Macroinvertebrate Colonization Research Articles

Effects of Leaf Species and Conditioning State of Fresh Leaves on Colonization by Stream and Pond Macroinvertebrates

Fresh, green leaves are increasing as resources in aquatic ecosystems due to more frequent severe spring and summer storms, but research on allochthonous resources typically uses senescent leaves. We examined macroinvertebrate colonization of green leaves of three native deciduous trees (red maple, red oak, and tulip poplar) over two weeks within both a stream and fishless pond. Leaf colonization varied depending on the taxa of leaves and colonizers, submersion time, and the ecosystem examined. Within the stream, the densities of isopods (Lirceus sp.) and snails (mostly the invasive Potamopyrgus antipodarum) did not vary significantly across leaf species. In contrast, mayflies (Tricorythodes sp.) in the stream colonized tulip poplar in greater numbers than red oak leaves, while higher densities of planarians (order Tricladida) occurred within red oak leaves. The numbers of mayflies and snails decreased significantly by the second week, but the densities of isopods and planaria within stream leaf packs were consistent. In contrast, within the pond, significantly more isopods (Caecidotea communis) were collected after the first than after the second week of submersion and in tulip poplar leaves. Clams (Sphaeriidae) in the pond, on the other hand, were more prevalent in the second week but did not discriminate among leaf species. While the number of leeches (mostly Helobdella stagnalis) was consistent across weeks, significantly fewer leeches resided within tulip poplar leaves than within red oak leaves. Our results suggest that there are no consistent colonization-preference rankings of species of fresh leaves across freshwater benthic macroinvertebrate taxa. Even within a functional feeding group (e.g., the two types of isopods and snails, all detritivore-herbivores), there were differences in colonization patterns. Therefore, increased allochthonous inputs of fresh leaf litter due to severe spring- and summer-time storms are likely to promote the populations of various taxa to different extents.

Aquatic macroinvertebrate community colonisation and succession in macadamia orchard and communal area reservoirs: a case study of Luvuvhu River valley, South Africa

The demand for macadamia nut production worldwide has led to increased use of pesticides and chemicals for pest and disease control. Reservoirs in these macadamia farming sectors are at . The current study investigated macroinvertebrate colonisation and succession associated with two macadamia orchards and two communal area reservoirs. The potential effects of stressors from these land uses was tested for and compared using stone substrates over a 6-week period. Stone substrates from both reservoir types were abundantly colonised over time and the total macroinvertebrate taxa and abundance showed an increasing trend across the sampled weeks, with macadamia orchards having the highest number of macroinvertebrate taxa. Strong ecological succession was observed across reservoirs, with the initial succession of early colonisers – i.e., Chironominae (, Ostracoda (and Anax sp. (predator) within communal area reservoirs, and Chironominae, Ostracoda Radix natalensis (scrapers) in macadamia orchard reservoirs – followed by predatory colonisers such as Gyrinidae larvae, Trithemis sp. (macadamia orchard reservoirs), and Ranatra sp. (communal area reservoirs). Macroinvertebrate community structure differed significantly across sites and weeks, with no similarity being observed for communities across the different reservoirs. Redundancy analyses further highlighted 11 sediment chemistry variables (i.e., pH, resistivity, P, K, Na, Ca, Mg, Cu, B, Fe and S) which were significantly related to macroinvertebrate community structure. Thus, sediment variables were found to be better predictors of macroinvertebrate community structure in macadamia orchard reservoirs than communal area reservoirs. Consequently, we concluded that differences in colonisation ability among taxa and environmental stressors were important factors driving succession. These results add to the understanding of the macroinvertebrate colonisation processes and environmental stressors within agricultural landscapes, which can aid in the development of conservation management of freshwater ecosystems.

