Observations on the distribution and relative abundance of the scyphomedusan Chrysaora hysoscella (Linne, 1766) and the hydrozoan Aequorea aequorea (Forskal, 1775) in the northern Benguela ecosystem

Observations on the abundance of medusae at the surface were conducted in t he northern Benguela ecosystem, over the period August 1997-June 1998. The results suggest that Chrysaora hysoscella is found inshore, whereas Aequore a aequorea tends to be found offshore. Although these relative observations are subject to bias caused by seasonal changes in the survey area, they ar e generally supported by the results of correlation analyses, and by the re sults of a more quantitative, cross-shelf trawl survey. Both species of med usae display marked patchiness, and can be very abundant. They appear to ha ve mostly non-overlapping patterns of distribution in the upper layers of t he water column, and so are able exert a consistent predation pressure acro ss the width of the continental shelf. The estimates of biomass obtained ar e used as input variables to existing models of energy flow within the ecos ystem.