Experimental methods and newly formulated principles have been introduced recently, which have increased the scope and possibilities of studying the population dynamics of aquatic organisms, both under strictly controlled conditions and under less controlled but more natural conditions, that is, in the field.
Controlled environmental chambers (Figure 2) can be used to maintain organisms under known conditions of light, temperature, and nutrient levels, so that the effects of each of these variables on specific populations as well as on the entire ecosystem can be studied. This also requires rather sophisticated biostatistics, sound experimental design, and reliable sampling protocols. More controlled conditions can be achieved in laboratory-controlled systems (microcosms), but inevitably with a lesser degree of realism. Experimental research data can never be assumed to apply reliably to field conditions, even those derived from results obtained in very large field-based containers or enclosures. The ultimate solution is clearly also to
Figure 2 Stainless steel constructions equipped with electronic sensors and loggers have been established to study simulated climate scenarios over several years.
perform large-scale experiments in the field, but this may often not be possible because of logistic and/or economic restrictions.
A number of new or improved methods are available for researchers, even at costs that are realistic. These methods include biotelemetry and other electronic tracking equipment to track, for example, individual fish over time and space or microelectrodes to measure gas fluxes over plant surfaces or sediments.
Radioisotopes and stable isotopes are used for tracing the energy flow through ecosystems, for determining the time and extent of transfer of organic matter and nutrients through the different components of the ecosystem, and for the determination of the length and complexity of food chains.
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