Invasion
Invasion Description
1st Record: Long Beach/CA/Inner Long Beach Harbor (2003, Miller et al. 2007)
Geographic Extent
Anacapa Island/CA/Pacific Ocean (2009; 6/1/2010, Marks et al. 2015); Kaplanis et al. 2016); Blue Cavern Onshore State Marine Conservation Area, Santa Catlaina Island/CA/Sotuhern California Bight (Looby and Ginsburg 2021); Santa Barbara Island/CA/Pacific Ocean /1/2010, Marks et al. 2015; Kaplanis et al. 2016) Twin Harbor, Santa Cruz Island/CA/Pacific Ocean (2009, Marks et al. 2015); Santa Cruz Island/CA/Pacific Ocean (6/1/2010, Marks et al. 2015; Kaplanis et al. 2016); West Breakwater, Redondo Beach/CA/Pacific Ocean (12/7/2004, Marks et al. 2015); Point Dume, Malibu/CA/Pacific Ocean (8/7/2012, Marks et al. 2015)); Hawthorne Reef, Palos Verdes/CA/Pacific Ocean (6/7/2009, Marks et al. 2015); Long Beach/CA/Inner Long Beach Harbor ((8/27/2003, Miller et al. 2007); Terminal Island, Long Beach/CA/Long Beach Harbor (2005 , Miller et al. 2007); Palos Verdes/CA/Pacific Ocean (8/30/2004, Marks et al. 2015); Little Corona Del Mar/CA/Pacific Ocean (11/2/2013, Marks et al. 2015); Laguna Beach/CA/Shaws Cove (2012, Kaplanis et al. 2016, 33º 32.6' N 117º 47.9' W); Orange County/CA/Crystal Cove (Miller et al. 2011); Laguna Beach/CA/Pacific Ocean (10/10/2009, Miller et al. 2011; Marks et al. 2015); Dana Point/CA/Salt Creek, Pacific Ocean (11/10/2013, Marks et al. 2015); South Jetty, Oceanside/CA/Pacific Ocean (12/8/2013, Marks et al. 2015); Mission Point San Diego/CA/Mission Bay (2012, Kaplanis et al. 2016; 6/17/2013, Marks et ak, 2015); Mission Point San Diego/CA/Mission Bay (6/17/2013, Marks et ak, 2015); La Jolla, San Diego/CA/La Jolla Cove (8/26/2008, Marks et al. 2015); New Hope Rock, Point Loma, San Diego County/CA/Pacific Ocean (9/1/2006, Engle 2006, http://www.ocdiving.com/content/view/54/2/); San Diego/CA/San Diego Bay (5/3/32011, Marks et al. 2015); Shelter Island South, San Diego/CA/San Diego Bay (7/30/2013); Intake Pipes a rocky point north of Big Fisherman Cove near the University of Southern California’s Wrigley Marine Science Center and the town of Two Harbors, Santa Catalina Island /CA/Pacific Ocean (3326¢N, 11829¢W, 2006, Miller et al. 2007); 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); 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); San Clemente Island/CA/Pacific Ocean (9/17/2004, Marks et al. 2015); Bird Rock, La Jola/CA/Pacific Ocean (013, 32º 48.9' N 117º 16.5' W); San Diego/CA/San Diego Bay (2011, California Department of Fish and Wildlife 2014); Baja California/Mexico/Todos Santos Bay (1/8/2004, Miller et al. 2011; Marks et al. 2015); Isla San Martin, Baja California/Mexico/Pacific Ocean (12/4/2011, Marks et al. 2015); Krutzio, Baja California/Mexico/Pacific Ocean (4/26/2009); La Guanera, Isla Natividad, Baja California/Mexico/Pacific Ocean (7/21/2007, Riosmena-Rodríguez et al. 2012, 27 ° 52 ? N, 118 ° 09 ?); Baja ; California/Mexico/Todos Santos Bay (2005, Aguilar-Rosas 2007, 31º 43.2' N 116º 40.2' W); Guadalupe Island/Mexico/Pacific Ocean (Bushing 2014, 29.030833, -118.28)
Vectors
| Level | Vector |
|---|---|
| Alternate | Hull Fouling |
| Alternate | Ballast Water |
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). In 3 marine protected areas (MPAs) on the coast of Anancapa Island, algal communities resisted the invasion of S. horneri in the oldest MPAs, with more intact kelp forest, but S. horneri was more successful in newest MPAs, and unprotected areas, with more disturbance by recent fishing for sea urchins, and spiny lobsters and California Sheepshead fish (Semicossyphus pulcher), both urchin predators. Fishing for urchin predators reduced overall grazing, favoring competition by native algae (Caselle et al. 2017). Removal of S. horneri from plots resulted increased Kelp (Macrocystis pyrifera), but no change in overall ner community production (Sulloway and Edwards 2020). Off Todos Santos Islands, Baja California, Mexico. a marine heatwave favored the partial replacement of the dominent native kelp Macrosysts pyrifera by the non-native seaweeds Sargaasum horneri and *Undaria pyrifera (Félix-Loaiza et al. 2022). | ||
| 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). Field studies suggested that the replacement of native kelps by S. horneri did not affect fish abundance and diversity, but long-term effects cannot be ruled out (Ginther and Steele 2020). | ||
| 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). | ||