Behaviourally mediated phenotypic selection in a disturbed coral reef environment.

Area of Science:

• Marine biology
• Ecology
• Climate change impacts

Background:

• Coral reefs face increasing threats from climate change and anthropogenic disturbances.
• Coral bleaching events cause significant stress and mortality in coral ecosystems globally.
• The mechanisms driving fish population declines following coral bleaching are not fully understood.

Purpose of the Study:

• To investigate how coral bleaching affects the mortality rates and selectivity of juvenile damselfish (Pomacentrus amboinensis).
• To understand the role of habitat availability and intraspecific interactions in fish survival post-bleaching.

Main Methods:

• Assessed the behavior and mortality of juvenile Pomacentrus amboinensis across three habitat types: live coral, bleached coral, and dead coral covered in algae.
• Manipulated fish densities to natural maximums to observe effects of intraspecific interactions.
• Compared survival rates and size-selective mortality between different habitat types.

Main Results:

• Juvenile damselfish exhibited low migration rates between habitat patches.
• Intraspecific interactions and space utilization varied significantly across live, bleached, and dead coral habitats.
• Larger fish displaced smaller fish from shelter on bleached and dead coral, increasing smaller fish mortality.
• Mortality was size-selective on bleached and dead coral, with small recruits suffering higher losses.
• Survival rates on live coral were three times higher than on bleached or dead coral.

Conclusions:

• Coral bleaching fundamentally alters habitat structure, leading to increased and size-selective mortality in associated fish populations.
• Behavioral interactions, driven by habitat degradation, are key mechanisms linking coral health to fish survival.
• These findings highlight the cascading effects of climate change on marine ecosystems and the evolution of life history strategies.