Phytoplankton Diversity Effect on Ecosystem Functioning in a Coastal Upwelling System

Abstract

Species composition plays a key role in ecosystem functioning. Theoretical, experimental and field studies show positive effects of biodiversity on ecosystem processes. However, this link can differ between taxonomic and functional diversity components and also across trophic levels. These relationships have been hardly studied in planktonic communities of coastal upwelling systems. Using a 28-year time series of phytoplankton and zooplankton assemblages, we examined the effects of phytoplankton diversity on resource use efficiency (RUE, ratio of biomass to limiting resource) at the two trophic levels in the Galician upwelling system (NW Iberian peninsula). By fitting generalized least square models, we show that phytoplankton diversity was the best predictor for RUE across planktonic trophic levels. This link varied depending on the biodiversity component considered: while the effect of phytoplankton richness on RUE was positive for phytoplankton RUE and negative for zooplankton RUE, phytoplankton evenness effect was negative for phytoplankton RUE and positive for zooplankton RUE. Overall, taxonomic diversity had higher explanatory power than functional diversity, and variability in phytoplankton and zooplankton RUE decreased with increasing phytoplankton taxonomic diversity. Phytoplankton used resources more efficiently in warmer waters and at greater upwelling intensity, although these effects were not as strong as those for biodiversity. These results suggest that phytoplankton species numbers in highly dynamic upwelling systems are important for maintaining the planktonic biomass production leading us to hypothesize the relevance of complementarity effects. However, we further postulate that a selection effect may operate also because assemblages with low evenness were dominated by diatoms with specific functional traits increasing their ability to exploit resources more efficiently.

Community Assembly Processes as a Mechanistic Explanation of the Predator-Prey Diversity Relationship in Marine Microbes

“…The importance of top-down control mechanisms revealed in this study contradicts with many studies that emphasize the impacts of bottom-up control mechanisms (e.g., Scherber et al, 2010;Hertzog et al, 2016;Otero et al, 2020). One possible explanation to this disagreement is the fact that our data come from an aquatic system, whereas the majority studies demonstrating bottom-up control mechanisms is conducted in terrestrial systems (as reviewed in Haddad et al, 2009).…”

Phytoplankton diversity affects biomass and energy production differently during community development

“…Its progressive dominance therefore impacted competitors and constrained productivity as indicated by the increase in selection effects and reduction in complementarity effects over time, which is expected in stable environments (Hodapp et al., 2016). Natural phytoplankton assemblages show similar positive selection effects where the identity and traits of dominant species affect BEF relationships (Hodapp et al., 2015; Otero et al., 2020). Nonetheless, biodiversity effects were up to five times stronger in communities than pairs.…”

Phytoplankton and Bacterial Communities’ Patterns in a Highly Dynamic Ecosystem (Central Mediterranean Sea)

“…The results demonstrated that larger phytoplankton taxa were in equilibrium and dominance phenomenalike those occurring during bloom events when opportunistic species (i.e., diatoms) tend to dominate over other phytoplankton taxa-were not observed. As evenness (distribution of taxa) responds more quickly than richness (number of taxa) to variation in the environmental conditions [31], this suggests that the MMW were in a "transition phase".…”

“…It is well known that phytoplankton diversity and community structure influence the functioning of ecosystems [29,30]. However, more information is needed to improve knowledge on relations between phytoplankton diversity and upwelling ecosystem functioning [31].…”