Aquatic Ecology最新文献

Invasive plants have been shown to alter ecosystem functions. However, there is limited information available on the effect of the invasive species litter input on native litter decomposition and home-field advantage (HFA, increased decomposition at a home environment compared to a guest environment). To investigate this, we conducted a field experiment using leaves of native Trapa natans and Typha orientalis with and without invasive species Alternanthera philoxeroides and then incubated them at T. natans and T. orientalis habitats in a eutrophic lake for 50 days. In control and treatment, the decomposition and N release rate of T. natans were significantly higher than that in T. orientalis species litter at two habitats, indicating no HFA occurrence. A. philoxeroides litter input promoted the decomposition and N decay rate of T. orientalis, not T. natans. The mean decomposition rate of T. orientalis in control and treatment were 0.0138 and 0.0342 day⁻¹; for T. natans, it was 0.0703 and 0.0754 day⁻¹, respectively. The mean N decay rate of T. orientalis in control and treatment were 0.0235 and 0.0468 day⁻¹; for T. natans, it was 0.0511 and 0.0544 day⁻¹, respectively. Invasive species presence increased microbial respiration rate of T. orientalis, but not for T. natans species litter in two habitats. These results suggested that A. philoxeroides litter input accelerated low quality litter decomposition though increased microbial activity. However, it did not influence the HFA performance, which may be closely related to the lake eutrophication.

Aquatic invasive species decrease biodiversity and disrupt economic systems worldwide. Apple snails (Ampullaridae) from the genus Pomacea are globally invasive species that are highly damaging to aquaculture and aquatic ecosystems. Pomacea maculata was introduced to Louisiana in the early 2000s and rapidly spread throughout the southern half of the state, where invasive populations now threaten valuable aquaculture economies and a large area of aquatic ecosystems that sustain biodiversity important to commercial and recreational fisheries. Despite these risks, little work has been dedicated to understanding how apple snails disperse through invaded areas in Louisiana. To shed light on potential dispersal dynamics, we assessed population genetic structure of P. maculata in Louisiana at multiple spatial scales using microsatellites of snails collected from seven sampling locations. Overall, genetic diversity was relatively high across all sampling locations. Significant genetic structure was observed among sampling sites, indicating Barataria Preserve and the four sampling locations within Terrebonne Basin as distinct populations. Genetic distances were smallest among the four sampling locations within Terrebonne Basin. These findings suggest that dispersal within hydrologic units is higher than between units, meaning that apple snails may primarily move through systems through passive downstream dispersal. However, geographically distant populations also showed evidence of genetic mixing, pointing toward human-aided long-distance dispersal events. Regular dispersal of apple snails within and among hydrologic units highlights the risk of invasions in highly interconnected aquatic systems where dispersal rates may be especially high due to human modifications.

Watercress (Nasturtium officinale) has spread widely from Europe and commonly occurs in Oklahoma (USA) springs. Watercress is usually an emergent plant and affects water flow patterns and may provide habitat for biota. Although watercress is not considered an invasive species, its impacts in springs have not been reported. With a goal to describe possible impacts of watercress in springs, 14 karst-associated springs (12 with watercress) were surveyed for sediment characteristics, macroinvertebrates, and diatoms in July 2021. The effects of watercress were evident. Sediment particle size was unaffected by the presence of watercress but sediment organic matter was higher under watercress beds than outside of beds. Although there was no difference in total benthic macroinvertebrate density or richness, higher organic matter was associated with slightly higher abundances of detritivorous and predatory macroinvertebrates (SIMPER). Submerged portions of watercress had significantly much lower diatom density than other spring substrates, with diatom composition similar to other plants but different from that of rocks. Self-shading or possible allelopathy may cause the low diatom density. The significantly lower macroinvertebrate density within watercress mats relative to that of other plants may result from a reduced food source because the plant’s low diatom density. Only predatory damselflies were more common in watercress than in other plants, which had more abundant grazers. Although watercress can increase heterogeneity in sediments and is sometimes valued as an edible plant, watercress supports low algal and macroinvertebrate densities, such that extensive growth of watercress can have an overall negative impact on spring ecosystems.

