Ecological studies of Didymosphenia geminata in New Zealand, 2006-2007 / Scott Larned... [et al].

"Dec. 2007"

Includes bibliographic references.

In 2006-2007, a follow-up study was conducted to determine the effects of didymo on native fish, invertebrates (benthic and drift), and water quality (dissolved oxygen and pH), as well as determining didymo biomass dynamics under different hydraulic, nutrient, light and disturbance conditions. In general, didymo proliferations led to increased invertebrate abundance and increased diversity, but the populations shifted from a predominance of EPT taxa to a predominance of crustaceans, non-EPT insects, and worms. These results are consistent with results in the Ecology 2006 study (1071 KB). No effect of didymo on the sizes of common invertebrates was detected in the current study. The highest density of New Zealand native galaxiids among the sites was measured at one of the Oreti River sites with moderate didymo cover. Few other differences in fish populations between didymo-affected and non-affected sites were detected. Results of the metabolism study indicated that high levels of didymo biomass can significantly alter the chemistry of river water. Elevated pH appears to pose a greater risk to river biota than reduced dissolved oxygen levels. The time between bed-mobilising floods is an important determinant of didymo biomass levels. This has application for managing didymo biomass levels in dammed rivers, provided the intentional water release can be of sufficient magnitude, frequency and duration to remove a large proportion of periphyton growth from the river bed.

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