Coral ReefsCoral ReefsMarine EcologyMarine Ecology

CORAL REEFS• Most diverse and

productive communities

• DIVERSITY!

• Protection from wave energy

• Foster ecological oases– Mangroves– Seagrass beds

• Iconic ecosystem

• Sensitive

• Threatened by humans

Development and Distribution

• Biogenic • 30* N and S of equator • Cover <0.1% of global

ocean surface area• Host >25% of fish

species• Better than

rainforests!– Species per unit area

http://data.unep-wcmc.org/datasets

Development and Distribution

• Hermatypic– Reef-building– Tropics– Growth and

distribution influenced by physical environment

• Ahermatypic– Non reef-building– Mostly world-wide

Development and Distribution

• Temp: 18-36*C• Types of reef based

on;– Underlying

substratum• Existing carbonate reef• Igneous rock

– Sea level changes– Light levels– Wave action

Patch Reefs

• Bommies• Small reefs • Grow in shallow

lagoonal areas• Surrounded by sand• Deeper • Don’t go above

surface at low tide

Fringing Reefs

• Develop on shelving shores

• Rocky tropical islands

• Corals settle and grow on well-lighted and shallows areas

• Grow toward surface

Barrier Reefs

• Surround tropical islands• Separated from land by

lagoon• Usually 1-10km wide• Line of breaking surf• May develop from

fringing– After sea level rise

• Grow quickly– Exposure to wind/currents

Atolls

• A ring of reef with low-lying islands surrounding a lagoon

• 10km (or more) across

• Biological diversity• Seabird colonies• Charles Darwin

– Formation theoryhttp://www.youtube.com/watch?v=vrD1O5hex6Y

Reef Growth

• Not continuous– Periods of rapid growth– Periods of bioerosion

• Net reef growth– Fastest: 20m in 1000yrs– Usual: 3m in 1000yrs

• Growth affected by sea-level– Glaciers

Corals and Coral Communities

• CaCO3 skeletons• Polyps

– Protection and nutrients

• Zooxanthellae – Photosynthesizers – Dinoflagellate– Can live independently– No flagella/motility in

polyp

Corals and Coral Communities

• Zooxanthellae– Transmitted during

reproduction– Obtained from seawater– Produce energy– Autotrophic

• Waste from host- RECYCLE!

– High rate of photosyn more calcium carbonate

Coral Reproduction

• Recruitment • Sexual and asexual• Hermatypic

– Polyps; asexual budding– Break off, settle, grow

• Sexual– Long-distance dispersal

• Gonochoric- one• Simultaneous- both• Sequential Hermaphrodites- change

http://www.youtube.com/watch?v=wsaZ8-I7akg

Coral Reproduction

• Brooding– Fertilized internally – Planula develops inside

polyp

• Broadcasting– Certain period of the year

• Lunar cycle

– Synchronized• Common cues• Too many eggs for the evil

predators to eat

http://www.youtube.com/watch?v=06BPlLATtgc

Coral Reproduction

• Fertilized eggs– Settle in 1-3 days

• Zooxanthellae aquired after settlement and metamorphosis– Brooder larvae contain them

• Calcified base plate• Grazing helps growth• Influenced by environment

http://www.youtube.com/

watch?v=_Mt0h5v4xos

Coral Reproduction

• LIGHTlightlightlightlight

• Reef accretion – 0-10m– Hermatypic

• Rare below 30m

– Shallow, well-lit zone• More light• Less predators

• Sunburn!• Stenothermal

Coral Growth

• Evolved in stable temp– Less tolerant

• Evolved in variable temp– More tolerant

• Salinity 33-35ppt• Wave action currents

– Nutrient spreading– Can be harmful

• Hurricanes

Coral Growth

• Sediments – Some coral can remove it– Smothering, abrasion,

shading, recruitment inhibition

– Pulse Sediment• Storms• Not as harmful

– Suspended Sediment• Human actions• Reduced light for coral

http://www.youtube.com/

watch?v=9pdmkckANH4

Productivity

• Production recycled within the reef

• Carbon fixation– Less than half the

carbon they fix is available

– Few organisms feed on coral directly

• Reef algae – Very productive

• Grazed on and carbon

Productivity

• Phytoplankton!– Support zooplankton

• Support larger consumers

• Currents carry them across reef

– Currents carry them from outlying water, and over the reef…• Then they can be

eaten- YUM!!

