Abstract

Invasive species are key components of the burgeoning global change in ecological communities. The green alga Codium fragile ssp. tomentosoides (Chlorophyta) is a recognized invader in marine ecosystems around the world, with described ecological effects ranging from minor changes in native species abundance to major changes in community structure, as well as negative economic effects on aquaculture species. The objective of this work is to provide an assessment of the extension of the C. fragile invasion along the coast of Chile, and characterize the pattern of temporal fluctuations in abundance, and potential economic effects of this algal invader in a Gracilaria chilensis farm in northern Chile. In 2005 we recorded C. fragile at 34 of 123 sites sampled along the Chilean coast, with over half of the invaded sites occurring between 26° and 30°S latitude. At 12 sites C. fragile was present only on artificial substrata, suggesting that artificial structures may act as corridors for the dispersal of this alga into subtidal or intertidal habitats where it is otherwise not able to survive. At one site (Calderilla Bay) C. fragile has reached high levels of abundance within G. chilensis farms. At this site we observed marked seasonality in the monthly C. fragile abundance index, with greater C. fragile abundances in summer and fall months, associated with higher sea surface temperatures (SST). In addition, we report a significant long-term trend of increasing C. fragile abundances over the 5 years of observations in the plantation. If the distribution of C. fragile in Chile is largely determined by SST, we expect faster spread of northern populations towards the north. Weedy species had a negative effect on the farmed species, G. chilensis. During the 4 months in which algae wet weights were measured, the estimated C. fragile biomass averaged 22.9 kg m- 2, compared with an estimated average of 18.5 kg m- 2 of the harvested red alga, G. chilensis. In addition, we recorded a negative effect of C. fragile abundances on the Catch Per Unit Effort (CPUE) of G. chilensis with a significant upper limit to CPUE at the 94th quantile. Since weedy species generate a great loss of time and money in G. chilensis farms, it is likely that without intervention, the costs associated with the C. fragile invasion threaten the persistence of G. chilensis farms in northern Chile. Stakeholders should implement preventative measures to stop C. fragile spread from focal points. © 2006 Elsevier B.V. All rights reserved.