# Cyanobacterial bloom causes expansion of isotopic niche areas and overlap in crustacean zooplankton

## TL;DR

Cyanobacterial blooms cause crustacean zooplankton to expand their isotopic niches and overlap more, indicating dietary adaptability.

## Contribution

The study reveals how zooplankton adapt their diets during cyanobacterial blooms using stable isotope analysis.

## Key findings

- Isotopic niche areas of crustaceans increased during cyanobacterial blooms.
- Overlap among crustacean groups' niches was greater during the bloom phase.
- Crustaceans shifted to alternative food sources despite reduced resource diversity.

## Abstract

We aimed to study how cyanobacterial blooms affect the use of the basal resources by three groups of crustacean zooplankton (calanoid and cyclopoid copepods, Daphnia spp.). We used measurements of naturally occurring stable isotopes of carbon (δ13C) and nitrogen (δ15N) to quantify the areas of isotopic niches (sample size-corrected standard ellipse areas; SEAc) of planktonic crustaceans during the pre-bloom and cyanobacterial bloom phases. In the pre-bloom phase, SEAcs accounted for 15.0‰2 in calanoid copepods, 21.2‰2 in cyclopoid copepods and 14.4‰2 in Daphnia spp. During the cyanobacterial bloom phase, the SEAcs of studied animals increased to 37.8, 27.0 and 43.6‰2 respectively. In addition, the overlap among the niches of the crustacean groups increased during the bloom phase compared to the pre-bloom phase. The results suggest that, despite reduced diversity of basal resources during the cyanobacterial bloom, crustaceans exhibited dietary adaptability. This involved a shift toward alternative food sources.