Adult Crassostrea gigas are completely sessile. The only time they are mobile is during their free-swimming larval stage. During this period, their primary means of dispersal is the water current (Pauley et al., 1988: 6). It has been hypothesized that, with water currents of 1 m/s, the larvae could spread up to 240 km, but no grown oysters have been observed that far from an established population. They are considered planktic larvae, but do have organs that allow for swimming. Eventually, they settle to the bottom of the water they float in, group together, and crawl around, searching for a suitable substrate (Nehring, 2006: 7). Larvae can be stimulated to settle by factors like temperature change, presence of suitable substrates, sufficient light, and surface irregularities of the substrate (Pauley et al., 1988: 17). The oysters have been known to attach themselves to the hulls of ships, thus achieving another means of dispersal (Nehring, 2006: 7).
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