Temperature variability regulates the interactive effects of warming and pharmaceutical on aquatic ecosystem dynamics.

Climate warming and pharmaceutical contaminants have profound impacts on population dynamics and ecological community structure, yet the consequences of their interactive effects remain poorly understood. Here, we explore how climate warming interacts with pharmaceutical-induced boldness change to affect aquatic ecosystems, built on an empirically well-informed food-chain model, consisting of a size-structured fish consumer, a zooplankton prey, and a fish predator. Climate warming is characterized by both daily mean temperature (DMT) and diurnal temperature range (DTR) in our model. Results show that DMT and high levels of species' boldness are the primary drivers of community instability. However, their interactive effects can lead to diverse outcomes: from predator collapse to coexistence with seasonality-driven cycles and coexistence with population interaction-driven cycles. The interactive effects are significantly modulated by daily temperature variability, where moderate DTR counteracts the destabilizing interactive effects by increasing consumer reproduction, while large temperature variability considerably reduces consumer biomass, destabilizing the community at high mean temperatures. Our analyses disentangle the respective roles of DMT, DTR and boldness in mediating the response of aquatic ecosystems to the impacts from pharmaceutical contaminants in the context of climate warming. The interactive effects of the environmental stressors reported here underscore the pressing need for studies aimed at quantifying the cumulative impacts of multiple environmental stressors on aquatic ecosystems.

Fish microplastic ingestion may induce tipping points of aquatic ecosystems.

Microplastics can be ingested by a wide range of aquatic animals. Extensive studies have demonstrated that microplastic ingestion-albeit often not lethal-can affect a range of species life-history traits. However, it remains unclear how the sublethal effects of microplastics on individual levels scale up to influence ecosystem-level dynamics through cascading trophic interactions. Here we employ a well-studied, empirically fed three-species trophic chain model, which was parameterized to mimic a common type of aquatic ecosystems to examine how microplastic ingestion by fish on an intermediate trophic level can produce cascading effects on the species at both upper and lower trophic levels. We show that gradually increasing microplastics in the ingested substances of planktivorous fish may cause population structure effects such as skewed size distributions (i.e. reduced average body length vs. increased maximal body size), and induce abrupt declines in fish biomass and reproduction. Our model analysis demonstrates that these abrupt changes correspond to an ecosystem-level tipping point, crossing which difficult-to-reverse ecosystem degradation can happen. Importantly, microplastic pollution may interact with other anthropogenic stressors to reduce safe operating space of aquatic ecosystems. Our work contributes to better understanding complex effects of microplastic pollution and anticipating tipping points of aquatic ecosystems in a changing world. It also calls attention to an emerging threat that novel microplastic contaminants may lead to unexpected and abrupt degradation of aquatic ecosystems, and invites systematic studies on the ecosystem-level consequences of microplastic exposure.