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

Aquaculture 495 (2018) 484–495

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

T

Fernández-Rodríguez M.J.a, Milstein A.b, Jiménez-Rodríguez A.a, Mazuelos N.c, Medialdea M.c, ⁎ Serrano L.d, a

Universidad Pablo de Olavide, Seville, Spain Institute of Animal Sciences, Agricultural Research Organization, Israel c Pesquerías Isla Mayor S. A, Seville, Spain d Plant Biology and Ecology Department, University of Seville, Seville, Spain b

A R T I C LE I N FO

A B S T R A C T

Keywords: Microalgae Haptophytes Ruppia PUFAs Guadalquivir estuary

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 growout 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.

1. Introduction

cultured species from 1995 to 2006 due to a higher contribution of vegetable oils in the diet (Tacon and Metian, 2008), fish oils remain the main source for long-chain polyunsaturated fatty acids (LC-PUFAs), which are key diet ingredients for many farmed species (Naylor et al., 2009). Cultured marine carnivorous fish are highly dependent on marine LC-PUFAs because they have a very limited capacity to synthesise them from short-chain fatty acid precursors commonly found in vegetable oils (Izquierdo et al., 2005). These compounds are essential during fish growth, particularly during earlier stages, but also for fish health and disease resistance (Torrecillas et al., 2007). Therefore, access to a sustainable source of fish meal rich in LC-PUFAs is a key factor for the cultivation of marine carnivorous finfish species, such as the European sea bass.

The demand for seafood is constantly increasing, and carnivorous marine fish species are highly sought after due to their health-giving benefits (Naylor et al., 2009). These high demands can only be met by the use of aquaculture, which has become the fastest growing animal food producing sector in the world, and in 2007, matched capture fisheries as a global food supplier of aquatic products (Muir et al., 2010). However, the immense growth of the aquaculture sector is accompanied by significant environmental costs and economic requirements of the intensive monoculture of fed species (Klinger and Naylor, 2012). Aquaculture has the fastest growing demand for fish meal and fish oil. Despite steadily decreasing fish-in/fish-out ratios for all

⁎

Corresponding author. E-mail address: [email protected] (L. Serrano).

https://doi.org/10.1016/j.aquaculture.2018.06.032 Received 6 December 2016; Received in revised form 29 August 2017; Accepted 11 June 2018 Available online 12 June 2018 0044-8486/ © 2018 Published by Elsevier B.V.

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It has been argued that it is not the quantity, but the quality of the primary production that sustains the production of higher trophic levels (Müller-Navarra et al., 2004). Therefore, understanding the dynamics of LC-PUFAs at the base of the food web is key to the sustainable production of nutritious fish. Achieving a high annual primary production coupled with high-quality microalgae rich in LC-PUFAs requires a finely-tuned balance. The part played by management in this balance becomes even more interesting because estuaries can be very unpredictable environments, with broad changes in water quality due to variable freshwater inputs (González-Ortegón and Drake, 2012). Therefore, this study demands the use of multivariate statistical analyses that are suitable to examine complex relationships. Factor analysis is a multivariate statistical technique that reduces the complexity of high-dimensional data, such as the large number of interactions developed in multitrophic polycultures. This technique has been applied to study relationships among ecological processes and management procedures in different types of aquaculture systems (e.g. Milstein et al., 2005; Uddin et al., 2008; Favaro et al., 2015). Our objective is to use this technique to explore the ecological interactions and relationships with management procedures carried out in the Veta la Palma IMTA system, with particular focus on the relationships supporting primary production. We aim to contribute to the overall understanding of IMTA systems in temperate regions by revealing the extent of technological investment, management and skills required to support this kind of sustainable aquaculture practice.

Integrated multitrophic aquaculture (IMTA) has the potential to reduce the supply of external feed in finfish aquaculture operations, because some of the food, nutrients and energy considered lost in finfish monoculture are recaptured and converted into other crops. In this way, all cultivation components have a commercial value and provide other benefits, such as improving water quality, preventing diseases and promoting habitat conservation (Troell, 2009). Polycultures are based on the idea that waste produced by one species may be used as input for others, and have thus been the main aquaculture system in Asia since long ago for centuries (Milstein, 2005). The cost of herbivorous fish production is low in polyculture compared to carnivorous (zooplanktivorous) fish, due to the loss of energy and food by the additional trophic level (Neori, 2011). Additionally, the integration of species from different trophic levels can be expected to increase complexity. Hence, multitrophic polycultures would require a higher degree of management procedures than traditional low input systems (Troell, 2009). Consequently, the implementation of IMTA at a commercial scale in Europe has recently been questioned due to the many trade-offs involved in its adoption (Hughes and Black, 2016). Despite IMTA implying extensive spatial requirements, new specific policies and challenging management approaches, this concept remains an attractive solution for aquaculture in the long run (Klinger and Naylor, 2012; Diana et al., 2013; Granada et al., 2016). In this sense, the aquaculture farm-wetland complex of Veta la Palma (SW Spain) is an example of a commercially viable land-based IMTA system, built on both traditional practices and technological innovations. Extensive fish polyculture, based entirely on the natural food web, has been traditionally developed across the Bay of Cádiz (Spain) for centuries. In the salt works associated with the Guadalete river marshes (or “esteros”), an average of 40 kg ha−1 yr−1 of mugilids have traditionally been produced, and production has recently increased to 200 kg ha−1 yr−1 due to an improved knowledge of natural fry recruitment and pond water management (Yufera and Arias, 2010). Veta la Palma farm is located in an extensive private estate on a formerly drained marshland of the Guadalquivir river, which later became protected. It is currently part of the Doñana Natural Park and the Doñana Reserve of the Biosphere designated by UNESCO in 1994. The cultured species are those naturally occurring in the food web of the Guadalquivir estuary, including the carnivorous European sea bass (Dicentrarchus labrax), meagre (Argyrosomus regius) and eel (Anguilla anguilla), as well as other more versatile predators, such as the gilthead sea bream (Sparus aurata), sole fish (Stigmatopelia senegalensis) and mullets (Mugil cephalus, Liza ramada), which all prey on the local crustacean ditch shrimp (Palaemonetes varians). This farm can reach an annual production of 1000 tons, of which 75% is sea bass marketed at premium prices. Additionally, Veta la Palma estate provides jobs for 100 families in the vicinity. This fact concurs with the socio-economic emphasis on local human capital that represents responsible aquaculture looking ahead to 2050 (Diana et al., 2013). Veta la Palma estate is also a Ramsar Site and an Important Bird Area, with 250 recorded bird species (Rendón et al., 2008). From the beginning, this estate has been designed and managed to cope with this two-fold function as a natural park and an aquaculture business. Therefore, it sustains extensive food webs with high primary production that has been estimated to fall within the upper range of natural coastal systems (Walton et al., 2015a). This high production is carefully promoted by an array of management procedures. Previous studies in this area have acknowledged that higher water flows lead to higher shrimp biomass (Walton et al., 2015b), while flushing can change phytoplankton assemblage composition (Cañavate et al., 2015). In addition, the environmental relationships among the primary producers are very complex, with low-phosphate and high-turbidity conditions dictating the blooms of different microalgae (Fernández-Rodríguez et al., 2015). Among these microalgae blooms, haptophytes rich in LC-PUFAs (Armada et al., 2013) are of great interest to the management of this farm.

