Invasion
Invasion Description
1st Record: Intake Pipes at a rocky point north of Big Fisherman Cove near the University of Southern California’s Wrigley Marine Science Center and the town ofTwo Harbors, Santa Catalina Island /CA/Pacific Ocean (4/8/2006, Miller et al. 2007, 3326¢N,11829¢W,)
Geographic Extent
Intake Pipes at a rocky point north of Big Fisherman Cove near the University of Southern California’s Wrigley Marine Science Center and the town ofTwo Harbors, Santa Catalina Island /CA/Pacific Ocean (4/8/2006, Miller et al. 2007, 3326¢N,11829¢W,); Cherry Cove, Santa Catalina Island /CA/Pacific Ocean (4/21/2006, Miller et al. 2007); Emerald Bay, Santa Catalina Island/CA/Pacific Ocean (4/24/2006, Miller et al. 2007); Emerald Bay, Santa Catalina Island/CA/Avalon Harbor (2011, California Department of Fish and Wildlife 2014); San Clemente Island/CA/Pacific Ocean (2007, Kaplanis et al. 2016; 9/17/2009, Marks et al. 2015); Blue Cavern Onshore State Marine Conservation Area, Santa Catlaina Island/CA/Sotuhern California Bight (Looby and Ginsburg 2021)
Vectors
| Level | Vector |
|---|---|
| Alternate | Natural Dispersal |
| Alternate | None |
| Alternate | Hull Fouling |
Regional Impacts
| Ecological Impact | Competition | |
| Observations by divers off Catalina Island indicate that Sargassum horneri may be displacing native seaweeds, and even Giant Kelp (Macrocystis pyrifera). The quick-growing S. horneri may shade out germlings of native seaweeds. This invasion took place during periods of warmer water temperatures, but halted during the cooler winter of 2010-2011 (Bushing 2014). Removal of S. horneri from plots resulted increased Kelp (Macrocystis pyrifera), but no change in overall ner community production (Sulloway and Edwards 2020). | ||
| Ecological Impact | Habitat Change | |
| Dense growths of Sargassum horneri may inhibit the movement and feeding of fishes and Spiny Lobsters (Panulirus interruptus sp). However, senescent plants, like S. horneri, are covered with other algae and invertebrates, which are food for fishes and invertebrates (Bushing 2014). | ||
| Ecological Impact | Food/Prey | |
| Sargassum horneri produces toxins which inhibit feeding by native herbivores (Bushing 2014). | ||
| Economic Impact | Aesthetic | |
| Dense growths, decaying fragments, and gametes of Sargassum horneri limit visibility and enjoyment of SCUBA divers (Bushing 2014). Experimental removal of S. horneri was attempted off Santa Catalina Island. Cleeared areas were re-colonized with higher densities of the seaweed, probably due to an unusaul imflux of warm water. Removal will probably be most effective in periods of cooler water, and when targeted to new intorduction sites and sites of biological importance (Marks et al. 2017). | ||