Eliminating coral-eating nudibranchs with potassium permanganate.

 

An Effective Solution

Discussion

Nudibranch Tests

     The tests performed on the nudibranchs yielded results that were, for the most part, as expected. It was anticipated that all concentration levels would kill the nudibranchs, but the 10mg/L and 25mg/L tests failed to do so. These tests did not, however, test the long-term effects of the immersion upon the adult nudibranchs. It is likely that the nudibranchs in the lower concentration test groups would have perished if returned to the holding tank. Overall, the nudibranch tests were successful. All concentrations of 50mg/L and above were shown to be effective.

 

Egg Tests

     Tests on the eggs took into account the long-term effects of the immersions, as the eggs were not likely to exhibit readily-identifiable signs of lethal damage. It was thought that the solutions would be less effective against the eggs due to the capsules surrounding each egg mass, but all tested concentrations of KMnO₄ were sufficient to kill the developing larvae. All tested concentrations were shown to be effective against the eggs.

 

Coral Tests

     The first set of coral tests, which investigated the effects of various concentrations of KMnO₄ on infested samples of M. capricornis, yielded some anomalous results. The solutions did not have as strong an effect on the nudibranchs and eggs as they did in the initial tests. The 25mg/L concentration was effective against the nudibranchs, but was not strong enough to kill the eggs. The 10mg/L solution was not effective against either the adult animals or the eggs. It is thought that the concentrations quickly fell during these tests due to the presence of other organic material, such as algae on the bottom of the sample corals. It is also likely that the mucous layer produced by the corals provided some protection for the nudibranchs and eggs as well. This may not be a problem with species that produce less mucous.

     Another anomaly in this set of tests was the coral sample tested at 75mg/L. After approximately 36 hours, this sample suddenly and completely disintegrated. As no other samples showed any similar reaction, or any negative reaction at all, it is thought that this was unrelated to the tests. The cause is likely a combination of stress from predation by nudibranchs and a secondary bacterial infection. Apart from this anomaly, all the concentrations equal to or greater than 50mg/L were effective in treating infested coral colonies.

     The survival tests on various species of coral were all successful. No coral specimens in this group showed any lasting adverse reactions.