Benthic ecosystems Flashcards
What are the three main types of material a benthic environment is made of?
- bedrock
- gravely sand
- mud
What dictates what organisms can exist in a benthic environment?
Sediment type
In terms if structure how is a benthic environment discussed?
It is discussed in terms of surface area. They are basically a 2D structure
Most benthic animals are infaunal. What is meant by infaunal?
Infauna usually construct tubes or burrows and are commonly found in deeper and sub-tidal waters. Clams, tube worms, and burrowing crabs are infaunal animals
What are the most important characteristics in a benthic environment?
Supply of water, oxygen, nutrients and stability of sediment
What sedimnet changes occur with depth?
Redox, suphide, iron complexes, methane and ammonia levels
What is a redox potential?
A measure that reflects the balance between oxidation and reduction processes.
What is the redox potential of the benthic surface and what does this show?
Benthic surface has a positive redox potential which shows oxygen is present.
What is the redox potential with increased depth and what does this show?
With depth redox decreases and becomes negative showing a reduced environment.
What are the three main colours of sediment and what does this show?
Yellow/brown - oxidised sediment
Black - reduced sediment
Grey - in between redox potential discontinuity zone
What is the redox potential discontinuity? (RPD)
This is a region of rapid change in potential.
What is the RPD like in sand and mud?
In sand RPD is very deep and wide
In mud RPD 1-2mm and abrupt
What is found in the RPD zone?
Only get bacteria and meiofauna (those that contain symbiotic bacteria)
What is the Wentworth scale?
This is a method for determining sediment particle size.
Phi units
Phi - -log2 particle diameter (nanometres)
What is meant by ‘well sorted sediments’?
grains of similar size
What particles bind sediments together making mud cohesive?
Clay particles
Give the characteristics of well packed sand (Dilitant sand)
High proportion of fine grains, low permeability, dense, firm
Give the characteristics of poorly packed sand (Thixotropic sand)
Few fine grains, high permeability, less dense, unstable
What is bioturbation?
the disturbance of sedimentary deposits by living organisms. This can be through burrowing or re-working sediments.
Re-working of sediment increases the water content from ~40% ~ 70%
give example species that use bioturbation.
E.g lug worms can increase oxygen and nutrients on sediment.
E.g Bamboo worms can change particle grading which increases organic matter.
E.g Macoma (bivalve) produces a layer of faecal pellets up to 1 cm deep. Can re-work 600 cm3 sediment per day.
E.g Nucula (bivalve) re-works sediment up to 5 times a day.
E.g Cerastoderma (bivalve) produces 100,000 tonnes material each year as faeces of pseudofaeces.
What species disturb sediment and why?
So the filter feeders and others cannot co-exist.
E.g Amphipods and Lug worms Corophium only exist where Arenicola densities are low.
E.g Amphipod Pontoporeia kills juvenile Macoma (bivalve) bu constant burrowing
How can sediment become more stable?
Micro-organisms (bacteria and diatoms) can make the sediment more stable by excreting mucilage (extracellular polymeric substance). This sticks particles together making the sediment more stable.
This is then enhanced as higher plants like seagrass and mangroves grow and stabalises the sediments further by roots.
