Taxonomic and size structures of phytophilous macroinvertebrate communities in Vallisneria and Trapa beds of the Hudson River, New York

Phytophilous macroinvertebrates (PMI) were sampled from the surfaces and surrounding water of two aquatic plant species, Vallisneria americana and Trapa natans, which have substantially different morphologies. It was expected that the plants would harbor invertebrate communities of different structure. Total density of PMI was consistently greater in Vallisneria than inTrapa, e.g. 6× greater per m³ water and 21× greater per m² leaf surface in August. Each macrophyte harbored taxa that were either significantly more abundant or present only with that macrophyte; the herbivore Galerucella nymphaceae (Coleptera: Chrysomelidae) was abundant on Trapa. Vallisneria harbored 34 taxa vs. 40 taxa in Trapa, but similarity was low (Morisita's C=0.55–0.66). Predaceous invertebrates were more prevalent in Trapa than in Vallisneria, as were larger individuals. Both PMI communities exhibited shifts in size distribution between July and August. Standing crop of Trapa was 3× greater than forVallisneria. These two macrophyte beds clearly support PMI communities of different taxonomic and size structure, which is believed to be related to the differences in macrophyte morphology.     

Floating-leaved macrophyte (<Emphasis Type="Italic">Trapa quadrispinosa</Emphasis> Roxb) beds have significant effects on sediment resuspension in Lake Taihu,China

Trapa quadrispinosa Roxb is a common floating-leaved macrophyte in China. In this study, the effects of Trapa on sediment resuspension in Lake Taihu, a large, shallow, eutrophic lake in eastern China, were investigated using sediment traps. The study was conducted at stations with and without Trapa beds from 7 September to 18 October, 2003. Results showed that sediment resuspension rates at the station without Trapa were significantly higher than those at the station with Trapa. During the study period (41 days), 10,970 g dw m⁻² of surface sediment was resuspended within the Trapa beds and 29,903 g dw m⁻² in the pelagic zone. These equate to phosphorus fluxes of 7.4 g m⁻² to the water column at the station with Trapa and 16.1 g m⁻² at the station without Trapa. Floating-leaved macrophytes, such as Trapa, may be important in sediment resuspension and internal phosphorus loading in shallow lakes.     

Impacts of a submerged plant (Elodea canadensis) on interactions between roach (Rutilus rutilus) and its invertebrate prey communities in a lake littoral zone

1. Using 5‐m² field enclosures, we examined the effects of Elodea canadensis on zooplankton communities and on the trophic cascade caused by 4–5 year old (approximately 16 cm) roach. We also tested the hypothesis that roach in Elodea beds use variable food resources as their diet, mainly benthic and epiphytic macroinvertebrates, and feed less efficiently on zooplankton. Switching of the prey preference stabilises the zooplankton community and, in turn, also the fluctuation of algal biomass. The factorial design of the experiment included three levels of Elodea (no‐, sparse‐ and dense‐Elodea) and two levels of fish (present and absent). 2. During the 4‐week experiment, the total biomass of euplanktonic zooplankton, especially that of the dominant cladoceran Daphnia longispina, decreased with increase in Elodea density. The Daphnia biomass was also reduced by roach in all the Elodea treatments. Thus, Elodea provided neither a favourable habitat nor a good refuge for Daphnia against predation by roach. 3. The electivity of roach for cladocerans was high in all the Elodea treatments. Roach were able to prey on cladocerans in Elodea beds, even when the abundance and size of these prey animals were low. In addition to cladocerans, the diet of roach consisted of macroinvertebrates and detrital/plant material. Although the biomass of macroinvertebrates increased during the experiment in all Elodea treatments, they were relatively unimportant in roach diets regardless of the density of Elodea beds. 4. Euplanktonic zooplankton species other than Daphnia were not affected by Elodea or fish and the treatments had no effects on the total clearance rate of euplanktonic zooplankton. However, the chlorophyll a concentration increased with fish in all the Elodea treatments, suggesting that fish enhanced algal growth through regeneration of nutrients. Thus, our results did not unequivocally show that Elodea hampered the trophic cascade of fish via lowered predation on grazing zooplankton. 5. In treatments with dense Elodea beds (750 g FW m^?2), chlorophyll a concentration was always low suggesting that phytoplankton production was controlled by Elodea. Apparently, the top‐down control of phytoplankton biomass by zooplankton was facilitated by the macrophytes and operated simultaneously with control of phytoplankton production by Elodea.     

