Reassessing the costs of biological invasion: Mnemiopsis leidyi in the Black sea

Invasions of ecosystems by exotic species have been the focus of a growing body of research in applied biology and ecology, but relatively little attention has been paid to their economic consequences. Even where economic estimates have been made these often make ad hoc assumptions about the biological relationships of interest and lack grounding in economic theory. This paper develops an integrated ecological-economic approach to assess the economic consequences of invasion for a commercially harvested endemic species whose population dynamics are altered by the invader. As a case study, the Black Sea anchovy fishery represents an interesting example of such a situation. In the early 1980s, the comb jelly Mnemiopsis leidyi invaded the Black Sea, eventually becoming established and experiencing a population explosion with dire consequences for the commercial anchovy fishery. In modeling the population dynamics of the Black Sea anchovy (Engraulis encrasicolus), the influence of Mnemiopsis is incorporated as a structural change in the anchovy stock-recruitment relationship. Then the economic loss associated with this structural change is assessed, using a discrete, dynamic bioeconomic model. It is shown that Mnemiopsis had a dramatic effect on the potential sustainable harvest from an optimally managed anchovy fishery but these losses were at least an order of magnitude lower than estimates cited elsewhere.