Home About us Contact
|
Home About us Contact | ||
|
|
||
Macrophyte Communities (macrophyte + community)
Selected AbstractsSubmerged macrophytes as indicators of the ecological quality of lakesFRESHWATER BIOLOGY, Issue 4 2010MARTIN SØNDERGAARD Summary 1. We analysed submerged macrophyte communities from 300 Danish lakes to determine the efficacy of different species, maximum colonisation depth (Cmax) of plants as well as coverage and plant volume inhabited (PVI) as indicators of eutrophication. 2. Most species occurred at a wide range of phosphorus and chlorophyll a (Chla) concentrations, but some species of isoetids (Lobelia, Isoëtes) and Potamogeton (Potamogeton gramineus, Potamogeton alpinus and Potamogeton filiformis) were mainly found at low nutrient concentrations and hence may be considered as indicators of nutrient poor conditions. However, species typically found in nutrient-rich conditions, such as Elodea canadensis and Potamogeton pectinatus, were also found at total phosphorus (TP) <0.02 mg P L,1 and Chla <5 ,g L,1 and therefore cannot be considered as reliable indicators of eutrophic conditions. 3. Submerged macrophyte coverage, PVI and the Cmax were negatively correlated with TP and Chla. However, variability among lakes was high and no clear thresholds were observed. At TP between 0.03 and 0.07 mg P L,1 plant coverage in shallow lakes ranged from nearly 0 to 100%, whilst at concentrations between 0.10 and 0.20 mg P L,1 only 29% of the lakes had coverage >10%. Cmax was found to be a useful indicator only in deep lakes with unvegetated areas in the deeper part, whereas the use of coverage was restricted to shallow lakes or shallow areas of deep lakes. 4. Overall, submerged macrophytes responded clearly to eutrophication, but the metrics investigated here showed no well-defined thresholds. We developed a simple index based on species richness, presence of indicator species, coverage and Cmax, which might be used to track major changes in macrophyte communities and for lake classification. [source] Effects of stream restoration and management on plant communities in lowland streamsFRESHWATER BIOLOGY, Issue 1 2006TINA CHARLOTTE MOUSTGAARD PEDERSEN Summary 1. We evaluated restoration success on macrophyte species diversity and composition in lowland streams using communities in 30 naturally meandering stream reaches in the western part of Jutland, Denmark, as reference target communities. Fuzzy set clustering was used to examine the floristic and environmental similarity among reaches, whereas fuzzy set ordination was used to relate floristic patterns to environmental variables. 2. Two major groups of streams were identified based on their floristic composition. One group consisted of reference and restored reaches and the other of the majority of channelised reaches. We found that management exerted a strong influence on the macrophyte communities and that the identified groups were related to differences in management intensity. 3. Our results also indicate that bank morphology and bed level affected macrophyte communities in the streams, particularly the richness and abundance of terrestrial species. The analyses performed suggest that shallow and wide banks allow for a larger migration of species from the stream banks into the streams, thereby enhancing species diversity within the stream channel. 4. The results of this study suggest that macrophyte communities in channelised lowland streams can recover following restorative interventions given that stream management (i.e. weed cutting and dredging) is minimised and that stream banks are reprofiled to improve the lateral connectivity between the stream and its valley. [source] Effects of the exotic macrophyte, para grass (Urochloa mutica), on benthic and epiphytic macroinvertebrates of a tropical floodplainFRESHWATER BIOLOGY, Issue 6 2003Michael M. Douglas SUMMARY 1.,We examined the effect of the exotic macrophyte, para grass (Urochloa mutica), on benthic and epiphytic macroinvertebrates of a tropical floodplain in northern Australia. Macroinvertebrates were sampled from four grass communities: (1) para grass, (2) hymenachne (Hymenachne acutigluma), a native perennial; (3) rice (Oryza meridionalis), a native annual, and (4) areas where para grass had been sprayed with herbicide. 2.,Macroinvertebrate richness, abundance and community similarity showed very few differences among the grass communities, particularly in the epiphytic habitat. Benthic invertebrates showed some differences among grasses, with lower richness and abundance and different community structure associated with hymenachne. Herbicide control of para grass had no apparent effect on benthic invertebrates but reduced the abundance of epiphytic invertebrates in the short term. 3.,The results of this study indicate that para grass has very little impact on macroinvertebrate communities, despite the changes to macrophyte communities. This is probably because para grass has similar physical structure to the native grasses and because none of these grasses contribute directly to aquatic food webs. Control of para grass using herbicide has little impact on aquatic invertebrates. This suggests that predicting the impact of weed invasion in wetlands requires an understanding of both the functional properties of macrophytes and the habitat preferences of the macroinvertebrates. [source] Lake restoration: successes, failures and long-term effectsJOURNAL OF APPLIED ECOLOGY, Issue 6 2007MARTIN SØNDERGAARD Summary 1Eutrophication constitutes a serious threat to many European lakes and many approaches have been used during the past 20,30 years to improve lake water quality. Results from the various lake restoration initiatives are diverse and the long-term effects are not well described. 2In this study we evaluated data from more than 70 restoration projects conducted mainly in shallow, eutrophic lakes in Denmark and the Netherlands. Special focus was given to the removal of zooplanktivorous and benthivorous fish, by far the most common internal lake measure. 