Floating-leaved macrophyte (<Emphasis Type="Italic">Trapa japonica</Emphasis>) drastically changes seasonal dynamics of a temperate lake ecosystem

Water chestnut (genus Trapa) is an annual floating-leaved macrophyte that produces dense beds known to drastically modify freshwater ecosystems. Although Trapa displays a distinct phenology that should alter the innate seasonal dynamics of ecosystems, the seasonality of these effects has rarely been investigated. Therefore, we examined seasonal changes in physicochemical conditions and assemblages of zoobenthos and zooplankton, and whether these changes were correlated with the rise and decline of dense beds of Trapa japonica in Lake Mikata, a temperate shallow lake in central Japan. Our results suggested that the formation of dense Trapa beds during summer resulted in hypoxia, which significantly decreased the abundance of Chironomidae and Oligochaeta in the benthic community, as well as that of Calanoida among zooplankton. When dense Trapa beds formed, we also detected growth of other taxa that were resistant to hypoxia, including Cladocera, Cyclopoida, Ostracoda, and Nematoda. Chlorophyll a concentration declined across the lake during summer, when dense Trapa beds formed. The decline in Trapa beds from autumn to spring resulted in increased dissolved oxygen concentration, chlorophyll a concentration, and invertebrate abundance (Chironomidae, Oligochaeta and Calanoida), as well as a decrease in taxa utilizing the dense Trapa beds. Our results suggest that the phenology of dense Trapa beds can drastically change the seasonal dynamics of physicochemical conditions and the lower components of the food web in a shallow lake ecosystem.     

The effects of nymphaeid (Nuphar lutea) density and predation by perch (Perca fluviatilis) on the zooplankton communities in a shallow lake

1. The effects of addition of juvenile perch (Perca fluviatilis) on the microcrustacean and rotifer communities associated with nymphaeid beds were studied, at three different plant densities [high (normal), medium (reduced by a half) and low (reduced to a third of normal)], in eighteen 2 m × 1 m enclosures in a shallow lake. 2. At the low and medium densities of lilies, Daphnia densities were high in the absence of perch but very low in the presence of perch. They increased, even in the presence of perch, to high densities (comparable with those in the absence of perch) at the highest plant density. Body sizes of Daphnia hyalina were consistent with high predation by perch at low and medium plant densities but reduced predation at high plant densities. Patterns of chlorophyll a concentration, in the presence of perch, inversely reflected those of D. hyalina density. 3. At naturally high densities but not at reduced densities, the plants appeared to act as refuges against predation for the Daphnia. Reductions in oxygen concentrations in the plant beds were not responsible for the refuge effect, nor could there be avoidance of the beds by the fish. The mechanism of the refuge effect must therefore lie in frustration of the process of capture of the Daphnia by the fish. 4. Numbers of other small Crustacea and rotifers were mostly unaffected by fish predation. Numbers of Asplanchna sp., Chydorus sphaericus and copepodites were higher in the presence of fish and, although there was no main effect of fish on numbers of Diaphanosoma brachyurum, there was a plant–fish interaction, with this species being less abundant in the presence of fish at low plant densities but more abundant in the presence of fish at medium and high plant densities. Main effects of plants were few, with only Asplanchna sp. and Keratella sp. decreasing in numbers with increasing plant density. Most taxa changed in numbers with time but interaction effects between time and plants, and fish and plants, were few.     

