Bacterioplankton dynamics in estuarine mesocosms: Effects of tank shape and size

Mesocosms provide a powerful tool for investigating bacterial dynamics at s mall scales; however, even these controlled studies are not exempt from spa tial influences. Differences in mesocosm shape and size may have profound e ffects on the enclosed community since these features may influence the beh avior of the system. Studies were conducted in mesocosms of varying dimensi ons (narrow, deep and wide, shallow tanks) and volumes (0.1, 1, and 10 m(3) ) in an attempt to decipher effects attributable to changes in container si ze and shape. Both mesocosm volume and shape affected the course of bacteri al growth following containment. Bacterial abundance and production were hi gh in both groups of 0.1 m(3) tanks and in the large, wide, shallow tanks w ith the greatest light supply at depth. Differences in bacterial growth bet ween differently shaped tanks (i.e., differing wall area to volume ratios) were observed among equal volume enclosures, with faster growth in the wide /shallow tanks. Light availability, phytoplankton growth, and primary produ ction differed among tanks, and bacterial growth and production were correl ated with these properties. During high nutrient conditions, mesocosm volum e and shape influenced bacterial growth, possibly because of periphyton gro wth on walls in small tanks and elevated light levels in wide/shallow tanks . These results suggest the importance of considering container dimensions when designing and interpreting mesocosm experiments and may allow deeper u nderstanding of the fundamental processes underlying patterns observed in t he real world.