My research program focuses on understanding ecological dynamics from the level of species interactions, through population and community ecology, to processes that link ecosystems in landscapes. Of particular interest to me are the ways in which human activities modify ecosystems on local scales, and how these small-scale changes influence dynamics on larger scales. I use kelp forests and seagrasses as model ecosystems, believing that they provide an interesting and tangible setting to explore questions in basic ecology and biology within the context of pressing local and global management issues.
Kelp carbon flow through detrital pathways
Over 80% of primary productivity in kelp forests enters detrital pathways, fueling high biodiversity and secondary production within kelp forests and in adjacent communities that are subsidized by kelp detritus (Krumhansl & Scheibling 2012 Marine Ecology Progress Series). Very little is known about dynamics of detrital production and processing in kelp forests despite the importance of this energy pathway in temperate coastal systems. Further, little attention has been directed towards understanding how anthropogenic stressors alter the magnitude and quality of material flowing through detrital pathways. This research has implications for coastal food webs, kelp population dynamics, and the long-term persistence of kelp forests.
My PhD work focused on examining spatial and temporal variation in the rate of detrital production from kelp forests in Nova Scotia, and identified key environmental variables and biotic interactions that directly and indirectly influence this rate (Krumhansl & Scheibling 2011 Marine Ecology Progress Series, Krumhansl & Scheibling 2011 Aquatic Biology, Krumhansl et al. 2011 Journal of Experimental Marine Biology and Ecology, O’Brien et al. 2013 Journal of the Marine Biological Association of the UK, Krumhansl et al. 2016 American Journal of Botany). My research showed that the magnitude of kelp blade fragmentation and loss drove seasonal changes in standing kelp biomass (Krumhansl & Scheibling 2011 Marine Ecology Progress Series). We used our empirical measurements to model the impact of changes in climate on detrital production rates and kelp biomass, predicting long-term losses of kelp with increases in temperature and wave action (Krumhansl et al. 2014 Ecology).
Trophic linkages between near shore ecosystems
Subsidy by kelp detritus influences the biodiversity, secondary production, and ecological dynamics in recipient systems, and is an important mechanism by which local dynamics within kelp forests are linked to dynamics occurring on larger spatial scales (Krumhansl & Scheibling 2012 Marine Ecology Progress Series, Kelly et al. 2012 Marine Ecology Progress Series). Anthropogenic stressors may alter the phenology and magnitude of cross-ecosystem exchanges of algal detritus through species range shifts and changes in species abundance, primary production, and decomposition rates. Little attention has been directed towards understanding how trophic subsidies in general are altered by human activities, and what consequences this has for subsidized communities.
My PhD research in Nova Scotia demonstrated that kelp detritus is an important subsidy for invertebrate communities in habitats offshore of kelp beds, influencing spatial patterns in the production and reproductive potential of sea urchins in rocky habitats, and diversity of faunal communities in soft sediments (Kelly et al. 2012 Marine Ecology Progress Series, Krumhansl & Scheibling 2012Marine Ecology Progress Series). Our work also demonstrated that subsidized communities respond to shifts in the algal species composition of detritus due to differences in nutritional quality (Krumhansl & Scheibling 2012 Marine Ecology Progress Series).
Climate change impacts on kelp ecosystems globally
Many kelp ecosystems around the world are undergoing phase shifts from kelp to algal turf dominated ecosystems. This has consequences for net ecosystem production, biodiversity, and the magnitude and nature of trophic subsidies to adjacent ecosystems. As part of a working group at the National Center for Ecological Analysis and Synthesis (https://www.nceas.ucsb.edu/), I’ve been collaborating with kelp forests ecologists around the world to synthesize knowledge and data surrounding the impacts of climate change on kelp ecosystems globally (Krumhansl et al. 2016 PNAS). Some of the key questions we’re addressing are: 1) How has the abundance of kelp changed globally over the past 50 years? 2) What is known about how kelp systems respond to multiple anthropogenic stressors? 3) What is the predicted response of strongly interacting species in kelp systems to changes in climate and local stressors such as fishing and nutrient run-off? My research also investigates the mechanisms behind losses of kelp dominance (O’Brien et al. 2015 Marine Ecology Progress Series).
Linking ecosystem change to shifts in ecological function
Human activities have complex impacts on marine ecosystems. Changes in species abundance and diversity are often used to characterize these impacts, despite wide recognition that these metrics may not align with changes in ecosystem functioning. One of my emerging areas of research is to investigate how shifts in species abundances and diversity link to changes in they key functions provided by coastal ecosystems. In particular, I’ve done work to compare more traditional metrics of ecological impact (e.g. species richness, abundance, and diversity) to trait-based approaches, which utilize shifts in the abundances of key biological traits to indicate shifts in ecosystem function (Krumhansl et al. 2015 Journal of Environmental Science and Technology, Krumhansl et al. 2016 Ecological Indicators). I am also interested in how conservation and management can be designed to more specifically target the protection of ecosystem functioning in biogenic habitats.
Shifts in kelp ecosystem services
Local stressors (e.g. fishing) have the potential to interact with global stressors (e.g. climate change) to cause rapid changes in kelp ecosystems. This has significant implications for local management efforts. In collaboration with the Heiltsuk First Nation in British Columbia, we are conducting research examining how harvesting canopies of Macrocystis integrifolia and Egregia menziesii impacts kelp ecosystem services. Of particular interest is the role of the environmental context in mediating the impacts of kelp canopy harvest on the productivity, reproductive output, and survival of the kelps, and associated rockfish and invertebrate species. This research is being used to guide harvest management practices for these key ecosystem-forming species in Heiltsuk territory and beyond.