Breeding waterbird wetland habitat availability and response to water-level management in Saint John River floodplain wetlands, New Brunswick

Vegetated areas of rivers and estuaries are capable of affecting the concentration of dissolved and particulate matter in water masses traversing those plant beds. We examined whether different sizes of water chestnut (Trapa natans) beds in the Hudson River, USA, alter dissolved oxygen, nutrients and turbidity of water masses. Ebb–tide water was sampled from four water chestnut beds in the tidal freshwater portion of the Hudson River estuary and each site was sampled multiple times during the growing season and once following plant senescence. Water quality variables included dissolved oxygen, turbidity, dissolved organic carbon, and inorganic nutrients. Samples from the small beds (575 m² and 624 m²) were compared with large beds (16 600 m² and 24 820 m²). Dissolved oxygen of water flooding vegetated beds in the hour before high tide was 7.18±1.03 mg/l (mean±standard deviation) with a range of 5.5–9.8 mg/l throughout the growing season. Water samples collected as water ebbed from the plant beds showed that only the large beds had an effect on dissolved oxygen with the largest declines in oxygen exhibited by the largest bed. Decline of dissolved oxygen in the water ebbing from the largest bed averaged 1.5±0.4 mg/l/h with a minimum of 4.5 mg/l, equivalent to 54% of saturation, a level at which sensitive fauna are negatively affected. There were no significant relationships between bed size or plant presence and inorganic nutrients, turbidity or DOC. Ebb–tide nitrate was never lower than 87% of flood tide means. Effective management of invasive plants must consider both the variability in effects among plant beds and the areal coverage of plant bed sizes.     

The role of macroinvertebrates and fish in regulating the provision by macrophytes of refugia for zooplankton in a warm temperate shallow lake

1. The zooplankton often undergoes diel horizontal migration (DHM) from the open water to the littoral of shallow lakes, thus avoiding predators in the former. This behaviour has functional impacts within the lake, as it enhances zooplankton survival, increases their control of phytoplankton and tends to stabilise the clear water state. However, most of the evidence supporting this migration pattern comes from cold north temperate lakes, and more evidence from tropical and subtropical areas, as well as from southern temperate areas, is needed. 2. We conducted a field study of the diel horizontal and vertical migration of zooplankton, and the horizontal distribution of potential predatory macroinvertebrates and fish, over two consecutive days in the summer in a temperate lake in the southern hemisphere. We took zooplankton samples at two depths, at three sampling stations (inside beds of aquatic macrophytes, at their edge and in open water) along three transects running from the centre of a bed of Ceratophyllum demersum to open water. At each sampling station, we also took samples of macroinvertebrates and fish and measured physical and chemical environmental variables. 3. Zooplankton (pelagic cladocerans, calanoid copepods and rotifers) avoided the shore, probably because of the greater risk from predators there. Larger and more vulnerable cladocerans, such as Diaphanosoma brachyurum and Moina micrura, were two to four times more abundant in open water than at the edge of or inside beds of macrophytes, respectively, by both day and night. Less vulnerable zooplankton [i.e. of medium body size (Ceriodaphnia dubia) or with the ability to swim fast (calanoid copepods)] were distributed evenly between open water and the edge of the plant beds. Small zooplankton, Bosmina huaronensis and pelagic rotifers, showed an even distribution among the three sampling stations. Accordingly, no DHM of zooplankton occurred, although larger organisms migrated vertically inside C. demersum stands. 4. Macrophytes contained high densities of predatory macroinvertebrates and fish. The predator assemblage, composed of large‐bodied macroinvertebrates (including odonates and shrimps) and small littoral fish, was permanently associated with submerged macrophytes. None of these groups moved outside the plant beds or changed their population structure (fish) over the diel cycle. 5. Submerged macrophyte beds do not represent a refuge for zooplankton in lakes where predators are numerous among the plants, implying a weaker top‐down control of phytoplankton biomass by zooplankton and, consequently, a more turbid lake. The effectiveness of macrophytes as a refuge for zooplankton depends on the associated assemblage of predatory macroinvertebrates and fish among the plants.     

