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Littoral Zone (littoral + zone)
Kinds of Littoral Zone Selected AbstractsTop-Down Control of Reed Detritus Processing in a Lake Littoral Zone: Experimental Evidence of a Seasonal Compensation between Fish and Invertebrate PredationINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2007Giorgio Mancinelli Abstract We investigated whether predatory fish exert a top-down control on reed leaf packs processing in a lake littoral zone through a trophic cascade. Exclosure experiments were repeated in summer and winter, under high and low natural fish abundance, respectively. Fish exclusion effects on detritus processing and fungal conditioning were consistent with trophic cascade predictions only in summer. In winter, however, results indicated that a trophic cascade was induced by predatory invertebrates. In both seasons, variations in detritivores abundance generally supported a cascade scenario, whereas several taxon-specific departures occurred during the experimental periods. We conclude suggesting that predators may continuously regulate leaf detritus processing in lake littoral zones, through a seasonal shift in the relative contribution of fish and invertebrate predation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The effects of water-level manipulation on the benthic invertebrates of a managed reservoirFRESHWATER BIOLOGY, Issue 5 2010DANIEL C. McEWEN Summary 1. Reservoir creation and management can enhance many ecological services provided by freshwater ecosystems, but may alter the natural conditions to which aquatic biota have adapted. Benthic macroinvertebrates often reflect environmental conditions, and this community may be particularly susceptible to water-level changes that alter sediment exposure, temperature regime, wave-induced sediment redistribution and basal productivity. 2. Using a before,after control,impact experimental design, we assessed changes in macroinvertebrate community structure corresponding with changes in water-level management in two lentic systems in the Voyageurs National Park, Minnesota, U.S.A. Littoral zone (depths 1,5 m) benthic macroinvertebrate assemblages were sampled in Rainy Lake (control system) and Namakan Reservoir (impact system) in 1984,85, and again in 2004,05 following a change in water-level management that began in January 2000. The new regime reduced the magnitude of winter drawdown in Namakan Reservoir from 2.5 to 1.5 m, and allowed the reservoir to fill to capacity in late May, a month earlier than under the prior regime. Rainy Lake water levels were not altered substantially. 3. We found changes in macroinvertebrate community structure in Namakan Reservoir relative to Rainy Lake at 1,2 m depths but not at 3,5 m depths. These shallower depths would have been most directly affected by changes in sediment exposure and ice formation. 4. In 2004,05, Namakan Reservoir benthos showed lower overall abundance, more large-bodied taxa and an increase in non-insect invertebrates relative to 1984,85, without corresponding changes in Rainy Lake. 5. Changes in the benthic community in Namakan may reflect cooler water in spring and early summer as well as lower resource availability (both autochthonous production and allochthonous inputs) under the new regime. [source] Fish distribution and diet in relation to the invasive macrophyte Lagarosiphon major in the littoral zone of Lake Dunstan, New ZealandECOLOGY OF FRESHWATER FISH, Issue 1 2008T. O. Bickel Abstract,,, Invasive macrophytes are usually associated with negative impacts on habitat quality and a threat to native biodiversity. However, they might provide the same beneficial functions of native macrophytes, i.e., the provision of food and shelter for fish, in the absence of native macrophytes. To assess the value of the invasive macrophyte Lagarosiphon major as a fish habitat, we investigated the spatio,temporal variation in the distribution of a small littoral fish species (common bully) in the littoral of Lake Dunstan, a New Zealand hydro lake. Large- and fine-scale common bully distribution could partly be explained by the occurrence of dense L. major stands. Additionally, variability in catch per unit effort was partly explained by season and recruitment. Diet analysis indicated that common bullies in the Lagarosiphon-dominated littoral fed on invertebrates (Mollusca, Trichoptera, Chironomidae) found on exotic L. major, therefore suggesting its role as a food provider in the system. These results indicated that invasive macrophytes can provide important ecosystem functions in disturbed habitats that are otherwise devoid of native macrophytes. Any macrophyte management strategy should therefore carefully consider the costs and benefits associated with macrophyte control. [source] Habitat and food choice of Arctic charr in Linnévatn on Spitsbergen, Svalbard: the first year-round investigation in a High Arctic lakeECOLOGY OF FRESHWATER FISH, Issue 1 2007M.-A. Svenning Abstract,,, Habitat and diet of Arctic charr Salvelinus alpinus (L.) were studied by monthly sampling from late autumn to early summer in Linnévatn, Svalbard (78°3,N, 13°50,E). This is the first year-round study of a population of charr in the High Arctic, with samples being taken every 5,7 weeks. The ice cover lasted for more than 9 months, from mid-October to late July, with the greatest thickness in mid-May. Although most charr occupied the littoral zone during winter, the highest densities in April and October were found in the deeper areas (20 m) of the lake. The fish fed at all times of the year, but the number of stomachs with food and the stomach-filling indices were lowest during the darkest part of the season. The diet of smaller charr (<15 cm) varied strongly with season, showing a dominance of zooplankton in late autumn and chironomids in winter (larvae) and summer (pupae). The food choice was in accordance with the density of food items available. Larger fish (,15 cm) were mostly cannibalistic during the entire year. [source] Is scuba sampling a relevant method to study fish microhabitat in lakes?ECOLOGY OF FRESHWATER FISH, Issue 3 2001Examples, comparisons for three European species Abstract , We compared fish microhabitat use patterns in the littoral zone of a lake using a new direct method (point abundance sampling by scuba, PASS) and the widely used point abundance sampling by electrofishing technique (PASE). We collected microhabitat data for age 0+ roach (Rutilus rutilus L.), perch (Perca fluviatilis L.), and pike (Esox lucius L.). The two methods yielded different results for fish assemblage structure and microhabitat patterns. Using PASE, fish were mainly found in "shelter habitats" such as shallow waters and dense