Effects of temperature and salinity on the larvae of Sacculina polygenea (Crustacea: Cirripedia: Rhizocephala)

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The responses of the larvae of the rhizocephalan barnacle Sacculina polygenea, a parasite of the intertidal crab Hemigrapsus sanguineus, to different temperatures and salinities were examined. Its development comprises five naupliar stages and the cypris stage. The phototaxis of the nauplii remained undisturbed at 22℃ and 26-34‰. The number of true naupliar moults decreased at lowering of temperature and salinity. Successful naupliar development occurred in temperature and salinity ranges of 1825℃ and 18-34‰ respectively. At 20-25℃ and the optimum salinity of 24-28‰, development to the cypris stage took 2-3 d. Under the most severe conditions imposed (15℃ and 18‰) the cyprids appeared in 6.5 d. The cypris larvae showed wider tolerance range against decreased salinity than the naupliar stages. At 1520℃ and 14-34‰, 85-95% of cyprids died hi 7 d. In the tolerance to different salinities S. polygenea larvae occupy an intermediate position between those of estuarine and marine species. The continuous presence of planktonic cypris larvae in wide range of temperature and salinity represents a potential infestation hazard for the host crabs.