Fine-mesh Bags Research Articles

Plant detritus origin and microbial–detritivore interactions affect leaf litter breakdown in a Central Apennine (Italy) cold spring

The decomposition of dead organic matter is a key process for the metabolism and functioning of lotic ecosystems. Particulate organic matter from fallen leaves is the main source of energy input also in forested springs. However, detritus processing in spring habitats has been rarely investigated. The present paper is aimed to assess, for the first time, the influence of detritus origin on leaf litter breakdown in a hydrologically, thermally and chemically stable cold spring and to evaluate the relative contribution of microorganisms and invertebrate detritivores to the decomposition process. For this purpose, we used leaves of the native black poplar (Populus nigra) and the invasive common reed (Phragmites australis) enclosed in leaf-bags of different mesh sizes. We demonstrated that leaf detritus of native black poplar decomposed twofold faster than the invasive common reed. We also found that the percentage of dry mass loss was significantly higher in medium/coarse litter bags compared to fine ones. However, microorganisms alone in fine mesh bags were able to decompose about 80% (poplar) and 60% (common reed) of the initial dry mass. No substantial differences were detected in structure, composition and functional organization of assemblages colonizing poplar and common reed leaf-bags. Therefore, differences in microbial activity and microbial/detritivore interactions rather than composition, diversity and abundance of the detritivore guild could better explain the faster breakdown of native leaves. Our results suggest that the substitution of natural riparian vegetation with invasive low-quality leaf plant species will have severe impacts on spring ecosystems. Alterations of structural and functional attributes of springs will be strictly related to the specific characteristics of plant invaders and to local conditions which may influence the detritivore/microbial contribution to leaf litter decomposition/breakdown.

Characterization of the reproductive performance of a collection of grapevine cultivars

Genetic, physiological and environmental factors interact to determine the number of flowers in the inflorescence and the fruitset rate of grapevine. Abnormal behavior in reproductive performance may cause coulure or millerandage, which may affect yield. In this work, the reproductive performance of a set of 120 wine-grape and table-grape cultivars was studied in two consecutive growing seasons (2016 and 2017). Reproductive performance was measured in ten inflorescences from different plants in each cultivar. It included flower number per inflorescence, berry number per bunch, fruitset rate, coulure index, and millerandage index. The number of flowers per inflorescence was estimated from the number of flower caps collected in fine mesh bags set just before bloom. After flowering, flower caps from each individual bag were scanned and the digital images were used for manual or automatic counting, using a specially dedicated tool developed with ImageJ software. The same clusters used for flower counting, conveniently tagged, were cropped at harvest time, and several bunch components were measured. The average fruitset rate among all the cultivars was about 44%. The range of variation among cultivars was very high for fruitset, more than 90% every year. Differences in fruitset between seasons were also very variable among cultivars, with an average difference of around 9-10% and a range of 0-40%. Regarding coulure and millerandage, there was also great variability among cultivars, while, between seasons, they were stable: on average, about 1 point of difference on a scale of 0-10. The results obtained for these reproductive performance variables allowed us to establish a preliminary clustering of the cultivars in three separate classes. The high variability found for these key parameters between grapevine cultivars provides a very suitable base to study the genetic processes involved in grapevine reproductive performance.

The outcome of an exclusion experiment depends on the method: shrimps, shredders and leaf breakdown in a tropical stream

