Jellyfish blooms are important events controlling plankton dynamics in coastal waters worldwide, yet factors that influence bloom development are not well understood. We used the scyphomedusa Chrysaora quinquecirrha as a model to examine physical factors that control jellyfish populations and to develop an ecological forecasting system. Over 700 in situ observations collected from Chesapeake Bay and its tributaries during 1987-2000 were used to develop habitat models that predict the probability of occurrence and the likely concentration of medusae as a function of seasurface temperature and salinity. Medusae were found within a relatively narrow range of temperature (26 to 30°C) and salinity (10 to 16). Regression analyses reveal that a combination of temperature and salinity is a significant predictor of medusa occurrence. Assessments of the predictive performance of these models using medusae and environmental data collected at independent survey sites (n = 354) indicated that model-predicted medusa occurrence and concentration correspond well with observations. Our models can be forced with near-real time and retrospective estimates of temperature and salinity to generate probability of occurrence maps of C. quinquecirrha medusa presence and abundance in order to better understand how this top predator varies in space and time, and how this species could potentially affect energy flow through the Chesapeake Bay system.

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Surveys of larval striped bass Morone saxatilis and zooplankton in thePotomac River upper estuary were made in 1981. In addition to distribution and abundance, nutritional state of larvae was assessed by morphometric, histologic, and two biochemical techniques: RNA: DNA ratio and fatty acid composition and concentration. All four techniques gave evidence of poor nutritional state early in the season but not later. Analyses of distribution indicated a significant correlation among nutritional indices and copepod and cladoceran densities. It has long been held that stock size of fishes is determined largely, if not completely, by events occurring during early life history (Hjort 1914, 1926). One of the more frequently hypothesized causes of mortality among fish larvae is a shortage of appropriate food (Hjort 1914; Hunter 1981; Lasker 1981). Starvation or conditions affected by starvation have been offered as important factors in mortality of striped bass Morone saxatilis larvae (Boynton et al. 1981). Several laboratory studies have been performed on the relationship between survival of striped bass larvae and food density (Daniel 1976; Miller 1977; Eldridge et al. 1981; Eldridge et al. 1982) or delays in feeding (Rogers and Westin 1979, 1981; Martin and Malloy 1980; Eldridge et al. 1981). Some field studies have shown circumstantial evidence that food densities influence survival of striped bass larvae (Kernehan et al. 1981; Setzler-Hamilton et al. 1981). The study we present here is the first to attempt direct measurement of starvation in wild larval striped bass and to correlate it with prey densities. Methods Striped bass typically spawn in the PotomacRiver from about kilometer 100 (measured from the river's mouth at Chesapeake Bay) to kilometer 170 just below Washington, District of Columbia. This spawning reach was divided into eight sampling areas, each approximately one tidal excursion in length (Fig. 1). Sampling oc-1 Contribution of the University of Maryland Center for Environmental and Estuarine Studies. curred at 1-week intervals for 9 weeks, 13 April to 9 June 1981. Within each of the eight areas, weekly sampling stations were established randomly. At each station, bottom, midwater, surface, and oblique ichthyoplankton samples and bottom, midwater, and surface pumped zooplankton samples were taken by procedures described in Setzler-Hamilton et al. (1981). Striped bass larvae from the oblique samples were used for morphometric and histologic analyses. At three randomly determined stations each week,

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