SUMMARYGracilaria spp. are dominant macroalgae inhabiting the intertidal zone and are exposed to constant wave action and currents. In wild Gracilaria populations, fronds tend to occur in clusters, being grouped close to one another on the shore. It is rare to find thalli growing individually, but the reason for such a clustering development is unknown. In this study we traced the early development of tetraspores of Gracilaria sp. and examined the adhesion strength of discs. We recorded two different tetraspore‐derived disc developmental patterns: in the first pattern, individual tetraspores developed into discs; whereas in the second pattern, multiple tetraspores that had attached in proximity to each other, coalesced to form a single composite disc during early development. We found that more uprights grew from coalesced discs and that the attachment areas of coalesced discs were larger compared with those of individual discs. The adhesion strengths of coalesced discs and individual discs were analyzed. The retention percentage of coalesced discs after treatment with rapid water flow was higher than that of individual discs, suggesting that coalesced discs are better able to withstand wave flow when compared with single‐spore discs. Based on these results, we propose that the clustering of Gracilaria sp. plants at sites within the intertidal zone is a mechanism that enables this macroalgae to survive the wave action and currents that occur in this zone, and that plant recruitment in these areas is enhanced by the coalescence of holdfast discs during early development.