Impact of ocean acidification and warming on the feeding behaviour of two gastropod species

Abstract

Increased atmospheric CO2 produced by anthropogenic activities will be absorbed by the oceans over the next century, causing ocean acidification and changes in seawater carbonate chemistry. Elevated CO2 causes sublethal physiological and behavioural responses of the locomotion and foraging behaviour of marine organisms. This study aims to investigate the independent and synergistic effects of long term exposure to low pH and increased temperature on the feeding behaviour of two gastropod species, Hexaplex trunculus and Nassarius nitidus, both in adults and juveniles. The gastropods were kept under controlled temperature (ambient = 20°C, increased = 23°C) and pH (ambient = 8, low = 7.6) conditions for 2.5 years. The percentage of animals that successfully reached their food, response time, total time required to reach their food (duration), and total distance covered, was measured. The speed and path index (i.e. how straightforward the movement is) were estimated as means of foraging efficiency. Increased temperature (under ambient pH) resulted in faster responses, a shorter duration until food was reached and a higher speed in H. trunculus adults. H. trunculus (both adults and juveniles) were less successful in reaching their food source under low pH and ambient temperature compared to all other treatments. The response time, duration, speed and path index were not affected by low pH (at ambient or increased temperature) for H. trunculus adults and juveniles, as well as for N. nitidus. The foraging performance of juveniles hatched and developed under low pH (either at ambient or increased temperature) was more effective than the performance of adults of the same species, thus indicating a degree of acclimation. Also, the scavenger N. nitidus was more successful and responded faster in reaching carrion than the predator H. trunculus, whereas no significant effects were observed for N. nitidus under low pH.