Detritus Food Chain Research Articles

Microplastics and silver nanoparticles compromise detrital food chains in streams through effects on microbial decomposers and invertebrate detritivores.

Abundance of microplastics (MPs) in freshwater ecosystems has become an emerging concern due to their persistence, toxicity and potential interactions with other contaminants. Silver nanoparticles (Ag-NPs), which share common sources with MPs (e.g., personal care products), are also a subject of concern. Thus, the high probability of co-occurrence of both contaminants raises additional apprehensions. This study assessed, for the first time, the impacts of MPs and Ag-NPs, alone or in mixtures, on stream detritus food webs. Physiological and ecological responses of aquatic fungal communities, invertebrate shredders (Allogamus sp.) and collectors (Chironomus riparius) were examined. Additionally, antioxidant enzymatic responses of microbes and shredders were analyzed to unravel the mechanisms of toxicity; also, neuronal stress responses of Allogamus sp. were assessed based on the activities of cholinesterases. Organisms were exposed to environmentally realistic concentrations of polyethylene MPs, extracted from a personal care product (0.1, 0.5 and 10 mg L-1), for 7 days, in the absence or presence of Ag-NPs (0.1 mg L-1 and 1 mg L-1). The exposure to both contaminants reduced the growth rates of all tested organisms. MPs, Ag-NPs, and their mixtures led to a decrease in leaf litter decomposition by fungi and shredders. The availability of fine particulate organic matter, released by the shredders, increased when exposed to these contaminants. The negative effects of these contaminants were further strengthened by the responses of antioxidant enzymes that revealed high level of oxidative stress in both fungi and Allogamus sp. Moreover, the activities of cholinesterases showed that Allogamus sp. were under neuronal stress upon exposure to both contaminants. The impacts in mixtures were stronger than those of individual contaminants suggesting interactive effects. Overall, our study showed adverse effects of MPs and Ag-NPs across trophic levels and indicated that they may compromise key processes, such as organic matter decomposition in streams.

Species‐specific effects of leaf litter leachate on the aquatic microbial community and the ratio of heterotrophic to autotrophic biomass

Abstract Dissolved organic carbon (DOC) released from submerged leaf litter is an important allochthonous carbon source for heterotrophic bacteria that enhances the detrital food chain in freshwater ecosystems. In contrast, nitrogen (N), phosphorus (P) and micronutrients released during the leaching process support primary production and enhance the grazing food chain in these ecosystems. This study investigated how DOC and dissolved N and P from the leaf litter of two temperate broadleaf and two coniferous tree species affect heterotrophic and autotrophic biomass by incubating the freshwater microbial community in the culture media prepared from the leaf litter leachate. The results showed that heterotrophic biomass, including bacteria, heterotrophic‐flagellated protists and fungal zoospores, was the highest in the leaf litter leachate, which contained the highest DOC concentration relative to dissolved N and P (Japanese hemlock). In contrast, autotrophic biomass, including small algae, autotrophic flagellated protists and cyanobacteria, was associated with concentrations of dissolved N and P in the leaf litter leachates. Amendment of basal nutrients other than N and P, including micronutrients, trace elements and vitamins, increased autotrophic biomass in two leaf litter leachates (oak, Siebold's beech), suggesting that some elements other than N and P were deficient relative to the requirements of autotrophic organisms. These results indicated that the elemental composition of leaf litter leachates influences microbial community structure and heterotrophic versus autotrophic biomass in freshwater ecosystems. More importantly, the present results suggest that changes in forest vegetation surrounding freshwater ecosystems alter detritus‐based heterotrophic production relative to autotrophic production through the changes in the elemental composition (i.e. stoichiometry) of leaf litter inputs.