vegetation. It is likely that this behavior is caused by the disturbance of the observer stamping around. Using PASS, fish escapement behavior was rarely observed. Therefore, we concluded that this direct and nondestructive sampling technique can be used to provide an accurate microhabitat estimation of a fish community and is assumed to be more suitable than PASE for fish habitat studies., [source] Seasonal changes in abundance and age structure of burbot Lota lota (L.) and stone loach Barbatula barbatula (L.) in the littoral zone of a large pre-alpine lakeECOLOGY OF FRESHWATER FISH, Issue 1 2001N. Hofmann Abstract , Seasonal changes in the abundance and age structure of the stone loach and burbot populations in the littoral of Lake Constance, Germany were examined. The abundance of both species was lowest during the summer months and highest during autumn. The stone loach population in the littoral comprised age classes 1 to 3 plus, in autumn, age class 0. The burbot population showed distinct seasonal changes in both length and age composition. During spring and summer, only age class 1 was present in the littoral whereas, in autumn, only age class 0 was caught. This remarkably strict habitat segregation of two age classes by season is discussed with respect to a possible mechanism for avoiding conspecific predator risk in a cannibalistic species. [source] Resource partitioning between lake-dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.))ECOLOGY OF FRESHWATER FISH, Issue 4 2000L. Jørgensen Abstract , Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (,160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (,120 mm) had a higher diet overlap than larger parr (121,160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone., [source] A field-based microcosm method to assess the effects of polluted urban stream sediments on aquatic macroinvertebratesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2005Vincent Pettigrove Abstract A method using field-based microcosms was developed to determine the effects of contaminated sediments on aquatic macroinvertebrates. Fine sediments from nonpolluted, moderately polluted, and severely polluted bodies of water were placed in microcosms positioned within the littoral zone of a nonpolluted wetland near Melbourne (Victoria, Australia). In three experiments, 47 taxa, including 18 Chironomidae, 6 taxa from other Diptera families, and 7 Hemiptera taxa, colonized the microcosms, mostly via eggs deposited by flying adults. The effects of sediment type on the presence and abundance of common taxa were considered statistically. Pollution levels in sediments (indexed either by a principal components analysis or by the concentration of zinc, the predominant metal) resulted in reduced occurrence and abundance of eight taxa but had no effect on another five taxa. These findings were validated with an extensive field database for the distribution of macroinvertebrates and associated concentrations of zinc in sediments from streams and wetlands in the Melbourne region. The occurrence of eight taxa and the abundance of two taxa varied at similar zinc concentrations in sediments from both the microcosms and the field. Patterns for another two species did not match the microcosm results, but these groups contained multiple species with potentially diverse responses. The present results suggest that contaminant levels in sediments probably have a direct effect on the occurrence and abundance of macroinvertebrates in bodies of water in urban areas. The microcosm method can be used to gather information regarding the effects of sediment quality on macroinvertebrates in lentic habitats, particularly for indigenous species that cannot be easily reared or tested in laboratory conditions. Because almost all macroinvertebrates in microcosms develop from eggs, the most sensitive life stages (i.e., first and second instars) are exposed to polluted sediments. [source] Host plant development, water level and water parameters shape Phragmites australis -associated oomycete communities and determine reed pathogen dynamics in a large lakeFEMS MICROBIOLOGY ECOLOGY, Issue 2 2009Anna Wielgoss Abstract In a 3-year-study, we analysed the population dynamics of the reed pathogen Pythium phragmitis and other reed-associated oomycetes colonizing fresh and dried reed leaves in the littoral zone of a large lake. Oomycete communities derived from internal transcribed spacer clone libraries were clearly differentiated according to substrate and seasonal influences. In fresh leaves, diverse communities consisting of P. phragmitis and other reed-associated pathogens were generally dominant. Pythium phragmitis populations peaked in spring with the emergence of young reed shoots, and in autumn after extreme flooding events. In summer it decreased with falling water levels, changing water chemistry and rising temperatures. Another Pythium species was also highly abundant in fresh leaves throughout the year and might represent a new, as-yet uncultured reed pathogen. In dried leaves, reed pathogens were rarely detected, whereas saprophytic species occurred abundantly during all seasons. Saprophyte communities were less diverse, less temperature sensitive and independent of reed development. In general, our results provide evidence for the occurrence of highly specialized sets of reed-associated oomycetes in a natural reed ecosystem. Quantitative analyses (clone abundances and quantitative real-time PCR) revealed that the reed pathogen P. phragmitis is particularly affected by changing water levels, water chemistry and the stage of reed development. [source] Genetic diversity and distribution of periphytic Synechococcus spp. in biofilms and picoplankton of Lake ConstanceFEMS MICROBIOLOGY ECOLOGY, Issue 2 2004Sven Becker Abstract In various water depths of the littoral zone of Lake Constance (Bodensee) cyanobacteria of the Synechococcus -type were isolated from biofilms (periphyton) on three natural substrates and an artificial one (unglazed tiles). From one tile three strains of phycoerythrin (PE)-rich Synechococcus spp. were isolated, the first examples of these organisms in the epibenthos. Phylogenetic inference based on the 16S,23S rRNA intergenic spacer (ITS-1) assigned all periphytic isolates to two clusters of the picophytoplankton clade (evolutionary lineage VI of cyanobacteria). The sequence divergence in the ITS-1 was used to design specific PCR primers to allow direct, culture-independent detection and quantification of isolated Synechococcus strains in natural periphytic and pelagic samples. Denaturing gradient gel electrophoresis (DGGE) analysis revealed depth-related differences of Synechococcus spp. distribution on tiles placed in the littoral