Algae, or phytoplankton, are especially sensitive to changes in pollution levels, water clarity, temperature and salinity, and therefore serve as an excellent indicator of the health of the Bay’s surface waters.
While algae also make up the base of the food web in the Bay ecosystem, too much or the wrong type of algae can be detrimental to the overall health of the Bay by:
- Decreasing oxygen
- Blocking sunlight
- Harming aquatic life
In some cases, algae blooms can negatively impact human health as well.
A measurement called the Index of Biotic Integrity is used to rate the health of phytoplankton on a scale of 1 to 5. Scores are generated using monthly samples taken from 31 stations during the spring and summer. The goal is for all scores to be at least a 3.
*Note: The historic data featured in this indicator changed from that reported in the 2007 assessment due to the inclusion of additional data from Virginia.
Long-term trend (1986-2008)
Bay-wide, the score increased from 46.1 percent to 52.9 percent of goal achieved. The James and Rappahannock rivers saw improvements (increasing long-term trends), while conditions declined in the Choptank, Patuxent and Potomac rivers (decreasing long-term trends).
Short-term trend (10-year trend)
Between 1999 and 2008, the score Bay-wide decreased from 60.7 percent to 52.9 percent of goal achieved. There is no discernable trend because of too many extreme wet and extreme dry years.
Change from previous year (2007-2008)
The score Bay-wide decreased from 56.4 percent to 52.9 percent of goal achieved.
Overall Status of Phytoplankton
Water column clarity is currently too poor and nutrient levels too high to support healthy phytoplankton communities in the Bay. The overall status of the phytoplankton community is:
- Fair-poor in low-salinity waters
- Fair in high salinity waters
- Highly variable at many bay stations
An earlier downward trend in phytoplankton status in low-salinity waters has leveled off.
Phytoplankton Indicator
This indicator is area-weighted and thus heavily influenced by conditions in the larger mesohaline (moderately salty) and polyhaline (salty) segments, which tend to be better than those in low-salinity segments of the tidal tributaries and upper Bay.
For more information contact:
Jacqueline Johnson at 800-968-7229 ext. 729
Chesapeake Bay Program Office