Aquatic and terrestrial invertebrate drift in southern Appalachian Mountain streams: implications for trout food resources

Abstract

1. We characterised aquatic and terrestrial invertebrate drift in six south-western North Carolina streams and their implications for trout production. Streams of this region typically have low standing stock and production of trout because of low benthic productivity. However, little is known about the contribution of terrestrial invertebrates entering drift, the factors that affect these inputs (including season, diel period and riparian cover type), or the energetic contribution of drift to trout. 2. Eight sites were sampled in streams with four riparian cover types. Drift samples were collected at sunrise, midday and sunset; and in spring, early summer, late summer and autumn. The importance of drift for trout production was assessed using literature estimates of annual benthic production in the southern Appalachians, ecotrophic coefficients and food conversion efficiencies. 3. Abundance and biomass of terrestrial invertebrate inputs and drifting aquatic larvae were typically highest in spring and early summer. Aquatic larval abundances were greater than terrestrial invertebrates during these seasons and terrestrial invertebrate biomass was greater than aquatic larval biomass in the autumn. Drift rates of aquatic larval abundance and biomass were greatest at sunset. Inputs of terrestrial invertebrate biomass were greater than aquatic larvae at midday. Terrestrial invertebrate abundances were highest in streams with open canopies and streams adjacent to pasture with limited forest canopy. 4. We estimate the combination of benthic invertebrate production and terrestrial invertebrate inputs can support 3.3-18.2 g (wet weight) m )2 year )1 of trout, which is generally lower than values considered productive [10.0-30.0 g (wet weight) m )2 year )1 ]. 5. Our results indicate terrestrial invertebrates can be an important energy source for trout in these streams, but trout production is still low. Any management activities that attempt to increase trout production should assess trout food resources and ensure their availability.

Long-term nutrient enrichment decouples predator and prey production

“…Macroinvertebrate production not consumed by headwater stream predators can represent an important subsidy to terrestrial and downstream food webs (42,43). Thus, enrichment may have increased the export of prey production to terrestrial predators as adult emergence or to downstream predators as drift.…”

Habitat effects on invertebrate drift in a small trout stream: implications for prey availability to drift-feeding fish

“…Since increased prey availability enhances fish growth (e.g., Rosenfeld et al, 2005) and survival increases with body size (Holtby et al, 1990), food availability is an important index of habitat quality for fish (Nislow et al, 1998). Terrestrial invertebrates also represent a significant component of drift, particularly at the stream surface (Sagar & Glova, 1992) and are an important energy source for fish (Elliott, 1973;Allan et al 2003;Romaniszyn et al, 2007). Managing the production of drift-feeding fishes (e.g., stream salmonids) should therefore be informed by an understanding of the habitat factors that influence the abundance of both terrestrial and aquatic prey (Romaniszyn et al, 2007).…”

Causes and consequences of invertebrate drift in running waters: from individuals to populations and trophic fluxes

“…Empirically, flume experiments and a small number of field observations have given limited insights into transport and exit rates (e.g., Lancaster et al 1996). In contrast, field measurements of drift entry -expressed as a production rate per bed area -are virtually nonexistent (but see Romaniszyn et al 2007). Drift entry is a fundamental production parameter, the measurement of which will likely generate key insights into physical controls underlying spatial variation in drift flux and concentration.…”