How tolerances, competition and dispersal shape benthic invertebrate colonisation in restored urban streams

Biotic communities often respond poorly to river restoration activities and the drivers of community recovery after restoration are not fully understood. According to the Asymmetric Response Concept (ARC), dispersal capacity, species tolerances to stressors, and biotic interactions are three key drivers influencing community recovery of restored streams. However, the ARC remains to be tested. Here we used a dataset on benthic invertebrate communities of eleven restored stream sections in a former open sewer system that were sampled yearly over a period of eleven years. We applied four indices that reflect tolerance against chloride and organic pollution, the community's dispersal capacity and strength of competition to the benthic invertebrate taxa lists of each year and site. Subsequently, we used generalised linear mixed models to analyse the change of these indices over time since restoration. Dispersal capacity was high directly after restoration but continuously decreased over time. The initial communities thus consisted of good dispersers and were later joined by more slowly dispersing taxa. The tolerance to organic pollution also decreased over time, reflecting continuous improvement of water quality and an associated increase of sensitive species. On the contrary, chloride tolerances did not change, which could indicate a stable chloride level throughout the sampling period. Lastly, competition within the communities, reflected by interspecific trait niche overlap, increased with time since restoration. We show that recovery follows a specific pattern that is comparable between sites. Benthic communities change from tolerant, fast dispersing generalists to more sensitive, slowly dispersing specialists exposed to stronger competition. Our results lay support to the ARC (increasing role of competition, decreasing role of dispersal) but also underline that certain tolerances may still shape communities a decade after restoration. Disentangling the drivers of macroinvertebrate colonisation can help managers to better understand recovery trajectories and to define more realistic restoration targets.

Winter dynamics of functional diversity and redundancy of riffle and pool macroinvertebrates after defoliation in a temperate forest stream.

Headwater streams are highly heterogenous and characterized by a sequence of riffles and pools, which are identified as distinct habitats. That higher species richness and density in riffles than in pools is considered a general pattern for macroinvertebrates. As temperate winters can last long up to half a year, however, macroinvertebrate communities of riffles and pools may assemble differently under ices or snows. Particularly, defoliation concentrating in autumn can largely change habitats in both riffles and pools by litter patching. According to the absence or presence of litter patches, there exist four types of subhabitats, i.e., riffle stones, riffle litters, and pool sediments, pool litters, which are selectively colonized by macroinvertebrates. To study the spatial pattern and temporal dynamics of colonization, macroinvertebrates were surveyed in a warmer temperate forest headwater stream in Northeast China during four periods: autumn, pre-freezing, freezing, and thawing periods. Our study focused on functional trait composition, functional diversity and functional redundancy of macroinvertebrate communities. The colonization of macroinvertebrates was found to be significantly different in these subhabitats. Riffle stones supported higher taxonomic and functional diversities than pool sediments; litter patches supported higher total macroinvertebrate abundance and higher functional redundancy than riffle stones or pool sediments. The functional trait composition changed significantly with seasonal freeze-thaw in both riffle stones and pool sediments, but not in litter patches. Macroinvertebrate community in litter patches showed seasonal stability in taxonomic and functional diversities and functional redundancy. Thus, this study strongly highlights that litter patches play an important role structuring macroinvertebrate community over winter, supporting high abundance and maintaining functional stability.

Compare the efficiency of artificial substrates and leaf litter substrates in macro invertebrates aggregation samples at Gilgel Gibe Watershade, Southwest Ethiopia

