Sentinel Organisms and In Situ Biomonitoring

In many instances, monitoring of an ecosystem has been attempted by the sampling of organisms from a particular environment. Another approach has been the introduction of organisms that can be readily recovered. Upon recovery, these organisms can be measured and subjected to a battery of biochemical, physiological, and histological tests. Lower and Kendall (1990) have published a book of these methods for terrestrial systems. 

Many factors other than pollution can lead to poor reproductive success. Secondary effects, such as the impact of habitat loss on zooplankton populations essential for fry feeding, will be seen in the depression or elimination of the young age classes. 

Mortality is certainly easy to assay on the individual organism however, it is of little use as a monitoring tool. Macroinvertebrates, such as bivalves and cnidaria, can be examined and as they are relatively sessile, the mortality can be attributed to a factor in the immediate environment. Fish, being mobile, can die due to exposure kilometers away or due to multiple intoxications during their migrations. Also, by the time the fish are dying, the other levels of the ecosystem are in a depleted state. 

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