Leaf Litter Processing Research Articles

Leaf Litter Translocation and Consumption in Mangrove Ecosystems: the Key Role Played by the Sesarmid Crab <i>Neosarmatium malabaricum</i>

Nutrient cycling in mangrove forests is strongly linked to detrital processing of leaf litter, as compared to direct herbivorous consumption. Sesarmid crabs play a key role in detrital pathways in mangrove forests by processing a large amount of leaf litter produced in the ecosystem. We studied the rate of leaf litter translocation and consumption by a sesarmid crab, Neosarmatium malabaricum , through an ex situ experiment simulating field conditions. We supplied weighed senescent leaves of Aegiceras corniculatum, Avicennia officinalis , Excoecaria agallocha and Rhizophora mucronata to the crab. When provided separately, the crab translocated leaf litter of E. agallocha the maximum, and that of Rhizophora mucronata the minimum to the burrows. When litter mixed together was provided, the rate of translocation was the highest. The crabs consumed up to 80.24% of the litter that they translocated. We found this species capable of translocating 4.39 ±1.68 g of leaf litter m -2 per day and that its population had the potential to translocate 1.81 times more leaf litter than the ecosystem produced, based on comparisons of translocation rate, density of N. malabaricum and leaf litter production in the study area. Our experiments emphasize the key role played by this crab in detrital pathways of mangrove ecosystem.

The impact of the invasive amphipod Dikerogammarus haemobaphes on leaf litter processing in UK rivers

The impact of invasive gammaridean species on native biodiversity is well documented, but the potential for them to disrupt ecosystem functioning is less well understood. Native freshwater amphipods are considered to be archetypal leaf shredders and are considered key to leaf litter processing within rivers. It is possible that invasions may interfere with key ecosystem processes such as leaf litter breakdown, due to behavioural traits displayed by the invasive species. In two laboratory experiments, we compared the leaf shredding efficiency of the native Gammarus pulex and Dikerogammarus haemobaphes, a recently established Ponto–Caspian invader in the UK. We hypothesised that in isolation G. pulex would have a greater shredding efficiency than D. haemobaphes and that, in the presence of the invasive, leaf shredding and survival of G. pulex would be reduced. The results supported our hypothesis that, in isolated conditions, G. pulex consumed significantly more leaves than D. haemobaphes. Under mixed treatments, G. pulex leaf consumption and survival, although not statistically significant, appeared to be reduced. The implications of our findings suggest that the potential displacement of G. pulex from its native range, by D. haemobaphes, could lead to a decline in leaf litter processing and recycling in rivers within the UK.

Phagotrophic protists are a key component of microbial communities processing leaf litter under contrasting oxic conditions

Summary The transformation of leaf litter, a key process in aquatic systems, is known to be reduced with decreasing oxygen concentrations, mainly due to lower abundance of and/or less active shredding macroinvertebrates. Aquatic fungi and phagotrophic protists involved in leaf litter processing can tolerate low oxygen, but little is known about their role in leaf litter processing under these conditions. We aimed to unravel the importance of phagotrophic protists within microbially mediated leaf litter processing under contrasting oxic conditions. We hypothesised that respiration, abundance of aquatic bacteria and biomass of aquatic fungi, and thus leaf litter processing, are enhanced in the presence of phagotrophic protists, both under normoxic and low oxic conditions. Lower leaf processing was expected under low oxic than under normoxic conditions. In microcosms, oxygen concentration was adjusted to either normoxic or low. For a total of 105 days, leaf litter was cocultivated with three microbial communities: (i) a multispecies bacterial community enriched from stream leaf litter, (ii) the aquatic fungus Heliscus lugdunensis added to the bacterial community and (iii) the phagotrophic protist Glaucoma scintillans added to the bacteria–fungi community. Oxic condition had no significant effect on microbially mediated leaf mass loss. The leaf mass loss was faster in the presence of the aquatic fungus and further accelerated by adding the phagotrophic protist. After 105 days, leaf mass remaining approximated 64–79%, 57–68% and 55–61% of initial leaf mass in the bacteria, bacteria–fungi, and bacteria–fungi–phagotrophic protist communities, respectively. Under both oxic conditions, the lower leaf toughness indicated that the aquatic fungus had the potential to process leaf structural components more efficiently than bacteria alone. The combination of lower ergosterol concentrations and enhanced leaf mass loss indicated that phagotrophic protists stimulated the efficiency of leaf processing by the microbial community. Under normoxic conditions, leaf‐associated respiration increased when successively adding an aquatic fungus and a phagotrophic protist to bacterial communities, which matches the faster leaf litter processing in these treatments. Under low oxic conditions, respiration of all three microbial communities was comparable. Thus, enhanced leaf litter processing in treatments with aquatic bacteria, fungi and phagotrophic protists was presumably caused either by other metabolic pathways such as fermentation and anaerobic respiration, or by changes in community composition and growth efficiency of the microbial community. Microbial communities composed of aquatic bacteria, fungi and phagotrophic protists play a crucial role in leaf litter processing under a range of oxic conditions. Although processing of leaf litter by microbial communities alone is slower than in the presence of shredding invertebrates, the interaction of aquatic bacteria, fungi and phagotrophic protists can modulate leaf quality and subsequently carbon flow within the microbial food webs of aquatic ecosystems.

