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Codium fragile is considered one of the most invasive marine seaweeds. It has invaded coastal habitats worldwide in temperate regions (30°–60° in both hemispheres), but it is rarely found at lower latitudes (i.e., tropical and subtropical regions). Here we document the distribution of C. fragile together with relevant size and reproductive parameters across the intertidal zone in a recently invaded bay at 23° S on the SE Pacific coast of Chile, close to its equatorial/warm range limit in the South-East Pacific. Codium was primarily found in mid and high tidepools, with only a few individuals on exposed rock surfaces. Larger individuals were found in the high intertidal pools, but reproductive individuals were more common in mid tidepools. Typical grazing invertebrates were common in low tidepools but decreased in densities towards the upper intertidal zone, suggesting that consumer pressure on Codium is lower in the upper tidepools. The higher temperatures and salinities in the high intertidal pools likely exclude important generalist grazers, allowing the more tolerant invasive seaweed Codium to successfully colonize these pools. These results suggest that Codium can colonize these coastal habitats at low latitudes because it can find a refuge from consumers in the high tidepools and is highly tolerant to extreme environmental conditions. [ABSTRACT FROM AUTHOR]

Artificial reefs have been introduced onto the subtidal sandy or rocky bottoms of Japanese coasts to expand the marine macroalgal beds that enhance the production of commercially important organisms. Previous studies showed that these artificial reefs were sequentially colonized by annual and perennial macroalgae. However, little is known about the competitive relationship between these annual and perennial species during succession. In the present study, we examined the successional change in macroalgal biomass on an artificial reef in Wakasa Bay, Japan, and tested the effects of removing annual and perennial species on the thallus length of successional perennial and annual species, respectively. The reef introduced between March and April 2008 was dominated by the annual brown alga Sphaerotrichia divaricata in July 2008, the annual brown alga Sargassum horneri in March 2009, and the perennial species Sargassum patens and Sargassum piluliferum in February 2010. The removal of S. horneri during autumn 2008 resulted in an increased thallus length in S. patens/S. piluliferum in March 2009, but had no effect in February 2010. Similarly, the removal of S. patens/S. piluliferum during autumn 2008 resulted in an increased thallus length in S. horneri in March 2009, but had no effect in February 2010. These results suggest that S. horneri and S. patens/S. piluliferum have a negative effect on the growth of each other in the first year of colonization, although the presence of S. horneri in the first year seems to have a minimal effect on the dominance of S. patens/S. piluliferum in the second year. [ABSTRACT FROM AUTHOR]

Seaweeds represent one of the largest groups of marine aliens in Europe and constitute a large percentage of all introduced marine species. In Brittany, the red macroalga Gracilaria vermiculophylla has invaded the bare areas of brackish waters in saltmarshes. In the Bay of Brest, the alga forms dense monospecific mats on the mud surface and occupies an empty ecological niche, in association with the invasive halophyte, Spartina alterniflora. The phenology of G. vermiculophylla was studied through seasonal monitoring of biomass, density and size of fragments, complemented by metabolomic monitoring using H HR-MAS NMR chemical footprinting analyses. Moreover, lipids and pigments were quantified, using high-performance thin layer chromatography for the former and high-performance liquid chromatography and spectrophotometry for the latter. This rhodophyte is present throughout the year, never fixed to a substrate on the mud, with a maximum biomass in the summertime. Phenological observations on algal populations demonstrated a high capacity for fragmentation, with a majority of fragments shorter than 3 cm. Metabolomic analyses highlighted a temporal variability of lipids, pigments and osmolytes between seasons. These results, combined with ecological data, improve our understanding of the acclimation of G. vermiculophylla in Brittany, where it is mainly present in a vegetative state throughout the year. Our study represents an important contribution to understanding the ecological strategies used by this invasive seaweed to colonize and persist in the Bay of Brest. [ABSTRACT FROM AUTHOR]

Changes in macroalgal community structure caused by invasive seaweeds have strong impacts on the associated macrofauna due to the role of macroalgae as autogenic ecosystem engineers. This study investigates the effect of Undaria pinnatifida on the abundance and diversity of benthic macrofauna in Golfo Nuevo, northern Patagonia, using a manipulative experiment involving the systematic removal of Undaria microthalli from strips of hard bottom during its eighth-month growing period. Species richness and diversity were higher in plots covered by Undaria than when Undaria was removed. Also, the abundance of two species of crustaceans, one species of sea urchin, one species of nemertina and several species of polychaetes was higher. We attribute these effects to the provision of new habitat structure by Undaria, a larger and structurally more complex species than the local native seaweeds. These results support the hypothesis that complex habitats enhance abundance and species richness, by offering different shelter and foraging opportunities compared to morphologically simpler habitats. Based on a review of diet studies in the region, we speculate that Undaria could potentially produce a bottom-up effect on local food chains by increasing abundance of prey for a wide variety of predators, from invertebrates to marine mammals. While our study has a narrow temporal and spatial scale, we expect similar effects of Undaria on the macrofauna in other sites of the Argentine coast, especially those dominated by small native macroalgae. [ABSTRACT FROM AUTHOR]