651 / 2024-09-18 20:01:43

Twilight Struggles: the declining diel Vertical migrators in a warming shelf sea

ocean warming,zooplankton,bioacoustics,vertical migration

Many zooplankton and fish undertake diel vertical migration to evade predators, spending daylight hours in deeper, darker waters and rising to prey-abundant surface waters at dusk to feed, then descending back to the depths before dawn. The way this seeming routine behavior responds to warming in shelf seas may have a more profound impacts on local ecosystem compared with deep oceans. We have spent three years investigating the vertical migration of various organisms in the East China Sea, utilizing both hydroacoustic and underwater video. It showed that the warming-induced intensified thermocline strength and shallower mixed layer depths present new challenges for vertical migrators, particularly weakly swimming zooplankton. In warming shelf sea, the migration of many organisms is diminished or even completely halted. Using structural equation models, we found that sea surface, bottom temperature, and thermocline strength had significant negative effects on DVM, while sea surface chlorophyll had a positive effect. This overlooked phenomenon of declined DVM in shelf seas may become widespread in various shelf seas with the climate change, and are likely to bring significant consequences on food web structures and biogeochemical cycles in the global coastal ecosystems.