Non-Trophic Role of Animals in Mediation of Algal-Microbial Interactions Via the Nitrogen Cycle

EPA Grant Number: FP917489
Title: Non-Trophic Role of Animals in Mediation of Algal-Microbial Interactions Via the Nitrogen Cycle
Investigators: Moulton, Orissa Merritt
Institution: University of Chicago
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2012 through August 31, 2015
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2012) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecology


This study will address two questions: (1) Is the relationship between nitrogen-utilizing microbes and seaweeds competitive (negative) or facilitative (positive) in terms of ammonium use, and how is the net interaction among microbes and macroalgae mediated by the supply of nitrogen? (2) How do rocky intertidal microbial communities vary at the landscape scale and across a gradient of faunal nitrogen input, specifically in terms of high animal biomass marine preserve/corresponding control comparisons?


This work will be conducted in NW Washington state, with mesocosm experiments at the University of Washington Friday Harbor Laboratories and field work in the San Juan Islands and along the Strait of Juan de Fuca. The study will use mesocosm manipulations, stable isotopes (natural abundance in tissues samples and enrichment in small-scale tracer experiments), and microbial metagenomics to test the net effect of microbial metabolism and N transformation on primary producers, particularly seaweeds, to determine how the net interaction among microbes and seaweeds is mediated by the supply of nitrogen. The study will investigate the effect of high animal biomass marine preserves on algal productivity and microbial metabolism via microbial settlement surveys, environmental monitoring, stable isotopes and microbial metagenomics. These comparative methods will quantify how microbes contribute to rocky shore productivity via interactions with ammoniumexcreting animals and the microbial potential to retain nitrogen in coastal waters in marine preserves versus corresponding control sites.

Expected Results:

Animals play a quantitative role as nitrogen recyclers in shallow marine systems, so seaweed and microbe communities dependent on ammonium excretion are linked intimately to animal community abundance. Ammonium constitutes a shared resource for seaweeds and microbes, so microbial nitrification could pose a competitive (negative) force on seaweeds via rapid removal of ammonium from the water column. By utilizing ammonium, though, nitrifying microbes could facilitate (positively affect) seaweed productivity by retaining nitrogen onshore as nitrate and nitrite in high-energy areas where nitrogen advection is expected. Both interaction signs are likely to occur under different environmental contexts. In regions where marine animal density has decreased as a result of overharvest, onshore seaweed-microbe interactions likely will be modified due to a reduction in available ammonium.

Potential to Further Environmental/Human Health Protection
Improved knowledge of natural nitrogen-cycling and development of a predictable nitrogen budget for primary producers will allow for better protection of the temperate coastlines, where fisheries are most developed. Understanding the responses of microbes and seaweeds globally to changing environmental factors (e.g., temperature, pH, N-availability) will improve the ability to predict specific responses of rocky intertidal microbes, including community composition and function shifts. Ideally, marine reserves are sited based on criteria that maintain biodiversity and ecosystem functioning at large scales; this work will evaluate the effectiveness of restricted-use marine reserves for ecosystem-scale nitrogen cycling and disentangle linkages between ecosystem function and environmental context.

Supplemental Keywords:

non-trophic interactions, microbial ecology, nitrogen cycle

Progress and Final Reports:

  • 2013
  • 2014
  • Final