Invertebrate community dynamics in soft‐bottomed streams of northern New Zealand: A spatio‐temporal hierarchy

Abstract

Environmental and macroinvertebrate data collected across a range of spatial and temporal scales are synthesised to investigate factors influencing invertebrate community structure and composition in soft-bottomed streams ( 50% of streambed substrata in sand-silt) of northern New Zealand. A total of 75 macroinvertebrate taxa was recorded from sand-silt substrata at 13 Waikato sites (54 taxa) and 8 Northland sites (53 taxa) where faunas were dominated by Ephemeroptera, Trichoptera, Chironomidae, and Mollusca. Differences in upstream geology, climate, land cover, and hydrology, potentially coupled with biogeographic factors, appeared to contribute to a regional separation in invertebrate community structure (taxa presence-absence). In the Waikato, site-specific conditions had a stronger influence on community structure and composition than substratum (sand-silt, macrophyte or wood). However, within sites, substratum type had strong effects on macroinvertebrate communities that persisted through time. On macrophytes, faunal composition varied considerably over time and among sampling patches, reflecting phenological shifts in the species and biomass of plants present, successional changes in invertebrate taxa, and micro-scale variations in water velocity. Macrophytes can provide important sites for energy transfer, although pathways leading to invertebrate nutrition appeared site-specific and temporally variable. Collectively, these data point to a spatio-temporal hierarchy of factors that influence invertebrate community structure and composition in soft-bottomed streams. The major differences compared with stony streams occur at the micro-to meso-scales, with greater significance of nonbenthic substrata (wood and macrophytes) as invertebrate habitat and sites of energy transfer in soft-bottomed streams, and the temporally variable influence of changing macrophyte biomass on local hydraulic conditions and water quality. To help reduce the effects of high spatial and temporal variability and obtain a representative picture of reach-scale conditions for stream health assessment purposes, long-term invertebrate monitoring of softbottomed streams should incorporate all velocity and substrata conditions, and aim to collect samples at a consistent stage of the macrophyte phenological cycle.

Nitrogen dynamics in grassland streams along a gradient of agricultural development

“…Macrophytes also have large surface areas and probably contributed to the increased transient storage in the three most pastoral streams by slowing water velocity through macrophyte beds (Dodds and Biggs 2002). Abundant macrophyte growth is common in highly pastoral streams of New Zealand (Collier 2004) and is probably a response to the accumulation of fine sediments that macrophytes require for rooting. It appears that although the addition of fine sediment may be a stressor for some community components (epilithon, moss), it may be a subsidy for others (macrophytes).…”

Using Macrophytes in Urban Stream Rehabilitation: A Cautionary Tale

“…Aquatic macrophytes are important components of stream ecosystems, providing habitat and food for invertebrates and fish (Rooke 1986;Collier et al 1999;Cheruvelil et al 2002;Collier 2004); stabilizing substrates and modifying stream flow (Sand-Jensen & Mebus 1996); and altering water chemistry such as dissolved oxygen (Wilcock et al 1999;Kaenel et al 2000;Caraco & Cole 2002), free CO 2 , and pH (James et al 1999). In many lowland streams, macrophytes represent important habitats for both fish and invertebrate communities, and these habitats often have higher biodiversity than other typically available substrates such as fine gravel, sand, and silt (Collier 2004). Macrophytes can also be important habitat in urban streams, especially because in-stream habitat quality is often reduced.…”

Effects of forest disturbances on aquatic insect assemblages

“…Substrate condition in the stream influences aquatic insect community structure and composition. When the substrate types, such as sand/silt and wood, differ, the aquatic insect assemblage on the substrate varies (Collier 2004) because habitat preferences change among species. Various types of disturbances and physical conditions create heterogeneous substrates that act as patches for aquatic insect populations in streams (Reice 1994).…”