Michael J. Winterbourn

Are New Zealand stream ecosystems really different

Abstract New Zealand stream ecosystems differ from many of their North American counterparts, on which general stream ecosystem models are based, in several ways. In New Zealand, large particle detritivores (shredders) are poorly represented, and the dominant invertebrates are browsers which feed on fine particulate organic matter and stone‐surface organic layers. In contrast with the river continuum concept of Vannote et al. (Canadian Journal of Fisheries and Aquatic Sciences 37: 130–137, 1980), representation of functional feeding groups shows little change downstream and a temporal continuum of synchronous species replacements is not found. Many common benthic invertebrates are ecologically flexible species with poorly synchronised life histories. These differences appear to be associated with the non‐retentive, climatically unpredictable nature of the stream environment. The idea that stream communities are highly structured entities is questioned, as is the generality of the river continuum concept.

Diversity Patterns in Stream Benthic Invertebrate Communities: The Influence of Habitat Stability

Invertebrate diversity patterns were examined in 11 freshwater habitats (10 streams and a windswept lake shore) of similar physicochemical nature but different thermal and hydrologic stability in the Cass-Craigieburn region, New Zealand. Species richness and density were markedly higher at the more stable sites, but species evenness peaked at sites of intermediate stability. Of the 20 environmental variables examined, a multivariate instability index incorporating temporal variation in depth, temporal variation in current speed, substrate stability, the Pfankuch channel stability index, temperature range, and stream reach tractive force was the single best predictor of the number of species, whereas epilithic pigment concentration was the single best predictor of invertebrate density. The pattern in species richness did not support any of three diversity hypotheses considered. In contrast, the pattern in species evenness suggested competitive exclusion may be occurring patchily and that Hustons dynamic equilibrium model may have some validity, at least at the level of the patch. However, the strong link between productivity and stability apparent in these habitats, and a lack of information on the effects of increased productivity on competition in stream benthic communities makes any firm assessment of the latter model difficult. The observed diversity patterns are, however, consistent with the idea that high diversity is maintained in these habitats by an interaction between low levels of disturbance and habitat patchiness.

Effects of floods on epilithon and benthic macroinvertebrate populations in an unstable New Zealand river

Temporal changes in epilithon biomass and benthic macroinvertebrate density were investigated in the Ashley River, a flood-prone river with an unpredictable discharge regime. Biomass, primary production and respiration of the epilithic community were highest in spring when filamentous algae were present and lowest following two large floods that occurred in close succession. Sixty invertebrate species were taken in benthic samples including 24 species of Trichoptera, 15 Diptera and 4 Ephemeroptera. Larvae of the mayfly Deleatidium (Leptophlebiidae) were numerically dominant and comprised up to 83 % of the fauna in any one month. Mean benthic invertebrate density was highest (9170–18 580 m−2) following long periods of low stable flow (< 30 m−3 s−1) and lowest (230 m−2) after a major flood (454 m−3 s−1). Reductions in benthic density occurred when flow exceeded about 30 m−3 s−1, the minimum discharge at which small cobbles are moved. Refuge seeking behaviours, flexible life histories and effective recolonization mechanisms enable the benthos of the Ashley River to persist and recover from frequent, temporally unpredictable disturbances.

Effects of contrasting land use on physico‐chemical conditions and benthic assemblages of streams in a Canterbury (South Island, New Zealand) river system

Abstract Physico‐chemical conditions and benthic invertebrate assemblages in streams draining catchments dominated by different land use activities were investigated near Hanmer Springs, South Island. Four streams in pastoral, scrubland, exotic pine plantation forest (primarily Pinus spp.), and native beech forest (Nothofagus spp.) catchments were sampled in four seasons. Alkalinity, pH, and calcium concentrations were highest among scrubland streams, whereas iron and potassium concentrations were highest in pastoral streams. Both taxonomic richness and invertebrate biomass were greatest in the beech forest streams where most species of Ephe‐meroptera, Plecoptera, Coleoptera, and Diptera were found. Forest streams were dominated by the mayflies Deleatidium and Coloburiscus humeralls, the stonefly Stenoperla prasina, and the caddisfly Olinga feredayi. The facultative shredder Austroperla cyrene was also abundant in pine forest streams. However, mayfly, stonefly and caddisfly taxa were poorly represented in...

