Data from: Turning defence into offence? intrusion of cladoceran brood chambers by a green alga leads to reproductive failure

Microalgae are the foundation of aquatic food webs. Their ability to
defend against grazers is paramount to their survival, and modulates their
ecological functions. Here we report a novel anti-grazer strategy in the
common green alga Chlorella vulgaris against two grazers, Daphnia magna
and Simocephalus sp. The algal cells entered the brood chamber of both
grazers, presumably using the brood current generated by the grazer’s
abdominal appendages. Once inside, the alga densely colonised the eggs,
significantly reducing reproductive success. The effect was apparent under
continuous light or higher light intensity. The algal cells remained
viable following removal from the brood chamber, continuing to grow when
inoculated in fresh medium. No brood chamber colonisation was found when
the grazers were fed the reference diet Raphidocelis subcapitata under the
same experimental conditions, despite the fact that both algal species
were readily ingested by the grazers and were small enough to enter their
brood chambers. These observations suggest that C. vulgaris can directly
inflict harm on the grazers’ reproductive structure. There is no known
prior example of brood chamber colonisation by a microalgal prey; our
results point to a new type of grazer-algae interaction in the plankton
that fundamentally differs from other antagonistic ecological
interactions.