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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Disturbance Ecology I
HABITAT MODIFICATION BY THE EMERGENT RIVERINE MACROPHYTE JUSTICIA AMERICANA (L.) VAHL.
K.M. Fritz, M.M. Gangloff, and J.W. Feminella. Department of Biological Sciences, Auburn University, Auburn, AL 36849
The macrophyte Justicia americana often forms dense beds within eastern North American streams. We conducted a seasonal experiment in Halawakee Creek, Alabama, to determine if Justicia stems (above-streambed) and rhizomes (below-streambed) modify benthic habitat and associated organisms. We used a randomized block design within Justicia beds including stem removals, stem/rhizome removals, and controls (no removals), and measured streambed stability (force needed to move rocks), streambed packing (embeddedness and wedging). Prior to Justicia manipulation, habitat variables did not differ within beds. After manipulation, stability and embeddedness were significantly lower in stem/rhizome removals than controls in both spring and summer; stem/rhizome removals did not differ from stem removals in spring. Abundance of Elimia snails, moss and Podostemum was significantly higher in stem and stem/rhizome removals than in controls. In contrast, abundance of unionid mussels was higher in controls than in stem/rhizome removals, within abundances being intermediate within stem removals. These data suggest that Justicia may have fundamentally opposite effects on benthic organisms, depending on resource requirements, by 1) increasing streambed stability that favors sedentary organisms (Unionidae) within beds, while 2) discouraging colonization of organisms such as snails and other plants that rely on light or periphyton, which may be reduced within beds.
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