Limits...
Oceanographic Conditions Limit the Spread of a Marine Invader along Southern African Shores.

Assis J, Zupan M, Nicastro KR, Zardi GI, McQuaid CD, Serrão EA - PLoS ONE (2015)

Bottom Line: The mussel Mytilus galloprovincialis is native to the Mediterranean and is the most successful marine invader in southern Africa.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.

View Article: PubMed Central - PubMed

Affiliation: Center of Marine Sciences, University of Algarve, Faro, Portugal.

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.

No MeSH data available.


Potential connectivity matrices for the Lagrangian Particle Simulations performed on the (a) west and (b) southeast coasts of southern Africa using a PLD of 30 days.Black circles show locations where M. galloprovincialis occurs, while the open red circles show where the niche models predicted northern edges.
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pone.0128124.g004: Potential connectivity matrices for the Lagrangian Particle Simulations performed on the (a) west and (b) southeast coasts of southern Africa using a PLD of 30 days.Black circles show locations where M. galloprovincialis occurs, while the open red circles show where the niche models predicted northern edges.

Mentions: The particle simulations fed by HYCOM velocity fields over the entire 5-year period allowed the release of 5040 particles per site (3,512,880 tracked particles in total). The aggregated trajectories resulted in different connectivity matrices corresponding to how long the passive particles were allowed to drift (30 or 90 days of PLD) and to where the simulations took place (west or southeast coasts). Regarding the experiments using contrasting PLDs, we verified high resemblances (Fig 4; S2 Fig), no statistical differences and strong correlations between connectivity matrices (west coast: Mantel r = 0.944, p-value < 0.001; southeast coast: Mantel r = 0.927, p-value < 0.001). Therefore, we centre further analysis and assumptions on the matrices produced for the west and southeast coasts using 30 days PLD, which is the more likely scenario for pelagic states of M. galloprovincialis. These matrices showed a high probability for larval retention (matrix’ diagonals), although their general trends were found to be contrasting. The particles tracked on the west coast (Fig 4A) displayed a marked northward trend, with an exception from Benguela (12.50° S) to Tombua (16.50° S), where particles also moved southward, though for shorter distances. On the southeast coast of Africa (Fig 4B) the particles moved mostly along southward trajectories. In this region, with the exception of a few oceanographic discontinuities, particles were also found to move northward, though for shorter distances when compared to the general trends for this region.


Oceanographic Conditions Limit the Spread of a Marine Invader along Southern African Shores.

Assis J, Zupan M, Nicastro KR, Zardi GI, McQuaid CD, Serrão EA - PLoS ONE (2015)

Potential connectivity matrices for the Lagrangian Particle Simulations performed on the (a) west and (b) southeast coasts of southern Africa using a PLD of 30 days.Black circles show locations where M. galloprovincialis occurs, while the open red circles show where the niche models predicted northern edges.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482700&req=5

pone.0128124.g004: Potential connectivity matrices for the Lagrangian Particle Simulations performed on the (a) west and (b) southeast coasts of southern Africa using a PLD of 30 days.Black circles show locations where M. galloprovincialis occurs, while the open red circles show where the niche models predicted northern edges.
Mentions: The particle simulations fed by HYCOM velocity fields over the entire 5-year period allowed the release of 5040 particles per site (3,512,880 tracked particles in total). The aggregated trajectories resulted in different connectivity matrices corresponding to how long the passive particles were allowed to drift (30 or 90 days of PLD) and to where the simulations took place (west or southeast coasts). Regarding the experiments using contrasting PLDs, we verified high resemblances (Fig 4; S2 Fig), no statistical differences and strong correlations between connectivity matrices (west coast: Mantel r = 0.944, p-value < 0.001; southeast coast: Mantel r = 0.927, p-value < 0.001). Therefore, we centre further analysis and assumptions on the matrices produced for the west and southeast coasts using 30 days PLD, which is the more likely scenario for pelagic states of M. galloprovincialis. These matrices showed a high probability for larval retention (matrix’ diagonals), although their general trends were found to be contrasting. The particles tracked on the west coast (Fig 4A) displayed a marked northward trend, with an exception from Benguela (12.50° S) to Tombua (16.50° S), where particles also moved southward, though for shorter distances. On the southeast coast of Africa (Fig 4B) the particles moved mostly along southward trajectories. In this region, with the exception of a few oceanographic discontinuities, particles were also found to move northward, though for shorter distances when compared to the general trends for this region.

Bottom Line: The mussel Mytilus galloprovincialis is native to the Mediterranean and is the most successful marine invader in southern Africa.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.

View Article: PubMed Central - PubMed

Affiliation: Center of Marine Sciences, University of Algarve, Faro, Portugal.

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.

No MeSH data available.