Feedbacks between flooding and plant growth that help to stabilize marshes against rising sea level are being investigated in estuaries at Plum Island, Massachusetts, and North Inlet, South Carolina. Net annual primary production of the marsh grass Spartina alterniflora has been quite variable through the years, and correlates positively with sea level during the growing season at both sites. The elevation of the marsh surface relative to mean high water determines the duration of flooding, or hydroperiod, that in turn affects plant growth. The effect of flooding was tested experimentally using an in situ bioassay to simulate growth at different relative elevations. At North Inlet, we found a parabolic response to relative elevation, with clear evidence of minimum and maximum vertical limits and an optimal elevation for growth. The Plum Island bioassay provided evidence of the super-optimal side of the growth curve. In both marshes, the responses of S. alterniflora to rising sea level, at their current elevations, are consistent with the bioassay results. This growth curve is important because it defines suboptimal elevations that are unstable for marshes and super-optimal elevations that are stable. Instability results when an increase in sea level decreases primary production, leading to declines in mineral sedimentation and sediment organic matter accretion. Conversely, stability results when rising sea level stimulates primary production, leading to increased sedimentation and organic matter accretion. There also has been interannual variability in the maximum standing biomass (a proxy for productivity) of another marsh grass, Spartina patens, but no significant correlation has been found with sea level, possibly due to methodological limitations. Finally, both Spartina species responded positively to nitrogen and have remained highly productive for 13 years of fertilization at Plum Island and 30 years at North Inlet.

Morris, J.T., K. Sundberg, and C.S. Hopkinson. 2013. Salt marsh primary production and its responses to relative sea level and nutrients in estuaries at Plum Island, Massachusetts, and North Inlet, South Carolina, USA. Oceanography 26(3):78–84, https://doi.org/​10.5670/oceanog.2013.48.

Anisfeld, S.C., and T.D. Hill. 2011. Fertilization effects on elevation change and belowground carbon balance in a Long Island Sound tidal marsh. Estuaries and Coasts 35:201–211, https://doi.org/10.1007/s12237-011-9440-4.

Baart, F., P.H.A.J. van Gelder, J. de Ronde, M. van Koningsveld, and B. Wouters. 2012. The effect of the 18.6-year lunar nodal cycle on regional sea-level rise estimates. Journal of Coastal Research 28:511–516, https://doi.org/10.2112/JCOASTRES-D-11-00169.1.

Barbier, E.B., S.D. Hacker, C. Kennedy, E.W. Koch, A.C. Stier, and B.R. Silliman. 2011. The value of estuarine and coastal ecosystem services. Ecological Monographs 81:169–193, https://doi.org/10.1890/10-1510.1.

Blum, L.K., and E. Davey. 2013. Below the salt marsh surface: Visualization of plant roots by computer-aided tomography. Oceanography 26(3):85–87, https://doi.org/​10.5670/oceanog.2013.49.

Boon, J.D. 2012. Evidence of sea level acceleration at US and Canadian tide stations, Atlantic Coast, North America. Journal of Coastal Research 28:1,437–1,445, https://doi.org/​10.2112/JCOASTRES-D-12-00102.1. 

Deegan, L.A., D.S. Johnson, R.S. Warren, B.J. Peterson, J.W. Fleeger, S. Fagherazzi, and W.M. Wollheim. 2012. Coastal eutrophication as a driver of salt marsh loss. Nature 490:388–392, https://doi.org/10.1038/nature11533.

Fagherazzi, S., G. Mariotti, P.L. Wiberg, and K.J. McGlathery. 2013. Marsh collapse does not require sea level rise. Oceanography 26(3):70–77, https://doi.org/10.5670/oceanog.2013.47.

Hopkinson, C.S., J.G. Gosselink, and R.T. Parrondo. 1978. Aboveground production of seven marsh plant species in coastal Louisiana. Ecology 59:760–769, https://doi.org/10.2307/1938780.

Hopkinson, C.S., J.G. Gosselink, and R.T. Parrondo. 1980. Production of coastal Louisiana marsh plants calculated from phenometric techniques. Ecology 61:1,091–1,098, https://doi.org/​10.2307/1936828.