The study of detrital food webs of streams has revealed a variety of dynamics, often implying the importance of invertebrate fauna in the breakdown of leaves and sometimes showing effects of predators and trophic cascades. Such studies generally involve the experimental manipulation of the component leaves and fauna. Leaf breakdown (or ‘processing’) is often studied by isolating leaves in litter bags, which in turn can have different mesh sizes used to exclude or permit the action of fauna. Such manipulation always carries the risk of introducing experimental artefacts, and care and appropriate controls must be applied. More recently and less commonly, electrical exclusion has been used for such studies, which potentially reduces the artefacts produced by bags, but care must be taken not to introduce other artefacts. Here we compared bag-exclusion and electrical-exclusion in a study of the effects of shredding fauna and predators on leaf processing in a coastal, tropical stream. The methods differentially excluded fauna of different sizes: high-intensity electrical shocks and fine-mesh (0.2 mm) bags excluded medium and large invertebrates; low-intensity shocks and medium-sized mesh (2 mm) bags excluded principally 2 species of shrimps (Macrobrachium olfersii and Potimirim brasiliana); no electric shocks and large mesh-size mesh (14 mm) bags permitted access to all fauna. Leaf packs of 2 species (Erythroxylum pulchrum and Miconia prasina) were either tethered free of bags in the electrical treatments or tied inside bags. The rate of leaf processing was higher (1.9–2.5×) for tethered leaves than for leaves inside bags indicating bags inhibited processing. The type of exclusion markedly affected differences in leaf processing between treatments. Leaf processing was 1.6 to 2.3× faster in the presence of medium-sized fauna in the treatment with the low-intensity electricity than when they were excluded by high-intensity electricity but was 1.9 to 2.0× faster in coarse-mesh bags, in which Potimirim shrimps aggregated at densities ~100× those observed outside bags, compared with treatments where the mesh size excluded shrimps. In the electrical exclusions, large fauna (possibly Macrobrachium shrimps) apparently inhibited medium-sized fauna (Ephemeroptera:Leptophlebiidae) in Erythroxylum but not in Miconia, producing a trophic cascade and reduced leaf processing. We conclude that the bag method produced artificially low rates of leaf processing and altered the dynamics of the fauna associated with leaf processing by attracting fauna, principally large shrimp, into the bags and masking the action of medium-sized fauna.

Seasonal variations overwhelm temperature effects on microbial processes in headwater streams: insights from a temperate thermal spring

Carbon cycling in headwater streams is mostly driven by the decomposition of allochthonous organic matter, and to a lesser extent by primary production. Quantifying the influence of temperature on these processes is therefore essential to better anticipate the consequences of global warming for stream ecological functioning. In this study, we measured alder litter microbial decomposition and associated fungal biomass and diversity, using leaf discs enclosed in fine-mesh bags along a natural geothermal temperature gradient, in both spring and winter. We monitored the chlorophyll-a accrual in biofilms growing on ceramic tiles. The temperature gradient, from upstream to downstream, ranged from 15.3 to 14.2 °C in spring and 18.2 to 13.2 °C in winter. Autotrophs and heterotrophs exhibited contrasting responses to temperature. The expected positive effect of temperature was actually observed for chlorophyll-a accrual only, while an apparent temperature-independence of litter decomposition rate was found. Moreover, temperature effects on heterotrophic and autotrophic organisms depended on the season, with higher litter decomposition rates, sporulation rates, fungal biomass and chlorophyll-a in spring, despite a lower mean water temperature than in winter. Together, these results suggest that the influence of temperature remained largely overrode by seasonal effects. This result is likely due to annual variations in light availability, and may involve indirect positive interactions between microbial primary producers and decomposers.

Leaf litter decomposition in Guinean savannah streams

ABSTRACTLow-order streams of Upper Guinea receive substantial leaf litter inputs and are characterized by intermittent flow. The ecosystem functioning of such streams flowing in savannah, a common tropical vegetation and the dominant biome in West Africa, remains largely overlooked. We hypothesized litter decomposition in such streams to be (1) fast due to the expectedly high nutrient content of tropical litter, and (2) mostly driven by microorganisms due to the widely revealed paucity of tropical macroinvertebrate consumers, and even exacerbated in these systems by water temporariness. Decomposition rates of 2 common riparian tree species, Alchornea cordifolia and Pterocarpus santalinoides, in 2 streams ranged from 0.0287 to 0.0649 d−1. The process was clearly governed by microbial decomposers, as shown by the exceptionally low mass loss discrepancy between fine and coarse mesh bags, a lack of shredders, and high leaf-associated fungal biomass (measured as ergosterol: up to 0.92 and 0.37 mg g−1 litter of ash-free dry mass for Alchornea and Pterocarpus, respectively), together with moderate conidial production rate. In such savannah streams, the absence of leaf-shredding invertebrates seems to be compensated by a high microbial activity, providing an ultimate case for the reported preponderance of microbial decomposers over invertebrate decomposers at low latitudes. In contrast with temperate temporary streams, the processing of leaf litter from riparian trees, characterized by high nitrogen and phosphorus content, is sufficiently fast to be unaffected by flow intermittency.

