Aquatic Productivity under Multiple Stressors

Aquatic ecosystems are responsible for about 50% of global productivity. They mitigate climate change by taking up a substantial fraction of anthropogenically emitted CO2 and sink part of it into the deep ocean. Productivity is controlled by a number of environmental factors, such as water temperature, ocean acidification, nutrient availability, deoxygenation and exposure to solar UV radiation. Recent studies have revealed that these factors may interact to yield additive, synergistic or antagonistic effects. While ocean warming and deoxygenation are supposed to affect mitochondrial respiration oppositely, they can act synergistically to influence the migration of plankton and N-2-fixation of diazotrophs. Ocean acidification, along with elevated pCO(2), exhibits controversial effects on marine primary producers, resulting in negative impacts under high light and limited availability of nutrients. However, the acidic stress has been shown to exacerbate viral attacks on microalgae and to act synergistically with UV radiation to reduce the calcification of algal calcifiers. Elevated pCO(2) in surface oceans is known to downregulate the CCMs (CO2 concentrating mechanisms) of phytoplankton, but deoxygenation is proposed to enhance CCMs by suppressing photorespiration. While most of the studies on climate-change drivers have been carried out under controlled conditions, field observations over long periods of time have been scarce. Mechanistic responses of phytoplankton to multiple drivers have been little documented due to the logistic difficulties to manipulate numerous replications for different treatments representative of the drivers. Nevertheless, future studies are expected to explore responses and involved mechanisms to multiple drivers in different regions, considering that regional chemical and physical environmental forcings modulate the effects of ocean global climate changes.

Automated summary

Aquatic ecosystems contribute 50% of global productivity and play a crucial role in mitigating climate change. Factors such as water temperature, ocean acidification, nutrient availability, deoxygenation, and exposure to UV radiation interact to either enhance or decrease productivity. While ocean warming and deoxygenation may have opposite effects on mitochondrial respiration, they synergistically affect plankton migration and N-2-fixation of diazotrophs. Ocean acidification and elevated pCO(2) have controversial effects on marine primary producers, but they can worsen viral attacks on microalgae and reduce calcification of algal calcifiers when combined with UV radiation. Field observations over a long period of time are limited, but future studies are expected to explore the responses and mechanisms to multiple drivers in different regions.