A natural history model of New England salt marsh die-off

Abstract

Natural history gave birth to ecology and evolutionary biology, but today its importance is sometimes marginalized. Natural history provides context for ecological research, a concept that we illustrate using a consumer-driven vegetation die-off case study. For three decades, local predator depletion promoted the formation of high-density crab (Sesarma reticulatum) grazing and burrowing fronts, resulting in the spread of vegetation die-off through southern New England and Long Island marshes. We review results from a decade of research on this phenomenon and synthesize these findings with new field surveys, experiments, and historical reconstructions to test the hypothesis that the locations and processes of vegetation die-off and recovery are spatially predictable. We discovered that crab-driven die-off consistently begins on marsh creek heads, where peat and high flow conditions overlap, before spreading to inner creeks following peat availability, stunted cordgrass, and flow. Eventually, die-off eliminates most low marsh vegetation, leaving behind unvegetated substrate too soft to support burrows. Vegetation recovery exhibits the reverse patterns of die-off; it consistently begins in the low marsh within inner creeks, where soft substrate and low flow conditions overlap, before spreading to creek heads. This spatially explicit, substrate-dependent recovery eventually leads to ungrazed cordgrass abutting grazed cordgrass on the high marsh border. We present a conceptual model of die-off through recovery progression to provide managers and landowners with a diagnostic tool for identifying marsh die-off and recovery status. Collectively, this work illustrates the fundamental importance of long-term, natural history-based investigations of ecosystem dynamics in informing ecology, conservation, and management practices.

Pattern and scale: evaluating generalities in crab distributions and marsh dynamics from small plots to a national scale

“…Complementing this perspective, there has been an emerging focus on biological factors, especially consumers, such as mammals (Bakker et al 1993), birds (Jefferies et al 2006), and snails (Silliman et al 2005). Conceptually, to advance estuarine theory, as well as for applied management, there is a need to better understand the relative importance of different drivers of marsh sustainability, and how they vary across scales (Pettengill et al 2018). The scale of most crab studies is typically small (plots within a marsh), while the scale of studies assessing sea-level rise is typically larger (entire estuary or region).…”

“…The scale of most crab studies is typically small (plots within a marsh), while the scale of studies assessing sea-level rise is typically larger (entire estuary or region). Conceptually, to advance estuarine theory, as well as for applied management, there is a need to better understand the relative importance of different drivers of marsh sustainability, and how they vary across scales (Pettengill et al 2018).…”

Using Remote Sensing to Identify Drivers behind Spatial Patterns in the Bio-physical Properties of a Saltmarsh Pioneer

“…The effect of vegetation properties on spatial patterns in this valuable ecosystem is still poorly understood. Previous studies mainly focused on the effects of vegetation zonation on spatial patterns [2,[26][27][28][29][30]. These vegetation zonation studies reported various influential factors; highly influential factors are: Inundation time [2,26,31,32], wave forcing [33][34][35][36][37], competition [2,38,39], and creek influence [26,27,31,40,41].…”

Sea-level rise and the emergence of a keystone grazer alter the geomorphic evolution and ecology of southeast US salt marshes

“…On adjacent, higher-elevation marsh platforms, dense root mats cause the substrate to be too hard for Sesarma burrowing (>2 kg⋅cm −2 ; refs. 29 and 37 ). Recent research has suggested that if sea-level rise outpaces salt-marsh vertical accretion, the resulting extension in the duration of tidal flooding will drive a shift in plant-tissue allocation from dense-packed fine roots to larger rhizomes that better aerate the soil and increase pore space, thereby softening the marsh platform and enhancing the system's overall vulnerability to Sesarma intensive burrowing and overgrazing ( 29 ).…”

“…Since the 1970s, high-density Sesarma fronts that leave denuded, burrow-riddled creekbanks in their wake ( 34 ) have been documented from New York to Massachusetts ( 35 ), particularly where recreational fishing has extirpated Sesarma ’s predators ( 36 ). In the northeastern United States, Sesarma fronts form exclusively on lower-elevation creekbanks, where elevated water velocities flush sediment and toxins from their burrows, Sesarma recruitment rates are high, and marsh substrates exhibit suitable hardness (∼1.4 kg⋅cm −2 ) for Sesarma burrow excavation and maintenance ( 37 ). On adjacent, higher-elevation marsh platforms, dense root mats cause the substrate to be too hard for Sesarma burrowing (>2 kg⋅cm −2 ; refs.…”