New Zealand Journal of Marine and Freshwater Research abstracts
Trophic basis of production for a mayfly in a North Island, New Zealand,
forest stream: contributions of benthic versus hyporheic habitats and implications
for restoration
Kevin J. Collier
Aslan E. Wright-Stow
Brian J. Smith
National Institute of Water and Atmospheric Research Limited
P.O. Box 11 115
Hamilton, New Zealand
email: k.collier@niwa.co.nz
Abstract The leptophlebiid mayfly Acanthophlebia
cruentata (Hudson) is restricted to the North Island and some associated
offshore islands of northern New Zealand where it commonly occurs in benthic
and hyporheic habitats of forested streams. We investigated: (1) life history;
(2) secondary production in benthic and hyporheic habitats; and (3) major
energy sources contributing to nutrition and production of this species in
a pristine forest stream. Most nymphal size classes were present throughout
the year, and emergence extended over several months, peaking from February
to April. Despite apparently having extended emergence and recruitment periods,
Acanthophlebia exhibited a predominantly univoltine life history.
Annual benthic production (calculated by the size-frequency method) was 0.318
g dry mass (DM) m-2 year-1, compared to 4.601 g DM
m-2 year-1 in high-density benthic habitats at the
tails of pools, and 34.476 g m-3 year-1 for colonisation
baskets set at 15-45 cm deep in the substratum. On a habitat weighted basis
averaged out over the entire sampling reach, it was estimated that 76% of
annual production occurred in hyporheic habitats >10 cm below the streambed
surface. Gut contents were dominated by fine particulate matter (FPM) ≤75
µm and larger inorganic material on all dates in individuals from both
benthic and hyporheic habitats. Fungi were relatively abundant in guts of
benthic animals collected on some dates, whereas spores and pollen were relatively
common food items in both habitats on occasions. Analysis of the trophic
basis of production, based on gut contents and assumed assimilation and net
production efficiencies, indicated that benthic secondary production was
supported largely by fungi (48% of production) and FPM (37%), whereas FPM
supported a higher level of hyporheic production (52%) than fungi (27%).
Although stable carbon isotope values suggested dependence on epilithon,
the enriched δ15N values for this food source implicated the involvement
of a microbial loop whereby a substantial proportion of Acanthophlebia
nutrition appeared to be derived from heterotrophs growing in FPM and epilithon
that had assimilated dissolved organic carbon. This study has highlighted
the significant role that hyporheic habitats can play in the ecology of Acanthophlebia
populations in pristine native forest streams. Re-establishment of hyporheic
function would appear to be an important component of stream restoration
work to enable the successful recolonisation of Acanthophlebia populations
at sites where they historically occurred.
Keywords Ephemeroptera; Leptophlebiidae; stable isotopes;
carbon; nitrogen; size-frequency; hyporheos; Allen paradox; New Zealand
M03030; Received 27 June 2003; accepted 10 October 2003; Online publication
date 8 June 2004
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38:
301-314
0028-8330/04/3802-0301 © The Royal Society of New Zealand 2004
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