Sarah Cohen

Sarah Cohen

Professor of Biology
Evolutionary Ecology and Genetics
Phone: (415) 338-3750

Cohen Lab Website

Cohen Biology Department Webpage


I am interested in how ecological, behavioral, and environmental features shape evolution and genetic systems in diverse organisms. Most of our work in marine and estuarine settings has asked questions about how life history, physiological, or behavioral attributes of species affect population structure. Often the results directly address questions about coastal and marine conservation related to our ability to detect, predict, and remediate anthropogenic effects on natural populations. In addition, I have a particular interest in the ecology and evolution of recognition systems and have been investigating this both in colonial invertebrates and estuarine fishes.

Current projects include: immunogenetic (Major Histocompatibility Complex) variation in fish populations of varying size, the use of genetic markers to detect anthropogenic effects related to invasions, reproductive ecology of sea stars, distributions of parasites in estuarine and marine hosts, evolved tolerance for contaminants in estuarine populations, genetic tools for estimating population linkage in estuarine and marine species including urchins, lobsters, fish, seastars, copepods, seagrasses, and tunicates, and phylogenetic relationships between various marine taxa at the family level (e.g., fish and tunicates). Other projects have included oxygen diffusion in egg masses of snails and worms and implications for egg mass design, mating systems and inbreeding depression in tunicates, intertidal biodiversity surveys and methods, and behavioral variation in colonial marine invertebrates. We use research methods ranging from the high to very low tech, indoor to outdoor, and dry to wet.

Selected Papers

(* graduate student author, ** undergraduate author, ***Cohen lab postdoc)


