Top-down and bottom-up control of infauna varies across the saltmarsh landscape

Abstract

Responses of infaunal saltmarsh benthic invertebrates to whole-ecosystem fertilization and predator removal were quantified in Plum Island Estuary, Massachusetts, USA. Throughout a growing season, we enriched an experimental creek on each flooding tide to 70 µM NO 3 -and 4µM PO 4 -3 (a 10 x increase in loading above background), and we reduced Fundulus heteroclitus density by 60% in a branch of the fertilized and a reference creek. Macroinfauna and meiofauna were sampled in creek (mudflat and creek wall), marsh edge (tall form Spartina alterniflora) and marsh platform (Spartina patens and stunted S. alterniflora) habitats before and after treatmentswere begun; responses were tested with BACI-design statistics. Treatment effects were most common in the mid-range of the inundation gradient. Most fertilization effects were on creek wall where ostracod abundance increased, indices of copepod reproduction increased and copepod and annelid communities were altered. These taxa may use epiphytes (that respond rapidly to fertilization) of filamentous algae as a food source. Killifish reduction effects on meiobenthic copepod abundance were detected at the marsh edge and suggest predator limitation. Fish reduction effects on annelids did not suggest top-down regulation in any habitat; however, fish reduction may have stimulated an increased predation rate on annelids by grass shrimp. Interactions between fertilization and fish reduction occurred under S. patens canopy where indirect predator reduction effects on annelids were indicated. No effects were observed in mudflat or stunted S. alterniflora habitats. Although the responses of infauna to fertilization and predator removal were largely independent and of similar mild intensity, our data suggests that the effects of ecological stressors vary across the marsh landscape.

Seascape ecology of coastal biogenic habitats: advances, gaps, and challenges

“…Lewis & Eby (2002) investigated the spatial patterns of gastropods (periwinkle snails) and blue crab, their predators, along the edge of a North Carolina (USA) Spartina alterniflora marsh and found that pursuant to the concept of increased inhibition of crab foraging with increasing distances into dense S. alterniflora marsh, snail densities increased positively with increased distance from the marsh edge. Although responses were found to be highly taxa specific, Fleeger et al (2008) also found that marsh edge (as well as adjacent tidal channel wall) exhibited the strongest response by invertebrates to experimental predator removal and nutrient additions.…”

Stable isotope addition reveals dietary importance of phytoplankton and microphytobenthos to saltmarsh infauna

“…A total of 19 species of annelids and 38 species of copepods were found in quantitative studies across 41 Mar Ecol Prog Ser 359: 37-49, 2008 habitats in PIE (Johnson et al 2007, Fleeger et al 2008. Isotope analyses were conducted on the more abundant infaunal species, including the annelids Nereis diversicolor (mudflat and creek wall), Streblospio benedicti (mudflat), Paranais litoralis (mudflat, Spartina alterniflora and S. patens understories), Manayunkia aestuarina (creek wall, S. alterniflora and S. patens understories), Fabricia sabella and Pygospio elegans (both creek wall), and the abundant harpacticoid copepod Heterolaophonte sp.…”

“…Meiofaunal communities are dominated by nematodes and harpacticoid copepods (Fleeger et al 2008). Potential predators on infauna include the killifish Fundulus heteroclitus, the green crab Carcinus maenas and the grass shrimp Palaemonetes pugio (Deegan et al 2007).…”

Coastal Habitats of the Gulf of Mexico

“…The effects of ecological stressors vary across the salt marsh landscape (Fleeger et al 2008). Duration of tidal inundation (i.e., relative intertidal elevation) is a key factor determining infaunal and epifaunal community changes across the marsh landscape, and also controls intertidal access for nekton.…”