Temporal variation in gametophyte and sporophyte presence for Hedophyllum nigripes, Laminaria digitata and Saccharina latissima (Laminariales, Phaeophyceae)

Abstract

Kelp communities in the Bay of Fundy are shaped by macrotidal ranges, strong currents, short-term thermal variability, and long-term warming. To examine kelp temporal dynamics, we quantified both macroscopic sporophytes and microscopic stages (gametophytes and early sporophyte juveniles) of Hedophyllum nigripes , Laminaria digitata , and Saccharina latissima at Lepreau (permanent intertidal transect), New Brunswick, in spring and fall in 2020–2021. Macroscopic sporophytes were sampled with species identities verified via barcoding (nuclear ribosomal internal transcribed spacer region). Microscopic stages were sampled using standardized rock scrapes followed by barcoding with species-specific primers. Sporophyte community structure differed mostly seasonally: H. nigripes dominated in spring, while L. digitata did so in fall. Microscopic life stages of H. nigripes and L. digitata were detected persistently across most sampled quadrats in both years, indicating a relatively stable local bank of microscopic forms. In contrast, macroscopic S. latissima sporophytes were not observed, yet its microscopic stages were detected in some quadrats, which is consistent with a recruitment-limited population at a wave-exposed site. Together, our results highlight the value of integrating macroscopic and microscopic life stages to evaluate kelp population resilience and better anticipate climate-driven community shifts in cold-water intertidal ecosystems such as the Bay of Fundy.