APPLYING TAPHONOMIC APPROACHES TO LOW-IMPACT MONITORING OF INVASIVE SPECIES IN FLORIDA’S FRESHWATER SPRINGS AND RIVERS

Invasive species are a pervasive problem in many ecosystems, as they often outcompete or prey on native taxa, drive habitat changes, and exert other negative impacts on local biota. In Florida’s freshwater springs and rivers, the harmful effects of invasive species, coupled with climatic and anthropogenic stresses, are driving changes in biotic communities at the expense of native species. Assessing the presence, spread, and abundance of invasive species is critical to mitigating their effects. However, as invasive species often become interwoven into an ecosystem, monitoring and bioinventorying often negatively affect modern communities through ‘high-impact’ collection methods. For molluscan communities, this includes destructive harvesting or collection of live specimens of both native and invasive species. Analysis of the death assemblage, the loose collection of shells accumulating along the river bottom, could provide a ‘low-impact’ method of monitoring molluscan communities using already dead specimens.

This project explores taphonomic patterns within live (living mollusk), dead (surficial shell accumulation) and fossil (late Pleistocene to early Holocene, river-bank sediments) molluscan assemblages from Florida’s Wakulla, Silver, and Ocklawaha Rivers. Taphonomic scoring of seven traits were conducted on 2309 specimens of two gastropod species, the native Elimia floridensa (n=2184) and the invasive Melanoides tuberculata (n=124), selected for their similar sizes and ecological roles. Scores were standardized and aggregated to build a total taphonomic grade (TTG) for each specimen. In live assemblages, both species had similar average TTGs of about -7.3, as little alteration occurs on living organisms. Fossil E. floridensa show a more degraded average TTG of 2.18. Being a recent invasive species, M. tuberculata was absent in fossil assemblages. In death assemblages, the two species show statistically distinct average TTGs (M. tuberculata = -2.2, E. floridensa = 1.4), with the recent invasive species notably less altered than the native taxon. Application of discriminant analysis using fossil and live assemblage TTGs can parse the death assemblage into its recent and reintroduced fossil components. Once fossil components can be separated, the remaining death assemblage may provide a ‘low-impact’ estimate of the molluscan community affected by invasive species.