Biodiversity and ecosystem processes in heterogeneous environments

Abstract

The decline in biodiversity over the last decade has motivated researchers to investigate the relationship between species richness (biodiversity) and ecosystem function. Empirical approaches are becoming more realistic as more factors have been included. Spatial heterogeneity is an example. Heterogeneity is an inherent part of the environment and apparent in all habitat types creating a patchy, mosaic of natural landscape. Researchers have reported the extent of heterogeneity in the landscape, but surprisingly not yet included heterogeneity into biodiversity and ecosystem function (BEF) studies.

In recent years, empirical studies of marine systems have enhanced the BEF debate. Depauperate estuarine systems are ideal candidates for establishing model systems. In this study, estuarine microphytobenthos (MPB) were used as a response variable since the relationship between MPB and primary productivity is well-known. This relationship was exploited to employ MPB biomass as a proxy for primary productivity. Benthic chambers were used to assess the effect of macrofauna in single species and multi-species treatments on both ecosystem function and net macrofaunal movement. Heterogeneity was created through enriching sediment ‘patches’ with Enteromorpha intestinalis, providing areas of high and low nutrient. Heterogeneity, macrofaunal biomass, species richness, species diversity and flow were all varied in order to assess combined effects on the functioning of the system.

Heterogeneity was found to have a significant influence on ecosystem functioning and on macrofaunal movement, however, patch arrangement did not. MPB biomass was highest in patches containing organic enrichment suggesting that nutrients were obtained locally from the sediment/water interface rather than the water column. There was variation in MPB biomass with macrofaunal species, probably resulting from differences in behavioural traits. It was also evident that flow altered species behaviour, as there was a significant difference between static and flow treatments. This work shows the importance of heterogeneity for BEF relationships.