2. Methods 2.1. Study area The Guadalquivir estuary has great importance for the Doñana wetlands as well as for the fisheries in the Atlantic region (GonzálezOrtegón et al., 2012). The protected areas of the Guadalquivir estuary include a fish reserve (~190 km2) and about 350 km2 of marshland within both the Doñana National Park and the surrounding buffer zone of the Natural Park (Fig. 1). The climate in the Doñana region is Mediterranean with some Atlantic influence (dry subhumid), with mild winters and variable rainfall with an erratic yearly average of about 580 mm (Serrano et al., 2006). In 1982, about 115 km2 of marshland, which had been drained and used for cattle ranching, was purchased by a private company that re-flooded it to introduce fish farming to the area under the terms authorised by the Natural Park management plans in the early 1990s. A total of 3200 ha are currently devoted to aquaculture production, while a 300 ha wetland has been restored to become a bird sanctuary. 2.2. Aquaculture in Veta la Palma Aquaculture in Veta la Palma has been developed as an integrated multitrophic system based on the efficiency of the natural food web. It combines two different culture methods: extensive production carried out in artificial polyculture lagoons, and semi-intensive production in adjacent grow-out fish ponds. There are about 40 earthen polyculture lagoons, with an average surface area of 70 ha each. They are occupied by a large shallow central platform (< 0.5 m depth) where local species of shrimp and fish, entering passively from the estuary as larvae and juveniles, find shelter, reproduce and feed on natural resources until they are too big to escape (extensive fish and shrimp production). Additionally, shrimp reproduction is actively promoted in some lagoons with higher salinity to maintain a large stock of shrimp across the farm. Each lagoon is surrounded by an earthen peripheral canal (20 m wide and 1.5 m deep) where fish are gathered for harvesting. Stretches of the peripheral canal (300–900 m long, about 0.6 ha each) are used as growout fish ponds for cultured species (mainly D. labrax). This fish growth is supported by a combination of natural food all year round and a specifically formulated aquafeed, supplied by demand feeders only 485

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that reaches back the estuary (Fig. 2). In open-circuit conditions, the tidal flood gate is open to let in some estuarine water, although about 40% of the total circulating flow comes from the discharge of the polyculture lagoons across the farm. Depending on environmental conditions and fish crop requirements, this system can also be operated in total recirculation, avoiding estuary water inflow (closed-circuit conditions). During the present study, the open-circuit periods extended from early 2009 or mid-April 2010 to mid-November, while the closecircuit periods were up to early 2009, from mid-November 2009 until mid-April 2010, and from mid-November 2010 on. 2.3. Field work and laboratory analyses The study was conducted in two cultivation units (A3 and C6) that each combined a polyculture lagoon and several grow-out fish ponds (four and three ponds, respectively), which were located immediately upstream of each polyculture lagoon (Fig. 1). The studied polyculture lagoons had a surface area of 70 and 92 ha (A3 and C6, respectively), and A3 was flooded one year after C6 (in 2008 and 2007, respectively). Water samples were collected in triplicate, biweekly from March 2009 to December 2010, at the following sample stations (Fig. 1): pond output (discharge water of a grow-out fish pond into the adjacent lagoon), lagoon (surface and near-bottom water at the lagoon central platform) and lagoon output (discharge water of the lagoon into the draining channel). Two monitoring stations (GRWS100 and data logger CR1000, Campbell Scientific Ltd.) were installed on a platform in the open water of each polyculture lagoon with a standard suite of weather and water sensors that recorded data every half hour. Due to the shallow depth, water column transparency was estimated in situ as the percentage of the Secchi disk depth (Ø 25 cm) with respect to the total water column depth: 100% means that the Secchi disk was visible at the bottom level, whereas 50% means that it disappeared halfway through the water column (Facca and Sfriso, 2009). The following variables were measured in the laboratory: turbidity as formazin turbidity units (Hanna Instruments), the concentrations of planktonic chlorophyll a (Chla) after filtration on Whatman GF/C filters (Marker et al., 1980), dissolved reactive inorganic phosphate (DIP) (Murphy and Riley, 1962) and total P in the water as phosphate after acid digestion of the total sample (Golterman, 2004). Particulate-P was measured as the difference between total P and DIP. The concentration of dissolved inorganic N (DIN), which is equivalent to the sum of nitrite, nitrate and ammonium, was measured only in the output water samples (Golterman, 1991). Water samples were diluted with de-ionised water (up to 10 times when necessary) prior to their DIN determination. Samples of surface sediment were collected with an Ekman-Birge bottom sampler (144 cm2) at the shallow central platform of each lagoon. A fraction of each top sediment sample was analysed in triplicate for the concentration of chlorophyll a by adding 40 ml of methanol to a sediment subsample (0.5 g f.w.) in a pre-weighed centrifuge tube. Therefore, the volume of extraction solvent was more than twice as high as the sediment sample volume to ensure maximal extraction (Grinham et al., 2007). The concentration of benthic chlorophyll a (B_Chla) was then measured after centrifugation (20,000 rpm, 15 min), as in the plankton samples, and the pellet was weighed after desiccation (90 °C). The

Fig. 1. a) Location of the Doñana region in Western Europe; b) map of the Doñana National and Natural Parks and location of Veta La Palma (VLP); c) location of the studied cultivation units within VLP (A3 and C6) indicating the main water flow circulation scheme through irrigation and drainage channels; d) an extensive polyculture lagoon with several adjacent grow-out fish ponds, and their sampling stations: pond output (1), lagoon (2) and lagoon output (3).

during summer when the fish metabolic demand is higher (semi-intensive production). Fish and shrimp are harvested all year round to meet the end-user's demand. Shrimp are collected with fyke nets deployed daily around the farm. Sea bass are harvested by netting in the fish ponds, while fish in the lagoons are netted after lowering the water level to concentrate the fish at the end of the cultivation cycle. Both grow-out fish ponds and polyculture lagoons undergo a rotation cycle with a productive life of about three years, followed by a drying phase. These culture units are all interconnected through a 300 km long network of irrigation/drainage channels linked to the Guadalquivir estuary. Tidal water can flow daily from the estuary through a tidal floodgate towards the pumping station, where it is actively pumped towards the irrigation channels (at a maximum flow rate of 9 m3 s−1 during summer). Then, water flows into the peripheral fish ponds and outflows into their corresponding adjacent polyculture lagoon, where it circulates until it is discharged into a draining channel

