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Keywords:

  • catchment size;
  • deforestation;
  • forest type;
  • land use;
  • litter;
  • nutrient;
  • tributary stream

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Natural and human-made disasters such as floods and logging occur in and around rivers. Stream-dwelling aquatic insects respond to these disturbances in various ways. Primary consumers among them rely greatly on algae and leaf litter from riparian vegetation as food. Therefore, once a disturbance such as a flood has occurred, insects may find it difficult to find food in a stream, and the aquatic insect assemblage can be impacted greatly as a result. Disturbances in riparian areas also increase fine sediment loads into streams, damaging habitat and altering the aquatic insect assemblage. Deforestation impacts not only terrestrial but also aquatic animals. In this review paper, aquatic insect assemblages are assessed according to alterations in land use in and around streams. Following this paper, it is expected that clarification of aquatic insect fauna and their life cycles will progress and that the distribution and habitat use of aquatic insects will be afforded greater attention in forest management.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Rivers run through various regions of the earth like capillary blood vessels in the body. The characteristics of rivers differ depending on various factors such as geology, climate and topography. The flow of the Amazon River, which mainly runs through forested regions, is 100 times greater than that of the Nile, which mainly runs through a desert, although both rivers are longer than 6000 km (Horne & Goldman 1994). Large rivers have rapid velocities and high amounts of suspended organic and inorganic materials. Therefore, light can not easily penetrate into the rivers and primary productivity is very low. The organic matter in these large rivers depends on inputs from inflows from upper reaches. Rivers that run through desert regions, such as the Nile River, do not have large supplies of organic matter, and thus primary productivity and biodiversity are low. Rivers that run through forested regions, such as the Amazon River, are supplied with organic matter, and therefore, the total productivity and biodiversity are high in these rivers (Horne & Goldman 1994; Cushing & Allan 2001). This reliance on organic matter from outside the river is similar to the ecology of small basins in forested streams. However, river width can extend to several kilometers in large rivers, and thus the organic matter from riparian forests is not sufficient to sustain primary productivity. Large rivers have continuous yearly flows that change with deluges. Deluges always bring various nutrient-rich materials into rivers, which compensates for the scant primary production. Species in and around these river systems have evolved their life cycle strategies in response to variability in discharge.

Globally, forested areas comprised about 6.2 × 109 ha 10 000 years ago (Bryant et al. 1997). Currently, forested areas cover about 4 billion ha and account for 30% of the land area of the world (FAO 2010). The total forested area consists of 95% natural forests and 5% artificial forests. The decrease in forested area continues even now, and 13 million ha of forest (natural forests in most cases) disappear each year (FAO 2001, 2010). Most of this decrease is the result of clear-cutting in tropical rainforests, with the forests around the Amazon River at the head of the list. Rivers that run through tropical rainforests, such as the Amazon and Mekong Rivers, have higher productivity because of organic material deposited from riparian forests (allochthanous sources). However, if these forests are clear-cut, allochthanous sources decrease substantially with significant impacts on biodiversity and abundance of primary and secondary consumers.

Many freshwater animals inhabit rivers that flow through forested regions. Most of these animals are fishes and aquatic insects, and they use materials deposited from riparian forests as both food and habitat. Changes in forest management may have huge impacts on the fishes and aquatic insects in rivers. Many unknown aquatic insect species exist in the world, and changes in forest management might lead to the extinction of aquatic insects that we do not even know are there. Because nature does not exist to serve humans, the remodeling of nature, even if the changes are useful to humans, can threaten human existence itself. This review paper considers the biodiversity of rivers, especially freshwater aquatic insects, in relation to land use in forested areas. Hopefully this review paper will help managers pause before commencing forest alterations.

