Aspects of the biology of Laminarja hyperborea IV. Growth of early sporophytes

Abstract

Sporophytes of Laminaria hyperborea have been grown under various conditions in the laboratory up to the stage of 1000 cells. Some larger plants have been observed after exposure in the sea. Growth was not increased by artificial aeration of the normally stagnant cultures, nor by introducing a dark period each day. The cell number per sporophyte was found to increase exponentially with time. In from 10- to 1000-celled plants the logarithm of the cell number was proportional to the logarithm of the plant length; the relationship corresponded to two-dimensional growth in the presence of increase in cell length. In this size range, when the plants were mainly monostromatic, the growth rate in the laboratory was 0.5 cell divisions/day and 22% increase in length/day. The growth rate of larger sporophytes, partly polystromatic, in the sea, was 10% increase in length/day. A sporophyte would take at least 54 days from the release of the parent zoospores to reach a length of 1 cm. The minimum continuous irradiance necessary for growth was 2 μg.cal/cm²sec (20 lux) at 10° C and 4–5μg.cal/cm²sec (40–50 lux) at 17° C. The saturating continuous irradiance was at about 100 μg.cal/cm²sec (1000 lux) at 10° C and about 150 μg.cal/cm²sec (1500 lux) at 17° C. Up to 360 μg.cal/cm²sec (3600 lux) from fluorescent lamps was not inhibitory. Growth at 15–20° C was approximately the same as at io° C.