Active buoyancy adjustment increases dispersal potential in benthic marine animals

Area of Science:

• Marine Biology
• Ecology
• Conservation Science

Background:

• Oceanic dispersal studies often focus on pelagic species and larval stages.
• Benthic species, like sea cucumbers (Holothuroidea), are generally assumed to have limited dispersal capabilities due to slow movement.
• Sea cucumbers play crucial ecological and economic roles, necessitating effective conservation strategies.

Purpose of the Study:

• To investigate an overlooked dispersal mechanism in post-settlement benthic stages of sea cucumbers.
• To challenge the traditional view of benthic species' limited dispersal potential.
• To explore the phenomenon of active buoyancy adjustment (ABA) in sea cucumbers.

Main Methods:

• Studied two focal sea cucumber species over several years, representing different taxonomic orders and distributions.
• Documented active buoyancy adjustment (ABA) through rapid increases in water-to-flesh ratio, leading to detachment and movement.
• Conducted experimental trials to identify ABA triggers, including conspecific density, salinity, and water turbidity.

Main Results:

• Observed ABA in juveniles as early as 6 months post-settlement and in wild adult populations.
• ABA involves a significant increase in water-to-flesh ratio (up to 740%), causing bloating and substrate detachment.
• Field footage revealed ABA-assisted speeds up to 90 km/day, significantly exceeding benthic crawling speeds.

Conclusions:

• Active buoyancy adjustment (ABA) represents a substantial dispersal capacity for benthic sea cucumbers, potentially exceeding larval dispersal.
• ABA challenges the notion of sedentarity in benthic marine invertebrates.
• ABA may be a generalized dispersal mechanism for benthic animals, with critical implications for global marine conservation and management.