I see this when moving frags from one system to another, same water params, same flow, but different lighting bulbs. The golden brown "tanning" is actually high levels of Zooxanthellae, and may be the result of:
- too little light (the zoox are stimulated to produce more to make up for the low intensity of light)
- too much light (the zoox are stimulated into reproduction within the host such that pops are high and densities are high as well. This may or may not lead to the holobiont dumping some zoox if temps are high and lighting begins superoxidase production)
- too RED a light (old bulbs or inappropriate temp bulbs stilulate the reproduction of the algal symbiont)
- too high a nutrient level (this stimulates and fertilizes the algal symbiont into high density pops as well, most often nitrates, although phosphate may play a role if it is not so high that it stops calcification)
The trick is to find the balance of the above intensity factors that stimulates protective pocilliporins yet does not drive overt zoox growth. This may occur after an initial browning of the specimen (zoox growth over-coloring the specimen's protective pigments, followed by partial zoox dump under high intensity lighting and low nutrient loads). Some species will brown under very intense lighting no matter what, as untimate coloration will depend on the conditions that the specimen originally grew and developed under (i.e., deep water Vs. reef top, lagoonal understudy Vs. fore-reef, etc.)
Sometimes it's a crapshoot. I have intentionally bought dull, drab-colored specimens (usually cheap) and brought them here just to see what comes from them. I have a Poillipora that was absolutely dark brown on acquisition, that under good water params and 250 watt mixed MH lighting is now a bright PINK, almost fuschia color. Even better example, I have a Purple tipped Millepora specimen that I received from Don (Cyberchef) as a colorful specimen that actually lost color and became almost black it was so dark. Upon changing bulbs (new Iwasaki 6.5kK from 6 mo old Sunburst 12kK) 3 months into frag growth, this specimen is now an absolutely beautiful med brown with heavy purple coloration throughout the tissue, not just the tips. I have others that will turn brown if left under the
Iwasaki bulbs, but will color up nicely when moved to a growout tank with VHO/PC intense lighting. Much depends on the conditions where the specimen was collected from and the prevailing conditions that the specimen will be grown under. I have similar experiences with the Ushio 10kK bulbs.
Sorry, there is no clear-cut answer, much will depend on the luck of the draw and the ability to determine which conditions will bring out the best coloration. I currently have a specimen that came from ******'s tank (
edit-tdwyatt) that was yellow-green in his system, but became a beautiful tan and blue and purple tri-
color acro in my prop system, so remember that even with great lighting and water params, that there is no guarantee that your system will maintain or duplicate the coloration you see for a specimen in someone else's tank.
HTH
