Structural modification of aquatic environments by shells: implications for human-mollusc interactions

JORGE LUIS CEFERINO GUTIERREZ

Paris

Workshop; Interdisciplinary Approaches to the Study of Human and Mollusc Interactions: from Prehistory to Present; 2018

Physical ecosystem engineering is the structural modification of environments by organisms. Many mollusc speciesare noticeable physical ecosystem engineers, not least because of their ability to produce shells. Here I postulate threegeneral structural roles of mollusc shells in aquatic ecosystems, namely: (1) substrata for organismal attachment, (2)refuges from predation, physical or physiological stress, and (3) controllers of near-bed flows and material transportin the benthic environment. Then, I illustrate (a) that changes in resource availability or abiotic conditions caused byshell production have important consequences for other organisms, (b) that colonization of shelled habitat dependson individual shell traits and spatial arrangement of shells, which determine access of organisms to resources andthe degree to which biotic or abiotic forces are modulated, (c) that shell production will increase species richnessat the landscape level if shells create resources that are not otherwise available and species are present that usethese resources, and (d) that changes in the availability of resources caused by shells and the resulting effectson other organisms have both positive and negative feedbacks to the engineer in question. Last, I exemplify howongoing changes in shell production and distribution resulting from human activities (e.g., exploitation, introductionand invasion of shelled molluscs; use of mollusc shells in habitat restoration) can affect the structure of benthicenvironments as well as the composition and functioning of aquatic ecosystems.