Annette Summers Engel
Donald H. Jones Professor of Aqueous Geochemistry
University of Tennessee at Knoxville
Department of Earth and Planetary Sciences
Engel Lab Research -
Dimensions of Lucinid Chemosymbiotic Associations 
Lucinids are common infaunal bivalves in shallow coastal marine habitats, including seagrass meadows and mangrove forests, where they position themselves near the oxic-anoxic interface. With abundances of up to 1500 individuals/m2, the lucinids can have a substantial impact on the productivity and diversity of nearshore habitats.  Lucinids are the most taxonomically diverse clade of chemosymbiotic bivalves. All known lucinids harbor endosymbionts and our recent molecular investigations have uncovered novel genetic and functional diversity among the endosymbionts. Lucinids are very abundant in  ediments and affect porewater composition, nutrient suspension, sediment biogeochemistry and vegetation productivity. However, their roles in sediment nitrogen and methane cycling are current unknown, as well as what ecological and geochemical (including contaminant) parameters affect their diversity and distribution. It is unclear how a decline in lucinid population and/or functional diversity may impact the coastal biome ecosystem, or even what processes, such as sea level rise or increased ocean temperatures, could lead to lucinid population declines. We hypothesize that diversity symbiotic associations may be a mechanism for lucinids to cope with changing or stressful environmental conditions. Therefore, lucinid-chemosymbiotic systems in coastal biomes are ideal for understanding the underexplored “dimensions in biodiversity” of chemosymbiosis in ecological and evolutionary processes.
This project came from an earlier study that focused on Phacoides pectinatus hosts from marine seagrass beds in Florida and The Bahamas that have substantial diversity among lucinid endosymbionts, with some microbes being phylogenetically affiliated with the gammaproteobacterial class of bacteria, and presumed to be thiotrophs, but other bacterial sequences affiliated with other proteobacterial classes may also be methane-oxidizing groups (methanotrophs). Dual symbiosis has not yet been thoroughly described in lucinids, so the research has revelance for identifying novel metabolisms and functional diversity, but also for increasing our understanding of methane cycling in climatically sensitive, nearshore marine systems.
The current research at UTK includes characterizing the geochemical, ecological, and sedimentological properties of sediments in lucinid habitats, microbial diversity analyses from sediments and hosts, and evaluation of 'omics data. 
Dimensions of Biodiveristy Summary of our project -- link
Current Support: National Science Foundation, Dimensions of Biodiversity program ( DEB-1342785 )
Previous Support: NSF EAGER Program ( IOS-1041941; IOS-1239903
Project Collaborators:
Dr. Laurie Anderson, South Dakota School of Mines and Technology
Dr. Barbara Campbell, Clemson University ( website )

Student Work

Long, B. (2016) Geometric morphometric analyses of environment related shell variation in Stewartia floridana (Bivalvia: Lucinidae). M.S. thesis, South Dakota School of Mines and Technology, Rapid City, SD. 

Doty, T.W. (2015) Environmental controls on the diversity and distribution of endosymbionts associated with Phacoides pectinatus (Bivalvia: Lucinidae) from shallow mangrove and seagrass sediments, St. Lucie County, Florida. M.S. thesis, University of Tennessee, Knoxville, TN.
Goemann, A. (2015) Rare occurrences of free-living bacteria belonging to Sedimenticola from subtidal seagrass beds associated with the lucinid clam, Stewartia floridana. M.S. thesis, University of Tennessee, Knoxville, TN.

Related Publications and Conference Abstracts from Group

Kokesh B, Anderson LC, Engel AS (2017) Assessing the diversity of lucinid bivalves from coastal and anchialine habitats on San Salvador Island, the Bahamas. Society of Integrative and Comparative Biology Annual Meeting, New Orleans, LA.

Lim SJ, Goemann A, Engel AS, Anderson LC & Campbell BJ (2016). Taxonomic, genetic and functional diversity of chemosymbiosis in lucinid bivalves from coastal biomes. American Society for Microbiology South Carolina Branch 2016 Fall Meeting. University of South Carolina Upstate, South Carolina. (won best student oral presentation)

Long, B. (2016) Morphologic variation within a population of Stewartia floridana (Lucinidae: Bivalvia) from a coastal seagrass biome. 2016 Student Research Symposium, April 5, 2016, South Dakota School of Mines and Technology Abstract Book, p. 25-26.

Kokesh BS, Anderson LC, Engel AS (2016) Morphometric and ecological discrepancies of Lucinidae (Bivalvia) in various marine environments on San Salvador island, The Bahamas. Geological Society of America Abstracts with Programs, Denver, CO. Vol. 48, No. 7. doi: 10.1130/abs/2016AM-282275  

Long BL, Anderson LC, Engel AS (2015) Testing the association of Stewartia floridana shell morphology with environmental parameters in a coastal seagrass area. Geological Society of America meeting, Baltimore, MD, Nov. 1 – 4, 2015. (won best poster presentation, Geobiology and Geomicrobiology division
Doty TW, Engel AS (2015) Microbial diversity fluctuations within mangrove-associated sediments that harbor the lucinid bivalve, Phacoides pectinatus, and their free-living bacterial endosymbionts. 2nd Annual Southeastern Biogeochemistry Symposium, Atlanta, GA, March 28-29, 2015. (poster presentation)
Lim SJ, Goemann A, Engel AS, Anderson LC, & Campbell BJ (2015). Functional diversity of chemosymbiosis in lucinid bivalves from coastal biomes. First Gordon Research Conference on Animal-Microbe Symbioses. Waterville Valley Resort, New Hampshire (poster)