The utility of artificial and natural substrate samplers affects the distribution of macro invertebrates in freshwater ecosystems. This study evaluated the efficiency of litter substrates of Croton macrostachyus, Eucalyptus grandis, Ficus sure, and Salix subserrata and artificial substrates/ bricks in terms of macro invertebrates colonization, abundance, family richness, uniformity, and composition of the sampled macro invertebrates. Few researchers have evaluated the efficiency of artificial and natural substrates in the colonization and dispersal of macro invertebrates in freshwater ecosystems. The objectives of this assessment were to evaluate the efficiency of artificial and natural substrate samplers in collecting macro invertebrates for water quality assessments of the Gilgel Gibe Watershade and its tributaries. Five sampling areas were chosen to compare macro invertebrates colonization in relation to the effect of inorganic (bricks) and leaf litter as substrates. Four organic or bedding substrates were selected and collected from the upper and lower study sites based on native and exotic plant species and their diversity along the study sites. Therefore, the following litter species were collected: Croton macrostachyus, Eucalyptus grandis, Ficu ssure, and Salix subserrata. After 30 days, all samples from each site were collected. Past software was used for descriptive and diversity indices analysis. A total of 5491 macro invertebrates individuals were counted on both substrates (artificial/bricks and natural/litter species). The compositions of Ephemeroptera and Trichoptera differed by litter substrates and were consistently higher in litter bags containing artificial substrates. In general, the family richness, uniformity, and composition of the artificial substrate samplers for macro invertebrates were higher than those of the litter substrates, which may indicate that the artificial substrates was more efficient than the litter substrates in dispersing macro invertebrates due to its ability to allocate habitat support to macro invertebrates.

Rapid macroinvertebrate colonisation in restored channelised streams contiguous with natural stream reaches

Rapid macroinvertebrate colonisation in restored channelised streams contiguous with natural stream reaches

Drought and nutrient pollution produce multiple interactive effects in stream ecosystems.

Drought and nutrient pollution can affect the dynamics of stream ecosystems in diverse ways. While the individual effects of both stressors are broadly examined in the literature, we still know relatively little about if and how these stressors interact. Here, we performed a mesocosm experiment that explores the compounded effects of seasonal drought via water withdrawals and nutrient pollution (1.0 mg/L of N and 0.1 mg/L of P) on a subset of Ozark stream community fauna and ecosystem processes. We observed biological responses to individual stressors as well as both synergistic and antagonistic stressor interactions. We found that drying negatively affected periphyton assemblages, macroinvertebrate colonization, and leaf litter decomposition in shallow habitats. However, in deep habitats, drought-based increases in fish density caused trophic cascades that released algal communities from grazing pressures; while nutrient enrichment caused bottom-up cascades that influenced periphyton variables and crayfish growth rates. Finally, the combined effects of drought and nutrient enrichment interacted antagonistically to increase survival in longear sunfish; and stressors acted synergistically on grazers causing a trophic cascade that increased periphyton variables. Because stressors can directly and indirectly impact biota—and that the same stressor pairing can act differentially on various portions of the community simultaneously—our broad understanding of individual stressors might not adequately inform our knowledge of multi-stressor systems.

Pesticides drive differential leaf litter decomposition and mosquito colonisation dynamics in lentic conditions

Global contamination of freshwater ecosystems by chemical compounds, such as pesticides, may exert high pressure on biologically-driven organic matter decomposition. These pollutants may also impair the quality of organic substrates for colonising invertebrates and reduce primary productivity by decreasing the abundance of phytoplankton. In southern Africa, increasing pesticide usage associated with macadamia plantations, in particular, presents a growing risk to freshwater ecosystems. Here, we examined macadamia (Macadamia integrifolia) leaf litter decomposition following exposure to three pesticides (i.e., Karate Zeon 10 CS (lambda-cyhalothrin), Mulan 20 AS (acetamiprid), Pyrinex 250 CS (chlorpyrifos)) used commonly in macadamia plantations, via an ex-situ microcosm approach. We examined mosquito colonisation of these microcosms as semi-aquatic macroinvertebrates which form a significant component of aquatic communities within standing waters. Macadamia leaf litter tended to decompose faster when exposed to Karate and Pyrinex pesticide treatments. Additionally, chlorophyll-a, conductivity, total dissolved solids, and pH differed among pesticide treatments and controls, with pesticides (Karate Zeon and Mulan) tending to reduce chlorophyll-a concentrations. Overall, pesticide treatments promoted mosquito (i.e., Culex spp.) and pupal abundances. In terms of dominant aquatic mosquito group abundances (i.e., Anopheles spp., Culex spp.), the effect of pesticides differed significantly among pesticide types, with Pyrinex and Mulan treatments having higher mosquito abundances in comparison to Karate Zeon and pesticide-free treatments. These findings collectively demonstrate that common pesticides used in the macadamia plantation may exert pressure on adjacent freshwater communities by shaping leaf-litter decomposition, semi-aquatic macroinvertebrate colonisation dynamics, and chlorophyll-a.

