Regime shifts in exploited marine food-webs: detecting mechanisms underlying alternative stable states using size-structured community dynamics theory
Friday seminar by Anna Gårdmark
Many marine ecosystems have undergone 'regime shifts', i.e. abrupt reorganizations across trophic levels. Establishing whether these constitute shifts between alternative stable states, as opposed to phase shifts, is of key importance for the prospects of ecosystem recovery and for management. Because large marine food-webs are impossible to manipulate experimentally, other approaches are needed to identify alternative stable food-web states. We show how evidence of alternative stable states caused by predator-prey interactions can be found in field data, using analyses guided by theory on size-structured community dynamics. By combining data on individual performance with population level information, the mechanisms stabilizing the alternative states can be distinguished. We use cod and their prey in the Baltic Sea as an example to discuss four mechanisms that can cause alternative stable states preventing the recovery of overexploited predatory fish populations, and show how this data analysis framework can be used to identify the underlying mechanisms.
This is a collaboration with Casini, M., Huss, M., van Leeuwen, A., Hjelm, L., Persson, L. & A. M. de Roos.
Anna Gårdmark, PhD
Swedish University of Agricultural Sciences (Sveriges Lantbruksuniversitet, SLU)
Department of Aquatic Resources (SLU-Aqua)
Institute of Coastal Research (Kustlaboratoriet) Skolgatan 6
SE-742 42 Öregrund