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Coastal & Estuarine Science News (CESN)

Coastal & Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries & Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bimonthly basis.

November 2011


Habitat Fidelity of Coastal Birds: Do they Dine in the Forest or “Eat Out” in the Salt Marsh?
Nutrient Loading Not the Likely Culprit in LI Sound Marsh Drownings
Berm Breaching Opens the Door to Macroinvertebrate Community Changes, at Least for a Time
Do Impacts of Nutrient Enrichment Extend to Tidal Freshwater and Oligohaline Wetlands?

Habitat Fidelity of Coastal Birds: Do they Dine in the Forest or “Eat Out” in the Salt Marsh?

Coastal salt marshes, some of the most productive ecosystems on the planet, are usually located in a mosaic of habitats that includes terrestrial ecosystem types. How much trophic overlap is there between marshes and these adjacent habitat types? Do animals that are typically terrestrial rely on marshes as a food source?

A study of the diets of four passerine (perching) bird species found in terrestrial habitats near salt marshes of Sapelo Island, GA, used stable isotope techniques to quantify the contribution of terrestrial and salt marsh-derived primary production to the birds’ diets. All four bird species (brown-headed nuthatch, painted bunting, white-eyed vireo, and northern parula) are of conservation concern, particularly the painted bunting. Stable isotope analysis was conducted on feathers from each species as well as the primary producers (leaves, berries, seeds) and invertebrate herbivores (insects) that comprise the birds’ diets. The bird whose feathers revealed the strongest trophic ties to salt marshes was the painted bunting: this species relies as much on food originating from salt marsh as from the terrestrial habitats where they were captured and are most often observed. Northern parulas were shown to be most “terrestrial.” The nuthatches and vireos were intermediate, and are probably feeding on insects from the marsh that disperse into nearby shrub and woodlands.

This study emphasizes that even species that are typically associated with upland habitats, like these birds, are still somewhat dependent on salt marshes. Therefore, protection of marshes in close proximity to bird habitats (one study suggests within 700 m for the painted bunting) should be a priority when designing conservation programs for these species.

Source: Brittain, R. A., A. Schimmelmann, D. F. Parkhurst and C. B. Craft. 2011. Habitat use by birds inferred from stable carbon and nitrogen isotopes. Estuaries and Coasts 34(October 2011). DOI: 10.1007/s12237-011-9446-y.

Nutrient Loading Not the Likely Culprit in LI Sound Marsh Drownings

Coastal marshes can only keep their heads above water if a balance is struck between processes that increase and decrease marsh elevation. In Long Island Sound marshes are losing ground, despite the fact that sea level rise is not considered to have reached the critical threshold required to swamp salt marshes. Why? Some have suggested that high nutrient loading can reduce the rate of marsh elevation gain, hastening drowning. Long Island Sound certainly has a problem with nutrient enrichment, so a recent study set out to determine if there is a link between nutrient loading and marsh drowning in this estuary.

The five-year fertilization study manipulated nutrient (N and P) loadings to experimental plots in a Connecticut marsh that has not been impacted by human activity in many decades. Investigators then measured the individual processes that affect marsh elevation (plant production, decomposition, carbon dioxide flux) and the combined net effect of these processes on sediment surface elevation. N fertilization increased aboveground productivity over that of control plots (P did not), but did not have an impact on belowground productivity. Although increased respiration rates in fertilized plots resulted in an increased loss of carbon from the sediment, overall carbon balance and, notably, marsh elevation, were not affected by fertilization. The authors conclude that nutrient loading is unlikely to be a significant contributing factor to marsh drowning in Long Island Sound.

Source: Anisfeld, S. C. and T. D. Hill. 2011. Fertilization effects on elevation change and belowground carbon balance in a Long Island Sound tidal marsh. Estuaries and Coasts 34(November 2011). DOI: 10.1007/s12237-011-9440-4.

Berm Breaching Opens the Door to Macroinvertebrate Community Changes, at Least for a Time

Some types of estuaries are intermittently or temporarily blocked off from the ocean by the development of a berm at their mouths. When the berm is breached, either naturally, as by a storm, or as a management practice to alleviate flooding or maintain vessel access, big changes can result. Water flushes into and out of the estuary, and exchange of sediment and biota is enhanced. The influx of ocean water can significantly alter the estuary’s physiochemical regime by changing salinity, temperature, nutrients, and other factors. A study of three small intermittently closed estuaries in New Zealand asked whether such changes led to meaningful alteration of the hyperbenthic macroinvertebrate community in the estuary near the berm. Macroinvertebrates were collected before and after breaching in two studies: a) a natural berm breach that occurred at all three estuaries simultaneously and b) an anthropogenic breach of one of the three while the other two remained closed (and were used as control sites).

Berm breaches resulted in massive flushing of the estuary and habitat loss due to flooding followed by substantial salinity changes (although the salinity responded to breaching differently in each of the three estuaries). In all cases, changes in abundance of individual taxa, total CPUE, and community structure were observed within a day of the breach. However, they were barely perceptible at the scale of weekly sampling. Results also indicated that a substantial number of individuals were expelled into the ocean during the breach, while new taxa immigrated into the estuaries.

The authors discuss the potential impacts of breaches on community structure. For species whose life history includes ocean migration, the duration and timing of breaches is important for the exchange of propagules. Concurrent berm breaches at multiple small estuaries can translate into a large pulse of propagules into the ocean, and may enhance some species’ ability to successfully recolonize systems where they have become extirpated. The interval between successive breaches may also be an important factor in determining a breach’s impact.

Source: Lill, A. W. T., G. P. Closs, M. Schallenberg and C. Savage. 2011. Impact of berm breaching on hyperbenthic macroinvertebrate communities in intermittently closed estuaries. Estuaries and Coasts 34(November 2011). DOI: 10.1007/s12237-011-9436-0.

Do Impacts of Nutrient Enrichment Extend to Tidal Freshwater and Oligohaline Wetlands?

Thanks to decades of both scientific studies and unintentional “experiments,” it is now fairly clear that nutrient over-enrichment, with nitrogen and phosphorous in particular, can lead to changes in plant species richness, community composition, and productivity in salt marshes. Less work has been done on the impacts of these nutrients on tidal freshwater and brackish marshes. The results of one study in the Nanticoke subestuary of the Chesapeake Bay suggest that N and P might lead to changes in plant abundances, but effects differed by type of marsh and type of plant.

The investigators fertilized plots in marsh and swamp sites with N, P, and both for four years (in this study “marshes” and “swamps” were dominated by herbaceous and woody plants, respectively). Total aboveground biomass showed no significant response, but in many cases the balance between perennial and annual plants seemed to respond to nutrient loadings. In marshes, N increased abundance of perennial plants but decreased abundance of annuals, while P had the opposite effect. Addition of both nutrients generally resulted in no change in either type of plant, suggesting that a competitive balance was maintained between the types. In swamps, perennials responded positively to P.

So while the impacts of nutrient enrichment in this system were not as severe as they could have been (overall aboveground biomass was unaffected, for example), it is important to note that a spectrum of changes does occur with N and P additions, and those effects vary by type of nutrient, type of ecosystem, and type of plant, all of which need to be considered when managing a system or planning restoration.

Source: Baldwin, A. H. 2011. Nitrogen and phosphorus differentially affect annual and perennial plants in tidal freshwater and oligohaline wetlands. Estuaries and Coasts 34(November 2011). DOI: 10.1007/s12237-011-94445-z.