Macrobenthic recovery from hypoxia in an estuarine tidal mudflat

Abstract

Macrobenthic recolonisation patterns after complete defaunation resulting from exper- imentally induced hypoxia were investigated in a polyhaline, estuarine mudflat. Based on simultane- ous sampling of biotic and environmental variables in replicated 16 m 2 control and defaunated plots, with a high resolution in time during 6 mo, the ecological interactions related to the macrobenthos reassembly were elucidated. Colonisation was predominantly determined by juvenile recruitment, and 3 successional stages were identified, each characterised by different species assemblages and environmental characteristics. During recovery, a shift in functional group dominance from mobile surface deposit feeders to tube-dwelling surface deposit feeders to biodestabilising taxa occurred, while their proportional dominance remained quite stable in the control plots throughout the experi- ment. Species colonisation patterns of later colonists revealed positive interactions with early colonis- ing opportunistic tube-building polychaetes Pygospio elegans, while later successional species (Het- eromastus filiformis, Macoma balthica) adversely affected the stable, favourable conditions created by the tube-building infauna. Transitions between different successional stages were related to recruitment of species, changes in environmental characteristics (oxygenation state of the sediment), direct and indirect ecological interactions (bio(de)stabilisation, exploitation competition for food). In general, our study suggests that macrobenthic reassembly after hypoxia is related to different types of interactions, all acting in a unique manner. Hence, macrobenthic successional dynamics in a tidal mudflat habitat should be considered as a dynamic process, related to resource availability, natural temporal variation, life history traits (e.g. opportunistic behaviour) and bio-engineering capacities of the colonising species.