Leucothrix Mucor Infestation of Benthic Crustacea, Fish Eggs, and Tropical Algae1

Appendages and eggs of benthic marine crustacea are often populated with the characteristic filaments of the bacterium Leucothrix mucor. Planktonic crustacea and fish eggs free of L. mucor become infested when held in aquaria in the absence of antibiotics. Isolates from these organisms are grossly indistinguishable from isolates from algae. Although L. mucor is not a pathogen, it may be involved in high mortalities by causing pelagic eggs to sink below the surface and by interfering with the filtering apparatus of larval forms. Antibiotics that prevent development of L. mucor (and other microorganisms) reduce the mortality in developing eggs and larvae. Direct microscopic examination of 48 seaweeds from the lagoon at Majuro Atoll in the Marshall Islands for L. mucor indicated its presence on 81% of the samples. When 18 randomly chosen samples were put in enrichment culture, detection increased to 100%. These observations are at variance with a previous report that L. mucor is either absent or rare in warm waters.