Using nowcast model currents to explore transport of non-indigenous jellyfish into the Gulf of Mexico

In the spring of 2000, millions of the non-endemic jellyfish Phyllorhiza punctata were found in coastal regions of the Mississippi Bight in the northern Gulf of Mexico. The aggregations were large enough to seriously impact local fisheries by clogging shrimp nets and damaging gear. More importantly perhaps, the impact on plankton biomass and hence on fishery resources were potentially large, since P. punctala is a voracious filter feeder. In this study, we examine a hypothesis for their sudden appearance which involves advection from the Caribbean in an intruding Loop Current and subsequent flux onto the Mississippi Shelf through eddy-shedding processes which interact with the continental shelf/slope. Surface current data were obtained from an archived finite difference model of the Gulf of Mexico which used altimeter data assimilation and real wind forcing covering the time of the invasion. Model and satellite data showed that an exchange event occurred in late April at a time appropriate for the invasion. The results from tracing transport pathways suggest that mass redistribution of Caribbean populations into the northern Gulf of Mexico can be accomplished via Loop Current intrusion and flux of deep basin water onto the shelf. As such, the occurrence of the invasive species P. punctata in the northern Gulf in 2000 can be explained by a natural, but not necessarily common, sequence of events. This hypothesis is discussed as a means of redistribution of a species by invasion as opposed to redistribution by diffusive spreading.