Sustainable Management of Filamentous Algae in Freshwater Ecosystems: Insights from Cladophora sp. Life History, Reproductive Tactics, and Growth Ecology

Abstract

Freshwater ecosystems are increasingly degraded by Cladophora blooms, prompting a need to understand its reproductive characteristics for effective control. We combined continuous microscopical monitoring and single-factor and orthogonal experiments, to characterize the life history and reproductive and growth response to different nutrients, pH, temperature, and light conditions of a bloom-forming Cladophora sp. A novel mode was observed, in which mature sporangia and gametangia rupture to extrude a pyknotic cytoplasmic mass, inside which zoospores and gametes complete maturation and release. The peak zoospore production occurred in Aquatic No. 6 medium at pH 5, 35 °C, and 54 µmol m−2 s−1, whereas maximum gamete release was recorded in Knop medium at pH 4, 30 °C, and the same irradiance, with temperature being the principal driver for zoospores and nutrient regime for gametes. Growth trials further revealed that low-N and -P conditions sustain growth, whereas nutrient-rich conditions favor reproduction. In addition, pH 4–5, 35 °C, and 54 µmol m−2 s−1 conditions favored propagule formation, while pH 7–8, 25 °C, and 81 µmol m−2 s−1 maximized biomass. These findings provide a basis for predicting Cladophora bloom dynamics and offer references for sustainable management of Cladophora in freshwater ecosystems.