Impact of Intertidal Distribution on the Physiological Performance of the Filter-Feeder Bivalve Perumytilus purpuratus (Bivalvia, Mytilidae) from Southern Chile

Intertidal animals experience reduced feeding times and differentiated respiratory capacity associated with aerial exposure, the duration of which depends on their location within the intertidal zone. Perumytilus purpuratus is a sessile mussel that forms dense mats in the rocky mid-intertidal in southern Chile. For this species, we documented the impact of different times of aerial exposure (3 and 6 h) on rates of oxygen consumption and feeding, according to their vertical location (upper and lower limits) within the intertidal zone. Mean oxygen consumption rates in air for individuals located in the upper intertidal zone were 52% higher than those of individuals located at the lower limits of their intertidal distribution. Additionally, individuals from the lower intertidal region always presented higher rates of oxygen consumption and particle clearance rates (58% higher and 18% higher, respectively) during immersion compared to individuals collected from the upper limit of their intertidal distribution, regardless of the duration of previous aerial exposure. Although we found no significant habitat-related differences in the relationship between shell length and gill surface area, individuals sampled from the lower intertidal zone were 8% heavier in dry tissue weight than individuals with the same shell lengths collected from of the upper limit of their intertidal distribution. Our results suggest that the individuals of this species near the upper limits of their intertidal distribution can probably compensate (e.g., higher absorption rate) for the reduced time that they have available for clearance, which might help them to avoid a major energetic disadvantage.