Role of experimental approaches in marine microbial ecology

Examination of the contribution of experimental approaches to marine microbial ecology shows these approaches to receive 34.8% of the present effort in the field. Most of the experiments focus on bacteria or marine microbial communities and generally examine the importance of trophic interactions and associated flows of carbon and nutrients in these food webs. Microbial ecologists use experimental units ranging 8 orders of magnitude in size (10(-3) to 10(5)1), with a geometric median size of 0.81, and an exponential decline in the number of experiments performed at increasingly larger and smaller scales. The duration of experiments is scaled Linearly with the characteristic Linear dimension of the experimental units, corresponding to 20 d for each meter in characteristic dimension. The majority (70.3 %) of the experiments performed in the past 5 yr used natural communities or organisms, particularly in mesocosm (> 10(3) 1) experiments. Most (84.5%) of the experiments 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 experimental marine microbial ecology and other disciplines of marine ecology is the remarkable paucity of field experiments (only 2.6% of the experiments 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 ecosystem. Experimental approaches have played an important role in the development of marine microbial ecology, but no single experiment has had a large impact on the progress of the field, suggesting that the experiments so far conducted in marine microbial ecology have failed to provide the crucial tests of the main hypotheses needed to progress through strong inferences. The future effectiveness of experimental marine microbial ecology will be substantially enhanced through a larger allocation 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 ecosystem experiments.