Productivity

• 24-h cycle used to measure– Day- photosynthesis– Night- respiration– Excess Production- net

production which occurs (E)– Photosyn/Respiration ratio

• (P/R ratio)• E=0, P/R of 1

– E is relatively low• Competition• Nutrient recycling

Reef Fauna

• Could be home to over a million species

• Diiiiiiiiiverse!– Not uniform– Determined by reef history

and environment

• Reef building coral evolved over 200 mil yrs ago

• Large scale extinctions– Every 20-30 million years

Reef Fauna

• Diversity– Influenced by isolation

• Study– Began; 1950’s and

60’s– Focused on ecology– Realized instability– Research still young

THREATS!

• Humans (of course)– We suck!!

• Direct– Increased

sedimentation– Fishing– Ship stupidity– Pollution

• Indirection– Climate change– Over-fishin

Disease

• Yes, corals get sick too– Pathogens and parasites

• Can be aggravated by human influences

• Black band– 1st recorded– Affects brain coral– Caused by cyanobacteria– Create anoxia in the tissue– Physically damaged

• More susceptible

Bad Weather

• Storms– Branching corals– Reef fish

• Cyclones– (10-25* N/S)– Fast growing coral

that relocate

• Hurricanes– Fast growers – Acropora

Climate Change

• Climate change Rising sea level– Should be good for

shallow water coral– Increased ENSO due

to temp increase– HUMANS

• Nutrient input

– Deep corals will not do well

Coral Bleaching

• Stressed coral expel their zooxanthellae

• Skeleton becomes visible• Prolonged bleaching

leads to coral death• Bioerosion takes over• Algae move in

– Reduce reef accretion– Fish species will be lost

• High water temperature

http://www.youtube.com/

watch?v=aEdoizgeNJk

http://www.youtube.com/

watch?v=60jof35WuAo

Coral Predators

• Crown-of-thorns starfish– Feed on living coral– Free-spawners– 12-60mil eggs in a

spawning season– Evert their stomach on

coral, and secreting an enzyme which breaks down the coral

– Fishing may have reduced their predators

http://www.youtube.com/

watch?v=2fE2gIARQWA

Pollution, Sediments, Nutrients

• Deforestation, port development, and dredging– Run off

• Increased sediment load

• Nutrients from run-off– Increased algal growth– Phosphate; big no-no

• Oil pollution

http://www.youtube.com/watch?v=rkKs-5JGSoo

Fishing

• Expanding fisheries– Direct damage

• Habitat-destructive fishing– Reef drive netting– Trapping– Blast/chemical fishing

• Unselective • Illegal

Reef Growth

• Limestone produced– And broken down

• Coral rubble/sand

• Balance between accretion and bioerosion

• Erosion by organisms– Grazers

• Mollusc, echinoderm, fish

– Loss of hermatypic corals

Reef Animals

• Difficult to record densities

• Used as ‘laboratories’ – Behavior and ecology– Carrying capacity

• Recruitment limitation hypothesis– Population sizes limited

and determined by rates at which larval fish from plankton to adult

http://www.youtub

e.com/watch?

v=UB7tqiL-Eqs

Reef Animals

• No one species can out-compete the other

• Reef structure is complex

• Symbiosis – Coexist– Cleaner fish– Burrowers

http://www.youtube.com/

watch?v=UJbPej8uytw

http://www.youtube.com/watch?v=xaJdXO_j2MY

Reefs and Humans

• Provide food and income• Subsistence fishing

– Not recorded

• Tourism– Great Barrier Reef

• Over 10mil per year

– Towns can be supported by revenue

• Ecosystem services; help humans– Coastal defense – Coral mining, bleaching, sedimentation