To cite this article: Wayne Linklater & Michael J. Winterbourn (1993) Life histories and production of two trichopteran shredders in New Zealand streams with ...
New Zealand Journal of Marine and Freshwater Research
ISSN: 0028-8330 (Print) 1175-8805 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzm20
Life histories and production of two trichopteran shredders in New Zealand streams with different riparian vegetation Wayne Linklater & Michael J. Winterbourn To cite this article: Wayne Linklater & Michael J. Winterbourn (1993) Life histories and production of two trichopteran shredders in New Zealand streams with different riparian vegetation, New Zealand Journal of Marine and Freshwater Research, 27:1, 61-70, DOI: 10.1080/00288330.1993.9516546 To link to this article: http://dx.doi.org/10.1080/00288330.1993.9516546
Published online: 29 Mar 2010.
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New Zealand Journal of Marine and Freshwater Research, 1993: Vol. 27: 61-70 0028-8330/93/2701-0061 S2.50/0 © The Royal Society of New Zealand 1993
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Life histories and production of two trichopteran shredders in New Zealand streams with different riparian vegetation
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WAYNE LINKLATER* MICHAEL J. WINTERBOURN Department of Zoology University of Canterbury Private Bag, Christchurch New Zealand *Present address: Water Quality Centre, National Institute of Water and Atmospheric Research Ltd, P.O. Box 11 115, Hamilton, New Zealand
such a response will be found in many New Zealand running waters. Keywords Trichoptera; shredders; streams; life histories; riparian vegetation; aquatic insects; production; detritus
INTRODUCTION
Paniculate organic matter, particularly leaves derived from the riparian zone, is a major food resource utilised by many stream-dwelling invertebrates Abstract The life histories, microdistributions, and (Anderson & Sedell 1979; Gregory et al. 1991). Largeannual production of two trichopteran shredders particle detritivores that feed directly on decaying Oeconesus maori (Oeconesidae) and Pycnocentria leaves and wood are often described as shredders forcipata (Conoesucidae) were investigated in three (Cummins 1973), and include the larvae of numerous stoneflies, caddisflies, craneflies, and Amphipoda. small streams at Hinewai, Banks Peninsula, New Zealand. The riparian forest at the three sites was Winterbourn et al. (1981) considered that dominated by different tree species: mahoe, Melicytus shredders were underrepresented in the New Zealand ramiflorus; tree fuchsia, Fuchsia excorticata; and red freshwater fauna, and that they were either absent, or beech, Nothofagus fusca—each of which had a present in small numbers, in many forest streams. distinctive litterfall pattern. Mean annual biomass of They suggested that a major reason for the paucity of detritus (> 0.5 mm) on the stream beds was high shredders was the low retentiveness of many New (777-1982 g DW m-2) but temporal changes in Zealand mountain streams, a consequence of their biomass did not reflect litter fall patterns. O. maori instability caused in part by the frequent occurrence was most abundant in pools. Small larvae appeared of spates. Furthermore, the absence from New Zealand in late spring and most were in instars 4 and 5 in late of several insect families that include numerous autumn and winter. Mean larval densities in the three shredder species elsewhere, provides a biogeographic streams ranged from 90 to 1126 m -2 . Annual reason to help account for the small number of taxa in production was greatest in the mahoe-dominated this functional feeding group. stream. Larvae of P. forcipata were most abundant Nevertheless, Winterbourn & Davis (1976) on small falls and among root mats. Its life history described a large population ofZelandopsyche ingens was difficult to interpret. Mean larval densities ranged Tillyard (Trichoptera: Oeconesidae) in a small, South from 59 to 332 m-2 and annual production was again Island beech forest stream (estimated density 50-100 highest in the mahoe-dominated stream. We found larvae per m2), and Winterbourn (1982) reported that little evidence for a shredder response in these three the late instar larvae fed almost exclusively on dead streams (i.e., the maximisation of shredder biomass leaves, bark, and wood of mountain beech at the time of maximum litter conditioning). A general (Nothofagus solandri var. cliffortioides (Hook.f.) lack of predictably pulsed litter inputs to streams, and Poole). More recently, we have found large a species-poor shredder fauna make it unlikely that populations of leaf-shredding aquatic insects in several small, low-gradient streams in inland Canterbury where litter retention is high, and so has Chadderton M920S4 (1990) on Stewart Island. Received 21 September 1992; accepted 22 December 1992
