Increasing atmospheric levels of carbon dioxide are largely absorbed by the world's oceans, decreasing surface water pH 1 . In combination with increasing ocean temperatures, these changes have been identified as a major sustainability threat to future marine life 2 . Interactions between marine organisms are known to depend on biomolecules, but the influence of oceanic pH on their bioavailability and functionality remains unexplored. Here we show that global change significantly impacts two ecological keystone molecules 3 in the ocean, the paralytic toxins saxitoxin (STX) and tetrodotoxin (TTX). Increasing temperatures and declining pH increase the abundance of the toxic forms of these two neurotoxins in the water. Our geospatial global model highlights where this increased toxicity could intensify the devastating impact of harmful algal blooms on ecosystems in the future, for example through an increased incidence of paralytic shellfish poisoning (PSP). We also use these results to calculate future saxitoxin toxicity levels in Alaskan clams, Saxidomus gigantea, showing critical exceedance of limits safe for consumption. Our findings for TTX and STX 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 mediating species interactions such as foraging, reproduction, or predation in the ocean with unexplored consequences for ecosystem stability and ecosystem services.

The recent identification of uridine diphosphate (UDP) as the female sex-pheromone in the European shore crab Carcinus maenas demonstrated not only the link between moult and pheromone production, but also how it may have evolved from a 'simple' metabolic byproduct. Consequently, it is expected to be present in other moulting crustaceans, thus raising issues involving species specificity of the female pheromone. Bioassays were conducted using synthetic pheromone (UDP, 10 −3-10 −4 M) to examine if it induced sexual behaviour in other crustacean species that are neither closely related nor occur in the same ecosystem. The snow crab, Chionoecetes opilio, and the yellowline arrow crab, Stenorhynchus seticornis, both belonging to a different superfamily (Majoidea) and occurring in different habitats than C. maneas (Portunoidea), displayed significant sexual behaviour towards UDP treated objects (p < 0.005). These and other examples demonstrate that the female sex-pheromone UDP is not species-specific but is present and active in some other decapod crustaceans.

No abstract

No abstract

Arguably climate change is one of the biggest challenges faced by many organisms. One of the more significant of these is the decreasing pH level of the ocean, a consequence of the increasing amount of atmospheric CO2 being absorbed. With the current open ocean pH level of 8.15 projected to fall to just over 7.6 in 2100, the impacts could be devastating for marine species reliant upon olfaction to survive. Here, we show that Carcinus maenas (shore crab) can detect and respond to the presence of odour cues from predatory species with no significant change between both current and projected pH conditions. In contrast, C. maenas ability to detect and respond to prey cues is altered in the projected climate change conditions, with a delayed response being observed at pH 7.6. A difference can be seen between males and females, with males detecting prey cues faster than females in reduced pH, suggesting the potential for males to be better acclimated to future climate change conditions. The change in ocean chemistry is postulated to have a fundamental impact on chemical communication systems in aquatic species. Here, we show such negative impacts of altered pH on feeding responses in Carcinus maenas, a typically robust keystone intertidal species and confirm that not all behaviours are affected equally with potentially significant implications for such functional traits and species interactions.