Abundance and species composition of non-geniculate coralline red algae epiphytic on the South African populations of the rocky shore seagrass Thalassodendron leptocaule M.C. Duarte, Bandeira & Romeiras

• Detailed accounts of coralline epiphytes on seagrasses in South Africa are lacking.
• Thalassodendron leptocaule is unique in that it occurs on exposed rocky outcrops.
• We present descriptions of three corallines growing epiphytically on the seagrass.
• Some ecological data on the associations are also presented.
• Distribution of the epiphytes is explained by the longevity of the seagrass.

Seagrasses support a great diversity of epiphytic organisms and new research has shown that non-geniculate coralline red algae are important occupiers of space on the fronds of seagrasses. Except for a few scant records, there are no detailed published accounts of non-geniculate coralline algae epiphytic on seagrasses in South Africa. The seagrass Thalassodendron leptocaule (previously known as Thalassodendron ciliatum) is unique among southern African seagrasses in that it occurs on exposed rocky outcrops along the Mozambique and north eastern South African coast; most other seagrasses are restricted to sheltered bays and estuaries. Here we present descriptions of three species of non-geniculate coralline red algae which we have identified growing epiphytically on this seagrass in northern KwaZulu-Natal: Hydrolithon farinosum, Pneophyllum amplexifrons and Synarthrophyton patena. Two of the corallines (P. amplexifrons and S. patena) were restricted to the seagrass' stems while the third (H. farinosum) occurred only on the leaves. Of the three coralline epiphytes, P. amplexifrons contributed most to the biomass (average wet weight per plant 0.6 ± 1.18 g); its wet weight, however, varied between habitats. H. farinosum and other smaller turf algae amounted to no more than 0.1 g (wet weight) per leaf. S. patena was far sparser and contributed less than 0.1 g (wet weight) per stem. P. amplexifrons and H. farinosum appear to be pioneer epiphytes and form additional surfaces onto which other seaweed epiphytes attach and grow. Distribution of these epiphytes is explained by the longevity of the stems and leaves of the seagrass.