Benthic Macroinvertebrates

King Philip Came Over For Good Seafood

Kingdom

Phylum

Class

Order

Family

Genus

Species

Benthic Macroinvertebrates (BMI) are spineless bottom dwellers. They include crawfish, may flies, stone flies, snails, clams, and such organisms. The more we find of these organisms the more we learn about the stream itself. The cleaner the water, the more diverse the organisms. The more pollution, the less diverse the organisms and the more tolerant the organisms.

Biotic Index

Biotic Index is what we use to find the diversity, density, and tolerance level of different organisms. We find this by first counting how many organisms of a certain type there are in the designated area. We also needed to count the total number of organisms at the site. We took the number of the certain type then divided it by the total number of the organisms. This gave us the density of the certain organism. The diversity of the site was the number of the different species. We then took the density of the organisms and multiplied them by their tolerance levels. The tolerance levels range from one to ten, ten being the most tolerant organism.

Example of Tolerance Level Chart by Order

Ephemeroptera       2

Plecoptera           1

Tricoptera           3

Coleoptera           4

Odonata             5

Decapoda           6

Chionomidae         7

Isopoda             8

Oligochaeta         9

 Hirudinea           10

In the Huntington Audobon Center on theBrook Trail where the Sherman Hollow Brook and the Huntington River intersect, we took BMI samples and found the Biotic Index of the site. The specimens found are listed below with their tolerance levels and density beside them, by order.

1  Hirudinea (fish leech)  10

7  Coleoptera (water pennies, beetles)  4

19  Prosobrancia (snails)  0

15  Tricoptera  3

6  Plecoptera  1

28  Ephemeroptera  2 

From multiplying the density with the tolerance levels of the organisms we found the order, DT. We then summed all of the DTs we collected and divided them by the diversity (ie. the number of major classes).

          

NAME	TOLERANCE LEVEL	DENSITY	TOLERANCE and DENSITY
Ephemeroptera	2	28	56
Plecoptera	1	6	6
Tricoptera	3	15	45
Coleoptera	4	7	28
Hirudinea	10	1	10
Prosobrancia	0	19	0
TOTAL		76	145

 76 divided by 145 equals:

              Biotic Index for the site is 2.0. This means the site has no impairments.

This told us how clean the stream is. This chart is referred to as the Biotic Index.

       0 - 3.75 is good, no impairment

        3.76 - 6.5 is moderately impaired

          greater than 6.5 is severely impaired

Bug Anatomy

There are three segments to insects. There is the head, the thorax, and the abdomen. Stone flies have two appendages, needle-like things, attatched out from their abdomen. May flies have gills and three or more appendages from their abdomen. They also have split end-like parts on their back legs.

  Habitat Assessment

We examined the site where the brook and river intersected and assigned percentages to groups of objects in the habitat.

Boulders	greater than ten inches	ten percent
Cobbles	two to ten inches	eighty-five percent
Gravel	one tenth to two inches	five percent
Sand	less than one tenth of an inch	zero percent
Silt	fine	zero percent
organic material		zero percent
canopy cover		two percent
bedrock		three percent

                          We also took information from another site on the Brook at a waterfall.

Boulders	greater than ten inches	five percent
Cobbles	two to ten inches	ten percent
Gravel	one tenth to two inches	sixty percent
Sand	less than one tenth of an inch	twenty percent
Silt	fine	one percent
organic material		two percent
canopy cover		ninety-five percent
bedrock		two percent

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