Modeling food web and fisheries dynamics in Lake Baringo, Kenya

AbstractLakes are important in supporting ecosystem services and livelihoods. However, their food webs and ecological functioning are continuously threatened by anthropogenic influences. Food web models have been widely used in studying trophodynamics, fisheries impacts, and ecological functioning of temperate lakes, but less often in Afrotropical lake systems. We used Ecopath mass‐balanced trophic models annually in 1999, 2010, and 2020 to assess trends in ecosystem function, and the impact of fisheries on the Lake Baringo Ecosystem, a shallow freshwater lake in Kenya. Pre‐balance (PREBAL) and Pedigree analyses supplemented Ecopath models. Model input data were from field sampling, published and gray literature. Food web trophic models indicated a bottom‐up grazer and detrital food chains in all 3 years. Odum's ecosystem development indicators (total productivity to total biomass and total respiration ratios; TPP/TB and TPP/TR) showed that the lake was in a low to intermediate developmental stage, with room for bio‐manipulation, and a highly reduced mean transfer efficiency (TE) (6.4%–0.49%) indicated low trophic transfer of internal production. System omnivory (SOI) and connectance (CI) indices that varied among years indicated temporal variation in food web complexity. Indices of system resilience (overhead and ascendency) indicated an increasing potential for the lake to recover from perturbations. The mean trophic level of the catch (MTLc) increased from 1999 to 2010 and decreased in 2020, by fishing down the food chain as fishing pressure increased. Oreochromis niloticus, an endemic cichlid, was the keystone species (KSi >0) controlling community structure, while the lungfish Protopterus aethiopicus, the top predator in the lake, was not a keystone species (KSi <0). We recommend an integrated approach to lake management that incorporates watershed regulations, regulates fishing effort on the keystone species (O. niloticus), and monitors water quality for sustainable management of the Lake Baringo ecosystem.

Effects of nanoplastic exposure routes on leaf decomposition in streams

Polystyrene nanoparticles (PS NPs) released from plastic products have been demonstrated to pose a threat to leaf litter decomposition in streams. Given the multitrophic systems of species interactions, the effects of PS NPs through different exposure routes on ecosystem functioning remain unclear. Especially dietary exposure, a frequently overlooked pathway leading to toxicity, deserves more attention. A microcosm experiment was conducted in this study to assess the effects of waterborne and dietary exposure to PS NPs on the litter-based food chain involving leaves, microbial decomposers, and detritivores (river snails). Compared to waterborne contamination, dietary contamination resulted in lower microbial enzyme activities and a significantly higher decrease in the lipid content of leaves. For river snails, their antioxidant activity was significantly increased by 20.21%–69.93%, and their leaf consumption rate was significantly reduced by 16.60% through the dietary route due to the lower lipid content of leaves. Besides, the significantly decreased nutritional quality of river snails would negatively influence their palatability to predators. The findings of this study indicate that dietary exposure to PS NPs significantly impacts microbial and detritivore activities, thus affecting their functions in the detritus food chain as well as nutrient cycling.

Food Web Structure and Ecosystem Functions of the Water Source in the Middle Route of China’s South-to-North Water Diversion Project

The Danjiangkou Reservoir is the water source of the middle route of China’s South-to-North Water Diversion Project, encompassing the Dan Reservoir and Han Reservoir. However, little is known about the ecological functions of this important ecosystem. Based on a survey conducted in 2023 in the Dan Reservoir, a mass balance model was constructed using Ecopath with Ecosim 6.6 software to characterize its food web structure and ecosystem properties. The model consisted of 18 functional groups, including producers, consumers, and detritus, covering the entire process of energy flow in the ecosystem. The outputs indicated that the fractional trophic level of functional groups in the Dan Reservoir ecosystem ranged from 1.00 to 3.50. The ecotrophic efficiencies of the main economic fish species were all less than 0.9, and the ecotrophic efficiencies of phytoplankton and detritus were less than 0.5. There were two main food chains: the detritus food chain (39%) and the grazing food chain (61%). The total energy transfer efficiency between trophic levels was only 6.02%, and there was a significant phenomenon of energy transfer blockage between trophic levels II and V. Analysis of the overall characteristics of the ecosystem revealed that the total primary production to total biomass (67.96619), connectance index (0.274), and Finn’s cycling index (2.856) of the Dan Reservoir ecosystem all indicate that the ecosystem is immature, with low nutrient recycling efficiency and poor resistance to external disturbances. This may be related to the low proportion of silver carp and bighead carp in the reservoir and the unreasonable structure of the fish community. Our results suggest that it is necessary to scientifically adjust the structure of the fish community, enhance the proportion of filter-feeding and omnivorous fish to improve the energy flow efficiency, and promote the maturity and stability of the Dan Reservoir.

