EcoCheck banner

Browse History: Phytoplankton Index of Biotic Integrity (2010)
Indicator Icon Phytoplankton Index of Biotic Integrity

Phytoplankton (microalgae) is an important component of the Bay's food web. The Phytoplankton Index of Biotic Integrity (PIBI) is a measure of the microscopic algal community condition.

Chesapeake Bay - Indicator Details:

  Indicator Selection Diagram

Threshold Map

This map illustrates the overall Phytoplankton Index of Biotic Integrity (Phytoplankton IBI) scores for each of the 15 reporting regions. The Mid Bay region had the highest (best) phytoplankton community score in 2010, and increased from moderate in 2009 to moderately good this year. The Lower Bay continues to have moderate phytoplankton community condition. Seven regions of the Bay (the Upper Eastern Shore, Choptank, Elizabeth, York, Potomac, Lower Western Shore (MD), and Patapsco and Back Rivers) had very poor scores in 2010. No phytoplankton monitoring is conducted in the Lower Eastern Shore or Upper Western Shore regions.

Creating this map
The frequency that the Phytoplankton IBI scores exceeded the threshold level of 3, during the spring-summer sampling periods, was determined. In 2010, samples were collected approximately six times at each station. The overall reporting region scores were calculated by accounting for the surface area of the region represented by each sampling station.

Data Map

This map shows the average spring-summer Phytoplankton Index of Biotic Integrity (Phytoplankton IBI) score for 2010. In 2010, all sampling stations except one within the Bay's tributaries had average Phytoplankton IBI scores between 1 and 2.9 out of a possible 5, indicating that the phytoplankton communities were in degraded conditions relative to reference communities. In contrast, most monitoring stations within the Bay's mainstem had moderately good phytoplankton communities (scoring between 3-4). Some regions improved (Mid Bay, Patuxent River, Rappahannock River), and others declined (Potomac River, Patapsco and Back Rivers, Choptank River).

Understanding this map
In 2010, phytoplankton samples were collected at 31 stations during the spring (March-May) and summer (July-September). Samples were collected approximately six times at each station. Data from each sampling event were used to calculate a Phytoplankton IBI score. Phytoplankton IBI scores for each sampling station were then averaged and mapped.


Comparison of Bay Health Index scores for 2010 () compared to

Score Legend
 Score (%)
 0               20               40               60               80              100
Mid Bay  
Lower Bay  
Overall Bay  
Rappahannock River  
Patuxent River  
Upper Bay  
James River  
Upper Eastern Shore  
Choptank River  
Lower Western Shore (MD)  
York River  
Potomac River  
Elizabeth River  
Patapsco and Back Rivers  
Lower Eastern Shore (Tangier)  
 Insufficient data
Upper Western Shore  
 Insufficient data

This figure ranks each region from best to worst for the Phytoplankton Index of Biotic Integrity (Phytoplankton IBI). The Mid Bay region has had the highest Phytoplankton IBI score for six years in a row and increased the margin to 32% in 2010. The next highest-ranked regions were the Lower Bay and Rappahannock River. Interestingly, the overall Bay score is high because the Mid Bay and Lower Bay scores are so good and these regions represent a large area of the Bay. Regions with the lowest Phytoplankton IBI scores were the Elizabeth (which scored a zero), the Patapsco and Back Rivers, and Potomac River. The Potomac River score declined sharply in 2010. No phytoplankton monitoring is conducted in the Lower Eastern Shore and Upper Western Shore regions.

Excel Spreadsheet