Science Advisory Report 2016/014

Review of potential impacts of hydrated lime treatments associated with proposed expansion of mussel production in Malpeque Bay, PEI

Summary

• Hydrated lime application on mussel grow-out sites and seed lines in Malpeque Bay is used to manage the invasive clubbed tunicate (Styela clava) on aquaculture sleeves and associated infrastructure. Treatments typically occur from mid-July through to early November, with the most intensive application occurring in August and September.
• A saturated hydrated lime solution is highly alkaline, when it is introduced into the aquatic environment the immediate effect is an increase in pH of the receiving water. The pH change signal is characterized by both the time it takes the receiving water to return to ambient pH range and the distance at which the pH of the receiving water is changed from the ambient range.
• Application of hydrated lime in Malpeque Bay results in short term (minutes) and small scale (meters) effects on the pH characteristics of the water column in the vicinity of treatment activity.
• There is a limited number of studies on lethal and sublethal effects of hydrated lime on marine organisms. The lethal thresholds of pH (96 hr LC50) for several species are of similar pH but for longer duration than the measured field conditions during liming treatment. Therefore it is unlikely that lime treatments would have harmful effects on lobster and other non-target organisms.
• The planktonic life stages of crustaceans (lobster and rock crab) are present in the water column from mid-June through to mid-September and overlap with the periods of liming treatments.
• Benthic habitat classified as prime lobster ground that can support all life stages of lobster was found in one limited area that is being considered for expansion of mussel aquaculture. The remainder of the proposed area of expansion has benthic habitat that is classified as poor for lobster, serving as a transition zone.
• Liming activities associated with mussel lease expansions will result in an environmental footprint defined by transient increases in pH that last minutes and extend over a few meters when treatments occur.

This Science Advisory Report is from the February 8 and 9, 2016 meeting on the Review of potential impacts of hydrated lime treatments associated with proposed expansion of mussel production in Malpeque Bay, PEI. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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