The putative impacts of the non‐native seaweed Sargassum muticum on native communities in tidepools of Southern California and investigation into the feasibility of local eradication

Abstract

The ecological impacts of introduced seaweeds have been relatively understudied. Current research suggests that seaweed invasions often result in alterations of native marine communities and disruptions of normal ecosystem functioning, but the effects on native communities can vary among invasive seaweed species, among habitats and over small and large spatial scales. In this study, the impacts of Sargassum muticum, a non‐native brown alga introduced into southern California, USA, several decades ago, were examined by comparing community structure in rocky inter‐tidal pools with and without the seaweed. Sargassum muticum appeared to have little impact on the native community despite measures revealing changes in the abiotic conditions of pools, with S. muticum presence reducing light penetration and ameliorating pool temperature changes during low tides. In other regions and habitat types, S. muticum presence often, but not consistently, resulted in declines in macrophyte diversity and/or abundance and increases in faunal assemblages. The lack of effects of S. muticum in this study, combined with variable impacts by S. muticum and other invasive seaweeds worldwide, suggests that predicting the effects of introduced seaweeds is problematic and warrants further research. Regardless of the effects on native communities, there is often a desire to eradicate or control the spread of non‐native seaweeds. In this study, localized S. muticum eradication attempts, including manipulations of a native canopy and herbivorous urchins, proved unsuccessful as full recovery occurred in ~9 months. While eradication efforts conducted worldwide have resulted in mixed success, there is a trend that early detection and rapid response can increase success, highlighting a need for systematic monitoring and establishment of regional rapid response plans.

Growth and competition in a warmer ocean: a field experiment with a non-native and two native habitat-building seaweeds

“…All three species are canopy-forming, but have different morphologies and growth patterns (Figure 1), suggesting that their competitive relationships might vary depending on environmental conditions. In the sublittoral, Sargassum muticum competes for light by forming a floating canopy which can shade other algae below (Ambrose & Nelson 1982, Britton-Simmons 2004, Lang & Buschbaum 2010, Engelen et al 2015), although its effect on seaweeds in the littoral zone is inconsistent , Harries et al 2007, Olabarria et al 2009, Smith 2016.…”

Spatiotemporal variation of the epifaunal assemblages associated to Sargassum muticum on the NW Atlantic coast of Morocco

“…The introduction of non-indigenous macroalgae causes many serious ecological impacts affecting native marine communities, eroding biodiversity and modifying and/or disrupting the normal functioning of ecosystems (Schaffelke and Hewitt 2007;Bedini et al 2015;Smith 2016). However, in some cases, the effects are not detectable or even positive (Thomsen 2010;Guerra-García et al 2012;Thomsen et al 2013).…”

The introduction ofSargassum muticummodifies epifaunal patterns in a Moroccan seagrass meadow

“…Interactions between macrophytes and their associated fauna are susceptible to be influenced by marine biological invasions in coastal habitats. Biological invasions have been recognised as one of the main threats to marine biodiversity due to impacts on native populations, community dynamics and ecosystem processes (Bax, Williamson, Aguero, Gonzalez, & Geeves, 2003;Grosholz, 2002;Schaffelke & Hewitt, 2007;Smith, 2016). Nonnative macroalgae can spread beyond their initial points of introduction to become abundant, monopolising space and reducing the diversity and biomass of the native species (Salvaterra, Green, Crowe, & O'Gorman, 2013).…”