Menden-Deuer Lab

Planktonic organisms are fascinating and important to study. These single-celled eukaryotes are ecologically and phylogenetically diverse, globally important and methodologically tractable. Plankton are major conduits of matter and energy in the surface ocean. Plankton feed fisheries production, facilitate global cycles of carbon, nitrogen and many other elements. Plankton are subject to anthropogenic and environmental change. These broad ecosystem functions make it paramount to gain a mechanistic understanding of plankton population dynamics.

Research in the Menden-Deuer lab aims to improve our understanding and predictive ability of plankton and their function in the environment. Predator-prey interactions are the central topic. Our research is guided by three foci: 

• the importance of spatial-scales to ecological processes, 
• the importance of species and strain-specific differences
• the importance of individual level behaviors in ecological interactions. 

We devote considerable effort to developing new empirical methods, analytical tools and statistical techniques.

We approach the study of plankton ecology by studying small-scale individual processes (such as predator/prey interactions) to try to understand large-scale, population processes (such as phytoplankton blooms). In our work, we combine approaches used in ecology, mathematical modeling and computer-assisted video analysis. This research is conducted in-situ, in-vitro and in-silico. Philosophically, we strive to test the relevance of our modeling and laboratory results under realistic conditions in the coastal ocean. As web pages are difficult to keep up to date, our publications are the best source for information.

Currently funded research includes:

1. Quantifying biological drivers of plankton patch formation

This field-work in a shallow, coastal fjord (East Sound, Orcas Island, Washington) aims to determine how much growth and mortality of plankton contribute the the formation of plankton patches, their persistence and decline. Combining frequent small boat surveys with laboratory measurements, we concurrently quantify the physical, chemical and biological parameters associated with patch occurrence and dissipation with biologically meaningful resolution (meters and days).

This work is funded by the Office of Naval Research and results were published in Menden-Deuer (2008), Menden-Deuer & Fredrickson, (2010)

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2. Identifying regulatory mechanisms for Heterosigma akashiwo bloom formation: predation interactions with algal behavior and resource use

This collaborative project, together with Suzanne Strom (WWU) and her lab investigates the regulation of Heterosigma akashiwo blooms by protistan predators. H. akashiwo causes fish kills yearly in coastal waters of the Pacific. Food web interactions involving H. akashiwo, a raphidophyte that may have multiple modes of toxicity, are poorly understood. Our study focuses on the interactions between H. akashiwo layer-forming behavior, nutrient use, and susceptibility to predation mortality. Predation and behavioral experiments will utilize heterotrophic protists, the major consumers of phytoplankton in the world’s oceans, and will address both toxicity and predator deterrence as phenomena with different implications for bloom formation and maintenance. This is a novel approach that integrates traditionally separate ‘bottom up’ and ‘top down’ aspects of HAB ecology.

This work is funded by EPA/NOAA's ECOHAB: Ecology and Oceanography of Harmful Algal Blooms project. Results were presented at the international Harmful Algae meeting in Hong Kong (Nov. 2008), and in Crete (Nov 2010). Publications to date from this project are Menden-Deuer et al. 2010 and Harvey & Menden-Deuer 2011 as well as Graham & Strom 2010.
 
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3. Deciphering planktonic predator-prey interactions: a mechanistic approach

This research combines theoretical and emperical approaches to measure planktonic predator-prey interactions at the individual-level and embed these empirical observations in a theoretically-motivated model that predicts predator distributions and consumption rates. The motivation for this study is that although heterotrophic protists are important consumers of phytoplankton biomass and productivity in marine microbial food webs, we still have an incomplete understanding of the processes that drive ecologically relevant rates of plankton growth and mortality. The large number of biological and abiotic variables makes it impossible to quantify phytoplankton predation rates by heterotrophic protists empirically.

A major obstacle in understanding the population dynamics and ecology of marine planktonic food webs is rooted in the mismatch in investigative scales: uptake of nutrients and prey, that drive plankton growth and grazing rates, occur at the microscopic, individual level, whereas their ecological significance and most of our investigations occur at much larger scales. However, processes at these separate scales are tightly linked because there is a causative relationship and feedback between organisms’ microscopic interactions and the ultimate, macroscopic predator abundance and ecological function. To overcome this missmatch in scales, I combine video analysis of microscopic predator-prey interactions and population distributions with traditional methods of measuring prey disappearance and predator growth through enumeration at the population level. Together, these three independent measures aim to identify key factors necessary to characterize predator foraging behaviors and success.

Comparison of these redundant but independent measures provides the opportunity to identify key factors essential to predicting predation rates. Tight integration of laboratory and theoretical work will improve model assumptions, validate model predictions and most importantly, provide a tool that parameterizes a complex biological process. Ultimately, a mechanistic understanding of protist foraging behaviors is key to predicting the ecological role of these phytoplankton predators and thus, the population dynamics of planktonic food webs.


This work is funded by the National Science Foundation. The results were presented at several meetings, including the invited speaker to a Microbial interactions session at ASLO 2009. Publications to date are Menden-Deuer 2010 and Harvey & Menden-Deuer 2011.

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