Hydrilla [Hydrilla verticillata (L. f.) Royle], an invasive aquatic weed, has had a rich introduction history into the United States, with multiple subspecies being introduced since the 1960s. The most recent occurred before 2016, when northern hydrilla (Hydrilla verticillata ssp. lithuanica) was discovered in the Connecticut River. By 2021, following a 3-yr survey from Agawam, MA, to the Long Island Sound by the Connecticut Agricultural Experiment Station Office of Aquatic Invasive Species, H. verticillata ssp. lithuanica was found in more than 113 km of the river, occupying 344 ha. Since this survey, there has been concern that H. verticillata ssp. lithuanica would spread to nearby waterbodies and have a significant negative impact. Here, we report the first documented spread and establishment of H. verticillata ssp. lithuanica from the Connecticut River to five waterbodies in Connecticut and one in Massachusetts. Of the eight sites where H. verticillata observations were made, 75% (n = 6) were confirmed to be H. verticillata ssp. lithuanica and 25% (n = 2) to be Hydrilla verticillata ssp. peregrina (wandering hydrilla). Except for one site, all six locations infested with H. verticillata ssp. lithuanica provide watercraft access through public or private boat ramps. The authors also postulate on the mechanisms facilitating the spread and establishment of this subspecies.

Desiccation following prolonged air exposure challenges survival of aquatic plants during droughts, water drawdowns, and overland dispersal. To improve predictions of plant response to air exposure, we observed the viability of vegetative fragments of 10 aquatic plant species (Cabomba caroliniana, Ceratophyllum demersum, Elodea canadensis, Egeria densa, Myriophyllum aquaticum, Myriophyllum heterophyllum, Myriophyllum spicatum, Potamogeton crispus, Potamogeton richardsonii, and Hydrilla verticillata) following desiccation. We recorded mass loss, desiccation rate, and plant fragment survival across a range of air exposures. Mass loss accurately predicted viability of aquatic plant fragments upon reintroduction to water. However, similar periods of air exposure differentially affected viability between species. Understanding viability following desiccation can contribute to predicting dispersal, improving eradication protocols, and disposing of aquatic plants following removal from invaded lakes or contaminated equipment.

Total nonstructural carbohydrate (TNC) reserves support growth, formation of reproductive structures, and sprouting of plant tissues, and nitrogen (N) is essential for amino acid synthesis and photosynthetic enzyme production. Timing of weed management to periods when these critical resources are most limiting might improve efficacy. We examined seasonal changes in carbohydrate and nitrogen concentrations in Brazilian egeria (Egeria densa), a common submersed aquatic weed, from two locations in the United States. Plants were collected from a coastal Oregon reservoir and from California's Central Valley in the Sacramento–San Joaquin Delta. Starch comprised between 35 to 51% of the TNC in lower stems and root crowns. Seasonal changes in resource concentrations were not consistent between years within a population or for the same plant part between different populations. Lowest TNC concentrations were observed earlier in the growing season (March) in Disappointment Slough than in Big Creek (May to June). Conversely, highest concentrations were observed in October in Disappointment Sough and from August to March in Big Creek. Nitrogen concentrations were highest in stem tips in both populations, with more distinct seasonal changes in the California population. These data suggest western populations of E. densa might exhibit less-discernible low points in root crown and lower stem energy storage for targeting management activities to vulnerable phenological stages. Brazilian egeria has high phenological plasticity despite its low genetic diversity and lack of specialized reproductive and perennating structures, which allows the plant to invade and dominate submersed plant communities in areas with mild winters.

This paper describes the species composition, vertical distribution, and the seasonal changes in the biomass of subtidal macrophytes in Sobol Bay (Peter the Great Bay, Sea of Japan). The samples were collected in the depth-range from 0.5 to 4 m. A total of 65 macrophyte species were identified, among which were 10 species of Chlorophyta, 17 of Phaeophyceae, 37 of Rhodophyta and 1 of Magnoliophyta. Multivariate analyses were performed to detect spatial and temporal variations. Maximum species richness was registered in June, with a particularly dramatic biomass increase of brown algae. Both the number of species and the biomass of macrophytes decreased with increasing depth. Depth clearly affected the patterns of seasonal fluctuations of the species composition and biomass. In the study area, the species composition of the shallow-water algal assemblages was more stable throughout the year compared to that of the algal assemblages found in deeper waters. In total, four macrophyte assemblages were identified in the bay. A Phyllospadix iwatensis and Coccophora langsdorfii dominated assemblage occupied muddy-gravel bottoms in depths from 0.5 to 2 m throughout the year. An assemblage, co-dominated by annual brown algae Desmarestia viridis and Costaria costata, occurred at depths more than 3 m at late spring. Two other assemblages occurred on the rock and boulder bottom at 0.5–2 m depths, but they were temporally separated. An assemblage co-dominated by annual laminarian algae (Undaria pinnatifida and Costaria costata) developed at late spring and was succeeded in the autumn and winter by a Tichocarpus crinitus, Ulva lactuca, Sargassum pallidum and Codium fragile co-dominated assemblage. A comparison between the data obtained in the present study and the results of a previous study conducted in 1927 shows that the macrophytes assemblages in Sobol Bay underwent little change.

