Nekton utilization of intertidal salt marsh creeks: Tidal influences in natural Spartina, invasive Phragmites, and marshes treated for Phragmites removal

Abstract

Intertidal creeks provide an extensive and direct interface with the marsh surface during periods of tidal inundation, and as such they represent a critically important corridor between the marsh surface and subtidal habitats. However, invasion by Phragmites can potentially alter this intertidal creek function. Habitat restoration was conducted in the oligohaline Alloway Creek watershed of Delaware Bay, USA, to ameliorate the deleterious effects of Phragmites invasion and restore marshes to pre-invasion form and function. Intertidal creeks in three marsh habitat types (natural Spartina-dominated, sites treated for Phragmites removal and now dominated by Spartina, and invasive Phragmites-dominated) were sampled during summer 2004 with seines during ebb and flood tides to determine juvenile nekton habitat and tidal utilization patterns and identify possible effects of marsh restoration efforts on intertidal nekton. Total nekton abundance was greater at Spartina and Treated marshes than Phragmites marshes. The overall nekton assemblage did not vary between habitat types, but the nekton assemblage did vary between tide stages, with low tide stages dominated by resident nekton (primarily Fundulus heteroclitus) and high tide stages consisting of a mix of transient and resident species (e.g., Anchoa mitchilli, Morone americana, Anguilla rostrata, Morone saxatilis). The effect of marsh restoration efforts on intertidal creek nekton was inconsistent, but most metrics examined indicated that restoration efforts had little effect in intertidal creek habitats, likely because the intertidal assemblage in all creek types was greatly influenced by many species moving from subtidal habitats and primarily a single (but abundant) species, F. heteroclitus, moving from the marsh surface.