Life History & Behaviour

​Basic anatomy

All species of pearl oyster and indeed many of the Lamellibranchs have similar anatomy, feeding structures and behaviours that allow for some generalisations to be made. Other traits such as size, life-cycle, reproduction and other aspects both behavioural and physiological can be more genus and species-specific. Below is information about P. albina collated from sources found on members of the genus Pinctada in regards to respiration, feeding, locomotion, reproduction and growth.

​Basic anatomy of a pearl oyster visible with the removal of one valve. Key anatomical components are labelled. The image has been rotated to simulate the attachment of the oyster to a horizontal surface. The base of the image is the dorsal surface, the left of the image is the anterior, the top of the image the ventral and the right of the image the posterior surface. (Adapted from Queensland Government, 2014)


Respiration

P. albina belongs to Bivalvia, a class within the phylum Mollusca, which is comprised of soft-bodied organisms enclosed by a set of calcareous outer valves (shells). All of the bivalves respire through gills (ctenidia) by creating a water current that passes into the mantle cavity and flows through the gills (Ruppert et al., 2004). The surfaces of the gills are highly vascularized allowing for oxygen to diffuse easily across the thin membranes into the circulatory system (Southgate & Lucas, 2008) similar to the process of respiration in people. There are three gill arrangements in Bivalves and these determine both respiration and feeding (Beninger & St-Jean, 1997, Ruppert et al., 2004). Protobranchs use their gills only for respiration, Septibranchs use their gills for respiration and have a secondary structure used to "vacuum" up prey items and Lamellibranchs have a highly folded gill system used for both respiration and filter feeding (Ruppert et al., 2004).


​Diagrammatic cross sections displaying the three distinct gill arrangements that divide Bivalves into (from the left); Protobranchs, Lamellibranchs and Septibranchs. The shells appear as the dark outlines and the gills are located either side of the mantle (middle of the shells)(Adapted from Ruppert et al., 2004)


​Feeding

P. albina feeds by sucking in water and creating a current over the gills within the mantle. The gills trap small organic food particles in the water on their highly ciliated and mucus covered surface (Beninger & St-Jean, 1997, Jorgensen, 1996). The cilia then sweep the particles toward the mouth of the animal located near the stomach and foot (Southgate & Lucas 2008). From here the particulate matter is expelled as pseudofaeces or passed in the stomach and then the intestine to digest and absorb nutrients with waste leaving through the anus at the end of the digestive tract (Southgate & Lucas, 2008).


P. albina feeds in the same way as other suspension feeding bivalves. If the water were full of sediment in the video (above) then over time the sediment would be cleared from the water and the clarity would improve. In the video small particles may be seen entering the oyster through the opening of the shell (Video by Nicholai Cushing, filmed in the Marine Aquarium at the School of Biological Sciences, University of Queensland, St. Lucia)

Locomotion

There is very little movement in P. albina and therefore little need for a well-developed locomotion system (Southgate & Lucas, 2008). Mainly the pearl oysters grow attached to the substrate by the byssus (Ruppert et al., 2004), but may move around by using the muscular foot in the early stages of settlement (Southgate & Lucas, 2008). After settlement the foot of the oyster becomes more of a sensory and tactile appendage used to sense the surrounding environment (Southgate & Lucas, 2008).

P. albina are hermaphroditic usually having protandry male sex organs whilst young and female later in development (O’Connor, 2002). This ability to change sex with maturation is also seen in other species within the genus Pinctada such as Pinctada margaritifera (Southgate & Lucas, 2008). Sexual inversion may occur under certain environmental conditions and this process is thought to be rapid due to a lack of bisexual animals in collected specimens (Tranter, 1958, Southgate & Lucas 2008). External fertilisation and development is present in all members of the genus Pinctada with a planktonic larval stage (Ruppert et al., 2004, Tranter, 1958). A peak occurs when the water temperature begins to decrease due to seasonal changes around the months of April and May (Southgate & Lucas, 2008, Tranter, 1958) although spawning is continual throughout the year (Tranter, 1958). Sexual maturity is usually reached within 4-5 months