zone. Synechococcus genotypes were observed which occurred in both the periphyton (on tiles) and in the pelagic picoplankton. A strain with one of these genotypes, Synechococcus sp. BO 8805, was isolated from the pelagic zone in 1988. Its genotype was found on tiles that had been exposed at different water depths in the littoral zone in spring and autumn of the year 2000. Quantitative analysis with a genotype-specific TaqMan probe and real-time Taq nuclease assays (TNA) confirmed its presence in the pelagic zone, although appearance of this and related genotypes was highly irregular and exhibited strong differences between consecutive years. Our results show that the ability to form significant subpopulations in pelagic and periphytic communities exists in three out of four phylogenetic clusters of Synechococcus spp. in Lake Constance. This versatility may be a key feature in the ubiquity of the evolutionary lineage VI of cyanobacteria. [source] N2 -fixation and complementary chromatic adaptation in non-heterocystous cyanobacteria from Lake ConstanceFEMS MICROBIOLOGY ECOLOGY, Issue 2 2001Christine Postius Abstract Non-heterocystous, mostly filamentous cyanobacteria were isolated from the crust of stones, from the periphyton of two macrophytes from the littoral zone and from the pelagic environment of Lake Constance. All isolates were cultivated as unialgal strains. DNA analysis by restriction fragment length polymorphism with the psbA gene probe revealed high genetic diversity among the strains from the littoral zone. For all genotypes, the occurrence of the nifH gene encoding a nitrogenase subunit and of genes encoding subunits of phycoerythrin and phycocyanin were tested by Southern blot hybridization. In addition, the isolates were investigated for their ability for complementary chromatic adaptation (CCA) and for anaerobic N2 -fixation. With respect to these characteristics, all cyanobacteria included in this study were assigned to four different types: (1) strains without the capability to fix N2 or to perform CCA of the group III type (CCA III); (2) strains which show both features; (3) strains with the ability to fix nitrogen, but that do not show any CCA III; and (4) strains that produce phycoerythrin, but without the capacity for CCA III or N2 -fixation. By examining the frequency distribution of isolates, these types were shown to prefer different habitats. While cyanobacterial strains capable of N2 -fixation, but without CCA III, were mainly obtained from stone crusts in the supralittoral zone, those with the potential for N2 -fixation as well as for CCA III were largely isolated from submersed macrophytes. Cyanobacteria that produce phycoerythrin, but do not perform CCA III or N2 -fixation, were found in the pelagic zone only. [source] Convergence of fish communities from the littoral zone of reservoirsFRESHWATER BIOLOGY, Issue 6 2009KEITH B. GIDO Summary 1.,Understanding factors that regulate the assembly of communities is a main focus of ecology. Human-engineered habitats, such as reservoirs, may provide insight into these assembly processes because they represent novel habitats that are subjected to colonization by fishes from the surrounding river basin or transported by humans. By contrasting community similarity within and among reservoirs from different drainage basins to nearby stream communities, we can test the relative constraints of reservoir habitats and regional species pools in determining species composition of reservoirs. 2.,We used a large spatial database that included intensive collections from 143 stream and 28 reservoir sites within three major river basins in the Great Plains, U.S.A., to compare patterns of species diversity and community structure between streams and reservoirs and to characterize variation in fish community structure within and among major drainage basins. We expected reservoir fish faunas to reflect the regional species pool, but would be more homogeneous that stream communities because similar species are stocked and thrive in reservoirs (e.g. planktivores and piscivores), and they lack obligate stream organisms that are not shared among regional species pools. 3.,We found that fish communities from reservoirs were a subset of fishes collected from streams and dominant taxa had ecological traits that would be favoured in lentic environments. Although there were regional differences in reservoir fish communities, species richness, patterns of rank abundance and community structure in reservoir communities were more homogonous across three major drainage basins than for stream communities. 4.,The general pattern of convergence of reservoir fish community structure suggests their assembly is constrained by local factors such as habitat and biotic interactions, and facilitated by the introduction of species among basins. Because there is a reciprocal transfer of biota between reservoirs and streams, understanding factors structuring both habitats is necessary to evaluate the long-term dynamics of impounded river networks. [source] Benthic metabolism in two turbid dryland riversFRESHWATER BIOLOGY, Issue 2 2009CHRISTINE S. FELLOWS Summary 1.,Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River. 2.,Both rivers have similar variable hydrology and high levels of turbidity (photic depths < 0.4 m), but fish abundance in Cooper Creek is 10 times than that of the Warrego River. Therefore, an additional aim of the study was to determine if fish abundances reflected underlying differences in benthic primary production. 3.,Benthic gross primary production (GPP), benthic respiration, nutrient concentrations and light penetration were measured immediately after flow had ceased (,post-flow') and after at least 2 months of zero flow (,no-flow') in 15 waterholes from each river. A subset of four waterholes from each river was sampled on two additional occasions to determine if patterns were consistent over time. 4. Cooper Creek generally had higher rates of GPP and a more autotrophic benthic zone than the Warrego River. As a result, the expected positive relationship between fish abundance and GPP was generally observed at a broad catchment scale. 4.,Light was the major control in benthic GPP in both rivers, as nutrient concentrations were high on all sampling occasions. However, for similar values of photic depth, GPP was greater in Cooper Creek than in the Warrego River. This suggests that more frequent disturbance of the littoral zone may inhibit biofilm development in waterholes of the Warrego River. 