Hyporheic Production is Substantially Greater than Benthic Production for a Common New Zealand Caddisfly

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Life-history and production of Olinga feredayi in both benthic and hyporheic stream habitats were investigated in a pristine Waikato, New Zealand, forest stream over two years to investigate the contribution of hyporheic habitat to total secondary production. O. feredayi had a univoltine life-history with adult emergence occurring from November to March. Larvae with case lengths < 2 mm were present on most dates suggesting delayed egg hatching. Benthic densities were inversely related to maximum peak daily flow in the month prior to sampling, and positively related to the dry mass of particulate organic matter present in samples. Reach-average benthic production calculated by the size-frequency method was 0.024 g DM m-2 year-1. Hyporheic production was 4.276 g DM m-3 year-1 and 6.462 g DM m-3 year-1 in colonisation baskets set at 15-30 cm and 30-45 cm within the substratum, respectively, 2.3-3.4 times greater than production in surface baskets (0-15 cm). Averaged out over the reach scale, it was estimated that 96% of annual secondary production of O. feredayi occurred in hyporheic habitats >10 cm below the streambed surface. Our study clearly demonstrates that only sampling benthic habitats can lead to gross under-estimation of population-level annual production, and provides evidence for the role of the hyporheos as a source of secondary production that may partly account for the Allen Paradox.

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