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

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 (δC) and nitrogen (δN) to quantify the areas of isotopic niches (sample size-corrected standard ellipse areas; SEA) of planktonic crustaceans during the pre-bloom and cyanobacterial bloom phases. In the pre-bloom phase, SEAs accounted for 15.0‰ in calanoid copepods, 21.2‰ in cyclopoid copepods and 14.4‰ in Daphnia spp. During the cyanobacterial bloom phase, the SEAs of studied animals increased to 37.8, 27.0 and 43.6‰ 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.