Abstract
Black Sea is one of the most severely degraded and exploited large marine ecosystems in the world. For the last 50 years after the depletion of large predatory fish stocks, anchovy (with the partial contribution of sprat) has been acting as the main top predator species and experienced a major stock collapse at the end of 1990s. After the collapse, eastern part of the southern Black Sea became the only region sustaining relatively high anchovy catch (400,000 tons) whereas the total catch within the rest of the sea was reduced to nearly its one-third. The lack of recovery of different fish stocks under a slow ecosystem rehabilitation may be attributed, on the one hand, to inappropriate management measures and the lack of harmonized fishery policy among the riparian countries. On the other hand, impacts of multiple stressors (eutrophication, alien species invasions, natural climatic variations) on the food web may contribute to resilience of the system toward its recovery. The overfishing/recovery problem therefore cannot be isolated from rehabilitation efforts devoted to the long-term chronic degradation of the food web structure, and alternative fishery-related management measures must be adopted as a part of a comprehensive ecosystem-based management strategy. The present study provides a data-driven ecosystem assessment, underlines the key environmental issues and threats, and points to the critical importance of holistic approach to resolve the fishery-ecosystem interactions. It also stresses the transboundary nature of the problem.
Highlights
At global scale, evidence is unequivocal for multitude of changes on ocean biogeochemical cycles and ecosystems due to ocean warming, acidification, and deoxygenation in response to the rising atmospheric CO2 levels (Hoegh-Guldberg and Bruno, 2010; Doney et al, 2012; Bopp et al, 2013; Poloczanska et al, 2013)
The Black Sea is a nearly enclosed and zonally elongated basin with the zonal dimension of about 1,200 km and the meridional dimension varying from 500 km on the western side to 250 km Controls of Stressors on the Black Sea Fishery toward the eastern side (Figure 1)
Following the major characteristics features of climate variability and the past and present states of fishery, the present study describes the characteristic features of nutrient over enrichment and alien species invasions
Summary
Evidence is unequivocal for multitude of changes on ocean biogeochemical cycles and ecosystems due to ocean warming, acidification, and deoxygenation in response to the rising atmospheric CO2 levels (Hoegh-Guldberg and Bruno, 2010; Doney et al, 2012; Bopp et al, 2013; Poloczanska et al, 2013). Shelf, and semi-enclosed seas providing important economic resources experience additional stressors arising from the local/regional natural climatic variations, eutrophication, eutrophication-induced changes (such as acidification, de-oxygenation, loss of biodiversity, degradation of food web, etc), overfishing, and alien species invasion (Boldt et al, 2014). For these ecosystems, both CO2 and non-CO2 related stressors acting together have potential to alter trophic structure, food-web dynamics, energy and material flows, and biogeochemical cycles and impact considerably the ecosystem services for humans, as in the case of Baltic Sea (Niiranen et al, 2013; Jutterström et al, 2014). It identifies the major knowledge gaps in relation to ecosystemlevel management strategies (what to do and how to proceed forward) and gives the concluding remarks
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