Use of both benthic and drift sampling techniques to assess tropical stream invertebrate communities along an altitudinal gradient, Costa Rica

1. Two sampling techniques were used to characterize invertebrate communities in eight, low-order streams along an altitudinal gradient in Costa Rica that represents the last continuous tract of primary forest spanning such extremes in elevation (i.e. near sea level to 2900 m a.s.l.) along the Caribbean Slope of Central America. A standard Surber sampler was used to sample invertebrates on the stream bottom, and drift sampling nets were used to sample invertebrates drifting in the stream flow. 2. Sites were established at 30, 50, 700 1800 and 2700 m a.s.l. In one to two streams per site, six Surber samples were collected, and drift was sampled every 3 h over one 24-h period between April and August 1994. All sites were in primary forest, with the exception of the lowest elevation site (30 m) which was located in banana plantations. 3. Both sampling techniques indicated that Diptera (Chironomidae) and Ephemeroptera were the dominant insect groups at all sites. Disturbed streams draining banana plantations were dominated by Chironomidae and had lower taxon richness and diversity than other sites. 4. While data from benthic samples indicated that insects were the major faunal component (> 90%) at all sites, drift samples were dominated by larval shrimps (> 50%) at the 30 m and 50 m sites. 5. Drift periodicity of invertebrates was observed at those sites characterized by predaceous fishes: nocturnal drift densities were higher than diurnal densities at 30, 50 and 700 m a.s.l., however, no periodicity was observed at 1800 and 2700 m a.s.l. where fish were absent. 6. This study shows the importance of measuring invertebrate drift, in addition to directly sampling the benthos. Drift sampling provided data on a major community component (shrimps) of lowland tropical streams, that would have been overlooked using traditional benthic sampling techniques, and in some cases provided additional information on taxon richness. 7. Based on results of the present study, it is recommended that drift sampling be included as a standard complementary tool to benthic sampling in biological assessments (e.g. bioassessment protocols) of tropical streams, which are often characterized by migratory invertebrate species such as shrimps. Drift samples provide critical information on the presence or absence of shrimps and also on the timing and magnitude of their migration which is an important link between many tropical rivers and their estuaries.     

Benthic Community Structure and Invertebrate Drift in a Pacific Island Stream,Kosrae, Micronesia1

Tropical Pacific island streams have poorly understood communities that deserve scientific attention. We examined benthic macroinvertebrates and fishes of the Inem River on Kosrae, Federated States of Micronesia. Larval chironomids, lepidopterans, odonates, and freshwater shrimps dominated the benthos and drift. Diel periodicity in drift was not evident. Nine fishes, two shrimps, and one snail species were identified. Kosrae's stream fauna appears even more depauperate than other Pacific high islands, possible due to its extreme isolation.     

Macroinvertebrate drift in a Rocky Mountain stream

An extensive series of drift collections from a Rocky Mountain stream was used to investigate quantitative patterns in the taxonomic composition of drift throughout spring, summer and fall for 1975–1978. Drift was estimated by drift rate, the number of organisms drifting past a point per 24 h; and by drift density, the numbers of organisms collected per 100 m³ of water sampled.Drift densities were up to ten times greater by night than by day, and 24 h drift densities for the total fauna approached 2000 per 100 m³ in June–July, declining to <500 by autumn. Ephemeroptera, and especially Baetis, dominated the drift. Drift rates were greatest in late spring, around 10⁶ per 24 h, which are among the highest values reported for small trout streams. Drift rates declined to <10⁵ during the summer, and shifts in the taxonomic composition are described.Multiple regression analysis of the relationship between drift rate and density, and the independent variables discharge, benthic density and temperature, showed that discharge typically was a significant predictor of 24 h drift rate, usually the best single predictor. In contrast, 24 h drift density most frequently was independent of discharge, indicating that this measure tends to correct for seasonal variation in discharge, as suggested in the literature. However, this was not invariably true. Drift density significantly correlated with benthic density in five of eight taxa inspected, thus seasonal declines in the benthos probably accounted for parallel declines in drift density.     

