Biodiversity effects on productivity and stability of marine macroalgal communities: the role of environmental context

Abstract

The influence of biodiversity on ecosystem functioning has been the focus of much recent research, but the role of environmental context and the mechanisms by which it may influence diversity effects on production and stability remain poorly understood. We assembled marine macroalgal communities in two mesocosm experiments that varied nutrient supply, and at four field sites that differed naturally in environmental conditions. Concordant with theory, nutrient addition promoted positive species richness effects on algal growth in the first mesocosm experiment; however, it tended to weaken the positive diversity relationship found under ambient conditions in a second experiment the next year. In the field experiments, species richness increased algal biomass production at two of four sites. Together, these experiments indicate that diversity effects on algal biomass production are strongly influenced by environmental conditions that vary over space and time. In decomposing the net biodiversity effect into its component mechanisms, seven of the eight experimental settings showed positive complementarity effects (suggesting facilitation or complementary resource use) countered by negative selection effects (i.e. enhanced growth in mixture of otherwise slow growing species) to varying degrees. Under no conditions, including nutrient enrichment, did we find evidence of positive selection effects commonly thought to drive positive diversity effects. Species richness enhanced stability of algal community biomass across a range of environmental settings in our field experiments. Hence, while species richness can increase production, enhanced stability is also an important functional outcome of maintaining diverse marine macroalgal communities.

Marine biodiversity and ecosystem function relationships: The potential for practical monitoring applications

“…Both negative (Kraufvelin et al, 2010;Bracken and Williams, 2013) and positive BEF relationships have been reported within macroalgal assemblages in the context of photosynthetic carbon fixation Arenas et al, 2009;Boyer et al, 2009;Griffin et al, 2009). Although not using an experiment designed to specifically test the relationship between diversity and productivity, Kraufvelin et al (2010) observed declining primary production within increasing macroalgal species richness in temperate rocky shores (SE Norway) driven by strong identity effects associated with the resident fucoids.…”

Additive effects of physical stress and herbivores on intertidal seaweed biodiversity

“…Here, we focus on biodiversity patterns in the intertidal seaweed community, exclusive of other sessile organisms, to facilitate understanding of the drivers of natural patterns in biodiversity and the functional role of seaweeds as key marine primary producers and foundation species. There is often, but not always, a positive relationship between seaweed ecosystem function and biodiversity (Allison 2004, Arenas et al 2009, Boyer et al 2009, Bracken et al 2011, Aquilino and Stachowicz 2012. In prior work, we found that both biomass and nitrogen acquisition increase with seaweed richness (Bracken and Stachowicz 2006, Stachowicz et al 2008.…”

Propagule supply limits grazer richness equally across a resource gradient

“…Survivorship, and therefore total lifespan, is dependent on the type and quality of food (Duffy and Hay 1991, Cruz-Rivera and Hay 2000a. Given that some ovigerous females in their first or second v www.esajournals.org ovulation likely migrated into our communities via the seawater or were added as propagules, and water temperatures of ;298C during our experiment (Boyer et al 2009), we estimate 2-3 overlapping generations passed during our experiment.…”