Resource biology of Pterocladia capillacea (Gelidiales, Rhodophyta) populations in Brazil

Pterocladia capillacea is a commercial source of agar. The factors that control the distribution and production of P. capillacea in Brazil are examined. The effects of sea urchin predation and tidal activity were investigated. The populations were perennial varying from 323 to 600 g dry weight throughout the year. Horizontal distribution was affected by irradiance with higher biomass in shaded areas and by water movement with higher biomass in intermediate areas. Vertical distribution was limited above by desiccation and below by herbivore grazing. Sargassum vulgare was the principal competitor for space and its removal from areas of contact between both populations increased the coverage of P. capillacea by 80 per cent. The production of P. capillacea in Brazil could be increased by controlling sea urchins and Sargassum spp at sites with adequate light and water movement.