Fig. 2. Schematic representation of the hydraulic water flow across Veta la Palma farm. 486

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Table 1 Cultured species, stocking year (spring), fish density and individual weight, duration of aquafeed supply (summer), year of harvest and total biomass harvested in each culture unit. Culture unit

Cultured species

Stocking

Aquafeed

Harvest

Weight (g)

(Months yr−1)

Year

Biomass (kg)

2008 5 2007 5 2007 5 2007 5 Natural recruitment

130 180 180 180

3 3 3 3 0

2006 4 2006 4 2006 4 Natural recruitment

150–190 150–190 150–190

3 3 3 0

2009–11 2009–10 2009–10 2009–10 2011 2008–11 2008–09 2009–11 2009–11 2011 2007–11

10,294 12,291 15,516 18,485 16,763 2200 8634 10,047 26,344 18,651 2500

Year A3

Fish ponds

A3

Polyculture lagoon

C6

Fish ponds

C6

Polyculture lagoon

1 2 3 4

2 3 4

D. labrax D. labrax D. labrax D. labrax Mugilidae Palaemonidae D. labrax D. labrax D. labrax Mugilidae Palaemonidae

Density (fish m−3)

maximum value recorded on the sampling day in the data-logger. The multivariate statistical technique of factor analysis was run as an exploratory tool to identify the groups of organisms and environmental variables that accounted for the main variability of the data (Kim and Mueller, 1978; Milstein, 1993). Factor Analysis refers to a variety of statistical techniques, from which the simplest and the one herein used is the Principal Components method. The objective of factor analysis techniques is to explain the relationships among a set of variables in terms of a limited number of new variables (or factors), which are assumed to be responsible for the co-variation among the observed variables. The first factor is the linear combination of the original variables that accounts for as much of the variation contained in the samples as possible. The second factor is the second such function that accounts for most of the remaining variability, and so on. The number of factors that can possibly be calculated equals the number of variables included in the analysis. However, since most of the variability is accounted for in the first few combinations, the last ones can be discarded. The factors are independent of one another, have no units and are standardised variables (normal distribution, mean = 0, variance = 1). The coefficients of the functions defining the factors allow the interpretation of their meaning, using the sign and relative size of the coefficients as an indication of the weight to be placed upon each variable. In the tables, the coefficients of the variables considered for interpretation of the factors are presented in bold. For each factor, variables with the same sign correlate positively among them, while those with opposing signs are negatively correlated. The analysis was run using the Statistical Analysis System (SAS) package version 9.2 (SAS 2002–2008). Its PROC FACTOR without rotation or other options were run on the raw data matrix, which by default computes the correlation matrix among those variables as a starting point to extract factors using the principal components method.

remaining surface samples were made into a sediment suspension to measure the following P fractions: phosphate in the pore water (sediment DIP-pw) after centrifugation (Murphy and Riley, 1962), P in the inorganic fractions (sediment inorg-P) extracted with Na2 EDTA and total sediment P after acid digestion of the ignited sediment (Golterman, 2004). The organic P fraction (sediment orgeP) was thus calculated as the difference between total P and the inorg-P fractions in the sediment. All colourimetric analyses were performed with a Hitachi U-2000 spectrophotometer (Hitachi Ltd., Tokyo, Japan). A set of samples of 125 ml each were collected at the surface and bottom sites of the open water station in each lagoon and preserved in situ with Lugol's iodine solution for the quantification of cell densities of each taxon with an inverted microscope, following Utermöhl's method (Edler and Elbrächter, 2010). For the complete record of phytoplankton taxa, see Fernández-Rodríguez et al. (2015). The biomass of submerged macrophytes was determined in six samples collected with an open PVC 35-cm-diameter cylinder every 10 m along a 100 m long transect from the open water to the inner shoreline of each lagoon. The samples were thoroughly rinsed with tap water to remove inorganic suspended particles; however, epiphytic and, occasionally, filamentous algae were included in the resulting composite sample that was dried at 90 °C. A previous study reported that Ruppia maritima L. accounted for the entire composition of these submerged macrophyte samples (FernándezRodríguez et al., 2015). 2.4. Statistical methods A data matrix (80 variables × 172 observations) was constructed with environmental, management and phytoplankton group abundance data recorded at each sampling date in each polyculture lagoon and station. The identifying variables included pond name, station and sampling date. The environmental variables included depth, wind velocity, macrophyte biomass, lagoon water characteristics (temperature, conductivity, water column transparency, turbidity, concentrations of oxygen, DIP, particulate-P, chlorophyll-a) and lagoon sediment characteristics (concentrations of DIP in pore water, inorganic and organic P-bound to sediment fractions, and benthic chlorophyll-a). The management variables included water circulation (estuary water entrance open or closed), fish feeding (supplied or not), fish pond and lagoon output water characteristics (turbidity, DIP, particulate-P, DIN, chlorophyll-a). The phytoplankton variables included the density of Diatoms, Chlorophytes, Cryptophytes, Cyanobacteria, Dinophytes, Euglenophytes and Haptophytes, as well as total phytoplankton density. The environmental and management data of each station were considered the same for the surface and near-bottom phytoplankton samples. The phytoplankton counts were log transformed to normalise the data. Temperature and dissolved oxygen concentration (DO) corresponded to the minimum values, and wind velocity corresponded to the

3. Results and discussion 3.1. Aquaculture production Mugilidae and shrimp (Palaemonidae) were naturally recruited in the polyculture lagoons and grown extensively until harvested (Table 1). Considering fish and shrimp biomass as the accumulated fresh weight of each harvest throughout each cultivation cycle, the productivity of Mugilidae was 77 and 52 kg ha−1 yr−1 in A3 and C6, respectively, which is close to the average of 65 kg ha−1 yr−1 of this farm in 2009 and 2010. In contrast, the shrimp harvest in the studied polyculture lagoons was three times lower (14 kg ha−1 yr−1) than the average production of the total farm, because breeding was favoured over extraction in the studied lagoons. Each semi-intensive fish pond was stocked with fingerlings of D. labrax that had been grown in the farm nursery facilities to 130–190 g, from fish larvae obtained from an 487

