DOI: 10.5066/p13jybae
title: Molluscan Assemblages and Salinity Regimes from Three Southwest Coast Cores in Everglades National Park, Florida

description: Paleoecologic analyses of cores from the estuarine areas of Everglades National Park (ENP) by the U.S. Geological Survey began in the mid-1990s. Results of these analyses have contributed to an understanding of changes in salinity regimes, freshwater flow, and habitats of the Greater Everglades Ecosystem over the last several thousand years. Twentieth century changes to salinity and freshwater flow into the estuaries are of particular interest for resource managers responsible for setting flow and salinity targets for restoration of the Greater Everglades Ecosystem. In addition, understanding species distributions prior to twentieth-century canal construction can help identify indicator taxa to track restoration progress. In 2004, the three cores included here were collected from inner bays of the southwest coast of ENP: Big Lostmans Bay (GLW504 LM-A), Broad River Bay (GLW504 BR-A), and Tarpon Bay (GLW504 TB-A). Sediment descriptions, x-radiographs, and molluscan presence absence data were published in 2005 (USGS OFR 2005-1360 - https://pubs.usgs.gov/publication/ofr20051360). The original objective was to obtain a relatively complete record of sea level changes, flow regimes, and coastal storm events. However, analysis of age data from the cores in 2012 (USGS OFR 2012-1275 - https://pubs.usgs.gov/publication/ofr20121275) revealed significant gaps in the record and as a result the cores were designated lower priority for continued analysis. Recently, there has been renewed interest in refining estimates of flow through the Shark River Slough and the southwest coastal area of ENP and resource managers have been developing lists of indicator taxa. Despite the depositional gaps, these cores shed light on salinity regimes, and by extension freshwater flow, and provide information on molluscan faunal assemblages found in the region. Here we have re-examined the three cores using our modern analog data set with current taxonomy (https://doi.org/10.5066/P1MSMSNT) to provide counts and percent abundance data for molluscan assemblages and occurrence data for non-molluscan taxa. Only the upper 26 cm portion of the Tarpon Bay core (TB-A) contains any calcareous remains and several lines of evidence indicate deposition in the 20th century: pollen and lead-210 data (https://pubs.usgs.gov/publication/ofr20121275) and presence of an invasive gastropod (Melanoides tuberculatus, introduced into south Florida ~1971; Wingard et al. 2008; https://pubs.usgs.gov/fs/2008/3006/pdf/fs2008-3006.pdf). The presence of significant numbers of fish remains in the 18-32 cm segment of the TB-A core is an indication of a possible storm deposit, and the hiatus between the surface of the peat at ~30 cm and the overlying muds at 20 cm may have been the result of erosion from a storm surge. The Broad River Core (BR-A) contains a long record of ecosystem change. The lower portion of BR-A from 112-130 cm represents deposition in a freshwater marl prairie, indicating an age of 2000 to 5000 ybp based on regional records, although the preliminary age model (https://pubs.usgs.gov/publication/ofr20121275) did not include this portion of the core. The interval from 4-112 cm of BR-A is a peat with no calcareous remains. The upper 4 cm of BR-A do not contain any age indicators, but most likely represent very recent deposition. The lower portion of Big Lostmans Bay (LM-A) from 10-58 cm is a peat with only a few scattered calcareous remains. Preliminary age information (https://pubs.usgs.gov/publication/ofr20121275) indicates the peat was deposited more than a thousand years ago, with a conventional radiocarbon age of 1230 ybp at 20 cm. The 0-8 cm portion of the core was deposited post-1971 based on the presence of Melanoides tuberculatus. The molluscan fauna present in all three cores demonstrate the strong influence of freshwater flow on the southwest coastal region of ENP in the 20th century.