Temperature tolerance of embryos and larvae of five bivalve species under simulated power plant entrainment conditions: a synthesis

Abstract

Thermal tolerance studies on three larval stages of five species of bivalve are compared: Crassostrea virginica, Mulinia lateralis, Argopecten irradians, Mercenaria mercenaria, and Spisula solidissima. Experiments were designed to simulate possible larval entrainment in the cooling systems of power plants and involved an 11 (temperature)x8(time-exposure) experimental matrix. Temperatures ranged from about 17.4° to 43°C at approximately 2C° intervals, and exposure times ranged from 1 min to 6 h (sometimes longer in the case of C. virginica). For all species, larval mortality generally increased with increasing exposure temperature and with increased time-exposure at any one temperature. In some species (M. mercenaria and A. irradians), a cold-shock was also apparent (i.e. increased mortality at temperatures below those at which the larvae were spawned). In the case of A. irradians, this effect was more noticeable at the trochophore stage than at the other two stages, although for all species investigated, there was a general trend of decreased thermal sensitivity with increasing age. Despite some interspecies variability from temperature to temperature and from stage to stage, S. solidissima was the most sensitive species and A. irradians was intermediate in thermal tolerance between this and the other three species. At temperatures as high as 40°–41°C, straight hinge M. mercenaria and C. virginica sustained low mortality for more than 2 h and on this basis were judged to be the most “temperature-shock” resistant of all larvae investigated. However, younger stages showed no significant differences between M. mercenaria, C. virginica or M. lateralis, and we conclude that these three species are generally very similar in their larval resistance to thermal increase. All three are more euryhaline than are the remaining two polyhaline or marine species.