Contribution of aquatic shredders to leaf litter decomposition in Atlantic island streams depends on shredder density and litter quality

It has been widely reported that shredders play an important role in leaf decomposition, especially in continental temperate streams. However, the paucity of shredders in many oceanic island streams leads to a greater contribution of microbes to litter decomposition in these streams. In this study, we investigated the importance of shredder presence and density (three levels) and leaf litter identity (Alnus glutinosa, Clethra arborea and Acacia melanoxylon) on leaf litter decomposition in one stream located in the Azores Archipelago. Coarse and fine mesh bags were used to allow natural colonisation of leaf litter by benthic macroinvertebrates or to exclude macroinvertebrates respectively. Treatments with one and three shredders were accomplished by enclosing one or three shredders in the fine mesh bags. Rates of litter decomposition differed significantly among shredder density treatments only for A. glutinosa and C. arborea. Decomposition rates were significantly faster for the natural within-stream shredder density treatment than for other shredder treatments. Shredder density differed significantly among litter species, being higher in A. glutinosa than in C. arborea and A. melanoxylon. The results indicate that when shredders are present at high densities in oceanic island streams they can substantially contribute to the decomposition of high-quality leaf litter, whereas the decomposition of hard leaf litter is mostly performed by the microbial community.

Leaf litter decomposition as a bioassessment tool of acidification effects in streams: Evidence from a field study and meta-analysis

Atmospheric acid deposition affects many streams worldwide, leading to decreases in pH and in base cations concentrations and increases in aluminum (Al) concentration. These changes in water chemistry induce profound changes in the diversity, structure and activity of biological communities and in ecosystem processes. However, monitoring programs rely only on chemical and structural indicators to assess stream integrity. Nevertheless, the ability of ecosystems to provide services rely on their functional integrity and thus ecosystem processes should be considered in monitoring programs. We assessed the potential for leaf litter decomposition, a fundamental ecosystem process in forest streams, to be used as a bioassessment tool of acidification effects on stream ecosystem functioning. In a field study in the Vosges Mountains (North-eastern France), using three leaf litter species (Alnus glutinosa, Acer pesudoplatanus and Fagus sylvatica) enclosed in fine and coarse mesh bags and incubated in streams flowing over granite or sandstone bedrock along an acidification gradient, we assessed if the response of litter decomposition to acidification depended on litter species, mesh size, parent lithology and acidification level. In a meta-analysis of 17 primary studies on the effect of acidification on leaf litter decomposition, reporting 67 acidified – reference stream comparisons, we assessed the consistency in the response of litter decomposition to acidification cross studies and the robustness of litter decomposition to be used as a bioassessment tool. Both the field study and meta-analysis revealed an overall strong inhibition (>60%) of leaf litter decomposition in acidified streams likely resulting from previously well described altered decomposer community structure and activity. No effect of leaf species was found in the field study, while in the meta-analysis inhibition of leaf litter decomposition in acidified streams was stronger for Fagus than for Acer, Quercus and Liriodendron. However, differences among leaf species in the meta-analysis might have been confounded by other differences among studies. The response of leaf litter decomposition to acidification was stronger in coarse than in fine mesh bags, indicating strong impairment of detritivore community structure and activity. The magnitude of inhibition also depended on parent lithology, but this is likely related to differences in the degree of acidification. Indeed, the magnitude of the inhibition of leaf litter decomposition increases with increases in H+ in Al concentration. Litter decomposition has the potential to be used as a bioassessment tool of acidification effects in streams since it shows consistent response to acidification across regions and is robust to experimental choices.

Descomposición de hojas y colonización de macroinvertebrados acuáticos en dos microcuencas tropicales (Manizales, Colombia)

