Ocean Acidification

Phenotypic plasticity allows organisms to cope with environmental variability, yet its role in sustaining aquaculture systems in the face of global change stressors remains poorly understood. We conducted a 90-day mesocosm experiment to test whether spat origin influences morphological, physiological, and periostracum responses in the Chilean mussel Mytilus chilensis under sustained experimental acidified conditions. Juveniles were collected from two contrasting habitats: an estuarine and dynamic/fluctuating environment, strongly influenced by freshwater discharges, and a marine, more stable environment; and then exposed to two pH regimes (8.0 and 7.5). Morphological traits showed subtle origin effects: estuarine mussels tended to exhibit higher shell length and calcification rates, though origin × pH interactions were not significant. Physiological responses were largely similar between both seed sources, with metabolic rates remaining stable while the clearance rate increased under acidified conditions in both populations. Periostracum analyses revealed some non-significant variation in organic composition, but no consistent effects of the pH were detected. Together, these results suggest that M. chilensis relies on conservative metabolic maintenance combined with flexible clearance responses possibly to cope with natural acidification pulses, while also tolerating sustained low-pH conditions, with only weak signals of origin-driven divergence. Our findings highlight the importance of phenotypic adjustments over local origin, suggesting that spat provenance may not be a primary determinant of performance under projected acidification scenarios tested here.

Leppes N. M., Hughes D., Martel S. I., Vargas C. A., Lagos N. A. & Lardies M. A., in press. Spat origin does not affect phenotypic plasticity in the farmed mussel Mytilus chilensis facing experimental acidification. Aquaculture Environment Interactions. Article (subscription required).