Toward a conceptual framework for managing and conserving marine habitats: A case study of kelp forests in the Salish Sea

Abstract

Kelp forests are in decline across much of their range due to place‐specific combinations of local and global stressors. Declines in kelp abundance can lead to cascading losses of biodiversity and productivity with far‐reaching ecological and socioeconomic consequences. The Salish Sea is a hotspot of kelp diversity where many species of kelp provide critical habitat and food for commercially, ecologically, and culturally important fish and invertebrate species. However, like other regions, kelp forests in much of the Salish Sea are in rapid decline. Data gaps and limited long‐term monitoring have hampered attempts to identify and manage for specific drivers of decline, despite the documented urgency to protect these important habitats. To address these knowledge gaps, we gathered a focus group of experts on kelp in the Salish Sea to identify perceived direct and indirect stressors facing kelp forests. We then conducted a comprehensive literature review of peer‐reviewed studies from the Salish Sea and temperate coastal ecosystems worldwide to assess the level of support for the pathways identified by the experts, and we identified knowledge gaps to prioritize future research. Our results revealed major research gaps within the Salish Sea and highlighted the potential to use expert knowledge for making informed decisions in the region. We found high support for the pathways in the global literature, with variable consensus on the relationship between stressors and responses across studies, confirming the influence of local ecological, oceanographic, and anthropogenic contexts and threshold effects on stressor–response relationships. Finally, we prioritized areas for future research in the Salish Sea. This study demonstrates the value expert opinion has to inform management decisions. These methods are readily adaptable to other ecosystem management contexts, and the results of this case study can be immediately applied to kelp management.

Microclimate predicts kelp forest extinction in the face of direct and indirect marine heatwave effects

“…The effective management of kelp forest ecosystems will depend on our ability to understand and mitigate the stressors limiting their resilience and distributions (Hollarsmith et al, 2022); our data contribute critical insights in this regard. Our study illustrates how variation within even a relatively small region could lead to substantially different levels of resilience across local kelp forest habitats, and this should be considered when designing monitoring schemes or interpreting monitoring data.…”

Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana, Phaeophyceae)

“…In a warming global ocean, it is critical to determine the thermal tolerance of foundation species such as bull kelp so that we can model the future effects of climate change on kelp forest ecosystems. Although we cannot lower seawater temperatures in the Salish Sea without significant efforts to mitigate climate change on a global scale, we can use this information to prioritize management and conservation actions (Hollarsmith et al, 2022). We observed that high nitrogen concentrations did not enhance the survival of microscopic stages of bull kelp that were exposed to elevated temperatures.…”

Temperature and food chain length, but not latitude, explain region-specific kelp forest responses to an unprecedented heatwave

“…Evidence collected over the past two or more decades indicates that kelp forests are decreasing in abundance and extent across certain parts of the world due to combined effects of climate change and localized threats, including fishing, sewage run-off, invasive species and changes in freshwater outflow (Krumhansl et al, 2016; Filbee-Dexter & Wernberg, 2018; Wernberg et al, 2019; Hollarsmith et al, 2022). However, the trajectories of kelp forests around the world have been highly variable, with some regions showing stability (e.g., Chile and the Falkland Islands; Mora-Soto et al, 2021) or even increases in abundance (e.g., South Africa; Bolton et al, 2012), highlighting the importance of refugia at global, regional and local scales (Krumhansl et al, 2016; Wernberg et al, 2019).…”

“…Various abiotic and biotic factors may make kelp more resilient in the face of warming and shifts in trophic dynamics (Hollarsmith et al, 2022). Spatial variation in temperature and other environmental variables can mediate the responses of kelp forests to large-scale warming (Wernberg et al, 2016; Cavanaugh et al, 2019; Starko et al, 2019; Filbee-Dexter et al, 2020), with factors like water motion, upwelling dynamics, and nutrient pollution leading to complexity in the distribution of environmental variation across the coastal fringe (Druehl, 1978; Hollarsmith et al, 2022; Spiecker & Menge, 2022; Starko et al, 2022).…”

“…Various abiotic and biotic factors may make kelp more resilient in the face of warming and shifts in trophic dynamics (Hollarsmith et al, 2022). Spatial variation in temperature and other environmental variables can mediate the responses of kelp forests to large-scale warming (Wernberg et al, 2016; Cavanaugh et al, 2019; Starko et al, 2019; Filbee-Dexter et al, 2020), with factors like water motion, upwelling dynamics, and nutrient pollution leading to complexity in the distribution of environmental variation across the coastal fringe (Druehl, 1978; Hollarsmith et al, 2022; Spiecker & Menge, 2022; Starko et al, 2022). For example, while inland waters may warm up in the summer, areas on the outer coast with high wave exposure or currents can stay cool and nutrient rich through upwelling and mixing, potentially facilitating kelp persistence (Berry et al, 2021; Starko et al, 2022).…”