The interaction of environmental nutrient load and fish waste concentrations Dicentrarchus labrax L. on the waste nutrient removal efficiency of sea lettuce Ulva lactuca L.

Aim of the study : The aim of this study was to investigate the interaction of environmental nutrient load and fish waste concentrations on the waste nutrient removal efficiency of seaweed in a fish-seaweed IMTA, using sea lettuce (Ulva lactuca L.) and sea bass (Dicentrarchus labrax L.) as model species. Materials and methods : Sea lettuce was reared indoors in 10 liter tanks under controlled conditions (temperature 17.0±0.5°C, photon flux density 150µmol.m-2.s-1, photoperiod 12D:12L). Four media were created which differed in macronutrient (N, P & K) concentrations thereby simulating 4 environmental nutrient loads; oligotrophic environment (0.03mg N.l.-1, 0.003mg P.l.-1 & 0.37mg K.l.-1), mesotrophic environment (0.15mg N.l.-1, 0.014mg P.l.-1 & 0.37mg K.l.-1), eutrophic environment (0.41mg N.l.-1, 0.035mg P.l.-1 & 0.35mg K.l.-1) and ultra-eutrophic environment (1.2mg N.l.-1, 0.1mg P.l.-1 & 0.35mg K.l.-1). Different concentrations of sea bass waste were added to each simulated environment. Growth and tissue content of sea lettuce were determined and nutrient concentrations in the water were measured to investigate the interaction of environmental nutrient load and fish waste concentrations on the waste nutrient removal efficiency of sea lettuce. Results & Discussion : Results on growth and tissue composition of sea lettuce exposed to different environmental nutrient loads and fish waste concentrations will be presented. These results should give more insights in the waste nutrient removal efficiency of sea lettuce reared in open sea IMTAs.