David G. Kimmel

Regional scale climate forcing of mesozooplankton dynamics in Chesapeake bay

A 16-yr (1985–2000) time series of calanoid copepod (Acartia tonsa andEurytemora affinis) abundance in the upper Chesapeake Bay was examined for links to winter weather variability. A synthesis of sea level pressure data revealed ten dominant, winter weather patterns. Weather patterns differed in frequency of occurrence as well as associated precipitation and temperature. The two dominant copepod species responded differently to winter weather variability.A. tonsa abundance showed little response to winter weather and did not vary in abundance during wet or dry springs.E affinis responded strongly to winter weather patterns that produced springs with high freshwater discharge and low salinities. During wet springs,E. affinis abundance increased overall and its area of dominance extended further down estuary. The different response of the two species is likely related to several factors including residence time, development time, salinity tolerance, food limitation, and life history strategy. Important fish species that rely on zo oplankton as food resources were also related to winter weather variability and spring zooplankton abundance.Morone saxatilis (striped bass) andAnchoa mitchilli (bay anchovy) juvenile indices were positively and negatively correlated toE. affinis abundance, respectively. *** DIRECT SUPPORT *** A02BY003 00004

Spatial variability in plankton biomass and hydrographic variables along an axial transect in Chesapeake Bay

[1]xa0High-resolution, axial sampling surveys were conducted in Chesapeake Bay during April, July, and October from 1996 to 2000 using a towed sampling device equipped with sensors for depth, temperature, conductivity, oxygen, fluorescence, and an optical plankton counter (OPC). The results suggest that the axial distribution and variability of hydrographic and biological parameters in Chesapeake Bay were primarily influenced by the source and magnitude of freshwater input. Bay-wide spatial trends in the water column-averaged values of salinity were linear functions of distance from the main source of freshwater, the Susquehanna River, at the head of the bay. However, spatial trends in the water column-averaged values of temperature, dissolved oxygen, chlorophyll-a and zooplankton biomass were nonlinear along the axis of the bay. Autocorrelation analysis and the residuals of linear and quadratic regressions between each variable and latitude were used to quantify the patch sizes for each axial transect. The patch sizes of each variable depended on whether the data were detrended, and the detrending techniques applied. However, the patch size of each variable was generally larger using the original data compared to the detrended data. The patch sizes of salinity were larger than those for dissolved oxygen, chlorophyll-a and zooplankton biomass, suggesting that more localized processes influence the production and consumption of plankton. This high-resolution quantification of the zooplankton spatial variability and patch size can be used for more realistic assessments of the zooplankton forage base for larval fish species.

Chesapeake Bay plankton and fish abundance enhanced by Hurricane Isabel

Hurricane Isabel made landfall east of Cape Lookout, North Carolina, as a Category 2 (Safford-Simpson scale) hurricane on 18 September 2003. The storms center tracked to the northwest, passing west of Chesapeake Bay (Figure 1) in the early morning of 19 September. Hurricane Isabel brought the highest storm surge and winds to the region since the Chesapeake-Potomac hurricane of 1933 and Hurricane Hazel in 1954 (http://www.erh. noaa.gov/er/akq/wx_events/hur/isabel_2003. htm). Storm surge was variable in the region, reaching a high of 2.7 m on the western side of the bay where the heaviest rainfall occurred. The highest sustained wind in the bay region reached 30.8 m s−1 at Gloucester Point,Virginia, with gusts to 40.7 m s−1.

Climate Change: Coastal Dead Zones

Many of the anticipated changes (increased streamflow, warmer temperatures, calmer summer winds, and increased depth due to sea-level rise) associated with global climate change would move the Chesapeake Bay ecosystem in the direction of worsening hypoxia (harmful oxygen depletion).