Boat noise impedes vocalizations of wild plainfin midshipman fish

Marine noise is recognised as a growing threat that can induce maladaptive behavioural changes in many aquatic animals, including fishes. The plainfin midshipman is a soniferous fish with a prolonged breeding period, during which males produce tonal hums that attract females, and grunts and growls during agonistic interactions. In this study, we used acoustic recordings to assess the effects of boat noise on the presence, peak frequencies, and durations of plainfin midshipman calls in the wild. We found that all three call types were less likely to occur, and the peak frequencies of hums and grunts increased in the presence of boat noise. We also show that loud and quiet boat noise affected plainfin midshipman vocalizations similarly. As anthropogenic noise is likely to increase in the ocean, it will be important to understand how such noise can affect communication systems, and consequently population health and resiliency.

Phase Behavior and Rheological Properties of Size-Fractionated MXene (Ti3C2Tx) Dispersions

Understanding the dispersion behavior of MXenes is interesting from a fundamental colloid science perspective and critical to enabling the fluid-phase manufacturing of MXene devices with controlled microstructures and properties. However, the polydispersity, irregular shape, and charged surfaces of MXenes result in a complex phase behavior that is difficult to predict through theoretical calculations. As two-dimensional (2D) nanomaterials, MXenes can form lyotropic liquid crystal phases, gels, and aggregates. This work aims to elucidate the effects of MXene (Ti3C2Tx) sheet size on their phase behavior and associated rheological properties. Aqueous dispersions of large sheets with an average lateral dimension of 3.0 μm, small sheets with an average lateral dimension of 0.3 μm, and a bimodal mixture of the two sizes were investigated by using cross-polarized optical microscopy and rheology. At low concentrations, the large MXene dispersions exhibited lyotropic liquid crystal behavior and extended aligned textures, but increasing concentration resulted in the formation of dense flocs. Dispersions of small sheets formed small birefringent domains with increasing concentration but lacked long-range ordering. A bimodal mixture of these sizes enabled the formation of liquid crystalline phases with extended aligned textures with less floc formation. These results provide insights into using polydispersity to tune dispersion microstructure and rheological properties that can be applied to designing dispersions for fluid-phase manufacturing methods, such as direct ink writing.

Global COVID-19 lockdown highlights humans as both threats and custodians of the environment

The global lockdown to mitigate COVID-19 pandemic health risks has altered human interactions with nature. Here, we report immediate impacts of changes in human activities on wildlife and environmental threats during the early lockdown months of 2020, based on 877 qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of reports of unusual species observations from around the world suggest that animals quickly responded to the reductions in human presence. However, negative effects of lockdown on conservation also emerged, as confinement resulted in some park officials being unable to perform conservation, restoration and enforcement tasks, resulting in local increases in illegal activities such as hunting. Overall, there is a complex mixture of positive and negative effects of the pandemic lockdown on nature, all of which have the potential to lead to cascading responses which in turn impact wildlife and nature conservation. While the net effect of the lockdown will need to be assessed over years as data becomes available and persistent effects emerge, immediate responses were detected across the world. Thus, initial qualitative and quantitative data arising from this serendipitous global quasi-experimental perturbation highlights the dual role that humans play in threatening and protecting species and ecosystems. Pathways to favorably tilt this delicate balance include reducing impacts and increasing conservation effectiveness.

Regional heterogeneity in coral species richness and hue reveals novel global predictors of reef fish intra-family diversity

Habitat heterogeneity shapes biological communities, a well-known process in terrestrial ecosystems but substantially unresolved within coral reef ecosystems. We investigated the extent to which coral richness predicts intra-family fish richness, while simultaneously integrating a striking aspect of reef ecosystems-coral hue. To do so, we quantified the coral richness, coral hue diversity, and species richness within 25 fish families in 74 global ecoregions. We then expanded this to an analysis of all reef fishes (4465 species). Considering coral bleaching as a natural experiment, we subsequently examined hue's contribution to fish communities. Coral species and hue diversity significantly predict each family's fish richness, with the highest correlations (> 80%) occurring in damselfish, butterflyfish, emperors and rabbitfish, lower (60-80%) in substrate-bound and mid-water taxa such as blennies, seahorses, and parrotfish, and lowest (40-60%) in sharks, morays, grunts and triggerfish. The observed trends persisted globally. Coral bleaching's homogenization of reef colouration revealed hue's contribution to maintaining fish richness, abundance, and recruit survivorship. We propose that each additional coral species and associated hue provide added ecological opportunities (e.g. camouflage, background contrast for intraspecific display), facilitating the evolution and co-existence of diverse fish assemblages.