Spatial and temporal variability in algal epiphytes on Patagonian Dictyota dichotoma (Dictyotales, Phaeophyceae)

•Algal epiphytes on a Patagonian population of Dictyota dichotoma consist of 32 taxa.•Only a few epiphytes were present throughout all seasons, with most being occasional or rare.•Epiphyte richness and abundance were highest in middle and basal host regions.•Only Bacillariophycean did not show a differential spatial distribution.•The epiphytic load was seasonally variable being higher in winter.

The present study investigates the epiphytic communities on individuals of a population of the brown macroalga Dictyota dichotoma, from Las Grutas beach (40°82′ S, 65°09′ W), growing on the Patagonian coast, Río Negro Province, Argentina. The composition and spatial and temporal variability were investigated during an annual cycle, to relate the seasonal variations of vegetative and reproductive characteristics of the thallus with the richness, diversity and evenness of the epiphytic community, and their relationship with daylength and seawater temperatures. The epiphytic community consisted of 32 different taxa. The most abundant epiphytic groups were Chlorophyceae, Bacillariophyceae and Cyanophyceae. Only a few epiphytes were present throughout the year. Epiphytic richness and abundance were highest in the middle and basal host regions. The high basal abundance was accounted for by four epiphytic species: Microchaete aeruginea, Pylaiella tenella, Ulvella marchantiae and Audouinella secundata. Seasonally, the epiphytic load was highest in winter, and largely accounted for by Grammatophora marina, Cocconeis sp. and P. tenella. The epiphytic load did not show variation among the different host reproductive stages, and no relationship was observed between thallus host length and dry mass.