Life history phases and the biomechanical properties of the red alga Chondrus crispus (Rhodophyta)

Chondrus crispus Stackhouse alternates between two isomorphic life history phases that differ in cell-wall phycocolloid composition. It has been long hypothesized that the gametophyte, with strong-gelling kappa-type carrageen ans, is mechanically superior to the tetrasporophyte, with nongelling lambd a-type carrageenans, which could contribute to the observed gametophytic do minance in many wave-swept environments. Standard mechanical tests were per formed on distal tissues of C crispus sampled from a range of environments in Narragansett Bay, Rhode Island, using a tensometer equipped with a video extensometer. Life history phase was by far the most important determinant of mechanical properties, whereas environmental factors had only modest in fluence (vertical distribution) or no effect (exposure); gametophytic dista l tissues were 43% stronger, 21% more extensible, and 21% stiffer than tetr asporophytic distal tissues. However, the superior strength of gametophytic tissues was not evident at the stipe/holdfast junction (where breakage typ ically occurs), and the two phases were equally susceptible to dislodgment by a given force. The primary ecophysiological role of carrageenans in C cr ispus may not be the provision of a structure to resist wave action.