Direct release of embryonic sporophytes from adult Nereocystis luetkeana (Laminariales, Ochrophyta) in a high latitude estuary

Abstract

Kelp life history pathways alternate between macroscopic sporophytes that produce spores and microscopic gametophytes that produce gametes. Occasionally, an alternative pathway is seen. This study examined the circumstances by which the high latitude estuarine bull kelp, Nereocystis luetkeana, foregoes the “free-living microscopic stages by releasing embryonic sporophytes directly from sori. Sori were collected from adult N. luetkeana sporophytes from eight locations within Kachemak Bay, Alaska in 2018 and 2020 to examine spatial and temporal development of embryonic sporophytes on sori. Distinctions were made between sori collected from first-generation and overwintered adults to assess the influence of parental age on embryonic sporophyte release. Further distinctions were made between sori collected from attached and drifting individuals to assess the influence of the status of parental attachment to substrate on embryonic sporophyte release. Inspection of propagules released from sori after 48-h incubations indicated that embryonic sporophytes were occasionally released alongside viable spores. Though embryonic sporophytes were released from sori as early as spring, it was not evident that they were bound by seasonal or spatial limits. The percent of propagules that were embryonic sporophytes ranged from 0% to 100% but were not significantly different between firstgeneration and overwintered adults, nor were they different between attached and drifting individuals. Nevertheless, the characteristic of directly releasing embryonic sporophytes from adult sporophytes might have ecological advantages for N. luetkeana.