Anderson LC (2014) Relationships of internal shell features to chemosymbiosis, life position, and geometric constraints within the Lucinidae (Bivalvia). In: Hembree DI, Platt BF, Smith, JJ (eds.) Experimental Approaches to Understanding Fossil Organisms: Lessons from the Living. Springer, Topics in Geobiology 41:49-72.
Long B, Anderson LC, Engel AS (2014) Calibrating morphometric proxies of chemosymbiosis: A test case using Lucinidae (Bivalvia). Abstract Volume, 4th International Palaeontological Congress, p. 741.
Goemann A, Engel, AS (2014) Physical and geochemical parameters governing the distribution of lucinid clams and associated symbiotic bacteria. International Society for Environmental Biogeochemistry Short Course and Research Colloquium, on "Interfacial Processes in Environmental Biogeochemistry," Cancun, Mexico, November 16-21, 2014. ( pdf of talk hosted by ISEB )
Green-Garcia AM, Engel AS (2012) Bacterial diversity of siliciclastic sediments in a Thalassia testudinum meadow and the implications for Lucinisca nassula chemosymbiosis. Estuarine, Coastal and Shelf Science. 112: 153-16.
Engel AS, Anderson LA, Harris S (2011) Endosymbiont diversity from lucinid bivalves: potential dual symbiosis in shallow marine environments. 1st Annual Congress of Marine Biotechnology (WCMB-2011), Dalian, China. April 25-29. (Invited oral presentation in Marine Extremophiles session)
Engel AS, Green-Garcia AM, Gwin K, Thiessen M (2010) Bacterial endosymbiont diversity from Lucinisca nassula and Phacoides pectinata (Bivalvia: Lucinidea). 7th OBC Workshop, Kakegawa, Japan, p. 27. (Invited oral presentation).
Engel AS, Green-Garcia AM, Gwin K, and Thiessen M (2009) Bacterial endosymbiont diversity from Lucinisca nassula and Phacoides pectinatus (Bivalvia: Lucinidea): Hints of dual symbiosis in some hosts. Proceedings of the 6th International Symbiosis Society, Madison, WI, p. 84-85. (poster presentation)
Garcia A, Thiessen M, Aronowsky A, Anderson L, Bao H, Engel AS (2007) Evolutionary implications of endosymbiont diversity within lucinid bivalves. Eos Trans. American Geophysical Union, 88(52), Fall Meet. Suppl., Abstract B43E-1650. (poster presentation)
Peng Y, Bao H, Anderson LC, Engel AS (2007) Carbonate-associated sulfate in lucinid (Bivalvia) shells. Eos Trans. American Geophysical Union, 88(52), Fall Meet. Suppl., Abstract B31D-0611. (poster presentation)
Green-Garcia A, Thiessen M, Aronowsky A, Anderson L, Engel AS (2007) Implications of bacterial diversity within a modern lucinid bivalve habitat. Geological Society of America Abstracts with Programs, 39: 66. (poster presentation)

Press and Social Media 

2 016
•  Article featuring Brooke Long, student at SDSM&T.

Article about Dr. Barb Campbell, winning local Sigma Xi Outstanding Young Investigator of the Year at Clemson University 
Article about Dr. Campbell's research at Clemson, including lucinid research
•  Article about research in Earth and Planetary Science annual newslettter, Fall 2015, "Clamming it up" (pg 3).
• MS student Brooke Long at SDSM&T received a Student Poster Award from the Geobiology and Geomicrobiology Division at the GSA Meeting in Baltimore in November. 
• Annual research summarized in National Science Foundation Dimensions of Biodiversity booklet; link to report (pdf) with 1-page research details (pg 38)
• Blog entires by Brooke Long, MS student at the South Dakota School of Mines and Technology, Museum of Geology
     " Symbiosis " January 23, 2015
     " Morphology " February 6, 2015
• Research announced in the National Science Foundation Press Release, September 27, 2013, for the Dimensions of Biodiversity awards; link to pdf report with 2-page research details
• Research featured by (Science Alerts Social Network),,,, and other outlets (based on publication “Bacterial diversity of siliciclastic sediments in a Thalassia testudinum meadow and the implications for Lucinisca nassula chemosymbiosis”)
Brooke Long at the Geological Society of America meeting, 2015 (photo by LA Anderson).
Broc Kokesh from SDSM&T presenting his
poster at GSA, Denver, CO, Sept. 2016.
Dimensions project field team, 2014.

Field Photographs

Photographs from May-June 2016, San Salvador, Bahamas - collection as part of course, "Field Studies in Coastal Biomes" at University of Tennessee and South Dakota School of Mines. Students led the sampling design, hypothesis testing, and are collecting data back at their home institutions during Summer 2016 session. Ctena orbiculata became the center of attention. More photos can be found in the Photo Galley
Photographs from April 2015, San Salvador, Bahamas - collection of sediment and the clams Codakia orbicularis, Lucina pensylvanica, Ctena orbiculata, Divalinga quadisulcata, and Anodontia alba. Also seen on the trip were fossil lucinids (Codakia) in a 125,000 year old reef.
Photographs from July 2014, Wildcat Cove, Fort Pierce, Florida - collection of sediment and the clam Phacoides pectinatus
Photographs from July 2014, Bokellia Pier, Pine Island, Florida - collection of sediment and the clam Stewartia  floridana
Geochemistry. Geomicrobiology. Geology. Ecology.

Interdisciplinary Research at the University of Tennessee