Evolution of trends in Sri Lankan mangrove research and future prospects

The trend of sporadic surveys and qualitative descriptions of Sri Lankan mangrove flora in the first half of the 20th century has gradually changed to include quantitative studies on floristics, nevertheless, studies on quantification of fauna associated closely with mangrove ecosystems are scarce. Microbial diversity, especially in soil, and its ‘contribution to the detritus cycle are the least studied. The tendency to engage in short-term research at convenient sites affects the quality and relevance of research output with some redundancy, resulting in a marginal contribution to the knowledge base on mangrove ecology. Studying mangrove ecosystem functions/ services demands long-term collection of data that would have made them less attractive research ventures. Research on trophic relationships, detritus and nutrient cycling, habitat and pollination functions too have had the same fate. The Indian Ocean tsunami in 2004 triggered a considerable interest in the coastal protection function of mangroves, as it was evident that mangroves and other coastal vegetation provided superior resistance to tsunami waves than hard engineering coastal protective structures. This has led to an unprecedented trend of mangrove afforestation for coastal defense, more than to research on planting techniques and maintenance to enhance the survival and growth of seedlings. This is still an under-researched aspect. Escalating recognition of blue carbon as a climate-smart solution and the development of market mechanisms for blue carbon trading have induced a considerable research interest in quantifying the mangrove blue carbon stocks, especially in the soil. Research on atmospheric carbon removal capacity/rates of mangrove plants/forests through photosynthesis however, lags behind for the reason that it requires data collection for a longer period that demands greater financial and labour investment. The urgency created by the current climate change crisis for effective solutions to reduce atmospheric greenhouse gases may provide a conducive environment for mangrove research.

Revealing Diversity in Gammarus (Amphipoda: Gammaridae) in the Freshwater Ecosystems of Armenia Using DNA Barcoding

Gammarus plays a central role in the detritus cycle and constitutes an important component in food webs. At the same time, taxonomy and morphological identification to species level is highly challenging in this genus. Thus, the freshwater gammarid diversity in the Caucasus biodiversity hotspot remains largely unstudied to date. We use DNA barcoding for the first time in assessing the biodiversity and taxonomy of gammarids within the amphipod genus Gammarus in the limnic ecosystems of Armenia. The results expand the knowledge on possible diversity and evolutionary lineages of Gammarus in the region. DNA barcodes obtained from our Armenian specimens consistently indicate four to six well-defined molecular operational taxonomic units (MOTUs) within three distinct morphospecies clusters. One to three MOTUs correspond to the Gammarus balcanicus species complex, two MOTUs to the G. komareki complex, and one MOTU to the G. lacustris complex. Five BINs out of six were unique and new to BOLD.

Trophic fingerprinting of a pristine but rapidly deteriorating downstream region of a Western Ghats River.

Chalakudy River is renowned for its pristine waters and rich ichthyofaunal biodiversity. The downstream area of the river is confronting a series of risks, including pollution, saline water ingression, sand mining, illegal and intensified fishing practices, and invasion of exotic and alien species. A mass balanced ecosystem model was constructed for the downstream region of Chalakudy River (DCR) using Ecopath with Ecosim (EWE), incorporating 12 functional groups to delineate the food web and network flow indices for the period 2020 to 2021. The trophic level (TL) of the ecosystem network ranged from TL-1 (detritus) to TL-3.4 (birds). High fishing pressure is one possible cause for the high ecotrophic efficiency values as evidenced by the fish groups. Both the grazing food chain and detritus food chain (detritivory: herbivory ratio 0.94) contributed more or less equal to the energy transfer between TL. Network analysis of the model indicated a mean transfer efficiency of 12%, with shares from primary producers (14%) and detritus (11%). A mixed trophic impact analysis demonstrated a strong positive impact of primary producers and detritus groups on most of the other ecological groups at higher trophic levels. The DCR model showed a high system throughput (32,464.7 t km-2 year-1), low system omnivory (0.09), low connectance index (0.36), low Finn's cycling index (4.9), and mean path length (2.8), low relative ascendency (37.5%), and high system overhead (62.5%). These indices propound that DCR is an immature and developing ecosystem with moderate strength in reserve to resist external perturbations.

