Estuaries provide critical habitat for many economically and ecologically valuable species that are adapted to a wide range of conditions and environmental variability, but the often turbid water presents challenges to monitoring efforts. This study explored fish habitat use in Richardson Bay, California (a sub-estuary of San Francisco Bay) at two points in time: one following a dry winter (2016) and the other following a historically wet winter (2017). Dual-frequency Identification Sonar (DIDSON) was used to record finfish and ray (>10 cm) abundance (MaxN) and size distribution, putative ray foraging pit size and abundance (MaxN), and eelgrass (Zostera marina) presence. We measured temperature, salinity, and dissolved oxygen (DO) at each site, and water samples at a subset of sites for nutrient analysis (urea, ammonium, nitrate, silicate, phosphate). Relationships between these data were explored using an information-theoretic modeling approach. Finfish abundance was best predicted by nutrient concentration in 2016 (–) and eelgrass presence in 2017 (–), whereas fish length was best predicted by salinity in 2016 (–) and eelgrass presence in 2017 (+). Foraging-pit abundance was strongly related to nutrient concentrations (+) in both years. This work presents a first attempt to establish relationships between fish distributions and environmental variables in Richardson Bay, and highlights the value of imaging sonar for studying fish communities in turbid estuaries.

As biological invasions continue to increase globally, eradication programs have been undertaken at significant cost, often without consideration of relevant ecological theory. Theoretical fisheries models have shown that harvest can actually increase the equilibrium size of a population, and uncontrolled studies and anecdotal reports have documented population increases in response to invasive species removal (akin to fisheries harvest). Both findings may be driven by high levels of juvenile survival associated with low adult abundance, often referred to as overcompensation. Here we show that in a coastal marine ecosystem, an eradication program resulted in stage-specific overcompensation and a 30-fold, single-year increase in the population of an introduced predator. Data collected concurrently from four adjacent regional bays without eradication efforts showed no similar population increase, indicating a local and not a regional increase. Specifically, the eradication program had inadvertently reduced the control of recruitment by adults via cannibalism, thereby facilitating the population explosion. Mesocosm experiments confirmed that adult cannibalism of recruits was size-dependent and could control recruitment. Genomic data show substantial isolation of this population and implicate internal population dynamics for the increase, rather than recruitment from other locations. More broadly, this controlled experimental demonstration of stage-specific overcompensation in an aquatic system provides an important cautionary message for eradication efforts of species with limited connectivity and similar life histories.

Strategies for managing biological invasions are often based on the premise that characteristics of invading species and the invaded environment are key predictors of the invader's distribution. Yet, for either biological traits or environmental characteristics to explain distribution, adequate time must have elapsed for species to spread to all potential habitats. We compiled and analyzed a database of natural history and ecological traits of 138 coastal marine invertebrate species, the environmental conditions at sites to which they have been introduced, and their date of first introduction. We found that time since introduction explained the largest fraction (20%) of the variability in non-native range size, while traits of the species and environmental variables had significant, but minimal, influence on non-native range size. The positive relationship between time since introduction and range size indicates that non-native marine invertebrate species are not at equilibrium and are still spreading, posing a major challenge for management of coastal ecosystems.

Understanding the likely future impacts of biological invasions is crucial yet highly challenging given the multiple relevant environmental, socio-economic and societal contexts and drivers. In the absence of quantitative models, methods based on expert knowledge are the best option for assessing future invasion trajectories. Here, we present an expert assessment of the drivers of potential alien species impacts under contrasting scenarios and socioecological contexts through the mid-21st century. Based on responses from 36 experts in biological invasions, moderate (20%-30%) increases in invasions, compared to the current conditions, are expected to cause major impacts on biodiversity in most socioecological contexts. Three main drivers of biological invasions-transport, climate change and socio-economic change-were predicted to significantly affect future impacts of alien species on biodiversity even under a best-case scenario. Other drivers (e.g. human demography and migration in tropical and subtropical regions) were also of high importance in specific global contexts (e.g. for individual taxonomic groups or biomes). We show that some best-case scenarios can substantially reduce potential future impacts of biological invasions. However, rapid and comprehensive actions are necessary to use this potential and achieve the goals of the Post-2020 Framework of the Convention on Biological Diversity.