Seasonal and inter-annual variability of plankton chlorophyll and primary production in the Mediterranean Sea: a modelling approach

Abstract

This study presents a model of chlorophyll and primary production in the pelagic Mediterranean Sea. A 3-D-ecosystem model (OPATM-BFM) was adopted to explore specific system characteristics and quantify key biogeochemical variables covering a 6-yr period, from 1999 to 2004. <br><br> We show that, on a basin scale, the Mediterranean Sea is characterised by a high degree of spatial and temporal variability in terms of primary production and chlorophyll concentrations. On a spatial scale, important horizontal and vertical gradients have been observed. In particular, notable differences between surface net primary production variability and the corresponding vertically integrated production rates have been identified, suggesting that care must be taken when inferring productivity in such systems from satellite observations alone. The present study indicates that seasonal variability dominates inter-annual differences. <br><br> According to the simulations over a 6-yr period, the developed model correctly simulated the climatological features of deep chlorophyll maxima and chlorophyll west-east gradients, as well as the seasonal variability in the primary offshore regions that were studied. The integrated net primary production highlights north-south gradients that differ from surface net primary production gradients and illustrates the importance of adopting a spatial and temporal description to calculate basin-wide budgets and their variabilities. According to the model, the western Mediterranean, in particular the Alboran Sea, can be considered mesotrophic, whereas the eastern Mediterranean is oligotrophic. <br><br> Finally, specific simulations that were designed to explore the role of ecosystem boundary conditions were performed. The subsequent results show that the effects of atmospheric and terrestrial nutrient loads on the total integrated net primary production account for less than 5 % of the annual budget, whereas an increase of 30 % in the light extinction factor impacts primary production by approximately 10 %

Anchovy (<em>Engraulis encrasicolus</em>) otoliths reveal growth differences between two areas of the Spanish Mediterranean Sea

“…Though both areas are productive (Bellido et al 2008), the chlorophyll and primary production values in the Alboran Sea are higher than those in the Delta zone (Siokou-Frangou et al 2010, Lazzari et al 2012, Salgado and Lorenzo 2014. By contrast, the surface temperature is lower in Alboran Sea than in the Ebro Delta area, although the main trend in both areas is an increasing temperature (Shaltout and Omstedt 2014) .…”

Seasonal changes in growth and condition of anchovy late larvae explained with a hydrodynamic-biogeochemical model simulation

“…The use of such models in interpreting changes in larval growth and condition and identifying temporal windows of increased growth and survival will probably become very popular in the future as such models are being implemented, validated and becoming operational in most regional seas around the world (e.g. Kishi et al 2007, Siddorn et al 2007, Lazzari et al 2012.…”

Temporal and inter-specific variations in forage fish feeding conditions in the NW Mediterranean: lipid content and fatty acid compositional changes

“…Climate and ecosystem variability in the GoL operate over a range of spatial and temporal scales that affect phytoplankton biomass and production (Gaudy et al 2003, Siokou-Frangou et al 2010. Both temperature and primary production follow annual cycles characterized by strong seasonality (Razouls & Kouwenberg 1993, Lazzari et al 2011. Forage fishes in this region are classified as omnivores, having trophic positions between 2.2 and 3.7 (Plounevez & Champalbert 2000, Stergiou & Karpouzi 2001, Costalago et al 2012.…”