Bacteria and fungi identified on horseshoe crabs, Tachypleus gigas and Carcinoscorpius rotundicauda in the laboratory

Abstract

In Malaysia, reduction of horseshoe crab sightings in their natural habitat has prompted studies on the ecology of this invertebrate and potential threats to its survival. In this study, eggs and newly hatched Tachypleus gigas, collected from a natural spawning ground in Banting, Selangor (Malaysia), were conditioned and cultured in the laboratory to test the potential of fungal or bacterial infections to occur and impair development and growth. During the culture period, evidence of bacterial and fungal infestation was observed. Identified species included bacteria (Shewanella putrefaciens, Bacillus cereus, Corynebacterium sp. and Enterococcus faecalis) and fungi (Aspergillus sp., Aspergillus niger, Peniclillium sp., Gliocladium sp.). Eggs infected with bacteria or fungi usually turned reddish, grey or black and ceased to develop. Larvae became passive and coated with black spore and in some cases died soon after molting into the larval stage. The species with greatest potential to affect the growth and survival of horseshoe crab eggs and larvae sampled in this study were S. putrefaciens (a Gram-negative bacterium) and A. niger (a fungi). The suite of species identified during this study were different from those previously identified on horsehose crabs in culture, suggesting possible species, location, and/or condition-specific variation in communities of infectious microbes brought in from the natural environment and propagated in culture. Infected horseshoe crabs, therefore, may require different management or treatment strategies and additional study.