LONG‐TERM CHANGES IN THE STRUCTURE OF INTERTIDAL ASSEMBLAGES AFTER INVASION BY SARGASSUM MUTICUM (PHAEOPHYTA)¹

Abstract

The macroalgal assemblages at the low intertidal zone were studied at three localities on the north coast of Spain between 1977 and 2002. Two of these localities were invaded at the end of the 1980s by the brown seaweed Sargassum muticum (Yendo) Fensholt (Phaeophyta, Sargassaceae), whereas the third locality remained free of the invader. In 2002, distinct algal assemblages were noticed in invaded and noninvaded localities. No major changes were detected in the noninvaded locality. Apart from the obvious presence of S. muticum, the changes observed in the invaded localities included a significant reduction in abundance of the previous dominant species (the red alga Gelidium spinosum (S. G. Gmelin) P. C. Silva) as well as an increased number of species and diversity, increased primary productivity, and variations in the seasonal abundance patterns of some species. We speculate that the arrival of S. muticum had a negative effect on the dominant native G. spinosum, probably related to competition for light. This resulted in indirect positive effects on other species of the assemblage (such as Bifurcaria bifurcata R. Ross). Other small epiphytic opportunistic species might also have been benefited from the presence of S. muticum, because the invader has a rich associated epiphytic assemblage.

Competitive interactions between the invasive green alga Codium fragile ssp. tomentosoides and native canopy-forming seaweeds in Nova Scotia (Canada)

“…Although many non-indigenous macrophytes are assimilated into host communities without obvious affect, others have caused major alterations in community structure through competitive displacement or exclusion of native species. Well documented examples include the tropical green algae Caulerpa taxifolia and C. racemosa in the Mediterranean Sea and southeastern Australia (Meinesz & Hesse 1991, Verlaque & Fritayre 1994, Balata et al 2004, York et al 2006, the Asian seagrass Zostera japonica along the western coast of the USA (Posey 1988), the Asian kelp Undaria pinnatifida (Laminariale) in central Patagonia (Casas et al 2004) and Tasmania (Valentine & Johnson 2003), and the Asian brown alga Sargassum muticum (Fucale) in western Europe and western USA (Staehr et al 2000, Britton-Simmons 2004, Sanchez et al 2005, Buschbaum et al 2006.…”

Invasion of alien macroalgae in different Mediterranean habitats

“…In fact, the spread of introduced benthic algae can lead to a complete cover of substrata, strongly affecting native assemblages and eroding biodiversity (Viejo 1997;Casas et al 2004;Britton-Simmons 2004;Buschbaum et al 2006). The substitution of native organisms with alien macroalgae can modify the environmental conditions and the functioning of ecosystems, causing an impoverishment of littoral systems (Rueness 1989;Staehr et al 2000;Wikstrom and Kautsky 2004;Sanchez et al 2005). …”

Resource availability and invasibility in an intertidal macroalgal assemblage

“…The experiment was carried out from March 2003 to April 2004 in the low intertidal (0.4 to 0.8 m above the lowest astronomical tides, LAT) at a locality in northern Spain, Aramar (43°36' N, 5°46' W). The invasive seaweed Sargassum muticum and the native algae Gelidium spinosum (S. G. Gmelin) P. C. Silva and Bifurcaria bifurcata R. Ross codominate at this intertidal level (Sánchez et al 2005). Aramar is a gently sloping rocky shore facing NE, located on the eastern face of Cape Peñas.…”