Tropical Fish Hobbyist - October 2010

comparison. First you could test different levels in your current tank to determine and record the intensity at which the various corals are thriving. Then you could temporarily (a matter of minutes) remove your metal halide fixture and put the 260- watt compact fluorescent fixture over the tank and take light-intensity measurements to a depth of 12 inches. That will give you a pretty good sense of where you would need to position corals in the 12-inch-deep frag tank—and/or how high you would need to position the lights—so the corals will receive approximately the same level of light intensity and, therefore, continue to thrive as they have been.

As for lighting the proposed 300-gallon tank, as long as you place the corals in approximately the same position relative to the lights—in both the vertical and horizontal planes—you should be able to use the same light fixture you’re using now. Remember, those watts-per-gallon rules aren’t worth very much. After all, a coral positioned 6 inches below the surface of the water with a 250- watt metal halide lamp directly overhead receives the same amount of light regardless of whether the aquarium holds 30 or 1000 gallons of water. You’ll just need to arrange your rockwork and corals in such a manner that uses the available light to greatest advantage.

Identifying
Acropora

Why is it so difficult to identify certain stony corals, such as the various Acropora corals, to the species level? I often see specimens identified only as “Acropora sp.”

Connie Barker Columbia, Maryland

Q

intensity of water movement or illumination
they’re exposed to. For instance, a specimen
that is regularly buffeted by surging waves
will tend to develop more robust branches,
while another specimen of the same species
found in calmer waters might develop more
spindly branches. Coloration is no guide,
either, as different specimens of the same
species can differ significantly in color—even
those occurring in very close proximity to one
another.

Iggy Tavares

One of the biggest challenges in identifying Acropora corals to the species level, apart from the staggering number of species that exist in nature, is the amazing plasticity of form these corals exhibit. Two specimens of the same species can look remarkably different depending on a variety of factors, such as the Like many corals, Acropora are very difficult to identify to the species level when alive.