Addressing the misidentification of sporangia as “embryonic sporophytes” in Nereocystis luetkeana (Mertens) Postels & Ruprecht Algae

Bull kelp (Nereocystis luetkeana) possesses a heteromorphic lifecycle that alternates between two phases: a large, diploid sporophyte and a microscopic, haploid gametophyte. Recent research has suggested that bull kelp may be capable of bypassing the microscopic gametophytic stage via the direct release of structures identified in the literature as embryonic sporophytes. In order to verify the identity of these structures, we isolated and cultured multiple directly released structures over the course of three weeks in the lab and monitored their growth and development. We were able to track 67 directly released structures for more than one time interval, and found no evidence that the development of these structures followed that of embryonic sporophytes. We present the alternative hypothesis that these directly released structures are sporangia that have not yet released their spores. We conclude that even with the direct release of microscopic structures such as sporangia, there is currently no evidence that bull kelp are bypassing their established biphasic life history.