Effect of nutrient dispersal on diversity and resource use efficiency in a marine meta-ecosystem experiment

Background/Question/Methods

The understanding of spatio-temporal dynamics and their effects on communities plays an important role in the diversity-stability debate. Many studies therefore used the approach of metacommunity framework. However, most studies only consider mainly the dispersal of organisms. In the last decade spatial ecosystem ecology was extended by the concept of meta-ecosystems, which includes the understanding of all kinds of spatial flow among patches. Only few studies investigated simultaneously, the effects of material flow (e.g. nutrients) and organisms on community diversity and stability patterns. In this study we used the metacommunity framework to address the impact of nutrient dispersal on diversity and resource use efficiency by using marine phytoplankton as model organism. One metacommunity set-up consisted of five microcosms (patches), which were connected by silicone tubes allowing different dispersal rates. Two nutrient treatments (gradient and uniform) with low and high dispersal rates were conducted. In the gradient treatment patch one contained the entire nitrogen concentration, while patch five contained the entire phosphorus concentration. In the uniform treatment each patch contained one-fifth of the entire nitrogen and phosphorus concentration, respectively. Each patch was inoculated with the same species pool of six marine phytoplankton taxa. The experiment was monitored over four weeks with a weekly sampling interval.

Results/Conclusions

Biodiversity indices (species evenness and species richness) were determined by microscopical counting. We found that both species richness and species evenness were affected by dispersal independent from the treatments. The biovolume (µm³ * ml^-1) at regional scale was significantly higher (p=0.009) for low dispersal compared to high dispersal among treatments. Furthermore, the local biovolume differed among treatments according to patch position. Additionally, species evenness decreased more rapidly at low dispersal than at high dispersal over time. However, species richness at local scale was more affected by dispersal at the graduate treatment in comparison to the uniform treatment. Both, resource use efficiency for nitrogen and phosphorus at local scale were influenced by the treatment and dispersal rates. Therewith, we can contribute to the meta-ecosystem approach by addressing nutrient dispersal in response to species richness, evenness, and resource use efficiency in a metacommunity context.