Hydrobiologia最新文献

In recent years, trait-based studies have gained importance as an extension of taxonomic studies to better understanding ecosystem processes. However, these studies are still very limited in Mediterranean freshwaters. The aim of the study was to link functional groups with environmental factors and ecosystem processes for zooplankton in the Lake Iznik, which is an alkaline lake in Türkiye. Morphological, physiological and behavioural categories have been selected as response traits. Physical and chemical variables and trophic state are important predictors of functional traits. A total of 26 zooplankton taxa belonging to four taxonomic groups were classified into five functional groups according to functional traits. It was found that functional groups were significantly affected by seasonally changing environmental conditions, but not by depth. The main predictor of zooplankton functional groups was electrical conductivity. As a result of the alkaline conditions and the deterioration of the trophic state of the lake (meso ~ to eutrophy), the low taxonomic richness, dominance of the microphagous feeding type and small-bodied taxa indicate ecosystem degradation leading to functional depletion (homogenisation). The results showed that temporal variations of environmental variables can affect zooplankton functional groups and that trait-based zooplankton studies will enable a better understanding of ecosystem processes in deep alkaline lakes.

Trout-perch (Percopsis omiscomaycus) is an abundant, small-bodied, benthic fish species often found in deeper regions of large lake ecosystems. Historical evidence suggests that Trout-perch may participate in nearshore lake food webs by migrating from deep to shallow areas at night. However, little is known about Trout-perch ecology or their potential role in nearshore food webs. We used Trout-perch abundance estimates, diet analysis, and benthic invertebrate community surveys to (1) assess Trout-perch trophic ecology in Lake Champlain, USA/CAN, and (2) determine whether deepwater prey resources existed at sufficient densities to support Trout-perch populations or whether supplemental prey resources were required. Trout-perch showed variability in size and biomass across lake regions, but diet patterns were largely consistent across the lake, with > 50% of diets consisting of emergent insect larvae and oligochaetes. Results suggest that migrations into nearshore habitats may be required to sustain Lake Champlain’s Trout-perch populations, and therefore, Trout-perch could function as conduits of allochthonous energy across distinct lake habitat boundaries. This study is one of only a few that have examined the trophic ecology of Trout-perch in deep lakes and fundamentally improves our understanding of energy flow and coupling between distinct lake food web compartments in large lakes.

The environment-species relationships can be mediated by functional traits. In this study we investigated how the functional traits of periphytic community respond to environmental variation in streams along a gradient of anthropically modified landscapes in the Brazilian Cerrado. We expect the association of traits with flow gradients, turbidity, productivity, and nutrients directly impacted by changes in land cover around streams. We use the RLQ analysis to test this hypothesis. The first RLQ axis revealed a gradient associated with variation in the local physical and chemical characteristics, nutrients and productivity of the streams, while the second axis was associated with a gradient of impact on land use and nutrients related to the trophic state. The main traits associated with the first axis of RLQ (physical and chemical, and productivity gradient) were life form, substrate adherence, and active mobility, while size, life form, and substrate adhesion were associated with the second axis of RLQ (land use, primary productivity, and orthophosphate gradient). Our results highlight the importance of the trait-environment approach to predict community composition. Furthermore, they suggest that functional traits can be used to predict the responses of periphytic communities to environmental changes at local and landscape scales.

We investigated the individual and combined impacts of manipulation of submerged macrophytes, large-bodied cladocerans, and nutrients on plankton communities in a tropical hypereutrophic shallow reservoir. We tested how the addition of the macrophyte Ceratophyllum demersum, the cladoceran Sarsilatona serricauda, and nutrients affected phytoplankton and zooplankton diversity, composition, and structure using mesocosms and a factorial design (3 × 3) with eight treatments. During the experiment, the reservoir experienced an intense bloom of algae (207 mg l⁻¹ of biomass), mainly composed of cyanobacteria (> 98%). The submerged macrophytes were found to significantly reduce the biomass of cyanobacteria (by 85%), diatoms (80%), and green algae (78%), while the addition of zooplankton and nutrients led to a 96% reduction for diatoms. While both submerged macrophytes and the added cladocerans impacted the native zooplankton community, the macrophytes exerted stronger effects on phytoplankton and zooplankton diversity, composition, and structure. Intriguingly, nutrient addition did not alter the main effects of macrophytes and large cladocerans. Our findings reveal the positive potential of introducing submerged macrophytes in tropical shallow lakes, even at a low to moderate percentage of the volume inhabited, to control toxic cyanobacterial blooms. Under our experimental conditions, the method was effective even without extra zooplankton grazing and at increased nutrient input.

Early juveniles of the swimming crab Portunus trituberculatus are known to use drifting seaweed before transitioning to benthic habitats in a behaviour that is thought to be a strategy to avoid shallow water predators. However, little is known about whether the predation risk of P. trituberculatus juveniles is reduced in such seaweed. To assess the nursery function of drifting seaweed for P. trituberculatus as a refuge from predation, we conducted field experiments to compare the relative survival of first to fifth instar (i.e. small to large body size) juveniles tethered to floating macroalgae that mimicked drifting seaweed and to unstructured sand habitats. The survival of tethered juveniles was higher in floating algae than in sand. This was particularly evident among first- to third-instar juveniles, which exhibited less burying behaviour. Thus, first- to third-instar juveniles with small body size and less burying habits are likely to be most vulnerable to predation, and drifting seaweed may function as a nursery vehicle, providing refuge from predators.

