Desiccation tolerance of different life stages of the invasive marine kelp Undaria pinnatifida: Potential for overland transport as invasion vector

Overland transport in open-air-exposed conditions, including the translocation of specimens fouled on trailered boat hulls, aquaculture ropes or entangled in fishing gear, is recognized as a short-distance vector for the introduction of invasive aquatic species. Here, the desiccation tolerance for different life stages of the invasive kelp Undaria pinnatifida was determined to test the likelihood of air-exposed transport. Water content, photosynthetic quantum yield (Fv/Fm) as well as the capacity to release viable spores were monitored for mature sporophylls during a five-day exposure to air conditions. For newly settled spores (16 h post-release) and developing gametophytes (30 h post-release) survival and growth were observed after 1, 3, 6, 12 and 24 h of desiccation. Additionally, spore settlement and desiccation survival (after 3, 12 and 48 h) were determined for seven-day-old gametophytes growing on different rope materials (hemp, polypropylene, polyethylene, nylon) in high (99% relative air humidity, RH) and typical (59% RH) air humidity conditions. Viable spores were released from mature sporophylls after three days of desiccation. < 0.4% of spores and gametophytes survived air exposure. Of those surviving, however, individual gametophytes could endure 12 h of desiccation. These specimens exhibited enhanced average lengths, growing up to 70% larger than control gametophytes. Attached to ropes, gametophytes survived 48 h of desiccation; settlement and desiccation survival did not differ between rope materials. Overall, this study demonstrates that air-exposed transport, especially the translocation of mature sporophylls, represents a potential spread mechanism for the invasive U. pinnatifida. This is a vector that should be considered for pest management.