Temporal variation in the taxonomic structure of microphytobenthos (MPB) in a riverine mangrove ecosystem was studied along the southwest coast of India. About 122 species of microphytobenthos comprising diatoms (113 species), cyanobacteria (seven species), dinoflagellate (one species), and euglenophyte (one species) were observed, in which pennate diatoms dominated by 92%. Major subclasses of diatoms identified were Bacillariophycidae, Fragilariophycidae, Thalassiosirophycidae, Melosirophycidae, and Coscinodiscophycidae. Average levels of fluvial nutrients estimated in the porewater were NO₃–N (28 ± 19.7 µmol L⁻¹), PO₄–P (3.77 ± 4.6 µmol L⁻¹), and SiO₄–Si (33.12 ± 27.2 µmol L⁻¹). The colonization and persistence of dense cyanobacterial mats during monsoon resulted in less abundance and diversity of diatoms than in other seasons. The numerical abundance of MPB was at its maximum during July (monsoon season) due to the dense cyanobacterial mat formed by Oscillatoria princeps. MPB diversity was at its maximum during MON (H´- 3.2), followed by POM (H´- 3.08) and lowest during PRM (H´- 2.23). The statistically significant seasonal variations in the diversity of MPB were noticed during the study period (ANOVA F value 8.120; df 2; p value < 0.05). The present study identifies sediment temperature and porewater salinity (freshwater preference) along with rainfall, sediment pH and C:N ratio as the major governing factors in the benthic microalgal mat formation of the study area.

Lakes are among the main sources of protein and livelihood to huge communities of rural people, and some of them house endemic fish species. The livelihood of about 200,000 rural people depends on Lake Manyara resources which also houses a population of the endemic and endangered fish, the Manyara Tilapia (Oreochromis amphimelas). Despite this importance, fishery in the lake is nearly under open access and it is not known how this has affected fish stocks. The lake is also under strong influence from overgrazing and poor farming practices in the highlands and adjacent areas which are polluting the lake. However, it is also not known how this has affected the growth and survival of fish in the lake. We assessed the impact of artisanal fishing and anthropogenic pollution on the stock of Manyara Tilapia and Nile Tilapia in Lake Manyara. We found that fish stocks in the lake are under heavy fishing pressure. Nearly all harvested Nile Tilapia were immature, and the majority of Manyara Tilapia were first time spawners caught at the length of their first maturity. This prevented the fishes from spawning at least once in their lifetime. Anthropogenic pollution has also hypereutrophied the lake and degraded the ecological quality for growth of Tilapia fish. Therefore, urgent site-specific mitigation measures and conservation actions are required to safeguard community livelihood and continued existence of the endangered Manyara Tilapia.

Dunaliella salina (microalgae), Fabrea salina (ciliate) and Artemia salina (crustacean) are the most abundant halophile Eukaryote organisms present in solar salterns at Sfax (Tunisia) when salinity is up to 150 PSU. We analysed the predator/prey relationship between the three organisms in laboratory conditions. In this study, aquatic food web relations were analysed by studying the grazing and energy transfer rates. In solar saltern, the dynamic population of Dunaliella displays a negative relationship with that of Fabrea and Artemia. Grazing experiments confirm that Fabrea and Artemia exercise a top-down control on Dunaliella populations. While Artemia and Fabrea occupy the same trophic level in food chain, the grazing rate of Fabrea on Dunaliella is strongly high reaching 0.85 × 10⁶ ± 0.05 cells mL⁻¹ day⁻¹. The fatty acids (FAs) appeared as good tracers to define the energy transfer along the food chain studied. Effectively, the FA composition of consumers appeared correlated to the FA of their prey. In parallel, the saturated fatty acids (SFAs) content decreased according to the trophic levels, and the opposite was observed for monounsaturated fatty acids (MUFAs). Therefore, palmitic acid (C16:0) showed trends that rendered it useful for tracing trophic transfer to consumers (Artemia). The polyunsaturated fatty acid (PUFA) and especially linoleic acid (C18:2) and linolenic acid (C18:3) were able to be traced across the transfer to Fabrea. This study increased our knowledge of the energy transfer between the major halophile organisms living in the solar salterns at Sfax (Tunisia). We proposed also that the fatty acids are used in future investigations to understand the predator/prey ecological relationship in marine eukaryote organisms.