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external supplier (Table 1). The low stocking fish density (4–5 fish m−3) ensured a low rearing fish biomass during the grow-out period (initial biomass: 0.7–0.9 kg m−3; final biomass: 10–30 kg m−3). Fish mortality was considered negligible, as the fish ponds were covered with nets to avoid birds preying on small juvenile fish, and no anoxiarelated mortality events took place during the study. Fish were reared with a combination of natural food and aquafeed supplement and harvested once they reached commercial weight (~1 kg mean weight) during the following three years. Taking into account a three-year culture period, the average productivity was 7.9 and 8.3 t ha−1 yr−1 of sea bass in the semi-intensive grow-out fish ponds of A3 and C6, respectively. A specific aquafeed for sea bass was supplied through demand feeders each summer when the warm temperature increased fish metabolism. The semi-intensive fish ponds received a total of 46.3 and 48.2 t of aquafeed in A3 and C6, respectively. The average feed conversion ratio (FCR) for the rearing of D. labrax in the semi-intensive fish ponds was 0.96, calculated as the total dry weight of applied aquafeed divided by the fish biomass gain at harvest. Regarding the water quality, no significant differences (MannWhitney test, p > 0.05) were found between the output waters or between both polyculture lagoons, except for the concentration of benthic chlorophyll a, which was higher in lagoon A3 (Table 2). This suggests a large degree of homogenisation in the water of both lagoons, although they were separated by over 1 km, and were of different age and size. This is probably due to about 40% of the water entering this integrated aquaculture system coming from water flowing through the polyculture lagoons that recirculated across the farm. The DIN concentrations were significantly lower in the output water of the lagoons compared to those of the fish ponds (Mann-Whitney test, p < 0.01, Table 2). As each lagoon received the output of several fish ponds, the total DIN concentration discharged into A3 and C6 lagoons was about 5.5 and 5.2 times larger, respectively, than the measured DIN concentrations (assuming the same relationship between the fish biomass and the DIN concentration in each fish pond). Therefore, the actual decrease of the DIN concentration in the lagoon output water can be estimated to reach an average of 91% of the total incoming DIN concentration. This indicates that the DIN discharged by the fish ponds was efficiently removed by the adjacent polyculture lagoon. The phytoplankton total cell density showed a slightly different seasonal pattern in each studied lagoon (Fig. 3). Cell density was consistently high in late spring and low in winter, and it peaked in both lagoons in autumn 2009. However, during summer 2009, phytoplankton density was higher in C6 than in A3, while it became lower in the former than in the latter during autumn 2010. In contrast, the composition of phytoplankton was very similar in both polyculture lagoons. They were alternatively dominated by chlorophytes or haptophytes most of the time, with frequent single-taxon blooms of > 106 cell ml−1 per sample. Diatoms dominated twice in A3 and cryptophytes

once in C6, while cyanobacteria dominated only once in the plankton of both A3 and C6 in summer 2010. The rest of the planktonic taxa generally occurred at a low density and corresponded to dinoflagellates, euglenophytes and chrysophytes. 3.2. Factor analysis of the primary producers and environmental variables Factor analysis identified 10 factors, which together accounted for 72% of the overall environmental data variability (Table 3). The first factor (Factor1) explained 17% of that variability and is a bipolar factor that showed high positive correlation among conductivity, temperature, turbidity, phosphate and particulate P in the lagoons, as well as turbidity and P in both the output waters from the fish ponds and lagoons. All of these variables were negatively correlated with dissolved oxygen concentration and haptophyte density. Hence, Factor1 mainly reflects the large-scale seasonality of the weather and source water in the Guadalquivir estuary. The seasonal pattern of Factor1 showed some differences between the two sampled years (Fig. 4), with higher conductivity and P levels in the moderately rainy year of 2009 (478 mm) than in the extremely rainy 2010 (813 mm). The heavy floods of winter 2010 brought about the collapse of the estuary salinity to unprecedented low conductivity values of < 2 mS cm−1, which forced the farm to operate in closed circuit (no input from the tidal waters) until mid-April 2010 to avoid extreme salinity decrease in the aquaculture system. The second factor (Factor2) accounted for a further 11% of the overall data variability. The variables selected by this factor (Table 3) pointed to primary production circulation in the farm system and its seasonal changes. Cyanobacteria density was distinctively higher in summer, when chlorophytes dominated and bloomed. Summer blooms of chlorophytes occurred in both lagoons (Fig. 3) and were likely repeated across the farm, as in summer there were high chlorophyll concentrations in circulation through the output waters of both ponds and lagoons. Lower water depths and higher concentrations of phosphate in the sediment pore-water likely favoured the summer growth of diatoms and macrophytes (Ruppia maritima). The extensive development of a submerged macrophyte bed led to particle sedimentation that reduced turbidity, particulate P and increased water column transparency. The opposite conditions occurred in winter, when the lack of macrophytes and hence their sediment trapping effect led to an increase in turbidity output from the lagoons. The seasonal pattern of Factor2 showed differences between the two study years, with higher primary production in summer 2010. Fig. 5 presents the distribution of the samples in the space defined by the first two factors, identified by season and year. From winter to summer, points moved up and right (increasing Factor1 and Factor2 values) and from summer to autumn, back down and left. That is, there was a change from low salinity, low primary productivity, and P-poor

Table 2 Median values (minimum-maximum range) of the studied variables at each sampling station. A Mann-Whitney test revealed very few significant differences (p < 0.01) between A3 and C6 lagoons (aa) and between pond and lagoon output waters in A3 (bb) and C6 (cc). A3

Turbidity (FTU) Cond. (mS cm−1) Temp. (°C) D.O. (mg l−1) Phosphate (μM) Part-P (μM) Total-P (μM) DIN (μM) Chla (μg l−1) B_Chla (μg cm−2) Ruppia (g m−2)

C6

Pond output

Lagoon

Lagoon output

Pond output

Lagoon

Lagoon output

48.0 (0.9–155.7)

43.9 (3.3–411.4) 12.3 (5.4–34.2) 21.5 (8.9–28.5) 8.2 (2.9–18.9) 0.35 (0.06–0.89) 5.91 (3.14–20.11) 6.32 (3.26–20.34)

41.7 (0.4–157.3)

36.6 (0.0–304.3)

50.7 (0.3–173.7)

0.35 (0.05–1.02) 6.58 (2.79–12.32) 6.87 (2.88–12.44) 23.20bb (4.1–159.6) 112.2 (21.1–318.2)

0.42 (0.06) 8.05 (3.82–13.60) 8.72 (4.32–14.24) 105.6cm3 (18.2–428.3) 112.6 (13.0–435.3)

58.3 (0.5–372.5) 13.8 (5.4–32.8) 21.1 (8.9–28.3) 8.6 (0.7–18.8) 0.37 (0.08–1.59) 7.05 (2.40–29.03) 7.70 (2.62–29.32)

0.43 (0.08–1.21) 7.78 (4.07–11.69) 8.13 (4.19–12.40) 93.8bb (7.0–550.7) 117.7 (22.2–429.5)

93.9 (12.8–293.5) 54.5aa (25.4–217.2) 39.8 (0.0–187.6)

488

117.8 (10.1–440.0) 29.5aa (11.8–167.8) 44.1 (0.0–371.1)

0.37 (0.06–1.46) 6.51 (2.04–14.99) 6.86 (2.13–15.12) 22.7cm3 (6.8–248.8) 104.3 (8.6–462.8)

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Fig. 3. Changes through time of phytoplankton cell density and relative abundance of main taxa in each polyculture lagoon.

