Detecting Alaria esculenta and Laminaria digitata (Laminariales, Phaeophyceae) gametophytes in red algae, with consideration of distribution patterns in the intertidal zone

Kelp ecology is heavily biased toward the conspicuous sporophyte stage, whereas understanding of the microscopic gametophyte remains limited. Given that kelp gametophytes are known to grow in/on other species of algae, we sought to determine if species-specific polymerase chain reaction could detect kelp gametophytes in situ from coextracted host DNA. Upon verifying our molecular results, we also assessed distributional patterns of the kelp gametophytes according to site, host species, and vertical placement in the intertidal zone. We sampled Chondrus crispus, Mastocarpus stellatus, and Palmaria palmata (Florideophyceae) at Wallace Cove, New Brunswick, Canada, on 13 September 2016, where kelp sporophytes were abundant, and at an adjacent location without obvious sporophyte presence, L'Etete, on 26 September 2016. Species-specific primers were used to assess the presence of Alaria esculenta and Laminaria digitata DNA from coextracted red algal DNA. We successfully amplified kelp DNA from the host tissue of each red algal species, indicating that gametophytes were present at Wallace Cove and L'Etete during the fall of 2016, with significantly less gametophyte presence at L'Etete. Although no significant differences in gametophyte presence occurred according to host species, P. palmata had significantly less gametophyte presence when sampled from its upper range in the intertidal. Microscopy and additional field observations confirmed the presence of brown endophytes in a variety of hosts, including C. crispus and P. palmata. Our study showcases a simple method for detecting kelp gametophytes, with our preliminary results demonstrating that the distributional and ecological range of kelp gametophytes is broader than that of the sporophytic counterparts.