The objective of the present study was to examine the colonization of oligochaetes during the decomposition of leaves of the macrophyte Eichhornia azurea in a lentic system in southeastern Brazil. The experiment was conducted between September and November 2007, with the use of 21 nylon bags measuring 15×15 cm with 2 mm mesh, each containing 10 g of dried leaves. The bags were removed from the lake after 2, 5, 8, 12, 25, 45 and 65 days. At the end of the experiment, 31.40% of the initial mass remained, and the decomposition rate was 0.018 d−1. The mean density of oligochaetes during the experiment was 32.81±9.58 ind.g−1 DM. The sub-families Naidinae and Pristininae accounted for 99.83% of the oligochaetes. The substrate quality influenced the colonization of E. azurea leaves, as observed from the cluster analysis by the formation of two groups based on increased density during the experiment, indicating a degradative ecological succession. During the decomposition there were changes in the community of oligochaetes, resulting from differences in the ability to exploit various food sources, with predominance of predators in the first decomposition phase and of collectors at the end of the experiment.

Many natural and human-induced events create disturbances in seagrasses throughout the world, but quantifying losses of habitat is only beginning. Over the last decade, 90000 ha of seagrass loss have been documented although the actual area lost is certainly greater. Seagrasses, an assemblage of marine flowering plant species, are valuable structural and functional components of coastal ecosystems and are currently experiencing worldwide decline. This group of plants is known to support a complex trophic food web and a detritus-based food chain, as well as to provide sediment and nutrient filtration, sediment stabilization, and breeding and nursery areas for finfish and shellfish.

We define disturbance, natural or human-induced, as any event that measurably alters resources available to seagrasses so that a plant response is induced that results in degradation or loss. Applying this definition, we find a common thread in many seemingly unrelated seagrass investigations. We review reports of seagrass loss from both published and ‘grey’ literature and evaluate the types of disturbances that have caused seagrass decline and disappearance. Almost certainly more seagrass has been lost globally than has been documented or even observed, but the lack of comprehensive monitoring and seagrass. mapping makes an assessment of true loss of this resource impossible to determine.

Natural disturbances that are most commonly responsible for seagrass loss include hurricanes, earthquakes, disease, and grazing by herbivores. Human activities most affecting seagrasses are those which alter water quality or clarity: nutrient and sediment loading from runoff and sewage disposal, dredging and filling, pollution, upland development, and certain fishing practices. Seagrasses depend on an adequate degree of water clarity to sustain productivity in their submerged environment. Although natural events have been responsible for both large-scale and local losses of seagrass habitat, our evaluation suggests that human population expansion is now the most serious cause of seagrass habitat loss, and specifically that increasing anthropogenic inputs to the coastal oceans are primarily responsible for the world-wide decline in seagrasses.

Germination responses to 45 combinations of diurnal mean temperature and amplitude were examined in freshly collected seeds of two wetland perennials: Typha latifolia L. and Phragmites australis (Cav.) Trin. ex Steudel. Nearly all seeds (>95%) germinated in favourable temperature regimes. Mean temperature (range 10–30°C) and amplitude (range 0–20°C) affected final germination of both species. P. australis required a high amplitude (> 10°C) for germination over the entire range of mean temperatures. Final germination of T. latifolia was more sensitive to mean temperature than P. australis. The germinated proportion of T. latifolia had a maximum around 20°C, above which it decreased, and amplitudes were more stimulating at low than at high levels of mean temperature. The germination rate was rapid and increased with mean temperature for both species. More than 50% germination was achieved within 1–3 d at favourable temperatures. It is proposed that the thermal requirements provide the non-dormant seeds with a season-sensing mechanism which postpones germination of seeds dispersed during autumn, winter or early spring, until the soil surface is heated by the sun in the spring and sufficiently large diurnal fluctuations of temperature occur. Furthermore, the amplitude requirement implies a strong avoidance mechanism for germination of P. australis in sites with small temperature fluctuations (e.g. below water tables), whereas seeds of T. latifolia appear to be less exacting in the requirements when the soil or water becomes warmer.

La végétation de 12 cours d'eau répartis sur le territoire français a été étudiée selon le protocole standardisé d'échantillonnage «Milieu Et Végétaux aquatiques fixés» (M.E.V.) pour tester ce procotole. Le traitement des données par rivière puis pour l'ensemble des séquences étudiées permet d'établir des typologies floristiques. De façon préliminaire, le déterminisme de distribution des phytocénoses est envisagé. Les différences majeures s'expriment à l'amont en fonction de la géologie et de la minéralisation, des conditions d'écoulement et d'ombrage. Une homogénéisation s'effectue vers l'aval, à la faveur de l'eutrophisation et de l'accroissement des dimensions du cours d'eau. La dimension éco-régionale s'exprime d'abord au niveau de la géologie, et secondairement en fonction du climat (atlanticité) et des différences entre rivières de plaine et de piémont. Les résultats sont discutés en vue d'une amélioration du protocole et de la possibilité d'application de la notion de phytocénoses de référence.

Les relations spatiales et les évolutions entre les groupements végétaux d'un étang soumis à de fortes variations de niveau ontété étudiées par des croisements manuels des relevés et par Analyse Factorielle des Correspondances. Les résultats des deux approches concordent partiellement. Deux schémas évolutifs distincts sont mis en évidence, dans la zone principale et dans la queued'étang. De fortes disparités apparaissent en fonction d'une part, de la morphologie des rives et, d'autre part, des variations interannuellesdes niveaux d'eau. Des recommandations pour une gestion patrimoniale sont présentées.