Distribution, speciation, and bioaccumulation of potentially toxic elements in the grey mangroves at Indian Sundarbans, in relation to vessel movements

Sundarban is the world's largest mangrove wetland and home of 4.6 million people (Indian part), whose principal mode of communication is motorized boats (ferries). This study shed light on the role played by ferry movement in the speciation (following the BCR three-step sequential extraction method), ecological impact and bioaccumulation of potentially toxic elements (PTEs) in plant tissues (root and lamina) of grey mangrove (Avicennia marina) found near the five ferry ghats (ports). One-way ANOVA showed variation in major soil parameters (silt, clay, organic carbon, pH, Electrical conductivity) and PTEs (As, Cd, Cr, Cu, Hg, and Pb) between sites. Sequential extraction revealed that Cd was present in the ‘exchangeable’ form across the sites, Pb was in the ‘reducible’ form, and the rest of the PTEs were majorly found in ‘residual’ phase. Pollution indices revealed moderate to heavy contamination and considerable potential ecological risk due to Cd. Pearson correlation statistics and concentration variations indicate a relation between Pb and ferry movement frequency in the sites. Higher bioconcentration of Pb in the roots of A. marina, indicates phytostabilization action. Translocation factor for Cd in the leaves, indicates phytoextraction by A. marina. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a close association between vehicle movement and Hg, Pb, Silt fraction, electrical conductivity, Cr, and As. This study recommends regular pollution monitoring across Sundarbans, as the PTEs in sediment-plant matrix can impact the higher trophic levels, human health through possible biomagnification in the detritus food chain, and can adversely impact the existing conservation initiatives.

Sponge organic matter recycling: Reduced detritus production under extreme environmental conditions

Sponges are a key component of coral reef ecosystems and play an important role in carbon and nutrient cycles. Many sponges are known to consume dissolved organic carbon and transform this into detritus, which moves through detrital food chains and eventually to higher trophic levels via what is known as the sponge loop. Despite the importance of this loop, little is known about how these cycles will be impacted by future environmental conditions. During two years (2018 and 2020), we measured the organic carbon, nutrient recycling, and photosynthetic activity of the massive HMA, photosymbiotic sponge Rhabdastrella globostellata at the natural laboratory of Bouraké in New Caledonia, where the physical and chemical composition of seawater regularly change according to the tide. We found that while sponges experienced acidification and low dissolved oxygen at low tide in both sampling years, a change in organic carbon recycling whereby sponges stopped producing detritus (i.e., the sponge loop) was only found when sponges also experienced higher temperature in 2020. Our findings provide new insights into how important trophic pathways may be affected by changing ocean conditions.

Data driven toxicity assessment of organic chemicals against Gammarus species using QSAR approach

Nowadays, organic chemicals play an essential role in almost all walks of life and have become indispensable to modern society. However, the continually synthesized chemicals and the numerous potential adverse endpoints against living organisms increasingly promote the regulators regarding the computational approach as a crucial supplement and an alternative to the traditional animal tests in chemical risk assessment. In this present research, we evaluated the ecotoxicity of chemicals against four typical Gammarus species, which constituted a critical element in detritus cycle and also the recommended species for water monitoring. We first screened the molecular descriptors based on the Genetic Algorithm and then developed the Quantitative Structure-Activity Relationship models using the Multiple Linear Regression method. The statistical results from various validation metrics suggested that the obtained models were internally robust and externally predictive. The application domain analysis based on the leverage approach and standardized residual method demonstrated the broad application range of each model. The interpretation of molecular descriptors in each model suggested that the chemicals with higher polarity and hydrophilicity tend to be less toxic, whereas the lipophilic moieties would enhance the chemical toxicity. Meanwhile, the other selected descriptors, such as Chi-cluster, heterocyclic, and distance matrix descriptors, manifested that the chemical toxicity was also affected by molecular branching, connectivity, electrotopological state, and other various properties. In summary, the present work proposed well-performed QSAR models and clarified the possible toxic mechanism of chemicals against Gammarus species. The obtained models could help predict the toxicity data and conduct a preliminary risk assessment, thus guiding the subsequent animal tests and reducing the assessment cost.

