Sargassum muticum

Davidson, Alisha D., Campbell, Marnie L., Hewitt, Chad L. & Schaffelke, Britta, 2015, Assessing the impacts of nonindigenous marine macroalgae: an update of current knowledge, Botanica Marina (Warsaw, Poland) 58 (2), pp. 55-79 : 64-65

Sargassum muticum

Several of the case studies of the impacts of Sargassum muticum introductions showed negative effects, such as being an undesirable food source for herbivores ( Monteiro et al. 2009), suppression of native algal assemblages ( Olabarria et al. 2009), and space monopolization ( Thomsen et al. 2006). However, several of the studies had ambiguous results, with some taxonomic groups showing increased abundance and some showing decreased abundance ( Lang and Buschbaum 2010, Gestoso et al. 2012). Sargassum muticum also enhanced epibiotic diversity in soft-bottom environments ( Buschbaum et al. 2006), and at time scales of <1 week after colonization ( Rodil et al. 2008). This species was a preferred forage material for the snail Lacuna vincta Montagu ( Britton-Simmons et al. 2011) , and its presence increased overall faunal abundance ( Strong et al. 2006).

Impact of introduced macroalgal assemblages

In the 2007 review, several red algal species ( A. spicifera , Avrainvillea amadelpha , G. salicornia , H. musciformis , Kappaphycus spp. , and Eucheuma spp. ) were reported to have established at high abundances and to have spread on Hawaiian coral reefs ( Smith et al. 2002, Conklin and Smith 2005, Weijerman et al. 2008). Several factors are implicated in these invasions, including low herbivory on introduced species ( Vermeij et al. 2009) and increased nutrient pollution due to urbanization (e.g., stormwater outflows; Lapointe and Bedford 2011). These red algal species increase overall macroalgal productivity and biomass on coral reefs and reduce invertebrate diversity ( Longenecker et al. 2011) or shift community dominance (e.g., increased detritivore diversity; Fukunaga et al. 2014). Gracilaria salicornia reduces irradiance, increases sedimentation, and changes diurnal dissolved oxygen and pH cycles, potentially affecting the habitat quality for corals ( Martinez et al. 2009, 2012). Mats of C. rubrum and C. linum reduce oxygen in the water column and increase sulfide levels in the sediment, resulting in the degradation of the sea grass Zostera marina L. ( Holmer and Nielsen 2007).

Several studies examined mats with multiple introduced macroalgal species and found similar impacts. Interestingly, the relative importance of C. taxifolia and C. cylindracea varied in mats where they both occurred. Holmer et al. (2009) found limited effects from C. taxifolia compared with C. cylindracea , whereas Montefalcone et al. (2007a) found that the substitution of Posidonia oceanica ( L.) Delile by C. taxifolia was greater than that by C. cylindracea . The latter observation, however, is likely to have been influenced by the longer duration of the C. taxifolia invasion. In addition to effects on macroalgae, the co-occurrence of Womersleyella setacea and Acrothamnion preissii led to a fivefold reduction in recruitment and reduced biomass and a threefold increase in juvenile mortality of gorgonian coral Eunicella singularis (Esper, 1791) ( Linares et al. 2012) .

Economic impacts

Published information about economic and societal impacts of introduced macroalgae was scarce ( Table 3). Many reports consisted of control or eradication costs for species-specific management. Although there was some anecdotal information on governmental management, research, and education/extension costs, the information was too limited to draw any general conclusions. The best estimates came from indirect costs associated with response and control efforts ( Table 3). In one instance, we identified detailed costs of removal efforts: Longenecker (personal communication) for Avrainvillea amadelpha in Hawaii ( Table 3).

Amenity and recreational value impacts of introduced macroalgae can be expected at high abundances, or where aspect dominance is achieved. However, estimates of revenue loss caused by incursions of introduced macroalgae were not available and were limited to descriptions of potential losses. For example, U. pinnatifida may threaten UNESCO ecotourism sites that depend on high biodiversity and aesthetic quality ( Irigoyen et al. 2011b), and decomposing H. musciformis may reduce tourism via fouled beaches ( Huisman et al. 2007).

We were also unable to find any quantitative information about societal impacts or ramifications of macroalgal introductions, such as the effect of reduced availability of the native algal species in Hawaii (limu), which are important as food and medicine, and for ceremonial use ( Abbott 1984, McDermid and Stuercke 2003).