Intertidal community structure differs significantly between substrates dominated by native eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) and adjacent to the introduced oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis> (Thunberg) in British Columbia,Canada

Eelgrass beds represent important habitats for marine organisms, but are in decline in many coastal areas around the world. On Cortes Island, British Columbia, Canada, oysters coexist regionally with native eelgrass (Zostera marina L.), but eelgrass is typically absent directly seaward of oyster beds (the “below-oyster cobble zone”). We compared assemblage structure of nekton (fish and swimming macroinvertebrates) and epibenthos (macroinvertebrates and macroalgae) between eelgrass bed and below-oyster habitats. We sampled the intertidal zone on Cortes Island at low tide using two methods: quadrats to enumerate epibenthic macroinvertebrates and macroalgae, and beach seines to enumerate fish and swimming macroinvertebrates. Using multivariate analysis of similarity (ANOSIM), we found that the structure of nektonic and epibenthic assemblages associated with below-oyster cobble zones were significantly different from those in eelgrass-beds. Univariate measures showed that nektonic species richness and abundance were significantly higher in eelgrass beds than in below-oyster cobble habitat, whereas epibenthic species richness and abundance were significantly higher in below-oyster habitat. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Trexler     

Aquatic insects associated with two morphologically different submerged macrophytes, <Emphasis Type="Italic">Lagarosiphon ilicifolius</Emphasis> and <Emphasis Type="Italic">Vallisneria aethiopica</Emphasis>, in small fishless ponds

The study assessed the composition and abundance of insect assemblages associated with two submerged macrophytes, Lagarosiphon ilicifolius and Vallisneria aethiopica, in fishless ponds. Six ponds were used, with each plant occurring singly in two ponds, whilst the remainder had both plants. The insects were sampled using a 500-μm mesh. The number of insect taxa, diversity and total abundance on Lagarosiphon were greater than on Vallisneria when the plants occurred in separate ponds. In ponds comprising both plants, the total insect abundance on Lagarosiphon was greater than on Vallisneria. In all ponds, anisopteran naiads were dominant. Hemicordulia, Diplacodes and Trithemis made up 36.2, 27.1 and 15.2%, respectively, of the total number of insects on Lagarosiphon in single plant ponds. Trithemis was the only odonate in ponds comprised exclusively of Vallisneria and made up 68.7% of insects. In ponds that were cultured with both plants, four anisopteran taxa, Hemicordulia, Diplacodes, Trithemis and Tramea, were collected. In single plant ponds, the body-size class distribution of naiads on Lagarosiphon was characterised by a broader range, with significantly greater numbers of smaller and larger size classes than on Vallisneria (Kolmogorov–Smirnov test, P < 0.05). The study shows that in fishless waters, epiphytic insect assemblages may differ between the two plant species, especially when they are widely separated in space, probably due to greater predator–prey interactions on Vallisneria than on Lagarosiphon. The two plants may also differentially affect water physicochemical conditions, which may possibly influence insect ovipositing behaviour, and so affect insect community assemblage.     

Macroinvertebrates associated with two submerged macrophytes,Lagarosiphon ilicifolius and Vallisneria aethiopica,in the Sanyati Basin,Lake Kariba,Zimbabwe: effect of plant morphological complexity

