Controls of plankton production by pelagic fish predation and resource availability in the Alboran and Balearic Seas Temel Oguz a,b,⇑ , Diego Macias c,1 , Lionel Renault a , Javier Ruiz c , Joaquin Tintore a,d a SOCIB, Balearic Islands Coastal Ocean Observing and Forecasting System, Parc Bit, Naorte, Bloc A, Palma de Mallorca, Spain b Middle East Technical University, Institute of Marine Sciences, 33731 Erdemli, Mersin, Turkey c Department of Coastal Ecology and Management, Instituto de Ciencias Marinas de Andalucia (ICMAN-CSIC), Avd. Republica Saharauis/n, CP11510 Puerto Real, Cadiz, Spain d IMEDEA (CSIC-UIB), Miquel Marquès 21, 07190 Esporles, Spain article info Article history: Received 2 March 2012 Received in revised form 7 March 2013 Accepted 7 March 2013 Available online 17 March 2013 abstract A one-dimensional coupled physical and intermediate-complexity biochemical model comprising large and small phytoplankton and zooplankton groups, particulate organic nitrogen, ammonium and nitrate was developed to study the physical–biogeochemical interactions and parameters that control plankton production in the Alboran and Balearic Sea ecosystems. The model findings suggest that pelagic fish pre- dation and resource availability through lateral and vertical nutrient inputs jointly characterize the plankton community structures. In agreement with previous observations, a typical annual plankton structure of the mesotrophic systems involves a vertically homogeneous biomass of large groups of phy- toplankton and zooplankton within the upper 50-to-100 m layer from mid-November to April and a sub- surface biomass accumulation distributed roughly within 25–75 m depths in the following months. Their light and temperature limitations constrain the smaller groups into the thermocline zone (25–50 m) dur- ing late spring and summer. These obtained results were dependent on the zooplankton actively switch- ing between preys (i.e., the food preference coefficients dependent on prey biomass). In the case of no switching, spurious dynamic equilibrium solutions may arise in the case of a constant and weak fish pre- dation rate and using the quadratic predation formulation. The choice of a Holling Type II (i.e., hyperbolic) predation function may, however avoid ambiguous representation of the annual plankton structure in the case of a constant food preference choice under relatively weak predation pressures. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The Mediterranean Sea, generally recognized as an oligotrophic basin, possesses important geographical variations in terms of food availability (Bosc et al., 2004; Barale et al., 2008; D’Ortenzio and d’Alcala, 2009; Siokou-Frangou et al., 2010; Navarro et al., 2011). In general, productivity in the western basin exceeds that in the eastern basin. On a regional scale, the Alboran, the Balearic, the northern Adriatic, and the Northern Aegean Seas always appear to be biologically more productive sub-basins than other regions, and on local scales there are even more pronounced hotspots of biological production connected to river runoff, submarine can- yons, and regional upwelling centers (e.g., Gulf of Lions, the north- western Alboran Sea, the Ebro delta and the Catalan shelf-slope zone, and the Nile and Po deltas). The northwestern (NW) Alboran Sea along the Spanish coast between 5.0°W and 3.5°W longitudes (Fig. 1) supports high bio- logical productivity due to enhanced lateral and vertical nutrient fluxes (Ramírez et al., 2005; Reul et al., 2005; Mercado et al., 2007; Macías et al., 2008). The region also sustains one of the richest fish resources in the Mediterranean (Bellido et al., 2008) and serves as a favourable habitat and nursery ground for the European sardine (Sardina pilchardus) and European an- chovy (Encraulis encrasicolus) (Estrada, 1996; García-Lafuente et al., 1998; Rubín et al., 1999; García et al., 2003; Macías et al., 2011). These small pelagics fishes also serve as a rich food source for apex predators (Coll et al., 2011). Enhanced biological activity declines toward the interior of the oligotrophic Western anticyclonic Alboran Gyre (WAG) and as the Atlantic jet pro- ceeds eastward (e.g. Tintore et al., 1991; Viudez et al., 1998). In general, the Almeria–Oran front (Tintore et al., 1988) lying along the eastern flank of the Eastern anticyclonic Alboran Gyre (EAG) separates the relatively productive Alboran Sea from the less productive western Algerian basin. The oligotrophy of the latter system is related to the very limited vertical and lateral supply of nutrients into the photic layer throughout the year. 0079-6611/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.pocean.2013.03.001 ⇑ Corresponding author at: SOCIB, Balearic Islands Coastal Ocean Observing and Forecasting System, Parc Bit, Naorte, Bloc A, Palma de Mallorca, Spain. E-mail address: oguz@ims.metu.edu.tr (T. Oguz). 1 Present address: European Commission, Joint Research Center, Institute for Environment and Sustainability, Water Research Unit, Via E. Fermi 2749, 21027-Ispra, Italy. Progress in Oceanography 112–113 (2013) 1–14 Contents lists available at SciVerse ScienceDirect Progress in Oceanography journal homepage: www.elsevier.com/locate/pocean