A Study of the Relationship Between Freshwater Runoff and Benthos Abundance: a Scale-oriented Approach

In some coastal environments, freshwater runoff is one of the main potential sources of auxiliary energy. Little is known, however, about the mechanisms by which this energy input influences biological production, particularly at intermediate and high trophic levels. Moreover, the evidence available does not allow to link runoff variability one unambiguously to the dynamics of marine fauna. Here, an empirical approach based on exploratory data analysis is used to test for a link between these components of the ecosystem. Linear regression and correlation models were used to examine the relationship between runoff and abundance, biomass and mean weight per individual of juvenile populations (<1 year old) of five dominant epibenthic species sampled on suspended collectors (i.e.Obelia longissima, Hiatella arctica, Mytilus edulis, Semibalanus balanoidesandBalanus crenatus), over a 10-year period. The study was carried out in a large coastal ecosystem, the Estuary and north-western Gulf of St. Lawrence, for both regulated and non-regulated runoff situations. Notwithstanding the regression or correlation model, the spatial scale, the runoff signal, the runoff index, the species or the biological descriptor used, no significant relationships were observed. Results are discussed in light of current hypotheses proposed to account for the effects of runoff on marine fauna.