Exposure provides refuge from a rootless invasive macrophyte (original) (raw)
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Shading by an invasive macrophyte has cascading effects on sediment chemistry
Biological Invasions, 2009
The submersed freshwater macrophyte Utricularia inflata is a recent invader of Adirondack Mountain lakes (NY, USA). Previous experiments suggested that U. inflata can indirectly change nutrient cycling in Adirondack lake ecosystems by reducing the growth of native isoetid macrophytes, which in turn affects sediment chemistry. A 13-week greenhouse experiment was conducted to test the hypothesis that shading can explain the detrimental effect of U. inflata on the native short-statured isoetid, Eriocaulon aquaticum. Eriocaulon aquaticum has a dense root system that oxidizes sediment by releasing oxygen; it also takes up carbon dioxide from sediment. Growth and asexual reproduction of E. aquaticum grown under shaded conditions was reduced significantly compared to an unshaded control (P \ 0.001). Shading resulted in sediment changes: redox potential fell from 216 mV in the absence of shading to 76 mV under four layers of shade cloth (P \ 0.0001). Shading also increased the concentration of extractable sediment ammonium (P \ 0.01), as well as carbon dioxide concentrations (P \ 0.0001) and pH of porewater (P \ 0.05). The effect of U. inflata on the native isoetids and consequently on sediment chemistry closely matched the impact of shade cloth with similar light attenuation. Our results indicate that the principal mechanism by which U. inflata affects native isoetids and sediment chemistry is shading.
Dynamics of submerged macrophyte populations in response to biomanipulation
Freshwater Biology, 2001
of changes in submerged vegetation after biomanipulation was carried out in the eutrophicated Lake Finjasjo È n, Southern Sweden. Ten sites around the lake were revisited each year. At each site ®ve samples of above-ground biomass were taken at 10 cm water depth intervals. An investigation of the seed bank at the 10 sites, and a grazing experiment where birds and large ®sh were excluded was also conducted. 2. Between 1992 and 1996, in shallow areas (water depth < 3 m), vegetation cover increased from < 3 to 75% and above-ground biomass from < 1 to 100 g DW m ±2 . Mean outer water depth increased from 0.3 to 2.5 m. Elodea canadensis and Myriophyllum spicatum accounted for > 95% of the increase in biomass and plant cover. The following year (1997), however, cover and above-ground biomass decreased, mainly attributable to the total disappearance of E. canadensis. Secchi depth increased after biomanipulation until 1996, but decreased again in 1997. 3. Total and mean number of submerged species increased after biomanipulation, probably as a result of the improved light climate. However, after the initial increase in species number there was a decrease during the following years, possibly attributed to competition from the rapidly expanding E. canadensis and M. spicatum. The lack of increase in species number after the disappearance of E. canadensis in 1997 implies that other factors also affected species richness. 4. A viable seed bank was not necessary for a rapid recolonization of submerged macrophytes, nor did grazing by waterfowl or ®sh delay the re-colonization of submerged macrophytes. 5. Submerged macrophytes are capable of rapid recolonization if conditions improve, even in large lakes such as Finjasjo È n (11 km 2 ). Species that spread by fragments will increase rapidly and probably outcompete other species. 6. The results indicate that after the initial Secchi depth increase, probably caused by high zooplankton densities, submerged vegetation further improved the light climate. The decrease in macrophyte biomass in 1997 may have caused the observed increase in phosphorus and chlorophyll a, and the decrease in Secchi depth. We suggest that nutrient competition from periphyton, attached to the macrophytes, may be an important factor in limiting phytoplankton production, although other factors (e.g. zooplankton grazing) are also of importance, especially as triggers for the shift to a clear-water state.
Biological Invasions, 2011
Submersed aquatic plants have a key role in maintaining functioning aquatic ecosystems through their effects on the hydrological regime, sedimentation, nutrient cycling and habitat of associated fauna. Modifications of aquatic plant communities, for example through the introduction of invasive species, can alter these functions. In the Sacramento-San Joaquin River Delta, California, a major invasive submersed plant, Brazilian waterweed Egeria densa, has become widespread and greatly affected the functionality of the submersed aquatic plant community. Rapid assessments of the distribution and abundance of this species are therefore crucial to direct management actions early in the season. Given the E. densa bimodal growth pattern (late spring and fall growth peaks), summer assessments of this species may indicate which and where other submersed species may occur and fall assessments may indicate where this and other species may occur in the following spring, primarily because the Delta's winter water temperatures are usually insufficient to kill submersed aquatic plant species. We assessed community composition and distribution in the fall of 2007 and summer of 2008 using geostatistical analysis; and measured summer biomass, temperature, pH, salinity, and turbidity. In the fall of 2007, submersed aquatic plants covered a much higher proportion of the waterways (60.7%) than in the summer of 2008 (37.4%), with a significant overlap between the seasonal distribution of native and nonnative species. Most patches were monospecific, and multispecies patches had significantly higher dominance by E. densa, co-occurring especially with Ceratophyllum demersum. As species richness of non-natives increased there was a significant decrease in richness of natives, and of native biomass. Sustained E. densa summer biomass negatively affected the likelihood of presence of Myriophyllum spicatum, Potamogeton crispus, and Elodea canadensis but not their biomass within patches. Depth, temperature and salinity were associated with biomass; however, the direction of the effect was species specific. Our results suggest that despite native and invasive non-native submersed plant species sharing available niches in the Delta, E. densa affects aquatic plant community structure and composition by facilitating persistence of some species and reducing the likelihood of establishment of other species. Successful management of this species may therefore facilitate shifts in existing non-native or native plant species.
