Temperature elevation reduces the sensitivity of invasive cladoceran Daphnia lumholtzi to filamentous cyanobacterium Raphidiopsis raciborskii

Authors:

• Łukasz Wejnerowski,
• Anna Sikora-Koperska,
• Piotr Dawidowicz

Abstract

Exotic cladoceran Daphnia lumholtzi is a highly invasive species in the north and south American continents and can potentially also invade European freshwaters and outcompete native Daphnia populations. However, European waterbodies are frequently dominated by less edible filamentous cyanobacteria including also invaders such as Raphidiopsis raciborskii, which might affect the fitness of D. lumholtzi. Furthermore, temperature may influence the sensitivity of D. lumholtzi to R. raciborskii filaments. In this study, we determined whether the presence of R. raciborskii could obstruct the invasion of Europe by D. lumholtzi, through reducing its fitness, and whether this depends on temperature. We compared the population growth rate (r) and the somatic growth rate of D. lumholtzi maintained at two temperatures (20 or 26°C) and fed with two diets: green microalgae alone or green microalgae mixed with filaments of R. raciborskii. Three clones of D. lumholtzi were used to evaluate potential variation in response to the treatments among different clones. At 20°C, the population growth rate of D. lumholtzi fed with cyanobacterial filaments declined sharply. This reduction was caused by increased egg abortion, egg degeneration, and mortality of newborn daphnids. At 26°C, R. raciborskii lost its harmful effect on the population growth of D. lumholtzi. The presence of cyanobacteria did reduce the somatic growth rate of D. lumholtzi at both temperatures and in all three clones except for one that had a similar somatic growth rate on both diets at 26°C. The presence of filamentous cyanobacteria does affect growth in D. lumholtzi and may thereby substantially reduce its invasive potential, but only at lower temperatures. Therefore, the presence of filamentous cyanobacteria may not present an obstacle to the invasion of Europe by D. lumholtzi in a warmer future climate. © 2020 John Wiley & Sons Ltd.