Experimental observations on the behaviour of the ostracode Cypridopsis vidua (original) (raw)
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Uncoupling of omnivore-mediated positive and negative effects on periphyton mats
Oecologia, 2003
The riverine grass shrimp (Palaemonetes paludosus) and eastern mosquitofish (Gambusia holbrooki) consume periphyton and small invertebrates, potentially affecting periphyton through negative effects (i.e., consumption) and/or positive effects such as nutrient regeneration, physical stimulation, and trophic cascades. We performed field experiments in the Everglades in which omnivores and periphyton were maintained in cages, with a fraction of the periphyton held in omnivore-exclusion bags that allowed passage of nutrients but prevented its consumption or physical disturbance. In some instances, periphyton growth rate increased with increasing omnivore biomass. Omnivores probably stimulated periphyton growth through nutrient regeneration, possibly subsidizing periphyton with nutrients derived from ingested animal prey. The net balance of omnivore-mediated negative and positive effects varied among experiments because of seasonal and spatial differences in periphyton characteristics. Consumption of periphyton mats might have been reduced by the arrangement of palatable algae (green algae and diatoms) within a matrix of unpalatable ones (CaCO 3-encrusting filamentous cyanobacteria). In a laboratory feeding experiment, mosquitofish consumed more green algae and diatoms in treatments with disrupted mat structure than in those with intact mats. No difference in diet was observed for shrimp. Our study underscores the complexity of consumer-periphyton interactions in which periphyton edibility affects herbivory and consumers influence periphyton through multiple routes that cannot be fully appreciated in experiments that only investigate net effects.
Hydrobiologia, 1999
The effect of one-year-old common carp (Cyprinus carpio L.) on plants and seedlings of Potamogeton pectinatus L., and on periphyton development was studied in 100 l glass aquaria. Two 30-day experiments were conducted using a muddy sediment or a pebbly bottom. In both cases, three treatments based on different fish size (two fish/aquarium) were assayed. The control had no fish. In both experiments, chlorophyll content of the periphyton increased from the beginning to the end of the period, for the three fish treatments. Light attenuation by periphyton was high, with final values 12-30% higher than in the control. Periphytic communities acclimated to reduced light conditions when the bottom was muddy. It can be concluded that, in muddy conditions, small carp affected plant growth by shade stress, which is achieved by a combination of increase in turbidity and the developing of a leaf periphytic cover. Under pebbly conditions, plant damage was caused by collisions and the growth of epiphytic algae. Medium and large fish consumed plants in both experiments. Seedlings were affected by herbivory in all cases.
Hydrobiologia, 1993
The seasonal variation in periphyton dynamics has been studied upon artificial substratum (microscopic glass slides) under various light conditions during the periods May–October 1986 and May–September 1987, in Lake Veluwe. Some additional observations on the periphyton development upon leaves of Potamogeton pectinatus L. have been made simultaneously. Four different light conditions were created in an experimental setup by manipulating the photon flux density through artificial shading. Periphyton upon artificial substratum exhibited a relatively high abundance with a distinct seasonal pattern. Periphyton accrual rates were highest at the beginning of June and in August and September upon slides which were incubated for two weeks. Periphyton mass increased during May and June, decreased or remained about the same during July and subsequently increased until an upper plateau was reached upon slides which were incubated from the beginning of May onwards. Generally, periphyton mass was lower upon slides than upon P. pectinatus. The seasonal variation in periphyton mass was more pronounced upon P. pectinatus leaves than upon the slides. Attenuation by periphyton upon slides ranged from 5 to 65% after two weeks of incubation. Periphyton upon slides which had been incubated for more than two weeks demonstrated an attenuation of more than 85%. Water quality parameters other than photon flux density were probably more important in determining the periphyton dynamics, since only minor differences were observed in periphyton mass between the various light conditions. Chlorophyll-a content was higher with increased shading on various sampling dates. Periphyton, especially ‘older’ periphyton consisted largely of settled silt and clay particles and to a lesser extent of detrital matter on both substrata. Living epiphytes were only a relatively small fraction. It is concluded that a reduction of resuspension of sediment particles, giving less suspended matter in the water column, will result in lower periphytic mass. Consequently, the quantity of photosynthetically active radiation reaching the submerged macrophytes is expected to increase considerably.
The influence of periphyton, detritus and shelter on invertebrate colonization of aquatic bryophytes
Freshwater Biology, 1992
1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization. 2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship. 3. Reducing substratum 'stem' density (i.e. 'shelter') in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low-density substrata. Abundances of most of the twenty-two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced. 4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty-two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site. 5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrita! biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty-two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty-two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).
Grazing by a native and an exotic crayfish on aquatic macrophytes
Freshwater Biology, 1996
1. We compared grazing by native noble crayfish (Astacus astacus) and the exotic signal crayfish (Pacifastacus leniusculus) on seedling or well-established macrophytes. 2. In a pool experiment, seedlings of emergent Scirpus lacustris and floating-leaved Potamogeton natans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage. 3. In a preference experiment two submerged macrophytes (Chara vulgaris and Elodea canadensis), and both seedlings and established plants of S. lacustris and P. natans, were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans. 4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures. 5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating-leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating-leaved vegetation.
