Disturbances in the habitat of Macrocotyla glandulosa (Kenk)


Disturbances lead to the displacement or mortality of organisms or communities. In stream ecosystems, hydrologic disturbances (floods, spates, freshets) can dislodge organisms from the streambed habitat and in some cases dislodge the sediment itself (scour). The primary aim of this study was to characterize the relation between the scour and the magnitude of freshets through the sediment size distribution and the depth of water at numerous locations along a cave stream in the habitat of the imperilled Macrocotyla glandulosa (Kenk), the pink planarian. Our hypothesis is that areas of stable streambed sediment would serve as habitat, whereas areas of mobile streambed sediment would not serve as habitat. We have combined the use of a numerical model of a cave stream with the size distribution of streambed sediment to designate locations of streambed stability or instability. Using pink planaria census data collected since 1988, we have identified locations that the pink planaria occupy and locations where the pink planaria have not been found. Our results show that five locations along the cave stream that lacked scour corresponded with locations of pink planaria occurrence, that two locations that experienced scour correspond with locations where the pink planaria were not found and that one location experienced scour and planaria were found. Thus, there seems to be a relation between the stability of streambed sediment and the use of that sediment as habitat. Conservation efforts aimed at increasing the population of the imperilled pink planarian should account for the stability of the streambed sediment. © 2010 John Wiley & Sons, Ltd.

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Disturbance, Habitat, Macrocotyla glandulosa, Scour

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