Ontogenetic changes in the drifting of four species of elmid beetles elucidate the complexity of drift-benthos relationships in a small stream in Northwest England

1. This study aimed to quantify ontogenetic changes in the drifting of Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae), and to relate their drift to benthic density. Monthly samples were taken over 39 months, using three surface nets at each of two contrasting sites in a small stream: one in a deep section with abundant macrophytes, and the other in a shallow stony section. 2. Most larvae and adults were taken in the drift at night with little variation between catches in the three nets at each site. Day catches were very low, often zero. No significant relationships could be established between mean numbers in the drift catches and benthic densities. 3. When night catches were converted to drift densities (number caught per 100 m³ of water sampled), the latter were positively related to monthly losses in the benthos, but not to benthic densities. A linear regression described the relationship, and equations for the different life‐stages within each species were not significantly different from the equation for all life‐stages combined. However, drift losses were only about 0.07% of total losses in the benthos. A severe spate in October 1967 increased the number of larvae and adults in the drift, but not drift densities, except for immature adults of E. aenea, O. tuberculatus and E. parallelepipedus. 4. Key life‐stages with the highest drift density were the earliest life‐stage soon after egg hatching for E. aenea, the start of the larval overwintering period for O. tuberculatus and L. volkmari, and mature adults during the mating season for all three species. Drift density for E. parallelepipedus was too low to identify a key life‐stage. These key life‐stages corresponded with critical periods for survival in the life cycle, as identified in an earlier study in the same stream. Mortality was high during these critical periods, hence the strong relationship between drift density and benthic losses. The latter relationship was very consistent for different life‐stages within each species, and partially supported the rarely‐tested hypothesis that drift represents surplus production in the benthos.     

Nocturnal drift of mayfly nymphs as a post-contact antipredator mechanism

1. The predominantly nocturnal constrained drift of stream invertebrates is commonly regarded as a behaviour that avoids encounters with visually foraging fish in the water column. The alternative explanation, that drift peaks are caused by bottom-feeding, nocturnal predators, has rarely been tested.
2. We examined these hypotheses by collecting invertebrate drift in five streams in northern Finland: one with brown trout ( Salmo trutta , a drift-feeding fish), one with alpine bullhead ( Cottus poecilopus , a benthic fish), one with both species, and two fishless streams.
3. Drift by Baetis mayflies was aperiodic or slightly diurnal in both fishless streams on all sampling occasions. In contrast, drift was nocturnal in streams with trout and, to a lesser extent, in the stream with bullhead. Non-dipteran prey drifted mainly nocturnally in all streams with fish, whereas Diptera larvae were less responsive to the presence of fish.
4. In laboratory experiments, bullheads were night-active, causing a much higher frequency of drift by touching Baetis at night than during the day. Thus, increased nocturnal drift may serve to avoid both visual predators (a pre-contact response) and benthic fish (a post-contact response). In streams with bottom-feeding fish, nocturnal drift should be caused by increased drift by night rather than by reduced drift by day.     

Drift patterns in a high Andean stream

The drifting of invertebrates was sampled for six 24-hour periods from September 1976 to July 1977 in a small stream of the paramo of the Ecuadorian Andes. The composition of the drift is similar to that of the benthos, though percentages may differ markedly. Drift is relatively constant throughout the year, except in March when unusually high rates were noted; at this same period a marked reduction in the benthos was also observed. Diel periodicities in the drift are unclear, although on the whole drift is more important during the daytime; when individual data series are analyzed, weak patterns of day or night drifting can be recognized in some groups. The input of insects through drift from the small streams is thought to be an important source of food for the salmonid fish inhabiting the larger torrents.     

