Biomass-size spectra in aquatic communities in shallow fluctuating Mediterranean salt marshes (Emporda wetlands, NE Spain)

Abstract

The distribution of biomass among phytoplankton and free-living invertebrates was analysed in a shallow Mediterranean salt marsh submitted to fluctuating water level. Among phytoplankton, biomass accumulated in sizes dominated by mixotrophic species, indicating a competitive advantage for these species, which also prey on other smaller primary producers. Among invertebrates, biomass accumulated in the larger sizes, corresponding to species which partially exploit other nearby systems, such as the aerial environment (insects), or to those able to exploit particulated organic matter in marsh-bed sediment (amphipods). Biomass distribution models developed for pelagic systems are discussed in relation to fluctuating temporary waters. 7 he integrated spectrum approximated (r 2 = 0.96) a Pareto distribution with a slope of c = 1.38. Intense disturbances caused a decrease in r 2 and an increase in c. Under stable conditions, two different tendencies were observed, depending on the degree of eutrophy of the basins: higher values of c were measured in the more eutrophic basins, and lower values in the less eutrophic ones. We hypothesize that highly irregular nutrient input could explain these differences.