Lecture 6 - Benthic Ecosystems Flashcards
What is a continental shelf?
A shallow, horizontal seafloor extension from the shoreline to the upper continental slope.
What is the average gradient for a continental shelf?
What is the exception to this?
1 degree.
Unless when glacially structured.
What is the average depth of continental shelf ecosystems?
150m
Which zone is the continental shelf ecosystem in?
The euphoric zone.
Give some physical factors that the continental shelf is strongly influenced by.
- Waves
- Tides and currents
- Input of materials/nutrients from adjacent land masses
Where does seasonal stratification occur in the ocean?
Between 20 and 100m.
What has shaped the benthos?
Past glacial events
How are hard-bottomed habitats formed?
From strong currents removing sediments.
What kind of benthos is found in
a) Sheltered, deeper areas?
b) High energy/shallower areas?
a) Sheltered, deeper areas = muddy, silty.
b) High energy, shallower areas = bare rock, pebbles or sand.
Finish this sentence:
The more sheltered…
The finer the sand.
Other than fineness of substrate, what do waves and currents affect in the benthos?
The rate of food supply from pelagic to benthos; in strong currents, food at the surface is moved away before it reaches the bottom.
Give a description of an organism living in high current.
- Encrusting
- Very flexible (in order to avoid breaking)
- Burrowing
Describe the body structure of an organism living in low current.
- Delicate
- Elaborate
- Leafy/branched
What two factors affect light levels in water?
- Depth
- Turbidity
Where is water very turbid?
- At estuaries
- Near rivers
Describe the zonation of algae.
In deeper waters:
From green, to brown, to red.
What are macrofauna?
Fauna larger than 0.5mm
What are meiofauna?
Would pass through a sieve with a mesh diameter of 0.5mm, but retained on one of 0.063mm
What are microbiota?
Organisms smaller than 0.063mm (includes dinoflagellates, diatoms and bacteria)
What are infaunal organisms?
Organisms that bury within the mud.
What is the difference in habitat requirements of juvenile and adult mobile animals?
Juvenile mobile animals have specific habitat requirements for predator avoidance, but adults show more flexibility.
What is an ecological function?
The job that animals do in their environment.
Give 5 key feeding modes.
- Surface suspension feeder
- Sediment processors
- Suspension feeders
- Surface deposit feeder
- Carnivore/scavengers
What is a scavenger?
An animal that can feed on a dead carcass.
True or false:
Herbivores such as sea urchins, and suspension feeders such as brittlestars, are known to feed on carrion.
TRUE.
What is the largest amphipod family/
Lysianassoids
What is the ecological function of amphipods?
Scavengers; important for removing carcasses from seabed.
What are sea mice?
Epifaunal polychaetes, covered in bristles.
Scavengers that predate on small crabs and worms.
Spines act like optical fibres due to reflective properties.
Give an example of a carnivorous grazer.
Nudibranchs feast on bryozoans by scraping.
Give three examples of particle feeders.
- Mussels
- Clams
- Oysters
What are bulk sediment processors?
Give two examples.
Organisms that process sediment and remove microbes from the sediment.
- Heart sea urchin
- Sea cucumbers
What are biogenic reefs?
Where whole groups of organisms come together to form their own structure, e.g. mussel bed, coral reefs.
What percentage of shallow continental shelf is composed of
a) Muds?
b) Sands?
c) Rocky substrata?
d) Reef-structures?
a) Muds = 37%
b) Sands = 47%
c) Rocky substrata = 6%
d) Reef structures = 10%
How are hard bottom communities kept clean of sediment?
By flow or scouring by sand.
How do macroalgae compete for space in hard bottom communities?
Have pneumatocysts; large gas bubbles to help them float.
Give and describe two encrusting species.
- Sea squirts; filter feeders.
- Sponges, e.g. Cliona celata.
Describe pink sea fans.
- Protected species - Found in turbulent water; good at capturing particles in fast-flowing water.
- Can orientate itself perpendicular to the current.
Describe brittlestar beds.
- Live at high densities, living on bedrock
- Can find other invertebrates living within them as a microhabitat
Up to what depth can organisms live in burrows?
2m
How does particle/grain size determine what can live there?
- Larger particles hold more water
- Larger grains easier to burrow into.
- Microbes in fine sand use up oxygen quickly, gets anoxic more quickly.
What is bioturbation?
Moving mud around.
Why is bioturbation important?
Helps to keep water and oxygen circulating within the sediment.
What is the name of the biogenic reef formed by polychaetes?
Calcium carbonate rubes
What are ecosystem engineers?
Organisms that cause a biologically-mediated habitat modification.
What are cryptic fauna?
Organisms that live inside nooks and crannies
Name some cryptic fauna you might find in mussel beds.
- Perinereis cultifera
- Barnacles
- Periwinkle
- Hydroids
What are mearl beds?
Collective term for several species of red seaweed with hard, chalky skeletons.
Have calcium carbonate in the fronds of the seaweed, forming hard habitat structures when they grow in big aggregations.
Not attached to bottom.
Slow growing.
Name some method for sampling benthic ecosystems.
- Manta tow / scuba tow; dragged off the back of a boat, record everything you see.
- Sonars
- Grab sampling
- Trawling (nets dragged over the bottom)