Aquatic plants suffer stress caused by abiotic and biotic variables. In estuaries, salinity is one of the main abiotic factors responsible for stress. This study aimed to evaluate oxidative stress in two species of aquatic macrophytes (Crinum americanum and Spartina alterniflora) that are common in Brazilian tropical estuaries. We measured reactive oxygen species (hydrogen peroxide and malondialdehyde) and total nitrogen (TN) and total phosphorus (TP) in the aboveground and belowground biomass of the species. In addition, we measured salinity, TN, and TP content in the sediment. Statistical tests included t test and the analysis of variance (ANOVA) followed by the Tukey’s test. Our results showed that the greatest oxidative stress, in both species, occurred in areas of the estuary with lower salinity. For C. americanum, limitation by TN and TP content in the sediment is the main cause of oxidative stress. For S. alterniflora, the presence of C. americanum and the allelopathic compounds released by it seem to be the major cause of oxidative stress. Salinity did not induce oxidative stress in C. americanum and S. alterniflora in the estuary; however, the difference in TP and TN contents in the sediment played an important role in their responses to oxidative stress.

Leaf traits and chloroplast structure have a direct impact on plant growth rates. Fast-growing species allocate more carbon to growth, and slow-growing species invest more in storage. This study was conducted to investigate the fast-growing mechanism of the introduced mangrove species Laguncularia racemosa, by comparing the leaves of L. racemosa and three slow-growing native mangrove species (Kandelia obovata, Avicennia marina, and Aegiceras corniculatum) through analysis of anisotropic growth of leaf traits and leaf chloroplast ultrastructure. The results showed that the largest slope values were found in the leaf area compared to leaf perimeter relationship (2.035), while the slope of the leaf perimeter compared to leaf width relationship was only 0.832. And the leaf area of A. marina was most influenced by leaf perimeter, while the leaf area of L. racemosa was least influenced by leaf perimeter. Furthermore, the average area of thylakoid lamellae per chloroplast was the largest in L. racemosa leaves, with no accumulation of starch granules detected. While most of the chloroplast area of three native mangrove species was occupied by starch granules and lipid droplets, resulting in a reduction in the thylakoid lamellae contained per unit area of the chloroplasts. These results imply that the chloroplasts of L. racemosa can transport photosynthetic products to other organs of the plant in a timely manner, maximizing the area of thylakoid lamellae in the chloroplast and enabling its leaves to maintain high photosynthesis for its rapid growth.

The Portuguese man-of-war is responsible for the most common and severe stings worldwide. Jellyfish monitoring is essential to manage stings, and social media is a valuable data source for obtaining observations of this species. This study reports on using Convolutional Neural Networks for Portuguese man-of-war image classification extracted from social media posts. We created a suitable dataset and trained three different neural networks: VGG-16, ResNet50, and InceptionV3, with and without a pre-trained step with the ImageNet dataset. The pre-trained ResNet50 network presented the best results, obtaining 94% accuracy and 95% precision, recall, and F1 score. We conclude that Convolutional Neural Networks can be very effective for recognizing Portuguese man-of-war images from social media, helping in obtaining data about its occurrence and distribution.

This study focuses on the analyses of the gastral cavity contents of two species of Ceriantharia, namely Isarachnanthus nocturnus Hartog, 1977, collected in São Sebastião, Brazil, and Pachycerianthus magnus Nakamoto, 1919, collected from two points along the coast of Okinawa Island, Japan. Both morphological (light microscopy) and metagenomic (whole-genome shotgun sequencing) analyses were conducted with the aim of identifying the main classes of organisms that make up the diet of these species. The results revealed that morphological analyses were not sufficient for identifying prey organisms, but metagenomic analyses showed a diverse range of animal classes, indicating the varied diet of these ceriantharians. The most abundant classes observed in the contents of both species were Anthozoa, Aconoidasida, Kinetoplastea, Actinopterygii, Insecta, and Leptocardii. This finding suggests a cohesive feeding pattern among these two species from distant areas, providing a more comprehensive understanding of their feeding performance and contributing to studies on the subclass Ceriantharia.