Eliminating coral-eating nudibranchs with potassium permanganate.

An Effective Solution

Introduction

     Reef-building corals of the genus Montipora are very commonly kept in captivity due to their hardiness, fast growth, and colourful pigmentation. As these corals have been harvested, grown, and distributed, a species of nudibranch that feeds upon them in nature has been introduced into aquaria. Most reef aquariums do not include any natural predators of these nudibranchs, as the animals that feed upon them often prey upon corals as well. When given the stable conditions and lack of predators found in an aquarium, the pest nudibranchs multiply quickly and consume entire coral colonies over the course of several weeks or months.

     Various treatments have been attempted to remove or destroy nudibranchs on infested Montipora colonies. Methods such as manual removal, freshwater immersion, and Lugol’s solution dips have had limited success. The general lack of effectiveness of these treatments can be attributed to several factors. These techniques are somewhat effective against the adult pests but have little or no effect on the eggs, which then hatch and re-infest the affected coral colonies. With meticulous searching it is possible to manually remove all nudibranchs and their eggs from some coral colonies, but this is only plausible with small specimens of plating- or massive-type species. Also, these techniques are often highly damaging to the corals themselves.

     Immersion in dilute solutions of potassium permanganate has been used several times to remove nudibranch infestations on corals, and has shown promise as an effective treatment. Unlike other methods, potassium permanganate has been shown to have at least some effect on the eggs of the nudibranchs, as well as destroying the adult animals. Some initial tests have shown that hard corals of the genus Montipora have a far greater resistance to the damaging effects of the solution than the nudibranchs and eggs.