Quantifying Vegetation and Nekton Response to Tidal Restoration of a New England Salt Marsh

Abstract

Tidal flow to salt marshes throughout the northeastern United States is often restricted by roads, dikes, impoundments, and inadequately sized culverts or bridge openings, resulting in altered ecological structure and function. In this study we evaluated the response of vegetation and nekton (fishes and decapod crustaceans) to restoration of full tidal flow to a portion of the Sachuest Point salt marsh, Middletown, Rhode Island. A before, after, control, impact study design was used, including evaluations of the tide-restricted marsh, the same marsh after reintroduction of tidal flow (i.e., tiderestored marsh), and an unrestricted control marsh. Before tidal restoration vegetation of the 3.7-ha tiderestricted marsh was dominated by Phragmites australis and was significantly different from the adjacent 6.3-ha Spartina -dominated unrestricted control marsh (analysis of similarities randomization test, p Ͻ 0.001). After one growing season vegetation of the tide-restored marsh had changed from its pre-restoration condition (analysis of similarities randomization test, p Ͻ 0.005).Although not similar to the unrestricted control marsh, Spartina patens and S. alterniflora abundance increased and abundance and height of Phragmites significantly declined, suggesting a convergence toward typical New England salt marsh vegetation. Before restoration shallow water habitat (creeks and pools) of the unrestricted control marsh supported a greater density of nekton compared with the tide-restricted marsh (analysis of variance, p Ͻ 0.001), but after one season of restored tidal flow nekton density was equivalent. A similar trend was documented for nekton species richness. Nekton density and species richness from marsh surface samples were similar between the tide-restored marsh and unrestricted control marsh. Fundulus heteroclitus and Palaemonetes pugio were the numerically dominant fish and decapod species in all sampled habitats. This study provides an example of a quantitative approach for assessing the response of vegetation and nekton to tidal restoration.

Early Ecological Responses to Hydrologic Restoration of a Tidal Pond and Salt Marsh Complex in Narragansett Bay, Rhode Island

“…However, the responses of nekton and the emergent marsh vegetation community did not proceed as expected. In contrast to what was observed at other salt marsh restoration sites in Narragansett Bay (RAPOSA, 2002;ROMAN et al, 2002), and despite improved marsh access and water quality, nekton density actually decreased after restoration at Potter Pond. In addition, the composition of the emergent marsh vegetation community in the Lower Impoundment did not change even after 2 years of restoration; this was because most vegetation species typically found in New England salt marshes were already present in this area before restoration.…”

“…Comparisons are made between results from this study and those from previous studies in New England. This study adds a unique perspective because the tide-restricted Potter Pond was consistently impounded with excessively high water levels, whereas other restricted marshes described in the literature are instead typically deprived of adequate estuarine water (e.g., BURDICK et al, 1997;JIVOFF and ABLE, 2003;MYSHRALL et al, 2000;ROMAN et al, 2002).…”

“…These tidal restrictions result in altered hydrology and biogeochemistry, and degraded vegetation, nekton, and bird communities compared to unrestricted salt marshes (BURDICK et al, 1997;EERTMAN et al, 2002;GRAY et al, 2002;LLANSO, BELL, and VOSE, 1998;MYSHRALL et al, 2000;PORTNOY, 1991PORTNOY, , 1999PORTNOY and GIBLIN, 1997;RAPOSA, 2002;ROMAN, GARVINE, and PORT-NOY, 1995;ROMAN, NIERING, and WARREN, 1984;ROMAN et al, 2002;SINICROPE et al, 1990;VOSE and BELL, 1994;WARREN et al, 2002). Salt marshes are integral to the proper functioning of estuarine systems, and in recognition of the negative effects of tidal restrictions, efforts are now underway to restore tidal flow and ecological function to many of these degraded systems.…”

“…Ecological monitoring is critical to understand the effects of each individual restoration project and improve our understanding of how these systems respond to restoration in general in order to better guide future restoration efforts. Indeed, a growing number of case studies demonstrate that restoring tidal flow to restricted marshes can return ecological functionality by improving water quality conditions, vegetation, and nekton and bird communities (BARRETT and NIERING, 1993;BURDICK et al, 1997;JIVOFF and ABLE, 2003;ROMAN et al, 2002;TEO and ABLE, 2003;THOM, ZEIGLER, and BORDE, 2002;WARREN et al, 2002).…”

Comparison of salt marsh creeks and ditches as habitat for nekton

“…m -2 in Massachusetts, Raposa et al 2003;26.83 ind. m -2 in Rhode Island, Roman et al 2002). We did not attempt to evaluate the nekton carrying capacity of ditches or creeks, but based on similar density estimates from other marshes in the northeastern USA, it seems unlikely that existing creeks could support a substantial increase in nekton density.…”