Craig Williamson
Global Change Limnology Laboratory

Former Lab Members

Post Docs Graduate Students Undergraduate Students

Research Scientists

Robert Moeller
Robert Moeller, a research scientist with the Williamson Laboratory for over 20 years, was interested in the effects of UV on phytoplankton photosynthesis, photoprotective compounds, and the dietary transfer of these compounds to zooplankton. He analyzed concentrations of carotenoids and mycosporine-like amino acids (MAAs) in zooplankton from Argentina, Alaska, and the Beartooth Mountains of Wyoming as well as from Pennsylvania lakes, and found pronounced differences in MAA concentrations related to environmental UV exposure levels. Robert had a diverse range of talents, including paleolimnology, and he is pictured here with a freeze coring device that he uses to sort out paleoclimate signals in lakes in Pennsylvania.

Post-doctoral Researchers

Carrie Kissman
During her time in the Global Change Limnology Lab, Carrie led much of the trophic forcing and stable isotope research, working in both the Beartooth Mountain lakes and Lake Tahoe.
Kirsten Kessler
Kirsten was a postdoctoral fellow from Germany who worked in our lab on the effects of UV and temperature on zooplankton in both the Pocono lakes and the Beartooth Mountain lakes.
Marieke DeLange
Marieke was a postdoctoral fellow from the Netherlands who worked with Don Morris and Professor Williamson on the interactions between zooplankton, dissolved organic carbon (DOC), and the UV transparency of lake ecosystems.
Gabriella Dee
Gaby examined the reciprocity principle in zooplankton with and without photoenzymatic repair (PER), the effects of temperature on UV tolerance in rotifers, and the UV tolerance, photoprotection, and photorepair of different life history stages of zooplankton.
Horacio Zagarese
Horacio was a postdoctoral fellow from Argentina who worked with Dr. Williamson on his earliest experiments with the effects of UV radiation on lakes.
Peter Schulze
Peter was a postdoctoral fellow who worked with Dr. Williamson on food limitation in zooplankton and pioneering efforts with the use of a remotely operated vehicle to quantify zooplankton