Vallisneria aethiopica and Lagarosiphon ilicifolius are common and abundant submerged macrophytes in Lake Kariba, Zimbabwe. The two species have distinct structural morphologies, with Vallisneria consisting of long ribbon-like leaves, while Lagarosiphon has filiform stems with numerous small alternate leaves. This study investigated the effect of these architectural differences between the two plant species on their epiphytic macroinvertebrate assemblages in the shallow inshore waters of Lake Kariba. Ten sites were sampled on three occasions between May and July 2005. A total of 56 macroinvertebrate taxa was collected, 48 from Lagarosiphon and 45 from Vallisneria. Generally, the two plant species were associated with similar macroinvertebrate communities, but the average abundances of most taxa, and thus the overall macroinvertebrate abundances, were significantly greater on Lagarosiphon. The main macroinvertebrate functional feeding groups found on both plant species were collector-gatherers, grazers and predators, all of which were significantly more abundant on Lagarosiphon. Although the macroinvertebrate assemblages associated with Vallisneria and Lagarosiphon generally consisted of the same taxa, there were distinct and significant differences between them, probably due to the architectural differences between the two submerged macrophytes.     

Can artificial plant beds be used to enhance macroinvertebrate food resources for perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis> L.) during the initial phase of lake restoration by cyprinid removal?

Restoration of shallow lakes to a clear-water state, often characterized by high submerged macrophyte cover and a high proportion of piscivores such as perch, Perca fluviatilis L., frequently involves removal of a large proportion of the zoobenthivorous fish, such as bream, Abramis brama L., and roach, Rutilus rutilus L. (i.e. biomanipulation). However, establishment of submerged macrophytes is often delayed following fish removal. This is unfortunate because plant beds typically host high densities of the macroinvertebrates constituting the diet of small perch and thus help perch to go through the bottleneck from feeding on macroinvertebrates to feeding on fish. Establishment of artificial plant beds may be a useful tool to enhance macroinvertebrate population growth and thus food resources for small perch until the natural plants have established. To investigate this restoration option, we studied during two growing seasons (June–October) the composition and abundance of the macroinvertebrate community in artificial plant beds installed in shallow Lake Væng (Denmark) comprising the initial phase of a biomanipulation effort by fish removal. Lake areas with artificial plant beds exhibited substantially higher macroinvertebrate densities than the lake bottom. This suggests that artificial plant beds may be used as feeding grounds for small perch, similarly to the well-known refuge effect for zooplankton against fish predation. In this way, artificial plant beds could help maintain a clear-water state during the transient period when natural submerged vegetation is not yet established in the lake.     

三峡库区不同水文类型支流大型底栖动物对蓄水的响应

为探究三峡水库修建对库区不同水文类型支流大型底栖动物的影响,于2015年7月和2016年1月对三峡水库四条支流的大型底栖动物进行调研,分别对周期性受蓄水影响支流的非回水区与回水区和长期受蓄水影响支流的非回水区与回水区大型底栖动物群落结构进行比较研究,结果表明:⑴7月份三峡水库145米低水位时期共采集到底栖动物655头计59种(属),在受蓄水影响河段采集到底栖动物4种共40头,优势种为日本沼虾(占受蓄水影响区域的57.5%); 1月份三峡水库175米蓄水时期共采集到底栖动物1123头计69种(属),在受蓄水影响河段采集到16种238头,优势种为锯齿新米虾(占受蓄水影响区域的14.2%)。⑵周期性受蓄水影响支流的非回水区与回水区底栖动物密度、生物量和多样性指数无显著差异(P0.05);长期受蓄水影响支流的非回水区与回水区之间底栖动物密度和Pielou均匀度指数无显著差异(P0.05),但非回水区底栖动物生物量显著高于回水区(P0.05),底栖动物多样性和丰富度极显著高于回水区(P0.01)。⑶7月份影响底栖动物分布的主要环境因子共6个,分别是水深、流速、硝态氮、溶解氧、水温和电导率; 1月份影响底栖动物分布的主要环境因子共7个,分别是水温、溶解氧、总磷、流速、深度、电导率和透明度。     

Spatial patterns and population dynamics of plant-associated microcrustacea (Cladocera) in an English shallow lake (Little Mere, Cheshire)

