Molluscan Faunal Distribution in Florida Bay, past and present: An integration of down-core and modern data

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Introduction and Methods | Modern Field Data | Core Data | Water Quality and Salinity | Vegetation | Diversity and Abundance | Conclusion and Future Directions

Water Quality and Salinity

Brachidontes exustus Anomalocardia auberiana Low salinity sps (<12 ppt)

Percent abundance of 2 indicator species, Brachidontes and Anomalocardia, in four cores.[larger image]

Russell: Anomalocardia auberiana, present in low percentages prior to 1920, disappears after that time. Anomalocardia is typical of the Northern Transition Zone. Its disappearance at Russell may indicate less influx from the North.

Bob Allen: Between 1920 and 1930 Brachidontes exustus assemblage becomes dominant, indicating reduced water quality and/or increased fluctuation in salinity.

Whipray: Percent abundance of Anomalocardia auberiana and Brachidontes exustus remains relatively constant prior to 1960’s in Whipray Basin.

Taylor: Since ~1900, a steady decline in fresh water and mesohaline (<12 ppt) molluscs has occurred. Anomalocardia auberiana, has remained relatively constant. Although Taylor cannot be directly compared to the rainfall records, the decline in mesohaline species does not appear to correspond to rainfall.

• Onset of changes in eastern central Florida Bay around 1920 indicates a shift toward less stable conditions at a time when average monthly rainfall does not fluctuate significantly.
• Striking changes in upper portion of all 3 cores do correspond to a period of significant fluctuation in rainfall. These data suggest that significant changes in Florida Bay in the last few decades may be due in part to natural causes.
• Data indicate significant changes in salinity in the Northern Transition Zone during the 20th century, and the changes do not appear to be related to rainfall.
• Increased dominance of Brachidontes in all cores beginning around 1960 indicates decreased water quality and/or increased fluctuations in salinity, i.e. a less stable system.

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Related information:

SOFIA Project: Ecosystem History: Florida Bay and the Southwest Coast

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