L7 Coral reefs Flashcards
Where are coral reefs found?
Deep water corals in UK
Usually in tropical oceans due to ocean gyres.
What are some factors of tropical waters?
Strong pinocline, high SST, permanent thermocline. Tropical surface waters are heavily stratified so often nutrient poor.
Highest biomass/are in tropical waters- incredibly productive. 1500-3700g fixed C/m2/year.
What are the main producers in coral reefs?
Corals and zooxanthellae.
Consumed by plankton feeders and coral mucus feeders.
They make very heterogenic environments with many habitats.
What two groups of coral are there in reefs?
Hematypic - reef building, secrete CaCO3 to form massive skeletons. Dominant group are scleratinian coral eg fungia, porites. Solitary or colonial.
Ahematypic - Not reef building, eg soft coral. Can produce sclerites - CaCO3 needles.
How do colonies form?
Colonies form by asexual division, polyps connect into a single surface (tissue layer) above the skeleton. A colony can live for centuries whereas an individual polyp only lives for 4-6 years
What is a holobiont?
Whole coral animal + zooxanthellae.
What zooxanthellae are symbiotic with coral?
Dinoflagellates, genus Symbiodinium.
Held within coral endodermal tissue in v high densities - >million per cm2 of coral surface.
Supply up to 90% of energy required by tropical coral.
Explains distribution of coral in shallow,light, environments which are generally nutrient poor.
describe nutrient cycling in corals
photosynthesis by zooxanthellae provides huge amounts of organic carbon, O2 used by polyp.
CO2 and nutrients continually recycled between polyp and algae. CO2 and H2O diffuse across coral surface.
What are 3 methods that corals feed?
- Symbiosis with zooxanthellae
- Cnidocytes on polyp tentacles capture prey
- Mesenterial filaments - tubes attached to wall of gut and extrude through mouth to digest food outside body
- Mucus threads - secreted over colony surface to capture passing plankton. moved by cilia to mouth. Mucus is a polysaccharide so energetically expensive to make but v successful. Bacteria also feed on ‘mucus trap’.
How and where do Cold water corals grow?
Ahemotypic but can build mounds on top of seamounts
Slower growing as usually deeper and aren’t symbiotic.
Usually >40m depth - below photic zone
Not restricted by temp and light. Instead restricted by O2 and food (POM) availability.
What causes bleaching
Caused by increase in temp 1 degree above average seasonal maxima
Breakdown of symbiosis btw algae and coral host.
2 points about the extent of coral bleaching
1998, first estimated extent of bleaching using aerial images of Pandora reef in GBR - 80% of coral bleached.
Mass bleaching events - Feb 1998, most extensive bleaching event in GBR. Bleaching observed at 87% of inshore reefs.
What has monitoring of the pandora reef 2005 showed about species susceptibility to bleaching?
Acropora 95% mortality
Porites <5% mortality
it is highly variable
What alternative energy sources can coral use in response to bleaching?
capture of plankton, Lipid reserves, Night time mesenterial filament, feeding on neighboring algal turfs.
What other survival strategy can be used for bleached coral?
Study to demonstrate this
Shuffling population of symbiotic algae may increase threshold temp of bleaching (acclimatisation). Symbiont genetics are diverse , there are 8 symbiont clades with many species and strains.
Study by Berkelman and Van Oppen 2005 - GBR coral mainly have C and D types of algae - D more heat tolerant but growth penalty. Acropora with C grow 2-3x faster.