Invertebrate drift and benthic community dynamics in a lowland neotropical stream, Costa Rica

In this study we quantified invertebrate drift and related it to the structure of the benthic community, over a 6–8 month period, in a 4th-order tropical stream in Costa Rica. Relative to reports from similar-sized temperate and tropical streams, drift densities were high (2-fold greater: mean 11.2 m⁻³; range 2.5–25 m⁻³), and benthic insect densities were relatively low (>3-fold lower: mean 890 m⁻²; range 228–1504 m⁻²). Drift was dominated by larval shrimps that represented more than 70% of total drift on any given date; the remaining 30% was composed of 54 insect taxa. Among insects, Simuliidae and Chironomidae (Diptera) and Baetidae, Leptohyphes and Tricorythodes (Ephemeroptera) comprised 24% of total drift. Drift periodicity was strongly nocturnal, with peaks at 18:00 h (sunset) and 03:00 h. Our results, and those of previous experiments in the study stream, suggest that nighttime drift is driven by the presence of predatory diurnal drift-feeding fishes and nocturnal adult shrimps. There were no clear seasonal patterns over both ‘dry’ and wet seasons, suggesting that benthic communities are subject to similar stresses throughout the year, and that populations grow and reproduce continuously. This revised version was published online in July 2006 with corrections to the Cover Date.     

Field experiments on the relationship between drift and henthic densities of aquatic insects in tropical streams (Ivory Coast). III Trichoptera

SUMMARY. 1. Based on in situ gutter trials we related the drift of caddis flies to their benthic densities and to various abiotic factors in streams in the Ivory Coast (West Africa). Members of the families Hydropsychidae, Philopotamidae. Hydroptilidae and Leptoceridae were considered in detail.
2. The drift of larvae peaked at night in both early and late larval instars.
3. Drift of a larval group (a certain instar, species or higher taxon) was more often related to the benthic density of other larval groups than to its own benthic density.
4. Self-regulation of an upper benthic density of a larval group by emigration through drift was not statistically evident.
5. There was no straightforward relationship between drift and abiotic factors.
6. Drift rates differed between taxa as well as between larval instars (size groups) within a taxon. Newly hatched larvae had very high drift rates, whereas the last larval instar usually had the lowest drift rate.
7. We related these results to the violently fluctuating discharge of the streams in the study area and the consequent variability of space for lotic insects.
8. Drift estimates, made at the same time as a monitoring programme on possible side-effects of insecticides (Onchocerciasis Control Programme), failed to reflect benthic densities except in the night drift of Hydropsychidae.     

Upstream-downstream movements of aquatic invertebrates in a Rocky Mountain stream

Simultaneous collections of drift and organisms moving either upstream or downstream in association with the substrate were made using a specially designed sampler. Samples were taken in a diel series along a transect across the study riffle of a Colorado foothills stream on six dates over an annual cycle. In addition to longitudinal movements, taxonomic composition and diel periodicity were evaluated. The insect-dominated fauna showed a net downstream displacement. Only the caddisflies Helicopsyche borealis and Hesperophylax occidentalis exhibited net upstream movement, primarily a result of low drift frequencies. The taxonomic composition of moving invertebrates differed from that of the benthos. Drift resembled downstream moving substrate-associated invertebrates in composition, but differed from that of the upstream directed fauna. Taxa collectively exhibited four types of diel patterns: 1) similar downstream (drift and substrate-associated movements) patterns, which generally differed from the upstream pattern; 2) similar benthic (upstream and downstream) patterns, which differed from that of drift; 3) aperiodic patterns; and 4) independent patterns for each type of directional movement. Analysis of size classes based on head capsule width for the mayfly Baetis tricaudatus showed significantly smaller size in stationary individuals compared with moving individuals in the population and revealed that nymphs moving during the day were smaller than those moving at night.     

