Sperm Diffusion Models and In Situ Confirmation of Long-Distance Fertilization in the Free-Spawning Asteroid...

Area of Science:

• Marine Biology
• Reproductive Ecology
• Population Dynamics

Background:

• The crown-of-thorns starfish (Acanthaster planci) is a significant coral reef predator.
• Understanding its reproductive strategies is crucial for reef management and conservation.
• Fertilization success in broadcast spawners is influenced by sperm dispersal and density.

Purpose of the Study:

• To compare field-measured fertilization rates of Acanthaster planci with predictions from sperm diffusion models.
• To investigate the impact of sperm release volume and distance on fertilization success in A. planci.
• To assess the role of starfish aggregation in fertilization success.

Main Methods:

• Experimentally induced spawnings of A. planci were conducted.
• Fertilization rates of broadcast eggs were measured at various distances downstream and laterally from male starfish.
• Sperm diffusion models were employed to predict fertilization rates based on observed sperm release.

Main Results:

• High fertilization rates were observed, with over 70% of eggs fertilized 8m downstream and measurable fertilization (5.8%) at 100m.
• Lateral sperm diffusion also resulted in significant fertilization rates.
• Models accurately predicted in situ fertilization rates, highlighting the importance of large sperm volumes released by A. planci.

Conclusions:

• Large sperm release volumes in A. planci facilitate high fertilization rates over extensive distances, reducing the necessity for high population densities or aggregation.
• The vast area for potential gamete encounters contributes significantly to overall fertilization success.
• Behaviors like migration to shallow waters may further enhance fertilization success in A. planci and other marine invertebrates.