Effects of riparian forest management on Chilean mountain in-stream characteristics

We assessed the effect of forest management practices on temporal differences in riparian litterfall input and autumnal leaf litter processing of 3 evergreen plant species, using independently 2 mesh sizes (for two of the three species), between two contrasting headwater streams draining (a) near-pristine and (b) harvested evergreen old-growth forests in Chile (39°S). Additionally, we compared rainfall, streamflow, suspended sediment concentration, and the in-stream invertebrate community, collected two years after logging in the harvested microcatchment. The harvested forested stream had higher runoff, suspended sediment concentration and input of litter (3377kgha−1yr−1) than the pristine stream (3166kgha−1yr−1). However, leaf-litter decay rates were faster for the pristine (ranging from k=−0.0120 to −0.0024day−1) than for the harvested forest stream (k=−0.0049 to −0.0023day−1) depending on leaf species and litterbag type. Likewise, the pristine stream revealed higher shredder taxa richness than harvested stream, suggesting a higher correlation with the decomposition rate and leaf mass losses. Therefore, the results of our study suggest that despite the implementation of best management practices on riparian forests, there are detectable shifts in the structure and functioning of aquatic invertebrate community in the Andean streams of south-central Chile.

Procesado de hojarasca en arroyos del Parque Nacional de la Sierra de Guadarrama (Madrid)

Le af litter breakdown in streams of Sierra de Guadarrama National Park (Madrid) The main goal of this study was to identify the main drivers of natural variability of leaf litter processing in six well preserved Mediterranean mountain streams in the Sierra de Guadarrama, through the analysis of the breakdown rates of alder litter, content and dynamics of leaf nutrients, and associated fungal and invertebrates communities. In general, breakdown rates of alder leaves, both exponential (k = 0.013± 0.005 dd –1 , k ′ = 0.041± 0.011 d –1 ) and lineal (b = 0.470± 0.121% PSLC dd –1 , b ′ = 1.522± 0.153% PSLC d –1 ) were very high. Variability in breakdown rates among streams was not correlated to environmental characteristics (discharge, slope or water temperature) neither to stream water characteristics (nutrient concentration, pH, or conductivity). This may be due to the low environmental heterogeneity observed among these streams and also because the physical factors that could regulate this process were outweighed by biological processes that mask them. The highest breakdown rates were recorded in the coldest waters where the activity of decomposers aquatic fungi was very low (measured by sporulation rates, 98.36±148.84 conidia mg –1 PSLC d –1 ), suggesting that consumer invertebrates played a key role in the faster leaf litter processing rates in these sites. Family richness (13.67±3.44 fam. bag –1 ) and macroinvertebrate density (25.33±10.42 ind bag –1 ), as well as shredder density (16.17±7.44 ind bag –1 ) did not show any relationship with the breakdown rates (p> 0.100, neither linear nor exponential rates). A positive relationship was only found between percentage of leaf litter lost and abundance of Limnephilidae (p< 0.010), that pointed out a higher relevance of shredder traits than their total abundance. Limnephilidae are caddisfly shredders adapted to low thermal regimes, they have large body and are able to feed on unconditioned litter debris and poor colonized by aquatic hyphomycetes, which seem to exert a decisive control over leaf litter processing rate in this type of aquatic ecosystems. Therefore, we can suppose that in colder headwater mountain streams consumer macroinvertebrates (shredders) might have a major relevance in the processing of litter debris whereas decomposers (aquatic hyphomycetes) would play an increasing role in warmer streams.