Top-down and bottom-up processes in grassland and forested streams

The influence of predatory fish on the structure of stream food webs may be altered by the presence of forest canopy cover, and consequent differences in allochthonous inputs and primary production. Eight sites containing introduced brown trout (Salmo trutta) and eight sites that did not were sampled in the Cass region, South Island, New Zealand. For each predator category, half the sites were located in southern beech (Nothofagus) forest patches (range of canopy cover, 65–90%) and the other half were in tussock grassland. Food resources used by two dominant herbivores-detritivores were assessed using stable isotopes. 13C/12C ratios were obtained for coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), algal dominated biofilm from rocks, and larvae of Deleatidium (Ephemeroptera) and Olinga (Trichoptera). Total abundance and biomass of macroinvertebrates did not differ between streams with and without trout, but were significantly higher at grassland sites than forested sites. However, taxon richness and species composition differed substantially between trout and no-trout sites, irrespective of whether streams were located in forest or not. Trout streams typically contained more taxa, had low biomass of predatory invertebrates and large shredders, but a high proportion of consumers with cases or shells. The standing stock of CPOM was higher at forested sites, but there was less FPOM and more algae at sites with trout, regardless of the presence or absence of forest cover. The stable carbon isotope range for biofilm on rocks was broad and encompassed the narrow CPOM and FPOM ranges. At trout sites, carbon isotope ratios of Deleatidium, the most abundant invertebrate primary consumer, were closely related to biofilm values, but no relationship was found at no-trout sites where algal biomass was much lower. These results support a role for both bottom-up and top-down processes in controlling the structure of the stream communities studied, but indicate that predatory fish and forest cover had largely independent effects.

Distribution of benthic invertebrates in acid, brown water streams in the South Island of New Zealand

Acid, brown water streams are common on the west coast of the South Island, New Zealand. Acid precipitation is not a significant problem in this region where stream water acidity is brought about by high concentrations of humic substances. The interrelationships between pH, alkalinity, conductivity, DOC and total reactive aluminium were investigated at 45 running water sites. pH (range 3.5–8.1) was strongly correlated with alkalinity (range 0–49 g·m−3 CaCO3) and less strongly with conductivity (range 2.0–9.7 mS·m−1). A strong positive correlation was found between DOC and total reactive aluminium concentration both of which were correlated negatively with pH. In all brown water streams, most aluminium was probably in the non-toxic, organically complexed form. Benthic invertebrate assemblages were examined at 34 sites. Taxonomic richness was not correlated with pH and similar numbers of ephemeropteran, plecopteran and trichopteran taxa were taken from acidobiontic (pH ⩽ 5.5), acidophilic (pH 5.6–6.9) and moderately alkaline (pH ⩾ 7.0) groups of streams. Many species occurred over a wide pH range and had a lower limit of about pH 4.5. The mayfly, Deleatidium occurred at 33 sites and was amongst the five most abundant taxa at 32 of them. The stoneflies, Zelandobius confusus, Austroperla cyrene and Stenoperla maclellani, an elmid, Hydora sp. and a caddisfly, Psilochorema sp. also occurred in over half the streams and frequently were abundant. Few habitat specialists were found. Benthic assemblages were not associated strongly with measured physicochemical factors but streams in close proximity tended to have similar faunas. This suggests that the availability of suitable colonizers sets the limits to species richness and is important in determining the composition of benthic assemblages at a particular locality.

