Egg predation by copepods in Daphnia brood cavities

Area of Science:

• Aquatic Ecology
• Zooplankton Ecology
• Interspecies Interactions

Background:

• Daphnia are crucial freshwater zooplankton, forming the base of many aquatic food webs.
• Brood cavities protect Daphnia eggs and embryos, but their vulnerability to predation is not fully understood.
• Copepods are common aquatic invertebrates with diverse feeding strategies.

Purpose of the Study:

• To investigate the phenomenon of juvenile copepods feeding on Daphnia eggs and embryos within brood cavities.
• To document this behavior in both field and experimental settings.
• To assess the impact of this predation on Daphnia reproductive success.

Main Methods:

• Field observations in a mesotrophic lake.
• Enclosure experiments using algae-rich conditions.
• Identification and observation of copepodites within Daphnia brood cavities.
• Quantification of clutch size in infested versus uninfested Daphnia.

Main Results:

• Juvenile copepods (copepodites) of both cyclopoid (Acanthocyclops robustus) and calanoid (Eudiaptomus gracilus) species were observed consuming Daphnia eggs and embryos in vivo.
• Infested Daphnia exhibited significantly reduced clutch sizes.
• The observed predation can mimic the effects of severe food limitation on Daphnia populations.

Conclusions:

• Juvenile copepods are significant predators of Daphnia eggs and embryos.
• This intra-brood cavity predation represents a novel exploitation strategy with implications for zooplankton population dynamics.
• Distinguishing between predation and food limitation effects is critical for accurate ecological assessments.