Effects of density and predation risk on leaf litter processing by Phylloicus sp.

AbstractThe allochthonous detritus that accumulates in the substrate of streams is used by aquatic invertebrate shredders for shelter and food. Shredders are considered rare in tropical systems, and little information is available about the role of density effects and predation risk (associated with the perception of predators by prey) in relationship to the resources used by these organisms. The aim of this study was to examine experimentally the effects of increased predation risk and of the density of Phylloicus sp. (i.e. of two types of biological relationships) on the processing of the leaf litter of Nectandra megapotamica (Spreng.) Mez. Phylloicus sp. can use leaf litter for case building and as a food resource. The density effect was measured using four treatments that differed only in the number of individuals (one, two, three or four). A second experiment with five treatments was performed to test the risk of non‐lethal predation on detritus consumption (shelter and food) by Phylloicus sp. (T1: Caddisfly; T2: Mayfly; T3: Astyanax sp./fish; T4: Damselflies; T5: Stonefly). A single Phylloicus and one other organism (a potential predator blocked with 0.5 mm fine mesh) were placed in each tank (0.002 m3 volume). We observed a negative effect of density on per capita litter consumption (experiment 1). The low density of Phylloicus may be a natural factor that decreases intraspecific competition. In the presence of fish, Phylloicus showed the lowest amount of litter processing observed in the experiment, indicating top‐down control (experiment 2). In treatments that involved the presence of invertebrates (non‐predatory and predatory), Phylloicus showed the highest amount and an intermediate amount of leaf litter processing, respectively (experiment 2). This observation also suggests that the predation effect is more probable for specific predator–prey pairs. Population density and predation risk in Phylloicus may be important factors controlling leaf litter processing.

The profile of a ‘perfect’ invader – the case of killer shrimp, Dikerogammarus villosus

The ‘killer shrimp’, Dikerogammarus villosus, has been recognised as one of the 100 worst alien species in Europe, in terms of negative impacts on the biodiversity and functioning of invaded ecosystems. During the last twenty years, this Ponto-Caspian amphipod crustacean has rapidly spread throughout Europe’s freshwaters and its invasion and continued range expansion represents a major conservation management problem. Although a great deal of research has focussed on this almost ‘perfect’ invader as its damaging impacts, realised and potential, have become evident, we now present the first comprehensive review of D. villosus taxonomy, morphology, distribution, community impacts, parasites, life history, physiological tolerance and finally, possible eradication methods. We show the direct and indirect ecosystem impacts of this invader can be profound, as it is a top predator, capable of engaging in a diverse array of other feeding modes. It can quickly dominate resident macroinvertebrate communities in terms of numbers and biomass, with subsequent large-scale reductions in local biodiversity and potentially altering energy cycling, such as leaf litter processing. This damaging European invader has the potential to become a key invader on a global scale as it may be capable of reaching North American freshwaters, such as the Great Lakes. One positive aspect of this invader’s spread and impact is increased interest in alien species research generally, from decision-makers, stakeholders and the general public. This has resulted in greater financial support to study invasion mechanisms, preventative measures to stop invasion spread and ways to minimise damaging impacts. Our review provides a specific example, that studies identifying management strategies that mitigate against a potential invader’s spread should be undertaken at the earliest possible opportunity in order to minimise potentially irreversible ecosystem damage and biodiversity loss.

Litter processing and shredder distribution as indicators of riparian and catchment influences on ecological health of tropical streams

