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Adverse Eco-Feedbacks


Authors in bold are staff of the Institute for Ocean Conservation Science

Weeks, S.J., Anthony, K.N., Bakun, A., Feldman, G.C., Hoegh-Guldberg, O.. 2008. Improved predictions of coral bleaching using seasonal baselines and higher spatial resolution. Limnol. Oceanogr. 53(4), 2008, 1369–1.

Limnol. Oceanogr. Website

Abstract: Coral bleaching spread across the southern Great Barrier Reef in January 2006, after sea temperatures reached climatological summer maxima 2 months before normal. Current satellite-derived warning systems were unable to detect severe bleaching conditions in the region because of their use of a constant thermal threshold (summer maximum monthly mean) and low spatial resolution (50 km). Here it is shown that such problems can be ameliorated if the thermal threshold is adjusted for seasonal variation and a 4-km spatial resolution is used. We develop a seasonally and spatially improved thermal threshold for coral bleaching on the basis of a weekly climatology of sea surface temperatures extending from austral spring to late summer, and apply the method to two case-study sites. At both sites, and in particular at the nearshore site that was undetected by the 50-km satellite product, the seasonally adjusted thermal threshold produced a greatly improved consistency between accumulated heating and bleaching severity. The application of thermal stress algorithms that reflect the longterm mean pattern in seasonal variation allows coral bleaching to be forecast with higher precision.

Bakun A. 2006. Wasp-waist populations and marine ecosystem dynamics: navigating the “predator pit” topographies. Progress in Oceanography . 68: 271-288.

Abstract: Many marine ecosystems exhibit a characteristic "wasp-waist"structure, where a single species, or at most several species, of small planktivorous fishes entirely dominate their trophic level. These species have complex life histories that result in radical variability that may propagate to both higher and lower trophic levels of the ecosystem. In addition, these populations have two key attributes: (1) they represent the lowest trophic level that is mobile, so they are capable of relocating their area of operation according to their own internal dynamics; (2) they may prey upon the early life stages of their predators, forming an unstable feedback loop in the trophic system that may, for example, precipitate abrupt regime shifts. Experience with the typical "boom-bust" dynamics of this type of population, and with populations that interact trophically with them, suggests a "predator pit" type of dynamics. This features a refuge from predation when abundance is very low, very destructive predation between an abundance level sufficient to attract interest from predators and an abundance level sufficient to satiate available predators, and, as abundance increases beyond this satiation point, decreasing specific predation mortality and population breakout. A simple formalism is developed to describe these dynamics. Examples of its application include (a) a hypothetical mechanism for progressive geographical habitat expansion at high biomass, (b) an explanation for the out-of-phase alternations of abundances of anchovies and sardines in many regional systems that appear to occur without substantial adverse interactions between the two species groups, and (c) an account of an interaction of environmental processes and fishery exploitation that caused a regime shift. The last is the example of the Baltic Sea, where the cod resource collapsed in concert with establishment of dominance of that ecosystem by the cod's "wasp-waist" prey, herring and sprat.

Bakun A, Weeks S. 2006. Adverse feedback sequences in exploited marine systems: are deliberate interruptive actions warranted?. Fish and Fisheries. 7: 316–333. Abstract

Bakun A. 2005. Seeking an expanded suite of management tools: implications of rapidly-evolving adaptive response mechanisms (e.g., "school-mix feedback"). Bulletin of Marine Science. 76: 463-483.

Bakun A. 2005. Regime Shifts, in The Sea, Vol.13. Pages Ch.25, pp.971-1026. Ed. by Robinson A R and Brink K. Harvard University Press, Cambridge, Massachusetts.

Bakun A, S J Weeks. 2004. Greenhouse gas buildup, sardines, submarine eruptions and the possibility of abrupt degradation of intense marine upwelling ecosystems. Ecology Letters. 7: 1015-1023.

Abstract: Widespread hypoxia and massive eruptions of noxious, radiatively active gases currently characterize the world's strongest eastern ocean upwelling zone. Theory, modelling results and observations suggest that the world's coastal upwelling zones will undergo progressive intensification in response to greenhouse gas buildup. This presents the prospect of progressive development of similarly degraded marine ecosystems in additional regions and of a contributing feedback loop involving associated additions to the global buildup rate of greenhouse gases, resulting further increases in upwelling intensity, creation of additional sources of greenhouse gas emissions, and so on. Abundant sardine stocks might be a mitigating factor opposing the process.

Weeks S J, B Currie, A Bakun, K R Peard. 2004. Hydrogen sulphide eruptions in the Atlantic Ocean off southern Africa: Impliations of a new vieew based on SeaWiFS satellite imagery. Deep Sea Research . I 51: 153-172.

Bakun A, K Broad. 2003. Environmental 'loopholes' and fish population dynamics: comparative pattern recognition with focus on El Nino effects in the Pacific. Fisheries Oceanography. 12 (4-5): 458-473.


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