Food resources and ingestion patterns of insects along a west coast, South Island, river system

Abstract Food utilisation by benthic insect larvae at 6 sites along a West Coast, South Island river system (Devils Creek and the Inangahua River) was studied by gut content and stable carbon isotope analyses. At forested and open sites the dominant materials ingested by all species of Ephemeroptera, Plecoptera, and Trichoptera examined were fine detrital particles in the 0.45–75 urn size range. Diatoms and filamentous algae were eaten in varying amounts by some species. Larvae of Deleatidium (Ephemeroptera) and Chironomidae were the numerically dominant prey of the stonefly, Stenoperla prasina at all sites. Stable carbon analyses indicated that most species were dependent largely on carbon of terrestrial origin at forested sites, whereas autochthonous material was used increasingly further down Devils Creek. However, in the large, open Inangahuajliver 13C/12C ratios of insects were similar to those found in the forested tributaries and indicated a return to allochthonous dependence by the fauna. Although...

Do organic and anthropogenic acidity have similar effects on aquatic fauna

In Westland, New Zealand, there are many brownwater steams with naturally low pH (often around 4) brought about by high concentrations of organic acids. Up to 90% of dissolved aluminium in these humic streams is bound to organic matter and is therefore non-toxic. This condition enabled us to investigate the effects of long-term, natural acidity on aquatic biota without the compounding effects of high concentrations of toxic aluminium that are found in many anthropogenically-acidified, clearwater streams of the Northern Hemisphere. Most fish are absent from Northern Hemisphere clearwater habitats with pH < 5. However, in Westland 9 out of 14 native fish species were found in brown waters with pH below 5, and 7 species were taken from waters with pH < 4.5. Furthermore, 34 of the 37 most widespread aquatic insect taxa were recorded in Westland streams with pH < 5, and 24 were taken from sites with pH < 4.5. Clearly, many members of the freshwater fauna in Westland are well-adapted for life in waters of low pH. Physiological adaptations enabling this tolerance may be the same as those that evolved in response to the physicochemical variability associated with the unpredictable flow regimes of Westland streams. Tolerances of low pH have been documented in aquatic fauna from some naturally acidic, humic waters of the Northern Hemisphere, although degree of tolerance can vary within as well as between species. Colonisation of recently-acidified waters by acid-tolerant strains may cause more subtle changes in community structure than can be detected by conventional ecological techniques.

The macroinvertebrate fauna of a New Zealand forest stream

Abstract The distribution, abundance, and life histories of benthic invertebrates were investigated in a small, Nothofagus forest stream in North Canterbury, South Island, New Zealand. The fauna was dominated by Trichoptera and Plecoptera; Mollusca and fish were absent. Large particle detritivores and scrapers were the predominant functional groups found. Larval Philopotamidae (Trichoptera) were the only abundant filter feeders. Nymphs of the stonefly Spaniocerca zelandica and of mayflies, Deleatidium spp., were the most abundant animals on plant detritus; Deleatidium spp. were abundant on stones also. The distribution of invertebrates in riffles, loose stones, pools, and plunge pools was examined using mesh colonisation trays lifted in September, November, February, and May after respectively 88, 69, 98, and 94 days in situ. Most species were widely distributed, and sample densities of the more abundant insect species showed weak positive correlations with the biomass of detritus present in trays in most...

Fluxes of litter falling into a small beech forest stream

Abstract Fluxes of allochthonous litter were studied in a 93‐m long section of a small stream flowing through mountain beech forest at Cass in the South Island of New Zealand. Litter entered the stream throughout the year with maximum input from October to March. Mean annual input of beech litter was estimated to be 567 g.m‐2 (dry weight). Down‐stream movement of litter correlated strongly with maximum stream discharge during the collection period. The seasonal distribution and accumulation of litter within the stream was examined using 1‐mm‐mesh colonisation trays. Litter was unevenly distributed over the stream bed, but the average amounts taken from riffles, pools, and among large stones were similar. Litter accumulations were greatest in a pool in summer. The most important factor governing the quantity and transport of litter within the stream was stream flow.