Aquatic Botany最新文献

The phenology of Laguncularia racemosa (L.) Gaertn. (Combretaceae) was investigated from a population located near the species’ northeastern range limit in Florida. Height, leaf dimensions, and the number of flower buds, flowers, and propagules were recorded, on average, every 2–3 months from May 2021 to October 2023. Irradiance, temperature, and inundation depth were measured hourly with data loggers and compared among seasons and years. Although plant heights were negatively impacted by freeze events in 2022 due to defoliation, vertical growth rates were significantly greater following the freeze. Flower bud and flower production were observed during the summer months and differed among years with greater abundances in 2021. Propagules were recorded in summer and autumn with greater abundances in 2021 and 2022 than in 2023. Light intensity was unlikely to limit growth without a canopy of L. racemosa. Maximum inundation depths > 1.2 m were recorded in autumn and winter when propagule dispersal was likely to occur. The greatest depth of 2.2 m was more than the tallest individual in the study and occurred when hurricanes coincided with extreme high tides. The L. racemosa population was resilient to freeze and flooding events suggesting that population densities may continue to increase in northeastern Florida marshes.

Althenia (Potamogetonaceae) is a small genus of aquatic angiosperms from saline environments that includes the most recently evolved seagrass, Althenia marina. One or two species occur in Europe, both rare and considered Data Deficient at the regional level. We report the first records of Althenia in Portugal since 1853: two populations in the Algarve and a third in central Portugal. As in previous studies, all Portuguese populations include plants with and without visible nerves in the leaf sheaths, a character used to distinguish between A. orientalis and A. filiformis. We tentatively recognize a single Althenia species in Eurasia, pending further studies. We recommend further searches of suitable habitat, as Althenia species are small and easily overlooked, as well as monitoring and safeguarding of known populations through in situ and ex situ conservation.

Spate floods control sediment, nutrient and biodiversity patterns in river floodplains, but the diachronic effects of spate floods on these compartments are rarely assessed. The effects of a 10-year flood spate on substrate characteristics and aquatic vegetation (community composition and life-history traits) were assessed before and after the spate in eleven former river channels that had become wetlands and varied in flood frequency. The effects of spate flooding on sediment and vegetation were expected to be greater in the less frequently flooded channels. For life-history traits, we expected a greater effect of the flood on tall evergreen species with high leaf area, while species with ruderal traits were expected to be less affected. For sediments, the flood reduced fine sediment cover and organic carbon content, but did not affect nutrient content. Vegetation cover decreased particularly in the most and least frequently flooded channels. Species richness and functional indices were little affected. The disturbance had a significant effect on plant traits, reducing tall evergreen species. This effect on plant characteristics increased as the frequency of overflow increased. The results highlight the key role of erosive floods in maintaining poorly competitive aquatic plants and limiting successional processes in riverine wetlands. Given the importance of plants in maintaining spate floodplain biodiversity, these erosive spate floods are essential to maintain or restore in a context of extreme river regulation.

Non-geniculate coralline algae (NGCA), Corallinophycidae - Rhodophyta, are characterized by prominent calcified vegetative thalli. They exhibit broad phenotypic plasticity, and morphoanatomical convergences due to the simplicity of their thalli. These characteristics makes their taxonomy one of the most complex within Rhodophyta. The nomenclature and taxonomy of the NGCA have been controversial and subject to intensive debate even after the advent of molecular techniques. Until the mid-19th century, all calcareous organisms were classified as animals. Still, the algal nature of the NCG became evident with advances in microscopy and anatomical techniques, based on anatomical and reproductive attributes rather than thallus form. This review provides a comprehensive historical overview of significant milestones in the NGCA taxonomy. From 1890–1910, Mikael Foslie described about 400 species of NGCA. Since then, and after the advances in microscopy in the mid-20th century, the taxonomy of this algal group, traditionally based on morphological aspects, has been replaced by anatomical features. Paraffin and historesin-embedded microtomy and sectioning techniques allowed access to taxonomically relevant microanatomical features, while scanning and transmission electron microscopy allowed access to ultrastructural aspects. The subsequent use of molecular markers promoted a real revolution, by disclosing phylogenetic relationships between taxa. As perspectives, high-resolution confocal microscopy images can provide information on intricate three-dimensional structures and reveal unexplored aspects of NGCA morphoanatomy. Meanwhile, whole-genome sequencing and comparative genomics can uncover the genetic underpinnings of taxonomic variations, helping to elucidate the mechanisms driving the diversification of NGCA species. We envision that the recent expansion of sampling expeditions to previously unknown geographic and bathymetric regions along with the convergence of advanced morphoanatomy imaging, genomics, and bioinformatics, would clarify the complex tapestry of NGCA taxonomy and safeguard (e.g., through conservation action-plans) these ecologically important marine organisms.

Changes in nutrient concentration, temperature and light intensity due to climate change can alter the species composition of aquatic ecosystems, since global climate change can intensify the process of eutrophication. Eutrophication can enhance the biological invasion and the distribution of alien aquatic plants. Here we investigated the competition ability of alien Pistia stratiotes and native Hydrocharis morsus-ranae and the effect of different light intensities, temperatures and nutrient concentrations on the functional traits of the two species. In short term (8 days) monoculture experiment, we applied low (0.5 mg L^-1 N; 0.05 mg L^-1 P) and high nutrient concentrations (2 mg L^-1 N; 0.2 mg L^-1 P), four different light intensities (25–295 μmol m⁻² s⁻¹) as well as cold and warm (21.5; 27.5 ± 0.5°C) water treatments in full factorial design. In mixed cultures we cultivated the plants for 28 days with various biomass ratio, in shaded and well illuminated conditions, at a high nutrient concentration (4 mg L^-1 N 1 mg L^-1 P). In monocultures, the relative growth rate of P. stratiotes in warm water was significantly higher than that of H. morsus-ranae, however, this difference was not significant in colder water. In the co-culture experiment, P. stratiotes had significantly higher growth rate compared to H. morsus-ranae regardless of initial plant biomass ratio. Under shaded (65 ± 5 μmol m⁻² s⁻¹) conditions, P. stratiotes outcompeted H. morsus-ranae, resulting in its decay. Experimental results imply that with elevated temperature, the spread of alien P. stratiotes can be expected. Furthermore, under shaded conditions, P. stratiotes has a higher chance of occupying the water surface over the native plant H. morsus-ranae.

