Strength, drag, and dislodgment of two competing intertidal algae from two wave exposures and four seasons

SUMMARY Articulated coralline algae (Corallinales, Rhodophyta) dominate low-intertidal, wave-exposed habitats around the world, yet the mechanics of this diverse group of organisms has been almost completely unexplored. In contrast to fleshy seaweeds, articulated corallines consist of calcified segments (intergenicula) separated by uncalcified joints (genicula). This jointed construction makes calcified fronds as flexible as fleshy seaweeds,allowing them to `go with the flow' when struck by breaking waves. In addition to functioning as joints, genicula act as breakage points along articulated fronds. Here, I describe the allometric scaling of geniculum size, breaking force and tissue strength along articulated fronds in two species of Calliarthron. Genicular material is much stronger than tissue from fleshy macroalgae. Moreover, as fronds grow, genicula get bigger and their tissue strengthens, two processes that help them resist breakage. Within individual fronds, larger branches, which presumably experience greater drag force, are supported by bigger, stronger genicula. However, frond growth greatly outpaces genicular strengthening. As a result, Calliarthronfronds most likely break at their bases when critically stressed by incoming waves. Shedding fronds probably reduces the drag force that threatens to dislodge coralline crusts and may constitute a reproductive strategy.

Section: Benefits Of Breakagementioning

confidence: 99%

Size, strength and allometry of joints in the articulated corallineCalliarthron

Martone

2006

“…Unsurprisingly, intertidal seaweeds break frequently in this harsh fluid environment (Seymour et al, 1989;Dudgeon and Johnson, 1992;Dudgeon et al, 1999;Johnson, 2001;Pratt and Johnson, 2002). Wintertime reductions in algal populations frequently exceed 10-90% for intertidal macroalgae (e.g.…”

Section: Introductionmentioning

confidence: 99%

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

Mach

2009

SUMMARYOn rocky shores, wave-swept macroalgae experience dramatic and repeated wave-induced hydrodynamic forces. However, previous studies of macroalgal mechanics have shown that individual waves are not forceful enough to account for observed rates of breakage. Instead, fatigue may contribute to algal breakage, with damage accumulating over time in conditions of repeated loading. Here I examine the entire process of fatigue, from crack initiation to eventual specimen fracture, in the common red alga Mazzaella. Propensity for fatigue failure in laboratory tests varied with life history phase and species: at a given repeated loading stress, male gametophytes endured more loading cycles before breakage than tetrasporophytes, which in turn lasted longer than female gametophytes; likewise, M. splendens withstood more loading cycles at a given repeated loading stress than M. flaccida. Fatigue failure begins with formation of cracks, the timing and location of which were assessed. Cracks formed, on average, after approximately 80-90% of cycles required for failure had passed, although crack timing varied with life history phase. Also, crack formation frequently occurred in association with endophytes and female gametophyte reproductive structures, suggesting a cost of endophyte infection and a tradeoff between reproduction and mechanical survival. Comparison between laboratory and field loading conditions provides robust confirmation that fatigue breaks fronds in natural M. flaccida populations. Large, female gametophyte fronds are predicted to be most susceptible to fatigue failure in the field, whereas small, male gametophyte fronds are least likely to break.

“…First, this hydrodynamic force may be decreased in macroalgae by 'going with the flow' and reducing the velocity of the water relative to their blades (Koehl, 1984;Koehl, 1986;Koehl, 1999;Gaylord and Denny, 1997;Denny et al, 1997;Stewart, 2004). A second mechanism is called reconfiguration, where the size and shape of the macroalga changes with velocity to reduce drag (Vogel, 1984;Vogel, 1989;Sheath and Hambrook, 1988;Carrington, 1990;Gaylord and Denny, 1997;Johnson, 2001;Pratt and Johnson, 2002;Sand-Jensen, 2003;Harder et al, 2004). For macroalgae, the reduction in drag via reconfiguration is due to a passive bending of the organism in response to the force (Vogel, 1994).…”

Section: Introductionmentioning

confidence: 99%

The hydrodynamic effects of shape and size change during reconfiguration of a flexible macroalga

Boller

Carrington

2006

101

of the stipe) at low velocities (<0.2·m·s -1 ) and compaction of the crown (reduction in frontal area and change in shape) at higher velocities. Change in frontal area contributed more to drag reduction than change in drag coefficient. Drag coefficient and frontal area both decrease exponentially with increasing water velocity, and a mechanistic model of drag was developed with explicit functions to describe these changes. The model not only provides mechanistic parameters with which to compare reconfiguration among individuals and species, but also allows for more reliable predictions of drag at high, ecologically relevant water velocities.