Salt marsh die-off and recovery reveal disparity between the recovery of ecosystem structure and service provision

a b s t r a c t Coastal ecosystems, such as sand dunes, salt marshes, and mangroves, stabilize shorelines and protect coastal populations. In New England, salt marshes have experienced widespread cordgrass (Spartina alterniflora) die-off and habitat loss, and it is unknown how this has affected their ability to provide coastal protection. We quantified wave attenuation and shoreline stability on healthy, die-off and recovered marsh creek banks. We found that coastal protection has been severely compromised by salt marsh die-off, and that to date, S. alterniflora recovery, while superficially impressive, has not returned this ecosystem service to the levels of intact marshes. Climate driven sea-level rise and predicted increases in the frequency and severity of storms over the next century will likely further increase the vulnerability of coastal populations. Therefore, recovery of coastal protection is essential for maintaining the ecological and economic wellbeing of coastal communities. Our results suggest that quantification of the recovery of ecosystem services should be employed in order to successfully measure recovery in degraded ecosystems

Coverdale et al 2014 Data

This file contains raw data described in Coverdale et al. (2014) "Indirect human impacts reverse centuries of carbon sequestration and salt marsh accretion". Please contact the authors with any questions

Data from: Indirect human impacts reverse centuries of carbon sequestration and salt marsh accretion

Direct and indirect human impacts on coastal ecosystems have increased over the last several centuries, leading to unprecedented degradation of coastal habitats and loss of ecological services. Here we document a two century temporal disparity between salt marsh accretion and subsequent loss to indirect human impacts. Field surveys, manipulative experiments and GIS analyses reveal that crab burrowing weakens the marsh peat base and facilitates further burrowing, leading to bank calving, disruption of marsh accretion, and a loss of over two centuries of sequestered carbon from the marsh edge in only three decades. Analogous temporal disparities exist in other systems and are a largely unrecognized obstacle in attaining sustainable ecosystem services in an increasingly human impacted world. In light of the growing threat of indirect impacts worldwide and despite uncertainties in the fate of lost carbon, we suggest that estimates of carbon emissions based only on direct human impacts may significantly underestimate total anthropogenic carbon emissions

Trophic dysfunction and salt marsh die-off.

<p>As predator biomass decreases, predation mortality decreases (A), increasing <i>Sesarma</i> abundance (B), and leading to increased herbivory (C).</p

Nonlinear polynomial regression relationship between substrate hardness and die-off.

<p>Substrate hardness explained 46% of inter-site variation in die-off. Intermediate substrate hardness experiences the highest level of die-off. Soft substrate cannot support burrows while hard substrate is too hard to burrow in.</p

Historical reconstruction of study sites.

<p>Images and analysis of study site aerial photographs illustrate the progression from a healthy state in 2003 (Left) to a declining state with high levels of die-off in 2012 (Center). Please note that the color differences between the pictures are due to differences in picture quality between 2003 and 2012. Take note of the white line tracing die-off in the main pictures and the highlighted black area denoting die-off in the pictures in the upper right hand corners. Percent linear extent and cumulative width of marsh lost to die-off rapidly accelerated at Narragansett Bay salt marshes over the past decade (Right). Letters indicate significant differences in variables among time intervals (ANOVA, Tukey HSD).</p

Relationship between herbivory, eutrophication, pollution/disease and wave exposure on site variation in die-off.

<p>Multiple regression on the impact of herbivory (A), eutrophication (B), pollution and/or disease (C), and wave exposure (D) on salt marsh die-off. Multiple regression coefficients, standard errors and p values are shown in each graph. Only herbivory (A) significantly contributed to die-off.</p

New England salt marsh recovery: opportunistic colonization of an invasive species and its non-consumptive effects.

Predator depletion on Cape Cod (USA) has released the herbivorous crab Sesarmareticulatum from predator control leading to the loss of cordgrass from salt marsh creek banks. After more than three decades of die-off, cordgrass is recovering at heavily damaged sites coincident with the invasion of green crabs (Carcinusmaenas) into intertidal Sesarma burrows. We hypothesized that Carcinus is dependent on Sesarma burrows for refuge from physical and biotic stress in the salt marsh intertidal and reduces Sesarma functional density and herbivory through consumptive and non-consumptive effects, mediated by both visual and olfactory cues. Our results reveal that in the intertidal zone of New England salt marshes, Carcinus are burrow dependent, Carcinus reduce Sesarma functional density and herbivory in die-off areas and Sesarma exhibit a generic avoidance response to large, predatory crustaceans. These results support recent suggestions that invasive Carcinus are playing a role in the recovery of New England salt marshes and assertions that invasive species can play positive roles outside of their native ranges

Indirect Human Impacts Reverse Centuries of Carbon Sequestration and Salt Marsh Accretion

<div><p>Direct and indirect human impacts on coastal ecosystems have increased over the last several centuries, leading to unprecedented degradation of coastal habitats and loss of ecological services. Here we document a two-century temporal disparity between salt marsh accretion and subsequent loss to indirect human impacts. Field surveys, manipulative experiments and GIS analyses reveal that crab burrowing weakens the marsh peat base and facilitates further burrowing, leading to bank calving, disruption of marsh accretion, and a loss of over two centuries of sequestered carbon from the marsh edge in only three decades. Analogous temporal disparities exist in other systems and are a largely unrecognized obstacle in attaining sustainable ecosystem services in an increasingly human impacted world. In light of the growing threat of indirect impacts worldwide and despite uncertainties in the fate of lost carbon, we suggest that estimates of carbon emissions based only on direct human impacts may significantly underestimate total anthropogenic carbon emissions.</p></div

Schematic drawing of a typical die-off marsh creek bank.

<p>Experimental zones are labeled with brackets. Abandoned <i>S. reticulatum</i> burrows in the low marsh quickly collapse without maintenance, while active burrowing and herbivory create a characteristic grazing border at die-off marshes. Ungrazed <i>S. alterniflora</i> above the denuded border contributes to peat toughness, but becomes vulnerable to <i>S. reticulatum</i> grazing as the grazing front migrates into the higher marsh. (Credit: E. Suglia)</p