Aquatic Sciences最新文献

Estimations of ecosystem metabolism have rarely been used to quantify productivity in structural reductionist approaches for the description of phytoplankton composition. However, estimations of ecosystem metabolism could contribute to a better understanding of the relationship between phytoplankton composition and ecosystem functioning. To examine this, we investigated the community structure of phytoplankton in a set of Mediterranean coastal lagoons (natural and artificial) during a hydrological cycle to identify the most important environmental variables determining phytoplankton species composition. The focus of the study was on the quantification of productivity-related variables using estimations of ecosystem metabolism, such as different proxies for the estimation of the production-to-biomass ratio and of the relative importance of K- and r-strategies, which are commonly used conceptually but not quantified. Our results demonstrated differences in phytoplankton composition between seasons, due to the dominant hydrological pattern of flooding confinement in the salt marsh, and between lagoons that were caused by different levels of nutrient availability. Moreover, there was a notable decrease in the production/biomass ratio and a prevalence of K-strategists with seasonal succession, as predicted by Margalef’s mandala. Thus, the results showed that estimations of ecosystem metabolism are useful for the higher frequency quantification of important ecological variables, and contribute to a better understanding of planktonic assemblages, and physical and chemical changes, in these fluctuating ecosystems.

The taxonomic composition, abundance, diversity and spatial distribution of phytoplankton and zooplankton, as well as the prevailing hydrographic conditions, were examined in the Whin Estuary, which is considered one of the most pristine and productive coastal ecosystems of Ghana, which is located on the Gulf of Guinea. Hydrographic and plankton variables were determined along the gradient of the estuary between March and July 2022 across two seasons and tidal periods. A total of 50 genera of phytoplankton and 27 genera of zooplankton were recorded across the two seasons and sampling periods. Diatoms and copepods dominated the plankton communities across the estuary. Plankton genera such as Navicula, Nitzschia, Thalassiosira, Cyclops, Paracalanus and Temora were recorded across all the seasons and tidal periods, despite the varying hydrographic conditions. The environmental variables varied across the seasons, tidal periods and sampling stations in the estuary. For instance, temperature, DO, transparency, and chlorophyll a varied significantly (p < 0.05) across both the seasons and tidal periods. pH values were significantly (p < 0.05) lower in the rainy season compared to the dry season. There was a strong salinity gradient across the estuary, with the upper reaches dominated by freshwater organisms, such as cladocerans and cyanobacteria, and the lower reaches by marine organisms, primarily diatoms and copepods. In sum, the results reported here are important as they highlight the distribution of plankton communities in a tropical estuarine ecosystem and can serve as a reference for the management of tropical brackish ecosystems.

The Buenos Aires Lake Plateau, a unique semi-arid environment and priority area for waterbird conservation in Argentina, has recently shown reductions in lake sizes due to scarce rainfall. This study assessed the impact of contrasting hydrological conditions on the abiotic variables of lakes Chapu and Cervecero, as well as on the structure of plankton and how this affected the use of the lakes by waterbirds. We show that hydrological conditions shape the abiotic and biological features of these lakes. In 2015, both lakes were vegetated, but by 2016, their water level had dropped, causing decreased macrophyte coverage. In 2017, the lakes dried up completely, but were refilled the following year. The partial drought of 2015-2016 led to reduced concentrations of nutrients and food that support a high density and richness of birds, which are mostly aquatic and terrestrial feeders. After the extreme drought in 2017 and refilling phase in 2018, there was an improvement in the water quality of lake Chapu, as indicated by its increased clarity compared to that in 2015, while Cervecero remained turbid. Increased homogenization in plankton and waterbird species composition became evident in both lakes. There was a cyanobacteria bloom in Cervecero, while in Chapu Gammaproteobacteria were dominant. Both lakes supported few waterbirds, of which aquatic-terrestrial feeders and terrestrial herbivores were dominant. The abundance of the endemic and endangered hooded grebe (Podiceps gallardoi Rumboll 1974) declined with the cover of macrophytes, which these birds use when establishing their colonies. In sum, this study revealed changes in the conditions of lakes Chapu and Cervecero and their plankton communities in response to hydrological shifts, with implications for waterbird assemblages and, thus, biodiversity conservation.

