Investigating the ecology and biogeochemistry of the twilight zone, one of the least studied ecosystems on Earth

The mesopelagic zone of the ocean (~50-1000 m beneath the surface), often referred to as the 'twilight zone', remains one of the most poorly understood ecosystems on Earth. It hosts a diverse community of animals; some of these are presumed to feed on sinking particles of detritus, whereas others are thought to migrate into surface waters to feed on phytoplankton. These trophic interactions influence the storage of carbon in the ocean's interior, and hence contribute to global climate regulation. However, the current paucity of information on the ecology and physiology of mesopelagic zooplankton hinders our ability to represent their activities in global biogeochemical models, including those used by the IPCC to assess future climate. This project will investigate how the distribution and activities of mesopelagic zooplankton influence the fate of sinking organic matter. Changes in the trophic ecology and physiology of zooplankton with increasing depth will be examined using a combination of laboratory analyses and size-spectrum theory. Increased understanding of who is eating what in the mesopelagic food web will be used to examine the potential routes through which energy and organic matter cycle within this important ecosystem. This will help improve the representation of zooplankton in biogeochemical models.