Vertical migration and advection of bopyrid isopod cryptoniscid larvae in the Gulf of Carpentaria, Australia

To understand the distribution of bopyrid isopods and assess their impact on host penaeid prawn populations, studies on factors affecting their larval behaviour and dispersal were undertaken Three series of stratified plankton samples were taken in the Gulf of Carpentaria at three seasons of the year. The bopynd cryptoniscid larvae migrated nocturnally to the surface and migrated diurnally to the bottom waters A multiple correlation coefficient of 0 70 showed that the number of cryptonisci varied negatively with light intensity and positively with the plankton biomass and the sampled depth. Partial correlation decomposition of the correlation coefficient showed light, depth and biomass to have partial coefficient values of -0 45, 0 43 and 0.28 respectively In the Mornington Island area, a multiple regression analysis combining depth sampled and the copepod species Acrocalanus gibber and Corycaeus dahli gave a correlation coefficient of 0 91 with cryptoniscid abundance However, the largest single correlation coefficient was with Calanopia ethpnca (r = 0.77) which was highly correlated with depth sampled. Estimated advection distances were between 80 and 120 km As cryptonisci and prawn larvae both migrate vertically and also move over similar distances, postlarval prawns can be infected on the nursery grounds by the bopyrid cryptonisci