Community bioirrigation potential (BIP

BIOIRRIGATION: the animal-induced exchange of solutes between pore water and overlying water - is a key process in sediments with profound implications for biogeochemical processes such as nutrient cycling and organic matter regeneration at the sediment water interface. There is an urgent need to understand how a changing environment will affect the irrigation activity of macrofauna and vice versa. A shift in species composition (e.g. from deep burrowing species to smaller, more opportunistic and shallow burrowing species) will have large effects on bioirrigation and thus on ecosystem function (such as benthic pelagic coupling). Considering the difficulties to determine area-covering rates of bioirrigation (e.g. in terms tracer-based fluxes) and the complexity of interactions of multiple species in the community that prohibit a direct measure of bioirrigation attributable to each species, a mechanistically-based approach is needed to predict relative intensities of bioirrigation activity based on the fundamental functional traits. We propose a conceptual framework to develop an index of bioirrigation that takes into account the biological mechanisms of bioirrigation and provides a simplified, yet functionally based approach to quantify the bioirrigation potential of benthic communities. We developed the community bioirrigation potential (BIPc) that provides a biomass- and abundance-weighted scoring system considering functional traits related to pore water and solute exchange. It may be used as a supplement to established methods to assess the function of marine soft sediments related bioirrigation. In analogy to the particle-related community bioturbation potential of Solan et al. (2004), context dependent organismal traits that affect ventilation and bioirrigation (feeding type, morphology of burrows, and burrowing depth) are combined with the data on abundance and biomass of the respective species. These are subsequently summed up to a community bioirrigation potential (BIPc). This review considers ecological traits relevant for bioirrigation and their classification into a bioirrigation index. Furthermore the necessary simplifications in the index (e.g. limiting its applicability to interfacial nutrient fluxes) are discussed. We also provide a working example from the southwestern Baltic Sea to illustrate the practical application of the index and a compilation of key species related to this area containing their classification into the considered bioirrigation traits.