Biological control of phytoplankton by the subtropical submerged macrophytes Egeria densa and Potamogeton illinoensis: a mesocosm study

Abstract

1. In temperate regions, submerged macrophytes can hamper phytoplankton blooms. Such an effect could arise directly, for instance via allelopathy, or indirectly, via competition for nutrients or the positive interaction between submerged macrophytes and zooplankton grazing. However, there is some evidence that the positive interaction between submerged macrophytes and zooplankton grazing is less marked in warmer regions, where the interaction is less well studied, and that negative effects of higher water plants on phytoplankton biomass are weaker. 2. We carried out two consecutive mesocosm experiments in Uruguay (subtropical South America) to study the effects of two common submerged macrophytes from this region (Egeria densa and Potamogeton illinoensis) on phytoplankton biomass, in the absence of zooplankton grazing. We compared phytoplankton development between different macrophyte treatments (no macrophytes, artificial macrophytes, real Egeria and real Potamogeton). We used artificial macrophytes to differentiate between physical effects (i.e. shading, sedimentation and competition with periphyton) and biological effects (i.e. nutrient competition and allelopathy). 3. In Experiment 1, we found no evidence for physical effects of macrophytes on phytoplankton biomass, but both macrophyte species seemed to exert strong biological effects on phytoplankton biomass. Only Egeria affected phytoplankton community structure, particularly tempering the dominance of Scenedesmus. Nutrient addition assays revealed that only Egeria suppressed phytoplankton through nutrient competition. 4. We performed a second mesocosm experiment with the same design, but applying saturating nutrient conditions as a way of excluding the effects of competition for nutrients. This experiment showed that both macrophytes were still able to suppress phytoplankton through biological mechanisms, providing evidence for allelopathic effects.Our results indicate that both common macrophytes are able to keep phytoplankton biomass low, even in the absence of zooplankton grazing.

Allelopathic interactions between the macrophyte Egeria densa and plankton (alga, Scenedesmus acutus and cladocerans, Simocephalus spp.): a laboratory study

“…Macrophytes belonging to the genera Elodea, Stratiotes, Chara and Myriophyllum release chemical substances that alter the abundance of phytoplankton (Körner and Nicklish, 2002;Gross, 2003;Hilt, 2006), and have effects on zooplankton behavior (Pennak, 1973;Meerhoff et al, 2006) and lifetable variables of cladocerans (Burks et al, 2000;Cerbin et al, 2007;Gutierrez and Paggi, 2014). Most studies concerning the allelopathic effects of macrophytes have been on phytoplankton in temperate systems, while such works from subtropical and tropical zones are limited (Meerhoff et al, 2006;Vanderstukken et al, 2011;Dong et al, 2013). In addition, the information available regarding the effect of chemical cues from macrophytes on many genera of cladocerans including Simocephalus that inhabit lake areas with aquatic vegetation is inadequate (Hilt, 2006).…”

“…Moreover, this submerged macrophyte produces allelopathic substances which affect phytoplankton adversely (Nakai et al, 1999;Mulderij et al, 2007;Vanderstukken et al, 2011). These allelochemicals also affect the demography of Daphnia in different ways (Cerbin et al, 2007).…”

Effects of different aquaculture methods for introduced bivalves (Hyriopsis cumingii) on seston removal and phosphorus balance at the water–sediment interface

“…The complementary mechanisms between bivalves and macrophytes could promote the restoration of eutrophic waterbodies. First, submerged macrophytes could inhibit the primary productivity of pelagic and benthic algae by nutrition competition and allelopathy (Hilt and Gross 2008;Vanderstukken et al 2011). Our previous experiment proved that submerged macrophytes could promote the increasing of large zooplankton, thereby intensifying the removal of small sized algae that could not be grazed by bivalves (Wang et al 2017).…”

Outcomes of submerged macrophyte restoration in a shallow impounded, eutrophic river

“…Although potential for top-down control of phytoplankton through this approach appears limited in this mediterranean-climate system, it may be an advantage if applied in cool-temperate shallow lakes. In addition, submerged macrophytes do have potential to maintain water clarity through other mechanisms regardless of climate (Scheffer and van Ness, 2007;Vanderstukken et al, 2011), and particularly in warmer systems given their potential occurrence throughout the year (Beklioglu et al, 2007). Therefore their transplantation in some degraded systems may provide improved water quality outcomes.…”