Influence of macrofaunal assemblages and environmental heterogeneity on microphytobenthic production in experimental systems

Despite the complexity of natural systems, heterogeneity caused by the fragmentation of habitats has seldom been considered when investigating ecosystem processes. Empirical approaches that have included the influence of heterogeneity tend to be biased towards terrestrial habitats; yet marine systems offer opportunities by virtue of their relative ease of manipulation, rapid response times and the well-understood effects of macrofauna on sediment processes. Here, the influence of heterogeneity on microphytobenthic production in synthetic estuarine assemblages is examined. Heterogeneity was created by enriching patches of sediment with detrital algae (Enteromorpha intestinalis) to provide a source of allochthonous organic matter. A gradient of species density for four numerically dominant intertidal macrofauna (Hediste diversicolor, Hydrobia ulvae, Corophium volutator, Macoma balthica) was constructed, and microphyto- benthic biomass at the sediment surface was measured. Statistical analysis using generalized least squares regression indicated that heterogeneity within our system was a significant driving factor that interacted with macrofaunal density and species identity. Microphytobenthic biomass was highest in enriched patches, suggesting that nutrients were obtained locally from the sediment–water interface and not from the water column. Our findings demonstrate that organic enrichment can cause the development of heterogeneity which influences infaunal bioturbation and consequent nutrient generation, a driver of microphytobenthic production.

Despite the complexity of natural systems, heterogeneity caused by the fragmentation of habitats has
seldom been considered when investigating ecosystem processes. Empirical approaches that have included
the influence of heterogeneity tend to be biased towards terrestrial habitats; yet marine systems offer
opportunities by virtue of their relative ease of manipulation, rapid response times and the well-understood
effects of macrofauna on sediment processes. Here, the influence of heterogeneity on microphytobenthic
production in synthetic estuarine assemblages is examined. Heterogeneity was created by enriching
patches of sediment with detrital algae (Enteromorpha intestinalis) to provide a source of allochthonous
organic matter. A gradient of species density for four numerically dominant intertidal macrofauna (Hediste
diversicolor, Hydrobia ulvae, Corophium volutator, Macoma balthica) was constructed, and microphyto-
benthic biomass at the sediment surface was measured. Statistical analysis using generalized least squares
regression indicated that heterogeneity within our system was a significant driving factor that interacted
with macrofaunal density and species identity. Microphytobenthic biomass was highest in enriched
patches, suggesting that nutrients were obtained locally from the sediment–water interface and not from
the water column. Our findings demonstrate that organic enrichment can cause the development of
heterogeneity which influences infaunal bioturbation and consequent nutrient generation, a driver of
microphytobenthic production.

Archived with thanks to Proceedings of the Royal Society B: Biological Sciences