nodosum, even when the grazers were absent, indicating predators also detect chemical cues emitted by grazed seaweeds 17. obtusata were later found to preferentially orient towards previously grazed A. Crab ( Carcinus maenas) and fish ( Lipophrys pholis) predators of L. nodosum downstream of ungrazed conspecifics. nodosum downstream of conspecifics being grazed by snails ( Littorina obtusata) had higher phlorotannin concentrations. In marine macroalgae, the detection of waterborne cues generated during grazing on seaweeds by neighboring conspecifics was first described in the brown alga Ascophyllum nodosum 16. Inter-individual communication in marine seaweeds is similar to that in terrestrial plants, except that the transport of infochemicals typically occurs in water rather than air. For example, macroalgal VOCs can deter feeding by herbivores 13, 14 and inhibit microbial growth 15. Many of these compounds have secondary functions. Seaweed volatiles can also be released into the air or water during reproduction and when herbivores consume seaweeds 12. Their release is affected by abiotic factors such as irradiance, exposure to ultraviolet light, desiccation, and changes in seawater pH, salinity, and nutrient concentrations 11. Like terrestrial plants, marine macroalgae (seaweeds) produce a variety of VOCs, including sulfonium compounds and halogenated and non-halogenated terpenes, aldehydes, acids, alcohols, amines, amides, and other hydrocarbons 9, 10. The term “signal” is used to distinguish infochemicals that are generated to send a message to a receiver, and the term “cue” is used when there is no intention to send a message 3. However, because the emitting plant does not benefit from the receiver's response, the detection of emitted volatiles is more akin to receivers “eavesdropping” than emitters “talking” 8. Because the ability of plants to detect and respond to VOCs that are emitted by neighbors following herbivore attack was discovered in alders, willows, and poplars 5, 6, it was initially dubbed the “talking trees” phenomenon 7. The receiver then upregulates the production of defensive metabolites to prevent or reduce damage from future attacks by grazers or primes tissues so that they can respond more quickly in the event of an attack 4.

When used as indicators of herbivore attack, VOCs are released due to damage to the emitting individual, transported through the air, and detected by receptors on nearby plants or tissues. They also can be detected by neighboring plants or tissues to gain information about the emitter's physiological condition or whether herbivores are attacking it. These chemical messengers can mediate interactions among organisms, for example, by signaling pollinators, seed dispersers, beneficial microbes, and predators 3. Terrestrial plants use volatile organic compounds (VOCs) as airborne cues and signals to communicate and detect information about neighboring plants or plant tissues 1, 2.

Our study suggests that the ability to detect airborne compounds has evolved multiple times or before the divergence of terrestrial plants and green algae. To our knowledge, this is the first demonstration of a marine plant using an airborne molecule released when damaged to elicit defensive responses. fenestrata 1 m downwind of DMS emitters had 19% higher DMSP concentrations than upwind seaweeds after 11 days. fenestrata exposed to DMS had 43–48% higher DMSP concentrations, relative to controls, 6–9 days after exposure. We conducted laboratory and field experiments in which Ulva fenestrata was exposed to airborne dimethyl sulfide (DMS), a volatile antiherbivore and antioxidant metabolite released when the seaweed is grazed or physiologically stressed. We hypothesized seaweeds could use airborne VOCs as infochemicals and respond to them by upregulating a keystone defensive metabolite, dimethylsulfoniopropionate (DMSP). Like terrestrial plants, intertidal plants spend part of their lives emersed at low tide and release volatile organic compounds (VOCs) into the air when they are grazed or physiologically stressed.

Although the use of airborne molecules as infochemicals is common in terrestrial plants, it has not been shown to occur in an ecologically relevant context in marine seaweeds.

Normality test minitab