PRODUCTIVE POTENTIAL OF THE CLAM Venerupis corrugata UNDER OCEAN ACIDIFICATION AND WARMING SCENARIOS

The pullet carpet shell Venerupis corrugata (Gmelin, 1791) is a clam species distributed in the East Atlantic -from Norway to North Africa- and in the Mediterranean Sea. It has been traditionally harvested at the Southwestern and Mediterranean Europe, mainly in Portugal, Spain, France and Italy where overfishing, indiscriminate digging and pathogen-induced mortality determined stocks' reduction, forcing aquaculture production. The high market demand for this species, that supports its high market value (global average price over $20USD per kg), is mostly driven by fragile stocks' recovery under high consumption and increased mortalities due to disease outbreaks and extreme climatic events, predictably more frequent under modern to future climate conditions. The present study aims to assess the performance of the culture of this clam from early life, throughout ontogeny, metamorphosis, settlement and up to 1-month post settlement, under projected ocean acidification (OA) and warming (W) scenarios, in an attempt to foresee its productive potential in the expected future climate.

Broodstock  was collected in Ria de Aveiro (NW Portugal) and induced to spawn  in the laboratory by thermal stimulation. F ertilized eggs were incubated  to hatch in 1-μm filtered, UV-sterilized artificial saltwater under control conditions: unmanipulated pH (~8.2) and 18 ºC.  The D-larvae  retained  in  a 60µm-sieve 48 hours post fertilization (48h pf) were exposed to nine OA-W scenarios (Figure 1) resultant from a factorial design of three pH levels at three different temperatures.  Beyond  the unmanipulated pH control, two a cidified treatments were produced by CO₂ bubbling, while temperatures were  kept  constant by  immersion of experimental containers in continuously controlled water baths.

Mortality, development stage and  shell  growth were  assessed every 3 to 4 days until complete settlement (i.e., 100% settlement verified in all experimental treatments) recorded after 28 days of exposure (T28). Mortality and  shell growth of settled juveniles were reassessed at T60.

Apart from an initial increased survival under acidity, potentially due to changes in the microbiome, there was an apparent lack of effect of the treatments on mortality. Moreover, development and growth were notably accelerated by warming, despite a relatively delayed settlement and growth under acidity, effect attenuated by the concomitant rise in temperature. These results reveal the resilience of this species to future OA-W and its productive potential under the tested scenarios.