Biogeographic variability in ecosystem engineering: Patterns in the abundance and behavior of the tube-building polychaete Diopatra cuprea

Abstract

Ecosystem engineering is an important process influencing the structure and function of eco-systems worldwide. Geographic variation in a species' engineering processes can thus have important implications for spatial heterogeneity in ecosystem function. In this study I explore geographic variability in the engineering properties of an important organism in marine sedimentary habitats, the polychaete Diopatra cuprea. In the Northwest Atlantic, D. cuprea facilitates benthic communities by creating predation refugia and substrate-both density-dependent processes-and by actively attaching macroalgae to its tube. D. cuprea's ecosystem-engineering properties thus arise from both its abundance and its behavior. I show that both components of D. cuprea engineering decrease precipitously at low latitudes. I assess the relationship between these patterns and a suite of environmental parameters, finding that northern versus southern sites cluster separately in multivariate environmental space and that temperature, dissolved oxygen, and pH may contribute to both D. cuprea abundance and the biomass of facilitated algae. I present evidence that southern D. cuprea populations may be affected by post-recruitment mortality more severely than northern populations. Finally, I experimentally demonstrate that D. cuprea's failure to facilitate algae in its south-ern range is not due to latitudinal differences in algal availability, acceptability or retain ability, but rather is a behavioral shift driven by still-unknown factors. This study demonstrates dramatic geographic variability in both D. cuprea's density-with strong implications for its density-dependent engineering functions-and D. cuprea's algal facilitation. Disentangling the mechanisms underlying such variability is an important goal for understanding spatial heterogeneity in the structure and function of North west Atlantic shallowwater sedimentary systems. © 2012 Inter-Research.