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

Abstract

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 were therefore to examine actual survivorship of genets (i.e. holdfast + blades) 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 previous biomechanics study of the 2 species. The third and fourth objectives were, respectively, to determine the most frequent break location in the genet, and finally to ascertain if surviving blades are likely to be reproductive. Low intertidal transplant sites were established at a wave-sheltered site where the wide-bladed form of Mazzaella splendens (Setchell et Gardner) 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 (SC1, SC2, respectively) were included for each species because 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. transplanted to site of the other species) M. splendens was initially lower than for control (i.e. transplanted within native site) M. linearis presumably due to drag on the larger M. splendens blades. As predicted by the biomechanics model, long blades of control M. linearis survive better than those of experimental M. splendens, but not as well as short blades of experimental M. splendens. However, the narrow blade of M. linearis allows it to reach a reproductively mature length, whereas the short, broken survivors of experimental M. splendens are not long enough to be reproductive. In the sheltered transplant site, genet survival for control M. splendens and experimental M. linearis was similar, but replicate M. linearis populations located higher in the intertidal were stressed (i.e. bleached) and more likely to die. Survivorship for SC2 blades of experimental M. linearis was not greater than SC2 blades of control M. splendens as predicted by the biomechanics model; 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 reproductive 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 widebladed form of M. splendens is still at a hydrodynamic disadvantage relative to M. linearis, but M. splendens is able to survive long enough to produce wide, potentially reproductive blades because it is apparently more tolerant of abiotic conditions (e.g. high irradiance, desiccation) within these sites.

Failure by fatigue in the field: a model of fatigue breakage for the macroalga Mazzaella, with validation

“…We found, for example, that 50% of breakage occurred at the stipe-holdfast junction when testing frond strength with this method. However, measurements of waveinduced (not researcher-induced) breakage contradicted initial results, finding that fracture occurred more often in blades than at stipe-holdfast junctions (Shaughnessy and DeWreede, 2001). Thus, model predictions in this study assessed breakage where it often occurs, in frond blades, although other breakage locations are possible in M. flaccida fronds and thalli.…”

Applying DNA barcoding to red macroalgae: a preliminary appraisal holds promise for future applications

“…Using sequence of the large subunit of rubisco (rbcL), Hommersand et al (1994) were able to establish clearly genetic differences between M. f laccida and M. splendens, but not strongly between two samples of the latter and an isolate of M. linearis included in their study. A series of reciprocal transplant experiments, however, support recognition of M. linearis and M. splendens as distinct species, and indicate that plants of intermediate morphology were exposed variants of the latter (Shaughnessy 1996;Shaughnessy & DeWreede 2001). Ross et al (2003) outlined possible scenarios to explain the apparent morphological continuum observed in the field for the M. linearis/splendens complex: (i) a single species exists with substantial morphological plasticity in response to wave exposure; (ii) two species exist, but one or both display phenotypic plasticity such that the intermediate plants are strictly of one species or the other, or a mixture of plants from both; (iii) the intermediate plants may be tetrasporophytes of M. splendens, which was reported to have a possible heteromorphic aspect to its alternation of generations ; (iv) the intermediates are hybrids between the two species; and (v) combinations of the previous could also explain these individuals.…”

Mechanical and biological consequences of repetitive loading: crack initiation and fatigue failure in the red macroalga Mazzaella

“…There are other potential break locations: in stipes, at stipe-holdfast junctions, and at holdfast-substratum interfaces. Although initial examinations of M. splendens, in which investigators folded blades over experimental scale apparatuses and pulled on the macroalgae in the field, suggested breakage occurs primarily at stipe-holdfast junctions (Shaughnessy et al, 1996), subsequent measurements of wave-induced breakage found that fracture occurs within blades more often than at stipe-holdfast junctions (Shaughnessy and DeWreede, 2001). The current study thus evaluates a significant breakage location, the algal blade, but fracture may also happen elsewhere in Mazzaella thalli.…”

“…Holdfast and frond(s) together constitute the seaweed's thallus. Macroalgal breakage assumes a variety of forms, with some species' fronds tattering marginally (Black, 1976;Blanchette, 1997;Dudgeon et al, 1999), other species' thalli breaking in the middle of blades or at holdfast-stipe junctions (Carrington, 1990;Hawes and Smith, 1995;Shaughnessy et al, 1996;Shaughnessy and DeWreede, 2001;Carrington et al, 2001;Johnson, 2001), and still other species commonly dislodging due to holdfast or substratum failure (Black, 1976;Koehl, 1986;Seymour et al, 1989;Utter and Denny, 1996;Gaylord and Denny, 1997). For most seaweeds, such breakage ultimately results in the death of dislodged portions of algal thalli.…”