5.,Although flow variability in dryland rivers is extreme compared with other rivers worldwide, cycles of expansion and contraction of aquatic habitat in these two rivers were associated with a shift in the dominance of regional scale (subcatchments contributing to river flow) versus local scale (waterhole morphology) influences on ecosystem functioning, similar to floodplain rivers in tropical and temperate regions. [source] Effects of food-web structure on periphyton stoichiometry in eutrophic lakes: a mesocosm studyFRESHWATER BIOLOGY, Issue 10 2008M. DANGER Summary 1. Aquatic herbivores typically have much higher concentrations of nutrients (e.g. N and P) in their tissues than there is in the food they eat. These stoichiometric differences can cause herbivores to be limited by the elemental quality of their food, which could affect, in turn, the structure of consumer communities and even alter key ecosystem processes. 2. In streams and in the littoral zone of shallow lakes, periphyton is an important food resource for benthic animals. Studying the elemental composition of periphyton may help us to understand food-web structure, and any reciprocal effect of this structure on periphyton stoichiometry. 3. To understand how alterations in the food-web structure affect the elemental composition of periphyton in a eutrophic lake, we carried out a long-term experiment (14 months) in large-scale mesocosms (40 m3), in which we manipulated food-web structure, and which were dominated either by planktivorous fish (Rutilus rutilus) or herbivorous invertebrates (without fish). Periphyton was sampled monthly at three depths (0.5, 1.5 and 2.5 m) to determine its biomass and elemental composition (C/N/P ratio). Food-web structure, physical and chemical parameters were monitored throughout the experiment. 4. Fish had indirect positive effect on periphyton biomass, leading to twofold higher levels than in herbivore-dominated mesocosms. This result was probably due to control of benthic consumers by fish, suggesting a strong top,down control on periphyton by their consumers in fishless enclosures. 5. The elemental ratios C/P and C/N were lower in deep water in both treatments, mainly mediated by light availability, in accordance with the light/nutrient ratio hypothesis. These ratios were also lower in fishless treatments, probably due to increases in inorganic nutrient availability and grazing pressure in herbivore-dominated systems. During winter, periphyton elemental composition was similar in both treatments, and was unrelated to inorganic nutrient availability. 6. These results indicate that any alteration of food-web structure in lakes, such as in biomanipulation experiments, is likely to modify both the biomass and elemental quality of periphyton. Resultant effects on the consumers of periphyton and macrophytes could play a key role in the success of biomanipulations and should be taken into account in further studies. [source] Ecosystem CO2 exchange and plant biomass in the littoral zone of a boreal eutrophic lakeFRESHWATER BIOLOGY, Issue 8 2003T. Larmola Summary 1In order to study the dynamics of primary production and decomposition in the lake littoral, an interface zone between the pelagial, the catchment and the atmosphere, we measured ecosystem/atmosphere carbon dioxide (CO2) exchange in the littoral zone of an eutrophic boreal lake in Finland during two open water periods (1998,1999). We reconstructed the seasonal net CO2 exchange and identified the key factors controlling CO2 dynamics. The seasonal net ecosystem exchange (NEE) was related to the amount of carbon accumulated in plant biomass. 2In the continuously inundated zones, spatial and temporal variation in the density of aerial shoots controlled CO2 fluxes, but seasonal net exchange was in most cases close to zero. The lower flooded zone had a net CO2 uptake of 1.8,6.2 mol m,2 per open water period, but the upper flooded zone with the highest photosynthetic capacity and above-ground plant biomass, had a net CO2 loss of 1.1,7.1 mol m,2 per open water period as a result of the high respiration rate. The excess of respiration can be explained by decomposition of organic matter produced on site in previous years or leached from the catchment. 3Our results from the two study years suggest that changes in phenology and water level were the prime cause of the large interannual difference in NEE in the littoral zone. Thus, the littoral is a dynamic buffer and source for the load of allochthonous and autochthonous carbon to small lakes. [source] Methane efflux in relation to plant biomass and sediment characteristics in stands of three common emergent macrophytes in boreal mesoeutrophic lakesGLOBAL CHANGE BIOLOGY, Issue 1 2005Paula Kankaala Abstract Methane efflux was studied in stands of three emergent macrophyte species (Equisetum fluviatile, Schoenoplectus lacustris and Phragmites australis) commonly found in the littoral zone of boreal lakes. In vegetation stands with relatively low methane (CH4) emissions (<0.3 mol m,2 (ice-free period),1), the seasonal variation of CH4 efflux was better correlated with the dynamics of plant growth than variation in sediment temperature. In dense and productive vegetation stands that released high amounts of CH4 (2.3,7.7 mol m,2 (ice-free period),1), the seasonal variation in CH4 efflux was correlated with sediment temperature, indicating that methanogens were more limited by temperature than substrate supply. The bottom type at the growth site of the emergent plants significantly influenced the ratio of CH4 efflux to aboveground biomass of plants (Eff : B). The lowest Eff : B ratio was found in E. fluviatile stands growing on sand bottom under experimental conditions and the highest in P. australis -dominated littoral areas accumulating detritus from external sources. The future changes expected in the hydrology of boreal lakes and rivers because of climatic warming may impact the growth conditions of aquatic macrophytes as well as decomposition and accumulation of detritus and, thus, CH4 effluxes from boreal lakes. [source] Top-Down Control of Reed Detritus Processing in a Lake Littoral Zone: Experimental Evidence of a Seasonal Compensation between Fish and Invertebrate PredationINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2007Giorgio Mancinelli Abstract We investigated whether predatory fish exert a top-down control on reed leaf packs processing in a lake littoral zone through a trophic cascade. Exclosure experiments were repeated in summer and winter, under high and low natural fish abundance, respectively. Fish exclusion effects on detritus processing and fungal conditioning were consistent with trophic cascade predictions only in summer. In winter, however, results indicated that a trophic cascade was induced by predatory invertebrates. In both seasons, variations in detritivores abundance generally supported a cascade scenario, whereas several taxon-specific departures occurred during