Nutrient fluxes in low-order streams of both tropical and temperate regions depend on leaves and tree branches originated from their riparian forests. This substratum suffers physical, chemical and biological breakdown, and can be colonized by several benthic macroinvertebrates. However, the effect of different levels of disturbance and degradation operating on these forested streams such as livestock in cattle-dominated landscapes, remains poorly understood, this is particularly noticeable in many mountain areas of Colombia. Goals. To evaluate the breakdown rates and colonization dynamics of benthic macroinvertebrates on leaves of Eucalyptus sp. and Tibouchina lepidota in tropical streams immersed into livestock matrices. Methods. During March to May 2014, we conducted a field experiment using single and mixed (1:1) leaf treatments of both plant species into fine- and coarse-mesh litterbags, in two contrasting streams (reference [La Elvira]/ disturbed [Chuscales]) of the Chinchina River in central Colombia (Manizales, Caldas). Results. Leaf mass losses were significantly higher in Eucalyptus sp., followed by the mixed (1:1) and T. lepidota treatment into coarse vs. fine mesh bags. However, the higher decomposition rates (k days-1, mean ± SE) were registered at La Elvira for Eucalyptus sp. (fine mesh, k = - 0.0145 ± 0.0026; coarse mesh, k = - 0.0143 ± 0.0019) and, Chuscales for the mixed treatment (fine, k = - 0.0181 ± 0.0053; coarse, k = - 0.0153 ± 0.0046), comparatively. Contrary, macroinvertebrate abundance and density were generally higher in reference than in disturbed stream, and concomitantly to the diversity. However, these variables changed over the sampled period, with higher abundance values registered at 30 days (1129 individuals) and 45 days (958 individuals) in the reference and disturbed stream, respectively. Chironomids and the collectors’ functional feeding group were the most abundant during all sampling. Conclusions. The results showed that breakdown rate differences between streams cannot be attributed specifically to changes in macroinvertebrate community composition, structure or density and that mesh size more than the livestock effect can influence macroinvertebrate communities colonizing in-stream organic matter; however, further studies are necessary to confirm these results.

Factors controlling bark decomposition and its role in wood decomposition in five tropical tree species.

Organic matter decomposition represents a vital ecosystem process by which nutrients are made available for plant uptake and is a major flux in the global carbon cycle. Previous studies have investigated decomposition of different plant parts, but few considered bark decomposition or its role in decomposition of wood. However, bark can comprise a large fraction of tree biomass. We used a common litter-bed approach to investigate factors affecting bark decomposition and its role in wood decomposition for five tree species in a secondary seasonal tropical rain forest in SW China. For bark, we implemented a litter bag experiment over 12 mo, using different mesh sizes to investigate effects of litter meso- and macro-fauna. For wood, we compared the decomposition of branches with and without bark over 24 mo. Bark in coarse mesh bags decomposed 1.11–1.76 times faster than bark in fine mesh bags. For wood decomposition, responses to bark removal were species dependent. Three species with slow wood decomposition rates showed significant negative effects of bark-removal, but there was no significant effect in the other two species. Future research should also separately examine bark and wood decomposition, and consider bark-removal experiments to better understand roles of bark in wood decomposition.

Drought and detritivores determine leaf litter decomposition in calcareous streams of the Ebro catchment (Spain)

Drought, an important environmental factor affecting the functioning of stream ecosystems, is likely to become more prevalent in the Mediterranean region as a consequence of climate change and enhanced water demand. Drought can have profound impacts on leaf litter decomposition, a key ecosystem process in headwater streams, but there is still limited information on its effects at the regional scale. We measured leaf litter decomposition across a gradient of aridity in the Ebro River basin. We deployed coarse- and fine-mesh bags with alder and oak leaves in 11 Mediterranean calcareous streams spanning a range of over 400km, and determined changes in discharge, water quality, leaf-associated macroinvertebrates, leaf quality and decomposition rates. The study streams were subject to different degrees of drought, specific discharge (Ls−1km−2) ranging from 0.62 to 9.99. One of the streams dried out during the experiment, another one reached residual flow, whereas the rest registered uninterrupted flow but with different degrees of flow variability. Decomposition rates differed among sites, being lowest in the 2 most water-stressed sites, but showed no general correlation with specific discharge. Microbial decomposition rates were not correlated with final nutrient content of litter nor to fungal biomass. Total decomposition rate of alder was positively correlated to the density and biomass of shredders; that of oak was not. Shredder density in alder bags showed a positive relationship with specific discharge during the decomposition experiment. Overall, the results point to a complex pattern of litter decomposition at the regional scale, as drought affects decomposition directly by emersion of bags and indirectly by affecting the functional composition and density of detritivores.