Little Mere (Cheshire) is a small (2.7 ha) and shallow (average depth 0.7 m) fertile lake in Cheshire, UK. Nymphaeids cover almost 40 % of its entire surface during the growing season (April to October) and practically all the rest is covered by a mixed community of submerged plants. The lake was intensively sampled for plant-associated Cladocera and zooplankters from April 1998-April 2000. Samples were collected at five sites across the lake, three of them located within lily beds, the other two over submerged plant beds of mixed composition. Specific sampling techniques were developed for floating lily leaves, petioles, submerged plants and water. Significant horizontal differences were identified for most cladoceran species, both open-water and plant-associated, for chydorid periphyton scrapers and for filter-feeders. Daphnia hyalina (L.) and Ceriodaphnia sp were significantly more abundant in lily beds than in more open water in both growing seasons, suggesting lily beds are an effective refuge against fish predation. Size-structure and egg-ratio data support this contention. Egg-ratio models were examined for Daphnia hyalina and Simocephalus vetulus (O.F. Müller), a plant-associated cladoceran. The fertility of S. vetulus in lily beds was generally high throughout growing seasons. The construction of egg-ratio models for this species was hampered by their generally very patchy distributions.     

Macroinvertebrate size-distributions of two contrasting freshwater macrophyte communities

SUMMARY.

• 1 Macroinvertebrates (>0.1 mg, fresh weight) were collected every 2 weeks for 18 weeks from weedbeds dominated by either the macroalga Chara or rooted plants (mostly Isoetes sp., Potamogeton filiformis, Nuphar variegatum and Myriophyllum exalbescens) in Narrow Lake, Alberta, Canada. Significant differences in total biomass, taxonomic composition, and size-structure of the macroinvertebrate community were found between the two weedbed types.
• 2 Total biomass of macroinvertebrates in the Chara beds (seasonal mean 26.4 g m^?2) was consistently higher than in the rooted-plant weedbeds (seasonal mean 7.6 g m^?2).
• 3 The macroinvertebrate community of the Chara beds was dominated by chironomids, anisopterans, gastropods and sphaerid clams whereas amphipods dominated the community in the rooted-plant weedbeds.
• 4 On average, the proportion of total biomass in the various size-classes (biomass size-spectrum) of the macroinvertebrate community in Chara beds varied very little between 1 and 512 mg. In rooted plant weedbeds, the spectrum showed a strong peak in the 4–8 mg size-class, a weak peak in the 32–64 mg size-class, and proportionately low biomass in the 128–256 mg and 256–512 mg size-classes. The slope of the normalized size-spectrum for the macroinvertebrate community of the Chara beds (-0.89) was significantly different from that of the rooted plant community (-1.11). The biomass of large organisms (>64 mg) was 10 times greater in the Chara beds than in the rooted-plant weedbeds.
• 5 The species composition of aquatic macrophyte beds can greatly influence the abundance, taxonomic composition, and size-structure of the littoral zone macroinvertebrate community. Therefore, any changes in plant species composition of weedbeds, through introduction of exotic plant species or introduction (or loss) of an efficient grazer (e.g. crayfish), have the potential to alter greatly the structure of the macroinvertebrate community in a lake, with unknown consequences to fish and waterfowl dependent upon these prey.

     

Seed germination of three species of <Emphasis Type="Italic">Vallisneria</Emphasis> (Hydrocharitaceae), and the effects of freshwater microalgae

Two experiments were conducted to investigate seed germination under natural temperature and light regimes and to evaluate the influence of freshwater microalgae on seed germination of threeVallisneria species. Seeds exposed to natural seasonal temperature and light changes for 24 months germinated only in spring, perhaps indicating an annual dormancy/non-dormancy cycle. The ecological background of the natural habitat seems to play predominant roles in seed germinability. Mean cumulative seed germination percentages of Vallisneria natans, V. denseserrulata, andV.spinulosa of the first year were 35.2, 19.2, and 11.2%, respectively, and of the second year were 80, 72, and 32.4%, respectively. Germination rates differed significantly among the three Vallisneria species exposed to natural seasonal temperature and light changes in the first year, but differed only between Vallisneria spinulosa and the other two species in the second year. The differences of germination may influence the geographical distribution and thus be related to different survival strategies of the species. Seed germination rates in culture solution inoculated with algae were significantly higher than in solution with no algae. A strong correlation occurred between total biomass of freshwater microalgae and seed germination of the three studied species. Apparently, the extracellular products of freshwater microalgae may play an important role in seed germination. These results support the hypothesis that Vallisneria colonization may be mediated by algae facilitation.     