We developed an inexpensive light instrument (ILI) and protocol for the measurement of photosynthetically active radiation (PAR) at discrete depths underwater. We tested the accuracy of the ILI against a submersible radiometer (RAD) and a Secchi disk method. The ILI consists of a PAR sensor (HOBO MX2202; Onset) attached to a flat disk that ensures that the sensor faces upwards when lowered through the water column. The flat disk is attached to a rope marked at 1-m increments (to 20 m) that allows for the measurement of PAR at discrete depths. A weight is attached to the bottom of the flat disk to prevent it from drifting. The ILI is much cheaper (US $130), less bulky, and lighter (1.1 kg) than the RAD (US $40,000, weight 9 kg). We tested our method in a mesotrophic lake and in an oligotrophic lake in summer and fall 2023. The correlations between the RAD and ILI measurements of irradiance at depth (as a percentage of surface irradiance), and the depth to which 1% of the PAR at the surface penetrated the water (Z_1%PAR), were high and did not significantly differ. There was a difference of 8% in the Z_1%PAR determined by the ILI compared with that determined by the RAD. However, the estimated Z_1%PAR based on the Secchi disk data was 37% deeper than that calculated with the RAD data. Our method should enable the study of underwater PAR in remote regions where transporting bulky and expensive equipment is impossible due to logistic and/or financial constraints. Moreover, our method can be used for the direct measurement of PAR at discrete depths.

The expansion of oil palm and cattle grazing in the tropics continues to alter numerous ecosystem functions. The generated land-use change is potentially impacting stream leaf-litter breakdown, a fundamental process for freshwater ecosystems. To assess the effect of land-use change, we studied breakdown rates of forest (Pachira aquatica, Pouroma aspera, Sloanea ampla, and Hippocratea volubilis) and oil palm (Elaeis guineensis) leaves after a 26-day immersion in streams surrounded by rainforests, grazing lands, or oil palm plantations with and without riparian buffers. In addition, we assessed breakdown drivers by deploying litter bags (248) of two mesh sizes (15 mm and 0.5 mm) allowing or restricting macroinvertebrates’ access (134 coarse-mesh bags and 114 fine-mesh bags). Forest leaf breakdown by microbes (fine-mesh) was lower by 55% in the plantations compared to forests; while microbial oil palm-leaf breakdown was lower by 32% in the unbuffered plantations compared to forests (p < 0.05). Total litter breakdown was lower (p > 0.05) in the plantations but not when these preserved riparian buffers. Litter breakdown was driven primarily by microbes in all land uses except in the buffered plantations, possibly due to increased shredder biomass. These results suggest that oil palm agriculture may decrease microbial stream leaf-litter breakdown, especially in streams with no riparian buffers.

In Mediterranean climate regions, intermittent rivers (IRs) harbor highly dynamic communities with species and trait composition changing over time and space. Simultaneously considering multiple biodiversity facets and a spatiotemporal perspective is, therefore, key to developing effective conservation strategies for these ecosystems. We studied the spatiotemporal dynamics of aquatic macroinvertebrates in rivers of the western Mediterranean Basin by analysing (1) the taxonomic and functional richness and the local contribution to beta diversity (LCBD; measured considering taxonomic and functional facets) of perennial rivers and IRs over five sampling times, and (2) their relation with flow intermittence, local environmental uniqueness, and the number of anthropogenic impacts. Both analyses were also conducted for the subset of data including only IRs to compare values between their flowing and disconnected pool phases. According to our results, taxonomic and functional richness tended to be higher in perennial rivers than in IRs, while taxonomic and functional LCBD tended to be higher in IRs than in perennial rivers. When comparing IR sites over time, higher values of taxonomic and functional LCBD corresponded mostly to their disconnected pool phase. Flow intermittence, the number of anthropogenic impacts and the environmental uniqueness were significant predictors of taxonomic and functional richness, but only flow intermittence was an important predictor of taxonomic LCBD. For the IR-only data subset, disconnected pool permanence was the main predictor explaining spatiotemporal patterns. Our results highlight the importance of IRs to biodiversity conservation of Mediterranean climate rivers, especially during the disconnected pool phase, suggesting that these ecosystems cannot be ignored in conservation planning strategies.