The importance of shell debris for within-patch heterogeneity and disturbance-recovery dynamics of intertidal macrofauna

Shell debris increases habitat diversity and ecological heterogeneity, stabilizing sediments and providing substrate for encrusting and epifaunal animals and protection against predation. However, how shell debris influences disturbance-recovery dynamics in different habitats has not been evaluated. We experimentally tested the effects of shell debris on early colonization of macroinvertebrates into defaunated patches across 12 sites along a mud-to-sand gradient. The addition of shell debris enhanced species richness compared to plots without shells and increased variability in the local contributions to beta-diversity, mostly at the muddier sites. The variation in the strength of these effects along the mud gradient highlights the effects of shell debris on community structure and how the muddying of coastal sediments shifts species composition. Loss of shellfish and burying of shells with elevated rates of sedimentation diminishes the role of small-scale sediment heterogeneity for sustaining beta-diversity in low-energy environments.

Invasive fish (Gambusia affinis) as an ecological filter for macroinvertebrate colonization of experimental ponds

Invasive predators might serve as ecological filters for prey communities, either through non-consumptive or consumptive effects. The Western Mosquitofish (Gambusia affinis [Baird and Girard, 1853]) is an invasive non-native fish that affects native aquatic communities, potentially because of effects on oviposition or initial colonization of habitats (non-consumptive effects), post-colonization effects (i.e., consumptive effects), or a combination of both non-consumptive and consumptive effects. We conducted a mesocosm experiment to examine non-consumptive and consumptive effects of G. affinis on colonization of experimental ponds by native macroinvertebrates. We predicted that, if G. affinis affects macroinvertebrates through non-consumptive effects, there would be lower abundances in both the non-lethal (caged G. affinis) and lethal (free-ranging G. affinis) treatments compared to the control (no G. affinis), whereas, if the effect of G. affinis is primarily due to consumptive effects, there would be lower abundances of macroinvertebrates in the lethal treatment compared to the non-lethal and control treatments. Most macroinvertebrate taxa (dytiscid beetles, baetid Ephemeroptera, corixid and gerrid hemipterans, libellulid odonates) were less abundant, or even absent, in the presence of G. affinis in the lethal treatment compared to their abundance in the non-lethal G. affinis treatment; however, notonectids were not affected by treatment. The invasive fish predator, G. affinis, therefore, can act as an ecological filter for macroinvertebrates in invaded aquatic habitats, primarily through lethal consumptive effects.

Effect of substrates of native and exotic plant species on the initial period of colonization of benthic macroinvertebrates in the Cerrado biome

The introduction of exotic species can generate changes in the composition of organic debris of alien origin in aquatic ecosystems close to the places of introduction. This new debris can cause impacts at the level of communities and ecosystems. Therefore, the present work aims to answer the following question: are the macroinvertebrate communities present in substrates formed by leaves of the exotic species Pinus caribaea Morelet (Pinaceae) and Eucalyptus grandis Hill ex Maiden (Myrtaceae) similar to those found in substrates composed by the mix of these two species and substrates composed by a mix of native species? For the collection of macroinvertebrates, sets of four types of artificial substrates were submerged in a stream inside the Ecological Station of Panga (Uberlândia—MG, Brazil). The treatments were: leaves of P. caribaea, leaves of E. grandis, leaves of both exotic species and leaves of two native species. In the 20 sample units, about 250 individuals were found, belonging to the orders Coleoptera, Diptera, Ephemeroptera, Heteroptera, Megaloptera, Odonata, Plecoptera and Trichoptera. The effects of the treatments were observed in the exponential decay of the substrate mass and in the structure of the benthic macroinvertebrates communities. The composition of these communities differed among treatments, with high dissimilarity observed between P. caribaea treatments and the mix of exotic species. Therefore, the results demonstrate the importance of substrate complexity for benthic macroinvertebrates, as well as the possible effects of biological invasion and co-invasion by species widely used in silviculture activities.

