Ecology

Coral reefs have a huge diversity of species, of both flora and fauna, to the point that they are one of, if not the, most biodiverse habitats within any marine ecosystem. There are a number of species exclusively found within reefs, both cold-water and tropical, whilst corals themselves are only found within these habitats.

Cold water reefs naturally have lower numbers of species within their habitats, due to factors such as lack of light and more extreme conditions. The major species within deep/cold-water reefs, Lophelia pertusa, is an excellent indicator to where cold-water reefs are located, as seen on the post page (Cold Water Reefs – An Overview)

Despite having a larger number of species of coral found within formed cold-water reefs (29) than tropical reefs, it may come as a surprise than only a fraction of that number actually contribute to the formation of the deep-sea reefs. (6 species). The major one of these, as above, is Lophelia.

This species can be used very effectively as a cold water coral reef indicator, due to it’s temperature range within which it is only found: 4-12 degrees celcius, with a preferred range of  only 6-8 degrees. In comparison to warm-water corals, with a growth rate of between 10 and 20cm per year, Lophelia is a very slow growing coral, only growing between 5.5mm and 25mm per year. This is mainly due to the fact that Lophelia has no symbiotic algae to help form its structure.

Fauna within such reefs, however, are in much lower numbers than their tropical reef cousins. Fish tend to be the largest species present, with invertebrates (polychaetes and the like) and bacteria being the most common species found. Within a study on the fish species around cold-water reefs, only 25 different species were identified.

Tropical reef ecology varies massively in comparison, with a huge amount more animal species, faster growing corals and a complex yet fragile ecosystem. A good example of coral species from these reefs, faviidae – or brain corals, are only found in shallow warm water areas, living up to 900 years. These corals feed on drifting organisms, becoming an important reef forming coral.

Fish species and other non-coral fauna is huge in number compared to cold water reefs. In one single reef system alone ( the Philippines), over 900 different fish species and 400 coral species have been discovered. Tropical reefs tend to be larger in size as well as biodiversity than cold water reefs, with reef systems in the Indo-Pacific seas sprawling for hundreds, if not thousands of kilometres.

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