Size, survival and the potential for reproduction in transplants of Mazzaella splendens and M-linearis (Rhodophyta)

Biomechanical models of red algae have been developed that make predictions about blade survivorship based on tissue strengths, drag coefficients, and blade surface areas. The first 2 objectives of the present field study wer e therefore to examine actual survivorship of genets (i.e. holdfast + blade s) from wide- and narrow-bladed species of Mazzaella G. DeToni f., as well as to compare blade survivorship to predictions of their survival from a pr evious biomechanics study of the 2 species, The third and fourth objectives were, respectively, to determine the most frequent break location in the g enet, and finally to ascertain if surviving blades are likely to be reprodu ctive. Low intertidal transplant sites were established at a wave-sheltered site where the wide-bladed form of Mazzaella splendens (Setchell et Gardne r) Fredericq occurs, and in a high wave impact habitat of the narrow-bladed Mazzaella linearis (Setchell et Gardner) Fredericq. Short and long blades size classes (SCI, SC2, respectively) were included for each species becaus e separate population sampling established that SC1 blades are almost never reproductive, whereas SC2 blades are potentially reproductive, Within the high wave impact transplant site, genet survival of experimental (i.e. tran splanted to site of the other species) M. splendens was initially lower tha n for control (i.e. transplanted within native site) M, linearis presumably due to drag on the larger M. splendens blades. As predicted by the biomech anics model, long blades of control M. linearis survive better than those o f experimental M. splendens, but not as well as short blades of experimenta l M. splendens. However, the narrow blade of M. linearis allows it to reach a reproductively mature length, whereas the short, broken survivors of exp erimental M. splendens are not long enough to be reproductive. In the shelt ered transplant site, genet survival for control M, splendens and experimen tal M. linearis was similar, but replicate M, linearis populations located higher in the intertidal were stressed (i.e, bleached) and more likely to d ie. Survivorship for SC2 blades of experimental M. linearis was not greater than SC2 blades of control M. splendens as predicted by the biomechanics m odel; survivorship of these 2 treatments was similar. For both species, the junction between the stipe and holdfast was rarely the most frequent break location as predicted by previous studies of Mazzaella and other red algae . We conclude that M. linearis is more likely to survive and become reprodu ctive at high wave impact sites because its narrow blade can persist in the face of large hydrodynamic forces, In contrast, in a sheltered site the wi de-bladed form of M. splendens is still at a hydrodynamic disadvantage rela tive to M, linearis, but M splendens is able to survive long enough to prod uce wide, potentially reproductive blades because it is apparently more tol erant of abiotic conditions (e.g. high irradiance, desiccation) within thes e sites.