All kinds of things can effect all kinds of things in an eco system including heat. If you were to measure dissolved oxygen in water that's 95 and 65 you'll find that theres more oxygen in 65 degrees then 95. When 02 is low it can effect an eco-system - some of the bacteria like lots of dissolved 02 while others like a more oxygen deficient enviorment, difference in those bacterias is called aerobic and anerobic or Ammonia/Nitrite bacteria and de- Nitrifying bacteria. If the de-nitrifying bacteria is growing faster the the other 2 the rocks will get stringy brown dirty lookin' stuff and red slime algae can easily rear it's ugly head if the balance remains un-checked.
Theres a few sources of stuff that can cause this un-balance but like kevin8888 says - the root is organic decomp.It can be corrected by increased flow, more frequent water changes, reduced lighting, increased skimming,etc... - the list is quite long.
Best strating point is Test the water for - Nitrates, Phosphates, Silicates, and if using Tapwater for W/Cs the $80 TDS(Total dissolved solids) moniter. Or just stop using tapwater if you are and use R/O water to eliminate adding high levels of organic carbon decomp.
It gets expensive when planning a reef