REPLICABILITY OF MERL MICROCOSMS: 
INITIAL OBSERVATIONS 
Michael E. Q. Pilson, 
Candace A. Oviatt, Gabriel A. Vargo and Sandra L. Vargo 
Graduate School of Oceanography 
University of Rhode Island 
Kingston, Rhode Island 02881 
ABSTRACT 
Nine microcosms at the Marine Ecosystems Research Laboratory (MERL) 
were run in replicate during the fall of 1976. Each microcosm tank is 5.5 m 
high and 1 .8 m in diameter, contains 13 m of water and 0.8 itt of sediment, 
and sits outdoors exposed to ambient light. Water and sediment were from 
Narragansett Bay. Water from the bay was run through the tanks at a rate of 
330 ml per minute, resulting in a turnover time of about 27 days. 
In this paper a set of the data collected during the first four months of 
operation is examined to discover the extent to which the microcosms 
replicated or diverged from each other and from the bay. Total chlorophyll a , 
nutrients, counts of individual phytoplankton specifies, and some other 
observations show that while there was considerable variability among the 
tanks at any given time, their overall behavior in the major features of bloom 
dynamics and species succession was consistent with that observed in the field. 
INTRODUCTION 
The development of marine microcosms has accelerated in recent years, 
due to an increased interest in investigating the properties of complex 
ecological systems, in understanding the effects of pollutants or other 
pertubations on such systems, and in using microcosms to carry out 
biogeochemical experiments (13) (3) (8) (17) (16) (10) (9) (14). The 
imposition of artificial boundaries and the limitation in size inevitably cause 
microcosms to differ from the natural systems they model. Nevertheless, the 
need to carry out controlled experiments on systems which represent a higher 
level of organization than cultures of single species has encouraged various 
attempts to pursue microcosm research. 
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