Dying Coral in a Saltwater Aquarium

Coral can add color and beauty to a saltwater tank. Coral are a type of marine animal that live in colonies and consist of individual polyps. They build intricate structures, called exoskeletons, that are made out of calcium carbonate, some of which can resemble trees or other plants. When coral become stressed, they can become infected with bacteria, or spontaneously break down, and their skeleton can crumble as the coral die off. Depending on the cause, this can happen suddenly, sometimes overnight.

  1. Coral Bleaching

    • Stony corals come in a range of colors from yellow to brown. Their pigment is made by the photosynthetic pigments found in the coral's symbiotic zooxanthellae. When a coral is stressed, the zooxanthellae are expelled, which causes the loss of pigment and leaves a white coral skeleton visible. Bleaching may be caused by overexposure to high levels of light, increased ultraviolet radiation, bacteria, extremes in water temperature or water salinity, and high turbidity of the water. Bleaching reduces skeletal growth of the coral as well as its ability to reproduce and fight off invading species and diseases. If coral experiences bleaching for long periods of time, it can result in total colony death -- all the organisms that make up the coral will die off.

    Bacteria Infection

    • Bacteria such as Vibrio vulnificus can infect coral and cause them to rapidly slough off tissue from their skeletons. This bacteria also can cause bleaching in coral. Vibrio vulnificus thrives in warm tropical waters with low salinity levels. If you suspect that your coral has a bacteria infection, use Lugols dip or an iodine dip to attempt to kill off the bacteria. You can also transfer the infected coral to a quarantine tank and give it chloramphenicol -- which is a type of antibiotic that is soluble in ethanol.

    Rapid Tissue Necrosis

    • Rapid tissue necrosis or RTN is a state whereby coral rapidly dies off and the coral's skeletal structure dissolves or falls apart. RTN is also referred to as a "shut-down reaction." RTN can be caused by high levels of ammonia phosphate, nitrite, nitrate or harmful bacteria. If RTN occurs in your aquarium, check the levels of salinity, ammonia and nitrates in the water. If they are too high, replace 25 percent of the aquarium water and take appropriate measures, such as using a water conditioner to remove the toxic chemicals.

    Parasites

    • A parasitic ciliate protozoan takes the form of a bloblike brown or pinkish tan slime called brown jelly. Brown jelly grows over coral and consumes it. At the time of publication, it has not been scientifically proven if brown jelly kills the coral and then consumes it or if it just consumes dead coral that has been killed off by another cause. Brown jelly is thought be caused by protozoans called Helicostoma notata or Helicostoma nonatum. Eliminate brown jelly by treating the coral with the antibiotic chloramphenicol.