Invasive Alga Sargassum Muticum Research Articles

Native and Invasive Macrophytes Differ in Their Effectiveness as Nurseries for Juvenile Endangered Salmon

For marine biogenic habitats, such as kelp and seagrass, declines and local extinction events cause concern because of the loss of ecosystem services they provide. Many of these habitats function as valuable nurseries, but this function may be eroded when invasive species alter the structure of the habitats. For anadromous salmonids along the northeast Pacific, there is little known about the nursery role of coastal habitats, which presents a challenge for scientists to fully understand their complex life histories necessary for informing resource managers in decision-making processes regarding habitat protection and restoration. To address these issues, we ran a 3-week experiment testing the nursery functions of seagrass (Zostera marina), the invasive alga Sargassum muticum, mixed seagrass-Sargassum, and bare sand plots on the growth, survival, and prey availability for endangered Chinook salmon (Oncorhynchus tshawytscha) smolts. We found mixed effects of each habitat type when compared with each other. Chinook salmon smolts grew less in seagrass when compared with the three other habitats (bare sand, Sargassum, mixed seagrass-Sargassum). However, fish survival was lower in Sargassum habitat compared with seagrass and bare sand. Prey availability was greatest in mixed seagrass-Sargassum habitat compared with bare sand, Sargassum, or seagrass. We used a principal components analysis (PCA) to develop a nursery index using the smolts’ growth rate, percent survival, prey availability, and density of prey in gut contents. The nursery index showed that mixed seagrass-Sargassum habitat had the most positive effects on nursery performance. These results suggest that invasive species can serve positive habitat functions, but only when in the presence of a habitat-forming native species. Our study supports the theory that habitat diversity leads to greater nursery function of coastal ecosystems.

The chemical defences of the invasive alga Sargassum muticum (Yendo) Fensholt correlate to mesoherbivore diversity, but not to time-since-invasion

Populations of the invasive alga Sargassum muticum were sampled along a time-since-invasion (TSI) gradient to test the hypothesis that chemical defences would increase with TSI, and diversity of native mesoherbivores. Algal chemical defences, phlorotannins, were quantified as a proxy for top-down-pressure, and these were compared with both native enemy diversity and time-since-invasion at each of seven sites along the west coast of the UK. The defences in the annual fronds showed a strong positive correlation with the biodiversity of native mesoherbivores. The defences in the perennial holdfasts, whilst generally higher than those in the fronds, showed no relationship. In contrast, defences in neither the fronds nor the holdfasts showed any relationship with TSI. The majority of mesoherbivores found in this survey were small and probably juvenile. Many of these individuals are known to occupy the fronds of S. muticum for shelter or to feed on its epiphytes, and are probably less likely to feed directly on its tissues than adults. The low probability that any one species of grazer was feeding on S. muticum tissues may explain why the alga contained a greater level of phlorotannin when the diversity of potential enemies was high. This study highlights the importance of enemy diversity in invasion ecology.

Time-since-invasion increases native mesoherbivore feeding rates on the invasive alga, Sargassum muticum (Yendo) Fensholt

Invasive algae can have substantial negative impacts in their invaded ranges. One widely cited mechanism that attempts to explain how invasive plants and algae are often able to spread quickly, and even become dominant in their invaded ranges, is the Enemy Release Hypothesis. This study assessed the feeding behaviours of two species of gastropod herbivore from populations exposed to the invasive alga Sargassum muticum for different lengths of time. Feeding trials, consisting of both choice and no-choice, showed that the herbivores from older stands (35–40 years established) of S. muticum were more likely to feed upon it than those taken from younger (10–19 years established) stands. These findings provide evidence in support of the ERH, by showing that herbivores consumed less S. muticum if they were not experienced with it. These findings are in accordance with the results of other feeding-trials with S. muticum, but in contrast to research that utilizes observations of herbivore abundance and diversity to assess top-down pressure. The former tend to validate the ERH, and the latter typically reject it. The potential causes of this disparity are discussed, as are the importance of palatability, herbivore species and time-since-invasion when considering research into the ERH. This study takes an important, yet neglected, approach to the study of invasive ecology.

Long-Term Field Study Reveals Subtle Effects of the Invasive Alga Sargassum muticum upon the Epibiota of Zostera marina.

Invasive species can alter coastal ecosystems both directly, e.g. through competition for substratum and nutrients, and indirectly. Indirect effects may be mediated by creation of dissimilar or inimical habitats, changes in predator and/or prey assemblages, alterations in associated biota, and perturbations of water movement and thermal regimes. Previous studies have shown that invasive algae can modify native habitat architecture, disrupt intricately linked food webs and alter epibiotic assemblages. In the UK, the seagrass Zostera marina supports a diverse epibiotic assemblage, influencing key factors such as sediment dynamics, depositional regime and trophic linkages. Increasing encroachment of the invasive alga Sargassum muticum into seagrass meadows changes the physical and chemical characteristics of the local environment and creates the potential for changes in the epibionts associated with the seagrass blades, threatening the integrity of the seagrass ecosystem. We investigated the effects of S. muticum invasion upon the epibiota of Z. marina in a drowned river valley in SW England seasonally from spring to autumn over four years in an in-situ manipulative experiment, comparing permanent quadrats with and without artificially introduced S. muticum. Epibiota were weighed, identified to the most detailed operational taxonomic unit (OTU) possible, and unitary organisms were enumerated. Multivariate PERMANOVA+ analysis revealed significant differences in epibiont assemblages between Sargassum treatments. Linear mixed effects models indicated that differences in epibiota assemblage composition were not reflected as significant differences in mean biomass per sample, or number of epibiont OTUs per sample. We conclude that S. muticum invasion into Z. marina meadows may significantly alter the species composition and abundance distribution of epibiotic assemblages found on the blades of the seagrass. Thus S. muticum invasion could have more wide-reaching effects on processes within coastal ecosystems than predicted purely by direct effects.

