Northern Quahaug, Mercenaria mercenaria (notata variety), winter survival strategies
The northern quahog, Mercenaria mercenaria, is a temperate bivalve that experiences site-specific and variable losses when deployed for growout at small sizes (less than about 20 mm in shell height) at field sites in Atlantic Canada and the US. This study determined the long-term effects of low temperatures (1, 7 and 12℃) on survival, physiological rates (oxygen consumption, clearance rates and growth rates), and biochemical responses (gross proximate composition) of quahog juveniles held in a land-based nursery system supplied with a moderate diet of cultured algae. Quahog seed experienced progressive and variable mortality rates both at 7 and 1℃, but not at 12℃. Feeding rates were suppressed at 1℃, leading to progressive, linear tissue weight loss at this temperature. Organic weight loss could be entirely accounted for by the utilization of carbohydrate reserves, as there was no measurable utilization of either protein or lipid reserves. During simulated spring conditions following overwintering, quahogs showed reduced growth rates when subjected to both a temperature increase and reduced salinity (2 wks at 17 %), than those that only experienced an increase in temperature but remained at constant salinity (30 %), suggesting that the spring freshet may aggravate overwintering stress. Notata seed showed significantly higher mortalities during simulated overwintering at 1℃ than native seed from the same hatchery source. Preliminary data suggest that pre-conditioning at higher temperature (18 and 23℃) increased the survival of juvenile quahogs overwintered at 1℃. Acute cold shock (reduction in temperature from 12 to 1℃) induced the expression of heat shock or stress proteins HSP70 and HSP40 in juvenile quahogs, but this effect was more prolonged and greater in magnitude when the cold shock lasted 12 h vs. 3 h. Thus this study documents for the first time the timing and magnitude of overwintering losses of M. mercenaria seed and suggests several potential strategies for the mitigation of winter losses.
2002 - 2004
Atlantic: Gulf of Maine, Scotian Shelf
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