Hydromedusa blooms and upwelling events in the Bay of Panama, Tropical East Pacific

Abstract

Seasonal upwelling events dominate the coastal areas of some regions of the Tropical East Pacific. The effects of upwelling on gelatinous zooplankton are largely unknown and undocumented for this or any region, although upwelling is known to shape phytoplankton dynamics. Small hydromedusae, the most widespread and diverse representatives of gelatinous plankton, are often neglected in plankton ecology as they are inconspicuous and escape direct observation. Their occurrence is seasonal and standard plankton sampling techniques easily overlook their blooms. In order to investigate whether upwelling affects hydromedusae dynamics, we monitored their abundance and diversity in the Bay of Panama, a region on the Pacific Coast of Panama characterized by seasonal upwelling events. Our results show that, although the number of species is relatively constant throughout the year, hydromedusa abundance in the Bay of Panama can be up to two orders of magnitude higher during upwelling than non-upwelling conditions. The difference in the numbers of hydromedusae between the two seasons is mostly due to temporally short medusa blooms that occur only during the upwelling season. Our results point to a link between hydromedusa blooms and upwelling events, and the increased productivity associated with them. The results are consistent with a scenario in which upwelling events act on the benthic colonies thus inducing medusa production.