Behavioural response of bivalve molluscs to calcium hydroxide

Luc A. Comeau*, Rémi Sonier, Thomas Guyondet, Thomas Landry, Aaron Ramsay and Jeffrey Davidson
 
*Atlantic Veterinary College, 550 University Avenue, Charlottetown, Prince Edward Island, Canada. E-mail: luc.comeau@bellaliant.net

Blue mussels (Mytilus edulis) cultivated in Prince Edward Island, Eastern Canada, are susceptible to heavy fouling on their shells as a result of the rapid proliferation of invasive solitary tunicates. The clubbed tunicate (Styela clava) is particularly difficult to manage. Its leather-like tunic cannot be perforated easily using high-pressure water. To control S. clava mussel growers periodically raise longlines in order to spray a highly alkaline (~12.7 pH units) calcium hydroxide solution onto the fouled mussels (Figure 1).

Laboratory experiments were conducted to assess the response of various bivalves to alkalinity levels they may encounter during calcium hydroxide treatments in the field. Behavioural responses were assessed by connecting bivalves to a system that closely monitored their valve movements (Figure 2).

Bivalves responded to increased alkalinity by completely or partially closing their valves. For M. edulis the avoidance behaviour intensified over a 3-day treatment period, suggesting that its sensitivity to alkalinity increases over time. Nevertheless, all behavioural responses were short-lived (0.2-4.7 h) and generally confined to the treatment period. In conclusion, it seems that spraying calcium hydroxide onto cultivated mussels has limited impact outside its intended purpose of eradicating fouling tunicates.