Successful intertidal colonization of the invasive macroalga Codium fragile near its equatorial/warm range limit in the South-East Pacific

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.