Hydrobiologia, 2000
Logistic regression was used to analyse the relationship between six submerged macrophyte taxa (Chara spp., Potamogeton perfoliatus, Potamogeton pectinatus, Potamogeton pusillus, Myriophyllum spicatum, Alisma gramineum and sum of all species) and four environmental variables (turbidity, effective wind fetch, water depth and sediment silt percentage, including interactions and some quadratic terms). The models were based on intensive vegetation samples (total c. 72 000) and other monitoring data carried out in five Dutch shallow lakes in the IJsselmeer area from 1988 to 1998. Water depth and light extinction were the most important factors determining the occurrence of all studied species in Veluwemeer, while effective wind fetch had a moderate effect and sediment silt had only a minor effect on the occurrence. Water depth had a negative impact on all species, except A. gramineum, which showed an optimum response. Three species showed an optimum response at intermediate turbidity (M. spicatum, P. pusillus and P. pectinatus), whereas the other taxa were negatively related. Three species (Chara spp., P. perfoliatus and M. spicatum) were positively related to wind fetch or showed an optimum response at intermediate value, whereas P. pusillus, P. pectinatus and A. gramineum were negatively related. The models including interactions between the explanatory variables showed a high goodness of fit for Veluwemeer for Chara, P. pectinatus and M. spicatum (in more than 8 of 10 instances, a cell originally scored '1' are predicted to have a higher probability than the ones originally scored '0'). The models of the other species showed a moderate goodness of fit (between 6 and 8 of 10 instances correctly predicted). The models developed for Veluwemeer were valid for Chara in all the four other lakes (more than 8 of 10 instances correctly predicted), while the models of other species were valid in some instances. A succession of vegetation was recognised based on water depth and turbidity in Veluwemeer. P. perfoliatus and P. pectinatus dominated the shallow zones under turbid conditions, but a change to dominance by Chara occurred in clear water. Based on the observation of co-occurrence, competition has played an important role for the shift from P. pectinatus to Chara. Chara became dominant 2 years after initial colonisation of Chara in P. pectinatus beds. Competition between P. perfoliatus and Chara may have been of less importance, due to a more distinct habitat (deeper colonisation) of dense P. perfoliatus beds. The analysed species showed large differences in vegetation stability from year-to-year. Chara showed the highest year to year stability (c. 65% of the cells remained covered from one year to another), while A. gramineum showed the highest dynamics (c. 10% of the cells remained covered from one year to another). Species producing specialized vegetative propagules for over wintering showed a higher local stability than species without such propagules.
Submerged macrophyte decline in shallow lakes: What have we learnt in the last forty years?
Aquatic Botany, 2016
Over the last 40 years there has been substantial evidence that high biomasses of submerged aquatic plants and phytoplankton rarely occur together in shallow lakes, but it is clear that when present, plants have a competitive advantage over algae. Aquatic plants provide habitat structure, which influences the fish community such that zooplankton and other macroinvertebrates maintain a top-down control on algal growth, and this control is largely independent of the nutrient supply to the lake. Nonetheless it is clear that many, but not all, lakes lose their vegetation as nutrient loading increases. However, in eutrophic lakes, the subsequent dominance by phytoplankton is more likely to be a result of the loss of vegetation rather than the cause. At higher nutrient levels, grazing or mechanical damage can reduce plant cover allowing rapid development of algae. Changes to fish community structure or the influence of toxic chemicals can reduce invertebrate algal grazers, overcoming the positive feedback loops that stabilise the plant dominance. The longer-term stability of macrophyte dominance is also reduced if there are few surviving plant species. Such loss of species richness is associated with increased nitrogen loading. Submerged plants also depend on a spring clear-water phase to become established, and local weather conditions during *Manuscript Click here to download Manuscript: Review_Phillips_Willby_Moss_PostReview_v3.docx Click here to view linked References 2 winter and spring may determine the relative success of phytoplankton and plant growth, leading to a progressively longer period of algal dominance and fewer surviving plant species. The loss of submerged vegetation from lakes, although often perceived as a rapid change, is more likely to be the final conclusion of a process in which the competitive advantage of a diverse plant community is eroded by many pressures that are collectively interpreted as eutrophication. In attempts to manage our environment we hope to find simple, closed stable systems that will respond to measures designed to meet our perceptions of improved ecological quality. What we increasingly find are more complex open systems, which do not necessarily respond as expected. We look for simple and widely applicable explanations where none are likely to exist.