Prentiss Bay Index of Biotic Integrity 

The Cedarville Biology class recently completed the 9^th year of a marsh study at Prentiss Bay.  This study is an "Index of Biotic Integrity" survey that uses invertebrate numbers to indicate the overall health of the marsh. 

On September 26^th, biology students traveled to Prentiss Bay and put on the waders to collect invertebrate samples by net from the bulrush zones of the marsh.  After samples were collected and counted (we took six samples of 150 invertebrates) they were taken back to the lab for identification and scoring.

This study is conducted in cooperation with Michigan State and Grand Valley State Universities who have completed this study in our area during the summer months.  The study uses the following key invertebrates to assess the health of the marsh:

•1)      Dragonfly larvae 

•2)      snails        

•3)      fingernail clams       

•4)      crustaceans (such as crayfish and freshwater shrimp)

Aquatic invertebrates are used because they are considered "indicators" of overall marsh quality.  In other words, if there is a problem with water quality or habitat loss or destruction, they would be some of the first species to be effected.  So by monitoring these species, we can get a handle on the health of the marsh from year to year.  This year's class did a tremendous job doing the fieldwork and data analysis.  Their results are shown below.

Here are the scores for the past 9 years.

Year    Score

2000      39

2001      38

2002      38

2003      32

2004      40

2005      36

2006      34

2007      34

2008      40

What do the scores mean?

The study places a marsh into one of the four following categories (below) based on the score obtained in the analysis of the invertebrates.  The scores above show some fluctuation, but have remained fairly steady in the upper "mildly impacted" category since the fall of 2000.

8-14 = degraded,        14-28 = moderately degraded,          28-42 = mildly impacted

42-48 = reference conditions (best possible)

The graph shows the results from October of 2000 through 2008.