Long-Term Shifts in Faunal Composition of Freshwater Mollusks in Spring-Fed Rivers of Florida

Abstract

Florida’s freshwater spring and river ecosystems have been deteriorating due to direct and indirect human impacts. However, while the conservation and restoration strategies employed to mitigate these effects often rely on faunal surveys that go back several decades, the local ecosystem shifts tend to have much deeper roots that predate those faunal surveys by centuries or millennia. Conservation paleobiology, an approach which enhances our understanding of the past states of ecosystems, allows for comparison of modern faunal communities with those prior to significant human impacts. This study examines the historical record of freshwater mollusk assemblages from two spring-fed river systems, the Wakulla and Silver/Ocklawaha Rivers. Specifically, we compared fossil assemblages (latest Pleistocene - early Holocene) and live mollusk assemblages in the two targeted river systems. Bulk sampling of the fossil record (20 sites; 70 samples; 16,314 specimens) documented relatively diverse mollusk assemblages that consist of a suite of native freshwater species that is similar across the studied systems. In contrast, sampling of live communities (24 sites; 138 samples; 7,572 specimens) revealed depauperate species assemblies characterized by the absence of multiple native freshwater species commonly found in fossil samples, the widespread presence of introduced species, and dominance of brackish-tolerant species at the lower Wakulla River sites. Unlike fossil mollusk assemblages, live mollusk assemblages differ notably between the two river systems due to differences in relative abundance of introduced species (Melanoides tuberculata and Corbicula fluminea) and the presence of brackish-tolerant mollusks in the coastally influenced Wakulla River. The diverse, exclusively freshwater mollusk associations comparable across multiple river systems documented in the fossil record provide a historical perspective on the past state of freshwater river ecosystems complementing data provided by modern surveys. The conservation paleobiology approach used in this study reinforces the importance of considering the historical ecology of an ecosystem and the utility of the fossil record in providing a historical perspective on long-term faunal changes.

Conservation biology and conservation paleobiology meet the Anthropocene together: history matters

“…For example, micropaleontologists have used plant pollen to document the fossil and modern history of environmental change (Von Post, 1916;1924;Janssen, 1967;Brewster-Wingard and Ishman, 1999;Owens, 2020), while others have used singled-celled protists, such as diatoms and foraminifera, and tiny animals such as ostracodes, to reconstruct past aquatic environments, document pollution, and chart the history of sea level and climate change (e.g., Ehrenberg, 1829;Cleve, 1894;Patrick, 1957;Alve, 1991;Culver and Buzas, 1995;Hallock, 2000;Karlsen et al, 2000;Martin, 2000;Zachos et al, 2001;Cronin et al, 2003;Smol, 2009;Smol and Stoermer, 2010). Freshwater mollusks are also used to examine the history and effects of pollution in rivers and lakes starting in the 1800s (Ortman, 1909;Baker, 1922;van der Schalie, 1936;Ingram, 1957) and continues to this day (Dettman and Lohmann, 1993;Goewert et al, 2007;Lundquist et al, 2019;Kusnerik et al, 2022). The first application of stable isotopes (δ 18 O) for obtaining paleotemperature and climatic records was tested with marine mollusks (Urey et al, 1951;Epstein and Lowenstam, 1953;Valentine and Meade, 1960;Krantz et al, 1987) and as the ability to sample smaller organisms improved, deep-sea foraminifera have given us the best record of Cenozoic climate change (Zachos et al, 2001).…”

Marine conservation palaeobiology: What does the late Quaternary fossil record tell us about modern-day extinctions and biodiversity threats?

“…Over the last several decades, geohistorical approaches have been applied to study human impacts on terrestrial (e.g., Gorham et al, 2001;Behrensmeyer and Miller, 2012;Wood et al, 2012;Lyons et al, 2016;Barnosky et al, 2017;Jackson et al, 2017;Koch et al, 2017;Terry, 2018;Smith et al, 2022), freshwater (e.g., Brown et al, 2005;Smol, 2008;Erthal et al, 2011;Kusnerik et al, 2022;Czaja et al, 2023) and marine (e.g., Kowalewski et al, 2000Kowalewski et al, , 2015Jackson et al, 2001;Kidwell, 2007;Aronson, 2009;Tomašových and Kidwell, 2017;Hyman et al, 2019; Comparison of four major invertebrate phyla (arthropods, cnidarians, echinoderms and molluscs) across marine, brackish, freshwater, and terrestrial systems as recorded in the IUCN Red List Database (IUCN, 2023a). (a) The total number of species reported in the database for each of the four systems (numbers indicate the total number of species).…”