Modeling the impact of climate change on mussel aquaculture in a coastal upwelling system: A critical assessment

Forecasting of climate change impacts on marine aquaculture production has become a major research task, which requires taking into account the biases and uncertainties arising from ocean climate models in coastal areas, as well as considering culture management strategies. Focusing on the suspended mussel culture in the NW Iberian coastal upwelling system, we simulated current and future mussel growth by means of a multistructural net production Dynamic Energy Budget (DEB) model. We considered two scenarios and three ocean climate models to account for climate uncertainty, and applied a bias correction to the climate models in coastal areas. Our results show that the predicted impact of climate change on mussel growth is low compared with the role of the seeding time. However, the response of mussels varied across climate models, ranging from a minor growth decline to a moderate growth increase. Therefore, this work confirms that an accurate forecasting of climate change impacts on shellfish aquaculture should take into account the variability linked to both management strategies and climate uncertainty

Juvenile king scallop, Pecten maximus, is potentially tolerant to low levels of ocean acidification when food is unrestricted.

The decline in ocean water pH and changes in carbonate saturation states through anthropogenically mediated increases in atmospheric CO2 levels may pose a hazard to marine organisms. This may be particularly acute for those species reliant on calcareous structures like shells and exoskeletons. This is of particular concern in the case of valuable commercially exploited species such as the king scallop, Pecten maximus. In this study we investigated the effects on oxygen consumption, clearance rates and cellular turnover in juvenile P. maximus following 3 months laboratory exposure to four pCO2 treatments (290, 380, 750 and 1140 µatm). None of the exposure levels were found to have significant effect on the clearance rates, respiration rates, condition index or cellular turnover (RNA: DNA) of individuals. While it is clear that some life stages of marine bivalves appear susceptible to future levels of ocean acidification, particularly under food limiting conditions, the results from this study suggest that where food is in abundance, bivalves like juvenile P. maximus may display a tolerance to limited changes in seawater chemistry

Clearance rate of the mussel Mytilus galloprovincialis. I. Response to extreme chlorophyll ranges

Clearance rate (CR) measurements in Mytilus galloprovincialis were determined over 16 experiments in which the mussels were exposed to diets characterized by variable chlorophyll content (0.28–104.88 µg Chla L–1) in order to: (1) establish the lower trigger level and the saturation reduction, (2) elucidate whether these thresholds were controlled by an on/off switch or by a progressive response, and (3) determine whether the experimental time exerted an effect on the CR measurement under extreme conditions, quantified in terms of chlorophyll content. The results demonstrated that time exerted a significant effect on CR, which varied throughout the experiment in different diets. The CR response differed fundamentally in the significant reduction of CR after prolonged exposure to low and high chlorophyll-content diets compared with the medium ones. Taking into account the data from the sixth hour onwards, a sharp lower trigger level threshold was established at 2.08 µg Chla L–1, showing an on/off CR response. The threshold for saturation reduction was about 26.91 µg Chla L–1 and showed a progressive response to chlorophyll concentration.

Clearance rate of the mussel Mytilus galloprovincialis. II. Response to uncorrelated seston variables (quantity, quality, and chlorophyll content)

Clearance rate (CR) response of Mytilus galloprovincialis was determined over 32 experiments in which the trophic conditions of its natural habitat, the Galician rías (Spain), were reproduced. Experimental diets were prepared by mixing pulverized sediment, Tahitian Isochrysis aff. galbana, and pulverized Spartina sp., avoiding multicollinearity among the seston variables used to characterize the diets: total particulate matter (TPM), quality (f = particulate organic matter (POM)/TPM), and chlorophyll content. This approach allowed us to identify the seston variables that have the most important effect on CR, as well as develop a mathematical model of CR response to the environmental trophic characteristics, without worrying about the statistical problems associated with multicollinearity among explanatory variables. Each of the three seston variables had a significant effect on CR response. Maximum CR was observed at a seston concentration of 1.2 mg L–1. The CR was inversely correlated with the fraction of low digestible organic matter (fdet = POMSpartina sp./TPM), and was relatively consistent when poorly digestible diets (fdet > 0.4) were excluded from the analyses. This relative stability suggested that CR was regulated by a physiological feedback such as the fraction of poorly digestible organic matter.

A thin-layer chromatography-densitometry assay for intracellular lipase activity in bivalves (Argopecten purpuratus)

 This study provides a method for the determination of lipase activity in bivalves. Using this method, lipase activities were studied in extracts of digestive gland of Argopecten purpuratus fed a diet that mimics the food available in natural ecosystems over a short-term experiment (24–72 h). The scallops were acclimated to standard conditions seven days prior to initiating the enzymatic analysis. The diet consisted of a mixture of laboratory-cultured Isochrysis galbana and natural sediment. For the acclimation diet (control diet), a total particulate concentration of 3.9 mg L–1 was used with an organic content of 1.7 mg L–1 (42.5%), of which 28% were lipids. The experimental diet had a total particulate concentration of 20.8 mg L–1 with 26% of organic content, of which 20% were lipids. The effect of diet and experimental time on lipase activity was analyzed. The response of the intracellular lipases to changes in the food offered was abrupt and lower investment in enzymatic activity was observed with the experimental diet. No significant effects were observed either for the time or for the combined diet and time interaction