Research

Overview: Modern oceans are in an era of extraordinary change, reflecting increasing anthropogenic disturbance on top of longer-term natural climate variability. The McMahon lab is actively engaged in basic and applied research to examine the roles that food web architecture play in the function and resilience of marine ecosystems, and how climate change and human-environment interactions alter those relationships. Through controlled feeding experiments, our lab develops a quantitative understanding of the biochemical and physiological mechanisms that control resource acquisition and allocation. We then apply this knowledge in large-scale field studies to examine a wide range of questions from individual nutritional ecology and population connectivity to ecosystem-scale food web dynamics and the functioning of the biological pump. While the McMahon Lab’s research program is firmly rooted in fundamental oceanographic theory, it extends beyond the basic research questions to address the applied management and practical decision-making needed to resolve current and emerging coastal ocean challenges. This research is directly relevant to the recent decadal review of ocean science by The National Academy of Sciences, which highlighted 1) the relationship between ocean biogeochemical cycling and earth’s climate and 2) changes in food web structure over the next 50 to 100 years as high priority questions in ocean science over the next decade.

 

Gentoo penguin incubating an egg on the Antarctic Peninsula (Photo: Kelton McMahon)

The Southern Ocean is a classic “canary in the coalmine” for the impacts of rapid climate change and anthropogenic disturbance on ecosystem function and resilience. This research provides an unprecedented look into how past climate change and historic whaling altered polar food webs through time, using penguins as bioindicators of ecosystem health. This research provides a window into predicted future food web responses in a rapidly warming World.

 

 

 

 

Hawaiian gold coral is a long-lived, deep-sea coral found in the North Pacific Ocean. (Photo credit: HURL)

Deep-sea proteinaceous corals serve as “living sediment traps,” recording geochemical information about the organic matter sinking to depth from the sunlit surface ocean. In these projects, we are applying molecular geochemistry tools to deep-sea proteinaceous corals to reconstruct past changes in phytoplankton community dynamics and biogeochemical cycling on decadal to millennial time scales. This work provides insights into how changing food web architecture influences everything from ocean productivity to biogeochemical cycling and the efficacy of the biological pump.

 

 

  • Coastal Ecosystem Food Web Dynamics:
Large school of snapper on reefs of the Phoenix Islands Protected Area (Photo: Mark Priest)

Coastal marine ecosystems are among the most productive and biodiverse ecosystems on Earth and provide critical goods and services to humans. These systems are also under tremendous pressure from direct and indirect human-environment interactions. Our research looks to address how food web architecture influences the structure, function, and resilience of coastal ecosystems by quantifying the sources and cycling of organic matter supporting coastal food webs.

 

 

Photo (koi.pt)

Through controlled laboratory experiments, our lab seeks to better understand the underlying biochemical and physiological mechanisms behind how organisms acquire, modify, and allocate dietary resources. The two primary foci of our controlled laboratory studies are to: 1) develop, expand, and refine amino acid carbon isotope fingerprinting to reconstruct the phylogenetic identity of primary producers fueling food web dynamics, and 2) quantify mechanisms of nitrogen isotope fractionation associated with trophic transfer. In doing so, this work advances the development of cutting-edge new CSIA tools while also improving our understanding of organismal nutritional ecology.