M.A.J. Nederlof1,2*, H.M. Jansen2,3, M.C.J. Verdegem1 and A.C. Smaal1,2
1Wageningen University, Department of Aquaculture and Fisheries, De Elst 1, 6708 WD Wageningen, The Netherlands
2Wageningen IMARES, Aquaculture department, Korringaweg 5, 4401 NT Yerseke, The Netherlands
3Institute for Marine Research, Department of benthic habitats and shellfish, Nordnesgate 50, 5817 Bergen, Norway


Due to the increasing demand for food and energy and a shortage of terrestrial space, offshore production is expected to increase. Stakeholder conflicts and space limitations in the North-Sea area led to the exploration for development of Multi Use Platforms (MUPs). MUPs combine various activities at a shared offshore location, aiming to make offshore production more efficient. For example combining a wind farm and an aquaculture production site. Within the MUPs context it is important to implement responsible aquaculture practices in order to fulfil the aim of sustainable production (Stuiver et al., 2012).

In this respect, Integrated Multi-Trophic Aquaculture (IMTA) has been proposed as a promising approach which could contribute to increase the ecological sustainability of aquaculture. In IMTA, species from different trophic levels are linked in such a way that uneaten feed, wastes, nutrients and by-products of one species (i.e. fed species) can be recaptured and converted into resources for species at lower trophic levels (i.e. extractive species). Combining fed and extractive aquaculture is suggested to mitigate wastes resulting from aquaculture practices (Troell et al., 2009; Chopin et al., 2012).

Several studies have shown that various seaweed species are able to take up waste nutrients released by fed species (reviewed in Troell et al., 2003). Therefore seaweeds are often used as extractive species in IMTAs, aiming to reduce waste streams resulting from the fed species (Troell et al., 2003). Cultivating seaweed species in open sea IMTAs exposes the seaweed to nutrients released by the fed species (aquaculture waste nutrients), but also to nutrients which are already available in the environment (ambient nutrients). The ratio between these waste and ambient nutrients varies over time and space. Little information is available about the influence of this ratio on the waste nutrient removal efficiency of seaweed in IMTAs.



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.




Chopin T., J.A. Cooper, G. Reid, S. Cross and C. Moore. 2012. Open-water integrated multi-trophic aquaculture: environmental biomitigation and economic diversification of fed aquaculture by extractive aquaculture. Reviews in aquaculture 4: 209-220.

Stuiver M., A. Gerritsen, R.J. Fontein and H. Agricola. 2012. Multifunctional Platforms: perspectief voor de toekomst? Aquacultuur 5: 6-12.

Troell M., C. Halling, A. Neori, T. Chopin, A.H. Buschmann, N. Kautsky and C. Yarish. 2003. Integrated mariculture: asking the right questions. Aquaculture 226: 69-90.

Troell M., A. Joyce, T. Chopin, A. Neori, A.H. Buschmann and J.G. Fang. 2009. Ecological engineering in aquaculture - Potential for integrated multi-trophic aquaculture (IMTA)       in marine offshore systems. Aquaculture 297: 1-9.