Introduction
Rising carbon dioxide emissions pose a critical environmental challenge leading to ocean acidification. This process can alter the physiological status of calcifying species such as bivalve mollusks, like Ruditapes philippinarum. The present study investigated how different pH scenarios affect the biometric parameters and behavioral functions of Manila clam, including growth, filtration, and burrowing capacity. The aim was to provide data to guide conservation strategies under ongoing ocean acidification.
Materials and Methods
A batch of 420 juvenile Manila clams, averaging 0.74±0.03g and 15±1.05mm in length were collected from the hatchery Naturedulis located in the Goro lagoon (FE, Italy), an area with significant variability in chemical-physical parameters, especially pH.
At the University of Bologna's aquaculture laboratory, clams were exposed to four pH conditions for 90 days: one control group maintained at pH 8.2 and the others exposed to pH levels of 7.9, 7.7, and 7.4. Animals were reared in four independent systems of aquaria, were fed a mixture of live microalgae. pH levels were controlled automatically by a CO2 injection system. The temperature was maintained at 20±1°C, and salinity at 27±1��� throughout the experiment. Biometric indices were measured at the end of the experiment, along with the condition index and hepatosomatic index, clearance rate, and burrowing behavior was observed under different pH conditions.
Results and Discussion
Statistical analysis was performed using one-way ANOVA, and Tukey's post-hoc test was applied for significant results (p<0.05). The results from total weight and length at the end of the experiment did not exhibit statistical variation, even with exposure to lower pH levels. Similarly, the condition index and hepatosomatic index remained constant across all treatments, indicating no significant loss in tissue mass or energy reserves. The clearance rate test revealed no significant changes in filtration activity, suggesting that the clams maintained stable food acquisition under conditions that were not severely stressful. Behavioral responses, such as burrowing time and depth, were also unaffected by varying pH levels (Figure 1). The absence of significant changes suggests that clams were resilient to the experimental acidification conditions. This resilience may be due to the clams' origin in the dynamic Goro Lagoon, where natural pH fluctuations (ranging from a minimum of 7.06 to a maximum of 8.9 pH during the month of May) could have fostered adaptation to acidic conditions.
This study demonstrates that Manila clam possesses remarkable resistance to the ocean acidification scenarios predicted for the near future. An extraordinary plasticity likely links to the origin environmental. In conclusion, although ocean acidification represents a global threat, Manila clam could tolerate significant pH fluctuations, ensuring greater stability for future shellfish farming activities.
Figure 1: Total weight (A), length (B), Condition index (C), Hepatosomatic index (D), Clearance rate (E), Burrowed clams (F), Burrowing time (G), Burrowing depth (H). Data are presented as mean ± standard deviation.
References
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