Terrestrial plant litter is the main source of energy for food webs in forest headwater streams. Leaf litter quality often changes when native tree species are replaced by exotic ones and land use change in the watershed can alter physico-chemistry and functional composition of invertebrate communities, ultimately impairing associated ecosystem processes. We used the composition of invertebrate functional feeding groups (FFGs) and the ecosystem process of leaf breakdown as structural and functional indicators, respectively, of ecosystem health in upland Kenyan streams. During dry and wet conditions, invertebrates were sampled in 24 streams within forest (10), mixed (7) and agriculture (7) catchments. Five forest and five agriculture streams were subsequently used for leaf litter breakdown experiments using two native (Croton macrostachyus and Syzygium cordatum) and one exotic (Eucalyptus globulus) species differing in quality. Coarse- and fine-mesh litterbags were used to compare microbial (fine-mesh) with shredder+microbial (coarse-mesh) breakdown rates, and by extension, determine the role of shredders in litter processing in these streams. Seasonal influences on water quality were observed across catchment land uses. Total suspended sediments, turbidity and total dissolved nitrogen were consistently higher during the wet than dry season. However, seasonal influences on FFGs were inconsistent. Catchment land use influenced invertebrate functional composition: 21 taxa, including eight shredders, were restricted to forest streams, but abundance was a poor discriminator of disturbance. Breakdown rates were generally higher in coarse- compared with fine-mesh litterbags for the native leaf species and the relative differences in breakdown rates among leaf species remained unaltered in both agriculture and forest streams. Shredder and microbial breakdown of leaf litter displayed contrasting responses with shredders relatively more important at forest compared with agriculture streams. However, these patterns were inconsistent across leaf species over the dry and wet seasons. Overall, shredder mediated leaf litter breakdown was dependent on leaf species, and was highest for C. macrostachyus and lowest for E. globulus. This suggests that replacement of indigenous riparian vegetation with poorer quality Eucalyptus species has the potential to reduce nutrient cycling in streams, with foodwebs becoming more reliant on microbial processing of leaf litter, which cannot support diverse consumers and complex food webs.

Effects of flow scarcity on leaf-litter processing under oceanic climate conditions in calcareous streams

Although temporary streams represent a high proportion of the total number and length of running waters, historically the study of intermittent streams has received less attention than that of perennial ones. The goal of the present study was to assess the effects of flow cessation on litter decomposition in calcareous streams under oceanic climate conditions. For this, leaf litter of alder was incubated in four streams (S1, S2, S3 and S4) with different flow regimes (S3 and S4 with zero-flow periods) from northern Spain. To distinguish the relative importance and contribution of decomposers and detritivores, fine- and coarse-mesh litter bags were used. We determined processing rates, leaf-C, -N and -P concentrations, invertebrate colonization in coarse bags and benthic invertebrates. Decomposition rates in fine bags were similar among streams. In coarse bags, only one of the intermittent streams, S4, showed a lower rate than that in the other ones as a consequence of lower invertebrate colonization. The material incubated in fine bags presented higher leaf-N and -P concentrations than those in the coarse ones, except in S4, pointing out that the decomposition in this stream was driven mainly by microorganisms. Benthic macroinvertebrate and shredder density and biomass were lower in intermittent streams than those in perennial ones. However, the bags in S3 presented a greater amount of total macroinvertebrates and shredders comparing with the benthos. The most suitable explanation is that the fauna find a food substrate in bags less affected by calcite precipitation, which is common in the streambed at this site. Decomposition rate in coarse bags was positively related to associated shredder biomass. Thus, droughts in streams under oceanic climate conditions affect mainly the macroinvertebrate detritivore activity, although macroinvertebrates may show distinct behavior imposed by the physicochemical properties of water, mainly travertine precipitation, which can override the flow intermittence effects.

Effects of invasive European bird cherry (Prunus padus) on leaf litter processing by aquatic invertebrate shredder communities in urban Alaskan streams

European bird cherry (Prunus padus) (EBC) is an invasive ornamental tree that is spreading rapidly in riparian forests of urban Alaska. To determine how the spread of EBC affects leaf litter processing by aquatic invertebrate shredders, we conducted complementary leaf pack experiments in two streams located in Anchorage, Alaska. The first experiment contrasted invasive EBC with three native tree species—thin-leaf alder (Alnus tenuifolia), paper birch (Betula neoalaskana), and black cottonwood (Populus trichocarpa)—in one reach of Chester Creek; finding that EBC leaf litter broke down significantly faster than birch and cottonwood, but at a similar rate to alder. The second experiment contrasted EBC with alder in four reaches of Campbell and Chester creeks; finding that while EBC leaf litter broke down significantly faster than alder in Chester Creek, EBC broke down at a similar rate to alder in Campbell Creek. Although EBC sometimes supported fewer shredders by both count and mass, shredder communities did not differ significantly between EBC and native plants. Collectively, these data suggest that invasive EBC is not currently exhibiting strong negative impacts on leaf litter processing in these streams, but could if it continues to spread and further displaces native species over time.

