Does nitrogen mediate the interaction among animals, seaweeds and microbes?

What is the role of regenerated nitrogen in coastal systems?

Although it is recognized that the upwelling of nitrogen-rich water is a source of productivity in the northeast Pacific, our experiments and observations are also revealing that animal excretion is a significant source of ammonium in coastal waters and tidepools. Algal productivity within tidepools is boosted several-fold by the presence of mussels (Pfister 2007) and seawater in close proximity to Tatoosh Island has elevated ammonium levels compared with seawater away from the Island (Pfister et al. 2007). In collaboration with Mark Altabet and Santhiska Pather at UMass and David Post at Yale University, we have used stable isotopes in conjunction with enrichment experiments to quantify how regenerated nutrients supplied by animals affects microbial populations and coastal primary productivity. 

Using tracer ammonium, we find that high rates of ammonium regeneration are matched by rapid ammonium uptake, highlighting the importance of local nitrogen supply (Pather et al. 2014, L&O).

We have also compared the relative role of ammonium versus nitrate in nearshore and corresponding offshore areas and areas with increased and reduced animal abundance. We find that nearshore areas, particularly in the vicinity of the animal-rich Tatoosh Island, have a strong signal of nitrogen regenerated through animals and microbes (Pfister et al. 2014, Ecology). Our experiments indicate that microbial nitrogen transformations in the rocky intertidal are orders of magnitude more than open ocean areas, and that the California mussel contributes to this microbial nitrogen processing (Pfister et al. 2016, Biogeosciences).

Microbial nitrogen transformations seems ubiquitous in these coastal areas and, in collaboration with researchers at nearby Argonne National Labs (Folker Meyer, Dion Antonopoulos), we have sequenced microbial populations of Tatoosh Island to understand both the identity and function of microbes in this system (Pfister et al 2010, Pfister et al. 2014). We are currently looking at the diversity of mussel-associated microbes with 16s methods (collaborative with Jack Gilbert at UChicago and ANL) and the Earth Microbiome Project.

The new Microbiome Center at the University of Chicago is building collaboration and discovery among University of Chicago, Argonne National Labs and the Marine Biological Lab in Woods Hole. There is more about the collaboration here.  Our collaborative work already recognizes the importance of marine macrobiota as hosts for microbial diversity and function (Moulton et al. 2016, Frontiers in Ecology and the Environment).

Graduate student Orissa Moulton is investigating the nature of microbe and seaweed interactions along rocky shores, through manipulations at Friday Harbor Marine Labs.

This work was funded, in part, by an NSF grant from Ocean Sciences, #09-28232 to Pfister, Altabet and Post.

This cake tells the story . . . seabirds such as gulls play an important role in regenerating nutrients and contributing to a rich and diverse rocky intertidal.
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