Plankton Biodiversity Along a Gradient of Productivity and Its Mediation by Macrophytes

Abstract

We studied the effect of aquatic vegetation on the process of species sorting and community assembly of three functional groups of plankton organisms (phytoplankton, seston-feeding zooplankton, and substrate-dwelling zooplankton) along a primary productivity gradient. We performed an outdoor cattle tank experiment (n = 60) making an orthogonal combination of a primary productivity gradient (four nutrient addition levels: 0, 10, 100, and 1000 microg P/L; N/P ratio: 16) with a vegetation gradient (no macrophytes, artificial macrophytes, and real Elodea nuttallii). We used artificial plants to evaluate the mere effects of plant physical structure independently from other plant effects, such as competition for nutrients or allelopathy. The tanks were inoculated with species-rich mixtures of phytoplankton and zooplankton. Both productivity and macrophytes affected community structure and diversity of the three functional groups. Taxon richness declined with increasing plankton productivity in each functional group according to a nested subset pattern. We found no evidence for unimodal diversity-productivity relationships. The proportional abundance of Daphnia and of colonial Scenedesmus increased strongly with productivity. GLM analyses suggest that the decline in richness of seston feeders was due to competitive exclusion by Daphnia at high productivity. The decline in richness of phytoplankton was probably caused by high Daphnia grazing. However, partial analyses indicate that these explanations do not entirely explain the patterns. Possibly, environmental deterioration associated with high productivity (e.g., high pH) was also responsible for the observed richness decline. Macrophytes had positive effects on the taxon richness of all three functional plankton groups and interacted with the initial productivity gradient in determining their communities. Macrophytes affected the composition and diversity of the three functional groups both by their physical structure and through other mechanisms. Part of the macrophyte effect may be indirect via a reduction of phytoplankton production. Our results also indirectly suggest that the often reported unimodal relationship between primary productivity and diversity in nature may be partially mediated by the tendency of submerged macrophytes to be most abundant at intermediate productivity levels.

Influence of nutrients, submerged macrophytes and zooplankton grazing on phytoplankton biomass and diversity along a latitudinal gradient in Europe

“…A high grazing pressure is known to result in lower phytoplankton diversity (Padisák, 1993;Krasznai et al, 2010). In a mesocosm experiment investigating the influence of submerged macrophytes on phytoplankton diversity, submerged macrophytes had a positive influence on diversity (Declerck et al, 2007). In that experiment, zooplankton grazing pressure did not differ significantly between treatments with and without macrophytes due to the absence of fish (Vanderstukken et al, 2010).…”

Spatial and temporal variation of invertebrate community structure in flood-controlled tropical floodplain wetlands

“…Macrophytes not only provide shelter, but also influence invertebrate community composition by generating better habitat conditions through the production of dissolved oxygen, and by providing attachment and oviposition sites (S agov a-Mareckov a & Kvet 2002; Declerck et al 2007;MaiaBarbosa et al 2008). Macrophytes also promote aquatic invertebrates by reducing predation pressure from visual predators such as fish and other invertebrates (Diehl 1995).…”

Long-Term Trends and Temporal Synchrony in Plankton Richness, Diversity and Biomass Driven by Re-Oligotrophication and Climate across 17 Danish Lakes

“…This was probably indicative of water quality improvements, which might have promoted submerged macrophyte growth. The potential recovery of submerged macrophytes may also contributed to the increase in planktonic diversity [82][83][84][85].…”