During the warm period, concurrent with the inorganic turbidity decrease in the source water, fish in the semi-intensive sections of the aquaculture system were fed N-rich diets, hence increasing DIN input into the lagoons. Concurrently, cyanobacteria developed on the lagoon bottom and on the water surface where, being larger than the silt particles, they reduced the water column transparency. Fig. 6 presents the variability of suspended solids in the Guadalquivir estuary, in the water quality entering the lagoons, as accounted for by Factor4, and the timing of management procedures carried out during the studied years (see Section 3.3). The following three factors each accounted for 6% of the overall data variability and showed different bottom and water column processes that affected phytobenthos-phytoplankton relationships (Table 3). The fifth factor (Factor5) reflected bottom conditions that enhanced phytobenthos development: the higher the availability of P in the pond bottom, the more phytobenthos. The sixth factor (Factor6) indicated wind resuspension of diatoms (mostly benthonic organisms), dinoflagellates and euglenophytes (mostly planktonic organisms). The seventh factor (Factor7) represented water column conditions that are advantageous either for settled or motile primary producers: phytobenthos benefited from DIN input from the semi-intensive ponds, wind that spreads it through the lagoon, conductivity, since the salinityloving diatoms mostly formed this community, and was negatively affected by turbidity that reduced light penetration to the bottom. Conversely, dinoflagellates could move independently to satisfy their nutrient and light necessities, which gave them an advantage under calm and highly turbid conditions. The eighth factor (Factor8) also accounted for 5% of the overall data variability. It showed positive correlation between the concentration of phosphate in the sediment pore-water and Haptophyta (more precisely, Diacronema sp.), both negatively correlated with euglenophytes (Table 3). The present finding suggests that euglenophytes were

waters with haptophytes in the cool season to saline, P-rich, high primary productivity in the warm season. Again, some differences were apparent between both study years: values in 2009 are distributed up and left from those of 2010. That is, in 2009, there were more saline, turbid and P-rich conditions with less haptophytes, cyanobacteria, chlorophytes, diatoms and macrophytes than in 2010. The third factor (Factor3) accounted for a further 9% of the overall data variability, involving chlorophyll variables on one side and turbidity entering the lagoons and cryptophytes on the other (Table 3). This factor reflects circulation of organic turbidity in the system (i.e. turbidity produced by algae and/or detritus). Algal turbidity was likely related to the capacity of the lagoons to produce and export chlorophyll that circulated through the aquaculture system. Detritus turbidity was mostly related to fish activity in the semi-intensive ponds that discharged their water in the lagoons where samples were collected. The lack of participation of lagoon output turbidity in this factor indicates that the lagoons efficiently processed the organic detritus produced in the semi-intensive ponds. The predominance of algal or detritus organic turbidity input into the lagoons was highly variable throughout the sampling period. The fourth factor (Factor4) accounted for a further 6% of the overall data variability, mostly involving variables measured in the input water (Table 3). It showed negative correlation between (a) the input of inorganic turbidity due to silt particles loaded with adsorbed P particles that were so fine that Secchi visibility was not much reduced in the water column; this was higher during the wet, cool period (low values of Factor4) and (b) the input of DIN and development of cyanobacteria in the lagoons, both characteristic of the warm period (high values of Factor4). Inorganic turbidity originated in the Guadalquivir source water (Fig. 6). To avoid the entrance of high levels of turbidity into the pond system, the capture of estuarine water was stopped each winter and the water in the culture systems was recirculated across the farm.

489

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Table 3 Factor analysis results. Coefficients in bold were used for interpretation. Factors

Factor1

Factor2

Factor3

Factor4

Factor5

Factor6

Factor7

Factor8

Factor9

Factor10

Wind velocity Lagoon depth

0.21 −0.19

−0.23 −0.45

−0.21 −0.29

−0.07 0.23

0.13 0.26

0.59 0.27

−0.32 −0.21

0.25 0.33

−0.17 −0.04

0.02 −0.01

Lagoon water Temperature Conductivity Transparency D.O. Turbidity DIP Part-P Chla

