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РЫБЫ -ИНДИКАТОРЫ ВРЕМЕНИ, ПРОСТРАНСТВА, УСЛОВИЙ ОБИТАНИЯ Монография
Abstract
The present monograph examines various aspects of fish used as indicators of
time, space, and environmental conditions. Fish are indicators of processes over
geological time and on interannual, seasonal, and diurnal scales. The patterns of
transformation of species composition and distribution of fish in connection with
global geological changes of the Earth surface and climate zones were shown along
with the peculiarities of deep-sea ichthyofauna formation. Fish are also indicators of
ongoing large-scale phenomena and processes in large typical nearshore biotopes in
the World Ocean, peripheral and internal seas. Special attention is given to the use
of fish as indicators of various forms of anthropogenic impact on aquatic ecosystems.
The present book is targeted to ichthyologists, ecologists, hydrobiologists, lecturers, and students of high educational institutions.
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The yellowtail surgeonfish, Prionurus punctatus, regulates structure and composition of algal communities attached to several reefs off Punta Colorada, Baja California Sur, Mexico. The surgeonfish is, in general, a non-selective grazer that takes small, filamentous algae in a multi-species algal mat in the proportions that they occur. They do, however, exclude large brown (Dictyota, Padina, Sargassum) and red algae (Liagora) and a large, foliose bryozoan (Bugula) from the diet. Exclusion of brown algae meets predictions of digestibility based on carbohydrate chemistry; reasons for ignoring the red alga and bryozoan are unclear. Lightly grazed reefs have a high standing crop and heavily grazed reefs a low standing crop of large algae, even though these algae are not eaten by fishes. Non-selective grazing at high intensities precludes growth of disfavored algae to a size where they can be recognized and avoided. On lightly grazed reefs these algae attain a sufficient size for recognition and grow undisturbed. This intensifies grazing on the algal mat between tufts of large algae, produces a reduction in standing crops between tufts, and results in a refuge where delicate, edible algae grow to unusual size under the canopy of the large, tufted species.
Mangroves, the only woody halophytes living at the confluence of land and sea, have been heavily used traditionally for food, timber, fuel and medicine, and presently occupy about 181 000 km2 of tropical and subtropical coastline. Over the past 50 years, approximately one-third of the world's mangrove forests have been lost, but most data show very variable loss rates and there is considerable margin of error in most estimates. Mangroves are a valuable ecological and economic resource, being important nursery grounds and breeding sites for birds, fish, crustaceans, shellfish, reptiles and mammals; a renewable source of wood; accumulation sites for sediment, contaminants, carbon and nutrients; and offer protection against coastal erosion. The destruction of mangroves is usually positively related to human population density. Major reasons for destruction are urban development, aquaculture, mining and overexploitation for timber, fish, crustaceans and shellfish. Over the next 25 years, unrestricted clear felling, aquaculture, and overexploitation of fisheries will be the greatest threats, with lesser problems being alteration of hydrology, pollution and global warming. Loss of biodiversity is, and will continue to be, a severe problem as even pristine mangroves are species-poor compared with other tropical ecosystems. The future is not entirely bleak. The number of rehabilitation and restoration projects is increasing worldwide with some countries showing increases in mangrove area. The intensity of coastal aquaculture appears to have levelled off in some parts of the world. Some commercial projects and economic models indicate that mangroves can be used as a sustainable resource, especially for wood. The brightest note is that the rate of population growth is projected to slow during the next 50 years, with a gradual decline thereafter to the end of the century. Mangrove forests will continue to be exploited at current rates to 2025, unless they are seen as a valuable resource to be managed on a sustainable basis. After 2025, the future of mangroves will depend on technological and ecological advances in multi-species silviculture, genetics, and forestry modelling, but the greatest hope for their future is for a reduction in human population growth.
Several microcosm types are currently in use, most to study the fate and effects of toxic substances. An example of the use of microcosms for testing and further development of a model for methoxychlor is described. The finding of an additional dominant process previously unconsidered for methoxychlor is discussed. Three simple ecosystems are considered and compared for their steady state values.
Алимов А.Ф. Элементы теории функционирования водных экосистем. Санкт
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Петербург: Наука. 2000. 147 с.
Estimated changes in reef area and CaCO3 production since the last glacial maximum (LGM) are presented for the first time, based on a model (ReefHab) which uses measured environmental data to predict global distribution of reef habitat. Suitable reef habitat is defined by temperature, salinity, nutrients, and the depth-attenuated level of photosynthetically available radiation (PAR). CaCO3 production is calculated as a function of PAR. When minimum PAR levels were chosen to restrict reef growth to 30 m depth and less, modern reef area totaled 584-746×103km2. Global carbonate production, which takes into account topographic relief as a control on carbonate accumulation, was 1.00Gtyr-1. These values are close to the most widely accepted estimates of reef area and carbonate production and demonstrate that basic environmental data can be used to define reef habitat and calcification. To simulate reef habitat changes since the LGM, the model was run at 1-kyr intervals, using appropriate sea level and temperature values. These runs show that at the LGM, reef area was restricted to 20% of that today and carbonate production to 27%, due primarily to a reduction in available space at the lower sea level and secondarily to lower sea surface temperatures. Nonetheless, these values suggest that reef growth prior to shelf flooding was more extensive than previously thought. A crude estimate of reef-released CO2 to the atmosphere since the LGM is of the same order of magnitude as the atmospheric CO2 change recorded in the Vostok ice core, which emphasizes the role of neritic carbonates within the global carbon cycle. This model currently addresses only the major physical and chemical controls on reef carbonate production, but it provides a template for estimating shallow tropical carbonate production both in the present and in the past. As such, the model highlights several long-standing issues regarding reef carbonates, particularly in terms of better defining the roles of light, temperature, aragonite saturation state, and topography on reef calcification.
Trophic level interactions caused by an algicide, an insecticide, and two levels of organic enrichment were demonstrated in alga‐grazer‐bacteria microcosms; e.g., the insecticide caused an algal bloom by removing grazers. The technique was expanded to develop an unbiased bioassay of the effects of low levels of HgCl2, CdCl2, Toxaphene, and Aroclor (PCB) 1242. Problems of toxicant recovery, solvent effects, repeatability, and statistical analyses were uncovered.In an algal chemostat, Aroclor 1242 generally prevented the maintenance of steady state densities.
Increases in toxic chemical dissipation makes their control in the environment desirable. Environmental control of these substances requires thorough understanding of the functioning of ecosystems potentially receiving chemical input, and of the behavior and fate of released chemicals. Terrestrial microcosms are useful tools in chemical fate studies; however, critical assessment of their ability to simulate ecosystem processes has been limited. This paper provides a rationale for evaluating the utility of microcosms for prediction of chemical fate in natural ecosystems.