Factors affecting distribution and abundance of the mayfly Acanthophlebia cruentata (Leptophlebiidae) in North Island, New Zealand, streams

Abstract

We investigated factors affecting distribution and abundance of the leptophlebiid mayfly Acanthophlebia cruentata (Hudson) by (1) characterising large-scale environmental features of sites throughout the North Island where Acanthophlebia is known to occur, (2) evaluating relationships between land use and abundance of nymphs in a Waikato catchment, and (3) investigating small-scale habitat and hydraulic factors correlated with density in a native forest stream reach sampled monthly over two years. Toprock geology of catchments above known Acanthophlebia sites was dominated by argillite, greywacke, and volcanics, and landcover was largely native forest (median = 63% of upstream catchment area). Most records were from low order stream segments (1-3) at moderate elevations (100-300 m a.s.l) and with low to moderate channel slopes (>10%). In the Waikato, Acanthophlebia were rarely encountered in streams with entire catchments in pasture, but were relatively common in native forested streams where nymphal densities typically peaked around February-April. Pasture sites with headwater patches of native forest had densities intermediate between sites with catchments entirely in pasture or forest, but abundance was relatively low where native forest comprised >60% of total catchment area. Benthic densities at the intensively sampled native forest site were negatively correlated with maximum mean daily flow in the month prior to sampling and water velocity above sampling quadrats, and positively correlated with streambed cover by gravels and the dry mass of particulate organic matter in samples. This study has highlighted the importance that headwater forest remnants can play in moderating conditions for Acanthophlebia in downstream pasture environments, and has characterised the landscape setting where re-establishment of Acanthophlebia populations could indicate stream restoration success.

Keywords:

• Ephemeroptera
• land use
• native forest
• forest remnant
• density
• habitat
• recolonisation
• restoration