Effects of Submerged Macrophytes on Demography and Filtration Rates of <i>Daphnia</i> and <i>Simocephalus</i> (Crustacea: Cladocera).

Abstract

Macrophytes and cladocerans represent the main antagonistic groups that regulate phytoplankton biomass; however, the mechanism behind this interaction is unclear. In laboratory conditions, we separately evaluated the effects of three submerged macrophytes (<i>Ceratophyllum demersum</i>, <i>Myriophyllum aquaticum</i>, and <i>Stuckenia pectinata</i>), as well as their exudates, and plant-associated microbiota (POM < 25 µm) + exudates on the population growth of <i>Daphnia</i> cf. <i>pulex</i> and <i>Simocephalus</i> cf. <i>mixtus</i>. Living <i>Ceratophyllum</i>, exudates, and POM < 25 µm + exudates exhibited the most robust positive effects on <i>Simocephalus</i> density and the rate of population increase (<i>r</i>). Subsequently, we examined the effects of <i>Ceratophyllum</i> on the filtration and feeding rates of <i>Simocephalus</i> and <i>Daphnia,</i> revealing significant (<i>p</i> < 0.001) promotion of filtration and feeding in <i>Simocephalus</i> but not in <i>Daphnia</i>. To elucidate the specific effects of this macrophyte on <i>Simocephalus</i> demography, we assessed selected life table variables across the same treatments. The treatments involving exudates and living <i>Ceratophyllum</i> resulted in approximately 40% longer survivorship and significantly (<i>p</i> < 0.01) enhanced fecundity. Our findings indicate that exudates from submerged macrophytes positively influence <i>Simocephalus</i> demography by increasing filtration rates, survivorship, and fecundity. This synergy suggests a substantial impact on phytoplankton abundance.