Controles extrínsecos e intrínsecos en la descomposición de hojas de tres especies de árboles pioneros comunes en quebradas de bajo orden en los Andes Centrales de Colombia

ABSTRACT Riparian forests provide high amounts of leaf litter to tropical headwater streams (1–3 order) and its decomposition is controlled by interactions between leaf quality and macroinvertebrate activity. However, few studies have been conducted in North Andean streams. We conducted a leaf litter decomposition experiment using three native tree species (Heliocarpus americanus, Nectandra sp., and Cecropia telealba) in two headwater streams in the Colombian Coffee-growing Eco-Region. The interactive roles of intrinsic factors (quality) and extrinsic factors (presence/absence of macroinvertebrates) on decomposition rates were tested. Three single-species treatments, a species-mixture treatment, and an artificial substrate treatment were incubated in either coarse-pore mesh or fine-pore mesh bags to allow or exclude macroinvertebrate colonization, respectively. Bags were removed from the streams 7, 14, 28 and 56 days after starting the study. Toughness and chemical quality of senescent leaves of each species were determined in order to test their effect on the decomposition rates. The k-values for the three single-species and the species-mixture treatments indicated that decomposition occurred at medium to fast rates (0.009–0.01 day−1). H. americanus showed the greatest mass loss at the end of the trial, followed by C. telealba and Nectandra sp. Leaf toughness was positively correlated with carbon-to-nitrogen ratio (C: N) and carbon-to-phosphorus ratio (C: P) and, in turn, the three characteristics were negatively correlated with breakdown rate. A total of 3876 individuals from 13 orders, 35 families, and 47 genera colonized leaf-litter bags. Chironomidae, Lumbriculidae, and Hydropsychidae were the families with the highest abundance. The abundance and richness of macroinvertebrates in the leaf-litter bags showed no correlation with the descriptors of intrinsic characteristics (leaf quality). These results indicate that among the three tree-species in the study, the intrinsic characteristics of senescent leaves determine their mass loss rates, while the macroinvertebrate abundance or richness play a secondary role, probably due to the fact that shredders were not abundant.

Freshwater crabs (Decapoda: Pseudothelphusidae) increase rates of leaf breakdown in a neotropical headwater stream

Abstract Freshwater crabs are the largest macroconsumers in many neotropical headwater streams, but few studies have examined their roles in ecosystem processes such as leaf litter breakdown. As omnivorous macroconsumers, freshwater crabs affect multiple trophic levels. They may directly increase leaf breakdown through fragmentation and consumption or indirectly decrease breakdown by consuming other macroinvertebrates, including shredders and detritivores. In a headwater stream in Monteverde, Costa Rica, we conducted an in‐stream experiment with 40 enclosures to quantify the effects of pseudothelphusid crabs on both leaf breakdown and macroinvertebrate colonisation of leaves. Half of the enclosures were randomly selected to contain two crabs (mean carapace width = 30 mm) and half were controls without crabs. We sampled mixed leaf packs from the enclosures on days 11, 19, 28, 34, and 42. We found the leaves of one species (Koanophyllon pittieri) almost completely decomposed by day 28 in both treatments (crab versus no crab). The other two leaf species (Meliosma idiopoda, Quercus brenesii) composed the remaining leaf mass at the end of the experiment. At 42 days, enclosures with crabs had faster rates of leaf breakdown than those without crabs (with crabs: k = −0.020; without crabs: k = −0.016; p = 0.034). This suggests that the magnitude of direct leaf breakdown by crabs, due to fragmentation, consumption, or manipulation of leaves, was greater than any indirect effects on leaf breakdown via crab consumption of other leaf‐consuming species. Macroinvertebrate composition based on taxa abundances or biomasses did not significantly differ between treatments (ANOSIM; p = 0.73 and p = 0.65, respectively). Shredder and detritivore abundances and biomasses increased significantly through time (ANOVA; p ≤ 0.001), but there was no evidence of an effect of crab presence (p > 0.2), nor were there significant interactions between crab presence and time (p > 0.3). This is one of the first studies to quantify the effects of pseudothelphusid freshwater crabs on leaf breakdown rates. Our results suggest that these crabs can play a significant role in detrital processing in neotropical headwater streams. This study has also demonstrated that short‐term enclosure experiments are useful in measuring in‐stream effects of crab activity on leaf breakdown.

