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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 110 (1991), S. 315-321 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The unique hydrography of the Western Mediterranean Sea does not favour the formation of typical estuaries, although it does favour that of other land-sea systems. However, in Els Alfacs, a shallow-water bay situated in the Ebre Delta (northeast Spain), where there are considerable continental inputs, the distribution patterns of the macrofauna and the meiofauna reflect a hydrographical regime very similar to that of an estuary. During July 1987, 23 stations were sampled in the Alfacs Bay using plastic cores. The distribution pattern of the meiofauna follows a gradient and presents a less marked zonation than the macrofauna. Nevertheless, in both cases the peak densities of both faunal components are spatially separated from the principal site of freshwater inflow. The average density of the macrofauna (10 430 individuals/m2) and the meiofauna (704 100 individuals/m2) occurs in the bay during the period of maximum flow (spring-summer), and as such this bay is one of the most productive areas of the Western Mediterranean.
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  • 2
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The thalli ofHalimeda tuna (Ellis & Solander) grow horizontally from rocky surfaces and present an upper and lower surface which can be colonized by epiphytes. Thalli ofH. tuna were collected twice a month from March 1985 to March 1986 at Tossa de Mar (northeast Spain). Thirty five species of hydroid were recorded living onH. tuna thalli; of these, the 15 most abundant species were classified into three groups on the basis of their horizontal zonation on the thalli: those most abundant on the proximal, medial or distal articles. Those hydroids common on the proximal (oldest) articles were relatively large and were present throughout the year, those common on the medial articles were smaller and often occurred in dense monospecific patches, while those common on the distal (youngest) articles were present for only short periods and were the most opportunistic hydroids found onH. tuna. We hypothesize that this zonation reflects interspecific niche-selection, enabling successful competition for space with other hydroids, algae and bryozonas. Three hydroid species were more abundant on the upper surfaces of the algae than on the lower, probably because of gravitationally enhanced settlement of planula larvae coupled with (unusually) limited hydrorhizal growth on the underside. Three opportunistic species were more common on the lower surfaces of the thalli, possibly reflecting the greater availability of substratum in the shade, where epiphytic algae were less abundant. Many hydroids declined in abundance in summer because of the death of old thalli, the growth of new thalli and of apical articles on existing thalli, and possibly because of interspecific competition with epiphytic algae. The death of old thalli and the growth of new thalli reduced the abundance of epiphytic algae; this may have facilitated the increase in abundance of hydroids recorded in the autumn.
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  • 3
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the distribution patterns of ten zooplankton taxa of the Catalan coast (Western Mediterranean) using data collected in six research cruises along the continental shelf from April to July and September to October 1983. Zooplankton biomass ranged from 0.2–0.4 mg m-3 to 48–60 mg m-3, the greatest values being recorded between April and May, when gelatinous zooplankton concentrations were consistently present along the edge of the continental shelf. We identified the main factors contributing to the observed pattern of zooplankton distribution as the high degree of environmental fluctuation close to the coast (thermal gradient from north to south), the structural heterogeneity inherent to the continental shelf, and the persistence of a hydrographical front along the margin of the shelf.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 125 (1996), S. 365-373 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Campanularia everta is an epiphytic hydroid that may form dense populations on the macroalga Halimeda tuna. The main objects of this study were to quantify sexual reporduction and estimate sexual reproductive output of this hydroid. Sexual reproduction occurred from mid-October to mid-December 1991 along the Spanish Mediterranean coast. During this period, male and female colonies formed gonangia. Four oocytes mature in each female gonangium, and embryonic development starts probably after internal fertilization occurs. Planulae complete their development within a mucus sheath attached to the top of the gonotheca (acrocyst). Eight successive gonangia with a life-span of ≈1 wk each were formed over a 2 mo period. The fertile period was characterized by high initial production of gonangia followed by a progressive decline resulting from a decrease both in the number of fertile colonies and in the gonangia density of fertile colonies. Annual production was estimated at ≈42000 gonangia m-2, representing 83000 oocytes m-2. The high fertilization rates observed (77 to 100%) yielded a minimum production of 64000 planulae m-2. Reproduction in C. everta is characterized by: (1) a high number of larvae produced m-2; (2) formation and gradual release of larvae throughout the sexual reproduction period; (3) direct formation of planulae with no intermediate medusa stage; (4) low dispersive ability of the planula. All these mechanisms are part of a reproductive strategy designed to ensure the permanence of the population in its habitat.