AQUATIC INSECTS AND THEIR HABITAT

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Some aquatic insects live in still water (e.g. ponds, lakes and reservoirs) and others live in flowing water (e.g. streams). The main physiological difference among these systems lays in respiration. Because of the lower O2 levels found in water (<15 ppm O2; Merritt & Cummins 1996), obtaining oxygen from the water without any modification is difficult for animals. Aquatic insects that live in still water obtain oxygen from the air (200 000 ppm O2) by traveling to the water surface or from dissolved O2 in the water, either through their cuticle, across the gill or from air bubbles stored in various locations on the body.

Organic matter in streams consists of leaves from the surrounding land or algae, or both. This particulate organic matter (POM) feeds the majority of aquatic insects in streams of all sizes. Aquatic insects gather this organic matter in five fundamental ways: (i) as shredders of coarse particulate organic matter (CPOM, >1 mm); (ii) as collectors of fine particulate organic matter (FPOM, <1 mm) from substrates; (iii) as grazers of encrusting or filamentous algae; (iv) as filterers of FPOM; or (v) as predators (Table 1; Cummins & Klug 1979).

Table 1.  Functional feeding groups of aquatic insects
FFGFeeding mechanismDominant food
  1. CPOM, coarse particulate organic matter; FPOM, fine particulate organic matter; FFG, functional feeding group.

ShreddersChew detritus and macrophytes and mine macrophytesLeaf detritus, wood and CPOM
CollectorsFeed depositFPOM
GrazersGraze mineral and organic materials on stone surfacesAttached algae and biofilm
FilterersSuspend net and get foodFPOM
PredatorsCatch animals and feedLiving animals

The habitats of aquatic insects mainly include riffles and pools. In riffles, POM drifts and is sometimes caught by rocks, stones and branches. In pools, POM settles to the bottom. Aquatic insects that inhabit riffles have behaviors that facilitate the collection of floating POM, and species that inhabit pools have adapted to use benthic POM (Table 2). Because of the lower O2 concentrations found in pools, some aquatic insects that live in pools have slightly different respiration system from those found in riffles. Aquatic insects that typically inhabit lentic waters sometimes inhabit pools in streams (Ward 1992).

Table 2.  Examples of existence mode of aquatic insects
Type of streamMode of existenceDescriptionTypical example
RiffleNet spinnersSecrete thread and pitch net between stonesStenopsychidae, Hydropsychidaess
ClingerCling to rocks and migrate lessBlepharoceridae, Simuliidae
CrawlersCrawl on stonesPerlodae, Ecdyonuridae
PoolCase carriersMove with their own caseSome Trichoptera
SwimmersMove by swimmingIsonychiidae, Baetidae
BurrowersLive among sand and mudEphemeridae, Chironomidae

Geographical features, such as river width and altitude, change with stream flow from the upper to lower reaches. The particle size of POM derived from riparian areas is reduced by physical (broken by rocks) and biological (eaten) processes during transport from the upper to lower reaches. The fauna in streams also changes according to environmental transitions. The river continuum concept clearly shows these states (Vannote et al. 1980).

PHYSICOCHEMICAL FACTORS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Aquatic insect assemblages in streams and rivers are affected by physicochemical factors such as temperature, channel stability, seasonal shifts in weather, water pathways, substrate condition and the frequency of periods of favorable environmental conditions (Burgherr & Ward 2001). Water and air temperature are primary factors associated with aquatic insect assemblages (Ward 1992). Preferred water temperature differs among species and is dependent on the classification; for example, stoneflies often prefer lower water temperatures than mayflies (Brittain 1990). Egg hatching, larval growth and emergence phenology are influenced by water temperature. Egg hatching success is also related to water temperature, and the optimal water temperature differs among species.