Do omnivorous shrimp influence mayfly nymph life history traits in a tropical island stream?

Interspecific interactions can play an important role in determining habitat selection and resource use between competing species. We examined interactions between an omnivorous shrimp and a grazing mayfly, two co-dominant taxa found in Puerto Rican headwater streams, to assess how predator presence may influence mayfly resource use and instantaneous growth in a tropical rainforest ecosystem. We conducted a series of behavioral and growth experiments to determine the effects of the freshwater shrimp, Xiphocaris elongata, on the growth rate and resource selection of mayfly nymphs in the family Leptophlebiidae. For resource choice assessments, we conducted a series of five day laboratory experiments where mayflies were given access to two resource substrate choices (cobble vs. leaves) in the presence or absence of shrimp. To assess for the effects of shrimp on mayfly fitness, we measured mayfly growth in laboratory aquaria after five days using four treatments (cobble, leaves, cobble + leaves, no resource) in the presence or absence of shrimp. In resource choice experiments, mayflies showed preference for cobble over leaf substrata (p < 0.05) regardless of the presence of shrimps, however, the preference for cobble was significantly greater when shrimp were present in the leaf habitat. In growth experiments, there were no statistical differences in mayfly growth in the presence or absence of shrimp (p = 0.07). However, we measured increased mayfly nymph growth in the absence of predators and when both cobble and leaves were available. Our results suggest that interspecific interactions between these taxa could potentially influence organic matter resource dynamics (e.g., leaf litter processing and export) in Puerto Rican streams.

Land use effects on leaf litter breakdown in low-order streams draining a rapidly developing tropical watershed in Puerto Rico.

Land use has an important role influencing stream ecosystem processes, such as leaf litter breakdown. Here, we assessed rates of leaf litter breakdown in low-order tropical streams draining forest, agriculture, and urban land uses in Puerto Rico. To measure leaf breakdown rates, we placed litter bags made of coarse mesh in nine streams, three for each land use type. At each stream, we measured changes in leaf mass over time, leaf breakdown rates, macroinvertebrate assemblages, and stream physicochemistry. Streams differed in their water physicochemistry, with urban streams showing high values for most variables. Stream physical habitat was evaluated using a visual assessment protocol, which indicated that agricultural and urban streams were more degraded than forested streams. Leaf breakdown rates were fast in all streams (k values ranging 0.006-0.024). Breakdown rates were significantly related to the physical conditions of the stream channel (e.g., visual protocol scores), with fastest rates in forested streams. Invertebrates colonizing leaves were mainly mayflies (Leptophlebiidae, Baetidae, and Caenidae), dipterans (Chironomidae), caddisflies (Polycentropodidae), and beetles (Elmidae and Gyrinidae). Our streams lacked large decapod populations, contrasting with other Puerto Rican streams. We found little evidence for an insect effect on leaf breakdown. Results suggest that land use is an important factor affecting leaf litter processing in streams. In contrast to studies in temperate regions, we found little evidence for a positive nutrient related effect of agricultural land use on decomposition rates. Changes in the physical characteristics of streams appear to be the main drivers behind observed decomposition patterns.

Competitive displacement alters top-down effects on carbon dioxide concentrations in a freshwater ecosystem

Climate change and invasive species have the potential to alter species diversity, creating novel species interactions. Interspecific competition and facilitation between predators may either enhance or dampen trophic cascades, ultimately influencing total predator effects on communities and biogeochemical cycling of ecosystems. However, previous studies have only investigated the effects of a single predator species on CO2 flux of aquatic ecosystems. In this study, we measured and compared the individual and joint effects of predatory damselfly larvae and diving beetles on total prey biomass, leaf litter processing, and dissolved CO2 concentrations of experimental bromeliad ecosystems. Damselfly larvae created strong trophic cascades that reduced CO2 concentrations by ~46% relative to no-predator treatments. Conversely, the effects of diving beetles on prey biomass, leaf litter processing, and dissolved CO2 were not statistically different to no-predator treatments. Relative to multiplicative null models, the presence of damselfly larvae and diving beetles together resulted in antagonistic relations that eliminated trophic cascades and top-down influences on CO2 concentrations. Furthermore, we showed that the antagonistic interactions between predators occurred due to a tactile response that culminated in competitive displacement of damselfly larvae. Our results demonstrate that predator identity and predator-predator interactions can influence CO2 concentrations of an aquatic ecosystem. We suggest that predator effects on CO2 fluxes may depend on the particular predator species removed or added to the ecosystem and their interactions with other predators.

