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1.
Abstract. The frequency of parasitism of free ending prop roots of the red mangrove, Rhizophora mangle, by the wood boring isopod Sphaeroma terebrans, increased with increasing distance of the endings to established roots. In a field experiment, in which isolated endings were, surrounded by wooden sticks, the endings were colonized by S. terebrans at a lower rate than control endings, thus indicating that the wooden structures in the vicinity of the ending tended to reduce colonization rate by S. terebrans. It is concluded that S. terebrans may cause mangrove root density to increase by colonizing peripheral endings more readily than endings which are near established roots. 相似文献
2.
G. Ribi R. Tardent P. Tardent C. Scascighini 《Aquatic Sciences - Research Across Boundaries》1985,47(1):45-56
Hydra populations were sampled every two weeks for three years in Lake Zürich and for one year in Lake Maggiore.Hydra fusca was most abundant followed byH. circumcincta andH. attenuata. The first two species showed strong seasonal fluctuations in abundance. Most of the reproduction occurred by budding. In
all species, approximately one third of the individuals carried buds while the proportion of individuals carrying gametes
was 1.6% inH. fusca and 13% inH. circumcincta in Lake Zürich. In Lake Maggiore very few sexual individuals were found. The ciliate commensalsKerona polyporum andTrichodina pediculus were observed on approximately one third of the individuals. 相似文献
3.
J.-M. Ribi J.-L. Boillat A. Peter A. J. Schleiss 《Aquatic Sciences - Research Across Boundaries》2014,76(4):527-541
Peak power production in hydroelectric storage power plants results in frequent and intense flow variations in the rivers downstream of the plants. Fish populations can be negatively impacted when subjected to these so-called hydropeaking phenomena. In researching mitigation solutions, shelters in the riverbanks of channelized rivers have been identified as a means of protecting fish from excessive flow velocities. These shelters were studied systematically using juvenile brown trout (Salmo trutta fario) in an experimental configuration in which a straight channel was equipped with a lateral embayment. The purpose of the experiments was to generate hydrodynamic hydropeaking conditions in the channel that are undesirable for juvenile trout, thereby causing them to enter the shelter. The flow velocity distribution in the intersection plane between the main channel and the lateral shelter was found to be a significant parameter for attracting fish to the shelter. The utilization rate of trout in the shelter was used as a performance indicator. Using a basic rectangular shelter configuration without forced water exchange between the shelter and the channel, the utilization rate was only 35 %. This rate was more than doubled by introducing a deviation groyne to force water exchange between the channel and the shelter. The position and orientation angle of this groyne were systematically varied to maximize the utilization rate. Maximum utilization rates approaching 90 % were obtained for an optimum configuration in which an island-type groyne was placed in the shelter. The results of the systematic channel tests showed the potential of the shelter to attract fish. Such a shelter could be used in channelized rivers both for morphological revitalization and to improve fish habitats. As a next step in this research, prototype shelters will be built on a natural river and monitored for 2–3 years under a hydropeaking flow regime. 相似文献
4.
Georg Ribi 《Aquatic Sciences - Research Across Boundaries》1992,54(1):85-90
Larvae of perch (Perca fluviatilis L.) reared in tanks for 27 days survived better in lake water to which 2% of artificial sea water had been added (46.6% average survival rate) than in lake water only (13.5% survival). One week after hatching, over 90% of the larvae had their guts filled in all tanks. During the following week the populations divided into floaters (fish with an inflated swimbladder) and sinkers (fish apparently lacking a functional swim-bladder). Although they continued feeding, sinkers remained smaller than floaters and most of them died. 相似文献
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6.
We performed two experiments, one to test whether survival and initial swim bladder inflation of perchPerca fluviatilis are affected by population density (4 or 16 larvae 1–1) or salinity (0, 0.6 and 1.2), and the second to test the salinity tolerance of larvae. In experiment 1, survival was higher at low larval densities and at salinities of 0.6 and 1.2 rather than in fresh water. Initial swim bladder inflation was not affected by salinity or density. Average survival of fry 24 days after hatching varied from 29.6% to 86.3%, but only an average of 19.2% of the hatched larvae had grown into viable fish with an inflated swim bladder. In experiment 2, survival varied from 19% to 49%, but was not significantly affected by salinities of up to 4.8. At a salinity of 9.6, only 2 out of 344 larvae survived. 相似文献
7.
It follows from theoretical considerations that in species with few but large offspring there should be selection against offspring born small. We found no such selection inViviparus ater (Christ. & Jan). Caged offspring born small (40–120 mg) and large (150–200 mg) had similarly low mortality rates of 5% or less in two months. The small born offspring grew faster than the larger offspring, indicating that any possible disadvantage associated with a small size at birth decreases as the snails grow. 相似文献
8.
Markus Zeh Erich Ritter Georg Ribi 《Aquatic Sciences - Research Across Boundaries》1989,51(2):100-107
Egg survival and development rate of perch eggs were investigated in Lake Zürich, Switzerland. A transplant experiment was carried out to examine whether individual females choose different depths for spawning because of an expected advantage for the development of their eggs. Egg masses which had been deposited on fir branches stuck into the ground of the lake were either left untouched or transplanted horizontally or vertically at depths of 3 and 6 m. Spawning occurred between 28 April and 9 June 1987. Egg survival to the eye pigment stage (EPS) was high in all treatments (
, minimum 92%). There was no significant difference in egg survival between treatments, suggesting that females do not choose the spawning site because of individual fitness differences related to the depth of spawning. Early egg masses which were exposed to lower temperatures developed more slowly (120–140 day degrees to the EPS) than late egg masses which were exposed to higher temperatures (80–100 day degrees). The observed differences are in agreement with the hypothesis of a constant sum of day degrees necessary for egg development using the corrected formula derived by Guma'a (1978) which deducts an estimated threshold temperature of 5°C below which development of perch eggs effectively stops, from the actual temperature. 相似文献
9.
Populations of the prosobranch snailViviparus ater (Christ. and Jan) in Lake Zürich and Lake Maggiore (Switzerland) were compared in order to evaluate how soft water in Lake
Maggiore affects shell morphology and population dynamics. A low calcium concentration of the water (3.5 mg CaCO3l−1) was the main reason for shell dissolution in Lake Maggiore. At some places shell damage was augmented by a stony ground
and wave action. In Lake Zürich (11.5 mg CaCO3l−1) the shells were not damaged. The snails in Lake Maggiore were smaller, suffered higher mortality and had a shorter life
span than those in Lake Zürich. 相似文献
10.
Victims from volcanic eruptions: a revised database 总被引：2，自引：1，他引：1
The number of victims from volcanism and the primary cause(s) of death reported in the literature show considerable uncertainty.
We present the results of investigations carried out either in contemporary accounts or in specific studies of eruptions that
occurred since A.D. 1783. More than 220 000 people died because of volcanic activity during this period, which includes approximately
90% of the recorded deaths throughout history. Most of the fatalities resulted from post-eruption famine and epidemic disease
(30.3%), nuées ardentes or pyroclastic flows and surges (26.8%), mudflows or lahars (17.1%), and volcanogenic tsunamis (16.9%).
At present, however, international relief efforts might reduce the effects of post-eruption crop failure and disease, and
at least some of the lahars could be anticipated in time by adequate scientific and social response. Thus, mitigation of hazards
from pyroclastic flows and tsunamis will become of paramount importance to volcanologists and civil authorities.
Received: 3 August 1997 / Accepted: 10 April 1998 相似文献