Coastal urbanization and the integrity of estuarine waterbird communities: Threshold responses and the importance of scale

Abstract

Biological indicator ChangepointLand cover Watershed A B S T R A C T Estuarine ecosystems are becoming increasingly altered by the concentration of human populations near the coastline, however a robust indicator of this change is lacking. We developed an index of waterbird community integrity (IWCI) and tested its sensitivity to anthropogenic activities within 28 watersheds and associated subestuaries of Chesapeake Bay, USA. The IWCI was used as a tool to gain insight into how human land use affects estuarine ecosystem integrity. Based on Akaike's information criteria (AIC), a single variable model including percent developed land in estuarine watersheds was thirteen (2002) and twenty-six (2003) times more likely than models including percent agriculture and forest cover to fit the IWCI data. Consequently, we examined how suburban, urban, and total development shaped IWCI scores at three spatial scales: (1) watershed; (2) inverse-distance-weighted (IDW) watershed (land cover near the coastline weighted proportionally greater than that farther away); (3) local (land cover within 500 m of the coastline). Suburban, urban, and total development were all significant predictors of IWCI scores. Relationships were stronger at the IDW and local scales than at the whole watershed scale.Nonparametric changepoint analysis revealed a >80% probability of a threshold in IWCI scores when as little as 3. 7% (2002) and 3.5% (2003) of the IDW land cover within the watershed was urban. Our results indicate that, of the landscape stressors we examined, development near estuarine coastlines is the primary stressor to estuarine waterbird community integrity, and that estuarine ecosystem integrity may be impaired by even extremely low levels of coastal urbanization.

Geospatial method for computing supplemental multi-decadal US coastal land use and land cover classification products, using Landsat data and C-CAP products

“…For example, the USGS identified urbanization as the driver for the 4% reduction in forested cover from 1973-2000 across the eastern U.S. (Drummond and Loveland 2010). Deluca et al (2008) found that development (e.g., urbanization and agriculture) near the estuarine coastlines of the Chesapeake Bay region is the main stressor affecting estuarine water bird community integrity, and that estuarine ecosystem integrity can be impaired even with extremely low levels of coastal urbanization. Urbanized watersheds in coastal southern California reduced native amphibian biodiversity and increased numbers of non-native crawfish (Riley et al 2005).…”

Understanding the Potential Impacts of Global Climate Change on Marsh Birds in the Gulf of Mexico Region

“…Subsequently, most estuarine marsh birds, who occupy higher trophic positions, may be vulnerable to these disturbances via bottom-up controls (DeLuca et al 2008;Cardoni et al 2011). Because natural and anthropogenic activities structuring marsh bird communities can span several connected regions (e.g., aquatic, semiterrestrial marsh, and terrestrial upland; DeLuca et al 2008) conservation measures aimed at achieving resilience of these communities will require protection of and connectivity between multiple adjoining habitats (Pringle 2001). …”

Trophic Relationships of a Marsh Bird Differ Between Gulf Coast Estuaries

“…Predicting the response of estuarine ecosystems to changing environmental conditions is therefore challenging, as it necessitates understanding interactions among several trophic levels and multiple nutrient sources (marine, freshwater, and terrestrial) (Day et al 1993;Moody and Aronson 2007). Because birds are relatively well studied, they have been used to measure ecological conditions and evaluate the impacts of environmental change within tidal estuaries (Shriver et al 2004;DeLuca et al 2008). …”

“…An often cited rationale for the use of birds as ecosystem indicators is that most species occupy a relatively high trophic position; environmental conditions that affect basal productivity and physiochemical processes can affect marsh bird distributions from the "bottom up" (Novak et al 2005;DeLuca et al 2008). However, for some of these species, information on diet composition remains largely ancillary (based on gut content analysis and cast pellets), a situation particularly true for the clapper rail (Rallus longirostris).…”