The invasion and subsequent die-off of <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> in Langebaan Lagoon,South Africa: effects on natural communities |
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Authors: | T B Robinson C L Griffiths G M Branch A Govender |
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Institution: | (1) Marine Biology Research Institute, Zoology Department, University of Cape Town, Private Bag X 03, Rondebosch, 7701, South Africa;(2) Centre of Invasion Biology, Zoology Department, University of Cape Town, Rondebosch, South Africa |
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Abstract: | The alien mussel Mytilus galloprovincialis invaded sand banks in Langebaan Lagoon on the west coast of South Africa in the mid-1990s. However, by 2001 these beds had
completely died off, with only empty shells and anoxic sand remaining. In an effort to prevent the re-settlement of this aggressive
invader, all dead mussel shells were then cleared. This study considered the impacts of the invasion and subsequent die-off
on natural benthic communities. Community composition differed significantly between non-invaded and invaded areas (ANOSIM,
R = 0.685 and P < 0.01) as the physical presence of mussel beds created a new habitat that promoted invasion by indigenous rocky-shore species.
This dramatically increased faunal biomass from 1,132.9 g m−2 ± 3,454.7 SD to 53,262.4 g m−2 ± 23,052.6 SD and species richness from 38 to 49 species. Following the die-off of the mussel beds, communities remained
significantly different between non-invaded areas and those in which mussel shells remained (ANOSIM, R = 0.663 and P < 0.01). Species richness was significantly greater in non-invaded areas (18 species) than in uncleared areas with remnant
shells (four species) (Kruskal–Wallis ANOVA H
2,36 = 10.8964 and P = 0.032), as the previously dominant rocky-shore species became smothered by sediment and the compacted shells formed an
impermeable layer excluding sandy-shore burrowing organisms. After the shells were cleared, 50% of the sandy-shore species
associated with non-invaded areas returned within 5 months, but community structure still remained significantly different
to non-invaded areas (ANOSIM, R = 0.235 and P > 0.05). Invasion thus dramatically altered natural communities and although the subsequent removal of the dead mussel shells
appears to have aided recovery, community composition remained different from the pre-invasion state after 5 months. |
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