Environmental stressors, complex interactions and marine benthic communities’ responses

Abstract

The increasing number and diversity of anthropogenic stressors in marine habitats have multiple negative impacts on biological systems, biodiversity and ecosystem functions. Methods to assess cumulative effects include experimental manipulations, which may identify non-linear responses (i.e. synergies, antagonisms). However, experiments designed to test these ideas are uncommon, generally focusing on single biological responses. We conducted a manipulative experiment to investigate the isolated and combined effects of warming (+ 6 °C), salinity variation (freshwater pulses or presses), and nutrient enrichment (natural or enriched) following one and three month’s exposure, on responses measured at multiple levels of biological complexity in a simple bivalve assemblage. More specifically, we determined effects on bivalve mortality, growth, shell mineralization, and energy content, as well as microphytobenthos biomass. Salinity variation and nutrient enrichment, individually and combined, caused strong impacts on some of the measured variables and their effect varied through time. In contrast, warming had no effect. Our work highlights the prevalence of antagonistic interactions, the importance of examining effects of single and multiple stressors through time, and of considering multiple responses to understand the complexity behind stressor interactions.

Rapid, but limited, zooplankton adaptation to simultaneous warming and acidification

“…Instead, OW and OA had synergistic deleterious effects on fitness on generation 0, but antagonistic effects on generation that counterbalance the individual effects of OW and OA (Supplementary Table 4). We suggest that the limited evolutionary rescue under OWA conditions in our study must have arisen from an antagonistic interaction between warming and acidification, as has been hypothesized earlier in polychaetes 19,20,48 or for other co-occurring environmental stressors in bivalves 49 . Thus, since OW and OA are occurring simultaneously, even crude predictions of population performance under climate change should consider nonadditive effects of temperature and CO2 interactions on population fitness.…”

Multiple Driver Impacts on Rocky Intertidal Systems: The Need for an Integrated Approach

“…The "additive null model" (A+B) is derived by building the sum of the interactions. This null model can easily be used for continuous response variables such as growth, Chlorophyll a concentration, or shell mineralization, but can cause problems when being applied to limited response variables such as mortality (Piggott et al, 2015;Côté et al, 2016;Carrier-Belleau et al, 2021). For such variables using a "multiplicative null model" (A+B-A * B) can correct over-estimations exceeding 100%.…”

“…For a better understanding of how rocky shores will be affected, the inclusion of both fluctuations and mean values of temperature, CO 2 level, and pH in experiments is, therefore, essential (Wernberg et al, 2013). As these parameters won't change uniformly over the globe we propose to use a combination of globalized and localized climate models in order to set realistic experimental variables for the location you want to apply your investigations to Allendorf et al (2001) and Carrier-Belleau et al (2021).…”

“…Considering the multiple dimensions of stability (Donohue et al, 2013) and measuring compositional and functional responses in experiments will elucidate the shifts in rocky shore assemblages under climate change (Cimon and Cusson, 2018). Because the growing body of literature shows that species richness in a system is relatively robust to changes, there is a need to measure functional diversity in a system as well (McGill et al, 2006;Hillebrand and Matthiessen, 2009;Cadotte et al, 2011). This is particularly important as a loss in functional diversity will likely be accompanied by a loss in ecosystem function (Mori et al, 2013).…”

“…In many cases, management actions will be more quickly and effectively implemented on a local level. Carrier-Belleau et al (2021) propose management strategies on a local level in order to reduce those drivers that pose the largest potential stress for the system first, which can help to mitigate undesired effects of global change and provide a higher level of resilience. Proposed research priorities relate to the complexity of ecosystems and the importance of whole-system approaches.…”