Bennett Endowed Lecture: Drought, floods, and alternate states in algal-based river food webs: The thirsty Eel

How too much or too little water affects the nutrient balance in rivers.

Discharge is the master variable controlling river food webs and algal-mediated river-ocean linkages in the Eel and other rivers of Northwestern California.  Algal proliferations in river mainstems are initially dominated by filamentous green macroalgae (Cladophora glomerata). Over the summer growth period, Cladophora streams become overgrown with highly edible diatoms. Under extremely low summer base flows, however, cyanobacteria, some toxic, can smother Cladophora-diatom growths. 

Both diatoms and cyanotoxins are exported from the Eel to the coastal ocean. If summer droughts (and human water extraction) intensify under greenhouse warming, food chains could shorten further, from two to one trophic level, if warm stagnant conditions favor toxic cyanobacteria, recently linked to a number of dog deaths in the Eel River and to sea otter deaths offshore from Monterey Bay. Academic, agency, and citizen scientists are rallying throughout North Coast watersheds to monitor flow changes and their ecological consequences, and to discuss and implement ways to steward the Eel through the prolonged droughts that may lie ahead.

Dr. Mary E. Power is Professor in the Department of Integrative Biology at the University of California, Berkeley. She is also the Faculty Director of the Angelo Coast Range Reserve, an 8000-acre natural reserve protected for university teaching, research, and outreach. Power studies food webs in temperate and tropical rivers. Her research is often framed as "predictive mapping": by studying how controls over key ecological interactions change over space and time, she seeks insights that will help forecast how river-structured ecosystems will respond to watershed or regional scale changes in climate, land use, or biota.