Predominant Non-additive Effects of Multiple Stressors on Autotroph C:N:P Ratios Propagate in Freshwater and Marine Food Webs

Abstract

A continuing challenge for scientists is to understand how multiple interactive stressor factors affect biological interactions, and subsequently, ecosystems–in ways not easily predicted by single factor studies. In this review, we have compiled and analyzed available research on how multiple stressor pairs composed of temperature (T), light (L), ultraviolet radiation (UVR), nutrients (Nut), carbon dioxide (CO2), dissolved organic carbon (DOC), and salinity (S) impact the stoichiometry of autotrophs which in turn shapes the nature of their ecological interactions within lower trophic levels in streams, lakes and oceans. Our analysis from 66 studies with 320 observations of 11 stressor pairs, demonstrated that non-additive responses predominate across aquatic ecosystems and their net interactive effect depends on the stressor pair at play. Across systems, there was a prevalence of antagonism in freshwater (60–67% vs. 47% in marine systems) compared to marine systems where synergism was more common (49% vs. 33–40% in freshwaters). While the lack of data impeded comparisons among all of the paired stressors, we found pronounced system differences for the L × Nut interactions. For this interaction, our data for C:P and N:P is consistent with the initial hypothesis that the interaction was primarily synergistic in the oceans, but not for C:N. Our study found a wide range of variability in the net effects of the interactions in freshwater systems, with some observations supporting antagonism, and others synergism. Our results suggest that the nature of the stressor pairs interactions on C:N:P ratios regulates the “continuum” commensalistic-competitive-predatory relationship between algae and bacteria and the food chain efficiency at the algae-herbivore interface. Overall, the scarce number of studies with even more fewer replications in each study that are available for freshwater systems have prevented a more detailed, insightful analysis. Our findings highlighting the preponderance of antagonistic and synergistic effects of stressor interactions in aquatic ecosystems—effects that play key roles in the functioning of feedback loops in the biosphere—also stress the need for further studies evaluating the interactive effects of multiple stressors in a rapidly changing world facing a confluence of tipping points.

A meta-analysis on environmental drivers of marine phytoplankton C : N : P

“…This search yielded 4899 hits. We also closely inspected all the primary studies mentioned in the 8 recent review papers including meta-analyses studies on elemental stoichiometry of phytoplankton in aquatic environment (Flynn et al, 2010;Hillebrand et al, 2013;Moreno and Martiny, 2018;Persson et al, 2010;Thrane et al, 2016;Villar-Argaiz et al, 2018;Yvon-Durocher et al, 2015). The list is also augmented with data from additional four studies that did not appear in the literature https://doi.org/10.5194/bg-2019-440 Preprint.…”

“…For example, irradiance, temperature, and nutrient availability are often linked because the change in light availability will affect sea surface temperature, which in turn will alter vertical stratification in the water column and nutrient upwelling. Indeed, a meta-analysis on the pair-wise effects of environmental drivers on elemental stoichiometry of phytoplankton has shown that interactions of two environmental stressors can impose predominantly non-additive effects to C:N:P of phytoplankton, and that the effect of multiple environmental stressors is more than simply the sum of its parts (Villar-Argaiz et al, 2018). In addition, a recent multi-driver study carried for eight different drivers has shown that only a few dominant drivers can explain most of the evolutionary changes in population growth rates (Brennan et al, 2017).…”

Navigating the Future V: Marine Science for a Sustainable Future

“…Non-additive responses exhibit interactions between the effects of multiple stressors and are often complex and likely to be important in marine ecosystems, as demonstrated in studies of binary stressor combinations (e.g. Villar-Argaiz et al, 2018). The temporal aspects of short-lived versus continuous stressors, which may cause accumulated effects, should be taken into account.…”

The antagonistic effect of UV radiation on warming or nitrate enrichment depends on ecotypes of freshwater macroalgae (Charophytes)

“…, Villar‐Argaiz et al. ). More specifically, their possible antagonistic effects, for example, the mitigating effect of nutrients or temperature increases on the damaging effects of UVR observed in benthic marine algae (Marcoval et al.…”