Growth and mortality rates are key components to understanding population health. Changes in growth or mortality of estuarine species, including eastern oysters (Crassostrea virginica), can indicate alterations in water conditions or habitat suitability. Comparing rates of growth and mortality over various timeframes can be used to track the natural cycle of estuaries and to identify when conditions may be negatively impacting oyster populations.
In south Florida, oyster growth and mortality rates have been monitored as part of the Comprehensive Everglades Restoration Plan (CERP). Beginning in 2015 (St. Lucie estuary and Loxahatchee River estuary) or 2018 (Caloosahatchee River estuary), wild oysters were planted in open cages at representative reefs. Metrics included monthly measurements of shell heights and live and dead counts. From that data, the average oyster size, mortality, and mean growth rate was determined for each estuary.
Shifts in oyster health can be assessed through the degree and direction of fluctuations in mean oyster size, growth rates, or mortality of oysters. Assessing growth rates and mortality rates may help to evaluate the relative effect of water conditions versus predators or disturbance events. Evaluating how fluctuations in size, growth, and mortality align with changes in water conditions, such as salinity and temperature, or predator populations can be used to understand changes in estuary conditions and to provide guidance for future restoration of oyster habitat. The metrics of oyster growth and mortality will serve as baseline conditions used to evaluate system-wide change in hydrology as the full Everglades Restoration Plan is implemented.