Marine annelid - Platynereis dumerilii
Behavior Neurobiology

Under Pressure

Bezares Calderón Luis Alberto, Shahidi Réza, Jékely Gáspár (2024). Mechanism of barotaxis in marine zooplankton. eLife 13:RP94306.

Marine zooplankton larvae are known to migrate vertically in the ocean – from the high pressure environment of the deep ocean to the relatively lower pressure environment closer to the ocean surface, and back. This usually involves the zooplankton sensing light and the time of day (using a circadian clock).

Other than light and time, many of these zooplankton can also sense and respond to changes in pressure in the water column. This is especially important for marine larvae which have limited motility – to maintain their depth in the water column – so that they don’t get too close to the surface where they may be eaten, or sink to the bottom and succumb under pressure.

In a recent paper, researchers report how larvae of the marine annelid (segmented worm), Platynereis dumerilii, sense pressure and respond to it.

Figure 1. Adults of the marine annelid, Platynereis dumerilii. 

Under pressure? Swim up! 

Platynereis larvae (Figure 2) use cilia, which are hair-like structures, to swim up and down in the water column until they eventually become their adult worm forms which burrow in the sand (Figure 1).

Figure 2. Scanning Electron Micrograph (SEM) of 2, 3, and 6 day old Platynereis dumerilii larvae.

The researchers created a pressure chamber to test how Platynereis larvae respond to changes in pressure. When the pressure was increased, they observed that the larva swam upwards using their cilia. This means that the larvae knew to go up, where the pressure is lower in a water column. This raises the question, how can they sense and respond to the increased pressure?

Video 1. 2 day-old Platynereis larvae swim upwards when the pressure is increased by 1 bar. 

How do larvae sense changes in pressure?

By looking at the activity of ciliary photoreceptor cells – which normally respond to changes in light – the researchers found that these cells are responsible for the reception of both light and changes in pressure.

This is an interesting result because it shows us that the larvae are able to sense two very different environmental factors – light and pressure – using the same set of cells. A crude analogy to this would be if humans could hear and taste with their ears!

Life Under Pressure

Most land animals have a very 2-dimensional outlook – as opposed to marine animals, which exist in a 3D space. Discoveries such as these will help us understand how zooplankton navigate their 3-dimensional environment and are able to accomplish travelling up and down in the water column, from low to high pressures.


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