0.46 0.79 −0.33 −0.58 0.48 0.55 0.61 0.23

0.64 −0.05 0.36 −0.53 −0.55 0.26 −0.35 −0.16

−0.09 −0.01 −0.02 −0.06 0.10 0.13 0.31 0.74

−0.04 −0.13 −0.43 0.06 0.26 0.17 0.02 −0.07

0.03 0.04 0.11 0.06 0.09 0.01 0.05 0.15

0.18 −0.18 −0.19 0.16 0.05 −0.20 0.24 0.20

−0.16 −0.32 0.09 0.10 0.33 0.27 0.32 −0.26

−0.04 −0.00 0.13 0.03 −0.04 0.31 −0.22 0.20

0.14 0.10 0.02 −0.27 0.22 −0.40 0.08 −0.08

0.01 −0.01 −0.03 0.01 0.05 −0.07 0.05 −0.02

Lagoon sediment B_Chla DIP-pw Inorg-P Org-P

0.04 −0.39 −0.00 −0.39

0.09 0.31 0.23 0.16

−0.07 0.30 0.02 0.20

−0.07 0.33 0.04 −0.03

0.46 0.08 0.68 0.58

−0.18 0.07 0.26 0.03

−0.45 0.01 0.02 0.17

−0.34 0.44 −0.16 0.05

−0.22 0.03 −0.09 0.22

0.12 0.12 −0.25 −0.05

Fish pond output water Turbidity 0.40 DIP 0.47 Part-P 0.40 DIN 0.15 Chla −0.15

−0.19 0.24 0.11 −0.16 0.41

−0.58 −0.35 −0.22 0.03 0.50

−0.41 0.18 −0.72 0.48 −0.35

0.12 0.10 0.06 0.38 0.31

0.01 −0.17 0.08 −0.25 0.11

−0.05 0.29 0.18 −0.37 −0.01

0.19 0.20 0.15 −0.01 −0.03

0.21 −0.14 0.02 0.26 0.00

0.14 0.22 0.03 0.31 −0.08

Lagoon output water Turbidity 0.69 DIP 0.70 Part-P 0.74 DIN −0.05 Chla 0.29

−0.48 0.23 −0.18 −0.25 −0.03

0.03 0.13 0.25 0.27 0.77

0.12 0.15 −0.17 −0.02 −0.14

0.00 0.03 0.09 0.04 0.09

0.06 −0.20 0.19 −0.19 0.05

−0.03 0.27 0.11 0.28 −0.28

0.08 0.21 −0.14 −0.33 0.20

0.09 −0.26 0.02 0.32 −0.02

0.07 −0.06 0.05 −0.07 0.06

−0.04 0.01 0.36 0.22 0.17 −0.28 −0.05 −0.45 17

0.32 0.47 0.57 0.06 0.58 0.18 0.26 −0.29 11

0.08 0.01 −0.16 −0.36 0.09 −0.13 0.10 0.30 9

−0.10 0.10 0.28 0.05 0.43 0.13 −0.10 −0.10 6

0.31 0.18 0.29 0.29 0.23 0.05 0.04 0.17 6

−0.29 0.48 0.15 0.20 0.05 0.37 0.34 0.02 5

−0.09 0.09 −0.07 −0.05 −0.03 0.32 0.06 0.15 5

0.32 −0.04 −0.10 0.18 −0.03 0.06 −0.39 0.36 5

0.33 0.34 0.18 0.21 0.01 0.04 −0.30 0.21 4

0.46 0.00 −0.16 −0.30 −0.12 0.41 0.53 −0.02 4

Source water

Primay produc-tion

Organic

Inorga-nic

Bottom condition for phyto-benthos

Phyto-plankton resuspen-sion

Water column condition for phyto-benthos

Diacronema blooms

DIP uptake by Ruppia and Diatoms Macrophytes

Ruppia decomposition

Organisms Macrophytes Diatom Chlorophytes Cryptophytes Cyanobacteria Dinophytes Euglenophytes Haptophytes % Variability Explained Interpretation

Scale

Seasonality Aquaculture system

Turbidity

Lagoon maturity Individual lagoon

under both open- and closed-circuit conditions. A pumping station facilitated the distribution and recirculation of a considerable water flow volume across the farm. This hydraulic flexibility was essential to buffer the seasonal changes occurring in the estuary, regarding salinity and turbidity. Each winter, the farm operated for about five months under closed-circuit conditions to avoid a seasonal drop in salinity of the estuary. Likewise, the tidal flood gates were locked down for five months during the heavy floods of winter 2009–2010. Our results showed that a further benefit of closed-circuit conditions was related to low DIP concentrations (median value: ~0.4 μM) and a co-occurring haptophyte bloom (Factor1, Fig. 4). Then, the estuarine silt particles were prevented from entering the system, along with the P adsorbed to them. Haptophytes reached a higher density in the early winter of 2010–2011 than in the previous winter (Mann-Whitney test, p < 0.01). Likewise, DIP concentrations were significantly higher in September–December 2010 than in the same period of the previous year (Mann-Whitney test, p < 0.01). Finally, the supply of fish feed each summer was also a large-scale operation that influenced the seasonality of DIN input concentrations across the farm due to a corresponding increase in fish excretion. Summer cyanobacteria growth co-occurred with this increase in DIN input concentrations (Factor4), while haptophytes dominated during

outcompeted by Diacronema sp. in such conditions. The last two factors each accounted for 4% of the overall data variability and involved the macrophyte Ruppia maritima (Table 3). The role of macrophytes as a sedimentation trap was already accounted for by Factor2, but the relationships with algal groups are now identified. The ninth factor (Factor9) showed phosphate uptake by R. maritima and diatoms, while the tenth factor (Factor10) showed the influence of the decomposition of R. maritima on phytoplankton composition through the increase in density of euglenophytes and dinoflagellates. These groups were likely favoured by macrophyte decomposition after summer 2010, particularly in C6. 3.3. Relevance of management Factor analysis identified the main driving forces in the studied aquaculture system and how they were affected by several management procedures. The first four factors acted at the farm scale and involved the actual design of the farm. The remaining six factors referred to ecological processes occurring at the polyculture lagoon scale, and some of them were related to specific management procedures such as pond maturity during the rotation cycle (Table 3). At the farm scale, the channel network was designed to operate 490

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Fig. 4. Changes through time of electrical conductivity in the Guadalquivir estuary (Junta de Andalucia, 2011), rainfall and Factor1 in each polyculture lagoon. Variables in bold indicate those with higher coefficients in Factor1.

stop the flow of water through the interconnected culture units.

the rest of the year in low phosphate conditions (Factor1). The combined effects of these large-scale management operations were reflected in the factor analysis and accounted for particular differences between both years and/or between both polyculture lagoons (Figs. 4–6). The promotion of primary production through water recirculation brought further management practices into force, more so in earthen lagoons and channels prone to silt resuspension and erosion. Channels must be dredged regularly, and such maintenance operations were likely responsible for a higher input turbidity in A3 compared to C6 during winter 2010 (Fig. 6). On the other hand, submerged macrophyte growth was enhanced in these shallow earthen lagoons during clearwater events (high Factor2), but siltation gradually increases as the lagoons age. Pond maturity became an explanatory element of several differences between both lagoons (Fig. 7). In the young A3 pan, as phytobenthos developed and accumulated biomass on the lagoon bottom (Factor5), the effect of wind resuspension (Factor6) increased under a range of turbidity and dinoflagellate conditions (Factor7) (Fig. 7-A3, from rather low points in the front of the Factor6*Factor7 quadrant to higher points backward left and right within the 2009 cloud and further back, but not higher, in 2010). In the mature C6 lagoon, bottom conditions for phytobenthos development were rather variable during 2009, with more algal resuspension and more frequent development of dinoflagellates than in A3 (Fig. 7-C6, 2009 points back and right in relation to those of A3). In winter, algal resuspension was strong in this lagoon (Fig. 7-C6, 2010 points high in the back-left quadrants). During 2010, phytobenthos decreased and with it its resuspension (Fig. 7-C6, 2010 points decreasing right and forward) to lower values than in A3. Finally, the polyculture lagoons are drained every three to four years to prevent siltation, which would otherwise