Migratory drift of larval freshwater shrimps in two tropical streams, Puerto Rico

1. Migratory shrimps are often major biotic components of tropical stream communities, yet spatial and temporal patterns of their migration have yet to be described. This information is of increasing importance given the continued fragmentation of tropical streams by damming and water abstraction/diversion, which can disrupt migratory life cycles. 2. Larval amphidromous shrimps are released by adult females in freshwater streams. They then drift passively to an estuarine habitat where they metamorphose before migrating back upstream. Drift of larval shrimps was sampled over two to five 24-h periods at each of three sites along two rivers that drain the Luquillo Experimental Forest in Puerto Rico: the Espíritu Santo (10, 135 and 335 m a.s.l.) and the Mameyes (10, 90 and 290 m a.s.l.). A total of seventeen diel samplings were conducted. 3. Shrimp drift increased in the downstream direction in both catchments, and had a significant positive exponential relationship with length of stream channel above each site. There was no significant difference between catchments with respect to mean daily drift rate per km of stream channel. Maximum observed larval shrimp density was 69 102 larvae 100 m^–3 (1.7 g dry mass 100 m^–3), which is high relative to published invertebrate drift studies. 4. The pattern of shrimp drift agreed with the ’risk of predation hypothesis‘. In stream reaches with predatory fish, drift of larval shrimps occurred at night and was slight during the day. A nocturnal peak in drift occurred between 19.00 and 22.00 h. At a high-altitude site, where predatory fish were absent, no diel pattern was discernible. 5. The present study provides information on the timing of migratory drift of larval shrimps, which can minimize the adverse effects of water abstraction from streams draining the Luquillo Experimental Forest. Elimination of water withdrawal during peak larval drift after dark will significantly reduce shrimp mortality.     

Dynamics of Invertebrate Benthic Communities and Drift in a Regulated River of Central Spain

We document invertebrate benthic and drift dynamics in a regulated river in central Spain at two temporal scales: seasonal (for both benthos and drift) and daily (for drift). The benthic abundance of individuals and taxon richness generally increased in the summer. Drift abundance showed no seasonal or daily variation, but taxon richness of drifting individuals was higher in the spring. Both ben‐thos and drift showed clear seasonal changes in taxonomic composition. Interestingly, some benthic taxa showed their highest abundances in the spring, while others were more abundant in the summer. In contrast, most drifting taxa were more abundant in the spring. Different functional feeding groups showed different patterns of variation throughout the year, both in the benthos and the drift. Daily variations in drift were present in very few taxa and functional feeding groups, and only in some seasons. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A continuous study of the total drift of freshwater shrimps, Gammarus pulex, in a small stony stream in the English Lake District

1. The objective was to determine the major factors affecting the downstream dispersal (drift) of freshwater shrimps, Gammarus pulex. Sample replication and frequency are major problems in the quantification of drift. For the first time, these problems were avoided by sampling the whole stream continuously so that all the shrimps drifting downstream at the sampling point were caught in a net emptied at dusk and dawn in 1966, and every 3 days in 1967. 2. There was no consistent seasonal pattern in drift rates, but a high proportion of annual drift was taken in only a few samples. There was a nocturnal diel pattern of drift with peaks soon after dusk and just before dawn. A power function described the significant (P < 0.001) relationship between drift and flow, and was used to neutralise the dominant effects of flow by standardising total drift over 24 h, nocturnal drift and diurnal drift (drift per 50 m³). These were all significantly (P < 0.001) related to benthos density, but not to date, temperature, or length of the night or day. 3. The relationship between drift values and the independent variables, flow and benthos density, was well described (P < 0.001) by a multiple‐regression model. Adding temperature, date, and/or the length of the night or day did not improve model fit. Variations in flow and benthos density explained 94% of the variation in total drift over 24 h, 97% of the variation in nocturnal drift, but only 44% of the variation in diurnal drift. A power function described (P < 0.001) the relationship between total drift and the volume of water sampled over 3‐day periods in 1967. Flow explained 95% of this drift variation; it was unnecessary to add another variable such as benthos density. 4. The significance of this study is that it avoided the problems associated with the quantification of drift samples. Therefore, the conclusions are more robust than those of many previous studies. A high proportion of the annual drift losses would have been undetected by intermittent sampling. Temperature, season, night or day length had no significant effect on drift densities, and the relationship between drift and benthos densities was proportional, not density dependent. The nocturnal increase in drift could not be interpreted as an antipredator behaviour. The dominance of flow and benthos density was apparent but the quantitative relationships posed further questions, especially those related to drift distances at different velocities.     

