Lecture 27- Fauna of Coral Reefs

Question 1

What is special about coral reefs?

Answer 1

• Most complex of all marine ecosystems • Only major geological structure built by living organisms • Dynamic, living structure • High producGvity despite occurring in low-nutrient waters • Mutualism – coral polyps and zooxanthellae (more detail in acGvity manual) • 1% of world ocean surface but 25% of all marine species

Question 2

What is the Great Barrier Reef like?

Answer 2

• Largest coral reef in the world, largest living organism • Visible from space! • 2,300km along QLD coast • ~ 2,900 smaller reefs • ~8000 years old (formed ~500,000 years ago but changes components over time) • World Heritage LisGng in 1981 • Incredibly species-rich ecosystem

Question 3

What is world-wide coral distribution?

Answer 3

-usually around tropics

Question 4

What the physical environment of coral reefs?

Answer 4

-• Found in shallow, warm, clear water – need lots of light! • Optimum temperature: 23 – 29°C • Cannot tolerate temps <18°C • Max summer sea temps 2 – 3°C above normal can kill corals • Requires high salinity (32 – 40 ppt) • Low inorganic nutrients • Formation of calcium carbonate skeleton depends on low phosphate concentrations

Question 5

What does it mean when you have clear water?

Answer 5

clear water = low productivity = low nutrients = tropical water (oligatrophic waters)

Question 6

Why are coral reefs so biologically diverse?

Answer 6

-Because of the corals! • Very efficient at nutrient recycling because of mutalism with algae • Provide incredibly complex habitat structure that promotes diversity -also get much waste from the coral reef system and this allows and provides nutrients for the filamentous algae, can find out by doing caging experiments, herbivores are really important! allow the coral to not be overtaken by algae

Question 7

What is the coral-algae symbiosis?

Answer 7

• a solution to low nutrients -coral polyp+ symbiotic algae (zooxanthellae)-• Zooxanthellae photosynthesize • By-products of photosynthesis (O2 and sugars and lipids) are used by coral for growth • Waste products of coral (CO2 and nitrogenous waste) are used by zooxanthellae • Very little wasted! • Corals derive up to 95% of energy from zooxanthellae • Zooxanthellae gets protection from predators and ready supply of CO2 and nutrients it needs

Question 8

How do coral reefs form?

Answer 8

• Coral polyps live in a protective calcium carbonate (limestone) exoskeleton • Coral colony forms as they divide and grow • Old coral ‘skeletons’ form the hard substrate for more colony growth • This is what we recognise as a coral reef – limestone skeleton covered by a thin layer of living coral polyps • Most corals are very slow growers – 1 - 2cm/yr • Takes 10,000yrs to form a reef!

Question 9

What are the types of corals?

Answer 9

• Hard corals – excrete limestone skeleton, form reefs • Soft corals – don’t excrete limestone skeleton, flexible

Question 10

What are the types of coral reefs?

Answer 10

• Fringing reefs – located very close to shore, no distinct lagoon between reef and shore; most common type • Barrier reefs – like fringing reefs but much farther from shore; form lagoon between shore and reef; GBR is a barrier reef • Atolls – circular oceanic reef surrounding a large (deep) lagoon • Patch reefs – small, relatively isolated outcrops of coral, surrounded by sand/seagrass

Question 11

What are the typical reef zones?

Answer 11

• Reef flat – shore side of reef, sheltered
• Reef crest – highest point of reef, omen exposed at high tide, zone of highest wave action
• Fore reef – ocean side of reef

Question 12

What is the coral reef food web?

Answer 12

• Primary producers • zooxanthellae in corals • plankton • small fast-growing filamentous algae • Herbivores & PlankGvores • fish & sessile inverts • Predators of ahached animals • Predators of smaller fish and invertebrates

Question 13

What is the parrot fish like?

Answer 13

-can be quite big, easily spotted -lot of them are herbivores, niche herbivores -their front teeth formed into a beak like structure -they scrape algae from the coral reef -some species specialize on the zooxanthellae in the corals -as they scrape the algae off the coral reef they consume the coral and poop it out and that is the sand -90kg of sand a year per parrot fish!!! -also sex changes: often start out as males and then change into females

Question 14

What is the damselfish like?

