Epidemiology of cryptonisci (Bopyridae: Isopoda) in the Gulf of Carpentaria, Australia

Three Gulf-wide cruises were examined for cryptonisci and the data analysed for the effect of environmental variables on cryptoniscid abundance. Location, season and location-season interaction accounted for 80% of the variability, with each accounting for 65, 25 and 10% of the explained variability respectively. More cryptonisci were found offshore in the northern and north-western areas of the Gulf and autumn had the highest abundance. In decreasing order, depth, temperature, salinity, light and their interactions were components within season and location and they accounted for 13, 6, 6, 4 and 43% of the variability respectively. The depth effect was related to the main prawn host Penaeus semisulcatus which also had a preference for deeper water. Fourteen different copepod intermediate hosts were identified by direct observation of attached cryptonisci; Canthocalanus pauper and Paraeuchaeta concinna were the most important. Environment, however, was more important than intermediate hosts in explaining variation in cryptoniscid numbers.