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). Heterogeneity produces patchiness in stream environmental conditions, including food availability, which in turn creates high species diversity among aquatic insects (Godbout & Hynes 1982). Although disturbance produces substrate heterogeneity, large disturbances such as floods reduce substrate heterogeneity, variance of habitat type and aquatic insect density (Robinson et al. 2004). Catastrophic disturbances create debris flows that mobilize sediments and can remove riparian forests. Therefore, we often see fewer pieces of large wood, less benthic organic matter and a lower abundance of detritivorous stoneflies in streams that have been recently scoured by debris (Cover et al. 2010). The reduction in aquatic insect abundance by large disturbances is more obvious in pools than in riffles (Robinson et al. 2004). Taxa number and the density of aquatic insects recover to pre-disturbance levels within 5–7 months, but taxa-specific responses still remain; more than a year is required for the original aquatic insect assemblage to return (Collier & Quinn 2003). Habitat heterogeneity is the strongest predictor of aquatic insect assemblage richness and can be used to predict species richness at the landscape scale (Miserendino 2001).

Site-specific conditions, such as land use and water quality, influence aquatic insect growth and community structure. The annual production of aquatic insects is positively related to catchment alkalinity and nitrates (Krueger & Waters 1983). When stream water has a low pH, only shredders, collectors and predators are found (Townsend et al. 1983). The larval growth rate and abundance of Ephemeroptera such as Ephemerella funeralis are affected by the quality of nutrients in a stream (Fiance 1978). Lower pH leads to a lower abundance and lower growth rate of E. funeralis (Fiance 1978). Larval growth of the predaceous stonefly Acroneuria lycorias is slow in streams with lower cation concentrations. However, this slow growth rate and production are more related, although indirectly, to the complexity of physical, biological and habitat factors than to the stream water cation concentration (Eggert & Burton 1994).

EFFECTS OF LAND USE

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Riparian land use is an essential factor for considering stream habitats. Riparian land use varies with stream location: some riparian areas are forests while others are agricultural land and pastures, or urban residences. Riparian land use changes the stream habitat structure (including nutrient inputs) and has subsequent effects on aquatic invertebrates. Therefore, we find more shredders and fewer grazers in forest areas and fewer shredders and more grazers in pasture areas (Reed et al. 1994). When riparian land is covered with forests and/or wetlands, biotic integrity and habitat quality in streams increase, but when riparian land is used for agriculture, these measures of environmental health decline (Roth et al. 1996). Even in subtropical areas, the abundance of shredders is higher in forest areas and the abundance of grazers is higher in pasture areas (Encalada et al. 2010). In Trichoptera, the habitats of some genera, such as Anisocentropus, Dyschimus, Lepidostoma, Leptocerina, Athripsodes, Parasetodes, Aethaloptera, Hydropsyche and Polymorphanisusis, are restricted to undisturbed forest sites and Hydroptila is restricted to disturbed agricultural sites (Chakona et al. 2009). The development of riparian vegetation plays an important role in the succession of aquatic insects (Flory & Milner 1999).

Local observations of riparian land use alone are not sufficient to predict the biotic and habitat conditions in a stream. Catchment land use is also important (Richards et al. 1996; Roth et al. 1996; Allan et al. 1997). Differences in catchment land use, such as forests, agricultural land, and pastures, also affect aquatic insect assemblages (Quinn et al. 1997; Townsend et al. 1997). In-stream alkalinity is affected by the quality and quantity of catchment land use (Johnson et al. 1997) and it is indirectly related to invertebrate growth and faunal composition (Krueger & Waters 1983; Townsend et al. 1983). Several mayfly and stonefly taxa are common in pine and natural forest streams but absent in pasture streams. Chironomids, snails and worms are dominant in pasture streams. This difference in aquatic insect assemblages results from differences in tolerances to organic matter and other pollution (Quinn et al. 1997). Water quality in forest streams is different from that of urban streams. Therefore, the abundance of aquatic insects is higher in native bush catchments than in urban catchments (Hall et al. 2001). Responses to disturbance also depend on land use. In forested areas, stream disturbances immediately reduce the number of taxa and the total density of aquatic insects. However, a delay occurs in the response of aquatic insects to disturbances in pasture areas (Collier & Quinn 2003). Recognition of the variability in riparian areas, watersheds and in-stream landscapes is necessary to understand differences in aquatic insect assemblages and to improve our understanding of the life cycles of aquatic insects (Reed et al. 1994; Richards et al. 1996).

NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

In mountain streams, riparian forests cover the streams so that the amount of sunlight that reaches the substrate decreases and algae are not abundant on rocks. Leaves found in the streams are either transferred from the forest floor or fall directly from riparian trees. Fallen leaves, fallen branches, woody debris derived from riparian forests, terrestrial insects that fall accidentally from riparian forests, and aquatic insects would be the main constituents of organic matter in these streams. The input of riparian detritus is essential for the conservation or restoration of diverse stream food webs (Wallace et al. 1997; Whiles & Wallace 1997). Fallen leaves and branches initially pile on the substrate as CPOM, which is then enriched by microorganisms in the stream. Water-soluble ingredients flow out of the fallen leaves and fungi and bacteria begin to reproduce on the saturated leaves (litter).

Riparian-derived CPOM has a high nitrogen content, which makes it desirable as food for shredders. Shredders break the enriched litter into pieces while feeding. In this way, CPOM is converted to FPOM and feces contributes to dissolved organic matter. Mechanical disruption by battering on rocks also creates FPOM from CPOM. FPOM is used as food by collectors, grazers and filterers; it is also used by some Trichoptera as material for larval cases. Shredders, collectors, filterers and grazers are used as food by predators. These aquatic insects and terrestrial insects that fall into streams are eaten by fishes and other vertebrates.

Woody debris in streams not only provides a supply of organic material but also serves as habitat for aquatic insects and fishes (Fausch & Northcote 1992). Riparian forests provide shade from solar radiation and suppress increases in water temperature, especially in summer (Nakamura & Dokai 1989; Imholt et al. 2010). The composition of forests that surround streams and associated factors, such as shade, can affect the habitats of aquatic invertebrates (Hawkins et al. 1982).

The composition of aquatic insects differs depending on the catchment scale. Taxon richness is correlated with river width (Jenkins et al. 1984) and increases with stream size (Brönmark et al. 1984; Jenkins et al. 1984). Stream width and catchment area affect the diversity of aquatic insect genera, and the effect of forest area on aquatic insect diversity is greater than the effect of forest composition (Yoshimura 2006). Forest harvest also affects aquatic insect assemblages and the effect is more obvious in small catchments than in large catchments (Reid et al. 2010).

FOREST TYPE AND DETRITUS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Forest landscapes include forests of deciduous trees, evergreens, broad-leaved trees and coniferous trees. Different types of forests provide different species of leaves and each type of leaf provides a different nutrient composition to associated streams. Therefore, the presence of riparian forests affects stream water quality and the effect differs with forest type (Townsend et al. 1983, 1997; Friberg 1997; Friberg et al. 1997). Aquatic insect assemblages also differ with forest type. Shredders tend to inhabit streams in natural broad-leaved forests and filterers tend to inhabit streams in planted coniferous forests (Yoshimura & Maeto 2006). Differences in abundances because of forest type seem to be partially related to the retention of detritus in a stream (Friberg et al. 1997). Riparian red alder forests provide nutrient-rich litter to stream ecosystems (Volk et al. 2003) and support a greater biomass of aquatic invertebrates compared to riparian coniferous forests (Piccolo & Wipfli 2002). Although the biomass of detritus is higher in old-growth forests, the abundance of aquatic insects is higher in alder forests than old-growth forests (Piccolo & Wipfli 2002). The density of aquatic insects in small streams is high in almost monoculture beech forests and low in coniferous forests in Denmark (Friberg 1997). However, riparian willow forests, which do not provide nutrient-rich detritus, produce small numbers of aquatic insects (Lester et al. 1994). On the other hand, hemlock forests support more aquatic insect taxa than mixed hardwood forests (Snyder et al. 2002). Because old-growth forests tend to have a lower abundance of aquatic insects (Cole et al. 2003), forest age is related to differences in their abundances between forest types. Retention of detritus is an important factor for maintaining higher abundances of aquatic insects. However, other factors, such as substrate condition and forest age, may also be related to higher abundances of aquatic insects.

