Unraveling ecosystem functioning in intertidal soft sediments: the role of density-driven interactions

Stefano Schenone,Simon F. Thrush

doi:10.1038/s41598-020-68869-4

Abstract

Although they only occupy a relatively small portion of the surface of the planet, coastal habitats are some of the most productive and valued ecosystems in the world. Among these habitats, tidal flats are an important component of many harbours and estuaries, but their deterioration due to human activities poses a serious threat to biodiversity and ecosystem function. Benthic communities are usually arranged in patches dominated by key species with overlapping distributions. Understanding the ecological consequences of interactions between these species in transition zones where their habitats overlap is necessary in order to quantify their contribution to overall ecosystem functioning and to scale-up and generalize results. Spatial transition in abundance and the interaction of multiple factors that drive ecosystem function are complex processes that require real-world research. Through a multi-site mensurative experiment, we show that transition areas drive non-linear effects on biogeochemical fluxes that have important implications for quantifying overall functioning. In our study the main drivers of ecosystem function were the abundance of two large but functionally very different species rather than biodiversity per se. Furthermore, we demonstrate that the use of the biogenic features created by specific infaunal species at the sediment–water interface is a better predictor of ecosystem functioning than the density of the species per se, making this approach particularly appealing for large scale, mapping and monitoring studies.

Highlights

They only occupy a relatively small portion of the surface of the planet, coastal habitats are some of the most productive and valued ecosystems in the world
By quantifying these ecosystem functions at different locations with varying densities of target species, we were able to demonstrate how the co-occurrence of both species at high densities tends to decrease biogeochemical fluxes as compared to patches dominated by either species and how this negative effect changed with the relative density of the two organisms
The presence of M. liliana and M. stewartensis and their interaction were consistently important predictors, while the environmental variable that was most consistently retained in the models was sediment porosity

Summary

Introduction

They only occupy a relatively small portion of the surface of the planet, coastal habitats are some of the most productive and valued ecosystems in the world. Using in-situ benthic incubation chambers and an organic matter degradation assay we measured the fluxes of dissolved oxygen (O2) and ammonium (NH4+) as well as the organic matter degradation rate at the sediment surface (Co) and the extinction coefficient of organic matter degradation with sediment depth (k) By quantifying these ecosystem functions at different locations with varying densities of target species, we were able to demonstrate how the co-occurrence of both species at high densities tends to decrease biogeochemical fluxes as compared to patches dominated by either species and how this negative effect changed with the relative density of the two organisms. These sandflat communities are species rich (c 100–150 macrofauna species) and yet, using a methodology originally developed to understand the variation in community data (“variance partitioning”10), we were able to tease apart the role of these large species that leave signatures on the sediment surface from the role of the community (biodiversity) in driving ecosystem function

Methods

Results

Conclusion