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  • 1
    Electronic Resource
    Electronic Resource
    Ecological footprint for assessment of resource use and development limitations in shrimp and tilapia aquaculture (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Aquaculture research 28 (1997), S. 0 
    Details
    ISSN: 1365-2109
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We review estimates of the spatial ecosystem support required to run a typical semi-intensive shrimp farm in a coastal mangrove area in Carribean Colombia, and to produce food inputs and process wastes for large-scale industrially managed tilapia cage culture and small-scale, semi-intensive tilapia pond farming in Lake Kariba, Zimbabwe. The tilapia farming is discussed in relation to the pelagic kapenta, Limnothrissa miodon (Boulenger), fishery and to inshore fisheries in the Lake.The results show that a semi-intensive shrimp farm needs a spatial ecosystem support—the ecological footprint—35 to 190 times the surface area of the pond, mainly mangrove area. Based on the analysis, we conclude that shrimp farming in Colombia is already utilizing close to the full support capacity of its coastal environment. In intensive tilapia cage farming, the ecological footprint for feed production is 10 000 times larger than the area of the cages. In contrast, a tilapia pond farm maintained on offals from fisheries, agriculture and households depends very little on external ecosystem areas. As long as there is a direct market for human consumption of all kapenta caught in the Lake, fish cage farming based on fish meal from kapenta would be doubtful from ethical, ecological as well as resource management points of view, even if it was economically feasible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2109.1997.00940.x
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  • 2
    Electronic Resource
    Electronic Resource
    Environmental ecology: The impacts of pollution and other stresses on ecosystem structure and function - B. Freedman, Academic Press, London, 1989. £29.00. ISBN 0-1226-6540-6
    Amsterdam : Elsevier
    Ecological Economics 4 (1991), S. 168-169 
    Details
    ISSN: 0921-8009
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Economics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0921-8009(91)90028-D
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  • 3
    Electronic Resource
    Electronic Resource
    Growth and size structure in a baltic Mytilus edulis population (1982)
    Springer
    Marine biology 68 (1982), S. 117-133 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Since Mytilus edulis L. has very few predators and competitors for space, it has become a biomass dominant in the Baltic proper covering hard substrates from the water surface to more than 30 m depth. In order to investigate the factors controlling size and production in a Baltic M. edulis population, growth was studied by the analysis of annual growth rings, measurements of caged individuals and the analysis of size classes in the population, and on settlement ropes. The total number of mussels in a representative mussel bed at 4 m depth varied between 36 000 and 158 000 ind · m-2 during the year, mainly due to variations in very small mussels (〈2 mm), whereas the abundance of mussels ≧2mm was rather constant between about 17 000 and 28 000 ind · m-2. Maximum numbes of mussels 〈 2 mm, amounting to 132 000 ind · m-2, were found after settlement in summer, but still half a year later in spring, 65 000 ind · m-2 〈 2 mm were registered, due to very strong intraspecific competition for food and space leading to the competitive suppression of small individuals and large variations in growth rates. Due to the special size-structure of the population only the analysis of annual growth rings could be used to estimate natural shell growth. From being very low in the smallest mussels, growth was linear between about 2–10 yr of age, corresponding to about 3–20 mm length, after which it decreased with a L∞=32 mm. Over the linear interval, growth in the populations from 3–6 m and 10–15m depth was 3.1 and 2.2 mm · yr-1, respectively. Meat growth showed strong annual variations mainly due to gonad production. Starving mussels could, however, while utilizing energy reserves, survive losses of up to 78% of their meat biomass. This ability of M. edulis to “respire away its own biomass” and its apparent tolerance of weight loss has important implication. It will drastically reduce the energy flow to destruents from mussels dying naturally, which is of special significance in the Baltic, where predators and scavengers are scarce. It enables the mussels to endure bad food conditions and buffer strong seasonal variations in food abundance, maintaining the strongly food-and space-limited Baltic M. edulis population at the carrying capacity of the area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397599
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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative studies on gonad cycle, fecundity, reproductive output and recruitment in a baltic Mytilus edulis population (1982)
    Springer
