摘要:

1. Atyid (Decapoda: Atyidae) shrimps influence the distribution of algal communities over different scales in tropical montane streams of Puerto Rico. Within pools of an atyid‐dominated stream, atyid shrimps enhanced patchiness in algal communities along the depth gradient. Algal bands occurred in shallow pool margins where atyids did not forage (<3 cm below water surface), with significantly greater standing crop, taxon richness, and structural complexity than deeper areas. In deeper water, atyids reduced small‐scale patchiness in algal community composition and maintained a low‐growing understorey turf dominated by sessile diatoms (Bacillariophyta) and, sometimes, closely cropped, filamentous blue‐greens (Cyanophyta).2. Among pools of the atyid‐dominated stream, atyids interacted with light to determine algal patchiness between stream margins and deeper areas. In sunny pools, algal standing crop was 140‐fold greater in pool margins than in deeper areas where atyids foraged. In shaded pools, however, standing crop in pool margins was only 5‐fold greater than in deeper areas. Effects of light on algal standing crop were greater outside atyid foraging areas than within, indicating that shrimp grazing overrides the positive effects of light.3. In contrast to the atyid‐dominated stream, algal communities in an atyid‐poor stream were characterized by a high biomass of loosely attached epipelic diatoms and no depth zonation. Interstream rock and shrimp transplant experiments indicated that atyids significantly reduced algal standing crop and altered community composition on rocks from atyid‐poor streams within 24 h. Results support the hypothesis that atyid shrimps play a major role in determining observed interstream differences i

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00487.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. In streams, mayflies (Order Ephemeroptera) are at risk from fish feeding visually in the water column. The effect of fish odour on the behaviour ofBaetis bicaudatusfrom a fishless stream and a trout stream was investigated in four large oval tanks supplied with water from the fishless stream.2. For each mayfly population, mayfly positioning on the substratum and movement in the water column (drift) were measured during the day and night, over 3 days. Brook trout (Salvelinus fontinalis) odour was added to two tanks to test the effect of a threat from fish.3. Throughout the experiment more mayflies from the trout stream were observed on the substratum surface and in the water column during the night than the day, but the magnitude of night drift was less in tanks with fish odour.4.Baetisfrom the fishless stream also displayed a nocturnal periodicity in drift and positioning, but their night‐time drift was not affected by the presence of fish odour. On the first day of the experiment, however, more mayflies were observed on the substratum surface and drifting in tanks without fish odour during the day.5. Sensitivity to fish odour may enable mayflies to alter their behaviour according to the risk of predation from fis

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00489.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Drift from lotic and lentic side‐arms to the main channel was studied over 2 years in different sections of the Upper Rhône River (France). The hypothesis of an influence of drift on the main channel was tested by measuring drift in the main river at sites downstream and upstream from the confluences with two side‐arms, as well as in the two side‐arms themselves.2. Side‐arms were differentiated from the main channel by having a typical composition of macrofauna with a high propensity to drift, particularly in spring–summer and during spates. Drift densities in side‐arms averaged more than twice those measured in main channel sites, but these inputs did not significantly affect taxon richness and total drift density in the main channel.3. Nevertheless, some taxa found in the more lotic of the two side‐arms were more abundant downstream of the confluence than upstream, indicating that they had drifted into the main channel; no such direct effect was found throughout the sampling period for the more lentic side‐arm. The densities of two competitive filter feeders (Hydropsycheand Simuliidae) were significantly higher below the confluences than above, suggesting that side‐arms were also contributing substantial amounts of seston to the main channel.4. Therefore, side‐arms influence the community structure of drifting macroinvertebrates in the Upper Rhône River, both directly through immigration—depending on the degree of connectivity to the river—and i

