Organism-sediment interactions govern post-hypoxia recovery of ecosystem functioning.

Carl Van Colen,Steven Degraer,Maria G I Andersson,Jack J Middelburg,Britta Gribsholt,Francesc Montserrat,Magda Vincx,Peter M J Herman,Tom Ysebaert,Francesca Rossi

doi:10.1371/journal.pone.0049795

Abstract

Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.

Highlights

To date most ecosystems are profoundly affected by multiple human activities that alter the systems’ diversity, functioning and delivered services, e.g. [1,2]
In order to assess benthic community responses to hypoxia, the present study aims at understanding the dynamics of the relationship between reassembling macrobenthos communities and sediment properties determining ecosystem functioning following hypoxia
Deposit feeding and biodiffusing species always dominated the undisturbed community, indicating that the changes observed after hypoxia reflected successional dynamics imputable to recolonisation after disturbance (Figure 1)

Summary

Introduction

To date most ecosystems are profoundly affected by multiple human activities that alter the systems’ diversity, functioning and delivered services, e.g. [1,2]. [1,2] These activities range from single and recurring disturbances to continuous stress of which the consequences for ecosystem resilience (i.e. movement within and between stability domains) may depend on the magnitude of induced change and the diversity-stability relationships that occur during recovery [3]. Ecological theory indicates that increased levels of biodiversity often result in increased ecosystem functioning [5,6], which may insure stability against environmental change via compensatory processes and species performance-enhancing effects [7,8]. The magnitude and direction of the biodiversity-ecosystem function relationship was shown to be idiosyncratic and depending on the disturbance context [9,10,11,12]. Changes in species interactions and population dynamics during the recovery process are likely to affect the performances of particular ecosystem functions. Ecosystem resilience may depend on the time needed to restore ecosystem functioning by post-disturbance reassembling of those species with particular functional traits that have distinct effects on ecosystem processes

Methods

Results

Conclusion