Marine Topic Of The Week, 05/26-06/02

[steelhealr]

Zooxanthellae are the symbiotic algae that allow corals to survive in the reef system. They are unicellular dinoflagellates (yellow-brown algae) and take up haven in the gastrodermis of the coral polyps. These organisms use light to photosynthesize and provide nutrients for the corals to survive and build a reef. In return, the coral provides protection and a supportive framework to be exposed to light. These small plants are the what give many of our corals the beautiful colors they exhibit in the aquarium.

Zooxanthellae have some basic requirements:

• reside in water less than 100 meters (300 feet) deep
• reside in water temperature usually 20 C/68 F or higher
• are intolerant of low salinity and high turbidity

Present research suggests that there are at least 10 different species of zooxanthellae. The species believed to be the most common is Symbiodinium microadriaticum . Zooxanthellae can also be found in other animals beside Cnidarians. Three of these animals include Tridacna (giant clams), some jellyfish and nudibranchs. They reproduce by splitting (fission).

In times of stress, corals can bleach, or, lose their color which reflects trauma to the zooxanthellae. Bleaching can occur in 2 ways:

1. the densities of zooxanthellae decline and/or
2. the concentration of pigment in the zooxanthellae declines

Stress-inducing factors include:

• sudden change in irradiance (lighting)
• temperature changes, either too high (above 30 C/86 F) or too low
• exposure to air
• rapid drop in salinity
• deposition of substrate/sedimentation on the invert
• added chemicals such as antibiotics or copper
• infection or parasites

If bleaching occurs in your aquarium corals, it's necessary to determine the inciting factor and remedy it. With care, the zooxanthellae will reproduce in weeks to months and the coral can survive. HTH. SH

 

[bunjiweb]

Just one thing to add to that superb post.

It is my firm belief that a perfect reef ecosystem has some level of nitrate and phopshate to feed the zooxanthellae living within the corals. However obviously you can have excess of both of these which could be more detremental to the health of the coral.

It has been seen to great effect in corals such as pulsing xenia which seem to actively thrive in a nitrogen-rich environment, and so therefore are being used in refugiums more and more to help keep the nitrate down, although whether this benefits other corals in the system or not I am not sure.

Ben

 

[Navarre]

I had a 5 headed Branching hammer corals that bleached itself nearly 2 years ago. It went totally white and shrank to half its size. I eventually placed it in a friends coral system and left it to see what would happen. It took an entire year whith this coral completely bleeched (s o how it was getting food i will never know) and lost 3 of its 5 heads but slowly after about 14 months i was called over to see the hammer and to my suprise it was regaining some of its colour. It now sits back in my system on show to the world and is its former beautiful colration! Sadly its lost 3 of its 5 heads but at least the coral was saved and it can regrow over time.

Even when a coral bleeches it doesnt mean its the end of hte road for that specimen, just percivere with it and things can turn around.

 

[steelhealr]

Unpinned and released. SH