Biomass changes and trophic amplification of plankton in a warmer ocean

Abstract

Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3-D coupled physical-biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate-change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis, including European seas (NE Atlantic, Barents Sea, Baltic Sea, Black Sea, Bay of Biscay, Adriatic Sea, Aegean Sea) and the Eastern Boundary Upwelling System (Benguela). Results indicate that globally and in Atlantic Margin and North Sea, increased ocean stratification causes primary production and zooplankton biomass to decrease in response to a warming climate, whilst in the Barents, Baltic and Black Seas, primary production and zooplankton biomass increase. Projected warming characterized by an increase in sea surface temperature of 2.29 ± 0.05 °C leads to a reduction in zooplankton and phytoplankton biomasses of 11% and 6%, respectively. This suggests negative amplification of climate driven modifications of trophic level biomass through bottom-up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. Simulations suggest negative amplification is the dominant response across 47% of the ocean surface and prevails in the tropical oceans; whilst positive trophic amplification prevails in the Arctic and Antarctic oceans. Trophic attenuation is projected in temperate seas. Uncertainties in ocean plankton projections, associated to the use of single global and regional models, imply the need for caution when extending these considerations into higher trophic levels.

Reconciling fisheries catch and ocean productivity

“…Although regional NPP projections vary between ESMs (42-44), Fig. 5 joins a growing body of evidence for amplified climate change impacts at higher trophic levels (24)(25)(26). Projected regional changes in catch may exceed 50%, far above oft-cited modest-to-moderate global NPP trends under climate change (42), and adding urgency to efforts to understand the combination of large-scale and local processes influencing regional climate change impacts on marine resources (45)(46)(47)(48).…”

“…Numerous studies report strong relationships between NPP and catch within regions or subsets of systems (21)(22)(23), perpetuating the use of NPP as an indicator of fisheries catch and a driver of catch projections despite studies providing strong contrary evidence across global scales (15). The potential amplifying effect of trophodynamic processes on projected NPP trends under climate change (24)(25)(26) adds urgency to resolving this disagreement.…”

Projected Change—North Sea

“…These use the IPSL-CM4.0 ESM (Wakelin et al 2012a;Chust et al 2014;Holt et al 2014Holt et al , 2016 and MPIOM Gröger et al 2013) as global forcing. The resulting changes in SST from these experiments are typically very similar for different regional ocean models and differ only by around a tenth of a degree.…”

“…The POLCOMS, ECOSMO, HAMSOM, Delft3D, NORWECOM and MPIOM simulations were equipped with a lower trophic level model (Alheit et al 2012;Holt et al 2012Holt et al , 2014Holt et al , 2016Wakelin et al 2012a;Gröger et al 2013;Chust et al 2014;Skogen et al 2014;Pushpadas et al 2015). Some of these downscaling scenarios also considered carbonate chemistry, but published estimates of future ocean acidification are available only from two regional models: POLCOM-ERSEM and ECOSMO (Wakelin et al 2012a;Artioli et al 2013Artioli et al , 2014.…”

Disentangling the mechanisms behind climate effects on zooplankton

“…The area experienced increased water temperatures during the past decades (7) and is, like other high-latitude regions, predicted to warm substantially throughout the 21st century (8). Climate simulations further suggest globally increased ocean stratification, accompanied by decreased primary production in temperate regions but increased primary production in the subarctic (including the Barents Sea) (9,10).…”