Forest vegetation is an important factor when considering the stream habitats of benthic invertebrates. The composition of a riparian forest affects aquatic insect abundance and composition (Friberg 1997; Murphy & Giller 2000). Leaf litter that falls into a stream from a riparian forest plays several roles for the aquatic insect assemblage depending on the litter species (Cummins et al. 1989; Sweeney 1992). Deciduous broad-leaved litter can provide more shelter from predators than coniferous litter (Eggert & Burton 1994). The biomass of shredders is higher in maple litter than in pine litter (Whiles & Wallace 1997). Collectors and shredders are more abundant in leaves of Ocotea sp. and Miconia guyanensis, whereas filterers are more abundant in the leaves of Protium brasiliense, Pheptaphyllum spp. and Miconia chartacea in Brazil (Ligeiro et al. 2010). The nutrient value of litter as food for aquatic insects differs depending on the tree species and the rate of microbiological activity. Shredders essentially prefer older leaves that have been saturated in the stream for more than a few weeks and which have been colonized by microorganisms (Graça 2001; Hieber & Gessner 2002). Additionally, shredders tend to prefer nitrogen-rich leaves (Graça 2001). Leaf preference differs depending on the insect species. The biomass of aquatic insects increases in litter that has remained saturated in a stream for a long time. The assemblage of aquatic insects in the litter differs with the length of conditioning in water, increasing from one week to one month and greater than one month (Ligeiro et al. 2010). Food availability for aquatic insects is more important than the physical structure of the environment, especially at a small scale (Burdett & Watts 2009).

Early instar larvae of Taeniopterygidae (Plecoptera) consume the bacterial and fungal scum that grows on leaves that have soaked in streams, and larger larvae skeletonize leaves (Merritt & Cummins 1996). Larvae of Taeniopteryx nivalis prefer to feed under the midribs of leaves (Harper & Hynes 1972). Adults of Taeniopterygidae feed on epiphytic algae or young leaves and buds of riparian vegetation (Merritt & Cummins 1996). They inhabit old-growth forest basins and are not found in coniferous forest basins (Yoshimura & Maeto 2006). Adults of Nemouridae (Plecoptera) also prefer deciduous trees and shrubs (Harper 1973).

Sericostoma vittatum (Trichoptera) can use pine litter as food (Campos & Gonzalez 2009). Although eucalyptus leaves are generally low-quality food sources (Abelho & Graça 1996), Caenota plicata (Trichoptera) prefers eucalyptus leaves Eucalyptus obligua and E. globulus over alder Alnus glutinosa as food (Ratnarajah & Barmuta 2009).

Forest structure also affects the distribution of aquatic insects. Stenopsychidae (Trichoptera) are filter-feeders and construct nets between stones (Merritt & Cummins 1996). The survival rate of Stenopsychidae decreases with increases in precipitation (Nishimura 1984). The density of Stenopsychidae is higher when epiphytic algae is more abundant, which occurs in streams that are more stable (Nishimura 1984). Disturbances occur more often in old-growth forests than in managed coniferous forests, which would lead to the dominance of Stenopsychidae in coniferous forests (Yoshimura & Maeto 2006).

The distribution of Athericidae (Diptera) in old-growth forests and their absence in coniferous forests (Yoshimura & Maeto 2006) is related to their behaviors: adult Suragina satsumana tend to oviposit in certain places right above the water surface of a stream (Nagatomi 1962). However, Atherix spp. are not found in secondary or mixed forests (Yoshimura 2007). Other factors associated with old-growth forests are also related to the persistence of Athericidae.

