Egg-brooding, body size and predation risk in planktonic marine copepods

Area of Science:

• Marine Biology
• Predator-Prey Dynamics
• Zooplankton Ecology

Background:

• Copepod body size and reproductive status (presence of egg masses) are crucial factors influencing their vulnerability to visual predators.
• Understanding these interactions is key to comprehending marine food web dynamics and zooplankton population regulation.

Purpose of the Study:

• To investigate how copepod body size and the presence of egg masses affect predation risk from a visual predator, the three-spined stickleback (Gasterosteus aculeatus).
• To determine the relative importance of body size versus egg mass position in influencing predator selection among different copepod species.

Main Methods:

• Conducted selection experiments using three-spined sticklebacks as visual predators.
• Offered a range of copepod species with varying body masses (0.5 to 740 µg C) and reproductive states (ovigerous females).
• Analyzed predator choice based on species, body size, and egg mass location (ventral, dorsal, lateral).

Main Results:

• Sticklebacks preferentially preyed on ovigerous females of the two smallest copepod species (Oithona similis and Corycaeus anglicus).
• No significant selection for ovigerous females was observed in larger-bodied copepod species.
• Egg mass position significantly influenced predation risk, with cyclopoid and poecilostomatoid species facing higher risk than calanoid species.

Conclusions:

• Egg mass position can be a more critical factor than body size in determining predation risk for certain copepod species.
• The susceptibility of egg-brooding calanoid copepods to predation, relative to body size, remains an area requiring further investigation.
• Predator-prey interactions in marine ecosystems are complex, influenced by multiple traits beyond simple body size.