Graduate Students

Jennie Brentrup
Jennie's research focused on the role of microbes and light in altering dissolved organic matter in lakes. As part of the Global Lake Ecological Observatory Network (GLEON) she worked to collaborate with scientists collecting high-frequency data from buoys in lakes around the world. This enabled her to investigate water quality patterns across multiple spatial scales using advanced sensors, including a profiling buoy that she helped to design.
Taylor Leach
Taylor investigated how spatial and temporal gradients in environmental variables influence habitat selection, and diel vertical and horizontal migration of zooplankton. Her research employed the use of high -frequency acoustic instrumentation to understand the drivers of habitat selection across lakes of differing transparencies and trophic states.
Kevin Rose
Kevin worked in a variety of lakes, both within and outside the United States, to develop lake transparency indices that would serve as sensitive indicators of how lakes respond to environmental changes. He was part of the initial EARS IGERT cohort and actively involved with GLEON, which provided the opportunity to work with numerous sensors and sensor networks. He was an integral part of developing and deploying the portable buoy and advanced sensors used to study remote lakes.
Andrew Tucker
Andrew's research focused on the interaction of temperature and UV as factors influencing the invasion ecology of warmwater fish. In Lake Tahoe he assessed the role of UV and temperature in controlling the suitability of nearshore habitat for the reproduction of invasive warm-water fish. His work built on the research of previous lab members who demostrated that a UV and temperature gradient can affect survival of larval yellow perch in the Pocono lakes.
Sandi Connelly
Sandi studied the molecular level response of aquatic organisms to UV radiation. She looked at UV induced DNA damage, both potential and repaired, in freshwater organisms by measuring the molecular response of organisms to acute UV exposure. Other research investigated the impact of ecological stresses, namely UV, on Cryptosporidium, a freshwater human pathogen. While UV radiation has been used as a disinfectant to rid water supplies of Cryptosporidium, little is known about how natural levels of solar UV in reservoirs or other water supplies may alter the infectiousness of this organism.
Tim Guida
Tim studied the effects of UV and climate change on lakes in collaboration with Don Morris (Lehigh University) and Wade Jeffrey (University of West Florida). His research focused on UV effects on bacteria. He isolated several strains of bacteria from Pocono lakes and examined their UV tolerance as well as the importance of photoenzymatic repair of DNA damage. He also was heavily involved in looking at DNA damage in different size fractions of the plankton of some of the Pocono lakes.
Sandra Cooke
Sandra studied how interactions between UV radiation and chromophoric dissolved organic matter (CDOM) influence zooplankton communities. She looked at both short-term responses such as distribution, migration, reproduction, and life history, and longer term responses such as shifts in species composition. She found evidence for both temperature and UV effects on the vertical habitat selection of zooplankton in low DOC lakes.
Jeremy Mack
Jeremy received his M.S. degree from Lehigh University with Dr. Williamson working on how UV radiation influences benthic macroinvertebrates in streams within the context of land use patterns and climate change. His research examined differences in abundance and diversity of benthic macroinvertebrates in forested versus open streams. His results indicated that Chironomids are one of the benthic macroinvertebrates most responsive to UV radiation.
Aaron Clauser
Aaron studied the effects of UV and climate change on temporary pool ecosystems. These pools are critical breeding habitats for amphibians. Breeding success may be restricted by short hydroperiods that may in turn be altered by climate change. UV effects on temporary pool inhabitants are likely to vary with seasonal (within-pool) and spatial (among-pool) differences in canopy cover, water depth and transparency, as well as with the UV tolerance of the individual species.
Shawna Gilroy
Shawna studied the effects of UV radiation on the veliger larvae of zebra mussels. Zebra mussels are perhaps the most important invasive species in aquatic ecosystems in the USA. They have caused billions of dollars in damage to municipal and industrial water supplies. While UV radiation is used to protect intakes from zebra mussel infestations, little is known about how natural levels of UV alter the colonization success or depth distribution of this invasive species. Interestingly, zebra mussels increase water transparency after invasion and if UV transparency is also altered they may inhibit their own ability to colonize the shallow surface waters of low DOC lakes and rivers.
Laura Shirey
Laura looked at the effects of UV radiation on stream macroinvertebrates as part of an EPA-funded project on the interactive effects of UV radiation, climate change, and land use patterns on lotic ecosystems. While macroinvertebrate community structure has long been used to assess human impacts on streams, little is know about the sensitivity of stream invertebrates to UV in these shallow, often highly transparent systems. Laura used a compact submersible UV-PAR radiometer to relate water transparency to the UV tolerance of the dominant mayfly species. Using a UV-lamp phototron she assessed the contribution of photorepair versus dark repair and photoprotection to UV tolerance of mayflies.
Emily MacFadyen
Emily examined changes in molecular photoproducts resulting from UV damage. Emily exposed zooplankton to damaging UV in the presence and absence of photorepair radiation at different temperatures. Her experiments clearly demonstrated strong temperature effects on the level of UV-induced molecular photoproducts, suggesting that the temperatures at which zooplankton are exposed to UV may alter their ability to repair UV damage. David Mitchell at the University of Texas and Wade Jeffrey at the University of West Florida were close collaborators on this project.
Dina Leech
Dina worked on the tolerance and behavioral response of zooplankton to UV. Her in situ experiments with acrylic columns were the first to demonstrate that under full spectrum solar radiation Daphnia move upwards in the water column in the absence of solar UV radiation and downwards in the presence of UV (Leech and Williamson 2001).
David Huff
Dave worked on the effects of temperature and UV radiation on the spawning habitat of yellow perch (Perca flavescens). With Gaby Dee's assistance, he carried out extensive scuba dives and experimental manipulations of habitats to examine the depth distribution of perch eggs in high and low UV lakes in the Poconos. Dave found that in lakes with low dissolved organic carbon (DOC), perch spawn in deeper waters where the potential for UV damage is reduced, while in high DOC lakes perch spawn in the surface waters where warmer temperatures lead to more rapid development rates (Huff et al. 2004).

Other past graduate students include:

Timothy Vail
Susanne Metzgar
Carla Gutierrez
Paul Stutzman
Scott Carpenter
Kevin Wolbach
Eugina Novak
Jane Schoeneck
Mark Stoeckel
Lorraine Forcina
Sandra Smith