The abiotic environment Flashcards
What is the definition of a reef?
Rocky marine habitats or biological concretions that rise from the seabed. Includes artificial reefs and natural reefs.
What are artificial reefs?
Any manmade structure that has been dropped onto the seabed, sometimes accidentally, sometimes for a specific purpose (3D framework). Needs to be inert (not changing/breaking down over time) and have space for spatial settlement.
What types of reefs are found within natural reefs?
Rocky reefs and biogenic reefs
What are rocky reefs?
Submerged rock outcrops rising from the seabed
Surface area for colonisation of algae and invertebrates
Refuges for juvenile and smaller fishes
What are biogenic reefs?
Provide habitat for benthic organisms through rigid frameworks built by a combination of various ecosystem engineers and geological processes.
These biogenic reefs are classified based on the main organisms that are responsible for building the habitats (e.g., corals, molluscs, Algal ridges, polychaetes, and coralligenous).
What are five types of biogenic reefs?
- Coral
- Mollusc
- Algal ridges
- Polychaete
- Coralligenous
Describe coralligenous reefs
- Assemblages harbour approximately 10% of marine Mediterranean species.
- Algae and sessile invertebrates [sponges, corals]
- Formed by invertebrates, algae and corals (e.g., octocorals)
Note: these are not in the coral section as many don’t actually compose these reefs (sometimes exist there as part of the communities).
Describe polychaete reefs
- Intertidal reefs up to several metres across and a meter deep – grow out of seabed to form structure
- E.g., S. alveolata: gregarious segmented worms that builds tubes from sand or shell fragments.
Describe algal ridge reefs
Rhodophyta, coralinales (Lithophyllum)
Often found in the Med.
Specific species of algae (e.g., red encrusting algae) that grow over time to form these structures – not very diverse
Very tolerant to mechanical stress, so often in regions where waves break
What are the two main types of mollusc reefs?
Includes bivalves and vermetids (gastropods) - the latter are sedentary snails forming huge structures that are the basis for diverse ecosystems.
What are the two main types of coral reefs?
Cold water and warm water.
What types of warm-water coral reefs exist?
- Shallow
- Mesophotic (30/40 - 100 metres deep)
- Deep-sea (e.g., Red sea - very rare to have a deep-sea warm water reef)
Why are mesophotic warm-water reefs interesting to study?
- Exposed to different types of stressors
- May actually provide larvae for shallow reefs?
Describe cold-water deep sea reefs.
200-1000s of metres
Not symbiosis as in the darkness
Normally Scleractinian
List seven abiotic controls on coral reef distribution.
- Temperature
- Salinity
- Light
- Sediment
- pH/carbonate chemistry
- Wave energy
- Nutrients (N/P/Fe)
What are the hard limits of temperature for coral reefs?
16 </ Temperature >/ -35 degrees Celsius
Describe the rough global distribution of coral reefs.
Within the tropics and sub-tropics (mostly within the tropics).
This is why it is important to avoid using the term “tropical reef”
What is the spread of diversity? Where is the highest?
The Coral Triangle = highest reef diversity in the world (probably due to optimum conditions)
Diversity reduces nearer the limits (tropics) -> specialised organisms compose reefs outside of this optimal area.
What are the absolute limits of salinity for coral reefs? What is the optimum salinity?
Salinity ~36 is optimal
24 </ Salinity >/ 42
How does light attenuate through the water column?
Exponentially.
The rate depends on how clear the water is.
Why does the Red Sea support deeper corals than are normally expected?
The Red Sea is very oligotrophic and therefore has very clear (water), meaning light can penetrate to greater depths (100 metres in this case)
Why are nutrients so important to understand in coral reef systems in terms of global reefs?
Although oligotrophic, different regions/reefs are associated with small variations in nutrient availability.
Nutrients can be more easily controlled than other abiotic factors, so are therefore very important to understand.
What are the benefits of wave energy in a coral reef system?
Moves nutrients and waste products through the system.
Storms can mitigate heat stress through deep mixing.
What is the main negative of wave energy on coral reef systems?
Disturbances -> depends on storm intensity and frequency
