Responses of four isolates of marine naked amoebae to reductions in salinity

The salinity tolerances of four species of naked amoebae, isolated from a temperate sandy beach, to gradual and rapid reductions in environmental salinity were tested. The greatest resilience to both forms of salinity change was displayed by a small Platyamoeba sp. Following gradual acclimation, this isolate was able to show normal growth in salinities as low as 17‰ and altered growth rates down to 7‰ and was able to survive and grow normally in media after a rapid drop in salinity from 32‰ to 17‰. A non-eruptive limax isolate was as resilient and showed normal growth after gradual acclimation in 17‰ salinity media, in salinities lower than this generation times increased and cell yields decreased. The maximum rapid drop in salinity that this species could tolerate and still show normal growth was from 32‰ to 17‰. The poorest tolerance to reduced salinity was shown by populations of Mayorella sp. The lowest salinity this species showed growth in was 12‰ but populations in this salinity displayed very long generation times and very poor cell yields. The response of a Vahlkampfia sp. was intermediate between the responses of the other three isolates. All four of these species were able to survive as floating forms for 2 days or longer in 2‰ salinity media which was unable to support their growth and attachment. Viable cells were present after 48 h (Mayorella sp.) to 1 week and more (Platyamoeba sp. and limax amoebae). These results are potentially important in relation to the structuring of natural amoebae communities. In temperate marine habitats, amoebae which have a greater ability to attach (and remain attached) and display normal generation times under conditions of reduced salinity may be able to colonise a wider range of marine habitats and out-compete, other less resilient species.