Zooplankton and Nekton: Gatekeepers of the Biological Pump

Many zooplankton and nekton organisms migrate daily between the surface layer - where they feed at nighttime - and mesopelagic depth - where they hide from predation at daytime. Vertical migrators can increase the transfer of organic matter to depth by transporting surface-ingested material into the deep layers, where it is metabolized and excreted as a combination of dissolved and particulate matter. This process is known as active flux and can contribute significantly to the total downward export of carbon and nutrients. However, zooplankton and nekton also feed on and disaggregate particles, thereby reducing the vertical export and contributing to the attenuation of vertical particle fluxes with depth. Zooplankton and nekton can therefore be considered gatekeepers of the biological pump, influencing both the active and the passive export of carbon and nutrients to the ocean interior. A detailed understanding of these processes and their modulation by climate change is necessary, as the biological pump is responsible for a significant withdrawal of carbon from the euphotic, climate-active zone, but also supplies most of the organic matter for the ocean midwater and benthic food webs. Acoustic and in situ optical measurements allow us to monitor zooplankton, nekton, and particles at unprecedented detail, and to link these observations to environmental parameters. Laboratory experiments give insights into individual-based processes ranging from animal activity under different environmental conditions, to the colonization and consumption of particles by microzooplankton.

In this Research Topic, we welcome a broad range of contributions, from individual-based process studies, to local and global field observations, to modelling approaches to better characterize zooplankton and nekton as gatekeepers for the biological pump.