primary production (more food available)
• reaches the sea floor quicker compared to pelagic zone

Question 13

What burns off excess nitrogen in the sediment of the sea floor

Answer 13

Denitrification

NO3 —> N2

Question 14

What happens when the organic load in the sediment increases?

Answer 14

• Anoxic layer goes to the surface
• it becomes fully anoxic
• denitrification is shut off as oxic - anoxic baundary is necessary for the process