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00490.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Two types of gemmules were found, each in a different species of sponge, from the warm monomictic Lake Kinneret: (i) clustered gemmules, sharing the pneumatic layer of the gemmular capsule and resembling gemmules ofEunapius; (ii) gemmules that develop non‐synchronously, containing amphidisc spicules within the gemmular capsule and resembling those ofEphydatia. Algal cells were not detected within either type of gemmule although they exist in the developed sponges.2. Sponges began producing gemmules in the lake with the onset of lake drawdown and ceased when lake level was minimal. The gemmules hatched when the lake level began to rise.3. Under experimental conditions gemmules hatched between 13 and 35 °C. Germination was optimal at 20–25 °C. Chilling of young gemmules prior to incubation at 25 °C improved germination rate.4. The percentage of germinating dry gemmules diminished 4–6 months after their collection from the lake. None germinated after 10 months. Submerged gemmules maintained high viability with ageing (up to 100% germination 18 months after collection). Desiccation influenced gemmule viability over time, by both decreasing the percentage of germinating gemmules and increasing the lag time before onset of germination.5. Gemmules kept in the dark germinated significantly less than those illuminated for

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00486.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Lake temperatures vary with season, latitude, elevation and as a result of thermal pollution. In addition, lake temperatures may increase with global warming. Radiotracer experiments were conducted to determine the effects of temperature on the bioaccumulation of lipophilic organic contaminants by zooplankton.Daphnia pulexwere exposed to14C‐labelled DDE, a stable metabolite of the organochlorine pesticide DDT, in particle‐free water for 24 h. An increase in temperature from 5 to 25 °C resulted in a 314% increase in bioconcentration factor (the ratio of contaminant concentration in the organism to contaminant concentration in the water).2. To mimic the fluctuating temperatures experienced by zooplankton during diel vertical migration, we conducted experiments in which animals were exposed to 25 °C for 12 h in the light, then 15 °C for 12 h in the dark. Exposure to this fluctuating temperature regime for 48 h resulted in a 27–33% increase in bioconcentration factor relative to a constant 20 °C control.3. Live animals accumulated more than twice the amount of DDE than freshly killed animals, indicating that the activity of the organism is important in bioconcentration. This finding sheds light on the possible mechanisms for the increase in bioconcentration at higher constant temperatures.Daphniapump more water through their branchial chambers at higher temperatures. Thus, if the thoracic limbs are an important site of contaminant uptake, then animals are exposed to more contaminant molecules at higher temperatures. Other possible mechanisms include changes in the thickness of the diffusive boundary layer and changes in cell membrane per

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00472.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1.Arctopsyche ladogensis,Hydropsyche angustipennisandHydropsyche siltalailarvae were exposed to nominal aluminium concentrations of 0, 625, 1250, 2500 and 5000 μg Al l–1at pH 5.0 for 96 h. Larvae reared at pH 6.4 and without any aluminium treatment were used as controls. Morphological abnormalities in the anal papillae of the larvae were used as the response variable in estimating the median effective concentrations (EC50) of aluminium.2. No morphological abnormalities were observed in the control larvae. Only a few individuals ofA. ladogensishad darkened anal papillae at pH 5.0 without additional aluminium treatment, whereas increasing aluminium concentrations significantly increased the number of individuals in all species displaying darkening and reduction of the papillae.3.A. ladogensisappeared to be the most sensitive species to increasing aluminium concentrations, as reflected by the significantly lower mean EC50value for this species compared with those ofH. siltalaiandH. angustipennis.H. angustipennislarvae were the most tolerant to aluminium.4. The results indicate that interspecific differences in sensitivity to aluminium may be a key factor influencing the guild structure of filter feeding caddis flies in acidified streams. The results also imply that toxic effects of aluminium on filter feeding caddis larvae occur due to the impairment of normal osmoregulation processes via damage to the ion‐regulatory or

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00483.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The flow of phosphorus and nitrogen through the food web of the shallow, eutrophic lake Wolderwijd was analysed for 2 different years before and for 1 year after food web manipulation.2. After fish removal the water became clear and the growth of macrophytes began. Fish removal resulted in a significant reduction of the total nutrient pool in the water, but differences between the nutrient cycles before and after the experiment were mainly caused by a gradual change driven by a reduced phosphorus input.3. The zooplankton biomass before and after food web manipulation did not change significantly. Unfavourable food conditions and predation by young fish limited zooplankton biomass after the food web manipulation.4. After fish removal benthic algae, fish, zoobenthos and macrophytes form the largest pools of nutrients apart from the sediment top layer. However, they contribute only little to nutrient cycles in the water column.

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00488.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY