Karina J. Nielsen

Are meta‐ecosystems organized hierarchically? A model and test in rocky intertidal habitats

Ecosystems are shaped by processes occurring and interacting over multiple temporal and spatial scales. Theory suggests such complexity can be simplified by focusing on processes sharing the same scale as the pattern of interest. This scale-dependent approach to studying communities has been challenged by multiscale meta-ecosystem theory, which recognizes that systems are interconnected by the movement of “ecological subsidies” and suggests that cross-scale feedbacks between local and regional processes can be equally important for understanding community structure. We reconcile these two perspectives by developing and testing a hierarchical meta-ecosystem model. The model predicts local community responses to connectivity over multiple oceanographic spatial scales, defined as macro- (100s of km), meso- (10s of km), and local scale (100s of m). It assumes that local communities occur in distinct regions and that connectivity effects are strongest among local sites. Predictions are that if macroscale proce...

Persistent spatial structuring of coastal ocean acidification in the California Current System

The near-term progression of ocean acidification (OA) is projected to bring about sharp changes in the chemistry of coastal upwelling ecosystems. The distribution of OA exposure across these early-impact systems, however, is highly uncertain and limits our understanding of whether and how spatial management actions can be deployed to ameliorate future impacts. Through a novel coastal OA observing network, we have uncovered a remarkably persistent spatial mosaic in the penetration of acidified waters into ecologically-important nearshore habitats across 1,000 km of the California Current Large Marine Ecosystem. In the most severe exposure hotspots, suboptimal conditions for calcifying organisms encompassed up to 56% of the summer season, and were accompanied by some of the lowest and most variable pH environments known for the surface ocean. Persistent refuge areas were also found, highlighting new opportunities for local adaptation to address the global challenge of OA in productive coastal systems.

The complex net effect of reciprocal interactions and recruitment facilitation maintains an intertidal kelp community

Summary 1. Theoretical and empirical ecology has transitioned from a focus on the role of negative interactions in species coexistence to a more pluralistic view that acknowledges that coexistence in natural communities is more complex, and depends on species interactions that vary in strength, sign, and reciprocity, and such contexts as the environment and life-history stage. 2. We used a whole-community approach to examine how species interactions contribute to the maintenance of a rocky intertidal macroalgal canopy–understorey assemblage. We determined both the types of interactions in this network, and whether interactions were sensitive to environmental gradients. 3. Focusing on a structurally dominant canopy kelp Saccharina sessilis, and its diverse co-occurring understorey assemblage, we evaluated the role of the understorey in controlling S. sessilis recruitment and quantified the reciprocal effect of the S. sessilis canopy and understorey on one another using a removal experiment replicated across 600 km of coastline. We determined the sensitivity of interactions to natural variation in light and nutrient availability (replicated among four regions on the N.E. Pacific coast), and under different wave conditions (three wave regimes). 4. Surprisingly, species interactions were similar across sites and thus not context-dependent. Unexpectedly, the understorey community had a strong positive effect on the S. sessilis canopy, whereby the adult canopy decreased dramatically following understorey removal. Additionally, S. sessilis recruitment depended on the presence of understorey coralline algal turf. In turn, the canopy had a neutral effect on the coralline understorey, but a negative effect on non-calcifying algal turfs, likely eventually generating positive indirect canopy effects on the coralline understorey. Densitydependent intraspecific competition between S. sessilis adults and recruits may moderate this positive feedback between the S. sessilis canopy and coralline understorey. 5. Synthesis. Our research highlights the importance of positive interactions for coexistence in natural communities, and the necessity of studying multiple life-history stages and reciprocal species interactions in order to elucidate the mechanisms that maintain diversity.

An ecological framework for informing permitting decisions on scientific activities in protected areas

There are numerous reasons to conduct scientific research within protected areas, but research activities may also negatively impact organisms and habitats, and thus conflict with a protected area’s conservation goals. We developed a quantitative ecological decision-support framework that estimates these potential impacts so managers can weigh costs and benefits of proposed research projects and make informed permitting decisions. The framework generates quantitative estimates of the ecological impacts of the project and the cumulative impacts of the proposed project and all other projects in the protected area, and then compares the estimated cumulative impacts of all projects with policy-based acceptable impact thresholds. We use a series of simplified equations (models) to assess the impacts of proposed research to: a) the population of any targeted species, b) the major ecological assemblages that make up the community, and c) the physical habitat that supports protected area biota. These models consider both targeted and incidental impacts to the ecosystem and include consideration of the vulnerability of targeted species, assemblages, and habitats, based on their recovery time and ecological role. We parameterized the models for a wide variety of potential research activities that regularly occur in the study area using a combination of literature review and expert judgment with a precautionary approach to uncertainty. We also conducted sensitivity analyses to examine the relationships between model input parameters and estimated impacts to understand the dominant drivers of the ecological impact estimates. Although the decision-support framework was designed for and adopted by the California Department of Fish and Wildlife for permitting scientific studies in the state-wide network of marine protected areas (MPAs), the framework can readily be adapted for terrestrial and freshwater protected areas.