Zooxanthellae and Corals

Blue Ring Angelfish

Zooxanthellae are the symbiotic algae that live within the hard or stony corals. The symbiotic relation is based on the corals inability to generate sufficient amounts of food and the algae’s ability for photosynthesis and converting chemical elements into energy.

The coral in return provides protection as well as a nutrient rich environment for excellent algae growth.

Corals are completely dependent on the symbiotic algae. They would not be able to survive without them since they can’t produce sufficient amounts of food. The zooxanthellae can provide all the nutrients necessary, in most cases all the carbon needed for the coral to build the calcium carbonate skeleton.

Hard corals are reef builders and the symbiotic relation enables the coral to grow faster, which is not only partly responsible for the existence of coral reefs, but also vital and necessary.

Since light is essential for photosynthesis hard corals are not found below 300 feet (100 meters). The algae are sensitive towards low salinity levels and thrive in temperatures above 68 F (20 degrees C).

Zooxanthellae are not only responsible for providing energy via photosynthesis, but also take up nutrients released by the corals metabolism such as nitrogen and carbon dioxide.

Zooxanthellae, single celled algae that reproduce by simple cell division, are described as the variety of yellowish – brown dinoflagellates living symbiotic with many marine animals.

Different strains have adapted to environments as permitted by their depth and the available light. Corals can house multiple strains of dinoflagellates which makes them quite adaptable to environmental changes.

Zooxanthellae enter the host animal through the water column. Corals can adjust the algae population on a daily basis by releasing or by taking up algae as needed.

The coral itself can control the quantity of algae living in its cell tissues by regulating the amount of waste provided for algae growth, or by limiting the light exposure and intensity by opening the polyp and exposing more or less algae to the light as needed. The coral has also the ability to release algae directly, which is also known as bleaching. In cases of excessive algae growth or temporary nutrient shortage, the coral can directly feed off the excess algae.

Introducing corals to the reef aquarium will trigger some adjustments and changes can be observed depending on light levels and intensity, water flow, and nutritional levels.

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what is the molecular mechanism by which polyps maintain the exposure of zooxanthellae to sunlight?

Elijah Kweun

Very useful information for my project. Thx

Eileen Engel

So sunscreen effectively kills the Zooxanthellae ability to produce nutrients?

Dr. Aminul Islam

They utilize metabolic CO2 produced by the anthozoan to produce their own carbohydrate type of food. The symbiotic algae take up Ca++ from the seawater and metabolically form Ca (HCO3) 2, which is degraded to form CaCO3 and carbonic acid. The epidermal cells secrete this CaCO3 outside and deposit at the basal part of the polyps. Thus zooxanthellae are inevitable for the coral forming anthozoans. As they adopt photosynthesis, distribution of coral forming anthozoans are therefore restricted to the photic zone of seas and oceans.

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