Answer 14

-huge numbers -related to clown fish -herbivores -protect an algal turf, protect their algal territory -one species farms the algae, maintains a patch of the algae

Question 15

What is the surgeon fish like?

Answer 15

-major predators -herbivores -they can come through and munch on all the algae, and can overwhelm the damselfish and eat all their farmed algae

Question 16

What are some herbivorous invertebrates on the coral reefs?

Answer 16

-sea urchins: also aimportant algavores -xanthid crabs: specialized on feeding on algae and corals, helps clean the coral of algae usually, sort of symbiosis

Question 17

What are some sessile invertebrates on coral reefs?

Answer 17

-create habitat and food source -take food out of the plankton -sea anemones, cnidarians, sponges, soft corals and molluscs

Question 18

What is the angel fish like?

Answer 18

-eats sponges and bryozans -broad diet -eats soft invertebrates that live attached to the reef

Question 19

What is the butterfly fish?

Answer 19

-feeds on the mucous the corals secrete (protection from the UV) -bacteria form on the mucous and this is what the fish target via their thin stone

Question 20

What are predatory snails like?

Answer 20

-voracious predator -some have toxins, can inject into victims

Question 21

What are the stonefish?

Answer 21

-predator, venomous spines and fins -it is a sit and wait predator -can camouflage with their background -look like stone

Question 22

What are the coral trout?

Answer 22

-largely nocturnal predators

Question 23

What are the reef sharks like?

Answer 23

-sometimes in groups

Question 24

What are the reproductive strategies in the coral reefs?

Answer 24

• Most reef animals are broadcast spawners – Eggs and sperm released simultaneously into the water column • Coral reefs are like a forest of hungry mouths – How to prevent gametes from being eaten?

Question 25

How to prevent gametes from being eaten?

Answer 25

• Sex on the outgoing Gde – gametes washed away from the ‘wall of mouths’ on the reef • Do it on a high platorm – will be washed further from the reef • Do it at new / full moon - spring Gdes, carried faster • Do it at night – parents, eggs not seen by predatory fish • Do it all together - predators can’t eat all the eggs

Question 26

What are the spawning cues in corals?

Answer 26

• lunar phase (neap Gdes – slower currents) • Gme of day (sunset) • Different Gming for corals on East and West coast

Question 27

What are some alternative reproductive strategies?

Answer 27

• Defend a territory and guard eggs • Hide them (eg, in anemone, or in mouth!)

Question 28

What is the giant clam mutualism?

Answer 28

-Another mutualism with zooxanthellae -Allows clams to grow huge

Question 29

What is the mutualism with Seaslug Elysia?

Answer 29

-Mollusc that ‘steals’ chloroplasts from algae -Stores chloroplast in digestive glands -But does it derive energy from photosythesis?

Question 30

What is the cleaner fish mutualism?

Answer 30

Remove ectoparisites from body and mouth of other fish (ie, coral trout)

Question 31

What is the mutualism between amenomefish and anemones?

Answer 31

-Fish gets protection from predators and extra food -Anemone gets preened by fish, intruders kept away

Question 32

What is mutualism on coral reefs?

Answer 32

• Why so common on coral reefs? • Low productivity habitat – recycling of nutrients (corals, giant clams with algae) – many species living together – a consequence of diversity?

Question 33

What are the threats to coral reefs?

Answer 33

• Global climate change – coral bleaching – ocean acidification • Overfishing – loss of key functional groups leads to cascading effects in food web • Anthropogenic pollution – leads to sedimentaGon, nutrient enrichment, toxins, pathogens Specific threats to Great Barrier Reef • Crown of thorns seastar • Shipping traffic – accidents – dredging channels • Tourism

Question 34

What is the summary?

Answer 34

• Coral reefs highly complex and dynamic ecosystems • Particular physical environment required for growth (light and temp) • Very small area but high species diversity • High productivity despite low nutrient water • Tight recycling of nutrients • Food web: fish very important – fill many niches • Mutualism important strategy (esp. coral-zooxanthellae) • What are some of the threats to coral reefs?