Some Anatomical and Physiological Differences in Chorda Filum from Coastal Waters of Finland and Great Britain

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Abstract
A comparative study of Chorda filum populations from the British Isles (S 34‰) and the Baltic coast of Finland (S 6‰) has revealed differences in response by live adult thalli to treatment for 2 h with sea water of different salinities. Water uptake and loss by thalli differed significantly in salinities of х o‚ х 1/6, х ⅓ and х 1 ( = 34‰). British material showed severe cell disruption in freshwater whereas Finnish material did not. Killed thalli also behaved differently, British material showing little response to salinity treatment but Finnish plants continuing to react much as live tissues.Anatomical differences between populations were also observed, cortical cells in Finnish plants being significantly smaller than their British counterparts. Diaphragms traversing lumens of British material were simple, entire structures, but those in Finnish plants were deeply dissected and complex in organization.It is postulated that Baltic Chorda may have undergone a process of evolutionary divergence in response to its changed saline environment.INTRODUCTIONChorda filum (L.) Stackh. is one of several species of north Atlantic Phaeophyceae to be found in the inner Baltic Sea and Gulf of Bothnia; its geographical limit being associated with sea water salinity of approximately 4‰, (Waern, 1952; Hällfors et al. 1981). This species has been studied by Norton & South (1969) and South (1966) who traced the development of gametophytes and early sporophytes in culture media of different salinites. Although their cultures had been established from British material only, they felt able to argue from their results that the Baltic population did not constitute ‘… a different physiological strain specially adapted to the extreme environmental conditions prevailing there’.