3.4. General discussion The productivity of D. labrax was lower in Veta la Palma (~8 t ha−1 yr−1) than in other semi-intensive land-based farms (20–50 t ha−1 yr−1) with similar-sized earthen ponds (Hussenot, 2003). This lower productivity per area is the consequence of a low fish stocking density in Veta la Palma. This is, however, a suitable management strategy to avoid chronic stress during extended grow-out periods, as high fish densities can negatively affect fish performance and welfare through both crowding stress and changes in water quality (Santos et al., 2010). The large extension of the aquaculture facilities in Veta la Palma enabled this farm to account for 4.6% of the European sea bass farmed in Spain, which in turn totalled 11.4% of the world production in 2010 (APROMAR, 2012). Since then, the production of D. labrax has grown only slightly, while intensive culture in sea cages remains the main farming system for this species in Europe (Perdikaris et al., 2016). When juveniles weigh about 5 g, they are transferred to sea cages where they are fattened to commercial size (300–500 g) for the next 1.5–2 years, depending on water temperature (Besson et al., 2016). In contrast, the strategy developed by Veta la Pama relies on extending the grow-out period of D. labrax to produce fish with a higher weight (~1 kg). Our results showed that this extended grow-out period did not require a further increase of the FCR over that achieved by the initial stocked fish. This achievement required increasing the efficiency of the fish production by reducing the use of external aquafeed and promoting an extensive natural food web in the multitrophic polyculture lagoons that supplied the grow-out fish ponds with natural food 491

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Fig. 5. Distribution of sampled points in the Factor1*Factor2 space, by season and year. Variables in bold indicate those with higher coefficients in each factor.

Fig. 6. Changes through time of suspended sediments in the Guadalquivir estuary (Junta de Andalucia, 2011), management procedures and Factor4 in each polyculture lagoon. Variables in bold indicate those with higher coefficients in Factor4. 492

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Fig. 7. Three-dimensional plot of sampled points in the Factor5*Factor6*Factor7 space, by year in each polyculture lagoon. Variables in bold indicate those with higher coefficients in each factor.

cyanobacteria tends to dominate the phytoplankton (Müller-Navarra et al., 2004). Diatoms, chryptophytes and dinoflagellates, either directly or through assimilation from prey, can contain LC-PUFAs, while cyanobacteria lack them (de Carvalho and Caramujo, 2014). Therefore, a key management strategy for this farm is to keep P availability very low in order to prevent cyanobacteria development. Our results showed that cyanobacteria dominated only once in summer 2010, whereas the phytoplankton was more frequently dominated by either chlorophytes or haptophytes. The observed changes within the farm also reflected the inter-annual rainfall variability of this area. At 20 km from the river mouth, where the tidal water enters the farm, salinity can range between 2 and 16 and 3–23 psu, following the winter–summer seasonality of a wet and a dry year, respectively (González-Ortegón and Drake, 2012). Therefore, the farm operated under closed-circuit conditions to avoid a seasonal drop in salinity during winter, and likewise avoided the winter peaks of inorganic turbidity in the Guadalquivir source water, which originated from a combination of natural features (higher soil erosion in the Guadalquivir river basin produced by rainfall, stronger water flow, wind direction) and river dam discharges after heavy rainfall (González-Ortegón and Drake, 2012). Our results showed that a further benefit of operating in closed-circuit conditions during winter was related to very low DIP concentrations in the water. As particles were removed from the incoming water, the P adsorbed to these particles was also removed. The availability of DIP in the water will remain low as long as the release of P is tightly controlled by the large adsorption capacity of the sediment (Fernández-Rodríguez et al., 2015). To avoid siltation, the polyculture lagoons are regularly drained and dredged every three to four years to be re-flooded again after a dry phase that may last up to one year. This rotation cycle leaves about half of the

to the recirculating water. Similarly, Filbrun and Culver (2013) showed that using manufactured feed at low feeding rates increases production efficiency, because it increases dissolved oxygen levels and enhances the contribution of natural invertebrate prey to the diets of channel catfish cultured in earthen ponds. More generally, ecosystem-based aquaculture requires the efficient transfer of nutrients and energy from natural prey and feed to cultured fish (Filbrun and Culver, 2013). In the present study, the constant recirculation of water across the Veta la Palma farm likely contributed to the transfer of plankton (and dislodged benthos) from the polyculture lagoons into the grow-out fish ponds. Walton et al. (2015a) performed an isotopic trophic study in Veta la Palma in 2011–2012 and found that 22–31% of the sea bass diet consisted of natural prey items entering the ponds, particularly the mysid Mesopodopsis slabberi, which was also the most common prey for the Palaemonidae shrimps (González-Ortegón et al., 2015). Mysids play a key role in the food web of many estuaries as both consumers and prey, and M. slabberi exhibits a predominantly herbivorous diet, being the only mysid favoured by phytoplankton availability in the Guadalquivir estuary (González-Ortegón and Drake, 2012). Although the production of higher trophic levels (such as fish) ultimately depends on the primary production at the base of the food web (Neori, 2011), the efficiency with which biomass and energy are transferred through the food web can be highly variable. MüllerNavarra et al. (2004) stated that the production of key intermediate trophic levels (such as herbivorous zooplankton) depends more on the quality composition of the phytoplankton regarding LC-PUFAs than on the total biomass of the phytoplankton. Furthermore, they found that the phytoplankton content in LC-PUFAs strongly increased in lakes with low P loads, whereas the efficiency of the phytoplankton to sustain higher trophic levels decreased at high P lake concentrations where 493

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scale. Most system variability was due to seasonality (first two factors), followed by changes in the turbidity characteristics of the incoming water (subsequent two factors). Lagoon ecology was mostly affected by processes related to maturity (subsequent three factors), blooming conditions of the haptophyte Diacronema sp. (eighth factor) and macrophyte relations with other algal groups (last two factors). These factors were affected by 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) a pump station for the constant recirculation of the water flowing across the entire farm, which extends the benefits of the polyculture lagoons (water purification, microalgae and natural prey provision) to the semi-intensive fish ponds, and iii) management decisions to promote sustainability regarding the periodical drying of lagoons, the low fingerling stocking density and aquafeed supply limited to warmer months in the grow-out fish ponds. Contrary to traditional low-input polyculture strategies, this farm required high investment in technology and skilled managing procedures to succeed at a commercial scale in Europe. This was achieved by implementing a land-based IMTA system, which can produce European sea bass with no increase in FCR after nursery production.

