Ocean acidification foils chemical signals

THE CRUCIAL IMPORTANCE of chemical cues to reef resettlement was elegantly demonstrated by D. L. Dixson et al. (“Chemically mediated behavior of recruiting corals and fishes: A tipping point that may limit reef recovery,” Research Article, 22 August, p. 892). Similarly, waterborne chemical signals (pheromones) and cues are essential for mediating marine species’ behaviors, including those associated with mating, foraging, recruitment, and alarm (1).

Responses to these chemical signals and cues are in danger of global disruption by the effect of rising atmospheric CO2 levels on aquatic pH. At current rates, ocean pH will drop from the current and historic pH of 8.15 to 8.25 to about 7.8 or below by 2100 (2). Quite apart from effects on calcification, reduced pH has the capability to affect both the signaling (semiochemical) molecules themselves and their interaction with chemosensory receptor proteins. The interaction of semiochemical ligands with chemosensory receptors changes with pH, through the number, type, and alignment of intermolecular forces (e.g., hydrogen bonding, electrostatic potential, and hydrophilic/hydrophobic regions) on bothligand and chemosensory receptor (3, 4). Examples of the pH-affected semiochemicals are pheromones and cues, including peptides, nucleosides, thiols, and organic acids in nereid polychaete worms, Aplysia sea hares, crustaceans, and fish (3).

The current rate of oceanic pH decline is occurring faster than chemosensory systems can evolve; today’s systems have evolved over 50 million years under relatively constant pH (2). Every marine
species, at every trophic level, is potentially affected by disruption of chemical cues and signals, including responses to predator odors [e.g., (5)], sexual reproduction, sperm attraction, fertilization, social interactions, feeding, and larval settlement (1). Studies into not only the effects of disruption but also the mechanisms of action and resulting predictive ecological models are urgently needed. We risk widespread ecosystem damage by this additional silent danger from rising anthropogenic CO2 levels.

Wyatt T. D., Hardege J. D. & Terschak J., 2014. Ocean acidification foils chemical signals. Science 346(6206):176. Article (subscription required).

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