Growth and reproductive phenology of nine intertidal algae on the Murman coast of the Barents Sea

Monthly replicate samples of 30 plants of each of nine species were collected in the intertidal zone in the Dalnezelenetskaya Inlet, Murman coast, Barents Sea. Germlings and new shoots emerged in great quantities in March when temperature was near 0 degrees C and daylength 10-13 h. All nine intertidal species on the Murman coast exhibit a period of rapid vegetative growth in early spring, at temperatures far below the optimum temperatures in at least five of them for which experimental evidence from the literature is available. The increasing light level in early spring is probably responsible for this growth. In six of them (Ulvaria obscura, Monostroma grevillei, Chorda filum, Chordaria flagelliformis, Stictyosiphon tortilis, Dumontia contorta) summer peaks of reproduction are apparently responsible for the summer decline of the thalli. The last five of these six have heteromorphic life histories in which microthallus stages are thought to ensure approximate synchronization of early spring recruitment (for instance by short day induction of microthallus development at autumnal temperatures, as in D. contorta and M. grevillei). In one species (Membranoptera alata), with an isomorphic diplohaplontic life history, early spring recruitment is thought to be ensured by the release of tetraspores and carpospores in winter. Earlier expectations that southern species would shift their reproduction to the summer near their northern distribution boundary were not confirmed. The general conclusion is that each of the nine species has approximately the same seasonal cycle of growth and reproduction in various parts of its geographic range, with only minor shifts from spring towards summer (but precise data on seasonal cycles elsewhere are scarce). This suggests that there may be subtle differences in temperatures and photoperiods triggering the onset of reproduction; this aspect needs further experimental testing of strains from the Murman coast.