SPATIAL AND TEMPORAL SCALING OF PERIPHYTON GROWTH ON WALLS OF ESTUARINE MESOCOSMS

Although experimental ecosystems are basic and versatile tools widely used in coastal research, periphytic growth on container walls is an i ntrinsic artifact that must be considered when interpreting results. T o better understand how this artifact may confound extrapolation of re sults from controlled experiments to conditions in natural estuarine e cosystems, we examined how wall periphyton varied with container size and shape in summer and autumn experiments. Replicate (n = 3) cylindri cal mesocosms of 3 volumes (0.1, 1.0, 10 m(3)) were established in bot h constant-depth (depth = 1 m) and constant-shape (radius/depth = 0.56 ) series. Mesocosms were initiated with unfiltered estuarine water and homogenized sediments. Periphyton biomass and gross primary productio n (GPP) per unit of wall area increased with increasing radius (r) or decreasing ratio of wall area (A(W)) to water volume (V) for mesocosms in both series (A(W)/V = 2/r). As a consequence, periphyton biomass a nd metabolism expressed per unit of water volume increased as a quadra tic function of increasing A(W)/V ratio. Results also suggest a second ary scaling effect, whereby wall periphyton growth may be directly rel ated to mesocosm depth, although mechanisms for this effect remain unc lear. Significant correlations between periphyton biomass (per m(2) wa ll area) and 3 environmental factors (light attenuation coefficient, n utrient concentration, and zooplankton abundance) suggest that these f actors may have played important roles in regulating wall growth. Addi tionally, effects of wall periphyton growth on plankton community dyna mics were also indicated by the significant negative relations between periphyton biomass and measures of both phytoplankton and zooplankton abundance. The overall effect of periphyton on the experimental ecosy stems was evident in the fact that periphyton accounted or over 50% of total ecosystem GPP and biomass after 2 to 4 wk of these experiments. For mesocosm experiments designed to examine dynamics of planktonic-b enthic ecosystems, our results imply that growth of wall periphyton, w hich is controlled by factors scaling to the radius of experimental ec osystems, tends to dominate major biotic pools and rates within weeks.