Vinagre, C.,Costa, M. J.,Dunne, J. A.

Determining the spatial scale is a crucial stage in any ecological study. However, knowledge on the effect of spatial scale on food web network properties is still lacking in published literature. In this work, the effect of spatial scale on the network properties was determined for the Tagus estuary ecosystem. The food web of the Tagus estuary was assembled at three spatial scales, in terms of grain (resolution) and extent. In terms of grain, the three scales defined were: small grain (30 sites), medium grain (15 sites) and large grain (6 sites). In terms of extent, the three scales defined were: extended estuary (30 sites), strictly estuarine (20 sites), nursery area (6 sites). The lists of species for each site were merged and used to construct one major food web containing all species observed, at each of the spatial scales under analysis. It was concluded that the spatial extent of the sampling highly influenced food web networks properties, more than grain, and should thus be carefully chosen when conducting food web studies in estuaries, as well as in other ecosystems that exhibit strong environmental gradients. Studies that aim to characterize estuarine food webs should encompass the full extent of the salinity gradient.