Food acquisition by the intertidal filter feeder bivalve Perumytilus purpuratus: Can the gill explain a differential performance between smaller individuals and the larger ones?

The intertidal zone represents a challenging environment for filter-feeding marine invertebrates. Smaller individuals are more prone to intertidal stressors than their larger conspecific; thus, reaching refuge sizes is crucial for their survival. There is no clear consensus about the morphological adaptations that small filter-feeding individuals may use to compensate for its greater mass-specific metabolic requirement relative to that of a larger conspecific. Food acquisition in filter-feedings is not only determined by the gill size but also by the efficiency of particle retention and transport rate; trade-offs between these variables may explain why smaller individuals are more efficient at acquiring energy. In this study, we examined the mechanisms underlying feeding responses in relation to body size in the intertidal suspension-feeding bivalve Perumytilus purpuratus. Clearance rate, flow rate, particle transport rate, and gill cilia development were compared over a range of sizes (7–35 mm shell length). Our results showed that small individuals possess a gill activity that makes them more efficient at collecting and transporting food particles than their larger conspecifics. Water flow rate, clearance rate, and particle transportation throughout the gill were higher per standardized gill area in smaller than larger individuals. Although the gill filaments are not all fully developed in smaller individuals, the old filaments are functional in capturing and transporting particles, which makes them more efficient per gill area than larger specimens. Taken together, we demonstrated that juveniles of P. purpuratus are more efficient than their adult conspecifics in terms of feeding capacity.