Macroalgae traits and seasonality as drivers of polychaete assemblages on macroalgae of tropical sandstone reefs

Abstract

Benthic macroalgae are very important in structuring the biota of coastal reefs and are colonized by several species of animals and plants. The present study describes the polychaete assemblages associated with the macroalgae Gelidiella acerosa, Palisada perforata, Padina gymnospora, and Ulva lactuca on tropical sandstone reefs on the Brazilian coast and correlates the complexity of the macroalgae with the polychaete assemblages. Samples (10 fronds of each macroalgal species) were collected randomly during the dry (December 2018 and February 2019) and rainy (April and June 2019) seasons. The height, fractal dimension of the area and perimeter, and the Index of interstices were determined from macroalga photographs using the ImageJ software. Significant seasonal differences were found in the architecture of the macroalgae, and G. acerosa and P. perforata had the most complex structure. The macroalgae were colonized by 25 taxa of mobile polychaetes from seven families (Dorvilleidae, Eunicidae, Heisionidae, Polynoidae, Phyllodocidae, Syllidae and Nereididae), with dominance of syllids and nereidids in both seasons. Polychaetes were mostly carnivores and omnivores in the dry and rainy seasons, respectively. Platynereis dumerillii was the most abundant and frequent polychaete species. The structure of the assemblages varied significantly among macroalgae. G. acerosa and P. perforata had the most species-rich assemblages. The most important traits of macroalgae that structure polychaete assemblages are height, diameter of the area (Da), and diameter of the perimeter (Dp), with slight variation these traits between macroalgal species. Seasonal changes and macroalgal complexity (traits) were important drivers for polychaete assemblages on macroalgae in tropical coastal sandstone reefs.