Multivariate factor analysis reveals the key role of management in integrated multitrophic aquaculture of veta la Palma (Spain)

Understanding the extent of management required by integrated multitrophic aquaculture (IMTA) is essential to foster sustainable aquaculture practices at a commercial scale. The aquaculture farm-wetland complex of Veta la Palma (SW Spain) is an example of a currently viable land-based IMTA system that produced 657 t of European sea bass (Dicentrarchus labrax) in 2010. This farm combined the semi-intensive production of D. labrax in grow-out fish ponds with the extensive production of Mugilidae and Palaemonidae naturally recruited in multitrophic polyculture lagoons. Two sets of polyculture lagoons and their respective adjacent fish ponds were studied biweekly in 2009–2010. The polyculture lagoons promoted an extensive natural food web and removed an estimated 91% of the total incoming dissolved inorganic nitrogen discharged by the fish ponds. Water recirculation across the farm supplied the fish ponds with natural food from the polyculture lagoons and thus the feed conversion ratio (FCR) of D. labrax was <1.0 during a three-year rearing period after nursery production. The multivariate technique of factor analysis identified 10 factors, which together accounted for 72% of the overall environmental data variability in the lagoons, mainly due to seasonality followed by changes in the turbidity characteristics of the incoming water. Some of these factors were affected by specific farm management procedures related to i) an adaptive design that allows operation in open- or closed-circuit conditions and thus mitigates the natural variability of salinity and turbidity of the estuarine source water, ii) the constant recirculation of the water across the entire farm, which extends the benefits of the polyculture lagoons (water purification, microalgae and natural prey provision) to the fish ponds, and iii) management decisions to promote sustainability regarding the periodical drying of lagoons, a low fingerling stocking density (4–5 fish m−3) and an external aquafeed supply limited to warmer months in the grow-out fish ponds.