Influence of soil faunal properties and understory fine root on soil organic carbon in a “mesh bag” approach

The obstruction of fine mesh bag has been widely applied to study the functions of plant fine roots and soil fauna in ecosystems. However, plant fine roots and soil fauna can both be either excluded from the soil within fine mesh bags or admitted into the soil without mesh bags or within coarse mesh bags, because of their similar ranges of body width. As a result, both their effects could be influenced by fine mesh bags. In this study, we investigated the effects of soil fauna and understory fine roots on soil organic carbon, with a special type of fine mesh bags designed for obstructing the growth of understory fine roots into soil with free access of soil fauna. Results showed that both the biomass of understory fine roots and soil faunal diversity along with soil total carbon and microbial biomass carbon were significantly reduced by the fine mesh bags (P < 0.01). Boosting regression tree models showed that the understory fine roots contributed more in the variations of soil organic carbon than soil faunal properties. Faunal biodiversity represented by Pielou’s evenness index was more important than taxa richness and individual abundances of taxa. Results suggest that understory fine roots may be more influential in soil organic carbon than faunal factors, and both their functions could be influenced by fine mesh bags in a mesh bag study. Evenness of individual abundances between taxa could be more important than taxa richness for the influence of soil fauna community on soil organic carbon.

Differences in the sensitivity of fungi and bacteria to season and invertebrates affect leaf litter decomposition in a Mediterranean stream.

Microorganisms are key drivers of leaf litter decomposition; however, the mechanisms underlying the dynamics of different microbial groups are poorly understood. We investigated the effects of seasonal variation and invertebrates on fungal and bacterial dynamics, and on leaf litter decomposition. We followed the decomposition of Populus nigra litter in a Mediterranean stream through an annual cycle, using fine and coarse mesh bags. Irrespective of the season, microbial decomposition followed two stages. Initially, bacterial contribution to total microbial biomass was higher compared to later stages, and it was related to disaccharide and lignin degradation; in a later stage, bacteria were less important and were associated with hemicellulose and cellulose degradation, while fungi were related to lignin decomposition. The relevance of microbial groups in decomposition differed among seasons: fungi were more important in spring, whereas in summer, water quality changes seemed to favour bacteria and slowed down lignin and hemicellulose degradation. Invertebrates influenced litter-associated microbial assemblages (especially bacteria), stimulated enzyme efficiencies and reduced fungal biomass. We conclude that bacterial and fungal assemblages play distinctive roles in microbial decomposition and differ in their sensitivity to environmental changes, ultimately affecting litter decomposition, which might be particularly relevant in highly seasonal ecosystems, such as intermittent streams.

Seasonal Variability May Affect Microbial Decomposers and Leaf Decomposition More Than Warming in Streams.

Ongoing climate change is expected to affect the diversity and activity of aquatic microbes, which play a key role in plant litter decomposition in forest streams. We used a before-after control-impact (BACI) design to study the effects of warming on a forest stream reach. The stream reach was divided by a longitudinal barrier, and during 1year (ambient year) both stream halves were at ambient temperature, while in the second year (warmed year) the temperature in one stream half was increased by ca. 3°C above ambient temperature (experimental half). Fine-mesh bags containing oak (Quercus robur L.) leaves were immersed in both stream halves for up to 60days in spring and autumn of the ambient and warmed years. We assessed leaf-associated microbial diversity by denaturing gradient gel electrophoresis and identification of fungal conidial morphotypes and microbial activity by quantifying leaf mass loss and productivity of fungi and bacteria. In the ambient year, no differences were found in leaf decomposition rates and microbial productivities either between seasons or stream halves. In the warmed year, phosphorus concentration in the stream water, leaf decomposition rates, and productivity of bacteria were higher in spring than in autumn. They did not differ between stream halves, except for leaf decomposition, which was higher in the experimental half in spring. Fungal and bacterial communities differed between seasons in both years. Seasonal changes in stream water variables had a greater impact on the activity and diversity of microbial decomposers than a warming regime simulating a predicted global warming scenario.

