Near-future CO2 levels impair the olfactory system of a marine fish

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordData availability: All raw sequence data are accessible at the NCBI Sequence Read Archive through accession number SRP097118. Water chemistry, behaviour and electrophysiology data are available through Pangaea (https://doi.pangaea.de/10.1594/PANGAEA.884674).Survival of marine fishes that are exposed to elevated near-future CO2levels is threatened by their altered responses to sensory cues. Here we demonstrate a physiological and molecular mechanism in the olfactory system that helps to explain altered behaviour under elevated CO2. We combine electrophysiology measurements and transcriptomics with behavioural experiments to investigate how elevated CO2affects the olfactory system of European sea bass (Dicentrarchus labrax). When exposed to elevated CO2(approximately 1,000 µatm), fish must be up to 42% closer to an odour source for detection, compared with current CO2levels (around 400 µatm), decreasing their chances of detecting food or predators. Compromised olfaction correlated with the suppression of the transcription of genes involved in synaptic strength, cell excitability and wiring of the olfactory system in response to sustained exposure to elevated CO2levels. Our findings complement the previously proposed impairment of γ-aminobutyric acid receptors, and indicate that both the olfactory system and central brain function are compromised by elevated CO2levels.This study was supported by grants from Association of European Marine Biology Laboratories (227799), the Natural Environment Research Council (R.W.W.; NE/H017402/1), the Biotechnology and Biological Sciences Research Council (R.W.W.; BB/D005108/1), Fundação para a Ciência e Tecnologia (Portuguese Science Ministry) (UID/Multi/04326/2013) and a Royal Society Newton International Fellowship to C.S.P. C.S.P. is also a beneficiary of a Starting Grant from AXA

Saxitoxin and tetrodotoxin bioavailability increases in future oceans

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Increasing atmospheric CO2 levels are largely absorbed by the ocean, decreasing surface water pH1. In combination with increasing ocean temperatures, these changes have been identified as a major sustainability threat to future marine life2. Interactions between marine organisms are known to depend on biomolecules, although the influence of oceanic pH on their bioavailability and functionality remains unexplored. Here we show that global change substantially impacts two ecological keystone molecules3 in the ocean, the paralytic neurotoxins saxitoxin and tetrodotoxin. Increasing temperatures and declining pH increase the abundance of their toxic forms in the water. Our geospatial global model predicts where this increased toxicity could intensify the devastating impact of harmful algal blooms, for example through an increased incidence of paralytic shellfish poisoning. Calculations of future saxitoxin toxicity levels in Alaskan clams, Saxidomus gigantea, show critical exceedance of limits safe for consumption. Our findings for saxitoxin and tetrodotoxin exemplify potential consequences of changing pH and temperature on chemicals dissolved in the sea. This reveals major implications not only for ecotoxicology, but also for chemical signals that mediate species interactions such as foraging, reproduction or predation in the ocean, with unexplored consequences for ecosystem stability and ecosystem services