Stygobionts, namely animals with strong adaptations to subterranean environments that are unable to complete their life cycles outside groundwater, can be observed in spring ecotones, but their occurrence is generally considered accidental. The aim of this paper is to assess if stygobiont occurrence in springs is linked to specific environmental conditions or if it is random, irrespective of their features. For three years, we surveyed 59 spring sites recording the occurrence of vertebrate and invertebrate stygobiont species and assessing if spring features were related to their distribution. Moreover, we recorded the escape reactions of two easily identifiable stygobiont species. We detected six taxa usually considered as strictly stygobiont based on their troglomorphic features. Two of them were quite widespread: the salamander Proteus anguinus and the shrimp Troglocaris planinensis. Environmental characteristics were significantly related to the distribution of stygobionts. Hydroperiod and occurrence of flooding were the factors that played the strongest role in affecting occurrence. Our study suggests that the occurrence of stygobionts in springs is linked to specific habitat features rather than being a random mechanism and that the exploitation of ecotones can be important for the lifecycle of some species usually assumed to be strictly associated to caves.

Dissolved organic matter in open-canopy streams is mostly derived from autochthonous sources, but the role of autochthonous DOM to sustain heterotrophic communities has been poorly studied. We compared respiration rates of epiphytic and epipelic biofilms (measured by the Resazurin—Resorufin tracer system) when processing autochthonous and allocthonous DOM sources with different chemical and optical properties. We performed laboratory experiments to determine aerobic respiration rates of epipelic and epiphytic communities in different leachates from autochthonous (macroalgae and emergent and submerged macrophytes) and allochthonous (riparian grasses) DOM sources from a Pampean stream. We also determined dissolved organic carbon and nutrient contents and DOM optical properties of each leachate. We found that epipelon was more heterotrophic and showed a lower respiratory activity than epiphyton, regardless of the type of leachate. Epiphytic respiratory activity was positively associated with DOM of microbial origin with a lower degree of humification (i.e., autochthonous microbial-algal derived materials), while epipelic respiratory activity was related to autochthonous and allochthonous humic-like materials, with higher aromaticity, derived from grasses and macrophytes. This indicates that both autochthonous and allochthonous sources can sustain microbial respiratory activity in the stream, and highlights the role of primary producers in the carbon cycle of open-canopy streams.

Globally, human activities profoundly influence biodiversity, frequently favouring biological invasions. Crayfish, prominent invaders on multiple continents, pose significant varied threats. Using species distribution models (SDMs), this study explores the current and future potential distribution of Pontastacus leptodactylus, a widely introduced but under-studied crayfish, at Eurasian scale. Climate is crucial for most species’ distributions and historically SDMs focused primarily on these variables, while overlooking other environmental factors influencing species occurrence. This research employed 2 approaches: one climatic and one broader environmental model encompassing soil pH and elevation data. Both methods revealed high suitability for the species, particularly currently in Central-Europe. Future climate scenarios for 2050 do not seem to favour the species in terms of intermediate-high suitability regions, with contractions also in the native regions with both approaches. However, remarkable discrepancies were observed in some North-European regions; with the climatic approach predicting high suitability where the environmental approach did not. This study identifies P. leptodactylus as a widespread successful species outside its native range with potential for expansion under current conditions. The synthesised continental overview and projected distribution maps aid in prioritising monitoring and prevention efforts while underlining the importance for using environmental as well as climatic variables in SDMs.

Cichlids exhibit an outstanding diversity of pigment patterns among both teleosts and vertebrates in general. The role of endocrine regulatory mechanisms underlying the observed diversity of patterns remains poorly understood. Thyroid hormones are important signaling molecules that regulate a wide range of developmental processes in teleosts. Here, I review evidence for the influence of thyroid signaling on pigment pattern formation in Neotropical cichlids, and the role of hormone-mediated phenotypic plasticity and heterochrony in the evolution of cichlid pattern. The use of hormones as key factors in switching developmental programs in future studies will provide a better understanding of how environmentally-mediated changes in the endocrine regulation of ontogeny contribute to adaptive evolution and the phenotypic divergence of cichlids.

Our objective was to assess the effects of interactions between the native Percichthys trucha and both Salmo trutta and Oncorhynchus mykiss during the juvenile period. We conducted single and multipredator (conspecific and heterospecific) functional response (FR) experiments with Meridialaris chiloeensis as native prey and estimated the functional response ratio as a predator impact metric. Our results showed that all species have type II FR, with salmonids having a greater impact on prey than native fish. In multipredator experiments, O. mykiss had a greater negative impact on P. trucha than S. trutta. The individual feeding performance of P. trucha was better under conspecific than heterospecific conditions. This study shows that the vulnerability of juvenile P. trucha to salmonid competition could be a real threat in Patagonian lotic environments.