the experimental periods. We conclude suggesting that predators may continuously regulate leaf detritus processing in lake littoral zones, through a seasonal shift in the relative contribution of fish and invertebrate predation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Influence of Invertebrate Predators on Daphnia Spatial Distribution and Survival in Laboratory Experiments: Support for Daphnia Horizontal Migration in Shallow LakesINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2007Adrianna Wojtal Abstract The behavioural response of Daphnia cucullata to the presence of the pelagic invertebrate predator Leptodora kindtii, and the predation rate of littoral dragonfly nymphs on this species were investigated under laboratory conditions. Results of this study revealed a strong hiding response of Daphnia cucullata in the presence of the predatory cladoceran, L. kindtii, which was similar to the response of Daphnia in the presence of juvenile perch. This suggests that pelagic invertebrate predators may cause Daphnia to hide in the littoral zone which could result in increased exposure to predation by littoral invertebrates. A strong influence of dragonfly nymphs on D. cucullata, both in the presence and absence of macrophytes, was found. The average predation rate of Odonata larvae was about 5 prey ind,1 h,1 and did not differ significantly between treatments. Quantification of dragonfly pressure on Daphnia populations will require cross-verification with field experiments since in the natural conditions Daphnia seeks a shelter in the vegetation stands against predation by Leptodora, despite the occurrence of odonates. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Population Density of the Crayfish, Orconectes limosus, in Relation to Fish and Macroinvertebrate Densities in a Small Mesotrophic Lake , Implications for the Lake's Food WebINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5-6 2005Susanne S. Haertel-Borer Abstract The population density of Orconectes limosus in a mesotrophic lake was assessed in the context of fish and macroinvertebrate biomasses, and crayfish consumption by fish. The average O.limosus (,6 cm total length) abundance and biomass in the littoral zone was 2200 ind ha,1 and 32.2 kg ha1, respectively. O.limosus biomass accounted for a large percentage (49%) of the lake's macroinvertebrate biomass. O.limosus was equal to 35% of the non-predatory fish biomass and to 81% of the predatory fish biomass. O.limosus comprised 15 and 48% of the annual consumption of pike and predatory perch, respectively. Altogether, O.limosus was identified as quantitatively important for the lake's littoral food web, and might also subsidize the pelagic food web. This strengthens the need for an integrated view on lake food webs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Consequences of introducing the invasive amphipod Gmelinoides fasciatus into large shallow Lake Peipsi: present distribution and possible effects on fish foodJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2010K. Kangur Summary The objective of the study was to assess the effect of the Baikalian amphipod Gmelinoides fasciatus, a successful invader into Europe, as a fish food source in Lake Peipsi to where it was introduced in the 1970s. In 2002,2006, the littoral macrozoobenthos was studied along 17 transects (0.1,4 m depth, 384 quantitative samples) to determine the recent distribution of G. fasciatus and its share in the benthic community. Earlier records on the littoral macrozoobenthos from the years 1970, 1980, 1990 and 2000 were also used for comparison. Our results indicate that the invasive G. fasciatus is the dominant species (about 43% of total macrozoobenthos abundance) in the littoral zone of Lake Peipsi, while the native gammarids Gammarus lacustris and Pallasea quadrispinosa appear to be extinct and oligochaetes seem to have declined. G. fasciatus preferred hard substrates and it was mainly distributed close to water shallow beach areas (water depth <0.2 m), where its abundance reached locally up to 29 000 ind. m,2 (97% of total macrozoobenthos abundance). This distribution pattern of the invader in summer makes it mostly inaccessible for adult fish and increases its survival rate. Being highly mobile, G. fasciatus is not sensitive to water level fluctuations in shallow lakes. These behavioural characteristic increase its population success. [source] Spatial variations in the composition and abundance of zooplankton in the Bahir Dar Gulf of Lake Tana, EthiopiaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Tunde Ohiokhioya Thadeus Imoobe Abstract The zooplankton in the littoral and open water zones of Bahir Dar Gulf, Lake Tana, collected in June and July 2007, were investigated using basic statistical measurement of diversity indices and one way analysis of variance to characterize the zooplankton fauna, with respect to its composition, abundance and spatial distribution patterns. The zooplankton composition was typical of a tropical freshwater lake, with a total of 44 species made up of sixteen rotifers, sixteen c1adocerans and twelve copepods and their developing stages in the following order of dominance; Rotifera > Cladocera > Cylopoida > Calanoida. Variation in spatial distribution was noticeable, the abundance of zooplankton was significantly higher (P < 0.05) at the littoral zone (Stations 2 and 3) than the open water (Station 1) as a result of the preponderance of the small-bodied nauplii stages, small rotifers and c1adocerans particularly Bosmina longirostris. Species richness, evenness, and diversity also increased as abundance increased in the littoral zones of the lake. The rotifers, particularly the brachionids Keratella and Brachionus spp., which are considered good indicators of lake trophic status constituted the dominant zooplankton group in terms of abundance and diversity, thus indicating that the lake has a high fisheries potential. Résumé Le zooplancton des berges et des eaux ouvertes du golfe de Bahir Dar, récolté en juin et juillet 2007 dans le lac Tana, a étéétudié en utilisant des indices de mesures statistiques de base et une analyse de la variance à une voie, pour caractériser la faune du zooplancton, tant au point de vue de la composition que de l'abondance et du schéma de distribution spatiale. La composition du zooplancton était typique d'un lac d'eau douce tropical, avec un total de 44 espèces réparties entre 16 rotifères, 16 cladocères et 12 copépodes à différents stades de développement dans l'ordre de prépondérance qui suit : Rotifères > Cladocères > Cylopoïdes > Calanoïdes. Il y avait une variation notable de la distribution spatiale : l'abondance de zooplancton était significativement plus grande (P < 