Eels as natural samplers highlight spatial heterogeneity in energy flow in an estuary

The high spatiotemporal heterogeneity makes it difficult to ensure the representation of samples in estuarine studies. Using Japanese eels as natural samplers (n = 881), we revealed the spatial heterogeneity of energy flow among three successive estuarine segments (upper, middle, and lower estuaries) of the Hamana Lake−Miyakoda River system on the Pacific side of central Honshu, Japan. In the upper estuary which serves as the nursery ground for eels, the predominant small eels (body weight <30 g) fed mainly on polychaetes (58.8% IRI [index of relative importance]), mainly Hediste atoka. This polychaete species depends on the detritus food chain driven by terrestrial inputs, and the detritus food chain appears to be predominant in the upper estuary. However, large eels (body weight >150 g) fed directly on terrestrial subsidies in the form of fallen insects (49.0% IRI) and earthworms (20.2% IRI), indicating that the detritus food chain does not directly affect the diet of large eels. Terrestrial subsidies in the form of living organisms do not contribute to the diet of eels in the adjacent middle estuary, which is the main growth habitat for eels within an estuary. However, small eels depend on terrestrial subsidies by feeding on oysters (71.6% IRI), which assimilate terrestrial particulate organic matter. The predominant medium eels were highly dependent on the high diversity and biomass of prey groups, as indicated by the high % IRI values of several groups, such as infaunal bivalves (31.7% IRI), oysters (19.0% IRI), amphipods (22.6% IRI), and polychaetes (16.4% IRI). Eelgrass beds usually serve as shelters and foraging areas for medium and large eels in the lower estuary. Despite the high species diversity around seagrass meadows, the eels concentrated on infaunal bivalves (85.4% IRI) with high biomass, predominantly Anadara sp. In addition to being tools for monitoring fauna, eels as natural samplers provide insights into the energy flow in ecosystems.

New records of Trichodactylus fluviatilis Latreille, 1828 (Decapoda: Brachyura: Trichodactylidae) in Southeastern Brazil

Freshwater crabs play important ecological roles in lotic ecosystems, occupying different trophic levels and participating in the detritus food chain. Trichodactylus fluviatilis is a freshwater crab that occurs along the Brazilian coast and inland portions of southeastern Brazil. This species occurs in rivers and in coastal and mountain streams up to more than 1,100 m above sea level. Herein we report the occurrence of T. fluviatilis in one of the largest Atlantic Forest remnants located on flat terrain, which contains one of the most threatened vegetation types found within this biodiversity hotspot. We collected one adult female and 15 juveniles over four sampling occasions between February and September 2015. These records extend the number of locations where the presence of T. fluviatilis was confirmed and contribute to the knowledge about the geographical distribution of this species in Espírito Santo state and in the Atlantic Forest. This information will prove valuable in refining distribution maps and assessing the species' threatened status, aiding in the formulation of wildlife conservation strategies for streams in the Atlantic Forest.

Expansion of the Conceptual Model for the Accumulation of Selenium in Lentic Food Chains to Include Redox-Controlled Generation and Diffusion of Selenite and Dissolved Organo-Selenium Compounds.

The controls governing the availability of reduced selenium (Se) species, namely selenite (Se[IV]) and dissolved organo-Se (DOSe), to primary producers at the sediment-water interface in depositional environments (i.e., lentic systems) were assessed through consideration of theoretical principles and field data. Selenite is generated in suboxic sediment porewater via the microbially mediated reduction of selenate (Se[IV]) and/or reductive dissolution of Se-bearing iron oxides. Field data for lentic environments demonstrate that the production of DOSe in sediment porewaters can also be redox- and depth-dependent. In this manner, the remobilization depths of Se(IV) and DOSe in depositional environments are dependent on the vertical redox gradient (dEh/dz), where deeper depths of remobilization are observed in less reducing sedimentary environments (lower dEh/dz). In turn, remobilization depth has a direct bearing on the concentration of dissolved Se(IV) and DOSe that may be realized at the sediment-water interface because the depth of reaction governs the diffusive path length, concentration gradient, and rate of diffusional transport toward the sediment-water interface. The principles that link sediment redox gradients, depth of remobilization, diffusive transport processes, and concentration of reduced Se species at the sediment-water interface have a direct bearing on the potential for Se uptake by primary producers in lentic food chains (e.g., phytoplankton, biofilms, bacteria). Overall, these processes complement the current conceptual "benthic detrital food chain" model that describes the accumulation of Se in lentic systems. Environ Toxicol Chem 2022;41:2859-2869. © 2022 SETAC.

