ROLE OF EXPERIMENTAL APPROACHES IN MARINE MICROBIAL ECOLOGY

Examination of the contribution of experimental approaches to marine m icrobial ecology shows these approaches to receive 34.8% of the presen t effort in the field. Most of the experiments focus on bacteria or ma rine microbial communities and generally examine the importance of tro phic interactions and associated flows of carbon and nutrients in thes e food webs. Microbial ecologists use experimental units ranging 8 ord ers of magnitude in size (10(-3) to 10(5)1), with a geometric median s ize of 0.81, and an exponential decline in the number of experiments p erformed at increasingly larger and smaller scales. The duration of ex periments is scaled Linearly with the characteristic Linear dimension of the experimental units, corresponding to 20 d for each meter in cha racteristic dimension. The majority (70.3 %) of the experiments perfor med in the past 5 yr used natural communities or organisms, particular ly in mesocosm (> 10(3) 1) experiments. Most (84.5%) of the experiment s are conducted under closely controlled conditions in the laboratory and involve the manipulation of particles, resources and the food web structure, usually manipulating a single factor at a time, he fraction of experiments published declining exponentially with the increase in the numbers of factors tested. A major difference between experimenta l marine microbial ecology and other disciplines of marine ecology is the remarkable paucity of field experiments (only 2.6% of the experime nts in marine microbial ecology), where only the treatment factors are controlled, and the total absence of ecosystem experiments, which are field experiments where the treatment is applied to an entire ecosyst em. Experimental approaches have played an important role in the devel opment of marine microbial ecology, but no single experiment has had a large impact on the progress of the field, suggesting that the experi ments so far conducted in marine microbial ecology have failed to prov ide the crucial tests of the main hypotheses needed to progress throug h strong inferences. The future effectiveness of experimental marine m icrobial ecology will be substantially enhanced through a larger alloc ation of efforts towards field experiments, designed to interplay with observational and comparative approaches, leading to conclusive tests of key hypotheses and paradigms through carefully designed, crucial e cosystem experiments.