A life-stage conflict of interest in kelp: Higher meiospore settlement where sporophyte attachment is weak

Meiospores of Laminariales macroalgae must select a benthic substratum suitable for their attachment and survival, but also suitable for the development of the sessile sporophyte stage which can grow metres in length. In a controlled four month experiment, meiospores of Saccharina latissima were allowed to settle and develop on twelve different polymer surfaces. Highest meiospore settlement was seen where the attachment force of the developing macroscopic sporophytes was weak (<0.3 N), leading to the eventual detachment of the juveniles before they can grow 100 mm. The sporophyte holdfast cover (%) was strongly related to the biomass achieved (R2 = 0.68) and negatively correlated to the water contact angle (θw) of the polymer (R2 = 0.45). Yet, meiospore settlement was positively correlated to θw (R2 = 0.24). The study shows that the selective settlement of the meiospore conflicts with the requirements of the macroscopic sporophyte to attach firmly. It is hypothesised that higher θw is used by kelp meiospores as a cue for recently disturbed environments, allowing gregarious settlement in areas with reduced interspecific competition.