Mechanisms of Competitive Dominance Between Crustose Coralline Algae: An Herbivore‐Mediated Competitive Reversal

Abstract

Competitive superiority among encrusting species is established when the margin of one species consistently overgrows another. By measuring overgrowth patterns for the two most abundant tidepool species of crustose coralline algae (Lithophyllum impressum and Pseudolithophyllum whidbeyense) in the San Juan Islands of Washington State, we documented a reversal in competitive dominance that occurs at about the +1 m level; L. impressum wins in upper zones and P. whidbeyense in lower zones. Regardless of tidepool elevation or species, thicker crusts overgrow thinner ones and crusts of equal thickness are competitively equal. Both crust species are grazed by limpets (primarily Lottia pelta and Tectura scutum), which are the dominant herbivores in tidepools. Laboratory experiments show that limpet grazing can reduce crust thickness. Laboratory and field analyses of limpet grazing indicate that corallines in tidepools in the upper intertidal zone are subject to high frequency (bite rate per unit area) and low intensity (penetration depth per bite) limpet grazing, whereas those in low tidepools are subjected to opposite grazing characteristics. L. impressum is a thick crust, which has a multicellular covering over its meristem. This covering protects the growing portion of the plant from the frequent, low—intensity herbivory that occurs in the higher tidepools. In contrast, P. whidbeyense lacks a multilayered epithallus and is more susceptible to injury in high tidepools. In low pools, meristems of both crusts are injured. L. impressum heals these deep wounds by regenerating vertically, but the net result is a thinner plant that is easily overgrown. P. whidbeyense dominates the low zone because it is capable of much more rapid lateral growth including over its own deep wounds; the crust overgrows itself, thereby developing a thicker thallus and improving its competitive success over L. impressum. We suggest that a continuum of defensive and regenerative characteristics exists among organisms; the adaptive nature of these depends on the levels of production and the frequency and intensity of disturbance in their environment. It is evident that herbivory is important in this system, not by the traditional mechanism of releasing limiting resources (e.g., primary space), but by mediating competitive abilities through the relative susceptibility to, and recovery from, herbivory—induced disturbance.

Comparing community structure on shells of the abalone Haliotis midae and adjacent rock: implications for biodiversity

“…Conversely, geniculate corallines, specifically A. flabellata, were the climax species on abalone shells, dominating the older, less disturbed zones. Competitive superiority among encrusting algae is achieved when one species overgrows another, with thicker crusts generally being competitively superior to thinner crusts (Steneck 1986;Steneck et al 1991;Keats and Maneveldt 1994;Keats et al 1994;Maneveldt and Keats 2008). If space is seldom renewed and thus becomes limiting (as in older, undisturbed shell zones), thicker, slowergrowing, competitively superior crusts should become more abundant (Maneveldt and Keats 2008).…”

“…This has implications for the types of organisms that are likely to occupy the shells, as the different zones will support different successional groupings of organisms. For example, non-geniculate (encrusting) corallines are generally inferior competitors for primary space (Steneck et al 1991) due to their slow growth and are easily overgrown by foliar macroalgae (Steneck 1986;Eager 2010). High fecundity and an extended reproductive season, however, increase opportunities for encrusting corallines to occupy vacant space (Steneck 1986;Eager 2010).…”

The role of encrusting coralline algae in the diets of selected intertidal herbivores

“…Much of the research on herbivore-algal interactions in South Africa has focused on grazing interactions involving fleshy seaweed (Branch, 1971;. Although not common, encrusting coralline algae have been cited as important food sources for many intertidal herbivores (Steneck, 1982;Steneck & Watling, 1982;Paine, 1984;Steneck et al, 1991;Fujita, 1992;Littler et. al., 1995;Raffaelli & Hawkins, 1996;Littler & Littler 2003) and a few local studies have shifted their research focus toward herbivore-algal interactions involving coralline algae (Keats et al, 1994b;Maneveldt, 1995).…”

“…Encrusting coralline algae are important occupiers of space in rocky marine intertidal environments (Adey & McIntyre, 1973;Paine, 1984;Steneck, 1982;1986;Dethier et al, 1991;Steneck et al, 1991;Keats & Maneveldt, 1994;Keats et al, 1994a;b) and often become abundant in areas of intense herbivory (Adey & McIntyre, 1973;Steneck, 1983;Breitburg, 1984;Sousa & Connell, 1992;Dethier, 1994;Steneck & Dethier, 1994). Despite their ubiquity, they are a poorly known group of seaweeds (Keats et al, 1994a).…”

Importance of Timing of Panel Initiation on the Competitive Relationship and Succession of Sessile Organisms

“…Space competition among sessile organisms has been studied in different types of marine environment (Dayton 1971;Stebbing 1973;Buss & Jackson 1979;Buss 1979;Winston & Jackson 1984;Sebens 1985Sebens , 1986Schmidt & Warner 1986;Steneck et al 1991;Nandakumar 1995). On hard bottom substrata, space is a critical limiting resource (Jackson 1983) .…”