Recent evolutionary changes in the algae of the Baltic Sea

Abstract

A decrease in salinity and temperature over the past 3000 years has presented the marine algae of the Baltic Sea with very considerable problems in adaptation. The effects of salinity upon a number of Baltic algae have been measured. The results showed cell mortality to be severe in 0, 68 and 102%o, and minimal in 6 and 11%o: there was most variation in tolerance to 34 and 51°/oo . The salt tolerances of Baltic marine algae have proved more hyposaline than those of British intertidal algae. Water uptake and loss in tissues of Chorda filum and Fucus vesiculosus from Baltic and British populations have been measured in response to salinity changes. The results revealed significant population differences in both live and killed tissues. Receptacle development and oogonial maturation have been observed in Baltic and British F. vesiculosus, and found to differ in seasonality. Some observations were associated with local sea temperatures but differences in the timing of receptacle initiation and in oogonial size were not. The depauperate thallus, commonly ascribed to the effects of low salinity, was found to be a complicated phenomenon, comprising numerous attributes which are combined differently in different taxa. The morphological differences between Baltic and British marine algae were usually striking.

Increased resistance towards generalist herbivory in the new range of a habitat‐forming seaweed

“…Fucus vesiculosus, together with the rest of the present marine species probably recruited into the Baltic Sea at the beginning of the Littorina Sea phase ca. 7500-6000 BP, when the salinity was higher than today (Russell 1985). During this period, littorinid snails were also present and the F. vesiculosus community in the Baltic was probably more similar to the community in the North Sea/Skagerrak compared to the present situation.…”

Recent evolution in Baltic Fucus vesiculosus: reduced tolerance to emersion stresses compared to intertidal (North Sea) populations

“…It has been observed by Russell (1985) that the present flora of the Baltic is largely composed of species which are intertidal throughout the rest of their distributions, and he has suggested that intertidal species that commonly experience wide fluctuations in salinity might be 'preadapted' to a brackish-water existence because of their genetic plasticity. In highly (osmotically) variable environments like the intertidal zone, selection may simultaneously favour mechanisms to tolerate both water stress (freezing, desiccation) and hypoosmotic stress (precipitation, freshwater runoff).…”

“…The conditions currently prevailing in the Baltic are, therefore, very recent in evolutionary terms, raising the question of how much evolutionary change has been possible in this short period. Algal studies of adaptations to Baltic conditions have largely focused on salinity tolerances for survival and/or growth (Russell 1985, 1988, Rietema 1991, Bäck et al 1992a, Rueness & Kornfeldt 1992, ecophysiological responses to salinity (Bäck et al 1992b), and reproductive adaptations to salinity (Serrão et al 1996a(Serrão et al , 1999b. These studies have provided evidence that several marine macroalgae species from the Baltic may have undergone ecotypic differentiation with regard to salinity tolerance.…”

Functional divergence in heat shock response following rapid speciation of Fucus spp. in the Baltic Sea

“…Endemic F. radicans therefore represents a case of rapid speciation within the Baltic Sea during the recent postglacial Littorina Sea period (ca. 7500 BP) (Ignatius et al 1981;Russell 1985). Decreasing sea surface temperature (SST) from the western to the northern Baltic (Siegel et al 2006) has received less attention than salinity clines, despite the important role of thermal stress in marine biogeography (Somero 2005).…”