Marine Signalling — Chromatography Listens In

There are many examples of terrestrial life using signals — think of all the verbal and visual messages that we send out. Chemical signals are also used by plants and animals, including humans, for a wide variety of reasons — to advertise their presence, signal danger, that they’re ready to mate and when food is found are just a few of the many instances.

Underwater is a totally different environment, and with land and sea animals having evolved separately for over 400 million years, sea animals might have evolved something different. Aquatic animals do send and receive signals — sound waves, electrical impulses and visual signals are used by different marine animals. But what about chemical signalling underwater?

Working underwater

The research on terrestrial chemical signalling is well advanced compared to the research on aquatic chemical signalling — and this is down to the challenges presented by working in an aquatic environment, and sampling and analysing the water samples collected. Carrying out research in an aquatic environment is harder and requires more equipment — so the costs are much higher. Unlike terrestrial research, you cannot just walk out of the door and start your research — you need to be able to dive and use breathing apparatus.

To analyse terrestrial chemical signals, researchers need to sample, filter and analyse air samples — typically using GC-MS. In aquatic environments the molecules of chemical signalling are often at a concentration too low to measure, and vast quantities of water need to be sampled and filtered to obtain the samples. The analysis of volatile components in water is discussed in the article, Trace Level VOC Analysis in Different Sample Matrices.

Detecting chemical signalling

That is not to say that signalling hasn’t been seen. A 2012 paper published in Science, ‘Corals Chemically Cue Mutualistic Fishes to Remove Competing Seaweeds’ describes how coral signals to fish that toxic seaweed is present and might damage the coral. The fish respond by eating the seaweed, saving the corals from damage. As a result of eating the seaweed, the fish become toxic to other predators and the coral survived to give shelter to the fish— a win-win situation for all parties except the seaweed. But the researchers were unable to identify the molecule the responsible for carrying the signal from the coral to the fish.

However, research recently published in Proceedings of the National Academy of Sciences has for the first time identified two of the chemicals used in aquatic environment chemical signalling between plants and herbivores.

Researchers from the Georgia Institute of Technology, Atlanta studied the relationship between a sea slug, Elysia tuca, and its prey the seaweed Halimeda incrassate and were able to identify two of the chemicals, 4-hydroxybenzoic acid and halimedatetraacetate, that Elysia uses to find its prey. It is indicated that this is the first time that compounds used by herbivores to hunt prey in a marine environment have been identified and reported.

Image by U.S. Navy photo by Journalist 3rd Class Alicia T. Boatwright. via Wikimedia Commons