Larvae of Siphonoperla torrentium (Plecoptera) are found more frequently in moorlands and less often in forested areas. This tendency is the same in the adult stage. However, a preference for certain forest types as larval habitat does not always lead to the same preference in the adult stage. Larvae of Amphinemura sulcicollis (Plecoptera) are found more frequently in forested and replanted streams and less often in moorland streams, but adults are found more in moorland streams. These differences among species result from differences in flight ability: A. sulcicollis can fly farther than S. torrentium (Briers et al. 2002). Preferred forest type and aquatic insect distribution differ between adults and larvae, which means that adults move to moorlands after emergence and oviposit in forest streams, or that adults move to moorlands and larvae move back to forest streams after hatching.

DEFORESTATION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

The assemblage of aquatic insects changes when surrounding old-growth forests are clear-cut (Friberg et al. 1997; Fuchs et al. 2003; Price et al. 2003; Hernandez et al. 2005). Deforestation reduces the quantity of detritus in a stream, which leads to changes in the aquatic insect assemblage (Price et al. 2003). Deforestation also increases the peak flow of water, storm discharge and sedimentation in the stream (Macdonald et al. 2003). When fine sediments are added experimentally to forest streams, aquatic insects begin to drift to avoid the sediments, and the density of aquatic insects in the area where sediments are added decreases (Larsen & Ormerod 2010). However, in clear-cut streams, algae grow rapidly on substrates. Therefore, the abundance of algae scrapers increases after clear-cutting (Gravelle et al. 2009). The biomass of aquatic insects in streams that flow through newly logged forests is higher than in streams that flow through old-growth forests or older logged forests (Fuchs et al. 2003). The abundance of emerging aquatic insects is also higher in clear-cut catchments than in forested catchments (Banks et al. 2007).

Deforestation leads to increases in water temperature, especially in summer (Nakamura & Dokai 1989; Imholt et al. 2010). Because higher temperatures lead to increased metabolism, larval size of Baetis (Ephemeroptera) is larger in clear-cut streams than in forested streams in summer. However, clear-cut streams provide fewer CPOM inputs than do forested streams. Therefore, in other seasons, the larval size of Baetis is smaller in clear-cut streams than in forested streams (Imholt et al. 2010).

The impact of deforestation on aquatic insect assemblages is strong when riparian forests are harvested (Reid et al. 2010). Deforestation can alter aquatic insect assemblages and eliminate the most sensitive species. However, the impact can be reduced by preserving a riparian buffer forest (Lorion & Kennedy 2009). Preservation of riparian forests along streams is better than complete deforestation, but this preservation effort is insignificant compared to nonharvested areas because the reduction in litter still leads to fewer shredders (Lecerf & Richardson 2010). When harvesting occurs in areas that are less than 200 m long, no effect of riparian buffer forest harvest on aquatic insects is detected (Chizinski et al. 2010).

The taxon richness of aquatic insects in riffles is almost the same as in pools, and the impact of deforestation on taxon richness does not differ between pools and riffles (Lorion & Kennedy 2009). However, the density and biomass of aquatic insects are generally higher in riffles than in pools and the impact of deforestation on the density and biomass of aquatic insects is detected in riffles but is not observed in pools. Additionally, the assemblage of aquatic insects changes after deforestation in both pools and riffles (Lorion & Kennedy 2009).

When small gaps are created in the aquatic insect assemblage, insects that inhabit surrounding substrates colonize the space. Taxon richness recovers in three days and density recovers in one month (Hayashi 1991; Matthaei et al. 1996; Collier & Quinn 2003). Therefore, even if a gap is created by disturbance from deforestation, aquatic insects will move into the new gaps. However, the effect of deforestation on the abundance of benthic organic matter continues for more than a year (Ely & Wallace 2010). Therefore, because of the lower benthic organic matter found in streams disturbed by deforestation, the biomass of aquatic insects per unit of benthic organic matter increases and then the insects in streams disturbed by deforestation will always feel hungry due to few materials. Historical logging activities continue to influence aquatic insect assemblages more than one year later (Ely & Wallace 2010).