Effects of mesh bag enclosure and termites on fine woody debris decomposition in a subtropical forest

The role of insects in terrestrial decomposition remains poorly resolved, particularly for infrequently studied substrates like small diameter woody debris. Uncertainty about how mesh bags used to exclude arthropods may affect decomposition rates continues to impede progress in this area. We sought to (1) measure how insects affect the decomposition of small diameter (<2.5cm) Triadica sebifera L. “twigs” and (2) test for unintended effects of mesh bags on wood decomposition using machined wooden dowels of similar size and specific gravity. In subtropical forests, three twig diameter classes plus dowels were enclosed in two mesh sizes (0.3 or 1mm openings) or left unenclosed over a 20-month study period. Unenclosed twigs lost significantly more mass than those within fine mesh bags. Because this effect was consistent throughout the study (reaching nearly 80% mass loss), our findings suggest the invertebrate influence does not disappear or attenuate over time. Our dowel data (limited to dowels with no evidence of insect activity) show that fine and coarse mesh bags accelerate the decomposition of enclosed woody material, suggesting insects contributed even more to the decomposition of tallow twigs than our measure of 9 – 10%. Termites exhibited a strong preference for larger diameter twigs, resulting in temporary differences in decomposition rates among diameter classes. Our findings confirm the importance of insects to wood decomposition and highlight the need to incorporate these organisms in models of carbon and nutrient cycling.

Litter breakdown for ecosystem integrity assessment also applies to streams affected by pesticides

While the impact of various anthropogenic alterations, e.g. nutrient enrichment, has been docu- mented on leaf litter breakdown - a key process for stream ecosystems -, our objective was to assess the response of this process to pesticides in agricultural streams. We hypothesized the impairment to be correlated with the pesticides contamination gradient, and the invertebrate decomposers to be more affected than microbial ones. Alder total breakdown rate was found to strongly decrease along the pesticide con- centration in 12 French streams, only due to inverte- brate-driven breakdown (as determined in coarse- mesh bags) since microbial-driven breakdown (fine-mesh bags) remained unchanged. Coherently, litter-associated shredder taxa richness and abundance together with SPEARpesticide (a specific indicator based on invertebrate traits) were greatly reduced, whereas pesticide toxicity did not affect litter-associated fungal biomass and taxa richness. Consequently, the presence of pesticides compromised leaf breakdown, as microbial decomposers did not compensate for the invertebrate decomposers decline. This occurred while pesticides concentrations even in the most contaminated stream were under the European Union’s Uniform Principles thresholds for targeted species. Our study showed that litter breakdown, particularly the ratio of total to microbial-driven breakdown rate, is a pertinent proxy to assess the functional integrity of pesticide-contaminated streams.

Microbial colonisation and litter decomposition in a Cerrado stream are limited by low dissolved nutrient concentrations

Microbial colonisation and litter decomposition in a Cerrado stream are limited by low dissolved nutrient concentra- tions Litter decomposition in the streams of the Brazilian Cerrado (Savannah) is generally slow. In this study, we tested the hypothesis that leaf litter decomposition is limited by low dissolved nutrient availability. We measured the decomposition of the litter of the riparian species Protium heptaphyllum in a local stream under nutrient enrichment promoted by nutrient- diffusing substrates (nutrient-enriched treatment; N and P), and under control conditions (no added nutrients). Leaves were enclosed in fine (0.5 mm) mesh bags and immersed in the stream. Replicate samples were retrieved periodically over 56 days. At the end of the experiment, leaf mass loss, associated microbial biomass (ATP and ergosterol) and fungal sporulation rates were significantly higher in nutrient-enriched bags than in control bags. These results suggest that litter decomposition in certain Cerrado streams is partially limited by the low availability of dissolved nutrients.

Long-term consequences of a wildfire for leaf-litter breakdown in a Mediterranean stream

AbstractWildfire frequency and intensity are expected to increase as a result of climate change, but few studies have assessed the effects of wildfires on stream ecosystem processes. The aim of our study was to examine the long-term responses of leaf-litter breakdown to wildfire in a Mediterranean stream. Riparian canopy cover was reduced by a fire, resulting in higher temperatures and light levels and reduced leaf-litter inputs in the stream 8 y after the fire. Benthic invertebrate communities recovered quickly after the fire, and the abundances of different functional feeding groups (FFGs), including shredders, were not different between streams affected and unaffected by the fire after >2 postfire years. We compared microbially mediated (fine-mesh bags) and total breakdown rates (coarse-mesh bags) of Populus alba leaf litter incubated in the stream affected by the wildfire and a neighboring control stream. Microbial and total leaf-litter breakdown were faster in the stream affected by fire. Faster micr...