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Zoologica Scripta 20 (1991), S. 89-98 
    ISSN: 0300-3256
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Coral reefs 18 (1999), S. 141-145 
    ISSN: 1432-0975
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  The natural diet and prey abundance of the benthic coral reef hydrozoan Nemalecium lighti, a common tropical species, were studied by analysing the gastrovascular contents of polyps. Prey capture was estimated from 10 samples collected at 3-h intervals during a single diel cycle (1–2 September, 1995) in the San Blas Islands (Panamá). Prey size ranged from 5 to 550 μm, with invertebrate larvae being the main contributor to the diet of the species. Prey items were found in 56–88% of the polyps over the entire diel cycle. Gastrovascular contents varied between 0.93 and 2.13 prey items per polyp. These capture incidences are among the highest reported for cnidarian species. Such rates would allow for high production rates for Nemalecium lighti, consistent with reports of the species’ fast growth and high reproduction rates. The observations suggest that some hydrozoans may be active heterotrophic components in coral reef ecosystems.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Submarine caves are semi-closed subsystems within the marine littoral ecosystem. One of the most striking features is the progressive reduction of the number of phyla, species, and biomass towards the interior of such a cave. The decrease in biomass has been explained as the result of low exchange rates of the water inside the caves which limit the supply of oxygen and food particles from the exterior. Many authors have proposed that this reduced exchange rate is associated with the occurrence of marked gradients in temperature, salinity, oxygen and light. Measurement of faunal abundance of a cave in the littoral zone of the Medes Islands (Catalonia, north-east Spain) made between June 1983 and July 1984, revealed a zonation similar to that in other Mediterranean caves. Animal biomass decreased from 260 g ash-free dry weight m-2 at the entrance to 80 g ash-free dry weight m-2 at the end of the cave (50 m from the mouth). A special technique for remote water-sampling was developed to avoid problems due to turbulence caused by divers in this semi-closed system. This involved the installation of a series of plastic tubes at different points along the axis of the cave. The water was brought to the surface using a battery-powered electric pump. The reliability of this method was verified by comparing the results with samples collected directly by divers. Sampling both in winter and summer showed no longitudinal gradients for temperature, salinity, oxygen, chlorophylla and the number and volume of suspended particles. These results suggest that there is a constant circulation within the cave which guarantees water-exchange. The decrease in biomass cannot be explained by physico-chemical gradients due to insufficient exchange with the external system. On a finer scale, however, along the walls of the cave there may exist boundary layers that are not affected by the general circulation. This could account for the observed decrease in the biomass of benthic organisms.
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  • 8
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The calcareous cornices of the algaeLithophyllum tortuosum Foslie, the so-called “trottoirs”, are one of the most characteristic formations of the littoral in the Western Mediterranean. The marked inconstant insolation and wave action are the environmental factors that most affect the fauna colonizing the cornice, and the distribution of animal populations should thus be affected by these factors. To test this hypothesis, the distribution of a population of polychaetes located on the coast of North-East Spain was studied from May 1982 to May 1983, taking three types of variables into consideration: (1) Spatial-at three levels (upper, medium and lower levels of the cornice), with two fractions in each level (inner and outer), from three different sampling locations; (2) seasonal-during six different months of the year; (3) biological-number of species, number of individuals, sizes and feeding strategies. In the population studied, the Syllidae dominated (37% of total identified species);Fabricia sabella was the most common species throughout the cornice, its average abundance being 38% of the total number of individuals in the population. No significant differences were observed in individual sizes of the polychaete population or between sampling stations. The number of species, the number of individuals and diversity increased from the upper level to the lower level of the cornice. The discretely motile filter-feeding species were dominant in the upper level, and motile carnivores, motile herbivores and sessile filter-feeders in the lower level. These three latter groups also dominanted the outer fraction of the cornice, whereas discretely motile filter-feeders dominanted the inner fraction. Differences in biological variables between levels were more marked outside than inside the cornice. Seasonal differences arose from higher insolation and a low humidity in summer and, in general, were most marked in the inner fraction and the lower level of the cornice, i.e., the most sheltered zones. In these zones, biological factors play a predominant role, although environmental factors do govern the whole polychaete population of the “trottoir” to varing degrees.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Polar biology 23 (2000), S. 34-37 
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A new species of pandeid anthomedusa, Amphinema modernisme, is described from a single and complete specimen collected by a mid-water sediment trap placed at 500 m depth in open waters, over a 1066-m bottom in the Drake Passage near the South Shetland Islands. This new Amphinema is characterized by an egg-shaped apical chamber, partitioned by four narrow sacciform centrifugal prolongations of the radial canals, perradial gonads and cellular strands linking the radial canals to the exumbrella. Its morphological features are compared with those of the eight other species of the genus Amphinema and a new diagnosis for this genus is presented.
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  • 10
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Analysis of the gut contents and scanning electron microscopy examination of the benthic hydroid Silicularia rosea from intertidal communities of Potter Cove (King George Island, South Shetlands) suggest that diatoms are the principal source of food for this species. The great number of items captured daily by each polyp (a mean of 287 in January and 162 in December) and the benthic origin of these prey items suggest an adaptation to daily resuspension processes caused by tidal currents. This is an unusual trophic strategy for a benthic hydroid, which would result in an important degree of independence from the highly fluctuating planktonic food conditions in Antarctic waters.
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