Understanding Coral Reef Ecosystems and Their Threats

A greater biomass;

Higher levels of species diversity;

Better soil structure and greater water retention;

Lower pH;

Plant species will be taller and longer living;

Greater community complexity and stability/equilibrium;

Greater habitat diversity;

B Award [3-4 max] for human threats, [3-4 max] for natural threats

and [2-4 max] the consequences.

e.g. Great Barrier Reef off the coast of Queensland, Australia

Human threats:

• Tourism; coral is very fragile and easily damaged by divers’ fins, touching coral, or breaking bits off for souvenirs;
• Overfishing can disrupt the balance of species in the food chain;
• Inadvertent damage from anchors and pollution from boats;
• Run-off of fertilizers from sugar plantations on the coast;
• Sewage and pollution from coastal settlements such as Cairns can lead to excessive nutrients and algal blooms;
• Global warming increases sea temperatures, leading to coral bleaching;

Natural threats:

• All of these make coral more vulnerable to natural threats such as disease;
• Natural predators, e.g. crown of thorns starfish;
• Structural damage from storms and cyclones;
• Increased sea temperatures due to El Niño;
• Which has knock-on effects on the fish species that depend on the reef for food, protection, and nurseries for young;

Consequences:

Coral reefs are able to withstand some threats, but the collective effect of human and natural processes can lead to damage of the reef and species that depend on it, and the breakdown of the ecosystem;

When the “critical threshold is reached” (when even if threats stop, the ecosystem will not recover);

Loss of biodiversity;

C Award credit if a diagram is used to illustrate the concept of

negative feedback.

Feedback is the return of part of the output from a system as input, so as to affect succeeding outputs;

Positive feedback tends to amplify or increase change;

Negative feedback, on the other hand, tends to damp down or neutralize any deviation from an equilibrium and promote stability;

It is negative feedback, therefore, which leads to the regulation of equilibrium within ecosystems;

e.g. the effect of a storm on a rainforest – high winds blow down a tree, leaving a gap in the canopy, which lets in more light, encouraging new growth;

Rates of growth are rapid as light levels are high, so new saplings compete to take the place of the old tree in the canopy, and equilibrium is restored;