No abstract

The independent and interactive effects of nutrient concentration and epiphyte grazers on epiphyte biomass and macrophyte growth and production were examined in Zostera marina L. (eelgrass) microcosms. Experiments were conducted during early summer, late summer, fall, and spring in a greenhouse on the York River estuary of Chesapeake Bay. Nutrient treatments consisted of ambient or enriched (3× ambient) concentrations of inorganic nitrogen (ammonium nitrate) and phosphate. Grazer treatments consisted of the presence or absence of field densities of isopods, amphipods, and gastropods. epiphyte biomass increased with both grazer removal and nutrient enrichment during summer and spring experiments. The effect of grazers was stronger than that of nutrients. There was little epiphyte response to treatment during the fall, a result possibly of high ambient nutrient concentrations and low grazing pressure. Under low grazer densities of early summer, macrophyte production (g m d) was reduced by grazer removal and nutrient enrichment independently. Under high grazer densities of late summer, macrophyte production was reduced by enrichment only with grazers absent. During spring and fall there were no macrophyte responses to treatment. The relative influence of epiphytes on macrophyte production may have been related to seasonally changing water temperature and macrophyte requirements for light and inorganic carbon.

I. We studied the effects of seasonal flooding on macroinvertebrate abundance by manipulating water regime and detrital level within three contiguous experimental marshes in Manitoba, Canada, over 2 years. One area was seasonally flooded (standing water present through midsummer) with emergent vegetation left undisturbed throughout the study, one was semipermanently flooded {standing water present through the ice-free season) with the vegetation left undisturbed, and one was seasonally flooded with the vegetation harvested at the end of the first summer.2. Abundances of frequent macroinvertebrate taxa were compared between the seasonally flooded-undisturbed treatment area and each of the other areas.3. Densities of total invertebrates and of the dominant taxa (Cladocera, Ostracoda and Culicidae) were reduced dramatically by a year of semipermanent flooding, despite high levels of particulate organic food resources and low populations of predators. Densities were not reduced by lowering the availability of detritus under seasonally flooded conditions. 4. Taxa unaffected by water regime included Dytiscidae, Corixidae, Chironomidae, Ceratopogonidae and Ephydridae. 5. Semipermanent flooding may have eliminated environmental cues necessary for oviposition. embryonic development and hatch among dominant taxa. High invertebrate densities in temporary waters may be more dependent upon life history traits of resident fauna than upon habitat features such as food availability or predation pressure.

Assessing the response of salt marshes to tidal restoration relies on comparisons of ecosystem attributes between restored and reference marshes. Although this approach provides an objective basis for judging project success, inferences can be constrained if the high variability of natural marshes masks differences in sampled attributes between restored and reference sites. Furthermore, such assessments are usually focused on a small number of restoration projects in a local area, limiting the ability to address questions regarding the effectiveness of restoration within a broad region. We developed a hierarchical approach to evaluate the performance of tidal restorations at local and regional scales throughout the Gulf of Maine. The cornerstone of the approach is a standard protocol for monitoring restored and reference salt marshes throughout the region. The monitoring protocol was developed by consensus among nearly 50 restoration scientists and practitioners. The protocol is based on a suite of core structural measures that can be applied to any tidal restoration project. The protocol also includes additional functional measures for application to specific projects. Consistent use of the standard protocol to monitor local projects will enable pooling information for regional assessments. Ultimately, it will be possible to establish a range of reference conditions characterizing natural tidal wetlands in the region and to compare performance curves between populations of restored and reference marshes for assessing regional restoration effectiveness.