Projecting key benthic processes – new options by species distribution models?

Macrobenthic communities play a major role in marine nutrient cycles especially in shallow coastal areas. Biodeposition is one of the most relevant activities for benthic-pelagic coupling. It is forced by suspension feeders capturing food particles from the water column and depositing the indigested organic material. Suspension feeders might even control the pelagic primary production by significantly reducing phytoplankton density.

The filtering capacity of individual species can be linked to their biomass. One of the main drawbacks both to calculate the nutrient budget and to predict future changes on a regional or subregional scale is the lack of knowledge on the spatial distribution of key species. The aim of our study was to quantify the spatial distribution of filter capacity. We provide quantitative distribution maps of key species and by linking these maps with the available equations we also provide information on spatial distribution and intensity of the filtering capacity.

Our study area is the south-western part of the Baltic Sea, one of the largest brackish water systems of the world. Due to reduced salinity, a few large bivalve species dominate the benthic communities in soft substrates both in terms of biomass and in suspension-feeding capacity. For habitat suitability modeling, two approaches were tested: (1) building one model with the response variable “individual biomass” achieved by calculating the mean individual biomass at each station before modeling and (2) building two models for “overall biomass” and “abundance” respectively and calculating the mean individual biomass from the achieved model results. While the first approach failed to find a significant correlation between response variable and available predictors, the latter produced a profound basis for the linkage with filtering capacity. Based on these results we developed grid based maps as a basis to calculate the nutrient fluxes driven by suspension feeding.