<p>The gametophytic blades of <i>Pyropia suborbiculata</i> can release archeospores for reproduction and tolerates higher water temperatures. However, due to its small size and round shape, it does not meet the requirements for large-scale cultivation. Previously, we selected a new strain (<i>PS-M4</i>) of <i>P. suborbiculata</i> using artificial mutagenesis technology, with the feature of long-type blade, fast-growing, and heat-tolerant. In this study, in order to evaluate the stability of these traits and the suitability for cultivation of <i>PS-M4</i> compared with that of the local cultivar of <i>Pyropia haitanensis</i>, pilot cultivation of this strain in the sea area was carried out on contemporary comparison with the representative culturing strain (<i>PH-CS</i>) of <i>P. haitanensis</i>. The results showed that the conchospore release of <i>PS-M4</i> was 9.85 × 10⁶ spores per shell, which is 6.3 times that of <i>PH-CS</i>, meeting the production requirements. In the same mariculture farm, the blades of <i>PS-M4</i> grew significantly faster than that of <i>PH-CS</i>. During the 1st to 4th harvests, the length of its blades was 1.54, 1.20, 1.21, and 1.13 times that of <i>PH-CS</i>, respectively, and the width of the blades was 2.49, 1.65, 1.65, and 1.44 times that of <i>PH-CS</i>, respectively. Furthermore, the yield of <i>PS-M4</i> during the 1st to 4th harvests was increased by 8.3%, 26.8%, 21.5%, and 12.7% compared with <i>PH-CS</i>, respectively. Moreover, the blades of <i>PS-M4</i> were thicker than that of <i>PH-CS</i>, and the content of chlorophyll <i>a</i> and phycobiliproteins in the two strains was similar. In addition, during the cultivation process before fourth harvest, archeospore attachment on the rope of <i>PS-M4</i> could be observed, forming secondary germlings. The above results confirmed that the long-type variety of <i>P. suborbiculata</i> meets the production requirements in terms of shape and yield, and is expected to be cultivated on a large scale.</p>