Comparison between community structures of fishes in <Emphasis Type="Italic">Enhalus acoroides</Emphasis>- and <Emphasis Type="Italic">Thalassia hemprichii</Emphasis>-dominated seagrass beds on fringing coral reefs in the Ryukyu Islands,Japan

To clarify differences in community structures and habitat utilization patterns of fishes in Enhalus acoroides- and Thalassia hemprichii-dominated seagrass beds on fringing coral reefs, visual censuses were conducted at Iriomote and Ishigaki islands, southern Japan. The numbers of fish species and individuals were significantly higher in the E. acoroides bed than in the T. hemprichii bed, although the 15 most dominant fishes in each seagrass bed were similar. Cluster and ordination analyses based on the number of individuals of each fish species also demonstrated that fish community structures were similar in the two seagrass beds. Species and individual numbers of coral reef fishes which utilized the seagrass beds numbered less than about 15% of whole coral reef fish numbers, although they comprised about half of the seagrass bed fishes. Of the 15 most dominant species, 5 occurred only in the two seagrass beds, including seagrass feeders. Ten other species were reef species, their habitat utilization patterns not differing greatly between the two seagrass beds. Some reef species, such as Lethrinus atkinsoni and L. obsoletus, showed ontogenetic habitat shifts with growth, from the seagrass beds to the coral areas. These results indicate that community structures and habitat utilization patterns of fishes were similar between E. acoroides- and T. hemprichii-dominated seagrass beds, whereas many coral reef fishes hardly utilized the seagrass beds.     

The influence of large water level fluctuations and hurricanes on periphyton and associated nutrient storage in subtropical Lake Okeechobee,USA

The abundance, community structure and nutrient content of periphyton, and the host plant taxa Chara, Hydrilla, Potamogeton, Vallisneria and Scirpus were studied in Lake Okeechobee, USA. Water levels were generally high during the study period (August 2002–January 2006), but substantial fluctuations occurred. All host plant biomass was seasonally variable but only Vallisneria biomass was spatially variable. All submerged plant beds disappeared after the passage of two hurricanes in September 2004, and a third hurricane passed over the lake in October 2005. Periphyton assemblages were statistically separated most by substrate and then by season. Prior to the hurricanes, annual maxima of periphyton biovolumes and those of summer submerged plant coverage coincided. During all study years, the diatom taxa dominated periphyton total biovolumes. Periphyton biomass was generally highest during the summer or prior to the hurricanes (in the case of epiphytes) and was spatially variable in the case of both Scirpus and Vallisneria. Epiphytic nutrient contents within each host plant group seasonally varied except for nitrogen and carbon in the Vallisneria epiphytes. Epipelic nutrient contents were spatially variable and seasonally variable for carbon. Nutrient contents in epipelon were significantly higher than that in Scirpus epiphytes and were similar but lower among all epiphytic communities. The total annual areal potential epiphytic phosphorus storage extrapolated during this study (2.0 × 10⁻⁴ metric tons ha⁻¹ year⁻¹) was underestimated because storage estimates for epipelon, Chara and Hydrilla-associated epiphytes were omitted. The Chara and Hydrilla-associated epiphytic nutrient storage values were omitted because of limited data, whereas the epipelic data may have not been spatially representative. For periphyton biovolume, host substrate type, water level fluctuation and hurricane impacts on host substrates appear to be more important than seasonal variation in such factors as temperature and nutrients. Epiphytic nutrient storage appears to be influenced most by water level fluctuation and hurricane-related impacts, while the host substrate type appears to be a less important factor than it is for periphyton biovolume. Maximum periphyton biomass and high nutrient storage in shallow subtropical and tropical eutrophic lakes may only occur at consistently lower water levels and during infrequent periods of disturbance, which enhance host substrate colonizable area.     

