Combined effects of inorganic nutrients and organic enrichment on intertidal benthic macrofauna: An experimental approach

Abstract

Marine environments are affected by multiple anthropogenic stressors, but research to date has focussed primarily on the impacts and indicators of individual stressors. Nutrient and organic enrichment can occur separately or in combination with each other, but their combined effects are not fully understood. In a field experiment on a sheltered, sandy-mud, sedimentary intertidal shore, 3 levels of inorganic nutrient addition (nutrient sticks) were crossed with 2 levels of organic matter enrichment (rusks), and benthic macrofauna were sampled at 2 times. Organic matter caused greater impacts on benthic macrofauna than nutrients and had a significant effect on taxon richness and Shannon diversity. Total abundance responded to the interactive effects of nutrients and organic matter. The response observed in total abundance was largely driven by the small opportunistic polychaete Capitella sp., which responded primarily to organic matter, but its response was mediated by addition of nutrients to the system. This highlights that its abundance varies in response to interactions among stressors, so cannot be easily interpreted. The performance of 2 biotic indices, the AZTI Marine Biotic Index (AMBI) and Multivariate AMBI (M-AMBI), varied, but M-AMBI proved to be the most effective at detecting the combined effects of nutrients and organic enrichment. These findings show that effective management of coastal environments must take account of the potentially complex combined effects of multiple stressors. © Inter-Research 2012 · www.int-res.com.