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Predator - Proof “Sea Snail Backpack”: How Amphipods Protect Themselves

Amphipods are crustaceans who use the sea snails’ toxins to shield themselves from predators who want to consume them./ Photo by: Hans Hillewaert via Wikimedia Commons

 

Under the sea, there are kidnappers who grab snails and wear them like backpacks to keep them from being preyed upon. These are the amphipods, crustaceans who use the sea snails’ toxins to shield themselves from predators who want to consume them.

This parasitic relationship between snails and amphipods was discovered by biologists from the Alfred Wegener Institute and the University of Bremen. Their study was featured in the Marine Biodiversity journal. Dr. Charlotte Havermans, one of the authors of the study says, “A few of the amphipods carried something unusual on their backs. On closer inspection, I realized they were carrying pteropods piggyback. We were wondering whether these tandems occur as frequently in the open as in coastal waters--and whether both animals benefit from the relationship.”

In was in the austral summer of 2016 to February 2017 that they were able to make the observation. The ship Research Vessel Polarstem was used to help Havermans and her team of researchers to examine the amphipods’ ecological function, distribution and how abundant they were throughout the ocean. The study was supported by the German Research Foundation as part of the Priority Programme on Antarctic Research.

Previously, in 1990, they found that a study had been done by American researchers on the same topic but it only investigated their behavior in the high-Antarctic Coastal waters. No research about it had been done in the Southern Ocean. They had seen this backpacking behavior between the amphipod species Hyperiella dilatata and the sea snail Clione limacina antarctica, as well as between Hyperiella antarctica and Spongiobranchea australis.

 

Amphipods and Their Habitat

Quartz describes amphipods as tiny crustaceans that are similar to a shrimp. They reside in the Southern Ocean which is close to Antartica. They are usually attacked by large predators such as birds and fish.

What Are Sea Snails?

Sea snails are little snails without shells who only grow up to five centimeters long, Newsweek states. According to Live Science, they are pea-sized and are fragile and transparent. They are also known as pteropods and sea angels. They move around by flapping their foot wings and defend themselves from predators by using chemical deterrents. They are usually attacked by the ice codfish.

 

 

How Amphipods Capture Sea Snails

First, the amphipods look for the sea snails. Then, they kidnap them and use two pairs of legs to hold down the sea snail. After taking them hostage, they put them on their backs. While wearing the snails like backpacks, they take advantage of their chemical deterrents to keep away birds and fish.

It was found that this occurred both in male and female amphipods, who continued to cling to these sea snails even until they were killed. Since these sea snails are not able to hunt for their food, they would die from starvation as they got attached to their kidnappers’ backs.

When worn by the amphipods, the pteropods occupied from one-fifth to one-half of their bodies. The amphipods would take any gender of sea snails, even the females who had eggs with them.  

If any ice cod fishes or other predators see these poisonous sea snails on their backs, this makes them look for other prey instead because they are averse to the taste of the toxins released by the snails.

 

Sea snail releases toxins that predators don't like. / Photo by: Reto Kunz via 123rf

 

The Future Marine Tandem Research

The authors of the study A Survival Pack for Escaping Predation in the Open Ocean: Amphipod-Pteropod Associations in the Southern Ocean were only able to gather up 342 amphipods. However, only four of them had sea snails mounted on them. Havermans and his team are not able to identify whether they only try to capture a specific species of toxic snails or if any kind of toxic sea snails will suffice.

“We are probably overlooking associations numerous such associations between species, because they are no longer available after net sampling,” the researchers admitted.

The relationships between tiny sea creatures like the amphipods and pteropods are difficult to capture and make observations on. What makes it hard is that when they use collection nets to take some samples of these creatures, their fragile bodies easily get crushed in the process.

Gastropods and crustaceans are much easier to study because their shells help keep them undamaged even after being caught in a net. The researchers would also like to examine if the squid and lanternfish, which also prey on the amphipods and are often seen in the Southern Ocean, are also affected by the chemical deterrents used by the pteropods.

With the development of new high definition underwater cameras, they are looking forward to the possibility that even the tiniest of sea animals will be able to be monitored in their own habitats. The authors declare, “This will provide insights into numerous exciting mysteries of interspecific interactions, which have so far remained hidden from biologists--but which undoubtedly play an unimportant role in predator-prey relationships in the ocean.”

 

With the development of underwater camera, it will be easier for the researchers to monitor even the tiniest creatures in their habitats. / Photo by: Thanagon Srichanchom via 123rf

 

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