  • Nydam M, Lemmon A, Lemmon E, Ziegler K, Cohen CS, Palomino-Alvarez L, and C. Gissi. 2023. Phylogenomics and systematics of botryllid ascidians, and implications for the evolution of allorecognition. Front. Ecol. Evol. Sec. Evolutionary Developmental Biology. Vol 11 | doi: 10.3389/fevo.2023.1214191
  • Erickson O, Cole R, Isaacs J, Alvarez-Clare S, Arnold J, Augustus-Wallace A, Ayoob J, Berkowitz A, Branchaw J, Burgio K, Cannon C, Ceballos R, Cohen CS, Coller H, Disney J, Doze V, Eggers M, Farina S, Ferguson E, Gray J, Greenberg J, Hoffman A, Jensen-Ryan D, Kao R, Keene A, Kowalko J, Lopez S, Mathis C, Minkara M, Murren C, Ondrechen MJ, Ordonez P, Osano A, Padilla-Crespo E, Palchoudhury S, Qin H, Lugo JR, Reithel J, Shaw C, Smith A, Smith R, Summers A, Tsien F, and E Dolan. 2022. How do we do this at a distance? A descriptive study of remote undergraduate research programs during COVID-19. CBE-Life Sciences Education 21(1).
  • Nydam M.L., Lemmon A.R, Cherry J.R., Kortyna ML, Clancy DL*, Hernandez C*, Cohen CS. 2021. Phylogenomic and morphological relationships among the botryllid ascidians (Subphylum Tunicata, Class Ascidiacea, Family Styelidae). Scientific Reports, 11(1):8351. doi: 10.1038/s41598-021-87255-2.
  • Melroy, L.M.* and CS Cohen. 2021. Temporal and spatial variation in population structure among brooding sea stars in the genus Leptasterias. Ecology and Evolution.
  • Hossfeld D*, Ling L, Cohen CS. 2020. Experimental investigation of tidal and freshwater influence on Symbiodiniaceae abundance in Anthopleura elegantissima. PLoS ONE,
  • Jaffe N*, Eberl R***, Bucholz J**, Cohen CS. 2019. Sea star wasting disease demography and etiology in the brooding sea star Leptasterias spp. PLoS ONE 14(11): e0225248.
  • Weinberg RB*, Clancy DL*, Cohen CS. 2019. Genotypic variability following fusion in the invasive colonial tunicate Didemnum vexillum. Invertebr Biol. 2019;00:e12263.
  • Caballero S., Dove V., Jackson-Ricketts J., Junchompoo C., Cohen S, Hines E. 2018. Mitochondrial DNA diversity and population structure in the Irrawaddy dolphin (Orcaella brevirostris) from the Gulf of Thailand and the Mekong River. Marine Mammal Science, DOI: 10.1111/mms.12518.
  • Cohen CS. 2018. "Marine extinctions" guest essay in Chapter 3, Perspectives section of book, Endangered Species: A Reference Handbook, authored by Jan Randall. ABC-CLIO Contemporary World Issues series, pp. 177-180.
  • Melroy L.*, Smith R**., and CS Cohen. 2017. Phylogeography of direct-developing sea stars in the genus Leptasterias in relation to San Francisco Bay outflow in central California. Marine Biology 64: 152- .DOI: 10.1007/s00227-017-3184-z (Note: shared first authorship between Melroy and Smith)
  • Sheets, E*., Cohen, CS, Ruiz, GM, Rocha, RM. 2016. Investigating the widespread introduction of a tropical marine fouling species. Ecology and Evolution 6 (8): 2453–2471. DOI: 10.1002/ece3.2065
  • Cohen, CS. 2016. Revision of the Urochordata section in Brusca, RC and Shuster, SM, Chapter 27, Phylum Chordata: Cephalochordata and Urochordata. Invertebrates, 3rd edition, Sinauer Press.
  • Moczek, Armin P., and 22 co-authors including C.S. Cohen. 2015. The Significance and Scope of Evolutionary Developmental Biology:  A Vision for the 21st Century. Evolution & Development, Vol. 17, Issue 3, 198-219.
  • Ort, B.***, Cohen, C.S.; Boyer, K.E.; Reynolds, L.R.; Tam, S.H.***; Wyllie-Echeverria. Conservation of Eelgrass (Zostera marina) Genetic Diversity in a Mesocosm-Based Restoration Experiment. PLOS One, accepted for publication, January 2014.
  • Goulding, T.*. and C.S. Cohen. In press. Phylogeography of a marine acanthocephalan: lack of cryptic diversity in a cosmopolitan parasite of mole crabs. Journal of Biogeography, accepted for publication, November 2013.
  • Craig, C*., W. Kimmerer, C.S. Cohen. 2013. A DNA-based method for investigating feeding by copepod nauplii. J. Plankton Research, published 10.14.2013, 10.1093/plankt/fbt104
  • Ort, B, Cohen, CS, Boyer, KE, Wyllie-Echeverria, S. 2012. Genetic diversity within and among eelgrass (Zostera marina) beds in the San Francisco Bay. Journal of Heredity, doi: 10.1093/jhered/ess022.
  • Cohen, C.S., McCann, L, Davis, T., Shaw, L., Ruiz, G. 2011. Discovery and significance of the colonial tunicate Didemnum vexillum in Alaska. Aquatic Invasions: 6 (3): 263-271. doi: 10.3391/ai.2011.1
  • Robinson, G. and 19 authors including C. Sarah Cohen. 2010.  Empowering 21st Century Biology. BioScience 60:11, 923-930
  • Nacci, D.,M. Huber, D. Champlin, S. Jayaraman, S. Cohen, E. Gauger**, A. Fong*, M. Gomez-Chiarri.  2009. Trade-offs of contemporary evolution: pathogen susceptibility in a chemically-tolerant estuarine fish population. Environmental Pollution, 157: 857- 864.
  • Eberl, R.*, S. Cohen, F. Cipriano, and E. Carpenter. 2007. Genetic diversity and population structure of the pelagic harpacticoid copepod Macrosetella gracilis on rafts of the bloom-forming cyanobacterium Trichodesmium spp. Aquatic Biology, 1: 33-43.
  • Burnett, K., and 25 authors including S. Cohen. 2007. Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics. Comparative Biochemistry and Physiology, Part D 2, 257-286.
  • Cohen, S., J. Tirindelli*, M. Gomez-Chiarri, D. Nacci. 2006. Functional implications of Major Histocompatibility (MH) variation using estuarine fish populations.Integrative and Comparative Biology 46 (6): 1016-1029.
  • Cohen, S. 2002. MHC variation in natural populations of an estuarine fish: high levels of variation and relationship to severe environmental stress. Molecular Biology and Evolution 19 (11): 1870-1880.
  • Cohen, S. and D. Nacci. 2002. Effects of dioxin-like compound (DLC) contamination on an estuarine fish species: adaptive changes at specific loci. Conference proceedings, US/Vietnam Scientific Conference on Agent Orange/Dioxins, March 3-6, 2002, Hanoi, Vietnam.
  • Saito, Y., Shirae, M., Okuyama, M., and S. Cohen. 2001. Phylogeny of botryllid ascidians. In, "The Biology of Ascidians", ed H. Sawada, H. Yokosawa, CC Lambert, Springer, Tokyo, pp. 315-320.
  • Cohen, S. 2000. Botryllid ascidian invasions: genetic and behavioral evidence for multi-species invasions and character divergence following introductions. In, Proceedings of the First National Conference on Marine Bioinvasions, MIT Sea Grant.
  • Cohen, S., Saito, Y. and I. Weissman. 1998. Evolution of allorecognition in botryllid ascidians inferred from a molecular phylogeny. Evolution 52(3):746-756.
  • Cohen, S. 1996. The effects of contrasting modes of fertilization on levels of inbreeding in the marine invertebrate genus Corella. Evolution 50(5): 1896-1907.
  • Cohen, C. S. and R. Strathmann. 1996. Embryos at the edge of tolerance: effects of environment and structure of egg masses on supply of oxygen to embryos. Biol. Bull. 190: 8-15.
  • Dethier, M., Graham, E., Cohen, S., and L. Tear. 1993. Visual and random-point percent cover estimations: "Objective is not always better." Mar. Ecol. Prog. Ser. 96: 93-100.
  • Petersen, C., Warner, R., Cohen, S., Hess, H. and A. Sewell. 1992. Variation in pelagic fertilization rates: Implications for production estimates, mate choice, and the spatial distribution of mating. Ecology 73: 391-401.
  • Cohen, S. 1990. Outcrossing in field populations of two species of self-fertile ascidians. J. Exp. Mar. Biol. Ecol. 140: 147-158.
  • Hess, H., Bingham, B., Cohen, S., Grosberg, R., Jefferson, W. and L. Walters. 1988. The scale of genetic differentiation in Leptosynapta clarki (Heding), an infaunal brooding holothuroid. J. Exp. Mar. Biol. Ecol. 122: 187-194.