The EULIT project (Effects of Eutrophicated seawater on rocky shore ecosystems studied in large littoral mesocosms) has developed a pioneer design for rocky shore mesocosms able to maintain stable conditions and communities for at least mid term (3 years). The design includes nutrient loadings required, as well as tidal and wave simulation. The design has proved to be optimal to maintain and develop populations of macroalgae, periphyton, and herbivore and carnivore invertebrates. The design can be used for experimental purposes or for commercial mariculture purposes. The scientific results and facility may be used by coastal eutrophication management to test the buffering capacity in marine systems regarding nutrient inputs.
The response of the experimental rocky shore ecosystems to increased nutrient availability was examined in eight land-based mesocosms designed for hard-bottom littoral communities. Six of the basins received nutrient concentrations of 1-32 µM DIN and 0.06-2.0 µM DIP, with two basins serving as controls.
The EULIT experiment provided evidence of a high resilience of the biomass and metabolism of rocky shore communities to increased nutrient inputs. The growth rate of the periphyton and fast-growing macroalgae communities was stimulated by nutrient enrichment, while the response was less evident among the perennial fucoids. The structure of the macroalgal communities, however, did not change during 27 months measurements. In contrast, growth on artificial rock substrates during the same period of time revealed intensive growth of the fast-growing algae in high dosed basins compared with low dosed and control basins, which were dominated by the fucoids. The fauna communities exhibited only minor response to nutrient treatment. The total system metabolism tended to increase slightly, but not significantly, with increased nutrient loading.
The resilience of the biomass and metabolism is probably imposed by a nutrient-limited community. This is caused by the actions of top-down grazing which suffices to suppress the response of opportunistic macroalgae, and high organic carbon export from the dominant perennial macroalgae, which buffer the otherwise expected ecosystem-level responses to increased nutrient inputs. Maintenance of this buffering mechanism appears, therefore, as an essential requirement for the prevention of eutrophication effects on rocky shore ecosystems.