PARENT SESSION
Contributed Oral Session 10: Aquatic Trophic Systems I
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 B, Level 5, Palais des congrès de Montréal
Mechanisms driving changes in food chain length following restoration of a fragmented Bahamian estuary.
Layman, Craig*,1, Arrington, Albrey2, Post, David1, 1 Yale University, New Haven, CT2 Perry Institute for Marine Science, Jupiter, FL
ABSTRACT- The exchange of material and organisms between estuarine and coastal marine ecosystems suggests ecosystem fragmentation, via disruption of hydrologic connectivity, should have strong impacts upon many aspects of assemblage and food web structure, including food chain length (FCL). We are using Bahamian estuaries as model systems to empirically examine the relationship between hydrologic connectivity and FCL, and hypothesize that open estuaries should support longer food chains than fragmented estuaries of the same size. In this paper, we describe results of one ecosystem-scale experimental manipulation in which we restored hydrologic connectivity (i.e., tidal flow) to a previously fragmented estuary on Andros Island. FCL, as estimated by stable isotope ratio analyses, increased immediately (i.e., days) following restoration of hydrologic connectivity in Davis Creek, and remained significantly higher 3 months following the restoration. We further discuss the role of three proximate mechanisms in the regulation of FCL: 1) the addition or deletion of top predators (additive mechanism), 2) changes in the structure of the middle of the food web (insertion mechanism), and 3) changes in the degree of trophic omnivory (omnivory mechanism). Based on stable isotope and direct stomach content analyses, we show that the additive mechanism is the most important factor driving FCL increases following restoration of tidal flow, as large-bodied transient predators now utilize the restored estuary. Based on this empirical data set, we introduce a conceptual framework for incorporating ecologically-relevant spatial and temporal scales into the food chain length discourse.
Key words: food webs, predation, isotopes, fragmentation