Geology topics

Pam Schofield

Publications and source records attributed to Pam Schofield.

4 recordsLinked to original sources

USGS2022

Risk assessment of chanchita Cichlasoma dimerus (Heckel, 1840), a newly identified non-native cichlid fish in Florida

The risk of a newly discovered non-native fish species in Florida (USA): Cichlasoma dimerus ([Heckel, 1840]; Family: Cichlidae) is assessed. Its tolerance to cold temperatures was experimentally evaluated and information on its biology and ecology was synthesized. In the cold-temperature tolerance experiment, temperature was lowered from 24 °C by increments of 1 °C per hour, mimicking a typical cold weather front. Fish lost equilibrium at a mean temperature of 7.8 °C and died at 4.7 °C. Those values are lower than most other non-native fishes from the state that have been experimentally evaluated, and it appears C. dimerus is the most cold-tolerant cichlid established in Florida. The combination of cold-temperature tolerance and other biological/ecological factors (e.g., adult size, reproduction and parental care, diet, habitat, and other behaviors) along with the geographic range and habitat diversity of specimens vouchered in museums, indicate C. dimerus may be able to invade many freshwater ecosystems in the state, including environmentally sensitive freshwater springs.

Florida↗

USGS2021

Non-native Asian swamp eel, Monopterus albus/javanensis (Zuiew, 1973/Lacepede, 1800), responses to low temperatures

Asian swamp eel, Monopterus albus/javanensis [Zuiew, 1973/Lacepede 1800], has been established in the southeastern USA since at least 1994, yet little is known about its ability to survive low winter temperatures. We use standard thermal methodologies to quantify low temperature responses and provide a detailed description of swamp eel reactions to cold temperatures. When exposed to chronic temperature decreases of 1.0 °C day −1 , swamp eel ceased foraging at 15.0 °C, markedly diminished movements below 11.0 °C, and became incapacitated near 9.6 °C. During critical thermal minima trials, swamp eel exposed to acute temperature drops (0.25 °C min −1 ) tolerated temperatures as low as 6.2 °C. Swamp eel exhibited a moderate cold acclimation response, gaining 0.23 °C in cold tolerance for every 1 °C drop in acclimation temperature. Progressive time-series critical thermal minimum temperatures (CTmin) estimates for eel acclimated to 20.5 °C followed by an acute temperature decrease to 16.0 °C, revealed that cold acclimation may occur in only 8 days. Fringe populations of swamp eel in their native range periodically experience colder winter temperatures, which may explain the ability of introduced populations to survive winter cold fronts in Florida. Understanding Asian swamp eel acute and chronic thermal limits may be useful in assessing dispersal risk and range expansion in the southeastern USA.

Fish Physiology and Biochemistry↗

USGS2021

Invasion frustration: Can biotic resistance explain the small geographic range of non-native croaking gourami Trichopsis vittata (Cuvier, 1831) in Florida, USA?

Croaking gourami Trichopsis vittata is a non-native fish species that has maintained a reproducing population in Florida, USA, since at least the 1970s. However, unlike most other non-native fishes in Florida, T. vittata has not spread beyond its very small (ca. 5 km²) range. We suspected the inability of T. vittata to colonize new habitats may be due to biotic resistance by the native eastern mosquitofish Gambusia holbrooki. In laboratory experiments, we show that G. holbrooki causes physical damage to T. vittata and that T. vittata’s growth is reduced in the presence of G. holbrooki. While the effects of G. holbrooki on T. vittata were sub-lethal, they were severe enough to hamper its growth and could affect recruitment in the wild. These results support the hypothesis that small non-native fishes may be excluded from establishment or may only establish small ranges due to pressure from G. holbrooki. Biotic resistance may reduce invasion success and thus consideration of species interactions is useful for natural resource managers trying to evaluate the potential risk of new invaders.

Florida↗

USGS2019

Environmental DNA (eDNA) detection of nonnative bullseye snakehead in southern Florida

Bullseye Snakehead Channa marulius (Hamilton 1822) was first detected in the southern Florida town of Tamarac in 2000 and has been expanding its geographic range since. Environmental DNA (eDNA) analysis is a newly-developed technique used to noninvasively detect cryptic or low-density species or those that are logistically difficult-to-study. Genetic material shed into the environment through tissue and body fluids is concentrated from water samples and analyzed for the presence of target species eDNA. To help delineate Bullseye Snakehead’s geographic range, we developed and validated a species-specific eDNA assay for both quantitative and droplet digital PCR (ddPCR). We then used ddPCR to assess 16 locations in southeast Florida using 222 water samples collected from 2015 to 2018. Positive eDNA detections were obtained at all six locations that were within the known geographic range of Bullseye Snakehead. Furthermore, eDNA was detected in six of 10 locations that were previously thought to be outside the periphery of the range but hydrologically connected through the extensive canal system. Over the four years of sampling, estimated occurrence rates (ψ) remained stable and relatively high (ψ = 0.67 [95% credible interval (CI) 0.33–0.95]) near Tamarac, Florida, as compared to the most southern sampling locations (ψ = 0.0–0.37). Bulls- eye Snakehead eDNA estimated occurrence rates in the middle region increased between 2016 (0.28 [95% CI 0.03–0.94]) and 2017 (0.66 [95% CI 0.24–0.98]), potentially reflecting eDNA detections related to a growing or expanding population. Bullseye Snakehead eDNA was detected at low concentrations on the northern and eastern borders of Everglades National Park, which is an important conservation area and UNESCO World Heritage Site. Despite extensive sampling via electrofishing, no Bullseye Snakehead were visually detected in several locations that yielded positive eDNA samples. It is unclear whether eDNA was transported through flowing water or another vector. To date, collection records for this species are confined to urban canals; however, Bullseye Snakehead may use the interconnected system of canals to disperse to natural conservation areas such as Everglades National Park, Big Cypress National Preserve, and Water Conservation Areas, where it may impact native species via predation and competition.

Florida↗