Consequences of morphology and tissue strength to blade survivorship of two closely related Rhodophyta species

Abstract

In Barkley Sound, British Columbia, Canada, the wide-bladed red alga Mazzaella splendens occurs intertidally at low to intermediate wave exposure sites but not at adjacent high wave exposure intertidal sites that are occupied by the narrow-bladed sister species Mazzaella linearis. This study used morphological and biomechanical characteristics of both species to determine whether or not drag and acceleration forces could prevent blades of M. splendens from surviving at high exposure sites and hence account, in part, for their distributions For each species, these hydrodynamic forces were calculated for gametophyte and sporophyte phases and, when possible, short and long thalli. The most frequent break location when thalli were pulled by a spring-scale was the junction between the stipe and holdfast. The following predictions were made by a model that compared hydrodynamic forces which a blade would experience to the measured force required to break the stipe/holdfast junction: (1) long blades of M. splendens should not occur at high wave exposure sites, (2) within the range of wave exposure occupied by M. splendens, sporophytes should be more abundant than gametophytes when and where wave exposure is greatest and (3) long blades of M linearis are predicted to occur at high wave exposure sites. All 3 of these predictions agree with other studies of natural populations. Two predictions do not agree with field observations: (1) long M. linearis gametophytes are predicted to have greater survivorship at higher water velocities than long sporophytes but, in natural populations, sporophytes are actually more abundant when wave action is greater and (2) short blades of M. splendens are predicted to survive very high water velocities but, in reality, are absent from high wave exposure sites in Barkley Sound. The latter contradlct~on suggests that recruitment of M. splendens at high wave exposure sltes is prevented at a life history stage prior to the development of short blades.

Size, strength and allometry of joints in the articulated corallineCalliarthron

“…For instance, the stipe/holdfast junctions of long and short blades of the red alga Mazzaella splendens have similar tissue strengths (Shaughnessy et al, 1996). Furthermore, no correlation has been found between breaking stress and blade area (Nereocystis luetkeana: Johnson and Koehl, 1994), thallus size (Mastocarpus stellatus and Chondrus crispus: Dudgeon and Johnson, 1992), or thallus length (Chondracanthus exasperatus: Koehl, 2000).…”

“…Furthermore, no correlation has been found between breaking stress and blade area (Nereocystis luetkeana: Johnson and Koehl, 1994), thallus size (Mastocarpus stellatus and Chondrus crispus: Dudgeon and Johnson, 1992), or thallus length (Chondracanthus exasperatus: Koehl, 2000). However, the specimens in these last three studies were approximately the same size, and only Shaughnessy et al (Shaughnessy et al, 1996) explicitly compared young plants to mature, adult plants. Conversely, Delf (Delf, 1932) briefly noted that young Laminaria digitata had weaker breaking stresses than adult plants and, on this basis, discarded young plants from her analysis.…”

“…By comparing drag force to breaking force, past studies have successfully predicted the wave-induced failure of macroalgae in the field (e.g. Carrington, 1990;Dudgeon and Johnson, 1992;Shaughnessy et al, 1996;Bell, 1999). An evaluation of the risk factor suggests that, to reduce their risk of failure and increase their chance of survival, algae can decrease the effective drag force on their thalli or increase their physical strength.…”

“…(Carrington, 1990;Dudgeon and Johnson, 1992;Pratt and Johnson, 2002), Mazzaella spp. (Shaughnessy et al, 1996), Chondracanthus exasperatus (Koehl, 2000) and Chondrus crispus (Dudgeon and Johnson, 1992;Carrington et al, 2001;Pratt and Johnson, 2002), employ a similar breakage strategy. Jettisoned fronds may also be favorably linked to the reproductive cycle of Calliarthron, just as fragmentation plays a critical role in coral reproduction (Highsmith, 1982).…”

Extreme water velocities: Topographical amplification of wave‐induced flow in the surf zone of rocky shores

“…These extreme velocities and the forces attributable to them-each a major component of ''wave exposure''-can have substantial biological significance: They can limit the local range of species (e.g., Denny 1995;Shaughnessy et al 1996;Graham 1997), they can limit the size of individuals (e.g., Carrington 1990;Dudgeon and Johnson 1992), and they can cause disturbance that affects community dynamics (e.g., Dayton 1971;Menge 1976;Sousa 1979;Paine and Levin 1981).…”