85. The Future of an Ecosystem Engineer: Effects of Ocean Acidification and Rising Temperatures in Crassostrea gigas Juveniles

Catarina Santos (1,2), Inês Rosa (1), Jorge Machado (2,3), Mariana Hinzmann (2,3), Marta Pimentel (1), Sofia Francisco (1), Rui Rosa (1)*

1 MARE – Marine and Environmental Sciences Centre, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Cascais, 2750-374, Portugal
2 ICBAS‐UP– Abel Salazar Biomedical Sciences Institute, University of Porto, Porto, 4050-313, Portugal
3 CIIMAR– Centre of Marine and Environmental Research, University of Porto, Porto,
4050-123, Portugal

Background
Often described as an “ecosystem engineer”, the Pacific cupped oyster (Crassostrea gigas) has become the dominant farmed oyster. With high growth rate and great tolerance to environmental variations this it is able to out-compete indigenous species. Rising temperatures and ocean acidification pose serious challenges for sessile calcifiers, such as oysters, particularly during their early-life. As both the disruption and thrive of this species has the potential to induce cascading effects over the entire ecosystems while triggering important economic consequences, research is needed to improve stock management and mitigations politics.

Methods
Here we present a multidisciplinary assessment of the overall fitness of C. gigas juveniles in face of climate change related stressors. We evaluate the effects of a 3 month exposure to ocean warming (∆ 4ºC) and high pCO2, with concomitant acidification (Δ 0.5 pH units), on stress biomarkers [(i) Heat Shock Response and (ii) Lipid peroxidation], metabolic potential [(iii) Citrate synthase and (iv) Lactate dehydrogenase activity], haematological parameters [(v) total haemocyte count, (vi) viability and (vii) ratio of morphotypes] and calcification processes [(viii) shell microstructure].

Findings
The exposure to the experimental conditions triggered the activation of a stress response, although not sufficient to prevent cellular damage, particularly under hypercapnia. Our results also denote a shift from aerobic towards anaerobic metabolism. Haematological parameters were likewise affected by the experimental conditions, particularly acidification. Additionally, over time, the shell ultrastructure suffered major alternations as a consequence of the synergistic action of ocean warming and acidification.

Conclusions
Our results suggests that in a future scenario, with warmer temperatures and high pCO2 levels, the overall fitness of juvenile Pacific oyters may indeed be undermined. This study represents a comprehensive effort to increase the knowledge about the impacts of global change on this economically profitable and potentially invasive species.