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.

Natural ecosystems are experiencing unprecedented rates of change due to anthropogenic activities and global change, leading to either gradual changes in a given response or tipping points. While the tipping point concept has been tested in an array of habitats since the 1960s, the spatiotemporal superposition of multiple drivers in different ecosystems needs to be considered when investigating the response of species, communities, populations, and ecosystems along environmental gradients. Here, we (1) develop a historical and current perspective of tipping point studies in terrestrial, freshwater, and marine ecological systems; (2) portray the research effort in different freshwater and marine habitats; and (3) explore the results of experimental studies focusing on tipping points measured at the individual, communities, ecosystem level, as well as ecosystem functions and services in a context of single and multiple stressors. The number of studies mentioning the concept of tipping points increases every year, but very few studies have specific objective to identify them. Even fewer studies consider how the addition of another stressor into an ecosystem may alter a tipping point. In addition, many studies investigated multiple responses, but only one‐fourth (7 out of 28) of them concentrate their effort on multiple biological or ecological levels of complexity. This review allowed us to identify shortcomings in this research field and propose ways to make this ecological concept anew.

Environmental stressors have profound implications for species, communities, and ecosystems by altering fundamental processes. With increasing human impacts on aquatic ecosystems, two main scenarios have been reported:(1) the spatiotemporal superposition of multiple stressors, leading to interactions among them and (2) intensifying environmental gradients, leading to threshold responses. However, studies designed to assess the effects of multiple stressors (e.g., pulse stressors) along environmental gradients (e.g., press stressors) are uncommon, and interactions between pulse and press stressors may cause abrupt changes in biological responses. We conducted a laboratory experiment to investigate the effects of osmotic stress along a nutrient enrichment gradient on a freshwater community composed of periphyton, microorganisms, and zebra mussels (Dreissena polymorpha). Our objectives were to (1) quantify the individual and combined effects of stressors, (2) delineate thresholds along the nutrient gradient (press) in the absence and presence of osmotic stress (pulse), and (3) test for interactions between the two stressors. We evaluated effects on metabolic rates in D. polymorpha and on microbial activity, as well as phototrophic periphyton biomass and physiological status. We observed interactions between the two stressors for metabolic rates in D. polymorpha and periphytic phaeopigments. In contrast, we found an individual effect of osmotic stress on microbial activity and chlorophyll a content. Thresholds were only identified in the presence of osmotic stress for metabolic rates in D. polymorpha. Our work highlights the importance of combining multiple stressors with environmental gradients and the need to consider multiple biological compartments when evaluating the impacts of stressors on ecosystems.

In order to help safeguard biodiversity from global changes, the Conference of the Parties developed a Strategic Plan for Biodiversity for the period 2011–2020 that included a list of twenty specific objectives known as the Aichi Biodiversity Targets. With the end of that timeframe in sight, and despite major advancements in biodiversity conservation, evidence suggests that the majority of the Targets are unlikely to be met. This article is part of a series of perspective pieces from the 4th World Conference on Marine Biodiversity (May 2018, Montréal, Canada) to identify next steps towards successful biodiversity conservation in marine environments. We specifically reviewed holistic environmental assessment studies (HEA) and their contribution to reaching the Targets. Our analysis was based on multiple environmental approaches which can be considered as holistic, and we discuss how HEA can contribute to the Aichi Biodiversity Targets in the near future. We found that only a few HEA articles considered a specific Biodiversity Target in their research, and that Target 11, which focuses on marine protected areas, was the most commonly cited. We propose five research priorities to enhance HEA for marine biodiversity conservation beyond 2020: (i) expand the use of holistic approaches in environmental assessments, (ii) standardize HEA vocabulary, (iii) enhance data collection, sharing and management, (iv) consider ecosystem spatio-temporal variability and (v) integrate ecosystem services in HEA. The consideration of these priorities will promote the value of HEA and will benefit the Strategic Plan for Biodiversity.

Ports play a central role in our society, but they entail potential environmental risks and stressors that may cause detrimental impacts to both neighboring natural ecosystems and human health. Port managers face multiple challenges to mitigate risks and avoid ecosystem impacts and should recognize that ports are embedded in the wider regional coastal ecosystem. Cumulative impacts of anthropogenic stressors have the potential to further burden the existing suite of natural stressors, particularly where ports are located in embayments and estuaries. Environmental monitoring in ports should thus develop a comprehensive, holistic, multilayered approach integrated in the wider ecosystem that will help managers better achieve sustainable development, a major goal of the United Nations’ 2030 agenda and Decade of Ocean Science for Sustainable Development (2021–2030). This practice bridge showcases the experience of the second Canadian Healthy Ocean Network (CHONe2) in Baie des Sept Îles (BSI, Quebec; the fourth largest industrial port in Canada) laying the foundations of holistic environmental monitoring in ports. We describe the partnership model (i.e., engaging scientists, local authorities, an independent organization, and local industries), synthesize the multidisciplinary studies that turned environmental monitoring into a systemic investigation of the biological and physical components of BSI, integrate the developed scientific knowledge into a social–ecological–environmental system, present an innovative near real-time monitoring approach, and discuss implications for management and policy. The CHONe2 experience in BSI aligns with the decade’s road map for sustainable development and provides elements that could be adapted to other commercial ports. By suggesting a set of best practices (e.g., multidisciplinarity, transparency, inclusivity, participatory modeling), we hope to spark new interest in environmental monitoring as a path to conciliate development and sustainability of ports and other high-use marine areas.