ABSTRACT

Vinagre et al. (2011) noted that river flow variability influenced estuarine production, yet an understanding concerning flow effects on estuarine food webs is still scarce in the scientific literature. Using stable carbon and nitrogen isotopes in two main fish nursery areas of the Tagus Estuary, the authors showed that, during low river flow conditions, two distinct food webs were established in each nursery area. The food webs responded to small variations in the freshwater input. Winter floods disrupted localized trophic relationships established during low river flow periods. This led to the reestablishment of a wider food web. During wet years, this wide food web was maintained until spring when it underwent fragmentation into two localized and distinctive trophic organizations. Increased drought frequency caused by climate change was projected to lower the connectivity of the estuarine food webs, causing habitat fragmentation and consequent loss in complexity and resilience.