0.05) dans la zone littorale (Stations 2 et 3) qu'en haute eau (Station 1), suite à la prépondérance des petits corpuscules comme les stades nauplius, les petits rotifères et cladocères, et particulièrement Bosmina longirostris. La richesse en espèces, l'uniformité et la diversité augmentaient aussi en même temps que l'abondance dans les zones littorales du lac. Les rotifères, et particulièrement Keratella et Brachionus spp., qui sont considérés comme de bons indicateurs du statut trophique du lac étaient le groupe de zooplancton dominant en termes d'abondance et de diversité, ce qui indique que le lac a un fort potentiel piscicole. [source] Effect of wave exposure dynamics on gut content mass and growth of young-of-the-year fishes in the littoral zone of lakesJOURNAL OF FISH BIOLOGY, Issue 7 2010S. Stoll Total length, body mass and gut content mass of young-of-the-year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave-induced energy flux (EF) of the respective site and sampling day, while no correlation of gut content mass with EF was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high EF. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased EF. In P. fluviatilis, increased gut content mass during periods of high EF resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high EF, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes. [source] Comparison between two sampling methods to evaluate the structure of fish communities in the littoral zone of a Laurentian lakeJOURNAL OF FISH BIOLOGY, Issue 5 2004A. Brind'Amour The results of beach seining were compared with visual surveys, in habitats showing a gradient of macrophyte densities in Lake Drouin, Québec, Canada. Six community descriptors (species density, total fish density, relative abundance per species, presence or absence of given species, size structure of the fish community and total biomass of the fish community) were used to compare the sampling methods. Most of the fish community descriptors obtained by visual surveys were estimated with an accuracy similar to that of beach seining. Both methods sampled the same number of species (eight out of nine). Visual surveys assessed the relative abundance of the yellow perch Perca flavescens and white sucker Catostomus commersoni with an higher accuracy than the beach seine. The greatest discrepancies between the two sampling methods were for total fish density and the total fish biomass. Because of the sampling strategy, both descriptors were underestimated by visual surveys, notably in the higher macrophyte density. In a broad community survey to determine the relative importance of species abundance, the visual survey was effective and could be used to develop a within-lake regular and fine-scale sampling design of the spatial arrangement of fish communities and their habitats. [source] Oscillating vegetation dynamics in a wet heathlandJOURNAL OF VEGETATION SCIENCE, Issue 1 2005Katharina E. Urban Abstract. Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties. Location and Method: At a sod-cut stand within nutrient-poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting. Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloni-ferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically. Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re-colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re-colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time. [source] Molecular phylogeny of Enchytraeidae (Oligochaeta) indicates separate invasions of the terrestrial environmentJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 3 2010Bent Christensen Abstract Enchytraeidae is a family of soil inhabiting small- to medium-sized oligochaete worms using degradable plant material as a food source and primarily adapted to terrestrial or semi-terrestrial environments. The molecular phylogeny based upon both mitochondrial and nuclear genes indicates early segregations of the two genera Enchytraeus and Lumbricillus leaving the remaining genera included in this study as a later segregated major monophyletic branch. Extant members of the two former genera dominate in decaying seaweed in the littoral zone along the sea although members of in particular the genus Enchytraeus have also invaded other habitats. Historically the littoral zone of the sea is undoubtedly the first terrestrial or semi-terrestrial habitat where dead plant material accumulates to any greater extent and Enchytraeus and Lumbricillus may represent early successful attempts to exploit this resource. Inland soils probably had to await the emergence of land plants in order to provide a similar food resource and here the major branch of enchytraeid genera diversified into a high number of species in the numerous decomposer networks of this varied environment. A subdivision into the genera Enchytraeus and Lumbricillus on the one hand and a branch of mainly inland genera on the other is supported by differences in two somewhat neglected morphological features. Firstly, in Enchytraeus and Lumbricillus the testes are enclosed in a testis sac within which the male cells mature, by one possible exception a unique feature among Oligochaeta, The other enchytraeid genera studied and Oligochaeta in general lack this sac and the male cells mature directly in the cavity of the testicular segment. Secondly, species of Enchytraeus and Lumbricillus generally have a higher reproductive output than species of the inland terrestrial branch and this may represent an adaptation to the unpredictable littoral zone compared to the more stable nature of inland habitats. In the older literature the genus Mesenchytraeus is considered to have a basic position within the entire family but our molecular data do not support this expectation. In Enchytraeidae the nephridia are elaborate organs of a characteristic and constant shape covering species from different genera in a pattern following the molecular phylogeny. Other much used morphological features such as shape of setae, anteclitellar origin of the dorsal vessel and various modifications of the intestine have arisen more than once. Zusammenfassung Enchytraeidae sind eine Familie kleiner bis mittelgroßer edaphischer Oligochaeten, welche abbaubares Pflanzenmaterial als Nahrungsquelle nutzen und primär an terrestrische oder semiterrestrische Lebensräume angepaßt sind. Die hier vorgestellte, auf mitochondrialen und nukleären Genen beruhende molekulare Phylogenie indiziert eine frühe Abtrennung der beiden Gattungen Enchytraeus und Lumbricillus und beläßt die übrigen der in dieser Studie untersuchten Gattungen als eine später abgezweigte monophyletische Großgruppe. Rezente Glieder der beiden erwähnten Gattungen dominieren in verrottendem Strandanwurf