Polyphyly of the genus Stenurella (Coleoptera, Cerambycidae): Consensus of morphological and molecular data

Stenurella genus is represented by nine small-sized and widely distributed Palaearctic species. Representatives of the genus play a key role in the pollination of wild angiosperms, accelerate the detritus cycle and make a significant contribution to the forest food web. A number of species with heterogeneous morphological features found within the single Stenurella genus indicate the need for revision of the taxonomy this genus. The previous attempt to resolve the intrageneric composition of Stenurella was rather artificial because it did not take into an account evolutionary relationships. In this study we tested the existing model of Stenurella intrageneric subdivision using both morphological and molecular approaches. Our results showed that the genus Stenurella is polyphyletic and consists of two unrelated clades. The first clade comprises six species (S. jaegeri, S. novercalis, S. bifasciata, S. melanura, S. hybridula and S. approximans) and the second includes three species (S. septempunctata, S. vaucheri and S. nigra). Moreover, we found that the second clade is closely related to Rutpela due to both morphological and molecular phylogeny. Based on our findings, we revised the present structure of the genus Stenurella and transferred three species of the second clade to the genus Rutpela, sensu novo. The genus Rutpela was redescribed in the light of our results. Furthermore, we subdivided the genus Stenurella, sensu nov. into two subgenera, Stenurella, subgen. sensu nov. and Priscostenurella, subgen. sensu nov., respectively. Also, the genus Rutpela, sensu nov. was subdivided into four subgenera including Nigrostenurella, Rutpela, Eduardvivesia, subgen. nov. and Nigromacularia, subgen. nov. The assessment of the place of Stenurella, sensu novo and Rutpela, sensu novo within Lepturini based on molecular phylogeny, showed that Stenurella, sensu novo belongs to the Anoplodera-branch and Rutpela, sensu novo nested within the Leptura-branch. These together with morphological features confirmed our idea of the evolutionary distinctiveness of Stenurella, sensu novo and Rutpela, sensu novo. We assumed that the general external morphological similarity of Stenurella, sensu novo and Rutpela, sensu novo was the result of convergent evolution, driven by mimetic selection toward imitation of ants or wasps. Finally, our study establishes a natural phylogenetic taxonomy of Stenurella.

Evidence of micro and macroplastic toxicity along a stream detrital food-chain

Freshwater ecosystems are subjected to plastic extensive pollution because they are the direct link between plastic wastes and marine ecosystems. The aim of this study was to assess the impacts of different sizes of polyethylene plastics (micro: µPs and macroplastics: PBs) on freshwater decomposers of plant litter. We exposed leaf associated microbial assemblages to µPs (0.5 or 1.5 g L-1) and discs of PBs as follows: green plastic bags (PB-G) alone or in mixtures with transparent plastic bags (PB-Mix). Then, we conducted a feeding preference experiment with the invertebrate shredder Limnephilus sp. to assess their capacity to distinguish leaf discs from PB discs of the same size (12 mm). Leaf decomposition, activities of fungal enzymes and sporulation were inhibited by µPs and PB-Mix, and shifts in fungal community composition were observed. The invertebrate shredders preferred to feed on leaves treated with µPs avoiding those exposed to PB-G/PB-Mix. Our results demonstrated that plastics can have a direct effect on stream-dwelling microbial decomposers and an indirect effect on higher trophic levels (shredders), highlighting that trophic transfer is a route of plastic exposure. The plastic properties (size, concentration, colour) appear to influence plastic toxicity to microbes and shredders, indicating the importance of considering physicochemical properties when assessing their risks to freshwater ecosystems.

