Sometimes a given species such as oysters in an oyster bed is intermit- 

 tently monitored by taking grab samples; however, if this methodology is 

 used one must very carefully design the experiment so that the total number 

 of grabs will give reproducible results — in other words, that there will be 

 given degree of statistical reliability that if the procedure is repeated 

 the same kind of data will be obtained if no change occurs. This type of 

 monitoring has been developed by the laboratories of the Academy of Natural 

 Sciences (Patrick, in press). 



Another type of monitoring is that which has been developed for monitor- 

 ing communities of organisms. The most sophisticated of these has been 

 those developed by Patrick et al . (1954) for algal communities growing on 

 glass slides. In this method an apparatus known as a diatometer is intro- 

 duced into a body of water. It has been found that diatoms grow success- 

 fully on these slides. This fact was first pointed out by Butcher (1947). 

 However, the method used by Patrick is the first one to model the community 

 and to note by changes in the structure of the community as well as in the 

 kinds of species the effects of a pollutant. For example, it has been 

 found that under natural conditions the structure of the diatom community 

 conforms to a truncated normal curve (Figure 3) and that this curve remains 

 fairly constant over time (Table 1). However, if pollution high in 

 nutrients is introduced such as those high in nitrogen, phosphorus, and 

 carbon, certain species will become extremely common and produce a long 

 tail to the curve (Figure 4). Under toxic conditions typically one finds a 

 reduction in numbers of species and the sizes of populations, although in 

 some cases a few species that can withstand or tolerate the toxicant become 

 very common because there is little competition by other species for the 

 nutrients in the system and predator pressure has been greatly reduced 

 (Figure 5). 



By this diatometer method of studying algal communities one cannot only 

 study shifts in the diatom community, but can determine whether or not 

 shifts from diatoms to other species are occurring. 



These diatometers can also be inserted into various reaches of a river 

 to determine the relative degrees of eutrophication of the areas by the 

 total biomass and kinds of species produced on the slides. Thus they are 

 valuable in regional studies of eutrophication. In some instances they 

 have been found extremely useful in determining the presence of small 

 amounts of heavy metals or radioactive materials because some metals are 

 concentrated by the algae to amounts many thousands of times the concentra- 

 tion of the ambient medium. Algae growing on these slides can also be used 

 in determining primary productivity and P/R ratios of algal communities. 

 We have found that these measures are important in determining small or 

 sublethal shifts in the community. Likewise, one can extract pigments 

 from them and determine a shift in pigment concentrations. 



Periphyton are particularly good organisms to study because they have 

 short life cycles and often produce chronic effects due to low amounts of 

 toxicants much more rapidly than many larger macroinvertebrates . Further- 

 more, we know a considerable amount about the kinds of species and what 

 they indicate. For example, the diatoms Nitzschia palea and Gomphonema 



72 



