Lecture 33- Seaweeds of Coral Reefs Flashcards
What are coral reefs?
- marine, biogenic, wave resistant structures of hermatypic corals
- corals produce limestones
How much area do coral reefs take up globally?
- over 280 000 square kilometers
- most abundant in Indo Pacific
What are some characteristics of coral reefs?
- complex systems, polyps of corals have microalage etc.
- highly diverse (phyla)
- occur in nutrient poor tropical waters
- are very productive
What are the endosymbiotic microalgae that are crucial for corals?
- Zooxanthellae
- essential for coral reefs
- well developed periplast(outer shell thing)
- photosynthetic
- nutrients from coral
- have free living stage
- the coral ingests the zooxanthellae and they live in the coral, they photosynthesize and provide coral with energy
- in reverse the zooxantheallae receive CO2 and waste products (nitrogen, phosphorus) from the coral
- advantageous symbiosis
- zooxanthealle play a role in the calcification of the coral as it takes CO2 out of the ecosystem, increasing the pH in the water and calcium carbonate can preciptate more easily
What are zooxanthellae?
- most important are dinoflagellates
- 7-13 micromyteres in diameter
- 10 to the 6th per cm2
- give colour to the corals
What are the 4 types of coral reefs?
- Fringing reefs
- Platform reefs (and cays)
- Ribbon reefs
- Coral atolls
What are major algal habitats?
- intertidal reef flats
- shallow sheltered lagoons
- staghorn coral beds (on the reef)
- vertical bommies (on the reef)
- sand/coral rubble flats (on the reef)
What are the seaweeds on coral reefs like?
- encrusting coralline reds
- lithamnia
- mortar of reefs
- they grow over all the dead calcium environment, keep everything together
2.Calcified greens e.g. Halimeda, contribute to sediments
What are the forms of seaweeds on coral reefs?
-frandose forms, may be heavily grazed
-turfing forms: many fast growing
What is herbivory important for?
-in the balance between corals and seaweeds
What are some other microalgae on coral reefs?
- phytoplanton (not much), benthic species are present
- boring species: filamentous, endolithic, weaken reef
What are the characteristics of the Great Barrier Reef?
- 2300 km long
- world’s largest and longest contiguous coral reef system
- world’s largest biogenic structure
- visible from space
- it is made up of 3000 individual reefs
- 300 coral sand and shingle cays
- 617 high islands
- GBRMP (1975) - 344 000 km2 , only 6% are coral reefs on the great barrier reef, mostly seagrasses, sponges etc.
How is Lord Howe Island special?
- world’s southernmost coral reef
- world heritage listing
- marine habitats algal dominated
- over 350 seaweed species
- type locality for 50
- fewer corals, more algae than other coral reefs
What are the Houtman Abrolhos Islands like?
- low islands and shoals
- southernmost coral reefs in Indian ocean
- many rare and undescribed species
- some cold water species
- potentially valuable carrageenan producing species
- remnants of sand dunes
What are the natural threats to coral reefs?
- predation
- sediment loads
- storm surge
What are the anthropogenic threats to coral reefs?
- sediment loads
- excess nutrients
- industrial effluent
- ship grounding / oil spills
- anchor damage
- trawling
- plus the new threats, rising sea temperature and acidification
