Biofouling filamentous red algae have been responsible for disease and costly loss of productivity in Asian Kappaphycus farms. Despite this, there is little information on the composition of biofouling composition organisms, their origin and their influence on commercial seaweed production. The aim of this study was to identify and quantify biofouling organisms at three Kappaphycus alvarezii commercial farms in southeastern Brazil and the influence of biofouling on commercial cultivation of this seaweed using floating rafts system between May 2008 and August 2009. Environmental factors had a greater influence on biofouling community composition than temporal factors. Not all the organisms found on the cultivation rafts and seedlings are the same as those on adjacent rocky shores. Foliose and filamentous algae were dominant biofoulers at the site with lower water movement and were easier to manage. The site with higher hydrodynamics was dominated by calcareous organisms which reduced K. alvarezii production by causing the rafts to sink, decreasing solar irradiance; together with greater water movement, this hampered cleaning of the cultivation structures. Endobionts were not found. Seedlings of K. alvarezii were not found fixed at sampling sites and adjacent rocky shores, indicating that the introduced species had not escaped to the wild.

The commercial cultivation of Kappaphycus alvarezii is the main source of raw material for the carrageenan industry. Brazilian commercial farming uses floating rafts that serve as substrata for fouling organisms that may affect production of the carrageenophyte seedlings. The aim of this work was to identify and quantify the biofouling on floating rafts at Sepetiba Bay, Rio de Janeiro State (23°02′ 25″ S and 43°53′ 39″ W), and to evaluate seedling damage caused by epibionts and endobionts. Samples were collected from August 2006 to August 2007. In each assessment, organisms contained in random sampling areas of 18 quadrats of 0.10 m 2 (n=18) were removed from floating rafts. K. alvarezii seedling samples were collected to verify the presence of epibionts or endobionts (n=30). Twenty-four taxa belonging to seven groups of animals and three groups of seaweed were found. The percentage occurrence estimated 13 dominant organisms and

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