Limited Evidence for Depth Specialism in Isolated Seamount Reef Predators

Area of Science:

• Marine Ecology
• Ichthyology
• Oceanography

Background:

• Water depth creates gradients in light, temperature, and hydrodynamics, influencing marine ecosystems.
• Depth specialization in coral reef fishes is well-studied in shallow coastal areas, but less is known about deeper, isolated reef systems like seamounts.

Purpose of the Study:

• To investigate how depth influences predatory fish assemblages on seamount reefs.
• To assess changes in abundance, diversity, and community structure of predatory fishes across a 100m depth gradient.

Main Methods:

• Remotely operated vehicles (ROVs) were used to survey predatory fish communities.
• Surveys were conducted across a 100m depth gradient (5m to 95m) on three seamount reefs in the Coral Sea.

Main Results:

• Species richness and abundance of predatory fishes significantly decreased with increasing depth.
• Predator abundance declined fourfold and species richness was halved from shallow to deep zones.
• Despite declines, most predatory fish taxa spanned the full depth range, with minimal compositional differences between depth zones.

Conclusions:

• Seamount predatory fish assemblages show reduced diversity and abundance at greater depths but exhibit broad depth utilization.
• Reef sharks (Carcharhinidae) were the primary drivers of depth-associated compositional shifts, increasing in mesophotic zones.
• The ability of predatory fishes to use varied depths may enhance resilience to environmental change and facilitate access to thermal refugia.