# Effects of Submerged Macrophytes on Demography and Filtration Rates of Daphnia and Simocephalus (Crustacea: Cladocera)

## TL;DR

This study shows that submerged plants like Ceratophyllum improve the survival and reproduction of Simocephalus by boosting its feeding rates.

## Contribution

The study identifies macrophyte exudates as a key driver of Simocephalus population growth and filtration rates.

## Key findings

- Ceratophyllum exudates increased Simocephalus survivorship by ~40% and fecundity significantly.
- Filtration rates of Simocephalus were significantly promoted by Ceratophyllum, but not in Daphnia.
- Plant exudates and associated microbiota positively influenced Simocephalus demography.

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