Effects of freshwater inputs on the lower trophic levels of a temperate estuary: physical, physiological or trophic forcing?
The online version of this article (doi:10.1007/s00027-011-0240-5) contains supplementary material, which is available to authorized users. ; The aim of this 6 year study was to assess whether freshwater inputs (rainfall and dam discharges) were acting as physical, physiological or trophic forcing factors on phytoplankton pigment concentrations and the dominant mysids of a temperate estuary (Guadalquivir estuary; SW, Spain). The effects of natural and human-controlled freshwater inputs modified the physico-chemical conditions and consequently biological production (bottom up control). Nutrient (nitrogen hypernutrification), suspended particulate matter and allochthonous photosynthetic pigment imports linked to freshwater inputs from adjacent habitats were observed, as well as light-limited autochthonous primary production. Seasonal and/or spatial patterns were shown by all study variables, including mysids. Freshwater management effects on dominant mysids differed depending on the species' salinity tolerance (physiological forcing) and preferred prey availability (trophic forcing). Moreover, high inorganic matter content had a negative effect on the density of Mesopodopsis slabberi (physical forcing), which led to an increased detritivory/herbivory ratio (Neomysis integer/M. slabberi ratio). In conclusion, freshwater inputs appeared to effect estuarine lower trophic levels via a combination of different forcing mechanisms. Although several general patterns can be derived, the response of the system to freshwater inputs was not always univocal. ; The study was supported by the Spanish Ministry of Science and Innovation through the projects REN2000-0822 MAR and Consolider-Ingenio 2010 CSD2009-00065, the Environmental and Fishery Agency of Autonomous Andalusia Government ("Consejería de Medio Ambiente" and "Consejería de Agricultura y Pesca: Junta de Andalucía") and an EU Fishery Grant. ; Peer reviewed