Indirect effects of the intertidal burrowing crab Chasmagnathus granulatus in the habitat use of south west Atlantic saltmarsh birds

CARDONI, E; J.P. ISACCH; O. IRIBARNE

ESTUARIES

Estuarine Research Federation

Lugar: Missisipi; Año: 2007 vol. 30 p. 382 - 389

0160-8347

The burrowing crab, Chasmagnathus granulatus, is the dominant benthic macroinvertebrate of southwest Atlantic salt marshes and tidal flats, having strong ecosystem engineering effects by direct and indirect effects on soil, vegetation, invertebrates, fishes, and birds. Vegetation structure is a main component for bird habitat selection, since greater habitat complexity generates higher niche diversity. This environmental complexity can be modified by species interactions or disturbance events (i.e., by crabs), in turn modifying the associated community. The bird species of salt marshes of the southwest Atlantic are highly dependent on these ecosystems. We assessed the effects of the burrowing crab on the structure of the cordgrass, Spartina densiflora, marshes, and how these changes affected the composition and diversity of birds. This study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37u409S, 57u239W). S. densiflora marshes were classified within three categories: marshes without burrowing crabs, marshes with low burrow densities, and marshes with high burrow densities. We made vegetation and bird surveys during spring before S. densiflora produce seeds and in summer when seeds are abundant. We also manipulated inflorescence (i.e., spike) density (a variable affected by crabs) to assess the effect on bird habitat use. The highest inflorescence density of S. densiflora and highest bird diversity were recorded at low burrow densities. Cover and height of S. densiflora were negatively correlated with burrow density. The number of bird species and the number of red-capped wren-spinetail, Spartonoica maluroides, were negatively related with cover and height of S. densiflora. Experiments confirmed that granivorous species used areas with higher spike densities, a variable related to crab burrow density. Burrowing crabs directly and indirectly affect the cover, height, spike density, and morphologic characteristic of seeds of S. densiflora marshes. These effects indirectly affect the bird community that uses these marshes, being negatively related to S. maluroides and total bird abundance, and positively related to bird diversity.Chasmagnathus granulatus, is the dominant benthic macroinvertebrate of southwest Atlantic salt marshes and tidal flats, having strong ecosystem engineering effects by direct and indirect effects on soil, vegetation, invertebrates, fishes, and birds. Vegetation structure is a main component for bird habitat selection, since greater habitat complexity generates higher niche diversity. This environmental complexity can be modified by species interactions or disturbance events (i.e., by crabs), in turn modifying the associated community. The bird species of salt marshes of the southwest Atlantic are highly dependent on these ecosystems. We assessed the effects of the burrowing crab on the structure of the cordgrass, Spartina densiflora, marshes, and how these changes affected the composition and diversity of birds. This study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37u409S, 57u239W). S. densiflora marshes were classified within three categories: marshes without burrowing crabs, marshes with low burrow densities, and marshes with high burrow densities. We made vegetation and bird surveys during spring before S. densiflora produce seeds and in summer when seeds are abundant. We also manipulated inflorescence (i.e., spike) density (a variable affected by crabs) to assess the effect on bird habitat use. The highest inflorescence density of S. densiflora and highest bird diversity were recorded at low burrow densities. Cover and height of S. densiflora were negatively correlated with burrow density. The number of bird species and the number of red-capped wren-spinetail, Spartonoica maluroides, were negatively related with cover and height of S. densiflora. Experiments confirmed that granivorous species used areas with higher spike densities, a variable related to crab burrow density. Burrowing crabs directly and indirectly affect the cover, height, spike density, and morphologic characteristic of seeds of S. densiflora marshes. These effects indirectly affect the bird community that uses these marshes, being negatively related to S. maluroides and total bird abundance, and positively related to bird diversity.