Annette Summers Engel
Donald and Florence 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

Kokesh, B. (2018) Geometric morphometrics and biogeography of lucind bivalves. M.S. thesis, South Dakota School of Mines and Technology, Rapid City, SD. 

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

Paterson, A.T., Long, B.L., Kokesh, B.S., Anderson, L.C., Engel, A.S. (2018) Anchialine lakes serve as novel habitats for relict taxa, including chemosymbiotic marine bivalves. Geological Society of America Abstracts with Programs, Indianapolis, IN; 50(6) doi: 10.1130/abs/2018AM-323431. 

Lim J, Alexander LC, Engel AS, Anderson LC, Campbell BJ (2018) Novel symbiont species diversity within a Ctena orbiculata (Bivalvia: Lucinidae) population. American Society for Microbiology Microbe conference, June 7-11, Atlanta, GA.

Nachman E, Walton J, Lim SJ, Engel AS, Anderson LC, Campbell BJ (2018) Functional diversity of the Phacoides pectinatus (Bivalvia: Lucinidae) gill microbiome. American Society for Microbiology Microbe conference, June 7-11, Atlanta, GA.
Paterson AT, Long BL, Lim SJ, Kokesh BS, Harmon A, Anderson LC, Campbell BJ, Engel AS (2018) Intraspecific variability of valve morphology and endosymbiont diversity among Lucinidae from shallow marine habitats. Geological Society of America Seoutheastern section meeting, Knoxville, TN, Abstracts with Programs. Vol. 50, No. 3, doi: 10.1130/abs/2018SE-313129.

Paterson AT, Fortier CM, Long B, Kokesh B, Lim SJ, Campbell BJ, Anderson LC, Engel AS (2017) Redox-stratified bacterial communities in sediments associated with multiple lucinid bivalve species: implications for symbiosis in changing coastal habitats. AGU annual meeting, New Orleans, LA, Dec 11-15, 2017.
Fortier CM, Paterson A, Engel AS (2017) Ecology and endosymbiont diversity of six co-occurring bivalves (Bivalvia: Lucinidae) from an anthropogenically-impacted tidal flat on Sugarloaf Key, Florida Keys. GSA Annual Meeting, Seattle, WA, Oct 22-25, 2017.
Kokesh BS, Anderson LC, Engel AS (2017) Geometric morphometric analysis of Ctena orbiculata (Lucinidae: Bivalvia) from marine lakes of San Salvador island, The Bahamas, and surrounding coastal environments. GSA Annual Meeting, Seattle, WA, Oct 22-25, 2017.
Engel AS, Lim SJ, Paterson AT, Payne Z, Scheffler S, Tran A, Campbell BJ, Anderson LC (2017) Taxonomic and metabolic complexity among lucinid bivalve endosymbionts. 15th Symposium on Aquatic Micorbial Ecology, Zagreb, Croatia, Sept. 3-8, 2017. (poster presentation) 

Scheffler S, Paterson AT, Long B, Anderson L, Engel AS (2017) Microbial communities from gill tissues and patchy seagrass habitat of a chemosymbiotic bivalve, Stewartia floridana. 4th Southeastern Biogeochemistry Symposium, Athens, GA, March 31-April 2. (poster presentation)

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.

Payne Z, Kokesh B, Paterson AT, Anderson L, Engel AS (2017) Endosymbiont diversity and shell morphology differences for Ctena orbiculata (Lucinidae: Bivalvia). Southeastern Biogeochemistry Symposium, Athens, GA, March 31-April 2. (poster)

Lim SJ, Engel AS, Anderson LA, Campbell BJ (2017) Novel co-symbiosis in the lucinid bivalve Phacoides pectinatus. American Society for Microbiology, New Orleans, LA. (poster presentation)
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)


Gene sequence data
Engel, A.S., Doty, T.W. (2015) Coastal mangrove sediment and lucinid bivalve (Phacoides pectinatus) microbiomes (Florida) Targeted Locus (Loci) raw sequence reads targeted loci (78 experiments); NCBI BioProject Accession PRJNA300417

Engel, A.S., Goemann, A. (2015) Coastal seagrass sediment and lucinid bivalve (Stewartia floridana, Lucinisca nassula, Ctena orbiculata) microbiomes (Florida) Environment targeted loci raw sequence reads (71 experiments); NCBI BioProject Accession PRJNA302122

Lim,J.S., Engel,A.S., Anderson,L.C. and Campbell,B.J. (2017) Taxonomic and genetic symbiont diversity in the seagrass-associated lucinid bivalves Ctena orbiculata and Stewartia floridana (11OTU).NCBI GenBank accession numbers KY687497 - KY687507.

Whole genome shotgun sequencing projects
Lim,S.J., Davis,B.G., Gill,D.E., Engel,A.S., Anderson,L.C. and Campbell,B.J. (2017) Novel Co-symbiosis in the unique lucinid bivalve Phacoides pectinatus, Phacoides pectinatus symbionts, NCBI BioProject Accession PRJNA368737

Specimen archival
To date 1,311 lots representing 7,414 specimens have been digitally cataloged. These records are made publicly available online through the iDigBio portal 

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.

Press and Social Media 

• Annual research summarized in National Science Foundation Dimensions of
  Biodiversity booklet; link to report ( pdf ) with 1-page research details (pg 65)

•  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”)
Dimensions project field team, 2014.

Field Photographs

We spent New Year's in 2017 through 2018 on San Salvador, The Bahamas, to explore the lucinid diversity of inland marine lakes and collect additional lucinids from tidally influenced areas around the island. Working inland requires bushwacking through the jungle. The interior is not for the inferior! 
​All photographs by Dr. Annette Summers Engel.
Spring 2017, a few of us went on a recon trip to the Marco Island area of southeastern Florida, specifically within the Rookery Bay Reserve (with the help of Team Ocean), and then to the middle area of the Florida Keys to document lucinid diversity in areas that have been understudied in the past. We found new populations of Lucina pensylvanica, and occurrences for other lucinids on shoals and banks in the Keys. 
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