des Meereslitorals, obwohl Arten insbesondere der Gattung Enchytraeus auch andere Lebensräume erobert haben. Historisch gesehen ist das Meereslitoral zweifelsohne das erste terrestrische oder semiterrestrische Habitat, in dem totes Pflanzenmaterial in größerem Ausmaß akkumulierte, und Enchytraeus und Lumbricillus könnten frühe erfolgreiche Versuche der Nutzung dieser Ressource darstellen. Festlandsböden dagegen bedurften wahrscheinlich der Entwicklung von Landpflanzen, um eine vergleichbare Nahrungsquelle zur Verfügung zu stellen, und hier diversifizierte sich der Hauptzweig der Enchytraeidengattungen in viele Arten in den diversen Zersetzernetzen dieses vielgestaltigen Lebensraums. Eine Unterteilung in die Gattungen Enchytraeus und Lumbricillus auf der einen Seite und einen Zweig mit vorwiegend terrestrischen Gattungen auf der anderen wird durch zwei bislang eher vernachlässigte morphologische Merkmale gestützt. Erstens, bei Enchytraeus und Lumbricillus wird der Hoden von einem Testis-Sack, in dem die männlichen Zellen reifen, umschlossen. Dies ist mit einer möglichen Ausnahme einzigartig bei Oligochaeten. Bei den übrigen untersuchten Enchytraeidengattungen und bei Oligochaeten generell fehlt dieser Sack, und die männlichen Zellen reifen unmittelbar in der Körperhöhle des Hodensegmentes. Zweitens, die Reproduktionsrate von Enchytraeus und Lumbricillus ist generell höher als die der Arten des Festlandszweigs. Dies könnte eine Anpassung an die im Vergleich zu Festlandsböden instabileren Bedingungen des Meereslitorals bedeuten. In der älteren Literatur wird der Gattung Mesenchytraeus eine basale Position innerhalb der gesamten Familie zugewiesen, aber unsere molekularen Daten stützen diese Annahme nicht. Die Nephridien der Enchytraeiden sind komplexe Organe mit einer charakteristischen und artübergreifend konstanten Form, deren gattungsmäßige Abwandlungen der molekularen Phylogenie entsprechen. Andere oft verwendete morphologische Merkmale wie Borstenform, anteclitellarer Ursprung des Dorsalgefäßes und verschiedene Darmmodifikationen sind mehr als einmal entstanden. [source] A new case of intralacustrine radiation in Amphipoda.JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 2 2009A new genus, Amphipoda) from the ancient lake Fuxian Hu in Yunnan, China, three new species of Anisogammaridae (Crustacea Abstract Fuxian Hu is a deep freshwater lake in the high plateau in Yunnan Province, China. After a study and description of Fuxiana yangi Sket, 2000 from deep waters, some coastal samples of amphipods were taxonomically evaluated. Four species were recognized, which in winter co-occur along most of the shallow littoral zone around the lake; they were identified as members of the family Anisogammaridae. One species was recognized as a slightly differentiated Eurypodogammarus helobius Hou et al., 2005, and the others as new species of Fuxigammarus gen. n. Results of a cladistic analysis performed on morphological characters from published descriptions, which included all lacustrine taxa and representatives of all other anisogammarid genera, established the monophyly of the new genus. Endemic character and monophyly of the group testify to an intralacustrine radiation within Fuxigammarus. Fuxian Hu is the fifth known lake in the world to contain a radiation of amphipods and is the only one inhabited by members of Anisogammaridae. Fuxigammarus gen. n. is characterized by a small and slender body, scant dorsal setosity-spinosity, and single, sausage-shaped accessory lobes on coxal gills, antennae without calceoli and rod shaped uropod III. These species differ substantially from each other by characters that do not occur in other anisogammarid genera. The type species F. antespinosus sp. nov. has spiniform dorsal setae shifted forward. Fuxigammarus barbatus sp. nov. has extremely setose antennal bases and mandibular palps and an elongated proximal flagellar article of antenna II. Fuxigammarus cornutus sp. nov. has a pair of dorsal spiniform setae only on humped urosomite I and the usually spiniform setae replaced by flexible setae on the telson. These characters are a kind of counterpart to the specific body armature of the Bajkal amphipods. Zusammenfassung Fuxian Hu ist ein tiefer Süßwassersee auf dem Hochplateau der Yunnan-Provinz in China. Nach der Beschreibung von Fuxiana yangi Sket, 2000 aus den Tiefen des Sees wurden auch Amphipoden-Proben aus dem Litoralbereich taxonomisch ausgewertet. Vier Arten wurden erkannt, die im Winter gemeinsam das flache Litoral rund um den See bewohnen. Sie wurden der Familie Anisogammaridae zugeordnet. Eine der Arten konnte als leicht differenzierte Eurypodogammarus helobius Hou et al., 2005 bestimmt werden, während die anderen als neue Arten einer neuen Gattung, Fuxigammarus gen.nov., beschrieben werden. Die Monophylie der neuen Gattung wurde durch eine phylogenetische Analyse bestätigt, die alle im See bekannten Arten sowie Vertreter aller anderen Anisogammariden-Gattungen mit einbezog. Der Endemismus und die Monophylie der Gattung deuten auf eine intralakustrische Radiation von Fuxigammarus. Somit ist Fuxian Hu der fünfte See weltweit, in dem eine Radiation von Amphipoden nachgewiesen wurde, und der einzige davon mit Anisogammariden. Fuxigammarus gen. n. besitzt einen kleinen und schlanken Körper, eine arme Dorsalbestachelung, nur je eine Nebenast auf jeder Coxalkieme, Antennen ohne Calceoli und stabförmige Uropoden III. Sie unterscheiden sich deutlich in Merkmalen, die bei anderen Anisogammariden nicht vorkommen. Die Typusart F. antespinosus sp. nov. besitzt nach vorne verdrängte Dorsal-Stacheln. Fuxigammarus barbatus sp. nov. hat dicht setose Antennenenbasen und Mandibularpalpen sowie ein verlängertes proximales Glied im Flagellum der Antenne II. Fuxigammarus cornutus sp. nov. besitzt nur ein Paar stachelförmige Dorsal-Setae auf dem gewölbtem Urosomit I, und weiche anstatt der sonst normalen stachelförmigen Setae auf dem Telson. Diese Merkmale wirken wie ein Gegenstück zu den spezifischen Schutzstrukturen der Baikal-Amphipoden. [source] Lake morphometry predicts the degree of habitat coupling by a mobile predatorOIKOS, Issue 8 2009Rebecca Dolson Habitat coupling is an ecosystem process whereby semi-discontinuous habitats are connected through the movement of energy and nutrients by chemical, physical or biological processes. One oft-cited example is that of littoral,pelagic coupling in lakes. Theory has argued that such habitat coupling may be critical to food web dynamics, yet there have been few empirical studies that have quantified ecological factors that affect the degree of habitat coupling in ecosystems. Specifically, the degree to which habitat coupling occurs across important physical gradients has largely been ignored. To