红树林湿地相手蟹科动物摄食生态研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 红树林湿地相手蟹科动物摄食生态研究进展 DOI: 10.5846/stxb201301160110 作者: 作者单位: 国家海洋局第三海洋研究所,国家海洋局第三海洋研究所,国家海洋局第三海洋研究所,厦门大学,国家海洋局第三海洋研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41206108，41076049）；福建省自然科学基金项目（2011J05111）；海洋公益性行业科研专项项目（201205008） Feeding ecology of sesarmid crabs in mangroves Author: Affiliation: Third Institute of Oceanography, State Oceanic Administration,Third Institute of Oceanography, State Oceanic Administration,Third Institute of Oceanography, State Oceanic Administration,Xiamen University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:相手蟹科物种是红树林湿地的主要底栖动物类群，在生态系统中起着重要的作用。我国大陆地区目前已记录的相手蟹科物种数量为12种，低于其它红树林地区（国内常用的采样方法会造成螃蟹物种数量和密度的低估），其中褶痕相手蟹（Sesarma plicata）、无齿相手蟹（S. deaani）和双齿相手蟹（S. bidens）等是常见种。红树植物叶片是相手蟹科动物的主要食物来源，相手蟹科动物通过地表摄食和洞穴贮存的形为消耗了大量的红树植物凋落叶，使这些凋落叶的有机质和营养元素得以保留在生态系统内，在凋落叶的周转和物质归还方面起到重要的作用。它们同时也摄食红树植物的繁殖体并且对不同物种的繁殖体具有摄食偏好，这可能对一些红树物种的植被更新能力和红树植被群落结构产生影响。相手蟹科动物对不同物种和不同状态的红树叶片也存在摄食偏好，通常对腐烂的叶片摄食偏好较强；螃蟹的摄食偏好与叶片的营养成份、粗纤维和单宁含量以及C/N比等性质有关；但在恶劣的野外环境下，螃蟹则会表现出随机性摄食。目前关于相手蟹科动物生态学作用的认识仍不充分，例如它们的种群大小和对凋落物的转化作用等，有待于进一步研究。 Abstract:Sesarmid crabs, common macro invertebrates in mangrove ecosystems, influence the structure and function of mangrove habitats through their burrowing activities and processing of leaf litter. A total of 12 sesarmid species have been recorded in mainland China, which may be an underestimate since more sesarmid species have been reported in Hong Kong and other tropical mangrove regions. (The reason for this underestimation could be due to the method commonly used to locate the crabs within mainland China. The most common method used is to place plot frame on the soil surface and simply dig to about 20-30 cm, and sift through the soil to locate crabs which could allow sesarmid crabs to escape deeper into the soil during the digging.) The most common sesarmid species in China are Sesarma plicata, S. deaani and S. bidens, while Neosarmatium meinerti is widely recorded in tropical areas of Australia and Kenya. Mangrove plant tissues, mainly leaves, are the main food source of sesarmid crabs, but crabs also feed on sediment detritus and faunal tissue to supplement the nutrient limited mangrove leaves. Some dietary specializations among different mangrove crabs have been recognized. Some crabs feed on only live leaves obtained by climbing into trees, while some species feed only on dead leaves on the mangrove floor. Crabs also have frequently been observed burying fallen mangrove leaves, to enhance leaf nutrition quality, prevent leaf litter from being removed by tidal flushing and avoid competition and predation when food or time available for collecting food is limited, and predator abundance is high. The feeding preference of sesarmid crabs for mangrove leaves with different conditions or from different mangrove species also has been reported from the laboratory and the field research. For example, sesarmid crabs in China prefer leaves of Kandelia candel over those of Bruguiera gymnorrhiza and Aegiceras corniculatum. Leaf characteristics such as C/N ratio, tannin, water and crude fiber contents determine the feeding preferences. Generally, sesarmid crabs prefer decomposed leaves, ascribed to the decreased tannin content and C/N ratio, and increases in water during leaf decomposition. It also has been suggested that crabs need to consume more decomposed leaves to obtain adequate C and N since they have lower C and N assimilation rates from those leaves. Feeding preferences have been more often demonstrated in laboratory studies while some field studies have revealed a lack of selective feeding of different mangrove species. This is probably due to the environmental stresses in field like predation, limited feeding time, and limited food availability. The ability of sesarmid crabs to remove leaf litter has been studied frequently in the past decades, and crabs have been shown to consume a large proportion of annual leaf fall production, far in excess of the local production in some mangrove forests. The ability of crabs to remove litter seems to be stronger in tropical areas than in subtropical or warm temperate areas. In subtropical areas like China, removal of leaf litter is affected by temperature and showed significant seasonal variation. Not only sesarmid crabs but some snails (e.g. Terebralia palustris) and ocypodoid/grapsid crabs (e.g. Helograpsus haswellianus and Ucides cordatus) also have been reported to consume mangrove leaves. Direct grazing of leaf litter by crabs accounts for a small proportion of leaf litter removed from mangrove floor in China, while the stocking of leaves in crab burrows for later consumption is the key way by which leaf litter is retained in the ecosystem, preventing tidal export. Through shredding and grazing of leaf litter, crabs also initiate and enhance the breakdown of mangrove detritus and recycling of nutrients. Sesarmid crabs also have been found to graze mangrove propagules and seeds, thus play a critical role in determining seedling recruitment and vegetation regeneration. It also has been suggested that the predation preference on some non-dominant mangrove species regulates their distribution with the vegetation community. The feeding ecology of sesarmid crabs and its involvement of in mangrove restoration, their retention of C and nutrients in mangrove soils and predation of seeds/propagulse are worthy further studies. 参考文献 相似文献 引证文献

