Ecosystems at Risk Case Study - Coral Reefs Flashcards
What is the spatial patterns and dimensions of Coral reefs in general
- high light exposure (shallow water) –> for zooxanthellae to photosynthesize (2-30m)
- stable salinity levels (high), if large change it will cause the coral to stress and die
- clear water, (no algae), for photosynthesis (hence reefs aren’t grown near river mouths due to deposition)
- Nutrient deficient water as it decreases amount of algae
- high oxygen levels, coral needs to be continuously oxygenated by wave activity
- warm temperature (23 -29)
- Tropical latitude (23.5)
What is the spatial dimensions of the great barrier reef
- In the coral sea off the coast of QLD
- spans 2300km from papua New Guinea to Fraser Island
- Latitude 8S-24S
- 344400km squared area
- 500,000 - 1, 000, 000 years old
Biophysical processes in coral reefs - atmosphere
Tropical location is prone to tropical cyclones which - - damages the reef (hydraulic action and strong wind rips apart softer corals and chip away harder coral)
- increases turbidity
- decreases salinity with floodwater (rain depression)
- increases biodiversity as patches require recolonization and allow new species to move in
- Disruption to crown of throne starfish
- increase oxygen for the coral
Biophysical processes in coral reefs - lithosphere
Coral reefs produce solid limestone skeletons. The carbon dioxide produced by the algae reacts with calcium which polyps produce, forming a hard limestone skeleton which benefits the coral reef because when eh coral dies new coral can grow on the skeleton left behind, growing the reef
Sediment - increases turbidity in water which decreases the light penetrating the water limiting the zooxanthellae to photosynthesis = death from starvation
Sediment formation
- erosion by sea creatures create sediment
Biophysical processes in coral reefs - Hydrosphere
Wave action
the flow of water in the form of waves impact coral reefs in a number of ways
- waves oxygenate the reef providing the necessary oxygen for optimal coral growth
- powerful force of waves especially after cyclones are responsible for the breaking off of large coral pieces
current
- current helps move sediment weathered and eroded from other areas to be deposited onto the reef = building the reef
- aids migration of species
- currents enable the reproduction of coral
Biophysical processes in coral reefs - Biosphere
- 330 species
- polyps have built the rock structure which the
Reproduction
1. sing coral polyp
2. creates a colony through self reproduction
3. by using currents in coral spawning, coral polyps release eggs and sperm into warm water
4. by the current these sperm and eggs settle on limestone skeletons and starts to grow new coral
5. the old coral will die and their limestone skeleton will remain - high diversity due to high mass of nutrients due to the high rates of constant recycling of nutrients and production
- Polyps and zooxanthellae have a symbiotic relationship,
What are Human impacts on coral reefs (5)
- agriculture
- climate change
- overfishing
- oil spills
- tourism
How does agriculture impact coral reefs
- The use of fertilizers through the agriculture of sugar cane in Qld increases nitrogen based nutrients in the ocean through run off
= causes increased algae growth in reef (bad) –> Eutrophication (enrichment of minerals and nutrients in water which increases algae growth)
= acts as a food source for juvenile crown of thorns starfish, promoting outbreaks of this species
Especially sugarcane farming QLD
4 times more sediment and nitrogen nutrients have been deposited into the coast than ever before
Increases turbidity (Marine Snow)
- Nutrients from the river (Tully river) enter the marine environment and are consumed by living organisms forming sticky substances. This waste sinks onto the coral, like ‘snow’ smoothing it and increasing the turbidity of the water
10 times more sediment in the Tully River
How does climate change impact coral reefs
- CORAL BLEACHING causes ocean temperatures to increase, causing coral to become stressed , causing the polyps to expel the algae (zooxanthellae) = killing the coral as the algae provides the coral it’s nutrients
some animals depend upon the colours of coral for camouflage - OCEAN ACIDIFICATION The ocean absorbs 1/3 of the atmosphere’s excess carbon dioxide increasing the acidity of the ocean = ocean acidification - slows the rate at which coral reefs generate calcium carbonate, thus slowing the growth of coral’s skeletons
Shellfish are less able to create their shells due to decreasing pH
- OCEAN WARMING
impacts coral spawning as it decreases dispersal distance of coral
What is the rate at which climate change impacts coral reefs
- rapid increase in greenhouse gas emission has caused 0.13 degree increase in global sea levels per 10 years
- 29% of the GBR died in 2016
- Scientists predict that over 90% of coral reefs could be lost by 2050
- 67% of the northern region in Australia is dead
- 10% of coral have been degraded beyond recovery with another 30% likely to decline in the next 20 years (coral bleaching)
How does overfishing impact coral reefs
Fishing Nurseries
- nearshore habitats serve as nurseries for many fish = catching young fish in nets removed them before they can help replenish the population
Pollution
- As the fishing industry increases, more boats appear in the GBR contributing to a dramatic rise in pollution causing the reef to stuffer
Less biodiversity
- GBR is home to over 1500 species of fish and some are rare - many rarer species of fish end up being harvested
- Recreational fishing in the general use zone accounts for 75% of the fin fish taken from the reef each year
Habitat Loss
- Anchors and nets destroy many corals and thus habitats for the fish
Disruption of food chains
- over fishing reduces biodiversity and hence increases vulnerability of food chains collapsing
e.g.
Damselfish 2 main purposes
1. Creating pockets in the coral to facilitate algae growth
2. Be eaten by the grouper fish
Grouper fish is an overfished species in turn resulting in the damselfish population to increase causing algae growth to take over coral reefs
What is the rate at which overfishing impacts coral reefs
- population of dugongs has declined by more than 90% in the past 30 years
- 2003 estimates that 90% of the large predatory fish (large cod, sharks, tuna) will disappear
- large decrease in the density of fish within coral reefs
How do oil spills impact the coral reef
- Stress caused by oil spills/contamination on coral reefs includes histological effects such as tissue death, changes in the zooxanthellae primary production, and an increase in mucus production.
- Not biodegradable hence long lasting effects
- Reproductive effects such as larval premature expulsion, and a disruption/losses of larval settlement.
- Once oil comes into contact with corals, it can kill them or impede their reproduction, growth, behaviour, and development.
2. Rough seas can mix lighter oil products into the water column (like shaking up a bottle of salad dressing), where they can drift down to coral reefs.
3. As heavy oil weathers or gets mixed with sand or sediment, it can become dense enough to sink below the ocean surface and smother corals below.
Stats on impact of oil spills impacting coral reefs
- At the same time as the Gulf of Mexico disaster, in April 2010, the Chinese ship Shen Neng 1 ran aground near the great barrier reef. The accident was responsible for a spill of 3 to 4 tons of oil, reaching about 3 km in length and 250 m in width, the largest ever recorded in the region. Some damaged areas have become completely devoid of marine life. It is estimated that this disaster will cause considerable damage to the coral reef in the long term, lasting for approximately 20 years.
How does the Crown of Thorns Starfish impact coral reefs
Is a natural predator BUT humans are increasing their population by overfishing their predators- thus increasing their biomass and disturbing the dynamic equilibrium
Humans excessive use of fertilisers also causes runoff which increases the concentration of nitrogen in the water. This nitrogen increases rate of denser phytoplankton (algae) population growth which allow for better larval survival, yielding more adult crown-of-thorns starfish.
They eat coral by extruding their stomachs out from their bodies, wrapping it around corals and digesting their tissues- occurring at rates which exceeds coral rejuvenation.
