Leptophytum foveatum Chamberlain & Keats (Rhodophyta, Corallinales) retaliates against overgrowth by other encrusting algae

Abstract

The encrusting coralline alga, Leptophytum foveatum, is the most abundant crustose alga in the lower eulittoral zone at Yzerfontein and other exposed sites on the West Coast of South Africa. The surface of this species is usually imbricate (appears scaly) as a result of the aparently spontaneous regeneration of margins at the surface of the thallus. The thicker, fleshy, brown crustose alga, Ralfsia verrucosa, usually overgrows the margins of the thinner L. foveatum; however, L. foveatum counteracts this overgrowth by regenerating margins at the thallus surface, and these are able to grow up and over the encroaching margin of R. verrucosa. Experiments in which these regenerated margins were removed showed that the regenerated margins are able to slow or stop the encroachment of R. verrucosa. It is suggested that the regeneration of thallus margins at the surface, away from the primary thallus margin, allows L. foveatum to maintain the advantages of being thin (e.g. more rapid lateral growth), but also gain some of the advantages of being thick (e.g. improved competitive ability).