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:
The frequency that the Phytoplankton IBI scores exceeded the threshold level of 3 was determined during the spring-summer sampling periods. In 2011, samples were collected up to 6 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.
This map shows the average spring-summer Phytoplankton Index of Biotic Integrity (Phytoplankton IBI) score for 2011. In 2011, all sampling stations except two (~90% of stations) 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, ~55% of monitoring stations within the Bay's mainstem had moderately good phytoplankton communities (scoring between 3-4). Some regions improved (Upper and Lower Bay, Patapsco and Back Rivers and the Lower Western Shore (MD), and others declined (Mid Bay, Patuxent, Choptank and James Rivers).
In 2011, phytoplankton samples were collected at 31 stations during the spring (March-May) and summer (July-September). Samples were collected up to 6 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 2011 () compared to ()
|0 20 40 60 80 100|
|Patapsco and Back Rivers|
|Lower Western Shore (MD)|
|Upper Eastern Shore|
|Lower Eastern Shore (Tangier)|
|Upper Western Shore|
This figure ranks each region from best to worst for the Phytoplankton Index of Biotic Integrity (Phytoplankton IBI). The Lower Bay overtook the Mid Bay as the highest scored Phytoplankton IBI region. The Mid Bay had the highest Phytoplankton IBI score for six years in a row but decreased by 33% in 2011, though it still remains the second best score. The next highest-ranked region was the Rappahannock River. The overall Bay score is moderate because the Mid Bay and Lower Bay scores are 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), Potomac, Choptank, and Patuxent Rivers. No phytoplankton monitoring is conducted in the Lower Eastern Shore (Tangier) and Upper Western Shore regions.
This graph is dynamic, you can: a) show and hide items by clicking them in the legend, b) select year range (click and drag), and c) export as an image.