Attachment strength differs amongst life-history stages of an intertidal, isomorphic red alga

Complex haploid-diploid life cycles amongst marine organisms may be maintained by ecological differences in life-history phases. For red algal species within the Gigartinaceae, such differences may be driven, in part, by different cell wall composition and resultant biomechanical strengths of haploid and diploid phases. A field experiment tested the attachment strengths of gametophytes and tetrasporophytes of the isomorphic red alga, Chondrus verrucosus (with comparisons of fertile and vegetative fronds, with and without natural tissue damage across three wave-exposed sites). Seventy-nine percent of all fronds broke at the stipe-holdfast junction. There were significant differences in attachment strength (break force and break stress), but not gross morphology (frond length, number of branch axes, wet weight and cross-sectional area of fronds that dislodged at the stipe-holdfast junction) of life-history phases, with tetrasporophytes exhibiting weaker tissue strength and attachment, and therefore greater susceptibility to dislodgement by waves. However, fertility and tissue damage did not consistently influence dislodgement in pull-to-break tests simulating the effects of single waves. The ecological and evolutionary consequences of greater susceptibility to dislodgement of tetrasporophytes (relative to gametophytes) warrant further investigation.