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 repHcate 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 m of sediment, 

 and sits outdoors exposed to ambient Hght. 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 species, 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. 



361 



