Seasonal and annual variability in the spatial patterns of plankton biomass in Chesapeake Bay

Abstract

We conducted high-resolution, underway sampling in April, July, and October for 6 yr (1995)(1996)(1997)(1998)(1999)(2000) in the large estuary, Chesapeake Bay. This period included climatological extremes in freshwater inputs that strongly influenced both the overall stocks and spatial distribution of phytoplankton and zooplankton. Higher biomass of both phytoplankton and zooplankton occurred in springs, when freshwater input into Chesapeake Bay was above the average discharge. While whole-Bay productivity appears to be influenced by freshwater flow variability, mesoscale patterns in plankton biomass are driven by freshwater inputs, circulation, and bathymetry. Persistent maxima in plankton biomass occurred in areas of physical and topographic discontinuities such as the upper-Bay salt front, plume fronts, the hydraulic control region, tidal fronts, and near a topographically induced eddy. Although the contribution of these hot spots to the whole-Bay standing stock of plankton may vary due to changes in the background levels of plankton, controlled in part by freshwater discharge, they nevertheless represent predictable areas of higher forage for planktivorous fish. Enhanced trophic coupling between plankton and fish at these physical discontinuities may be one reason why estuaries have higher fisheries yields in relation to their primary production than lakes and other marine systems.

Laser Optical Plankton Counter and Zooscan intercomparison in tropical and subtropical marine ecosystems

“…Yet, it needs to be calibrated for the presence of fragile particles. In combination with conventional zooplankton net tows, the predecessor OPC was successfully applied to investigate zooplankton biomass distribution and size composition in a variety of coastal and oceanic ecosystems such as the Chesapeake Bay (Roman et al 2005;Zhang et al 2006), California current Laser Optical Plankton Counter and Zooscan intercomparison in tropical and subtropical marine ecosystems (Huntley et al 1995), Southern Ocean (Pollard et al 2002), and along latitudinal transects across the Atlantic (WooddWalker et al 2001). Developed as recently as the LOPC, the Zooscan allows rapid estimation of biomass, size distribution and taxonomic classification of the zooplankton community (Grosjean et al 2004).…”

Spatial and temporal variability in factors affecting mesozooplankton dynamics in Chesapeake Bay: Evidence from biomass size spectra

“…The aim of this study was to identify possible factors affecting the Chesapeake Bay normalized zooplankton biomass size spectrum and compare the size spectrum to spectra of other systems. Seasonal, interannual, and spatial fluctuations in zooplankton biomass have been demonstrated (Roman et al 2005); thus, we hypothesize that the normalized zooplankton biomass size spectrum in Chesapeake Bay is highly variable. We also hypothesize that temporally and spatially variable external forcing factors, such as phytoplankton biomass, gelatinous zooplankton biovolume, and fish biomass, will influence the shape of the size spectrum through bottom-up and top-down controls.…”

“…The regression coefficients and coefficient of determination were calculated for interannual comparisons. Zooplankton : phytoplankton biomass ratio estimates were calculated from data taken from Roman et al (2005), and fish : zooplankton biomass ratio estimates were calculated from data taken from Jung and Houde (2003). We converted fish wet weight into carbon assuming 10% of fish wet weight consisted of carbon (Nixon et al 1986).…”

Internal hydraulic control in the Little Belt, Denmark – observations of flow configurations and water mass formation

“…There may well be a great number of estuarine areas elsewhere in the world the functioning of which cannot be understood properly in the light of other prevailing physical processes, e.g. wind mixing, and where hydraulic control could play a decisive role (Roman et al, 2005). Again, knowing the relation between stratification and flow at the critical point, i.e.…”

“…On a regional scale, internal hydraulic control has also attracted attention, for example in connection with estuarine circulation and bottom water renewal in semi-enclosed shelf seas and biological and environmental effects thereof (e.g. Nielsen, 2001;Roman et al, 2005;Hietala et al, 2007;Gregg and Pratt, 2010).…”