Spatial and Temporal Variation of Macroinvertebrate Drift in Two Neotropical Streams1

The detection of spatial variation in macroinvertebrate drift depends on the spatial scale of investigation in streams of the La Selva Biological Station, Costa Rica. Drift samples were taken in a spatially nested design, with two streams, two reaches per stream, two riffles per reach, and four replicate samples per riffle. Drift showed little variation among streams, but varied significantly at the scales of reach and riffle, with variation among samples also high. In addition, sampling took place at two temporal scales: diel and at two different periods that differed in rainfall conditions. Drift diel periodicity was a clear pattern, while only density of individuals varied among sampling periods. This is the first study of macroinvertebrate drift at multiple spatial scales, despite the recognition that multi‐scale studies are essential for a more complete understanding of community patterns and processes.     

Composition and seasonality of benthic invertebrates,and drift in the Naro Moru River,Kenya

A survey was carried out to establish the nature and composition of the benthos along the Naro Moru, a tropical river in central Kenya using artificial substrate baskets, from November 1986 to October 1987. A clear longitudinal zonation existed for Diptera and Ephemeroptera which were the major benthic taxa. Maximum colonization took place after ten days of exposure. Seasonal variations in abundance were also observed. All taxa collected from the bottom samples were also collected in the drift samples, but the percentage composition of the benthos showed variations with that of the drift. Simulium sp. dominated the benthos whilst Baetis spp. dominated the drift. There was a positive correlation between drift rate and benthic fauna density.     

Effects of stream size on taxa richness and other commonly used benthic bioassessment metrics

Benthic macroinvertebrate samples were collected from natural substrates in disturbed and undisturbed South Carolina upper coastal plain streams to determine if taxa richness and other bioassessment metrics were significantly related to stream size as predicted by the River Continuum Concept (RCC). Linear, quadratic, and lognormal regression models indicated that stream width was positively related to total number of taxa; number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa; and total number of organisms. Linear regression showed that the expected number of taxa at undisturbed sites ranged from 35 in 2.0 m wide streams to 64 in 16.0 m streams. Comparable values were 8–20 for EPT and 109–261 for number of organisms. Stream width was inversely related to biotic index values indicating a decrease in average organism tolerance with increasing stream size. ANCOVA showed that the effects of stream size were similar for disturbed and undisturbed sites. Rank correlations and multidimensional scaling (MDS) showed that Lepidoptera and Trichoptera were more abundant in larger streams and Annelida in smaller streams. Stream size related changes in benthic macroinvertebrate community composition are often ignored in bioassessment protocols; however, failure to adjust metrics for stream size can lead to erroneous conclusions. Adjustments are possible by analyzing regression residuals stripped of stream size related variance, dividing the area beneath the maximum taxa richness line into equal size units for metric scoring, or scaling metrics based on predicted reference values. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Effects of headwater impoundment and channelization on invertebrate drift

The construction of a flood control impoundment on Twitty's Creek added large numbers of organisms of limnetic origin to the stream ecosystem. However, the number of limnetic organisms per unit volume of water decreased rapidly as the distance downstream from the reservoir increased and, during most sampling periods, made up an insignificant portion of the total drift biomass at 7.2 km downstream. Factors favoring the extended downstream drift of limnetic organisms were high stream discharge and low water temperature.Several taxa of benthic organisms had much lower drift rates in the station immediately below the dam than at other stations and several taxa commonly taken at other stations were not captured immediately below the reservoir outfall. One possible explanation is that these organisms may have longer drift recruitment distances than the distance from the reservoir outfall to the sample location.A comparison of drift densities of organisms of benthic origin and benthic standing crop densities in channeled and unchanneled streams revealed that drift densities were higher in channeled streams than in unchanneled streams for most taxa of invertebrates. In addition, channeled streams appeared to have lower benthic standing crops than unchanneled streams for most taxa of invertebrates.In stream sections impacted by either channelization or the Twitty Lake outfall, the energy dynamics of the stream ecosystems were altered by increased density of drifting invertebrates. From the standpoint of increasing food availability to the fish fauna of the stream, these changes would appear to benefit drift feeding species and negatively impact bottom feeding species.     

