Temporal and spatial patterns of zooplankton in the Chesapeake Bay turbidity maximum

Abstract

We measured the distribution of hydrographic parameters, currents, phytoplankton fluorescence, suspended sediments and zooplankton in axial transects through the Chesapeake Bay estuarine turbidity maximum (ETM) seasonally (May, July and October 1996) and over tidal cycles within seasons. Zooplankton abundance was estimated with a 6-frequency, Tracor Acoustical Profiling System (TAPS-6) at the same vertical (0.25 to 0.50 m) and horizontal (0.5 to 1.5 km) resolution as hydrographic parameters and suspended sediments. The general pattern exhibited in axial transects through the Chesapeake Bay ETM is that sediments, fluorescence and zooplankton are in higher concentrations up-Bay of the salt wedge (defined as the intersection of the 1 isohaline with the bottom). The salinity front appears to trap these particles in the upper portion of Chesapeake Bay. The highest acoustically determined zooplankton biomass generally occurred near the bottom, at the toe of the salt wedge. The convergence zone associated with this feature concentrates sediments and zooplankton (primarily the copepod Eurytemora affinis). Advection appeared to dominate changes in zooplankton abundance during time series studies at a fixed station in the ETM. Zooplankton biomass at the fixed ETM station increased/decreased with the tidal excursion of the salt wedge. Water column zooplankton concentrations and the vertical distribution of zooplankton biomass appeared to be influenced by currents. We often found that during maximum ebb and flood tidal currents, zooplankton biomass and sediments in the mid and upper water column increased. Thus the hydrodynamic processes that resuspend, advect and trap suspended sediments in the ETM likely have the same effects on zooplankton. The ETM of the Chesapeake Bay appears to act as an entrapment zone for zooplankton. The lack of diel vertical migration, carrying eggs until they are ready to hatch, possible reduced predation by visual predators in the turbid waters, and the ability to consume phytoplankton, protozoa and detritus all may allow Eurytemora to persist at high concentrations in the Chesapeake Bay ETM. KEY WORDS: Zooplankton · Estuarine turbidity maximum zone · Chesapeake Bay Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 213: [215][216][217][218][219][220][221][222][223][224][225][226][227] 2001 to 30 km along the N/S axis of the bay (Fig. 1). The location of the ETM varies seasonally and at shorter time scales due to variations in freshwater input and wind-forcing. The ETM region of the Chesapeake Bay has a mean volume of approximately 2.63 km 3 and a mean depth of 4 m. Almost all of the freshwater input to the ETM region comes from the Susquehanna River. At the average Susquehanna River flow of 1100 m 3 s -1 , the freshwater replacement time of the ETM region is approximately 1 mo. Suspended sediment concentrations in the ETM are generally 40 to 80 mg l -1 higher than concentrations upstream or downstream of the ETM, with the largest concen...

Ichthyoplankton dynamics in the Guadiana estuary and adjacent coastal area, South-East Portugal

“…Although the position of ETM varies seasonally and at short time scales due to variations in freshwater input and wind forcing (North and Houde, 2001), this indicates that the ETM was displaced upstream likely due to the reduced flow imposed during filling of the Alqueva reservoir. ETM has been identified as an important nursery area in several estuaries, such as the St. Lawrence (Winkler et al, 2003) and Chesapeake Bay (North and Houde, 2003), either by providing protection from predators (Cyrus and Blaber, 1987) or due to high productivity levels (Roman et al, 2001). However, in this study, ichthyoplankton diversity and abundance was low in the ETM.…”

Environmental cues and constraints affecting the seasonality of dominant calanoid copepods in brackish, coastal waters: a case study of Acartia, Temora and Eurytemora species in the south-west Baltic

“…Work on E. affinis at different sites suggests the production of eggs that did not rapidly hatch were related to short day lengths, cold temperatures and high copepod population densities (Ban 1992;Flinkman et al 1994;Katajisto 1996;Andersen and Nielsen 1997;Katajisto et al 1998;Roman et al 2001). For example, Ban (1992) collected nauplii of E. affinis in lake Ohnuma, Japan, during late autumn (November) and reared them in the laboratory under spring conditions (15°C, 12 h).…”

Zooplankton retention in the estuarine transition zone of the St. Lawrence Estuary

“…High concentrations of zooplankton biomass and suspended sediment are observed in the ETZ (Kimmerer et al 1998;Roman et al 2001), which is also called the estuarine turbidity maximum. With a constant river flow, the depthaveraged residual or mean current in the ETZ is downstream and seaward (Kimmerer et al 1998).…”