Hutchinson, G.E. 1957. Concluding remarks. Cold Spring Harbor Symposium on Quantitative Biology 22:415–442.

Kemp, A.C., B.P. Horton, S.J. Culver, D.R. Corbett, O. van de Plassche, W.R. Gehrels, B.C. Douglas, and A.C. Parnell. 2009. Timing and magnitude of recent accelerated sea-level rise (North Carolina, United States). Geology 37:1,035–1,038, https://doi.org/​10.1130/G30352A.1.

Kirwan, M.L., G.R. Guntenspergen, A. D’Alpaos, J.T. Morris, S.M. Mudd, and S. Temmerman. 2010. Limits on the adaptability of coastal marshes to rising sea level. Geophysical Research Letters 37, L23401, https://doi.org/​10.1029/2010GL045489.

McKee, K.L., and W.L. Patrick. 1988. The relationship of smooth cordgrass (Spartina alterniflora) to tidal datums: A review. Estuaries 11:143–151, https://doi.org/10.2307/1351966.

Mendelssohn, I.A., and J.T. Morris. 2000. Ecophysiological controls on the growth of Spartina alterniflora. Pp. 59–80 in Concepts and Controversies in Tidal Marsh Ecology. N.P. Weinstein and D.A. Kreeger, eds, Kluwer Academic Publishers.

Morris, J.T. 2000. Effects of sea level anomalies on estuarine processes. Pp. 107–127 in Estuarine Science: A Synthetic Approach to Research and Practice. J. Hobbie, ed., Island Press.

Morris, J.T. 2007. Estimating net primary production of salt-marsh macrophytes. Pp. 106–119 in Principles and Standards for Measuring Primary Production. T.J. Fahey and A.K. Knapp, eds, Oxford University.

Morris, J.T., and B. Haskin. 1990. A 5-yr record of aerial primary production and stand characteristics of Spartina alterniflora. Ecology 71:2,209–2,217, https://doi.org/​10.2307/1938633.

Morris, J.T., P.V. Sundareshwar, C.T. Nietch, B. Kjerfve, and D.R. Cahoon. 2002. Responses of coastal wetlands to rising sea level. Ecology 83:2,869–2,877, https://doi.org/​10.1890/0012-9658(2002)083[2869:ROCWTR]​2.0.CO;2.

Rahmstorf, S., G. Foster, and A. Cazenave. 2012. Comparing climate projections to observations up to 2011. Environmental Research Letters 7, 044035, https://doi.org/​10.1088/1748-9326/7/4/044035.

Redfield, A.C. 1972. Development of a New England salt marsh. Ecological Monographs 42:201–237, https://doi.org/10.2307/1942263.

Sebold, K.R. 1998. The low green prairies of the sea: Economic usage and cultural construction of the Gulf of Maine salt marshes. Doctoral dissertation, University of Maine, 315 pp.

Shelford, V.E. 1931. Some concepts of bioecology. Ecology 12:455–467, https://doi.org/​10.2307/1928991.

Shepard, C.C., C.M. Crain, and M.W. Beck. 2011. The protective role of coastal marshes: A systematic review and meta-analysis. PLoS ONE 6:e27374, https://doi.org/10.1371/journal.pone.0027374.

Singh, J.S., W.K. Lauenroth, H.W. Hunt, and D.M. Swift. 1984. Bias and random errors in estimators of net root production: A simulation approach. Ecology 65:1,760–1,764, https://doi.org/10.2307/1937771.

Smalley, A.E. 1958. The role of two invertebrate populations, Littorina irrorata and Orchelium fidicinium, in the energy flow of a salt marsh ecosystem. Doctoral dissertation, University of Georgia, Athens, GA, USA.

Sundareshwar, P.V., J.T. Morris, E.K. Koepfler, and B. Fornwalt. 2003. Phosphorus limitation of coastal ecosystem processes. Science 299:563–565, https://doi.org/10.1126/science.1079100.

Wiegert, R.G., and F.C. Evans. 1964. Primary production and the disappearance of dead vegetation on an old field in southeastern Michigan. Ecology 45:49–63, https://doi.org/​10.2307/1937106.

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.