    Marine biology 68 (1982), S. 143-160 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Since Mytilus edulis L. is a biomass dominant in the Baltic much interest is focused on the ecology of the species. In this paper an attempt is made to quantitatively cover the reproductive cycle of a Baltic M. edulis population in order to provide data for energy flow models and to discuss aspects of recruitment in this species. Histological preparations of gonads showed that gametogenesis started with declining temperatures in autumn and proceeded very slowly through winter. At the beginning of March when food was supplied during the spring phytoplankton bloom, rapid maturation took place. This was also revealed by an increase in meat weight of the mussels. Only one spawning period was recorded, from the middle of May until the beginning of June, due to food being strongly limited to the population during the rest of the year. The length of the larval period was estimated as being 5 to 6 wk and settlement was registered from the end of June through July. In general the large annual variations found in the Baltic with regard to temperature and food abundance give rise to a more marked annual pattern in the reproductive cycle than is encountered in other seas. Fecundity was assessed for two populations from 4-and 15-m depths from studies covering two annual cycles of the changes in the relation of shell length — meat weight. The size-related fecundity was found to be equal in both populations and related to food abundance and not to growth or age. Fecundity, expressed as weight loss at spawning, ranged from 0% in 2-mm mussels and increased from 38 to 52% in 10-to 30-mm mussels. The fecundity as percentage of biomass in full-grown Baltic M. edulis is of similar magnitude as in full-grown mussels from other areas despite the smaller size of Baltic mussels. The reproductive output for the total 160 km2 research area was calculated as being 1 200 tons dry weight or 80% of the standing stock, which, due to the particular features of the Baltic M. edulis population probably represents the larger part of the total mussel production. This reproductive output, calculated as 8·107 eggs·m-2 and corresponding to 50% of the total annual zooplankton production, may thus consitute an important food source for herring larvae and carnivorous zooplankton. Recruitment was divided into two phases: (1) Recruitment of juveniles (=settlement of larvae), and (2) recruitment to breeding stock. Monitoring studies of settlement on ropes and the year round presence of high abundances of mussels 〈2 mm indicate that settlement is in excess of the demands for maintaining population size and that most settled mussels form a pool of competitively suppressed non-growing individuals. Not until death of an already established mussel will these become recruited to the breeding population. Thus recruitment is possible throughout the year which stabilizes the population and maintains it near the carrying capacity of the area with regard to food and space availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397601
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of salinity and bromine on zygotes and embryos of Fucus vesiculosus from the Baltic Sea (1992)
    Springer
    Marine biology 114 (1992), S. 661-665 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Zygotes and young embryos derived from Fucus vesiculosus collected in the archipelgo of Stockholm in 1990, growing at a salinity of 6 to 7‰ S, were cultured under different salinity conditions and in media of different bromine concentrations. Optimum salinity was 10 to 12‰ S for germination (rhizoid initiation) while apical hair formation showed a broader tolerance curve with an optimum at 8 to 14‰ S. Bromine caused inhibition of early development of F. vesiculosus. At 6‰ salinity a 50% reduction in germination took place at 10.0 mM Br and at 1.25 mM Br only 4.7% of the embryos developed apical hairs, as compared to 32.7% in the control. Bromine toxicity decreased at higher salinities. The results indicate that F. vesiculosus in the Baltic Sea has diverged from its Atlantic progenitors and to some extent acclimated to low salinity. Still, the salinity in the normal environment of the tested population is lower than optimum, leading to a lower degree of germination of zygotes, a lower growth rate of young embryos and probably also a higher sensitivity to additional stress factors such as chemical pollution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357263
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  • 6
    Electronic Resource
    Electronic Resource
    A battery-operated, continous-flow enclosure for metabolism studies in benthic communities (1984)
    Springer
    Marine biology 81 (1984), S. 47-52 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Community metabolism is increasingly being used as a measure of functional activity in ecological research. In order to combine the advantages of measuring metabolism in open and closed aquatic ecosystems, a battery powered, portable, in-situ, continuous flow-through apparatus was designed. A gravity generated water flow through the enclosures ensures steady flow rates and allows continuous measurements of e.g. O2, temperature and nutrients over long time-periods. The setup is suitable for experimental purposes as it is possible to manipulate the incoming water (e.g. by increasing or decreasing temperature, food, oxygen and nutrient levels) and as several enclosures containing different ecosystem components can be serially coupled in order to evaluate aspects of their interdependence and functions in the total ecosystem. The device is also suitable in bio-assay studies for on-site effluent testing and dose-response testing of toxicants. By regulating the flow rate and size of the enclosure, the setup can be easily adapted to different sizes and activities of the components studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397624