Macroinvertebrate community patterns in relation to leaf‐associated periphyton under contrasting light and nutrient conditions in headwater streams

AbstractTemperate headwater streams traditionally have been considered heterotrophic and brown food web dominated with little primary production. Recent work, however, suggests algae on leaves in these streams may play a greater role than previously thought through interactions with microbial decomposers like fungi. Algae also may be important for macroinvertebrates colonizing leaves in streams. Algae are a more nutritious food resource for shredders than fungi and bacteria and provide a food resource for non‐shredder macroinvertebrates.In a field experiment, we manipulated light in three low‐nutrient and three high‐nutrient streams using leaf bags filled with red maple leaves in winter and spring. After four weeks we measured algal and fungal biomass, leaf stoichiometry, and macroinvertebrate abundance and biomass associated with the leaf bags. We also identified the macroinvertebrate community and examined differences in functional feeding guilds and taxa under ambient‐ and shaded‐light treatments and low‐ and high‐nutrient concentrations in relation to measured leaf characteristics.Algal biomass on leaves was greatest in high‐nutrient streams and ambient‐light treatments in both seasons. Fungal biomass on leaves was greatest in high‐nutrient streams and showed a moderate marginally significant positive correlation with algae during the winter. Leaf C:N was negatively correlated to algae in winter and fungi in both seasons, while leaf N:P and C:P were negatively correlated to fungi in winter and algae in spring. Interactions between fungi and algae on leaves and the nutritional importance of each for macroinvertebrates likely change across seasons, potentially impacting macroinvertebrate community composition.Macroinvertebrate diversity did not differ, but biomass was significantly greater in shaded‐light treatments during spring. Abundance was highest in the high‐nutrient ambient‐light conditions in both seasons, corresponding to greatest algal biomass. Functional feeding guild biomass and abundance were related to different leaf characteristics by season and guild. Higher algal biomass was an important factor for colonization of certain macroinvertebrates (e.g.,Ephemerella(Ephemeroptera: Ephemerellidae) andStenonema(Ephemeroptera: Heptageniidae)), while others were more abundant under shaded treatments with lower algal biomass (e.g.,Tipula(Diptera: Tipulidae)), indicating taxa‐specific responses.Leaf‐associated algae may be an important factor mediating macroinvertebrate communities associated with leaves in temperate headwater streams. Our results demonstrate that green and brown food webs intersect within leaf packs, and they cannot be easily disentangled. We therefore should consider both autochthonous and allochthonous resources within headwater streams when examining their communities or developing water management strategies.

Macroinvertebrate colonisation associated with native and invasive leaf litter decomposition

