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Coral Bleaching: Causes & Effects

Date Published - 6th July 2015 - Published by - iQuatics Ltd

Coral bleaching is a term used sporadically throughout the aquarium keeping industry, but few aquarists actually understand why it occurs, and even fewer know how to address it. As an umbrella definition, coral bleaching basically refers to the stark discolouration (and in some extreme cases, even whitening) of portions of the reef, owing to environmental instabilities which we’ll go into below. Whilst the effects of coral bleaching won’t always necessarily be permanent, they should receive your immediate attention, as the quicker you act, the more coral you can preserve.

A Mutually Beneficial Relationship
To better comprehend coral bleaching, you need to understand one of the most prevalent causes for it in the world of amateur aquarium keeping. As we’ve delved into before, your corals form a symbiotic relationship with a type of algae known as zooxanthellae cells, and continue to exist in a very delicate equilibrium that basically makes both parties happy. To explain things a little further, these cells live within the tissues of the coral, and produce carbohydrates necessary for growth and development as an off-shoot of their photosynthesis process. They’re also responsible for giving corals the vivid, rich colouring they’re famous for.
Going Through A Rough Patch
So, as you might expect, one of the leading causes of coral bleaching is the disruption of this careful balance between the algae cells and the corals themselves. As we probably don’t have to tell you, your corals are delicate creatures that react very strongly to any number of changes in their ecosystem, so you’ll probably understand that a wide variety of factors can easily disrupt this harmonious balance. Of all of these factors, including pollution, sedimentation and even salinity, temperature is by far the most likely to cause your corals to bleach.
In both artificial aquariums and natural environments, corals are extremely temperature sensitive, so it’s important to pay close attention to your aquarium lighting levels on a regular basis. When corals get too hot they basically become stressed, ejecting the zooxanthellae cells that they rely on, and disrupting the relationship that sustains them. A severe lack of these cells leads to the discolouration that we notice, and widely refer to as coral bleaching.
Addressing the Balance
Although it can appear alarming, there are a number of things you can do to prevent your corals from bleaching further. In the large part, coral bleaching points to an imbalance in your tank, whether that be the ambient water temperature, or even the nutrient levels. It is possible for your corals to re-absorb their zooxanthellae cells, but only if you take swift action. First of all you need to ascertain which part of your ecosystem is imbalanced; check your thermometer regularly to note any shifts in temperature, and carefully measure the amount of nutrients and salts you add to your aquarium. The issue could also be down to poorly positioned lighting, which can lead to an excessively high rate of photosynthesis, so take care to readjust your bulbs, and possibly increase the distance between them and your tank.
Above all, coral bleaching is a strong indicator that portions of your reef are undergoing un-due stress, which is causing them to expel more zooxanthellae cells than is necessary. As soon as you notice signs of coral bleaching, it is important to begin searching for the cause via a regimented trial and error method; if left untreated for prolonged periods of time, this superficial issue can lead to permanent damage and even death. If you’ve exhausted all of your options, and still can’t seem to address the problem, why not enlist the help of one of our aquarium specialists using our website’s live chat function?

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