Caselle, J. | Search bioRxiv

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

Drivers of spatio-temporal variability in a marine foundation species

Marine foundation species are critical for the structure and functioning of ecosystems and constitute the pillar of trophic chains while also providing a variety of ecosystem services. In recent decades many foundation species have declined in abundance, sometimes threatening their current geographical distribution. Kelps (Laminariales) are the primary foundation species in temperate coastal systems worldwide. Kelp ecosystems are notoriously variable and identifying the key factors that control the dynamics of kelp abundance is key to predicting the fate of kelp ecosystems under climatic change and informing management and conservation decisions such as forest restoration. Here, we used in situ data from long-term monitoring programs across 1,350 km of coast spanning multiple biogeographic regions in the state of California (USA) to identify the major regional drivers of density of two dominant canopy-forming kelp species and to elucidate the spatial and temporal scales over which they operate. We used generalized additive models to identify the key drivers of density of two dominant kelp species (Nereocystis luetkeana and Macrocystis pyrifera) across four ecological regions of the state of California (north, central, south-west and south-east) and for the past two decades (2004-2021). Our study identified that the dominant drivers of kelp density varied between regions and species but always included some combination of nitrate availability, wave energy and exposure, density of purple sea urchins, and temperature as the most important predictors explaining 63% of the variability of bull kelp in the north and central regions, and 45% and 51.4% of the variability in giant kelp for the central/south-west and south-east regions, respectively. These large-scale analyses infer that a combination of lower nutrient availability, changes in wave energy and exposure, and increases in temperature and purple sea urchin counts have contributed to the decline of kelp observed in the last decade. Understanding the drivers of kelp dynamics can be used to identify regions and periods of significant change and historical stability, ultimately informing resource management and conservation decisions such as site selection for kelp protection and restoration. Open research statementData (Giraldo-Ospina et al. 2023) are available in DataOne at doi:10.25494/P6/When_where_and_how_kelp_restoration_guidebook_2.

ecology↗