Interactive effects of aluminium and phosphorus on microbial leaf litter processing in acidified streams: A microcosm approach

Decline in pH, elevated aluminium (Al) concentrations, and base cations depletion often covary in acidified headwater streams. These parameters are considered as the main factors reducing microbial activities involved in detritus processing, but their individual and interactive effects are still unclear. In addition to its direct toxicity, Al can also reduce the bioavailability of phosphorus (P) in ecosystems through the formation of stable chemical complexes. A three week microcosm experiment was carried out in acid conditions to assess the interactive effects of Al (three levels: 0, 200, and 1000 μg L−1) and P (25, 100, and 1000 μg L−1) on alder leaf litter processing by an aquatic hyphomycete consortium. Our results showed that Al alone reduced fungal growth and altered fungal decomposer activities. High P levels, probably through an alleviation of Al-induced P limitation and a reduction of Al toxic forms, suppressed the negative effects of Al on detritus decomposition.

Diet of the freshwater crab Bottiella niceforei (Schmitt & Pretzmann, 1968) (Decapoda: Trichodactylidae) and its relationship with organic matter processing in an intermittent stream of northwestern Venezuela

In order to study the role of the freshwater crab Bottiella niceforei in processing the organic matter in an intermittent stream of northwestern of Venezuela, we studied its natural diet by analyzing the gut contents during the period between June 2009 and February 2010. The abundance was determined based upon the proportion of individuals captured by traps throughout all the sampling period and on each pool. The highest crab densities occurred in September (2.7 ind trap-1), followed by June (2.3 ind trap-1) and July (2.1 ind trap-1); while the lowest were obtained in November and February, possibly due to the erosive effect of the current during the rainy season. No significant differences in the abundance and diet between pools were found. During the period from June to November it was found that the most abundant item in the crab diet was the plant detritus, with an average of 68%, followed by animal matter (fish remains), 50% on the average, and amorphous vegetal detritus with 14%. These results demonstrate the important participation of B. niceforei on the leaf litter processing in the pools of cano Carichuano.

Leaf-litter processing in headwater streams of northern Iberian Peninsula: moderate levels of eutrophication do not explain breakdown rates

Agricultural and urban runoffs result in increased nitrogen and phosphorus inputs in rivers and are the cause of eutrophication. Headwater streams are less frequently affected by these impairments because of the low-to-moderate human activities there. Eutrophication can affect the structure and function of benthic communities in headwater streams, stimulating the activity of heterotrophic microorganisms and macroinvertebrates on a pivotal process such as leaf-litter decomposition. In this study, we monitored the breakdown of alder leaves in six headwater streams that constitute a moderate nutrient enrichment gradient. Breakdown experiments were conducted in autumn–winter and leaf carbon, nitrogen and phosphorus, and associated aquatic hyphomycetes and macroinvertebrates were determined. The increase in nutrient availability in the stream water enhanced leaf-litter quality and led to an increase in the hyphomycete assemblage evenness and a reduction of shredder densities. However, contrary to our expectations, dissolved nutrient availability did not explain the breakdown rates. Thus, the absence of a clear effect of nutrient enrichment of stream water on the leaf breakdown rate highlights the difficulties of predicting the response of this ecosystem process to slight levels of eutrophication in headwater streams.

