Ecological studies on Didymosphenia geminata / Cathy Kilroy ... [et al].

Contributor(s): Kilroy, Cathy. (NIWA. Christchurch) | Biggs, B. J. (Barry John Franklyn), 1955-. (NIWA. Christchurch) | Blair, Neil. (NIWA. Alexandra) | Lambert, Paul. (NIWA. Greymouth) | Jarvie, Bill | Dey, Katie. (NIWA. Christchurch) | Robinson, Karen. (NIWA. Christchurch) | Smale, Dan | Biosecurity New Zealand.
Material type: materialTypeLabelBookSeries: NIWA client report ; CHC2006-123; NIWA Project ; MAF05505.Publisher: [Wellington, N.Z.] : MAF Biosecurity New Zealand, 2006Description: 66 p. : ill. ; 30 cm.Subject(s): DIDYMOSPHENIA GEMINATA | RESEARCH PROJECTS | BIOLOGICAL INVASIONS | DIATOMS | ENVIRONMENTAL CONDITIONS | ECOLOGY | SOUTH ISLAND | LAKES | STREAMSHoldings: Electronic Online resources: Click here to access online | Click here to access online Abstract: Since didymo was first detected in New Zealand in 2004, extensive mats of the alga have developed in many river reaches. The presence of thick algal mats over large areas of river channel poses a risk of substantial changes in ecological properties (e.g., species diversity, population sizes, nutrient pools), and ecological processes (e.g., ecosystem metabolism, nutrient cycling, animal behaviours). Studies on the effects of didymo on river ecosystems and the environmental factors that affect didymo growth and biomass have been underway since 2005. Studies of the effect of didymo on river ecosystems may help to identify species and processes at high risk, and aid in prioritising conservation efforts. Studies of the effects of the external environment on didymo may contribute to control efforts. In 2005, three separate ecological studies were undertaken by NIWA, based on four surveys over time at sites in the Mararoa and lower Waiau Rivers. (1) The hydraulic habitat study showed that didymo thrived in a wide range of hydraulic conditions from very slow moving, shallow waters to beyond the range of depths and velocities that commonly occur in New Zealand rivers, with a minor peak in biomass at water velocities of approx. 0.5 m/s. (2) The temporal study on didymo biomass and condition in relation to hydrological changes and water chemistry showed that biomass accumulation is faster in higher nutrient and lower temperature waters along the ranges experienced in the two rivers studied, and that moderate-sized floods do not scour didymo very effectively unless there is considerable bed sediment movement. (3) The invertebrate study showed that didymo-affected sites had much greater densities of all classes of benthic invertebrates than the didymo-unaffected sites. However, the invertebrate community structure in the didymo-affected sites was altered, with lower proportions and lower mean size/biomass of "good" invertebrates (mayflies, stoneflies, caddisflies) desirable for fish food. Further studies (planned for 2006-2007) are needed to determine the effects of the larger absolute number, but lower relative number and lower mean size/biomass of "good" invertebrates on higher trophic levels.
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SIRIS 1 Not for loan 145611-2001

"30 January 2006"

Includes bibliographic references.

Since didymo was first detected in New Zealand in 2004, extensive mats of the alga have developed in many river reaches. The presence of thick algal mats over large areas of river channel poses a risk of substantial changes in ecological properties (e.g., species diversity, population sizes, nutrient pools), and ecological processes (e.g., ecosystem metabolism, nutrient cycling, animal behaviours). Studies on the effects of didymo on river ecosystems and the environmental factors that affect didymo growth and biomass have been underway since 2005. Studies of the effect of didymo on river ecosystems may help to identify species and processes at high risk, and aid in prioritising conservation efforts. Studies of the effects of the external environment on didymo may contribute to control efforts. In 2005, three separate ecological studies were undertaken by NIWA, based on four surveys over time at sites in the Mararoa and lower Waiau Rivers. (1) The hydraulic habitat study showed that didymo thrived in a wide range of hydraulic conditions from very slow moving, shallow waters to beyond the range of depths and velocities that commonly occur in New Zealand rivers, with a minor peak in biomass at water velocities of approx. 0.5 m/s. (2) The temporal study on didymo biomass and condition in relation to hydrological changes and water chemistry showed that biomass accumulation is faster in higher nutrient and lower temperature waters along the ranges experienced in the two rivers studied, and that moderate-sized floods do not scour didymo very effectively unless there is considerable bed sediment movement. (3) The invertebrate study showed that didymo-affected sites had much greater densities of all classes of benthic invertebrates than the didymo-unaffected sites. However, the invertebrate community structure in the didymo-affected sites was altered, with lower proportions and lower mean size/biomass of "good" invertebrates (mayflies, stoneflies, caddisflies) desirable for fish food. Further studies (planned for 2006-2007) are needed to determine the effects of the larger absolute number, but lower relative number and lower mean size/biomass of "good" invertebrates on higher trophic levels.

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