The influence of predatory fish on mayfly drift: extrapolating from experiments to nature

1. A knowledge of how individual behaviour affects populations in nature is needed to understand many ecologically important processes, such as the dispersal of larval insects in streams. The influence of chemical cues from drift‐feeding fish on the drift dispersal of mayflies has been documented in small experimental channels (i.e. < 3 m), but their influence on dispersal in natural systems (e.g. 30 m stream reaches) is unclear. 2. Using surveys in 10 Rocky Mountain streams in Western Colorado we examined whether the effects of predatory brook trout (Salvelinus fontinalis) on mayfly drift, that were apparent in stream‐side channels, could also be detected in natural streams. 3. In channel experiments, the drift of Baetis bicaudatus (Baetidae) was more responsive to variation in the concentration of chemical cues from brook trout than that of another mayfly, Epeorus deceptivus (Heptageniidae). The rate of brook trout predation on drifting mayflies of both species in a 2‐m long observation tank was higher during the day (60–75%) but still measurable at night (5–10%). Epeorus individuals released into the water column were more vulnerable to trout predation by both day and night than were Baetis larvae treated similarly. 4. Drift of all mayfly taxa in five fishless streams was aperiodic, whereas their drift was nocturnal in five trout streams. The propensity of mayflies to drift was decreased during the day and increased during the night in trout streams compared with fishless streams. In contrast to the channel experiments, fish biomass and density did not alter the nocturnal nature nor magnitude of mayfly drift in natural streams. 5. In combination, these results indicate that mayflies respond to subtle differences in concentration of fish cues in experimental channels. However, temporal and spatial variation in fish cues available to mayflies in natural streams may have obscured our ability to detect responses at larger scales.     

Stream hydraulics as a major determinant of benthic invertebrate zonation patterns

SUMMARY. 1. Studies on the zonation of benthic fauna in fourteen streams situated in a variety of latitudes from Alaska to New Zealand have been evaluated.
2. We suggest that physical characteristics of flow ('stream hydraulics') are the most important environmental factor governing the zonation of stream benthos on a world-wide scale.
3. From the source to the mouth of a stream, zones of transition in stream hydraulics' occur, to which the general pattern of stream invertebrate assemblages can be related. In these zones benthic community stability and resilience must be different from those upstream and downstream of the hydraulic transition zones.     

An assessment of mesh bags and plastic leaf traps as tools for studying macroinvertebrate assemblages in natural leaf packs

Aggregation of leat litter formed against small mesh obstacles — placebo traps — were studied in four streams differing in natural retentiveness and pH. In three of the streams, natural benthic accumulations of leaf litter were available for comparison, and in these the fauna in the plastic traps and the natural accumulations was similar. In two of the streams comparisons were made, in terms of percent composition, between the fauna of the stony benthos and that colonizing plastic traps and leaf-filled mesh bags. In an acid, naturally retentive stream, the fauna of the three treatments was similar, although shredders were relatively more abundant in plastic traps and mesh bags. In a circumneutral, non-retentive stream diversity of taxa was reduced in plastic traps compared with the stony benthos, and in mesh bags compared with plastic traps. Numbers of animals per g of leaf litter were similar in plastic traps and mesh bags in the retentive stream. In the non-retentive stream, however, there were fewer animals in mesh bags than in the plastic traps. For many purposes, the plastic traps produce leaf packs which closely mimic natural packs, but the results from mesh bags depend on the background retentiveness of the streams in question.     

The relation between invertebrate drift and two primary controls,discharge and benthic densities,in a large regulated river

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