3In more than half of the biomanipulation projects, Secchi depth increased and chlorophyll a decreased to less than 50% within the first few years. In some of the shallow lakes, total phosphorus and total nitrogen levels decreased considerably, indicating an increased retention or loss by denitrification. The strongest effects seemed to be obtained 4,6 years after the start of fish removal. 4The long-term effect of restoration initiatives can only be described for a few lakes, but data from biomanipulated lakes indicate a return to a turbid state within 10 years or less in most cases. One of reasons for the lack of long-term effects may be internal phosphorus loading from a mobile pool accumulated in the sediment. 5Synthesis and applications. Lake restoration, and in particular fish removal in shallow eutrophic lakes, has been widely used in Denmark and the Netherlands, where it has had marked effects on lake water quality in many lakes. Long-term effects (> 8,10 years) are less obvious and a return to turbid conditions is often seen unless fish removal is repeated. Insufficient external loading reduction, internal phosphorus loading and absence of stable submerged macrophyte communities to stabilize the clear-water state are the most probable causes for this relapse to earlier conditions. [source] The tripartite biogeographical index: a new tool for quantifying spatio-temporal differences in distribution patternsJOURNAL OF BIOGEOGRAPHY, Issue 4 2006Tom Schils Abstract Aims, First, to develop an index that quantifies biogeographical patterns based on the basic descriptors of presence/absence distribution patterns (F, frequency; C, connectivity; G, grouping). Second, to test the proposed biogeographical index on a data set of macrophyte communities in the Arabian Sea using distribution data of macro-algae and seagrasses throughout the Indian Ocean. Location, Arabian Sea (regional macrophyte community data) and the larger Indian Ocean (oceanic distribution data). Methods, The proposed index is derived from the Tulloss tripartite similarity index. The tripartite biogeographical index (TBI = ,F × C × G) is calculated for a specific taxon and incorporates several fundamental parameters of presence/absence data in grid cell (block) patterns. TBI accounts for the relative abundance of a taxon, the average grouping of its occurrences, the average of minimal absence intervals between taxon presences and the largest coherent cluster of taxon occurrences, and also incorporates dispersal aspects. The macrophytes from the case study are among the best documented marine organisms in the Indian Ocean. The regional distribution data from the Arabian Sea result from exhaustive species lists from Masirah Island (Oman) and the Socotra Archipelago (Yemen). Results, TBI values fit a linear scale corresponding to the proportional presence and the distributional spread of taxa within a given geographical area. The three functions that constitute TBI can be evaluated separately or in association with TBI, to give detailed information on the important factors that characterize the biogeographical distribution of a taxon (or larger entities consisting of multiple taxa such as communities). The case study on Arabian macrophytes clarifies the use and explanatory power of the index. Main conclusions, The biogeographical descriptors can be combined into an index which accurately quantifies taxon occurrences and distribution types on a single linear scale from rare/scattered to abundant/grouped. Together with its three functions, the index allows for a non-arbitrary selection of taxa and taxon groupings based on their distribution pattern. The analysis of TBI values for the Arabian macrophyte communities confirms previous biogeographical findings and enables more detailed statistical analyses of the distribution data. [source] Effect of observation method on the perception of community structure and water quality in a brackish water ecosystemMARINE ECOLOGY, Issue 2009Tiia Möller Abstract The EU Water Framework Directive is a Community legislative instrument in the field of environmental protection that establishes a common framework for keeping water quality at a favourable level. To implement the directive, classification systems need to be established that allow detection of human impacts at early stages and, thus, more effective management of coastal communities. Due to the spatial variability of communities, however, the results of any assessment are highly dependent on the selection of data. In this study we identified local spatial scales in which variability of macrophyte communities was maximised, quantified links between observed patterns of sediment types and communities and estimated how selection criteria impacted the outcome of the assessment of indicator class value in four different communities of the Northern Baltic Sea. The main findings of the study were that: (i) there were no clear local spatial scales in which the variability of benthic communities was maximised; (ii) hard-bottom communities were better predicted by the spatial arrangement of sediment characteristics than soft-bottom communities; (iii) the selection of method had no effect on the estimates of macrophyte cover and indicator class; but (iv) method impacted independently of habitat type on error estimates of macrophyte cover and indicator class. To conclude, in such homogeneous and low diversity macrophyte communities it is preferable to use methods that result in lower error estimates of algal coverage and, thus, result in lower uncertainties of estimates in the water quality class. [source] Reestablishment of the Southern California Rocky Intertidal Brown Alga, Silvetia compressa: An Experimental Investigation of Techniques and Abiotic and Biotic Factors That Affect Restoration SuccessRESTORATION ECOLOGY, Issue 2010Stephen G. Whitaker Previous research has indicated that many rocky intertidal macrophyte communities in southern California, and other locations around the world, have shifted