# Grazing Responses of Distinct-Sized Tropical Cladocerans to Different Filamentous Sizes of the Cyanobacterium Dolichospermum planctonicum

## TL;DR

This study explores how tropical cladocerans of different sizes feed on various filament lengths of the cyanobacterium Dolichospermum planctonicum, revealing how food context influences grazing behavior.

## Contribution

The study reveals how tropical cladocerans respond to different filamentous sizes of Dolichospermum planctonicum, highlighting the role of food context in grazing dynamics.

## Key findings

- Grazing rates decreased with increasing food concentration across all phytoplankton species.
- Daphnia gessneri was the most efficient filter-feeder, but responses to Dolichospermum strains varied with diet context.
- Shorter Dolichospermum was least consumed in single diets but most consumed in mixed diets, indicating context-dependent grazing mechanisms.

## Abstract

Cyanobacterial blooms directly influence the structure and function of zooplankton communities; however, the trophic interactions between small tropical cladocerans and the cyanobacterium Dolichospermum are still poorly understood. We evaluated how two strains of Dolichospermum planctonicum (differing in filament length) affect the grazing rates of three tropical cladocerans with distinct size and prey spectra—Daphnia gessneri, Ceriodaphnia silvestrii, and Macrothrix paulensis—in single and mixed diets with the chlorophyte Monoraphidium capricornutum. Overall, grazing rates decreased as food concentration increased across all phytoplankton species. Daphnia was the most efficient filter-feeder in all diets, yet the responses to different-sized Dolichospermum strains varied between animals and diets. Shorter Dolichospermum was the least consumed food item in single diets, as opposed to what was observed in the mixed diets, where it was the most consumed. This reversal suggests that the mechanism limiting grazing on Dolichospermum might change drastically depending on the food context (availability of other food sources). Positive selectivity for both Dolichospermum and Monoraphidium was observed for all cladocerans. These findings highlight that the morphology of Dolichospermum planctonicum and the availability of alternative food sources during its blooms are critical regulators of grazing. The results also provide evidence of diverse feeding strategies of tropical cladocerans to prey on the filamentous cyanobacterium Dolichospermum planctonicum.