Exploring the Vertical Ocean: A Comparative Review of Behavioral Strategies Across Marine Predators

Abstract

The ocean is a vertically structured environment in which physical and biological conditions change dramatically with depth, yet the exploitation of this three-dimensional habitat by marine predators has largely been investigated within isolated taxonomic groups rather than through a unified comparative perspective. Here, we conducted a comprehensive review of documented vertical habitat exploration across five major marine predator lineages: Elasmobranchii, Holocephali, Teleostei, Marine Mammalia, and Cephalopoda. Only species supported by direct behavioral evidence, including satellite telemetry, archival and pop-up satellite archival tags (PSATs), acoustic telemetry, biologging, time-depth recorders, remotely operated vehicle observations, or repeated direct observations, were included, whereas species lacking species-specific behavioral documentation were excluded. The compiled evidence demonstrates that recurrent vertical habitat exploration is widespread across phylogenetically distant marine predators despite profound differences in morphology, physiology, locomotion, and evolutionary history. Species exhibited diverse behavioral strategies—including diel vertical migration, reverse diel vertical migration, oscillatory diving, repeated deep exploratory dives, and prolonged bathypelagic foraging—but these behaviors consistently converged toward the repeated exploitation of multiple depth strata. Across taxa, vertical movements were primarily associated with prey acquisition, thermoregulation, predator avoidance, ontogenetic habitat shifts, and responses to environmental gradients such as temperature, dissolved oxygen, hydrostatic pressure, and prey distribution. This synthesis demonstrates that vertical habitat exploration represents a pervasive ecological strategy rather than an isolated behavioral phenomenon. By integrating evidence across major marine predator groups, this review provides a unified comparative framework for understanding how evolutionary diverse lineages repeatedly exploit the ocean's vertical dimension and highlights the importance of incorporating vertical habitat connectivity into future studies of marine ecology, conservation, and movement biology.