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Nonindigenous marine species continue to be one of the foremost threats to marine biodiversity. As an update to a 2007 review of the impacts of introduced macroalgae, we assessed 142 additional publications to describe species' impacts as well as to appraise information on the mechanisms of impact. Only 10% of the currently known nonindigenous macroalgal species were subjects of ecological impact studies, with changed community composition as the most commonly reported effect. Economic impacts were rarely published. Recent research has focused on the impacts of introduced macroalgal assemblages: red algal introductions to the Hawaiian Islands and turf algae in the Mediterranean. Several general issues were apparent. First, many publications included nonsignificant results of statistical analyses but did not report associated power. As many of the studies also had low effect and sample size, the potential for type II errors is considerable. Second, there was no widely accepted framework to categorize and compare impacts between studies. Information in this updated review was still too sparse to identify general patterns and mechanisms of impact. This is a critical knowledge gap as rates of introductions and hence impacts of nonindigenous macroalgae are expected to accelerate with climate change and increasing global trade connectivity. [ABSTRACT FROM AUTHOR]

We analyzed 69 publications on the impacts of introduced seaweeds. The predominant impacts were changed competitive relationships in the recipient habitat, indicated by high abundances of invaders, resultant space monopolization, and reduced abundances/biomass of native macrophytes. Changes in biodiversity, effects on fish and invertebrate fauna, toxic effects on other biota, and habitat change were also identified. The mechanisms underlying the manifestation of impacts are uncertain and inferences about common patterns were hampered because impact studies were available for only a few introduced seaweeds, covered only a fraction of their introduced distribution and generally were conducted over short time scales. There was no information about evolutionary effects or changes of ecosystem processes. Knowledge of socio-economic impacts of invasive seaweeds is poor. We collated costs associated with control/eradication activities and for national spending on marine biosecurity in Australia, New Zealand and the United States. Prevention of impacts is the driving force for costly surveillance, eradication and control programs. Until we are able to understand, predict and measure impacts of introduced seaweeds, the management of species incursions needs to remain focused on early detection, rapid response and control to reduce the likelihood of negative impact effects. [ABSTRACT FROM AUTHOR]

Macroalgae are a significant component of historic and modern invasions, with association to a wide variety of transport mechanisms. These transport mechanisms pose specific constraints on the ways by which species can be taken up, transported and released into a new environment. Currently operating transport mechanisms for marine macroalgae are either associations with intentional introductions (translocations for aquaculture, aquarium or live seafood trade) or accidental introductions (mainly as hull-fouling). A number of potential management options exist, including the development of international instruments and regional agreements. The development of treatment options for hull fouling, the most significant and poorly managed transport mechanism for macroalgae, is of urgent need. Our current ability to identify which species are likely to invade next is limited. However, an examination of the synergies between species' functional traits, transport constraints, and recipient community attributes will likely provide possible options in the future. [ABSTRACT FROM AUTHOR]

In areas of Tasmania and New Zealand, the introduced Japanese alga, Undaria pinnatifida, grows attached to unstable substrata such as small cobbles and shells. Observations suggest these algae may disperse by saltation (i.e., a series of jumps) while attached to their substratum. A predictive model was developed to estimate the dispersal rate of U. pinnatifida by this mechanism, depending on drag force (as a function of lamina surface area and water velocity), the buoyant weight of the attached substratum and the depth at which the alga was located. The model was parameterised based on empirical measurements of 89 tagged thalli in the field, and estimates of drag on different sized laminae determined from experiments in a large flume tank. Empirical observations and model predictions suggest that under typical conditions at moderately exposed sites, dispersal via this mechanism is likely to be of the order of at least 101–102 m per year. When compared to the likely dispersal of spores from the parent (?101 m per year), and the likely dispersal of fertile drift thalli (?103–104 m per year), we suggest that algae on unstable substrata may provide a mechanism for intermediate dispersal over moderate distances, providing sufficient spore density to ensure high fertilisation success. This is likely to enhance the rate of spread of U. pinnatifida in circumstances where habitat suitable for establishment is available. [ABSTRACT FROM AUTHOR]