Effects ofEucalyptusleachates and oxygen on leaf-litter processing by fungi and stream invertebrates

AbstractIn summer, streams in Portuguese eucalyptus forests frequently experience drought resulting in isolated pools, frequently saturated with leaf litter, in which the leaf leachates may generate toxic and hypoxic conditions. We assessed the ecological effects of Eucalyptus globulus leachate with and without aeration (i.e., low flow vs pool scenarios) on microbial decomposition of eucalyptus leaves and on toxicity to and survival, avoidance, and feeding behavior of Chironomus riparius Meigen (Diptera:Chironomidae), Echinogammarus meridionalis Pinkster (Amphipoda:Gammaridae), and Sericostoma vittatum Rambur (Trichoptera:Sericostomatidae). Eucalyptus globulus leaves immersed in a gradient of aerated or nonaerated eucalyptus leachate (100, 40.0, 16.0, 6.40, 2.50% volume/volume) were colonized by species-poor fungal assemblages. Leaf mass loss did not differ among treatments, but hypoxia suppressed conidia production and negatively affected fungal biomass. A concentration-dependent effect on fungal biomass...

Effect of leaf litter characteristics on leaf conditioning and on consumption by Gammarus pulex

Summary Terrestrial leaf litter inputs provide an essential energy source for many freshwater organisms. Processing of leaf litter involves several physicochemical and biological factors but always starts with the colonisation of leaves by aquatic hyphomycetes. Here, we document changes occurring on leaf tissues of three tree species, alder, hornbeam and oak, with contrasted leaf properties. Changes in the mechanical properties of leaves and in fungal growth were followed at 10, 25, 35, 45 and 55 days of immersion in natural winter conditions. We hypothesised that fungal growth will be faster and mechanical characteristics will decrease more rapidly in softer, nutrient‐rich, than in tougher leaves. In addition, we tested whether the consumption rate of conditioned leaves by the amphipod shredder Gammarus pulex was correlated with the mechanical properties of leaves and their ergosterol content (as a proxy for fungal biomass). Leaf toughness decreased (with different rates for the 3 litter species), whereas the leaf thickness remained stable. The mechanical properties of alder and hornbeam leaves changed similarly, in contrast to oak leaves. Ergosterol contents increased over time more rapidly for alder and hornbeam than for oak leaves for which the fungal growth was delayed. Ergosterol content, leaf toughness and leaf consumption rates by G. pulex were significantly correlated. Leaf consumption rates by G. pulex were higher for soft than for tough leaves. Our results suggest that the consumption of different types of leaves may be delayed according to the time required to acquire conditioning sufficient for shredder consumption. The presence of tough leaves in riparian vegetation may constitute a reservoir of trophic resources available for aquatic organisms at the end of the winter, when soft leaves have been entirely consumed. The diversity of riparian vegetation may hence contribute to sustaining the availability of food resources for adjacent aquatic ecosystems.

Interactions between aquatic bacteria and an aquatic hyphomycete on decomposing maple leaves

Abstract Processing of leaf litter is an important function in many environments and is influenced strongly by microorganisms. We investigated interactions between an aquatic hyphomycete, Tetrachaetum elegans , and two bacteria from the Cytophaga-Flavobacterium-Bacteroides group, that were isolated from decaying leaves in a stream. Laboratory experiments were used to examine interactions, as indicated by growth, between bacteria and fungi on sugar maple ( Acer saccharum ) leaves. Responses to amendments with labile dissolved organic carbon (DOC) were also examined. Fungal biomass was not affected by glucose amendment or bacterial presence. Likewise, bacterial biomass did not respond consistently to the glucose amendment, nor did the fungus affect bacterial biomass. In general, we found little evidence of resource competition or facilitation, in contrast to other studies. Our experiments suggest that fungal–bacterial interactions are not always significant and may depend on environmental conditions and the types of microorganisms examined.