Biology subjects

Bell, T. W.

Publications and source records attributed to Bell, T. W..

5 recordsLinked to original sources

bioRxiv2024

A site selection decision framework for effective kelp restoration

HighlightsO_LISite selection is one of the most important factors for ecosystem restoration success C_LIO_LIA spatial prioritization framework for application to kelp restoration in California C_LIO_LIThe framework merges kelp metrics derived from in-situ surveys and satellite imagery C_LIO_LISite prioritization classification for every kelp forest site in California C_LIO_LIThis framework can be applied to other species and regions with similar datasets C_LI We present a decision support framework in the form of a spatially explicit site classification scheme to prioritize locations for conducting kelp restoration. The framework was created for the entire coast of California, where kelp has been lost and restoration projects are increasingly proposed, but the framework is broadly applicable to other coastal habitats or species that are being considered for restoration. We first created spatial distribution models using almost two decades of in situ kelp forest monitoring data and a comprehensive suite of environmental and biological variables, and used the outputs to evaluate the historical stability of kelp forests prior to a marine heatwave (MHW). We then used kelp canopy abundance data derived from satellite imagery to measure the impact of the MHW (i.e. extent of forest loss) and the recent state of kelp forests, including the trend of increase or decrease following the MHW. Finally, we integrated these site-specific kelp metrics to construct a classification tree for prioritizing restoration sites. Outputs of site prioritization are mapped across the study region, readily usable for managers and restoration practitioners with site-specific recommendations for restoration approaches. The framework can be updated due to knowledge of the important predictors of kelp and with new satellite imagery. Further, the framework can be adapted to other species and regions with similar data sets. This regional site selection framework is intended to be used in addition to socio-ecological, socio-economic, and administrative considerations.

ecology↗

bioRxiv2024

Intensifying marine heatwaves and limited protection threaten global kelp forests

Kelp forests are one of the earths most productive ecosystems and are at the greatest risk from climate change, yet little is known regarding their future threats and current conservation status. By combining a global remote sensing dataset of floating kelp forests with climate data and projections, we find that exposure to projected marine heatwaves will increase [~]8 times compared to contemporary (2001-2020) exposure for intermediate climate scenarios. While exposure will intensify for all forests, climate refugia emerge for some southern hemisphere kelp forests, which have lower exposure to contemporary and projected marine heatwaves. Under these escalating threats, less than 3% of global kelp forests are currently within highly restrictive marine protected areas, the most effective conservation measure for providing climate resilience. Our findings emphasize the urgent need to increase the global protection of kelp forests and set bolder climate adaptation goals.

ecology↗

bioRxiv2024

Marine protected areas promote resilience of kelp forests to marine heatwaves by preserving trophic cascades

Under accelerating threats from climate change impacts, marine protected areas (MPAs) have been proposed as climate adaptation tools to enhance the resilience of marine ecosystems. Yet, debate persists as to whether and how MPAs may promote resilience to climate shocks. Here, we empirically assess whether a network of 85 temperate MPAs in coastal waters promotes resilience against marine heatwaves in Central and Southern California. We use 38 years of satellite-derived kelp cover to test whether MPAs enhance the resistance of kelp forest ecosystems to, and recovery from, the unprecedented 2014-2016 marine heatwave regime. We also leverage a 20-year time series of subtidal community surveys to understand whether protection and recovery of sea urchin predators within MPAs explain emergent patterns in kelp forest resilience through trophic cascades. We find that fully protected MPAs (i.e. no-take marine reserves) significantly enhance the resistance to and recovery of kelp forests to marine heatwaves in Southern California, but not in Central California. Differences in regional responses to the heatwaves may be partly explained by three-level trophic interactions comprising kelp, urchins, and predators of urchins. Urchin abundances in Southern California MPAs are significantly lower within fully protected MPAs during and after the heatwave, while the abundance of their predators are higher. In Central California, there is no significant difference in urchin abundances within protected areas as the current urchin predator, sea otters, are unilaterally protected. Therefore, we provide evidence that fully protected MPAs can be effective climate adaptation tools, but their ability to enhance resilience to extreme climate events depends upon region-specific environmental and ecological dynamics. As nations progress to protect 30% of the oceans by 2030 scientists and managers should consider whether protection will increase resilience to climate-change impacts given their local ecological contexts, and what additional measures may be needed.

ecology↗

bioRxiv2023

How environmental drivers of spatial synchrony interact

Spatial synchrony, the tendency for populations across space to show correlated fluctuations, is a fundamental feature of population dynamics, linked to central topics of ecology such as population cycling, extinction risk, and ecosystem stability. A common mechanism of spatial synchrony is the Moran effect, whereby spatially synchronized environmental signals drive population dynamics and hence induce population synchrony. After reviewing recent progress in understanding Moran effects, we here elaborate a general theory of how Moran effects of different environmental drivers acting on the same populations can interact, either synergistically or destructively, to produce either substantially more or markedly less population synchrony than would otherwise occur. We provide intuition for how this newly recognized mechanism works through theoretical case studies and application of our theory to California populations of giant kelp. We argue that Moran interactions should be common. Our theory and analysis explain an important new aspect of a fundamental feature of spatiotemporal population dynamics.

ecology↗

bioRxiv2021

Automated satellite remote sensing of giant kelp at the Falkland Islands (Islas Malvinas)

Giant kelp populations support productive and diverse coastal ecosystems in both hemispheres at temperate and subpolar latitudes but are vulnerable to changing climate conditions as well as direct human impacts. Observations of giant kelp forests are spatially and temporally patchy, with disproportionate coverage in the northern hemisphere, despite the size and comparable density of southern hemisphere kelp forests. Satellite imagery enables the mapping of existing and historical giant kelp populations in understudied regions, but automating the detection of giant kelp in large satellite datasets requires approaches that are robust to the optical complexity of the shallow, nearshore environment. We present and compare two approaches for automating the detection of giant kelp in satellite datasets: one based on crowd sourcing of satellite imagery classifications and another based on a decision tree paired with a spectral unmixing algorithm (automated using Google Earth Engine). Both approaches are applied to satellite imagery (Landsat) of the Falkland Islands or Islas Malvinas (FLK), an archipelago in the southern Atlantic Ocean that supports expansive giant kelp ecosystems. The performance of each method is evaluated by comparing the automated classifications with a subset of expert-annotated imagery cumulatively spanning over 2,700km of coastline. Using the remote sensing approaches evaluated herein, we present the first continuous timeseries of giant kelp observations in the FLK region using Landsat imagery spanning over three decades. We do not detect evidence of long-term change in the FLK region, although we observe a recent decline in total canopy area from 2017-2021. Using a nitrate model based on nearby ocean state measurements obtained from ships and incorporating satellite sea surface temperature products, we find that the area of giant kelp forests in the FLK region is positively correlated with the nitrate content observed during the prior year. Our results indicate that giant kelp classifications using citizen science are approximately consistent with classifications based on a state-of-the-art automated spectral approach. Despite differences in accuracy and sensitivity, both approaches find high interannual variability that impedes the detection of potential long-term changes in giant kelp canopy area, although recent canopy area declines are notable and should continue to be monitored carefully.

ecology↗