Lake and reservoir ecosystems are regarded as heterotrophic detritus-based habitats which are dependent on both autochthonous and allochthonous organic matter for the majority of energy inputs. In particular, allochthonous detritus is in particular important for the trophic dynamics of microbial organisms, macroinvertebrates and benthic plants in freshwaters. Here, we assess macroinvertebrate colonisation, and quantify decomposition rates, of leaf litter from species of native and invasive plants in a small agricultural reservoir. Native fig Ficus sycomorus and silver cluster–leaf Terminalia sericea were compared to invasive tickberry Lantana camara and guava Psidium guajava, whereby macroinvertebrate colonisation was assessed over time. Leaf treatments had a significant, group-specific effect on abundances and composition among focal macroinvertebrates. Invasive leaves reduced Physidae and Oligochaeta abundances, yet Ostracoda were significantly more abundant in the presence of invasive P. guajava. Chironomidae relative abundances increased under invasive L. camara treatments, whilst differences among leaf treatment effects on Coenogrionidae abundances were not statistically clear. In turn, macroinvertebrate diversity did not differ significantly among plant treatment groups. The decomposition rate of the leaf litter demonstrated differences among the species, following a decreasing order of L. camara > F. sycomorus > T. sericea > P. guajava. The study results highlight that leaf litter species identity among invasive and native plants plays an important role in the colonisation of macroinvertebrates in small reservoirs, thereby differentially supporting aquatic environments and food webs. However, differences were not uniform across invader-native groupings. Nonetheless, certain invasive leaf litter decomposes faster than native litter, with possible implications for broader nutrient dynamics and subsequent community composition.

First record of Pantala flavescens (Anisoptera: Libellulidae) from the remote Amsterdam Island, southern Indian Ocean

Natural colonization of macroinvertebrates into the Sub-Antarctic area is generally accepted to be a rare event. In February 2017, two live adults of Pantala flavescens (Libellulidae) were recorded on the isolated Amsterdam Island (37°50′ S, 77°30′ E), southern Indian Ocean. This circumtropical species, common name the Globe Skimmer, can fly several thousand kilometers. This paper analyzes the weather conditions in this sector of the Indian Ocean in February 2017 to assess the probability of arrival of the dragonflies by air from their known migration route at lower latitudes between India and East Africa. The probability that this species could establish and form a permanent population on Amsterdam Island is discussed. Some favorable habitats are present but temperatures are probably too low to allow the dragonflies to complete their development. Odonata have never been observed on Sub-Antarctic islands and reports of natural arrival of insects into these islands mainly concern Lepidoptera. Here we also report observations of Vanessa cardui (Nymphalidae) which has established a permanent population on Amsterdam Island and has been observed on several occasions in the Crozet Archipelago.

The effect of large predators on the decomposition rate and the macroinvertebrate colonization pattern of leaves in a Mediterranean stream

The goal of this study is to experimentally assess the possible effect of macroinvertebrate predators on the decomposition rate of leaves in a Mediterranean stream and to analyze the pattern of colonization by macroinvertebrates of the litter bags through time. We designed a factorial experiment with three types of litter bags (allowing the entrance of no macroinvertebrates, only small macroinvertebrates and small and large, top‐predators, macroinvertebrates). We measured the percentage of ash‐free dry mass remaining after 15, 30, and 45 days, as well as the macroinvertebrate community composition of the two types of litter bags where they were allowed to enter. We did not find differences in the ash‐free dry mass remaining between the two types that allowed the entrance of macroinvertebrates. The diversity of the community colonizing each type of litter bag was always relatively high and changed significantly with time and, in some cases, with the exclosure treatment studied. These results show the absence of important top‐down control of macroinvertebrates and particularly in those involved in the leaf decomposition in the food web of this Mediterranean stream that could have repercussions on the leaf decomposition process.

Levantamento da fauna de macroinvertebrados associados à macrófitas aquáticas

In aquatic ecosystems, the presence of macrophytes offers survival conditions for colonization of macroinvertebrates. This study aimed to characterize the fauna of macroinvertebrates associated with Pistia stratiotes L. (Araceae), in the Capivaras Lagoon, located inside the Baguaçu Ecological Park, in the municipality of Araçatuba, and to relate them to the physical and chemical parameters of the water. The sampling of P. stratiotes was in three points; the samples were sorted and later identified. It was observed a high density of Oligochaeta and Chironomidae larvae in the three points sampled, which may be related to the higher capacity of these organisms tolerate adverse environmental conditions, such as the low concentration of oxygen dissolved in the water obtained in the physical-chemical analyzes. The small lake has a history of pollution and currently suffers from low levels of oxygenation and infestation of P. stratiotes forming a long "rug" enclosed throughout its cover. Considering find solutions to recover the integrity of the environment and,, mainly, to recover the oxygenation of the water, it is suggested more investigations in the area, in several areas and the drainage of the inlet and outlet water channel of the lagoon, beyond the drainage of input and output of water of the lagoon, to improve the rapid circulation, avoiding the establishment of large banks of aquatic macrophytes.

