Turkish Journal of Fisheries and Aquatic Sciences
2013, Vol 13, Num, 4 (Pages: 581-592)
Quantification of the Synergistic Effects of Eutrophication, Apex Predator Pressure, and Internal Processes on the Black Sea Ecosystem
Baris Salihoglu 1 ,Nusret Sevinc 1
1 Middle East Technical University, Institute of Marine Sciences, Erdemli, Mersin, Turkey
DOI :
10.4194/1303-2712-v13_4_03
Viewed :
4804
-
Downloaded :
3212
In the present study, a model of the lower-trophic pelagic food web of the Black Sea is considered in order to provide a
quantitative understanding of the marked changes in the food web structure in response to changing top-down and bottom-up
control mechanisms due to eutrophication, overfishing, and climatic changes. The simulations consider three particular
parameters controlling the changes in the ecosystem structure due to these stressors; (i) the magnitude of the nitrate flux into
the euphotic layer from the chemocline layer (enrichment due to eutrophication), (ii) the magnitude of predation control
introduced by the planktivorous fish on mesozooplankton (fishery), (iii) the magnitude of the Q10 parameter controlling
temperature dependence of the Mnemiopsis growth (changing climatic conditions). A simulation assessing the level of
enrichment on the ecosystem indicates a shift of the major trophic energy flow towards Noctiluca and Aurelia and thus
showing how the ecosystem would degrade when a critical level of enrichment is passed. Increasing predation pressure of the
planktivorous fish during the enrichment phase is shown to reduce the mesozooplankton biomass that in turn declines its
predation pressure on Noctiluca population and thus allows Noctiluca biomass to increase, considering that mesozooplanton is
assumed to feed on Noctiluca (at a level of 15% food preference) in the current model.. Noctiluca then acts as a major
consumer and a critical element of the degraded food web structure. The overfishing of planktivorous fish stocks allows
Mnemiopsis biomass to increase considerably under changing (warmer) climatic conditions at the end of 1980s, following a
decade-long intense cooling phase. Thus, our results suggest that overfishing would not alone be able to promote a
Mnemiopsis population outburst in the absence of warming.
Keywords :
Black Sea, population dynamics, trophic levels, nutrient enrichment, predation control, mnemiopsis