Periphyton and phytoplankton associated with the tropical carnivorous plant Utricularia foliosa
Aquatic Botany, 2007
The abundance and taxonomic composition of periphyton attached to the bladders and phytoplankton associated with the aquatic carnivorous plant Utricularia foliosa were quantified, to determine whether periphyton associated with U. foliosa would enhances predation success. Bladder size, periphyton abundance and periphyton richness together explained 76% of the variation observed in the number of prey captured by the bladders. The abundance and richness of periphyton followed the same pattern as phytoplankton, i.e., both increased as dissolved inorganic phosphate concentration rose. This nutrient concentration explained 84 and 74% of the variation observed in richness and abundance of periphyton, respectively. This suggests that abundance and richness of the periphyton associated with U. foliosa depend mostly on environmental conditions rather than on facilitation mechanisms displayed by the plant. In conclusion, if periphyton affects U. folisosa negatively due to the competition for light or nutrients, the plant is “fated to get along with the enemy” but apparently without the capacity to manipulate this “enemy” to its own advantage.
Food selection in Eucypris virens (Crustacea: Ostracoda) under experimental conditions
Hydrobiologia, 2007
Ostracods have long been studied by scientists because their fossil remnants provide a valuable tool for the reconstruction of past environmental changes, including climate change and anthropogenic eutrophication. Relatively little is known about the physiology, behaviour and reproductive ecology of recent forms. We argue that filling this gap in knowledge requires stable cultures that can be used in laboratory studies. Here we provide quantitative information on the food preference of the common non-marine ostracod Eucypris virens. Using an experimental device allowing a free choice of eight food items, including both auto- and heterotrophic organisms, observations were carried out on groups of animals from different populations. Our results indicate that E. virens highly prefers spinach and the cyanobacterium Tolypothrix tenuis to other food items. The latter also plays an important role in maintaining the quality of the culture medium and provides a convenient substrate for moulting and egg-laying. As such, we recommend Cyanobacteria like T. tenuis as a food source for long-standing cultures of E. virens, and other non-marine ostracod species.
Mechanism and Adaptive Significance of Substrate Selection by a Sessile Rotifer
Ecology, 1986
We examined the nature and adaptive significance of substrate selection by larvae of the sessile rotifer Collotheca gracilipes. In a small artificial pond the preferred substrate was the anatomical undersurfaces (abaxial) of Elodea canadensis leaves, although four other macrophytes were present (Ceratophyllum demersum, Lemna minor, Myriophyllum spicatum, and Nymphaea odorata). Density of adults on Elodea at times reached >6 individuals/mm2, with >98% attached to abaxial surfaces. However, larvae offered plants in pairwise combinations selected substrates in the following order: Lemna > Elodea > Myriophyllum > Nymphaea. No larval loyalty to parental substrate was exhibited. Larvae preferentially selected abaxial over adaxial surfaces of Elodea leaves (91% on abaxial) in continuous illumination experiments, but the larvae did not discriminate between the two surfaces in total darkness (48% on abaxial).
Freshwater Biology, 1995
1. Fresh and decomposed Mougeotia sp. (a filamentous green alga) and Elodea nuttaltii (a vascular plant) were offered as food to three species of aquatic macroinvertebrates {Lymnaea peregra, Asellus meridianus and Endochironomus albipennis) to test: (i) if filamentous algae are preferred to aquatic higher plants (hereafter, called 'macrophytes') and (ii), as is known for higher plants, if decomposition also results in greater palatability of filamentous algae. 2. Compared with the alga, the macrophyte in both states was of higher nutritional value. Conditioning improved the nutritional value of both food types, but especially of the macrophyte. 3. Both fresh alga and fresh macrophyte were eaten little by all animals except A. meridianus feeding upon the macrophyte. Consumption was higher for both plants in their decomposed state. However, L peregra consumed more decomposed macrophyte than the decomposed alga. Both decomposed plants were eaten most by £. albipennis followed by A. meridianus and L. peregra. 4. Digestibility of both plants, but especially of the macrophyte, increased significantly after decomposition. The assimilation efficiencies of all animals on the fresh E. nuttallii were higher than on fresh Mougeotia sp. After decomposition, the efficiency increased significantly only on the alga. Consequently, both decomposed plants were assimilated with similar efficiency by all test atumals. 5. Amongst aquatic macrophytes, the increase of their consumption and digestibility upon decomposition has hitherto been known only for vascular plants but not for filamentous algae.
A review on the role of nutrients in development and organization of periphyton
Periphyton communities have not received wider attention and often misunderstood with 'biofilm' for their nature of development and role in aquatic ecosystem. To clarify its functional objective in aquatic ecosystem, present review proposes a functional definition for 'periphyton' in terms of ecological interactions and also outlines its ecological role in nutrient sharing with other aquatic components. The development and succession of periphyton is a function of nutrient and carbon (C) sharing with its constituent parts and ambient environment. Through mechanisms like entrapment, de novo synthesis, nutrient leakage, trophic upgrading etc., ambient nutrients are routed to periphyton and transferred to upper trophic levels. Periphyton communities stand next to phytoplankton for their contribution to primary productivity, in nutrient rich aquatic environment. Unlike phytoplankton, nutrient poor aquatic environment has no effect on periphytic primary productivity. As periphyton communities are attached to substratum, their ability to assimilate organic nutrient through substratum is an additional advantage over phytoplankton.