Abundance and distribution of large medusae in surface waters of the northern California Current

We used surface trawls to quantify abundance and distribution of four large medusae-Chrysaora fuscescens, Aurelia labiata, Phacellophora camtschatica, and Aequorea sp.-in the northern California Current, a coastal upwelling area, during June and August 2000 and 2002. C. fuscescens was most abundant, with a maximum of 77 per 1000 m3 (or 64 mg C/m3). Densities of A. labiata reached 10 per 1000 m3 (26 mg C/m3). Although medusae were widespread throughout the study region, a large proportion of the total catch of each species tended to be concentrated at relatively few stations. When we analyzed how the variability in distribution of medusae related to a suite of environmental parameters, latitude and either distance from shore or water depth proved important during each cruise. Analysis by species suggested habitat partitioning by C. fuscescens and A. labiata: C. fuscescens was more likely to be caught in nearshore shelf waters north of Cape Blanco, compared to A. labiata, which was more prevalent in south of Cape Blanco. These biological patterns were likely the result of a combination of physical processes, including advection and aggregation within regions of weak surface flow, coordinated behavior such as vertical migration, and location of benthic polyp stages. Studies such as this one provide important baseline information for ecosystem models and can be used to help evaluate impacts of jellyfish blooms in coastal upwelling regions.