Copepod habitat suitability estimates vary among oxygen metrics in Chesapeake Bay

Seasonal deoxygenation in coastal and estuarine systems leads to decreased available habitat for many planktonic organisms. However, the volume of available habitat can be defined in different ways, depending on the oxygen metrics employed. Here, we used monitoring data for water quality to estimate the seasonal and inter-annual variability in habitat for the copepod Acartia tonsa in Chesapeake Bay, defined using three different oxygen metrics: a concentration-based (2 mg l-1) definition of hypoxia, and two partial pressure-based definitions corresponding to limiting oxygen demand (Pcrit), and the minimum requirement for respiration (Pleth). We examined spatial and temporal trends in the oxygen habitat, and compared habitat estimates to zooplankton abundance and distribution and in relation to hydrologically wet, average, and dry years. Pcrit predicted the largest volume of unsuitable deoxygenated habitat over space and time, and dry conditions were associated with a decreased extent of deoxygenated habitat compared to average and wet conditions. No clear relationship between copepod abundance and habitat availability was observed, but the position of peak abundance of A. tonsa correlated to the extent of deoxygenated habitat using Pcrit. Species-specific metrics to describe oxygen habitat may be more useful in understanding the non-lethal impacts of deoxygenation.