Comparative Food Web Analysis of Two Peruvian Bay Systems Along a Latitudinal Gradient: Resource Use and the Environmental Envelope

The coast of Peru lies within the tropics under the influence of the cold, nutrient-rich waters of the Humboldt Current and the interannual onslaught of the El Niño phenomenon. The Peruvian upwelling system is exceptionally productive and is comprised of subsystems at different scales along the coast. We aimed to understand the differences between two shallow coastal systems along a latitudinal gradient: Sechura Bay in the north (at the convergence of Humboldt and tropical waters) and Independencia Bay in the central-south (under typical upwelling conditions). We compared their biodiversity, trophic dynamics, community energetics, resource use and underlying abiotic conditions. Our analysis revealed that over the past two decades, Sechura has shown a warming trend, while Independencia has maintained its cold water conditions. Chlorophyll concentrations have risen significantly in both systems, higher values in Sechura suggesting there is an increase in local pressures that could lead to eutrophication. Trophic models of the La Niña 07/08 period revealed that both systems are bottom-up driven with high biomass and production at the lower trophic levels, though top-down controls were also shown, particularly in Sechura. While primary productivity was similar in both systems, differences were found in the structure and size of energy flows. More cycling and higher transfer efficiency were found in Independencia, where phytoplankton-based food chains played the main role in the overall dynamic. In contrast, the detritus food chain appears to be more relevant for energy flow in Sechura. Differences in biota and flow structure relate to the systems’ environmental conditions, i.e., more diverse warm-water species in the north and mostly cold water adapted species (mainly invertebrate filter-feeders and their predators) in the central-south. Catches in both systems were dominated by the diving fisheries and comprised mostly scallops (bottom-cultured), snails and fish in Sechura, and mussels, clams, crabs and fish in Independencia. Overall, system indicators suggest that Sechura is a comparatively less developed system. Independencia shall likely maintain its general highly productive system features, whereas Sechura will continue to be more frequently disturbed by El Niño and ongoing human-driven activities, reducing its overall stability and functionality. In the context of climate change, acknowledging these differences is essential for future adaptive management regimes.

Hopf Bifurcation for Detritus Food Chain in Mangrove Ecosystem

We proposed a prey-predator model portraying interaction in Detritus food chains. The primary view of this paper is to describe the interaction in the Detritus food chain due to the presence of a predator in mangrove ecosystems. Predation by assuming that the predator takes more time to eat its prey. We analyze the local stability of the equilibria point. Numerical simulations are achieved to clarify the theoretical result and display the change in the equilibria point solution through a bifurcation diagram. The numerical continuity of carrying capacity parameters in the system solution indicated the presence of the Hopf Bifurcation.

Evidence of Micro- and Macroplastic Toxicity Along a Stream Detrital Food-Chain

Evidence of Micro- and Macroplastic Toxicity Along a Stream Detrital Food-Chain

Carbon Transfer Processes of Food Web and Trophic Pathways in a Tropical Eutrophic Seagrass Meadow

Seagrass meadows provide important habitats and rich organic carbon sources for consumers at different trophic levels but are threatened by accelerating eutrophication in coastal waters. Nevertheless, at present, carbon transfer processes throughout the food web and trophic pathways in eutrophic seagrass meadows are still poorly known. To resolve this issue, carbon sources of different trophic communities in a eutrophic tropical seagrass meadow [Xincun (XC) bay, South China Sea] under eutrophication were examined in summer and winter using dual stable isotopes. The δ13C value of omnivores and carnivores overlapped more with that of herbivores and planktivores/filter feeders, which mainly overlapped with that of epiphytes in summer and macroalgae in winter. Meanwhile, epiphytes and macroalgae exhibited high biomass and corresponding highest contribution to herbivores, omnivores, and carnivores in summer and winter, respectively. These results suggest that the grazing food chain was the main trophic pathway in this eutrophic seagrass meadow, and that the transfer of carbon flow in the grazing food chain was mainly dominated by the proliferating epiphytes or macroalgae carbon. In contrast, the contribution of seagrass to detritivores in both seasons was higher than that of other food sources. Our findings suggest that in eutrophic tropical seagrass meadows, the proliferation of epiphytes or macroalgae induced by high nutrient loading, as well as their seasonal changes, has a greater impact on the transfer of carbon in the grazing food chain than that in the detritus food chain, and the seagrass fueled the food web mainly through the detritus food chain.