TITLE:
Presence of Sargassum horneri at Todos Santos Bay, Baja California, Mexico: Its Effects on the Local Macroalgae Community
AUTHORS:
Giuliana I. Cruz-Trejo, Silvia E. Ibarra-Obando, Luis E. Aguilar-Rosas, Miriam Poumian-Tapia, Elena Solana-Arellano
KEYWORDS:
Annual Cycle, Community Structure, Diversity Index, Functional Forms, Invasive Alga, Species Richness
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.6 No.17,
October
30,
2015
ABSTRACT: To describe the annual cycle of Sargassum horneri in Mexican waters, we selected two sites differing
in their degree of wave exposure and sediment type: Rincón de Ballenas (RB), and Rancho
Packard (RP). From June 2009 to April 2010 we followed the seasonal changes in S. horneri density
and biomass along two intertidal transects per site. The effects of this non-indigenous species
on the local macroalgae community were assessed by comparing their species composition, density,
biomass, species richness, and diversity index in quadrats with and without S. horneri. There
were significant differences in S. horneri density and biomass between sites (P -2, with a mean biomass of 4 ± 0.95 g DW
m-2. At RP, S. horneri density average was 10 ± 0.96 individual m-2, and mean biomass of 102 ±
0.97 g DW m-2. At RB, the invasive alga promoted a significant reduction in the four selected
structural variables, and the corticated macrophytes and the foliose functional forms were severely
reduced. At RP, there were only marginally significant effects (P = 0.06) of S. horneri presence
on the local macroalgae community, and higher density, biomass, and diversity values were
found when S. horneri was present. Most of the functional forms were found, even if the invasive
alga was present. At both locations, the highest biomass corresponded to the articulated calcareous
functional form. These contrasting results could be due to the fact that the native macroalgae
community has already been altered by the early invasion of S. muticum, with the most resilient
species and functional forms remaining in place. One of the most important changes we noticed
is the severe reduction of the canopy forming species at both sites.