Multi-Scale Controls on Water Quality Effects of Submerged Aquatic Vegetation in the Tidal Freshwater Hudson River

Patches of submerged vegetation can be important sites of primary production and habitat for organisms in many aquatic ecosystems. In the tidal freshwater Hudson River they make up about 6% of the river bottom area. Direct sampling of water masses passing through patches of vegetation and week-long continuous monitoring of water characteristics were used to determine plant effects on dissolved oxygen and suspended sediments. Vegetated areas could have dissolved oxygen concentrations substantially higher than in the main channel and suspended sediments and turbidity were frequently higher in vegetated areas. Patches of Vallisneria americana had variable capacity to maintain super-saturated oxygen concentrations; patch size accounted for some of the variability whereas larger-scale differences in main-channel influent water also contributed. Differences in turbidity among sites were harder to account for; width of plant beds and abundance of neighboring vegetated areas contributed weakly to predictions of local turbidity. Functional heterogeneity within ecosystems is common and attempts to explain variability may require understanding different controlling factors for different functions and appreciating that factors operate at multiple scales.     

Ecological attributes of a native and exotic emergent subtropical marsh community in lake okeechobee, Florida (USA)

Ecological attributes of native Eleocharis cellulosa and exotic-invasive Panicum repens communities were compared in the western littoral marsh of Lake Okeechobee, USA. Water quality, periphyton and macroinvertebrates were monitored for 2 years. Fish and zooplankton were monitored during the second year. Mean dissolved oxygen, pH and Secchi transparency were significantly higher in Eleocharis while total phosphorus was marginally higher in Panicum. Periphyton biomass was higher in Panicum but biovolumes were higher in Eleocharis. There were clear differences in the within-habitat periphyton assemblages, less difference in the among-habitat assemblages and moderate to clear differences in periphyton over time in both habitats. Both habitats were dominated by small omnivorous fish. Habitat and date were the most influential factors in differences among both macroinvertebrates and zooplankton, although these differences were marginal to moderate in both cases. Macroinvertebrate densities were higher in Eleocharis while zooplankton densities were higher in Panicum. These data suggest that contrary to the paradigm that Panicum is undesirable as habitat, sparse (<1,000 stems m^?2) Panicum in close proximity to Eleocharis may exhibit a similar suite of ecological attributes. Both habitats also appear to contain similar food webs to nearby Everglades marsh communities.     

Microhabitat use by the rainbowfish <Emphasis Type="Italic">Melanotaenia duboulayi</Emphasis> in a subtropical Australian stream

Microhabitat use and feeding behavior of the rainbowfish Melanotaenia duboulayi (Castelnau) were investigated in a slow-flowing stream adjacent to riparian forest in south-eastern Queensland, Australia. Fish were more abundant in vegetated areas, but did not enter dense Vallisneria beds, where predators were observed. In sunny conditions shoals of juveniles occurred near the water surface feeding floating material on the surface, but larger fish tended to occur at the bottom near submerged vegetation, often utilizing the overhanging aquatic plant community as a refuge and food source. In the middle of the day, juveniles and small fish seemed to show behavioral thermoregulation at the surface in the warmest site. Under cloudy conditions, however, fish of all sizes preferred deeper water. The present study suggests that in still and sunny pools thermal change caused by sunlight influences the microhabitat choice of small fish. A field experiment using a kingfisher model implies that fish swimming at the surface could escape from aerial predators in sunlit conditions by responding to moving shadows, but could not do so under cloudy conditions. Electronic Publication