An artificial reef (250m x 50m) was constructed using natural boulders 1m in diameter. The reef was built next to a natural reef that had Sargassum present in the months where gametophytes are released to accelerate colonisation. Following colonisation of Sphaerotrichia divaricata, Sargassum horneri, Sargassum patens and Sargassum piluliferum, the thalli of these species were removed at different time points, and the growth response of other species was measured.
S. horneri and S. patens/S. piluliferum have a negative effect on the growth of each other in the first year of colonization.
The artificial reef was dominated by the annual brown alga Sphaerotrichia divaricata in July 2008, the annual brown alga Sargassum horneri in March 2009, and the perennial species Sargassum patens and Sargassum piluliferum in February 2010. The removal of S. horneri during autumn 2008 resulted in an increased thallus length in S. patens/S. piluliferum in March 2009, but had no effect in February 2010. Similarly, the removal of S. patens/S. piluliferum during autumn 2008 resulted in an increased thallus length in S. horneri in March 2009, but had no effect in February 2010.