Reproductive allocation and strategy of Sargassum elegans Suhr and Sargassum incisifolium (Turner) C. Agardh from Reunion Rocks, KwaZulu-Natal, SouthAfrica

The allocation of biomass to receptacle, holdfast and vegetative e tissues differed significantly between Sargassum elegans and Sar Sargassum incisifo lium, two sympatric dominant species of the upper intertidal at Reunion Roc ks, KwaZulu-Natal, South Africa. Sargassum elegans, a clumped (many axes pe r holdfast) species with short primary laterals and a prostrate holdfast al located a greater proportion of its biomass to the holdfast than did S. inc isifolium, an erect species with longer primary laterals, fewer main axes a nd a conical holdfast. Conversely, S. incisifolium allocated more biomass t o the production of receptacle tissue than did S. elegans. These different biomass allocation patterns have previously been considered indicative of d ifferent reproductive strategies, i. e. that of sexual reproduction vs, tha t of persistence and spread in a high wave action environment. At any one t ime, a low percentage (< 15%,) of the main axes of S. elegans thalli were f ound to be reproductive, whereas a significantly higher percentage (> 50%)) of main axes of S. incisifolium were found to be reproductive. Per main ax is, S. elegans has a greater reproductive effort than S. incisifolium, howe ver at the thallus level, the opposite was observed. It is suggested that t he main axes (modules of the genet) of S. elegans function co-operatively t o promote sexual reproduction, but minimize any associated costs.