Disturbed flow in an aquatic environment may create a sensory refuge for aggregated prey

Global meta-analysis deciphering ecological restoration performance of dredging: Divergent variabilities of pollutants and hydrobiontes

Global "Sustainable Development Goals" propose ambitious targets to protect water resource and provide clean water, whereas comprehensive understanding of restoration performance and ecological mechanisms are lacking for dredging adopted for purifying polluted waterbodies and maintaining navigation channels. Here, we conducted a global meta-analysis to estimate ecological restoration consequence of dredging as pollution mitigation and navigation channel maintenance measures using a dataset compiled from 191 articles covering 696 studies and 84 environmental and ecological parameters (e.g., pollutants and hydrobiontes). We confirm that dredging shows negative influences on 77.50% pollutants in the BA model (before dredging vs. after dredging) and 84.21% pollutants in the CI model (control vs. impact) as well as on sediment nutrient fluxes. Additionally, 57.14% attributes (i.e., richness, diversity, biomass, and density) of hydrobiontes in the BA model and 89.47% attributes of hydrobiontes in the CI model responded negatively to dredging. As a result, 76.32% of the pollutants and 61.11% of the hydrobiont attributes responded uniformly to dredging in the BA and CI models. Our findings emphasize that dredging generally decreases pollutants and mitigates algal blooms, controlling phosphorus is easier than controlling nitrogen by dredging, and attributes (i.e., richness, diversity, and biomass) of hydrobiontes (i.e., zooplankton, phytoplankton, and zoobenthos) are density-dependent in dredging-disturbed environments. Our findings broaden our knowledge on ecological restoration performance of dredging as a mitigation measure in global aquatic ecosystems, and these findings might be helpful to use and optimize dredging to efficiently and sustainably purify polluted aquatic ecosystems.

Parasite avoidance behaviours in aquatic environments

Parasites, including macroparasites, protists, fungi, bacteria and viruses, can impose a heavy burden upon host animals. However, hosts are not without defences. One aspect of host defence, behavioural avoidance, has been studied in the terrestrial realm for over 50 years, but was first reported from the aquatic environment approximately 20 years ago. Evidence has mounted on the importance of parasite avoidance behaviours and it is increasingly apparent that there are core similarities in the function and benefit of this defence mechanism between terrestrial and aquatic systems. However, there are also stark differences driven by the unique biotic and abiotic characteristics of terrestrial and aquatic (marine and freshwater) environments. Here, we review avoidance behaviours in a comparative framework and highlight the characteristics of each environment that drive differences in the suite of mechanisms and cues that animals use to avoid parasites. We then explore trade-offs, potential negative effects of avoidance behaviour and the influence of human activities on avoidance behaviours. We conclude that avoidance behaviours are understudied in aquatic environments but can have significant implications for disease ecology and epidemiology, especially considering the accelerating emergence and re-emergence of parasites.This article is part of the Theo Murphy meeting issue 'Evolution of pathogen and parasite avoidance behaviours'.