New Zealand Journal of Marine and Freshwater Research, 1992, Vol. 26
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The aim of the present study was to investigate the life histories, production, and small-scale distributions of two caddisfly species with leaf and wood shredding larvae, in three small streams draining coastal forest remnants on Banks Peninsula. Because the principal litter inputs to each stream were provided by different riparian tree species with different seasonal leaf fall regimes, we were able to interpret our findings in the context of the "shredder response model" of Cummins et al. (1989). They proposed that "shredder biomass in a given stream system will be maximised at a particular, predictable point in the sequence that begins with litter drop and proceeds to litter retention, litter conditioning, and shredder use." The predictable point was hypothesised to be that at which litter, in a state of conditioning that can support maximal shredder growth, is most available: this was found by Cummins et al. (1989) to be when litter weight had declined by about 50%. STUDY AREA The study sites were 15-30 m reaches of three headwater streams at Hinewai on the north-eastern side of Banks Peninsula (43°48'S, 171°01'E). They were within an altitude range of 350-420 m a.s.l. and all three had permanent flow for the duration of the study. Mahoe and Fuchsia Streams (informal names) flowed through stands of second-growth, mixedhardwood forest dominated by mahoe, Melicytus ramiflorus J.R. et G. Forst., and tree fuchsia, Fuchsia excorticata (J.R. et G. Forst.) Linn.f., respectively. Other prominent riparian plants were wineberry, Aristotelia serrata (J.R. et G.Forst.) Oliver, and bush lawyer, Rubus australis Forst.f. Tawai Stream drained 10-11 ha of red beech, Nothofagus fusca (Hook.f) Oerst. forest, one of the very few patches of beech on Banks Peninsula (Wilson 1988).
The beds of the three streams were a mixture of cobbles, fine gravels, sand, silt, and tree roots. Leaves and woody debris were also abundant during most of the year (see below). Mahoe and Fuchsia Streams were both very shallow, whereas Tawai Stream was larger and deeper (Table 1). All three, particularly Mahoe and Fuchsia Streams, had considerable standing water most of the time and a well-defined sequence of riffles or low falls and pools. Physicochemical characteristics of the three sites are summarised in Table 1. STUDY ANIMALS Oeconesus maori McLachlan belongs to the family Oeconesidae. Its final instar larva was described by Cowley (1978) who stated that the larval habitat was small streams with gravel and silt substrata, and an ample supply of plant detritus. The life history of O. maori has not been documented, although Cowley (1978) noted that larvae of most sizes occur throughout the year near Auckland where adults have been collected from August to the end of April. Larval cases are up to 17 mm long and are made from a mixture of mineral and plant materials. Gut contents of small larvae from Tawai Stream contained mainly fine, amorphous detritus, whereas middle and late instar larvae had ingested progressively more (and larger) fragments of leaf and wood. Pycnocentria forcipata Mosely is a species of Conoesucidae. Its larvae have not been formally described, but Winterbourn & Gregson (1989) noted that they resemble those of P. funerea McLachlan in head pattern and pigmentation. The tubular, secreted cases of early instar larvae are partly covered in sandgrains whereas those of later instars are usually bare and up to 8 mm long. The posterior aperture of the case lies beneath an overhanging "veranda" as in P. sylvestris McFarlane. The life history of P. forcipata
Table 1 Physico-chemical characteristics of the study sites on three small streams at Hinewai, Banks Peninsula, New Zealand. Mahoe Stream Altitude (m) Stream order Channel width (cm) Channel depth (cm) Stream slope (%) Temperature range (°C) pH (mean ± SD, n=5) Alkalinity (mg CaCO31 (mean ± SD, n=5)
Fuchsia Stream
Tawai Stream
350 350 420 1 1 2 20-90 20-140 35-140