Evaluating the effect of macroinvertebrate exclusion on leaf breakdown rates in two upland Colombian streams

Macroinvertebrate shredders have been widely recognized as an important functional feeding group that contributes to leaf decomposition in temperate streams, but little is known about their role in upland Neotropical streams. In this study, we investigated the effect of macroinvertebrate exclusion on leaf breakdown rates in two upland streams (Marianela and Peña Bonita with 1 911 and 2 560 m elevation, respectively) in Colombia. We hypothesized that leaf litter breakdown is mediated mainly by macroinvertebrate shredders in Colombian upland streams. The study was carried out between January and April of 2009, including the dry season and the beginning of the wet season. We measured leaf mass loss using coarse- (15 mm; accessible to macroinvertebrates) and fine- (200 µm; macroinvertebrates excluded) mesh litter bags that were anchored with wood stakes to the bottom of each stream and recovered after 7, 14, 21, 28, and 56 days. We selected leaves from two dominant plant species and used three leaf treatments: two single species (Palicourea cuatrecasasii and Critoniopsis ursicola) and mixed-species (P. cuatrecasasii and C. ursicola). We compared leaf breakdown rates between the Peña Bonita and Marianela stream, mesh-sizes, and leaf treatments. Macroinvertebrates that colonized the litter bags were measured for density and biomass and categorized in functional feeding groups. In general, there were no significant differences in breakdown rates between the streams and the mesh-sizes. In contrast, leaf breakdown rates had significant differences between all leaf species, where C. ursicola had higher breakdown rates than mixed-species, and P. cuatrecasasii. Macroinvertebrate exclusion did not affect leaf breakdown rates and their assemblages were composed by high densities of collectors (mainly Chironomidae) and few shredders with a large body size. The similar macroinvertebrate colonization between leaf species, the relatively slow breakdown rates, and the shredder scarcity, suggest that leaves were a refractory substrate. Further studies should include leaf species with different nutritional qualities and larger spatial-temporal scales to test the hypothesis of shredder presence and its role on leaf decomposition in upland Colombian streams.

Relationship between leaf litter decomposition and colonization of benthic macroinvertebrates during early frost period in a headwater stream in the Changbai Mountains, Northeast China

Annually, about 70% of the streams in the Changbai Mountains are frosted during November to April, with manifest seasonal freeze-thaw characters. By using monoculture and mixing leaf litters of Tilia amurensis, Acer mono and Quecus mongolica, this research attempted to disentangle the relationship between leaf litter decomposition and colonization of macroinvertebrates in the stream during early frost period. A 35-day investigation was carried out in a headwater stream of the Changbai Mountains. Nylon bags with two hole sizes (5 mm and 0.3 mm) were used to examine decomposition of the litters. The results showed that the mass losses were significantly different among the three kinds of leaf litters in monoculture, whose decomposition rates descended as A. mono, T. amurensis, and Q. mongolica, however, there existed no significant difference among the litter mixing. Mass losses in both mesh bags all showed little difference, except T. amurensis and the mixed litters. Litter mixing effects occurred in the coarse mesh bags with A. mono and Q. mongolica, but no mixture effects for others. Community structures of the macroinvertebrates colonizing in the litter bags differed with each other, but shredders' density had no significant difference among the three litters, and the mixing effects on shredders were poor. Our results implied that microbes play the major decomposers of leaf litters, and macroinvertebrates contribute little to the decomposition in the early frost period. Despite shredder's density is lower, they determine the mixing effects of litters. Macroinvertebrates are selective to food and habitats, however, due to the short term colonizing, and the influence of leaf litters on shredders is still unsure. Our results might contribute to understanding the cold season ecological processes and related management issues of headwater stream ecosystem.