Combined effects of warming and nutrients on marine communities are moderated by predators and vary across functional groups

Abstract

Warming, nutrient enrichment and biodiversity modification are among the most pervasive components of human‐induced global environmental change. We know little about their cumulative effects on ecosystems; however, even though this knowledge is fundamental to predicting and managing their consequences in a changing world. Here, we show that shifts in predator species composition can moderate both the individual and combined effects of warming and nutrient enrichment in marine systems. However, all three aspects of global change also acted independently to alter different functional groups in our flow‐through marine rock‐pool mesocosms. Specifically, warming reduced macroalgal biomass and assemblage productivity, whereas enrichment led to increased abundance of meso‐invertebrate consumers, and loss of predator species led to increased gastropod grazer biomass. This disparity in responses, both across trophic levels (macroalgae and intermediate consumers), and between detecting additive effects on aggregate measures of ecosystem functioning, yet interactive effects on community composition, illustrates that our forecasting ability depends strongly on the level of ecological complexity incorporated within global change experiments. We conclude that biodiversity change—and loss of predator species in particular—plays a critical and overarching role in determining how ecological communities respond to stressors.

Environmental context shapes the long‐term role of nutrients in driving producer community trajectories in a top–down dominated marine ecosystem

“…These results, combined with other terrestrial and marine studies showing that effects varied across time, abiotic drivers or scales of organization (e.g. Daleo et al, 2015;Kerimoglu, Straile, & Peeters, 2013;O'Connor & Donohue, 2013;Souza et al, 2016;White, Donohue, Emmerson, & O'Connor, 2018), underscore the importance of a mechanistic understanding of producer diversity response to altered nutrient and herbivore control (see also Groendahl & Fink, 2017;O'Connor et al, 2015).…”

Synergistic Effects of Climate Change and Marine Pollution: An Overlooked Interaction in Coastal and Estuarine Areas

“…Researchers using this approach must carefully design their experiments to guarantee the appropriate control treatments, since sampling, transportation, and husbandry in controlled settings are likely to cause stress to the organism of interest. Another approach to addressing multiple stressors’ interactions between climate-change and pollutants is mesocosms studies (e.g., [98,101]). They can be viewed as an intermediate design to laboratory and field-studies, or as a simplification of natural systems enabling mechanistic testing of single and multiple drivers in highly-replicable and controlled settings, and at ecologically relevant scales [102].…”

“…Individual and community-based studies can also be used to infer ecosystem effects, particularly if the measured indicators refer to processes that drive ecosystem functioning, such as resource processing, decomposition rates, or other processes and services that directly quantify ecosystem functioning [83]. As an example, changes in grazer communities driven by multiple stressors can act synergistically with eutrophication, thereby promoting shifts in biodiversity levels and nutrient cycling [98]. Results from the latter study also highlight that loss of predators can play a critical role in the capacity of marine coastal ecosystems to respond to environmental changes combined with anthropogenic pollution.…”

Rocky shores as tractable test systems for experimental ecology

“…Such mesocosms have been particularly powerful in disentangling the effects of multiple stressors or environmental context crossed with biodiversity loss (e.g. O'Connor et al ., 2015 – biodiversity loss and nutrient enrichment; Mrowicki & O'Connor, 2015 – wave action on warming and biodiversity loss; White et al ., 2018 – biodiversity of predators with warming and nutrient enrichment; Vye et al ., 2015 – impacts of invasive species with water temperature and nutrient enrichment).…”