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  • 7
    Electronic Resource
    Electronic Resource
    Ecological engineering in aquaculture: use of seaweeds for removing nutrients from intensive mariculture (1999)
    Springer
    Journal of applied phycology 11 (1999), S. 89-97 
    Details
    ISSN: 1573-5176
    Keywords: ecological engineering ; biofilter ; aquaculture ; seaweeds ; mariculture ; eutrophication ; Gracilaria ; shrimp farming ; mangroves ; ecological footprint
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rapid scale growth of intensive mariculture systems can often lead to adverse impacts on the environment. Intensive fish and shrimp farming, being defined as throughput-based systems, have a continuous or pulse release of nutrients that adds to coastal eutrophication. As an alternative treatment solution, seaweeds can be used to clean the dissolved part of this effluent. Two examples of successfully using seaweeds as biofilters in intensive mariculture systems are discussed in this paper. The first example shows that Gracilaria co-cultivated with salmon in a tank system reached production rates as high as 48.9 kg m−2 a−1, and could remove 50% of the dissolved ammonium released by the fish in winter, increasing to 90–95% in spring. In the second example, Gracilaria cultivated on ropes near a 22-t fish cage farm, had up to 40% higher growth rate (specific growth rate of 7% d−1) compared to controls. Extrapolation of the results showed that a 1 ha Gracilaria culture gave an annual harvest of 34 t (d. wt), and assimilated 6.5% of the released dissolved nitrogen. This production and assimilation was more than twice that of a Gracilaria monoculture. By integrating seaweeds with fish farming the nutrient assimilating capacity of an area increases. With increased carrying capacity it will be possible to increase salmon cage densities before risking negative environmental effects like eutrophication and toxic algal blooms sometimes associated with the release of dissolved nutrients. The potential for using mangroves and/or seaweeds as filters for wastes from intensive shrimp pond farming is also discussed. It is concluded that such techniques, based on ecological engineering, seems promising for mitigating environmental impacts from intensive mariculture; however, continued research on this type of solution is required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008070400208
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  • 8
    Electronic Resource
    Electronic Resource
    Abundance and distribution of inshore fish in fished and protected areas in Lake Kariba, Zimbabwe (1995)
    Springer
    Hydrobiologia 306 (1995), S. 67-78 
    Details
    ISSN: 1573-5117
    Keywords: abundance ; Kariba ; commercial ; comparison ; fished ; reserve area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Abundance and size distribution of inshore fish populations was assessed by fishing with standard Lundgren survey gill-nets in areas open to fishing and reserved areas that are protected from fishing activities. The direct gradient analysis technique — Detrended Canonical Correspondence Analysis — revealed that fish abundance and their composition in Lake Kariba are strongly structured by lake morphometry. The comparison between fished and reserve areas showed that there was a significant reduction in mean length of commercially fished species in the fished areas and the size distribution curves were skewed, lacking small and large length classes. There was a higher abundance of non-commercial species in the fished areas. It was also revealed that the mochokid Synodontis zambezensis Peters 1852, was the most abundant species and was present at all depths sampled in all the stations. There were indications that non-commercial species were important in terms of abundance in the fished areas. These included S. zambezenzis, Schilbe intermedius (Ruppell, 1832) and other smaller species. This was attributed to them being selected against in the gill-nets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007859
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  • 9
    Electronic Resource
    Electronic Resource
    Functional response of Fucus vesiculosus communities to tributyltin measured in an in situ continuous flow-through system (1989)
    Springer
    Hydrobiologia 188-189 (1989), S. 277-283 
    Details
    ISSN: 1573-5117
    Keywords: macroalgae ; disturbance ; primary production ; community metabolism ; hazard assessment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of antifouling paint leachate containing tributyltin on community metabolism and nutrient dynamics were measured in situ on natural communities dominated by Fucus vesiculosus. The measurements were made in two areas with different salinities and at various TBT concentrations up to about 5 µg 1−1. A portable continuous flow-through system was used in which the communities were incubated for a week. Continual measurements of oxygen, temperature, light and flow rate of water were made. A Perturbation Index (PI) and an Absolute Disturbance Index (ADI) were used to describe the changes due to treatment relative to the control, and to obtain a total picture of disturbance using all measured parameters. Photosynthesis was particularly strongly affected and changes were obvious in oxygen production and nutrient uptake at TBT levels as low as 0.6 µg 1−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027793
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