The habitat of a species is defined by multiple physical and biotic parameters. Though salinity and temperature are known to be important physical factors influencing the presence of sea nettles, a quantitative relationship between these variables has not been previously formulated for the entire Chesapeake Bay. Scientists developed a Bay-wide model to predict the probability of encountering sea nettles and their density in surface waters of the Chesapeake Bay by analyzing coincident data of nettle density, salinity, and sea-surface temperature collected during the spring, summer, and fall of 1987-2000 in surface waters of the Bay and selected tributaries.

Concentrations of Chrysaora were found within a relatively narrow, well-defined range of temperature and salinity (26-30° C and 10-16 PSU, Figure 1). 

The in-situ data were used to derive an empirical model that estimates the likelihood of sea nettle encounter, pnettles, as a function of salinity and temperature (Figure 2):

pnettles = elogit / [elogit + 1],

where logit = -6.995 + (0.30 * temperature) - (0.469 *salinityopt).

Temperature is in degrees celsius and salinityopt is the difference between ambient salinity and optimal salinity for nettles (= 13.5 psu) as determined from in-situ observations.

A graphical representation of this model is presented in Figure 2.

Figure 2. Graphical representation of the model describing
the likelihood of encountering sea nettles in surface waters of the Chesapeake Bay.

For details of the development and validation of the sea nettle habitat model used, please read Decker, et al.