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JPR Advance Access published online on September 25, 2008
Journal of Plankton Research, doi:10.1093/plankt/fbn094
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Invasion dynamics of the alien ctenophore Mnemiopsis leidyi and its impact on anchovy collapse in the Black Sea

Temel Oguz, Bettina Fach and Baris Salihoglu

INSTITUTE OF MARINE SCIENCES, MIDDLE EAST TECHNICAL UNIVERSITY, PO BOX 28, 33731 ERDEMLI, MERSIN, TURKEY

CORRESPONDING AUTHOR: T. OGUZ. E-MAIL: oguz{at}ims.metu.edu.tr

Received on June 9, 2008; revised on September 1, 2008; accepted on September 14, 2008


  Abstract

The mechanisms governing the unprecedented 1989-1990 anchovy-Mnemiopsis shift event in the Black Sea were evaluated with a coupled model of bioenergetic-based anchovy population dynamics and lower trophic food web structure. Simulations showed that a combination of direct and density-dependent effects of overfishing, eutrophication-induced nutrient enrichment, climate-induced over-enrichment, and temperature-controlled Mnemiopsis spring production were involved in the shift. Eutrophication made the system vulnerable to further enrichment through the change of regional climate to a severe winter regime during 1985-1987. While Mnemiopsis was acclimating to its new environment, increasing nitrate flux into the euphotic layer enhanced the carrying capacity of the system but a disproportionate Mnemiopsis biomass increase was delayed until spring temperature conditions returned to normal in 1988-1989. Enhanced carrying capacity provided a competitive advantage of food consumption to Mnemiopsis compared to anchovy, and warm spring temperature conditions promoted their spring-summer production. Prevalent high fishery pressure and increasing impact of Mnemiopsis on the food web further induced the anchovy stock collapse. However, the shift event did not result in alternation of the system to a new totally Mnemiopsis-invaded quasi-stable regime. Instead, anchovy started recovering when the subsequent strong 1991-1993 cooling regime limited the Mnemiopsis population growth. Our analysis indicated that the switch of a large marine ecosystem to a totally gelatinous invader-dominated state required extremely strong environmental perturbations. More often, environmental disturbances create a suitable niche for an alien gelatinous invader to become a member of the food web structure, and to share food resources with the native small pelagic fish community.

Key Words: Anchovy collapse • Black Sea • climate control • eutrophication • invasion dynamics • Mnemiopsis outbreak • nutrient enrichment, overfishing

Communicating Editor: Professor Mark Gibbons


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