Ammonium cycling in the rocky intertidal: Remineralization, removal, and retention

Santhiska Pather, Catherine A. Pfister, David M. Post and Mark A. Altabet

Limnol. Oceanogr., 59(2), 2014, 361-372 | DOI: 10.4319/lo.2014.59.2.0361

ABSTRACT: Rocky intertidal productivity is traditionally thought to be sustained almost solely by upwelled nitrate with remineralized forms of minor importance. Using tidepools as natural experimental mesocosms, we conducted 15N-tracer experiments to test whether ammonium remineralized within the rocky intertidal is also a significant source of fixed N to localized ecosystem production. Comparison of tidepools with and without the dominant bivalve Mytilus californianus allowed consideration of its role in cycling. Closed water-incubation bottles were used to investigate the contribution of suspended microbes to cycling. Tidepools with mussels had both greater remineralization (two times) and removal as compared with those without, with daytime rates greater than nighttime rates. Incorporation of tracer by particulate organic matter and macroalgae, and the persistence of this signal in tidepools for several days following the experiment, showed retention of autochthonous in the system. Remineralization rates were tightly correlated to removal rates when compared over all treatments and experiments, but remineralization was significantly greater than removal, suggesting a surplus available to nearshore primary producers.

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