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Abstract Environmental managers need a rapid and cost‐effective monitoring tool for tracking the spread of invasive species, particularly at the onset of introduction. The macroalgaeCaulerpa proliferais considered an invasive species outside its native range, colonizing large patches of seafloor, reducing native species, and altering ecosystem functioning. Here, we developed a droplet digital PCR assay for detection ofC. proliferafrom environmental DNA seawater samples using the internal transcribed spacer (ITS) region. While the assay itself was confirmed to be highly efficient, we discovered concentrations ofC. proliferaeDNA were present below detectable levels in the water column surrounding an outbreak. To understand why, we conducted tank‐based experiments for two California invasive algae species,Caulerpa proliferaandSargassum horneri. The steady‐state eDNA concentration (eDNA copies/ gram of biomass detected) ofC. proliferawas found to be two orders of magnitude lower thanS. horneri. A meta‐analysis of steady‐state concentrations reported in the literature showed a remarkable range from ~10⁴–10¹¹(copies/g), revealing C. proliferato have the lowest recorded steady‐state concentrations of eDNA of any known species. We attributeC. prolifera'slow steady‐state eDNA concentration to its unique biology as a unicellular macroscopic algae which reduces the possible modes of eDNA release compared to similarly sized multicellular organisms. Critically our results demonstrate the potential limits of eDNA approaches, the influence of shedding rates in the reliability of species detections, and the vital importance of benchmarking and validating eDNA assays in both field and laboratory settings. 

Seagrass beds are disappearing at a record pace despite their known value to our oceans and coastal communities. Simultaneously, our coastlines are under the constant pressure of climate change which is impacting their chemical, physical and biological characteristics. It is thus pertinent to evaluate and record habitat use so we can understand how these different environments contribute to local biodiversity. This study evaluates the assemblages of fish found at fiveZosterabeds in Southern California using environmental DNA (eDNA) metabarcoding. eDNA is a powerful biodiversity monitoring tool that offers key advantages to conventional monitoring. Results from our eDNA study found 78 species of fish that inhabit these five beds around Southern California representing embayment, open coastal mainland and open coastal island settings. While each bed had the same average number of species found throughout the year, the composition of these fish assemblages was strongly site dependent. There were 35 fish that were found at both open coast and embayment seagrass beds, while embayment seagrass sites had 20 unique fish and open coast sites had 23 unique fish. These results demonstrate that seagrass fish assemblages are heterogenous based on their geographic positioning and that marine managers must take this into account for holistic conservation and restoration efforts. 

Abstract Fire–vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation have yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in herbaceous vegetation abundance for burned versus unburned plots. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C₄grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the vegetation structure of savannas and forests. 

Abstract Environmental DNA (eDNA) data make it possible to measure and monitor biodiversity at unprecedented resolution and scale. As use‐cases multiply and scientific consensus grows regarding the value of eDNA analysis, public agencies have an opportunity to decide how and where eDNA data fit into their mandates. Within the United States, many federal and state agencies are individually using eDNA data in various applications and developing relevant scientific expertise. A national strategy for eDNA implementation would capitalize on recent scientific developments, providing a common set of next‐generation tools for natural resource management and public health protection. Such a strategy would avoid patchwork and possibly inconsistent guidelines in different agencies, smoothing the way for efficient uptake of eDNA data in management. Because eDNA analysis is already in widespread use in both ocean and freshwater settings, we focus here on applications in these environments. However, we foresee the broad adoption of eDNA analysis to meet many resource management issues across the nation because the same tools have immediate terrestrial and aerial applications.