Abstract
Invasive species can affect the function and structure of natural ecological communities, hence understanding and predicting their potential for spreading is a major ecological challenge. Once established in a new region, the spread of invasive species is largely controlled by their dispersal capacity, local environmental conditions and species interactions. The mussel Mytilus galloprovincialis is native to the Mediterranean and is the most successful marine invader in southern Africa. Its distribution there has expanded rapidly and extensively since the 1970s, however, over the last decade its spread has ceased. In this study, we coupled broad scale field surveys, Ecological Niche Modelling (ENM) and Lagrangian Particle Simulations (LPS) to assess the current invaded distribution of M. galloprovincialis in southern Africa and to evaluate what prevents further spread of this species. Results showed that all environmentally suitable habitats in southern Africa have been occupied by the species. This includes rocky shores between Rocky Point in Namibia and East London in South Africa (approx. 2800 km) and these limits coincide with the steep transitions between cool-temperate and subtropical-warmer climates, on both west and southeast African coasts. On the west coast, simulations of drifting larvae almost entirely followed the northward and offshore direction of the Benguela current, creating a clear dispersal barrier by advecting larvae away from the coast. On the southeast coast, nearshore currents give larvae the potential to move eastwards, against the prevalent Agulhas current and beyond the present distributional limit, however environmental conditions prevent the establishment of the species. The transition between the cooler and warmer water regimes is therefore the main factor limiting the northern spread on the southeast coast; however, biotic interactions with native fauna may also play an important role.
Highlights
Invasive species represent one of the main threats to global biodiversity, affecting the function and structure of natural ecological communities and causing annual economic losses amounting to billions of dollars worldwide [1,2,3,4]
When propagules arrive at new environments, the establishment success and abundance of invasive species are dependent on the availability of suitable habitats, which is largely determined by local abiotic conditions such as climate [9,11] and biotic interaction with the indigenous biota [26,27]
The contribution of each environmental predictor to the models was corroborated by previous studies focused on the physiology of M. galloprovincialis, which showed that extreme air and sea temperatures greatly influence its growth and survival [26,49,50,51]
Summary
Invasive species represent one of the main threats to global biodiversity, affecting the function and structure of natural ecological communities and causing annual economic losses amounting to billions of dollars worldwide [1,2,3,4]. Many studies have adapted Lagrangian Particle Simulations (LPS; see [16,17] for a review) to assess the potential for invasive species to disperse from neighbouring regions where establishment has already taken place [18,19,20,21] These simulations allow the tracking of virtual particles advected by ocean current fields (e.g., [22]), and their realism can be increased by including important biological parameters such as larval behaviour or the PLD of drifting particles (e.g., [23,24]). A crucial step in applying ENM for invasive species is to test the agreement between the environmental spaces used by both the native and the invasive populations [32]
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