Conrad Sparks

Jellyfish overtake fish in a heavily fished ecosystem

(Current Biology 16, R492–R493; July 11, 2006)The units in the y-axis label of Figure 1A, which shows historic fish landings in the Benguela (South East Atlantic Major Area 47, Western Coastal Subarea, Divisions 1.3 Cunene, 1.4 Cape Cross, and 1.5 Orange River) from data compiled by the United Nations Food and Agriculture Organization (FAO), are mislabeled as 106 tonnes instead of 105 tonnes. The text that refers to the figure (paragraph 2, lines 11–12) is similarly in error by a factor of 10 too high; fish landings actually fell from about 1.7 million metric tonnes to 0.1 million metric tonnes. This error has no bearing on the main thrust or conclusion of our paper—that jellyfish biomass in the Benguela now exceeds that of once prolific finfish—because the recent estimates of fish and jellyfish biomass we report are from our own observations and not our interpretation of FAO data.

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

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

Hydromedusae Off the Orange River Mouth, Southern Africa

A total of 242 zooplankton samples from the upper 100 m of the water column was collected discontinuously from March 1997 to January 1999 off the Orange River mouth on the west coast of southern Africa. Six species of hydromedusae were recovered at generally low abundance, of which Euphysa aurata, Leuckartia octona and Proboscidactyla menoni were dominant. E. aurata and L. octona showed evidence of seasonality in abundance. The low diversity of the fauna was remarkable and it is hypothesized that this might be attributable in part to sedimentation from the Orange River, and in part to locally weak circulation and the wide extent of the continental shelf.