Abundance and diversity of gastropods associated with dominant subtidal macroalgae from the western Antarctic Peninsula

Gastropod assemblages associated with eight common macroalgae from the hard-bottom subtidal communities near Palmer Station, western Antarctic Peninsula, were investigated in order to establish a species inventory and determine abundance, distribution, and diversity. Four different sites within the area were sampled. Using SCUBA, selected algae were gently removed from the substrate and enclosed in a fine mesh bag. Shortly thereafter, all epibionts were removed and preserved. Twenty-one different gastropod taxa were identified, two of which not to species level. A total of 3486 individuals were quantified with Skenella umbilicata the numerically dominant, followed by Laevilacunaria antarctica and Eatoniella calignosa. Most individuals (86 %) were <0.5-mm shell length; the largest specimens did not exceed 20-mm shell length. No difference in gastropod species abundance or species diversity was observed between the algal species. Mean densities of a given species of gastropod associated with a given algal species ranged from 0 to 38 individuals per 100 g wet wt of sampled alga with no discernable pattern of algal host preference. Additionally, no consistent pattern of gastropod community composition with either associated macroalgal species or collection site was demonstrated with a non-metric multidimensional scaling analysis. Gastropods may, however, work in concert with other epibionts, in particular amphipod assemblages, to in some way benefit the host alga. Specifically, gastropods may contribute to enhancing the photosynthetic capacity of the host alga by grazing upon fouling epiphytic microalgae and emerging endophytic filaments.

Potential Impact of Halyomorpha halys (Hemiptera: Pentatomidae) on Grape Production in the Finger Lakes Region of New York

New York State is the leading grape producer in the eastern US and third leading grape producer in the US. The generalist feeding invasive species Halyomorpha halys (Stål) is currently present in NY, although at relatively low densities. Our aim in this study was to determine how H. halys will affect grape production in NY if it becomes well established. We measured the impact of density, sex, and life stage of H. halys on Concord and Chardonnay grapevines by enclosing insects on a single grape cluster using a fine mesh bag. The insects remained caged on the clusters for 2 wk during and after the period of fruit set, after which damaged and undamaged berries were enumerated nondestructively. At this point, we found a strong positive correlation between density and both number and percentage of berries damaged for both nymphs and adults. In late summer, at harvest time, clusters were removed from the vines, damaged and undamaged berries were once again counted, and berries were weighed. Cluster weight for both Chardonnay and Concord cultivars decreased with increased density of adults. Furthermore, adult females were found to have a greater effect than adult males. In contrast to adult feeding, nymphs were found to have little impact on cluster weight. There was relatively little incidence of disease as a result of H. halys feeding. These results show that H. halys is potentially an economic threat to the grape industry in cool-climate regions, but only at high densities currently not observed.

Effects of insect and decapod exclusion and leaf litter species identity on breakdown rates in a tropical headwater stream.

High species richness of tropical riparian trees influences the diversity of organic detritus entering streams, creating temporal variability in litter quantity and quality. We examined the influence of species of riparian plants and macroinvertebrate exclusion on leaf-litter breakdown in a headwater stream in the Luquillo Mountains of Puerto Rico. Leaf litter of Dacryodes excelsa (Burseraceae), Guarea guidonia (Meliaceae), Cecropia scheberiana (Moraceae), Manilkara bidentata (Sapotaceae), and Prestoea acuminata (Palmae) were incubated in litter bags in a pool of Quebrada Prieta. Fine mesh bags were used to exclude macroinvertebrates during leaf breakdown, and coarse mesh bags allowed access to decapod crustaceans (juvenile shrimps and crabs) and aquatic insects (mainly mayflies, chironomids, and caddisflies). D. excelsa and G. guidonia (in coarse- and fine-mesh bags) had significantly higher breakdown rates than C. scheberiana, M. bidentata, and P. acuminata. Breakdown rates were significantly faster in coarse-mesh bag treatments for all leaf types, thus indicating a positive contribution of macroinvertebrates in leaf litter breakdown in this headwater stream. After 42 days of incubation, densities of total invertebrates, mayflies and caddisflies, were higher in bags with D. excelsa and G. guidonia, and lower in P. acuminata, C. scheberiana y M. bidentata. Decay rates were positively correlated to insect densities. Our study highlights the importance of leaf identity and macroinvertebrate exclusion on the process of leaf litter breakdown in tropical headwater streams.