Coral reefs - Biogeographical processes
Invasion
Corals are prone to invade the territory of neighbouring colonies. Corals send out long stinging tentacles to search for and destroy the invader. Defensive mechanisms that corals use to ward off such attacks and the onslaughts of other organisms include armour, camoflauge, and toxic and unpalatable substances incorporated in their body tissues. These kind of mechanisms provide some defence for outbreaks of Crown of Thorns starfish and Drupella.
Most invaders on coral cays are plants.
Succession
When communities of plants and animals are replaced over time by a series od different and usually more complex communities, it is called ecological succession. Coral reefs are built by millions of tiny animals called polyps, which form enormous colonies.
Reproduction: Every year in late spring or early summer, the coral release their eggs and sperm in a spectacular synchonised event. The eggs that are fertilised by sperm begin to divide rapidly forming larvae.
On coral cays, succession is aided by wind. Butterflies are known to travel up to 60km to outlying islands, spores of ferns, mites, aphids and ticks can travel similar distances by wind. Beetles, lizards, etc and their eggs can be carried by violent storms. Bird droppings provide the nutrients for plants to colonise.
Slideshare - Coral Reef zonation and succession.
Corals are prone to invade the territory of neighbouring colonies. Corals send out long stinging tentacles to search for and destroy the invader. Defensive mechanisms that corals use to ward off such attacks and the onslaughts of other organisms include armour, camoflauge, and toxic and unpalatable substances incorporated in their body tissues. These kind of mechanisms provide some defence for outbreaks of Crown of Thorns starfish and Drupella.
Most invaders on coral cays are plants.
Succession
When communities of plants and animals are replaced over time by a series od different and usually more complex communities, it is called ecological succession. Coral reefs are built by millions of tiny animals called polyps, which form enormous colonies.
Reproduction: Every year in late spring or early summer, the coral release their eggs and sperm in a spectacular synchonised event. The eggs that are fertilised by sperm begin to divide rapidly forming larvae.
On coral cays, succession is aided by wind. Butterflies are known to travel up to 60km to outlying islands, spores of ferns, mites, aphids and ticks can travel similar distances by wind. Beetles, lizards, etc and their eggs can be carried by violent storms. Bird droppings provide the nutrients for plants to colonise.
Slideshare - Coral Reef zonation and succession.
Resilience
For coral reefs in general, inertia and resilience are both low, so any minor changes in environmental conditions such as water temperature, turbidity levels, sedimentation and any forms of pollutant can place coral in a state where survival is unlikely.
The resilience of coral reefs comes predominantly from the wide range of genetic and species diversity within the ecosystem, and the time over which they have developed. Most reefs have developed over tens of thousands of years (most are between 5000-10 000 years old) and have been able to adapt to changing conditions. The resilience of ecosystems is threatened when reefs are separated from other reefs (by destruction of joining reefs). This restricts the ability of species to move to other areas. Sudden changes to the ecosystem (i.e. many human-induced changes) also restrict the ability of the ecosystem to adapt over time.
Many symbiotic relationships exist between species which add to the resilience of reefs.
Ancient reefs helped shape fish diversity.
For coral reefs in general, inertia and resilience are both low, so any minor changes in environmental conditions such as water temperature, turbidity levels, sedimentation and any forms of pollutant can place coral in a state where survival is unlikely.
The resilience of coral reefs comes predominantly from the wide range of genetic and species diversity within the ecosystem, and the time over which they have developed. Most reefs have developed over tens of thousands of years (most are between 5000-10 000 years old) and have been able to adapt to changing conditions. The resilience of ecosystems is threatened when reefs are separated from other reefs (by destruction of joining reefs). This restricts the ability of species to move to other areas. Sudden changes to the ecosystem (i.e. many human-induced changes) also restrict the ability of the ecosystem to adapt over time.
Many symbiotic relationships exist between species which add to the resilience of reefs.
- Corals and peanut worm: keeps the coral upright and stops it from being smothered by sediment.
- Shrimp can bore into the feet of Crown of Thorns starfish saving coral.
- Sponges act as "vacuum cleaners" filtering out bacteria, detritus and coral mucus.
Ancient reefs helped shape fish diversity.