We assessed the spatiotemporal co-occurrence patterns of a fish assemblage in the watershed of a stream in the western Amazon basin, and verified the influence of abiotic factors (physicochemical variables and the hydrological phase) on these patterns. We also examined whether species that were more similar in their tolerance of physicochemical variables tended to co-occur more frequently. The structure of the assemblage was evaluated using the standardized effect size (SES) of the C-score index and null models, with the SES being used as an indicator of the organization of the assemblage. We employed linear regression models to investigate the influence of precipitation levels and physicochemical variables on the SES. We calculated the outlying mean index and ran a Mantel test on the checkerboard unit matrix of the C-score and tolerance values to assess the influence of species tolerance on co-occurrence patterns. Finally, we examined the correlations between species pairs and both physicochemical variables and adjacent land use. We observed patterns of aggregation or randomness in varying degrees at different scales. Increased precipitation influenced the establishment of random patterns, while species pairs correlated primarily with the degree of preservation of the local habitat at each study site. During the dry season, species that were more similar to each other in their environmental tolerance tended to co-occur more systematically. If the current levels of change in land use in the study area continue, the fish assemblage investigated here may suffer a significant loss of diversity, as well as destabilization of its structure, with a high possibility of local extinction of the most sensitive species.

The ability of fish to cope with warm water temperatures in summer depends on factors including their thermal traits and the ability of individuals to access cool-water refugia. Knowledge is highly limited on the in situ responses of many fishes to elevated summer temperatures, including whether they express behavioural thermoregulation. The responses of two riverine species to summer water temperatures were tested here using the movement metrics, spatial habitat use and body temperatures of individual European barbel Barbus barbus (‘barbel’) and common bream Abramis brama (‘bream’) versus river temperatures. Acoustic biotelemetry was applied in the lower River Severn basin, western Britain, in summer 2021 (barbel) and 2022 (bream), where individuals could move across > 150 km of river, including a tributary of cooler water. Across all individuals, bream occupied 37 km of river length (mainstem only), with low inter-individual variability in their spatial habitat use, movements and body temperatures. In contrast, barbel occupied 62 km of river (main river/tributary), with relatively high inter-individual variability in spatial habitat use, movements and body temperatures, with higher variation in body temperatures as river temperatures increased (maximum mean daily temperature difference between individuals on the same day: 4.2 °C). Although warmer individuals generally moved more, their activity was greatest at relatively low temperatures and higher flows, and neither species revealed any evidence of behavioural thermoregulation during elevated temperatures. Enabling phenotypically diverse fish populations to express their natural behaviours and thermal preferences in summer water temperatures thus requires maintaining their free-ranging in thermally heterogenous habitats.

Dams affect aquatic biota in running water by altering the environmental dynamics. One of the communities affected are benthic invertebrates, that perform important functions such as nutrient cycling and energy transfer in reservoirs. We investigated the influence of the following factors: spatial, abiotic variables, reservoir characteristics and land use on the richness, biomass and composition of benthic invertebrates in 29 reservoirs in southern Brazil. Sediment samples and abiotic variables were collected in the littoral and profundal zones of reservoirs during the dry (July) and rainy (November) seasons in 2001. We used principal coordinates of neighbour matrices to obtain the spatial factors. We analysed the unique and overall effects of the four factors. We found that the factors analysed significantly influenced the composition and biomass of the invertebrates (22%). The percentage of variation explained by the unique effects of the different factors showed similar values, but the spatial factors showed the highest value (4%). This indicates that closer reservoirs have higher similarities in terms of composition and biomass of benthic invertebrates. On the other hand, the abiotic variables had the highest explained value when evaluating the overall effects (10%). Therefore, for invertebrate richness, only the reservoir characteristics were significant for the overall and unique effects (49%). More specifically, we observed lower taxon richness in older reservoirs, probably because the age of such artificial aquatic ecosystems influences other variables, which structure the benthic communities. In conclusion, the structure of benthic invertebrate communities in reservoirs of southern Brazil are mainly driven by spatial and reservoir characteristics.