address this, we investigate the degree of littoral habitat coupling (i.e. the degree to which a top predator lake trout, Salvelinus namaycush, derives energy from the littoral zone) along a gradient of lake shape, where lake shape modifies the relative quantity of coupled epilimnetic benthic and pelagic habitats within each lake. Herein we demonstrate that littoral habitat coupling is intensified in simple circular lakes compared to their reticulate counterparts in seven Canadian Shield lakes. Although the more reticulate lakes had larger areas of epilimnetic benthic habitat, littoral food sources comprised 11% compared to 24% of lake trout diet in reticulate and circular lakes, respectively. This heightened interaction in circular lakes also appears to translate into increased omnivory in more circular lakes compared to reticulate lakes such that lake trout of circular lakes have a significantly lower trophic position than lake trout of reticulate lakes (F1,5=6.71 p=0.05). These results suggest that it is the accessibility of littoral production via thermal refugia, and not the amount of littoral production, that determines the degree to which lake trout couple littoral and pelagic habitats in lakes. [source] Intraspecific competition drives multiple species resource polymorphism in fish communitiesOIKOS, Issue 1 2008Richard Svanbäck It has been hypothesized that inter-specific competition will reduce species niche utilization and drive morphological evolution in character displacement. In the absence of a competitor, intra-specific competition may favor an expansion of the species niche and drive morphological evolution in character release. Despite of this theoretical framework, we sometimes find potential competitor species using the same niche range without any partitioning in niche. We used a database on test fishing in Sweden to evaluate the factors (inter- and intraspecific competition, predation, and abiotic factors) that could influence habitat choice of two competitor species. The pattern from the database shows that the occurrence of perch and roach occupying both littoral and pelagic habitats of lakes in Sweden is a general phenomenon. Furthermore, the results from the database suggest that this pattern is due to intra-specific competition rather than inter-specific competition or predation. In a field study, we estimated the morphological variation in perch and roach and found that, individuals of both species caught in the littoral zone were more deeper bodied compared to individuals caught in the pelagic zone. Pelagic perch fed more on zooplankton compared to littoral perch, independent of size, whereas the littoral perch had more macroinvertebrates and fish in their diet. Pelagic roach fed more on zooplankton compared to littoral roach, whereas littoral individuals fed more on plant material. Furthermore, we sampled littoral and pelagic fish from another lake to evaluate the generality of our first results and found the same habitat associated morphology in both perch and roach. The results show a consistent multi-species morphological separation in the littoral and pelagic habitats. This study suggests that intra-specific competition is possibly more important than inter-specific competition for the morphological pattern in the perch-roach system. [source] Effects of oyster farming service vehicles on an intertidal sand flatAQUACULTURE RESEARCH, Issue 7 2009Catriona K Macleod Abstract A Tasmanian tidalflat receiving differing amounts of vehicle traffic associated with the servicing of oyster farm leases was sampled for sediment properties and benthic community structure. There was a gradient of vehicle usage in both the littoral zone (LZ) and the intertidal zone (IZ), with the highest usage in the intertidal zone equating to the lowest usage in the littoral zone (IZ2=LZ1). Results indicate that the littoral sediments were less compacted where vehicles were present. Species richness and diversity were reduced in the littoral sites (70%) and one intertidal site (50%) where there was vehicle traffic. Multivariate analyses confirmed the univariate findings. Large bivalves and epibenthic snails were generally less abundant where there was vehicle traffic. However, in the intertidal zone one snail showed the opposite pattern. There was less change in the community structure at sites where vehicles spread out across the foreshore than at sites where all vehicles travelled in a narrow lane, but this reduction in impact was offset by a greater area being affected. This study provides preliminary evidence of a measurable impact on sediment and community composition at 16 vehicle trips per day and suggests that management needs to consider the tradeoff between magnitude of impact and area affected. [source] Seagrass,sea urchin interaction in shallow littoral zones of Dar es Salaam, TanzaniaAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2009Florence Mamboya Abstract 1.Seagrasses biomass, canopy height, shoot density, percentage cover, and sea urchin abundance were intermittently (between July and November 2007) studied at four littoral sites in the Dar es Salaam area (Mjimwema, Mbweni, Bongoyo Island and Mbudya Island) in order to investigate the seagrass,sea urchin association. 2.Seagrass biomass ranged from 126.7±65.62,g,dwt,m,2 in the upper sub-tidal area at Bongoyo Island to 508.1±133.4,g,dwt,m,2 in the upper sub-littoral area at Mbudya Island. Canopy height ranged from 6.51±2.76,cm in the mid-littoral zone at Mjimwema to 23.8±8.93,cm in the upper sub-littoral zone at Mbudya Island. Shoot densities ranged from 363.6±268.9 shoots m,2 in the mid-littoral zone at Mjimwema to 744.0±466.9 shoots,m,2 in the lower littoral zone at Mbudya Island. 3.Seagrass biomass, canopy height and percentage cover differed significantly among study sites (P=0.001, 0.0001, 0.008 respectively). However, there was no significant difference in shoot density among the sites (P=0.376). 4.Ten species of sea urchins were recorded, Echinometra mathaei being the most abundant followed by Tripneustes gratilla. Total sea urchin abundance was significantly different among the study sites (P=0.001). Seagrass,sea urchin interaction was depicted by significant negative correlations between sea urchin densities with seagrass biomass, canopy height, shoot density and percentage cover. This suggests that grazing by sea urchins might have contributed to the reduction of above ground seagrass biomass in locations with higher sea urchin densities. However, further studies are required to corroborate the present results and assess effects of other factors (e.g. light, nutrients and currents), which also influence seagrass growth. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||