from larger, highly productive, fleshy seaweeds toward a smaller, less productive, disturbance-tolerant flora. In widespread decline are ecologically important, canopy-forming, brown seaweeds, such as the southern California rockweed species Silvetia compressa. Restoration efforts are common for depleted biogenic species in other habitats, but restoration within rocky intertidal zones, particularly on wave-exposed coasts, has been largely unexplored. In two phases, we attempted to restore Silvetia populations on a southern California shore by transplanting live plants and experimentally investigating factors that affect their survival. In Phase I, we implemented a three-way factorial design where juvenile Silvetia thalli were transplanted at four sites with a combination of simulated canopy and herbivore exclusion treatments. Transplant survival was low, although enhanced by the presence of a canopy; site and herbivore presence did not affect survival. In Phase II, we used a two-way factorial design, transplanting two size classes of rockweeds (juveniles and reproductive adults) on horizontal and partially shaded, north-facing vertical surfaces at a target location where this rockweed has been missing since at least the 1970s. Transplant survival was moderate but lower than natural survival rates. Larger thalli exhibited significantly higher survival rates than smaller thalli in both the transplanted and naturally occurring populations, particularly on vertical surfaces. Higher mortality on horizontal surfaces may have been due to differences in desiccation stress and human trampling. Transplanting reproductive adults resulted in the subsequent recruitment of new individuals. [source] Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition, species richness and functional diversityFRESHWATER BIOLOGY, Issue 6 2010THAÍSA SALA MICHELAN Summary 1.,The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2.,In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara, tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3.,Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free-floating species was positively affected. 4.,Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free-floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5.,Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity. [source] Stable nitrogen isotope ratios of macrophytes and associated periphyton along a nitrate gradient in two subtropical, spring-fed streamsFRESHWATER BIOLOGY, Issue 8 2007LORETO DE BRABANDERE Summary 1. An increase in human population and associated changes in land use have caused an increase in groundwater nitrate concentrations throughout central Florida. Within the region, this nitrate-laden groundwater returns to the surface via numerous large springs that serve as the origin of flow for many coastal streams and rivers. These rivers can exhibit strong nitrate gradients because of the high nutrient uptake potential of the rivers. 2. We hypothesised that downstream declines in nitrate concentrations would be manifested spatially as increases in the ,15N of the residual pool of nitrate, macrophytes and periphyton as a consequence of isotopic fractionation associated with preferential use of 14NO3,. This hypothesis was tested in two spring-fed river systems, the Chassahowitzka and Homosassa rivers, along Florida's central Gulf of Mexico coast. 3. In general, ,15N values of nitrate, macrophytes and periphyton increased with decreasing fraction of nitrate remaining in each of the two study systems. The fractionation associated with nitrate uptake by macrophytes and associated periphyton was determined from the relationship between ,15N of both constituents of the macrophyte community and the fraction of nitrate removed from the system. Values for fractionation by macrophytes and periphyton ranged from 1.9, to 3.6, and from 0.7, to 2.5,, respectively. [source] Community effects of invasive macrophyte control: role of invasive plant abundance and habitat complexityJOURNAL OF APPLIED ECOLOGY, Issue 2 2010Katya E. Kovalenko Summary 1. The control of invasive species has become a widespread management practice, yet information on the community effects of such efforts is very limited, there is no unified framework for monitoring their success and no guidelines exist to help minimize potential adverse impacts. 2. This study was conducted to determine how long-term efforts to control a widespread invasive macrophyte, Eurasian watermilfoil, affect native macrophytes, fish and macroinvertebrates. In addition, we examined how members of the aquatic fauna respond to changes in invasive macrophyte abundance and habitat complexity to understand the mechanisms underlying any potential community response. 3. Selective control of the invasive macrophyte had minor effects on habitat complexity due to timely recolonization by native macrophytes and it did not affect littoral fish richness and abundance. Macroinvertebrate communities were highly variable and some of that variation could be attributed to characteristics of the macrophyte community. Fish and macroinvertebrates were more affected by habitat complexity than by other attributes of the macrophyte assemblage. 4.Synthesis and applications. Management plans to control invasive species need to prioritize selective removal and timely restoration of the native assemblage. In this study, the invasive macrophyte was used by aquatic fauna, which emphasizes the need for immediate restoration of the native macrophyte community to mitigate for the lost habitat after invasive plant control efforts. As both fish and macroinvertebrates were more affected by complexity than other attributes of the macrophyte assemblage, re-establishment of habitat complexity appears to be a promising restoration strategy. On a more general note, we highlight the importance of assessing community response to the habitat provided by the invader and invader's function in the community when evaluating strategies to control invasive species. [source] | ||||||||||