Experimental studies on the spores and sporelings of the red alga Mastocarpus stellatus

Young sporelings of Mastocarpus regenerated faster than old sporelings following induced severe damage. The tendency was always to return to a discoid shape. Survival of 'islands' of living cells in dead sporelings allowed some partial recovery. The interactions between Mastocarpus sporelings with other juvenile algae showed that there was a some effect on growth, development and survival, especially with Ulva and Enteromorpha when sporelings of Mastocarpus died after 6 weeks. Germlings of Fucus on Mastocarpus sporelings showed close bonding of rhizoids to the Mastocarpus 'cuticle', and some evidence of penetration. Diatom mucilage material on the substratum had some effect on the morphogenesis and growth rate of Mastocarpus sporelings and Fucus germlings and on interactions between the two. Measurements of photosynthetic rates have shown that for Mastocarpus sporelings there was sensitivity to water movements, illumination levels and temperature and salinity change. Varying degrees of recovery of photosynthetic activity were observed after protracted storage of sporelings under cold and dark conditions. Juvenile erect fronds were more active than the attaching discs. The photosynthetic rates of both fertile and non-fertile papillae were evenly affected by exposure to dry air. Both types of papillae and the spore masses were affected to salinity change. Recovery was observed after short exposure periods and reimmersion in sea water.