Adaptive Responses of the Larvae of Cirripede Barnacle Peltogasterella gracilis to Changes in Seawater Temperature and Salinity

Abstract

The responses of the larvae of the cirripede barnacle Peltogasterella gracilis (Crustacea: Cirripedia: Rhizocephala) that parasitizes the hermit crab Pagurus pectinatus to different combinations of seawater temperature (25, 22, 20, 16, and 12°C) and salinity (from 34 to 8‰) were studied in a laboratory. The nauplii of P. gracilis completed the entire cycle of development at 22 to 12°C in a narrow range of salinity (from 34 to 28‰), which agrees well with the environmental conditions of the crab hosts' habitat. At favorable temperatures (22–20°C) and salinity (34–28‰), the nauplii reached the cypris stage in 88 ± 2 h, while at 12°C and 34–30‰, the naupliar development took 156 ± 5 h. The cypris larvae appeared more resistant compared with the nauplii, in terms of changes in both the temperature and salinity of seawater. They actively swam at all experimental temperatures and in the salinity range of 34–18‰. At temperatures (22–16°C) and salinities (34–24‰) favorable for the cyprids, their longevity in plankton equaled 6–10 days. Thus, the nauplii of P. gracilis is the more vulnerable stage of development in the life cycle of this parasitic barnacle. The tolerance against changes in environmental factors is due to the adaptive capabilities of parasitic larvae and the environmental conditions in the habitats of its host, a typical marine crustacean. The insignificant parasitization rate of the hermit crab by its rhizocephalan parasite may be explained by the death of the nauplii of P. gracilis, which occurs when they enter to the surface water layer.