Variation in Food Web Connectivity across Intertidal Gradients in Embayment and Fluvially-dominated Estuaries

Despite suggestions that extensive mixing and large-scale transport of organic matter occurs within estuarine systems and across fluvial-estuarine-coastal ecotones (Teal 1962, Odum 1980), more recent evidence in estuarine detritus-based food web systems has shown strong gradients in the sources of organic matter assimilated by consumers across diverse fluvial-estuarine-coastal ocean scales (Peterson et al. 1985, 1986, Deegan and Garritt 1997, McMahon et al. 2005, Howe and Simenstad, submitted). These emerging results challenge prior concepts of the scale of food web connections across the land margin, as they infer greater compartmentalization of food webs in relation to landscape setting than previously considered. It is now becoming evident that under some landscape settings the spatial scale of organic matter movement and assimilation can be extremely confined. Several new studies have documented that estuarine wetland consumers inhabiting fringing and non-fluvial embayment marshes feed exclusively on locally produced organic matter, indicating that the transport and assimilation of organic matter can be confined to a few tens of meters or less (Hsieh et al. 2002, Grenier 2004, Guest and Connolly 2004, Guest et al. 2004, Guest and Connolly 2006). However, the aforementioned studies have all occurred in microtidal environments or in areas receiving little to no riverine inputs, both of which may minimize detrital transport distances. Thus, given differences in the scale of food web connectivity previously documented in estuarine ecosystems, and given that little work has been devoted towards distinguishing the scale of food web compartmentalization in relation to landscape setting, it is critical to quantify the extent, strength, temporal and spatial scales of connectivity in different ecosystem types.