Assessment of the spatial variability of phenolic contents and associated bioactivities in the invasive alga Sargassum muticum sampled along its European range from Norway to Portugal

Sargassum muticum, an invasive brown macroalga presently distributed along European Atlantic coasts from southern Portugal to the south coast of Norway, was studied on a large geographical scale for its production of phenolic compounds with potential industrial applications and their chemical and biological activities. S. muticum can produce high biomass in Europe, which could be exploited to supply such compounds. S. muticum was collected in Portugal, Spain, France, Ireland and Norway (three sites/country) to examine the effect of the latitudinal cline and related environmental factors. Assays focused particularly on polyphenols and their activities. Crude acetone–water extracts were purified using solid phase extraction (SPE) and antioxidant and antimicrobial activities of crude extracts and semi-purified fractions measured. Total phenolic content was assessed by colorimetric Folin–Ciocalteu assay and reactive oxygen species activities by 2,2-diphenyl-1-picrylhydrazyl, reducing power, β-carotene bleaching method and xanthine oxidase assay. Antibacterial activities were tested on terrestrial and marine strains to evaluate potential use in biomedical and aquaculture fields. Purified active phlorotannins, isolated by SPE, were identified using NMR. Phenolic contents differ clearly among countries and among sites within countries. Quality did not change between countries, however, although there were some slight differences in phlorethol type. Additionally, some fractions, especially from the extreme north and south, were very active. We discuss this in relation to environmental conditions and the interest of these compounds. S. muticum represents a potential natural source of bioactive compounds and its collection could offer an interesting opportunity for the future management of this species in Europe.

Propagule pressure and functional diversity: interactive effects on a macroalgal invasion process

Invasive species are considered an increasing global threat to marine ecosystems. Understanding which factors can accelerate or reduce invasion success is one of the main goals of invasion ecology. The present study investigated the interactive effects of propagule pressure and native functional diversity on the invasion success of the invasive alga Sargassum muticum (Yendo) Fensholt over a 1 yr invasion process (i.e. settlement, recruitment and colonisation). The invasibility of macroalgal assemblages with different functional diversity was assessed under high and low propagule pressure. Synthetic assemblages resembling natural marine macroalgal assemblages were built and used as model systems. Recruitment discs were used to record early settlement in the assemblages. Recruitment and colonisation success were monitored in the field 2 and 10 mo after exposure to propagule rain in the laboratory. The availability of resources (space and photosynthetically active radiation (PAR)) was also monitored for each assemblage and used as predictive variables in the analyses. The effects of propagule pressure and functional diversity varied among the invasion stages. Space availability did not play a significant role in the recruit- ment success of the invader. However, PAR was a key resource in its invasion success. Overall, the invasion success of S. muticum was influenced differently by different traits of the recipient assemblages. Hence, invasion success may be better explained by the interaction of environmen- tal factors that co-vary with species diversity and identity at different invasion stages.

Variability of epifaunal assemblages associated with native and invasive macroalgae

Marine macroalgae harbour abundant and diverse assemblages of epifauna. Patterns of distribution and abundance of epifauna, which are often variable in space and time, differ markedly among macroalgae species. Non-indigenous seaweeds may alter composition and structure of epifaunal assemblages and therefore harbour different assemblages from those associated with native macroalgae. In this study, we analysed the epifaunal assemblages associated with the native algae Bifurcaria bifurcata and the invasive alga Sargassum muticum on the southern part of the Galician coast (north-west Spain). In particular, we tested the hypothesis that there were differences in the epifaunal assemblages associated with the native and invasive algae. We used a hierarchical spatial sampling design to identify if these differences were consistent over space and time. Results indicated that there were significant differences between epifaunal assemblages associated with both algae. The fact that such differences were, in general, consistent at different spatial scales suggests that biological factors related to the specific habitat might play a more important role than physical factors as determinants of epifaunal distribution. This study also showed that S. muticum seems to supply a new and additional habitat for the native epifauna, contributing to increases in the spatial and temporal variability of epifaunal assemblages.

The establishment of the invasive alga Sargassum muticum on the west coast of Scotland: Rapid northwards spread and identification of potential new areas for colonisation

The invasive alga Sargassum muticum has recently been reported in the Firth of Lorn, west coast of Scotland. This represents the first sighting of the species north of the Kintyre Peninsula, a land barrier that had been expected to slow the northwards spread of S. muticum. This paper presents a thorough review of literature concerning the dispersal and establishment of this invasive alga and predicts potential dispersal trajectories and likely areas for future establishment in Scotland. From previous dispersal rates, S. muticum is likely to spread throughout the west coast of Scotland in the next few years, predominantly via natural pathways although anthropogenic vectors may also contribute to dispersal. Sheltered and moderately exposed sea lochs and shorelines, on the west coast of Scotland in particular, are likely to provide favourable conditions for the establishment of persistent populations of S. muticum. Conditions on the north and east coasts of Scotland were considered less favourable, both for the dispersal and establishment of S. muticum. The spread of S. muticum is unlikely to cause serious widespread ecological impacts, however, it does have the potential to cause economic damage to the aquaculture industry which is a major employer on the west coast of Scotland. The establishment of dense highly visible canopies would also constitute a degradation of the natural heritage value of Scottish shorelines. It would be prudent to investigate means of preventing persistent populations from establishing in areas of economic importance or with high natural heritage value.