The Effects of Road Culverts on Nekton in New England Salt Marshes: Implications for Tidal Restoration

Abstract

In recent years, salt marsh restoration projects have focused upon restoring hydrology through culvert enlargement to return functional values lost due to reduced tidal flow. To evaluate culvert effects on upstream nekton assemblages, fyke nets were set upstream of tidally restricted creeks, creeks recently restored with larger culverts, and paired reference creeks in New Hampshire and Maine, U.S.A. Subtidal habitats created or enlarged by scour were found immediately upstream of undersized culverts. All marshes supported similar assemblages and densities of fish, suggesting that marshes upstream of moderately restrictive culverts provide suitable habitat to support fish communities. However, densities of Crangon septemspinosa (sand shrimp) were significantly reduced upstream of culverts. A mark-recapture study was conducted in tidally restricted, restored, and reference marsh creeks to evaluate culvert effects on the movement of Fundulus heteroclitus (mummichog), the numerically dominant fish species in New England salt marshes. Recapture data indicated that small culvert size and consequently increased water velocity significantly decreased fish passage rates. We infer that upstream subtidal habitats and greater water velocities due to undersized culverts decreased nekton movements between upstream and downstream areas, resulting in segregated nekton populations. Restoration of salt marsh hydrology by the installation of adequately sized culverts will support increased fish access to marsh habitats and nekton-mediated export of marsh-derived production to coastal waters.

Rethinking the Freshwater Eel: Salt Marsh Trophic Support of the American Eel, Anguilla rostrata

“…Decreased prey diversity, and subsequently the loss of trophic levels have been documented in tidally restricted mangrove systems (Layman et al 2007). Furthermore, decreased movement of important prey species (e.g., F. heteroclitus, C. septemspinosa) between upstream and downstream regions of tidally restricted marshes (Eberhardt et al 2011) may result in a loss of prey resources for A. rostrata in some marsh areas. As a result, the observed lower trophic position of eels in highly restricted systems may indicate an altered trophic structure in marshes subject to reduced tidal flushing.…”

“…For example, A. rostrata are frequently captured in New England salt marsh habitats (e.g., Dionne et al 1999;Eberhardt et al 2011;Nixon and Oviatt 1973) and in some studies were found to comprise the majority of fish biomass . Despite the abundance of A. rostrata in northeast salt marshes, little is known about their use of these habitats.…”

“…Colonization by invasive species as well as changes to the infaunal communities (Fell et al 1991) may shift the food base of tidally restricted salt marshes resulting in an altered food web. Furthermore, decreased flooding and accelerated water velocity through undersized culverts can limit fish movement and access to food resources (Eberhardt et al 2011;Weisberg and Lotrich 1982). Such barriers may result in changes to A. rostrata or prey movement as well as habitat degradation upstream, and as a result, some marsh areas may contribute disproportionately to fish populations within larger estuaries (Gillanders 2005).…”

Tidal Flushing Restores the Physiological Condition of Fish Residing in Degraded Salt Marshes

“…Decreases in bird species richness, density, and abundance were documented in restricted marshes [36], [38], but nekton response was variable across studies, with density, abundance, and species richness varying by site and species [25], [36], [37], [39], [40]. Tidally restored sites exhibit wide variation in support of nekton for several years post-restoration while hydrologic, environmental, and physical variables respond over time to increased tidal flooding and duration [25], [36], [41], [42].…”

Dedication: Dr. Michele L. Dionne (1954–2012)

“…Her efforts also went into garnering a trust that provides funds for a post-doctoral fellow to perform high-level research in conservation ecology. Michele, her students, and post-doctoral fellows performed a variety of research activities that included studying the utilization of marsh ecosystems by fish (Dionne et al 1999;MacKenzie and Dionne 2008), coastal restoration (Burdick and Dionne 1994;Burdick et al 1997;Koniski et al 2006), assessing human and climate threats on coastal systems (Chen et al 2009;Crain et al 2009;Dijkstra et al 2013;Eberhardt et al 2011), and investigating species-specific interactions in marsh ecosystems (Dijkstra et al 2012;Tyrrell et al 2012). She was a proponent of long-term monitoring that could provide effective baseline data sets to determine the conditions of these ecosystems (Neckles and Dionne 2000).…”