Metabolic Imbalance in Coastal Vegetated (Posidonia oceanica) and Unvegetated Benthic Ecosystems
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Community metabolism and dissolved organic and inorganic nutrient fluxes were assessed in impacted from fish farm discharges and reference vegetated (Posidonia oceanica) and adjacent unvegetated communities in the Aegean Sea, Greece. Both metabolism and nutrient fluxes significantly differed between impacted and reference communities, but the effect depended on community type and time of year. Net community production (NCP) in the impacted vegetated community decreased by 60%, respiration (R) by 34%, and gross primary production (GPP) by 44%. The GPP:R ratio declined more (35%) in the impacted unvegetated than in the corresponding vegetated community (15%), implying that proximity to the fish farm has a severe impact on the unvegetated community, leading to imbalanced metabolism (GPP < R) and heterotrophic (GPP:R = 0.9) conditions. Higher release of dissolved organic and inorganic carbon, nitrogen, and phosphorous was observed in the impacted vegetated community compared to the corresponding unvegetated one, implying intensification of mineralization in the seagrass community. On an annual scale, the impacted vegetated community supported increased DOC efflux by 204%, DON by 1639%, NH4 by 122%, and NO3 by 26%, whereas it supported release of DOP and PO4 compared to the reference community, which removed these dissolved nutrients from the water column. The impacted unvegetated community supported an annual increase of DOC efflux by 208% and PO4 by 42% and it released DON, NH4, NO3, and DOP, whereas the reference community took up these nutrients. Proximity to the fish farm altered the ecosystem state by lowering the productivity and by enhancing the nutrient release.
Keywordseutrophication net community production nutrient cycling dissolved organic matter seagrass fish farming Mediterranean
This study is part of the IBIS Project, co-financed by EU-European Social Fund (75%) and the Greek Ministry of Development-GSRT (25%). Thanks are due to T. Tsagaraki, I. Glabedakis, V. Pefanis-Vassilatos, N. Kouroubalis, V. Stasinos and S. Kiparissis for assistance with sampling; E. Dafnomili, S. Zivanovic, S. Iliakis, M. Anthoula, Y. Zachioti, A. Androni, E. Krasakopoulou, A. Pavlidou, and K. Giamalaki for assistance in chemical analyses; T. Wernberg, M. Thomsen, and M. Giannoulaki for helpful comments on statistical analysis; and two anonymous reviewers for criticism on the manuscript.
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