production area inoperative for farming at any given moment, but is a key management procedure that promotes sanitation of the organically rich sediment and renews the P-adsorption capacity of the sediment. In the present study, nutrients discharged by the semi-intensive fish ponds were assimilated through the natural food web of the polyculture lagoons, which efficiently removed the incoming DIN. Likewise, in the Veta la Palma farm, Walton et al. (2015a) estimated an average N removal efficiency > 90% during 2011–2012. Such a high degree of DIN removal can be expected to be achieved when N loading is relatively low, because DIN effluent removal is inversely related to the N load released by finfish farms, according to a 3D model for estuary bioremediation (Hadley et al., 2016). This model predicted that 81% of DIN discharged by a finfish farm with an annual load of 31.5 t of N could be potentially removed by adjacent macroalgae sites, which is a similar annual load to the amount of N (38.1 t) estimated for the yearly semiintensive fish production in Veta la Palma (Walton et al., 2015a). Regarding this N load, an isotopic trophic study showed that the external N source of the aquafeed used in Veta la Palma is entirely consumed by the fish growing in the semi-intensive ponds; thus, fish excretion is the source of DIN discharged into the polyculture lagoons (Walton et al., 2015b). In these polyculture lagoons, the nutrients assimilated by primary producers are further transferred through the food web. Mugilidae and shrimp naturally growing in these lagoons not only contributed to water purification, but they were also farm by-products of considerable commercial value in the region. The transfer of nutrients and energy through the trophic web also reaches the vast flocks of waterbirds feeding in the polyculture lagoons of Veta la Palma farm. Up to 300,000 ducks can concentrate in this artificially inundated farmwetland complex when rainfall is too scarce to flood the adjacent natural marsh of the Doñana National Park (Kloskowski et al., 2009). It is estimated that these bird populations are supported by the high amount of primary production, which is almost as high as that supporting the harvested biomass of fish and shrimp in this farm (Rodríguez-Pérez and Green, 2012; Walton et al., 2015a, 2015b). Water circulation across the Veta la Palma farm was pivotal to the horizontal integration of the extensive and semi-intensive cultures provided by lagoons and ponds, respectively. Other coastal land-based fish farms of temperate regions have also been designed for the horizontal integration of traditional grow-out fish ponds, with a variety of semi-intensive and intensive cultures of microalgae, seaweeds, shrimp or shellfish (Bunting and Shpigel, 2009). Although these horizontally integrated aquaculture systems enable a more efficient use of resources (by-products, nutrients, water) and thus reduce ecological footprints, they face a wide range of constraints, including high investment and operating costs, market competition and lack of institutional incentives to internalise the environmental costs and improve consumer perception (Bunting and Shpigel, 2009). The present study showed the feasibility of an ecosystem-based aquaculture farm that commercialised 0.5% of the world production of farmed D. labrax in 2010 (APROMAR, 2012). Nevertheless, ecologically based aquaculture management strategies are, by definition, dependent on natural processes and consequently open to external factors, notably environmental perturbations (Bunting and Shpigel, 2009). Marketing products at a premium price can provide resilience during periods of unfavourable conditions. Therefore, informed consumer choice still plays a fundamental role in fostering environmentally sound, socially responsible and sustainable aquaculture development.

Acknowledgements This study was supported by a research contract between the University Pablo de Olavide, the University of Sevilla and the company Pesquerías Isla Mayor, S.A., under a CENIT Programme from the National Center for Industrial Technological Development (CDTI). References APROMAR, 2012. La Acuicultura Marina En España. Informe Annual 2012. Spain. pp. 84. Armada, I., Hachero-Cruzado, I., Mazuelos, N., Ríos, J.L., Manchado, M., Cañavate, J.P., 2013. Differences in betaine lipids and fatty acids between Pseudoisochrysis paradoxa VLP and Diacronema vlkianum VLP isolates (Haptophyta). Phytochemistry 95, 224–233. Besson, M., Vandeputte, M., van Arendonk, J.A.M., Aubin, J., de Boer, I.J.M., Quillet, E., Komen, H., 2016. Influence of water temperature on the economic value of growth rate in fish farming: the case of sea bass (Dicentrarchus labrax) cage farming in the Mediterranean. Aquaculture 462, 47–55. Bunting, S.W., Shpigel, M., 2009. Evaluating the economic potential of horizontally integrated land-base marine aquaculture. Aquaculture 294, 43–51. Cañavate, J.P., Pérez-Gavilán, C., Mazuelos, N., Manchado, M., 2015. Flushing-related changes of phytoplankton seasonal assemblages in marsh ponds of the warm temperate Guadalquivir river estuary (SW Spain). Hydrobiologia 744, 15–33. Junta de Andalucia, 2011. Distrito hidrográfico del Guadalquivir -Informe año hidrológico 2009–2010. Consejería de Medio Ambiente, Secretaría General del Agua, Sevilla. pp. 60. de Carvalho, C.C.C.R., Caramujo, M.J., 2014. Fatty acids as a tool to understand microbial diversity and their role in food webs of Mediterranean temporary ponds. Molecules 19, 5570–5598. Diana, J.S., Egna, H.S., Chopin, T., Peterson, M.S., Cao, L., Pomeroy, R., Verdegem, M., Slack, W.T., Bondad-Reantaso, M.G., Cabello, F., 2013. Responsible aquaculture in 2050: valuing local conditions and human innovations will be key to success. Bioscience 63, 255–263. Edler, L., Elbrächter, M., 2010. The Utermöhl Method for Quantitative Phytoplankton Analysis. In: Karlson, B., Cusack, C., Bresnan, E. (Eds.), Microscopic and Molecular Methods for Quantitative Phytoplankton Analysis. Intergovernmental Oceanographic Commission of UNESCO, UNESCO, Paris, pp. 13–20. Facca, C., Sfriso, A., 2009. Phytoplankton in a transitional ecosystem of the Northern Adriatic Sea and its putative role as an indicator for water quality assessment. Mar. Ecol. 30, 462–479. Favaro, E.G.P., Sipauba-Tavares, L.H., Milstein, A., 2015. Ecological processes in extensive flow-through earthen tilapia ponds during the rainy and dry seasons in Southeastern Brazil. Braz. J. Biol. 75 (4, Supl. 1), S97–S107. Fernández-Rodríguez, M.J., Hidalgo-Lara, C., Jiménez-Rodríguez, A., Serrano, L., 2015. Bloom-forming microalgae in high-species phytoplankton assemblages under lightfluctuating and low phosphate conditions. Estuar. Coasts 38, 1642–1655. Filbrun, J.E., Culver, D.A., 2013. Can reduced production of manufactured feed improve fish production efficiency in ponds? N. Am. J. Aquac. 75, 64–76. Golterman, H.L., 1991. Direct nesslerization of ammonia and nitrate in fresh-water. Ann. Limnol. 27, 99–101. Golterman, H.L., 2004. The Chemistry of Phosphate and Nitrogen Compounds in Sediment. Kluwer Academic Publishers, Dordrecht/Boston/London, pp. 251. González-Ortegón, E., Drake, P., 2012. Effects of freshwater inputs on the lower trophic levels of a temperate estuary: physical, physiological or trophic forcing? Aquat. Sci.

4. Conclusions Factor analysis allowed the identification of the main processes affecting the ecological variability of multitrophic polycultures developed in the lagoons of the Veta la Palma aquaculture farm and revealed how they were affected by several management procedures. The first four factors described the large scale of the entire farm facilities, while the remaining six referred to ecological processes occurring at the lagoon 494

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