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

The temporal dynamics of biogeochemical variables derived from a coupled 3D model of the Mediterranean Sea are evaluated during the last 50 years (1960 – 2010) against independent data on fisheries catches per unit effort (CPUE) for the same time period. Concordant patterns are found in the time-series of all 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 1990’s 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, peaking circa year 2000 while the second one (less energetic) presents maximum values at around 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 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 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 could be considered as an additional indication of overexploitation of this marine ecosystem.

MACIAS MOY Diego;  GARCIA GORRIZ Elisa;  PIRODDI Chiara;  STIPS Adolf; 

2014-09-25

AMER GEOPHYSICAL UNION

JRC89413

0886-6236,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC89413,   

10.1002/2014GB004846,