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Death by Ulva
Citation:
Watson, E., C. Wigand, A. Oczkowski, K. Sundberg, D. Vendettuoli, K. Saliba, AND J. Morris. Death by Ulva. Presented at New England Estuarine Research Society (NEERS) Spring Meeting, Salem, MA, May 01 - 03, 2014.
Impact/Purpose:
This presentation will share information on recent findings on negative impacts of the macroalgae, Ulva, on salt marsh plant growth.
Description:
We report on a series of field and laboratory mesocosm experiments where we examined the effects of two levels of decomposing Ulva on Spartina alterniflora growth, soil biogeochemistry, and nitrogen dynamics. Monitoring of porewater revealed rapid mineralization to ammonium from decomposing Ulva, with porewater levels quickly attaining potentially toxic concentrations. In addition, Ulva soil amendments were associated with elevated porewater sulfide levels. Plant uptake of Ulva-derived nitrogen was documented using an 15N label, but higher nitrogen availability did not subsidize growth. In fact, higher levels of Ulva exposure resulted in pronounced reductions in above and belowground productivity, while lower levels of Ulva exposure resulted in reductions in belowground productivity only. Our findings support the hypothesis that decaying Ulva mats may create hotspots of adverse physiochemical conditions in salt marshes, similar to those reported for benthic and tidal flat habitats. Furthermore, decaying Ulva mats may compromise the erosion resistance of salt marshes via decreased plant belowground biomass. We conclude that additional field and laboratory studies are needed to establish more concretely which Ulva related stressors are primary, and whether similarly adverse responses are observed under natural field conditions.