Byssal attachment of juvenile mussels, Perna canaliculus, affected by water motion and air bubbles

The effects of water flow and air bubbles on byssal attachment were investigated for re-settled juvenile mussels, Perna canaliculus. Three water flow regimes (∼1, 5, and 10 cm/s), and with/without air bubble treatments were used to test the number of juveniles (3-5 mm in length) settled on filamentous plastic plants within flow-through tanks. As expected, mussel attachment was higher for mussels within high flow and lowest for mussels within low water flows, but air bubbles did not significantly affect initial mussel attachment. A subsequent increase in water flow to 13 cm/s for 5 min to all treatment combinations was used to test the strength of byssal attachment (measured by the number of detached mussels). These experiments indicate that both high water flow and air bubbles caused fewer mussel detachments than lower flows and no addition of air bubbles. Furthermore, the number of byssal threads was greater for mussels previously exposed to high water flows and air bubbles, indicating that these mechanical stimuli result in greater production of byssal threads as a means to attain a stronger hold on their substrates. The implications of these results are discussed for mussel settlement and retention under natural and farm conditions.