The effect of age and shell size on accumulation of fouling organisms on the Akoya pearl oyster Pinctada fucata (Gould)

Biofouling is a significant operational cost for pearl aquaculture. Understanding the factors that affect the settlement and development of fouling organisms contributes to improved management practices to control biofouling. Field experiments were carried out to document the accumulation of fouling organisms, measured as percentage cover, with respect to age (2-year-old and 3-year-old, independent of shell size) and shell size (45–55 mm and 65–75 mm dorso-ventral measurement, DVM, independent of age) of the Akoya pearl oyster Pinctada fucata. After 16 weeks, 3-year-old P. fucata were significantly more fouled than 2-year-old oysters. In contrast, there was no significant difference in fouling cover between 3-year-old P. fucata with DVM of 45–55 mm and 65–75 mm. Fouling communities were dominated by the hydroid Obelia sp., the bryozoan Parasmittina sp. 1, the bivalve Saccostrea sp. 1 and the ascidian Didemnum sp. To determine a potential relationship between the accumulation of fouling organisms and periostracum cover, differences in periostracum cover with age (2-year-old and 3-year-old) and shell size (45–55 mm and 65–75 mm DVM) of P. fucata were examined. Periostracum, measured as both area covered and area without periostracum, decreased significantly with age, but not with shell size. The high percentage cover of fouling on all oysters and the large area where periostracum was undefined makes any conclusion as to the role of the periostracum in preventing fouling unclear. These findings, however, support age as a key factor for the development of husbandry protocols, with older P. fucata shells being cleaned more frequently than younger shells to counteract the increased settlement of fouling organisms.