Biogeochemical control of marine productivity in the Mediterranean Sea during the last 50 years

Abstract

The temporal dynamics of biogeochemical variables derived from a coupled 3-D model of the Mediterranean Sea are evaluated for the last 50 years (1960–2010) against independent data on fisheries catch per unit effort (CPUE) for the same time period. Concordant patterns are found in the time series of all of the biological variables (from the model and from fisheries statistics), with low values at the beginning of the series, a later increase, with maximum levels reached at the end of the 1990s, and a posterior stabilization. Spectral analysis of the annual biological time series reveals coincident low-frequency signals in all of them. The first, more energetic signal peaks around the year 2000, while the second, less energetic signal peaks near 1982. Almost identical low-frequency signals are found in the nutrient loads of the rivers and in the integrated nutrient levels in the surface marine ecosystem. Nitrate concentration shows a maximum level in 1998, with a later stabilization to present-day values, coincident with the first low-frequency signal found in the biological series. Phosphate shows maximum concentrations around 1982 and a posterior sharp decline, in concordance with the second low-frequency signal observed in the biological series. That result seems to indicate that the control of marine productivity (plankton to fish) in the Mediterranean is principally mediated through bottom-up processes that could be traced back to the characteristics of riverine discharges. The high sensitivity of CPUE time series to environmental conditions might be another indicator of the overexploitation of this marine ecosystem.Key PointsBiogeochemical evolution of the Mediterranean over the past 50 yearsRiver nutrient loads drive primary and secondary productionsStrong link between low trophic levels and fisheries

Historical changes of the Mediterranean Sea ecosystem: modelling the role and impact of primary productivity and fisheries changes over time

“…In addition, our results indicated that the PP anomaly, representing the temporal variation of the primary productivity of the system, was the strongest driver upon the Mediterranean Sea ecosystem. This supports the results obtained from other studies4957 that have shown how the Mediterranean Sea is driven by bottom-up processes where nutrient availability controls the biological characteristics of the region. The use of relative PP trends from a regional biogeochemical model helped validating our predicted PP anomaly trend and improved the temporal dynamics of selected species in the ecosystem (particularly for forage fish: European pilchards and anchovies).…”

Major fertilization sources and mechanisms for Mediterranean Sea coastal ecosystems

“…GETM is coupled online to the MedERGOM biogeochemical model (Macias et al a,b ) by using the Framework for Aquatic Biogeochemical Models (FABM, https://sourceforge.net/projects/fabm/, Bruggeman and Bolding ). MedERGOM is a modified version of the ERGOM model (Neumann ) specifically adapted to represent the conditions of the pelagic ecosystem of the Mediterranean Sea.…”

“…MedERGOM is a modified version of the ERGOM model (Neumann ) specifically adapted to represent the conditions of the pelagic ecosystem of the Mediterranean Sea. It has proven useful to describe present (Macías et al b ), past (Macias et al a ), and future (Macias et al ) biogeochemical conditions in this semi‐enclosed basin. MedERGOM includes three phytoplankton types, three macronutrients (nitrate, ammonia, and phosphate), detritus and dissolved oxygen as main state variables.…”

The seasonal cycle of the Atlantic Jet dynamics in the Alboran Sea: direct atmospheric forcing versus Mediterranean thermohaline circulation

“…No horizontal currents were imposed at the open boundary. It has been demonstrated that for basinwide studies the location of this western boundary is not crucial (e.g., Macías et al 2013Macías et al , 2014c, but it does affects the performance of the model in the Alboran Sea in terms of absolute values of hydrological and biogeochemical properties (e.g., Macías et al 2014b). In those previous works, the open boundary of the model was located right on the strait itself as their focus was on the basin-wide properties and not on regional scales.…”