Work

Halocline boundary layer restricts the vertical distribution of the box jellyfish Tripedalia cystophora

Year: 2026

Type: article

Abstract: Haloclines - sharp salinity gradients frequently formed after heavy rainfalls in coastal habitats - can act as barriers for weakly swimming plankton, but their biomechanical constraints on relatively adept swimmers, such as cubozoan jellyfish, remain unexplored. We examined the vertical distribution of Tripedalia cystophora before and after establishing an artificial halocline (35→22 PSU) in an experimental swimming arena. After halocline formation, animals repeatedly entered the gradient layer but did not ascend beyond its upper boundary, despite repeated upward trajectories towards the gradient layer, indicating no obvious avoidance response. A hydrodynamic model supported these observations, demonstrating that stratification drag markedly increases thrust dissipation. Thus, centimetre-scale haloclines impose physical constraints that prevent T. cystophora from accessing surface waters through reduced effective upward momentum, rather than through behavioural change. Because the underlying hydrodynamic principles are general, we propose a stratification hypothesis to explain how sharp density gradients shape the vertical distribution of some aquatic animals.

Source: Journal of Experimental Biology

DOI: 10.1242/jeb.251708

Authors: Jan-Frederik Freiberg, Niels Röhrdanz, Hermann Kohlstedt, Jan Bielecki

Institution: Christian-Albrechts-Universität zu Kiel

Language: English

Topic: Marine Invertebrate Physiology and Ecology

Subfield: Paleontology

Field: Earth and Planetary Sciences

Domain: Physical Sciences

SDG: Life below water

Open Access status: hybrid

Funder: Deutsche Forschungsgemeinschaft