Exchange of nutrients and oxygen across the sediment-water interface below a Sparus aurata marine fish farm in the north-western Mediterranean Sea

Purpose: This study analyzes the effects of aquaculture activities in open seawater in the north-western coastal waters of the Mediterranean Sea. It is the first of its kind to be based on benthic flux data gathered in situ below fish farms for this particular area. Materials and methods: Samples were collected on four sampling campaigns over a 1-year cycle under a Sparus aurata fish farm facility where benthic fluxes were measured in situ using light and dark benthic chambers. Bottom water and sediment samples were also collected. Data were compared to those for a nearby control station. Results and discussion: Significant differences were found (ANOVA, p < 0. 05) between concentrations of organic matter (OM), total phosphorus and redox potentials in sediments located under the cages and those of the control station. The consumption of dissolved oxygen (DO) by sediment and positive ammonium (NH4 +) fluxes was stimulated by OM content, with correlations of r = -0. 60 (p < 0. 01) and r = 0. 70 (p < 0. 01), respectively. The OM content of sediments was found to be consistently higher under the cages than at the control station, with the highest value (1. 8 ± 0. 7 %) under the cages observed during the early summer; values of DO and NH4 + fluxes were -64 ± 17 and 12. 7 ± 1. 0 mmol m-2 day-1, respectively. PO4 3- fluxes were consistently higher in the fish farm sediments (between 0. 58 and 0. 98 mmol m-2 day-1) than those observed at the control station. Nitrate (NO3 -) fluxes were found to be consistently negative due to denitrification occurring in the sediments and were related to the concentration of NO3 - in bottom waters (r = 0. 92, p < 0. 01). Si fluxes were shown to be associated with water temperature (r = 0. 59, p < 0. 05). Conclusions: The results imply that sediments located below cages accumulate organic matter originating from aquaculture activities, especially during summer months when this activity increases. Sediments undergo biogeochemical changes that mainly affect fluxes of DO, NH4 + and soluble reactive phosphorus, although these do not seem to have a significant impact on the quality of the water column due to the hydrodynamic characteristics of the area. © 2012 Springer-Verlag.We would like to thank the Caja del Mediterraneo for a predoctoral fellowship fund for this research and Antonio Asuncion Acuigroup Maremar manager for the facilities and support in conducting the study. The translation of this paper was funded by the Universidad Politecnica de Valencia, Spain. We are grateful for the valuable comments of the anonymous reviewers on previous versions of the manuscript.Morata Higón, T.; Sospedra, J.; Falco Giaccaglia, SL.; Rodilla Alama, M. (2012). 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Effect of chronic exposure to ammonia on growth, food utilisation and metabolism of the European sea bass (Dicentrarchus labrax)

The chronic effects of exposing sea bass (average initial weight 100 g) to ammonia in water at 22 degreesC were first evaluated over a 61-day period (period 1, P1) during which nine different groups were submitted to nine ambient ammonia levels ranging from 0.014 to 0.493 mg 1(-1) NH3-N (0.53-16.11 mg 1(-1) total ammonia nitrogen (TA-N)) and fed using self-feeders. At the end of P1, the fish were starved for 10 days (P2). Their recovery capacity was tested over 43 days (P3) after which the exogenous ammonia supply was stopped in all treatments and the fish were allowed to feed. After 20 days of exposure a highly significant effect of ammonia was evident from the decrease in feeding activity, voluntary feed intake (VFI) and specific growth rate (SGR), and the increase in the feed conversion ratio (FCR). Ammonia exposure had no effect on circadian feeding rhythm or hourly actuation profiles. At the end of PI, the fish seemed to have adapted to all ambient ammonia concentrations tested since feeding and growth parameters were independent of ammonia levels. But they were unable to compensate for growth losses. Physiological adjustments were observed: plasma TA-N concentrations were positively related to ambient TA-N while there was no major disturbance in plasma urea. Plasma tri-iodo-thyronine concentrations were affected by ambient ammonia concentrations and there were no significant changes in hydromineral balance. During P2, oxygen consumption and urea excretion did appear to have been affected by ambient ammonia. When the exogenous supply of ammonia was stopped (M), fish exhibited hyperphagia and compensatory growth. In fish previously exposed to the highest ammonia levels, SGR and VFI were highest, and their FCR was improved. At the end of the experiment the final average weights were similar in all of the treatments (range 337-396 g). Depending on the concentrations used, ammonia exposure may enhance subsequent fish appetite and growth rate and have a similar effect on growth performances as restricting feeding level. Within the range tested, no detrimental effect of ammonia on the metabolic capacity of the fish, measured by oxygen consumption and urea excretion, or on their physiological status was recorded, and the fish had a good recovery capacity. In the conditions of the experiment, the non-observable effect concentration (NOEC) was 6 mg 1(-1).Les effets d'une exposition prolongée à l'ammoniaque, sur des bars (poids moyen 140 g) dans de l'eau à 22 °C, ont été évalués dans un premier temps durant une période de 61 jours (période 1, P1). Les poissons, nourris par des distributeurs « self-service », étaient alors répartis en neuf groupes soumis à neuf niveaux différents de concentration d'ammoniaque, de 0,014 à 0,493 mg l¿1 de NH3-N (0,53 à 16,11 mg l¿1 d'azote ammoniacal total (TA-N)). À la fin de P1, les animaux ont été mis à jeun pendant dix jours (P2). Leur capacité de récupération a été ensuite testée durant 43 jours (P3) après que l'alimentation en ammoniaque eût été supprimée et que les animaux aient pu de nouveau s'alimenter. Après 20 jours d'exposition, l'activité alimentaire, les aliments ingérés volontairement (VFI) et le taux de croissance spécifique (SGR) ont diminué significativement sous l'effet de l'ammoniaque, pendant que le taux de transformation de l'aliment (FCR) a augmenté. L'exposition à l'ammoniaque n'a pas eu d'effet sur les activités circadiennes d'alimentation, ni sur les rythmes horaires de demande alimentaire. À la fin de P1, tous les poissons ont semblé s'être adaptés aux concentrations testées. En effet, les paramètres de croissance et d'alimentation étaient revenus à la normale. Cependant, les poissons n'avaient pas compensé leur retard de croissance. Quelques ajustements physiologiques ont pu être observés : le taux de TA-N du plasma était positivement corrélé au taux d'ammoniaque ambiant, mais pas celui de l'urée. Le taux de tri-iodo-thyronine du plasma a été modifié, mais pas l'équilibre hydrominéral. Durant P2, la consommation d'oxygène et l'excrétion d'urée n'ont pas été affectées. Quand l'apport d'ammoniaque a pris fin (P3), les poissons ont montré de l'hyperphagie et ont manifesté une croissance compensatrice. Les poissons préalablement soumis aux plus fortes concentrations présentent les meilleurs SGR et VFI. À la fin de l'expérimentation, les poids moyens des poissons étaient comparables dans tous les traitements (entre 337 et 396 g). Selon sa concentration, l'ammoniaque peut entraîner une augmentation de l'appétit et du taux de croissance, ultérieurement, similaires à ceux d'un rationnement alimentaire. Dans la gamme testée, aucun effet préjudiciable de l'ammoniaque n'a été observé, ni sur les capacités métaboliques de l'animal, mesurées par sa consommation d'oxygène et l'excrétion d'urée, ni sur ses caractéristiques physiologiques. Les animaux ont montré une très bonne capacité de récupération. Dans les conditions de l'expérience, la concentration, pour laquelle aucun effet n'a pu être observé, était de 6 mg l¿1