General Impact
In tropical regions, blooms of indigenous algae (such as Gracilaria salicornia) have often been tied to reductions in grazing intensity and increases in anthropogenically derived nutrient levels (Miller et al. 1999, McClanahan et al. 2001, McCook et al. 2001, Smith et al. 2001, Stimson et al. 2001, Thacker et al. 2001, in Smith Hunter and Smith 2002). G. salicornia is likely to damage native coral environments by over-growing native benthic organisms such as algae and marine invertebrates. Because of its large morphological stature and the dense mats it forms (5 to 10cm thick), G. salicornia can have large effects on benthic ecology by monopolising stratum (Smith et al. 2004) In many cases, red alga becomes ecologically dominant and grows over coral reefs. For example, in areas of Hawaii such as Waikiki G. salicornia has become the single-most dominant benthic species in an area that before invasion was home to over 60 species of macroalgae (Doty 1969, in Smith et al. 2004. The long-term consequences of phase shifts from coral to algal dominance may include the loss of biodiversity, a decrease in the intrinsic value of the reef, changes in the community structure (eg: a reduction in the numbers of reef fish dependent upon corals for habitat and shelter), and erosion of the reef (Hughes 1994, in Smith Hunter and Smith 2002).
Location Specific Impacts:Oahu Is. (United States (USA)) 
Modification of natural benthic communities: G. salicornia appears to have altered benthic community structure and species diversity in Waikiki and Kaneohe Bay. Waikiki (United States (USA))
Human nuisance: More than 1800 kg of wet-weight biomass was recorded on a Waikiki beach after a 1.5- swell in a 120m² area. Such extensive accumulations of algae washed ashore can prevent beachgoers from utilising this area (Smith et al. 2004). Because this is one of the most popular tourist beaches in the world, such occurrences have the potential to result in economic losses for Hawaii.
Reduction in native biodiversity: G. salicornia likely competes with native algae, corals and other sessile organisms. Hawaii (United States (USA))
Economic/Livelihoods: Five species of algae are causing major problems on Hawaiin islands: the intentionally introduced Hypnea musciformis, Gracilaria salicornia, Kappaphycus spp.; the accidentally introduced Acanthophora spicifera; and the (origin unknown) Avrainvillea amadelphia. On Maui, 20,000 pounds (over 9000 kg) of algae wash up on Kihei beaches per week, costing more than US$100,000 per year to clean. In an economic study, algal biomass costs north Kihei more than US$20 million per year in lost of rental income, decrease in property value, and clean up (Eldredge, 2003).
Modification of natural benthic communities: Likely smothering and overgrowing the native biota.
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