How do you attach a GPS tracker to a jellyfish?  With a non-afflictive adhesive

How do you attach a GPS tracker to a jellyfish? With a non-afflictive adhesive

Attaching a GPS tracker to a jellyfish or squid is a difficult job. Their body is too soft and fragile. Still, ecologists want to be able to monitor the animals. A flexible hydrogel adhesive has now been developed to better secure sensors to soft marine species. Researchers from MIT and the Woods Hole Oceanographic Institute in the United States demonstrate the glue in the scientific journal Nature Communications.

Ecologists often work with trackers and sensors. In doing so, they hope to learn more about the behavior of marine species – including how they interact with the environment and the interaction between hunters and prey – and their migration movements. The trackers are also important for investigating the consequences of climate change for different species in the ocean.

Data collection is done using sensors attached to the animals. Collected data is automatically sent to researchers via satellites or stored in a data logger on the device itself. The sensors have become smaller and more advanced in recent years, making it easier to monitor small animals.

Attaching the trackers to the body is usually done with hardening glue, suction cups or hooks. This is problematic, especially for small species and species with a soft, vulnerable body. They can get injured. Applying also takes quite a long time, which causes stress, and a tracker does not always stay in place properly. There is a chance that behavior will change due to the discomfort of the sensor. The result is that there is less knowledge than desired about many species.

Soft rubbers

A patch with hydrogel glue on the bottom can solve this problem. The hydrogel that the US researchers developed consists of different types of polymers that cross-link with each other. When dry it does not stick, the adhesive strength is created in contact with seawater. The layer (150 micrometers thick when dry) absorbs the seawater on the skin of the soft species, then swells and becomes sticky. In about 20 seconds it has enough adhesive power to stick to the skin. The glue works in combination with various soft (biodegradable) rubbers in which the sensors can be packaged.

The researchers tested the sticker in a large aquarium on eighteen animals of different species, including squid, jellyfish, rays, lobsters and groupers. The adhesive strength differed per type, but the sensor always stayed in place. The glue proves to be robust and flexible at the same time, allowing it to move with the body. Over time, the adhesive strength decreases and after a few days the glue will come loose again.

They conducted a test in the sea near the Azores. The sensor was placed on a Northern squid (Loligo forbesii). Confirmation took 90 seconds, after which the squid swam 288 meters into the depths at 35 centimeters per second. The sensor measured temperature and light changes along the way. The movements of the squid were also recorded, which alternately swam fast and slow. The sensor contained an electromechanical release system, after which it floated to the surface and was retrieved by the researchers. The adhesive layer is probably left behind on the squid, the researchers write. “Based on previous observations in the lab, we assume that the layer has remained in place for 1 to 3 days.”