The present paper aims at contributing to the knowledge of rhodolith beds by describing the associated macroalgal assemblages of two beds in the western Mediterranean Sea: Gorgona Island in the Tuscan Archipelago National Park and Capo Carbonara Marine Protected Area in the southern Sardinia. Patterns of biodiversity and spatial variability were investigated through a multifactorial sampling design. A total of 84 macroalgal species was identified, 17 Heterokontophyta, 7 Chlorophyta, 1 Prasinodermatophyta and 59 Rhodophyta. Significant differences between beds were detected and the main species characterizing the two beds were highlighted. The mean number of species per sample was quite low and beta diversity high compared to most Mediterranean macroalgal assemblages.

Blue carbon ecosystems such as mangroves, salt marshes, and seagrass beds are found globally and are fundamental to fisheries production, storm surge protection, and carbon sequestration. The contribution of seagrass ecosystems to global carbon stocks is still not well understood, including in the United States Virgin Islands (USVI). No study has been published to-date assessing the sediment carbon density (SCD) in seagrass beds in the USVI. This study focused on the carbon storage ability of the invasive species, Halophila stipulacea, which is compact in size compared to common native seagrasses and has spread rapidly to become a dominant seagrass in the USVI. This species forms dense mats across a wide depth range (<1 m to 50 m) typically uninhabitable to its native counterparts (Syringodium filiforme and Thalassia testudinum). Several biotic and abiotic factors influence the carbon storage ability of seagrass, yet little is known about carbon storage sequestration along a depth gradient for H. stipulacea. This study provides the first assessment of the biological characteristics (shoot density, leaf area, leaf height, and percent cover) and carbon storage ability of H. stipulacea across a depth gradient (shallow: 5–10 m; medium: 15–20 m; deep: 25–30 m) at two sites in St. Thomas, USVI. Mean sediment carbon density (SCD) values per core reported for H. stipulacea in this study ranged from 3.88 to 15.67mgC/cm³; these were comparable to regional and global seagrass studies. Biological characteristics were not an accurate predictor of SCD. A significant interaction between water depth and site was found to affect mean SCD of H. stipulacea beds. It is likely that site-specific factors most likely account for variations seen within the data. Although carbon values in this study compared to values reported in the literature, other factors such as land use, proximity to carbon sources, sediment microbial community, and water current patterns may be driving SCD values. These findings highlight the need for site and species-specific carbon storage assessments on local to regional scales to accurately estimate current and forecasted blue carbon stocks.

Submerged aquatic vegetation, and especially charophytes, which are an important habitat for many species, have declined in the Baltic Sea due to changes in light climate, eutrophication and physical disturbance. Physical disturbance in the form of small-scale dredging activities is commonplace in Sweden due to land uplift, but causes fragmentation of coastal habitats. Here we test three planting methods for restoration of the charophyte Chara aspera on an area of deposited sediment, and a single method for restoration of C. tomentosa in a dredged area. We found that none of the planting methods tested was more successful than natural recolonization of C. aspera on the deposited sediment. C. tomentosa planting was unsuccessful in the dredged area and was likely outcompeted for light by taller species. The C. aspera meadow was resilient to smaller disturbances, as experimental removal of up to 2.5% of C. aspera and sediment from the donor area did not reduce C. aspera coverage a month after removal. Even after an uncontrolled event that removed up to 50% of C. aspera in the experimental plots, C. aspera coverage had returned to pre-removal levels a year after the disturbance. We suggest future restoration experiments test transplanting sediment rich in oocytes and bulbils into areas with suitable light climates and low competition with other species. Restoration efforts are costly and highly uncertain of success, therefore we recommend discontinuing dredging activities in charophyte meadows to protect this important habitat.

Shallow lakes have two stable ecological states, macrophyte dominated or algal dominated. The macrophyte dominated state is the more desired state as it generally has clearer water that is safe for contact recreation. Whereas the algal dominated state is considered degraded, resulting from high anthropogenic nutrient inputs, with turbid water that is often unsafe for contact recreation. These ecological states are somewhat resilient due to in-lake feedback loops that maintain or enhance conditions for the dominate primary producer. For the macrophyte dominated state, many of these feedback loops are theoretically plant density dependent, but rarely has the plant density required to initiate these feedback loops been identified. Here we illustrate the plant density dependence of a previously unstudied feedback loop present in the macrophyte dominated state. Increased densities of Isoëtes kirkii were able to reduce sediment oxygen demand through their root oxygen releases. This reduction in sediment oxygen demand occurred at 32 plants m⁻² in a garden soil and 63 plants m⁻² in the sediment of a hypo-eutrophic lake, a disparity likely due to the higher initial sediment oxygen demand present in the lake sediments. In a shallow lake, plants present in the hypolimnion will reduce sediment oxygen demand, increasing the amount of time required before anoxic conditions are created and the resulting release of dissolved reactive phosphorus. This will likely decrease the potential for subsequent algal blooms and the associated shading of submerged macrophytes, thus maintaining in-lake conditions that favour macrophytes.