When deforested areas are not afforested, the areas are colonized by grassland vegetation. After 20–30 years, broad-leaved trees colonize, forming a secondary forest. However, the composition of the aquatic insect assemblage that is developed 20–25 years after deforestation differs from that of old-growth forests, even though density and biomass may be the same (Fuchs et al. 2003). Additionally, the total density of aquatic insects decreases with forest age (Cole et al. 2003).

MAIN AND TRIBUTARY STREAMS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Main streams are fed by several tributaries. Because water flows from tributaries to the main stream, aquatic insects may drift from tributaries into the main stream. Aquatic insects sometimes drift with detrital transport (O'Hop & Wallace 1983). Individuals of Baetis can drift >30 m/day (Waters 1965) and most aquatic insects can move upstream at <8 m/day (Elliott 1971). When gaps in the aquatic insect assemblage are created by some kind of disturbance, aquatic insects that inhabit surrounding substrates colonize the available spaces, which means that larvae of aquatic insects are able to settle after moving to new suitable substrates. Even in large reservoirs, the genetic diversity of Fallceon quilleri (Ephemeroptera) is less than that of the flightless Hyalella azteca (Amphipoda). That is, mayflies can move across large reservoirs during the larval or adult stages (Zickovich & Bohonak 2007). Adult stoneflies Leuctra ferruginea also fly more than a few hundred meters along streams and can move into different tributaries from their place of emergence (MacNeale et al. 2005). Although aquatic insects move both upstream and downstream during their larval and adult stages, aquatic insect assemblages differ between tributaries and the main stream when the surrounding forest type is different (Yoshimura 2008). Consequently, even if these aquatic insects drift or fly from tributaries to the main stream, they might crawl back upstream into the tributary if the new habitat conditions are not satisfactory, which would result in a heterogeneous assemblage.

PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

Disturbances in riparian area impact on the existence of aquatic insects, as it affects nutrients, water quality, sediment, detritus and substrate, etc. The degree of impact would be different depending on each aquatic insect species. Currently, morphological species level identification is possible for adult males and some later larval stages of many aquatic insects. However, identification is difficult with females and early-stage larvae. So, the knowledge of the impact on aquatic insects up to now is restricted to the genus level in most cases. For broad-scale analyses, family-level identification is sufficient (Hewlett 2000) and species-level identification adds little useful information despite the longer time required for identification. However, when we focus on fine-scale analyses, species level identification becomes useful. The effects of deforestation on aquatic insects and the relationship of aquatic insect assemblages between main and tributary streams need to be clarified at the species level, which might raise another story. Nowadays, an easy identification method, the technique of DNA barcoding, is under development. DNA barcoding was first described by Hebert et al. (2003) in Metazoa (Jinbo et al. 2011). DNA barcoding aids in the identification of females and immature stages of aquatic insects, which helps with the assessment of unknown fauna and hidden biodiversity. Indeed, total richness estimates from the use of DNA barcoding are far higher than those created using morphological identification to the species level by experts (Sweeney et al. 2011). DNA barcoding would enhance taxonomic resolution and lead to an improved understanding of differences in aquatic insect assemblages in relation to forest types. It would lead to accurate bioassessments of stream and river ecosystems and would consequently help clarify species-specific tolerances to disturbances, pollution and water temperature.

ACKNOWLEDGMENTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES

This work was partly supported by a Grant-in Aid for Scientific Research Fund from the Japan Ministry of Education, Science, Culture, and Sports (no. 18580154) and Environment Research and Technology Development Fund (D1102) of the Ministry of the Environment, Japan.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. AQUATIC INSECTS AND THEIR HABITAT
  5. PHYSICOCHEMICAL FACTORS
  6. EFFECTS OF LAND USE
  7. NUTRIENT FLOW AND CATCHMENT SIZE IN MOUNTAIN STREAMS
  8. FOREST TYPE AND DETRITUS
  9. DEFORESTATION
  10. MAIN AND TRIBUTARY STREAMS
  11. PERSPECTIVE ON AQUATIC INSECT ASSEMBLAGES
  12. ACKNOWLEDGMENTS
  13. REFERENCES
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