Effects of temperature and ocean acidification on shell characteristics of Argopecten purpuratus: implications for scallop aquaculture in an upwelling- influenced area off northern Chile

Chair: Tommy Moore

Nelson A. Lagos (1)*, Samanta Benítez (1), Cristian Duarte (2), Marco A. Lardies (3), Bernardo R. Broitman (4), Christian Tapia (5), Pamela Tapia (5), Steve Widdicombe (6) & Cristian A. Vargas (7)

1 Centro de Investigación e Innovación para el Cambio Climático (CiiCC), Facultad de Ciencias, Universidad Santo Tomás, Santiago, Chile.
2 Departamento de Ecología y Biodiversidad, Facultad de Ecología y Recursos Naturales, Universidad Andrés Bello, Santiago Chile
3 Facultad de Ingeniería & Ciencias y Facultad de Artes Liberales, Universidad Adolfo Ibáñez, Santiago, Chile
4 Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile
5 Cultivos Invertec Ostimar S.A., Tongoy, Coquimbo, Chile
6 Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth, UK
7
Laboratorio de Funcionamiento de Ecosistemas Acuáticos (LAFE), Departamento de Sistemas Acuáticos, Facultad de Ciencias Ambientales, Universidad de Concepción, Chile

Background
Coastal upwelling regions already constitute hot spots of ocean acidification as naturally acidified waters are brought to the surface. This effect could be exacerbated by the ocean acidification and warming, both caused by rising concentrations of atmospheric CO2. Along the Chilean coast, upwelling supports highly productive fisheries and aquaculture activities. However, during recent years, there has been a documented decline in the national production of the native scallop Argopecten purpuratus.

Methods
We assesses the combined effects of temperature and pCO2-driven ocean acidification on the growth rates and shell characteristics of this species farmed under the natural influence of upwelling waters occurring in northern Chile (30°S, Tongoy Bay).

Findings
Regular observations of pH and temperature showed that the experimental conditions representing current ambient conditions (14°C/pH~8.0) were typical of natural values recorded in Tongoy Bay, whilst conditions representing the low pH scenario were typical of an adjacent upwelling area (pH~7.6). Shell thickness, weight and biomass were reduced under conditions of decreased pH (pH~7.7) and increased temperature (18ºC). At ambient temperature (14°C) and low pH (pH~7.7), scallops showed increased shell dissolution and low growth rates. However, elevated temperatures ameliorate the impacts of low pH, evidenced by an increase in the calcification rate of A. purpuratus.

Conclusions
The impact of low pH at current temperature on scallop growth, suggests that the upwelling could increase the time taken for scallops to reach the marketable size. Mortality of the harvestable scallops is discussed in relation with our observation on multiple environmental stressors in this upwelling–influenced area.