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Robert E. Knowlton
Professor of Biology

Physiological Ecology of Marine Decapod Crustacea (adults and larvae)
Department of Biological Sciences
The George Washington University
Lisner Hall 345, 2023 G Street, NW
Washington, D.C. 20052

Lab: (202) 994-9223
Office: (202) 994-6093
Fax: (202) 994-6100
Dept E-mail :


B.A. in Biology, Bowdoin College, 1960
Ph.D. in Zoology, University of North Carolina at Chapel Hill, 1970

Research Interests:

Experimental studies assessing the endocrinological mechanism of control of developmental processes such as morphogenesis (changes in morphology), including metamorphosis (the drastic transition from larva to juvenile), molting (the periodic sloughing of the external skeleton), and growth, using larvae of the “snapping shrimp” Alpheus heterochaelis as a model system. Neurosecretory tissue in the paired eyestalks is thought to be the main source of a “molt-inhibiting hormone” that acts on another organ which produces the hormone (20-hydroxyecdysone) that actually brings about the molt, and a factor that regulates morphogenesis, either directly or by acting on another organ that produces a “juvenile hormone.” Accordingly, effects of eyestalk removal are being studied.

Laboratory and field studies analyzing life histories and behavioral responses of various species of the “grass shrimp” Palaemonetes to differences in salinity, substrate, and cover (submergent vegetation). These differences could contribute to habitat partitioning, allowing the sympatric estuarine species P. pugio and P. vulgaris to coexist. Osmotic relations, substrate preferences, and competitive displacement have been suggested as factors determining the distribution of these two species. Laboratory work includes salinity tolerance experiments (adults and larvae), selection of substrate types and vegetative covers with and without predators present, and one-on-one interaction trials (to determine aggression). Field work consists of periodic sampling of grass shrimp populations from various localities in the mid-Atlantic and assessment of structural, reproductive, and developmental characteristics.

Descriptions of larval instars (stages) of various species of shrimps in families Alpheidae, Palaemonidae, Hippolytidae.

Survey of invertebrate and plant communities in saline conduit lakes of San Salvador, Bahamas.


2006. [with D. Marshalonis and H. Merchant] Acute toxicity of Permethrin to four populations of ovigerous grass shrimp, Palaemoneter pugio Holthuis. Bulletin of Environmental Contamination and Toxicology, 77:543-550.

2004. [with C.K. Vargo] The larval morphology of Palaemon floridanus Chace, 1942 (Decapoda, Palaemonidae) compared to other species of Palaemon and Palaemonetes, Crustaceana, 77: 683-715.

2002. [with H. H. Ganz] Reproductive differences among Delmarva grass shrimp (Palaemonetes pugio and P. vulgaris) populations, Virginia Journal of Science, 53: 35-49.

2002. [with P. S. Gross] Morphological variations among larval-postlarval intermediates produced by eyestalk ablation in the snapping shrimp Alpheus heterochaelis Say. Biological Bulletin, 202: 43-52.

2001. [with H. C. Merchant and R. N. Khan] The effect of macrophytic cover on survival of Palaemonetes pugio and P. vulgaris (grass shrimp) in the presence of predatory Fundulus heteroclitus (killifish). Contributions to Zoology, 70: 61-71.

1999. [with P. S. Gross] Variation in larval size after eyestalk ablation in larvae of the snapping shrimp Alpheus heterochaelis. Journal of Crustacean Biology, 19: 8-13.

1997. [with R. N. Khan and H. C. Merchant] Effects of macrophytic cover upon the distribution of grass shrimp Palaemonetes pugio and Palaemonetes vulgaris. Invertebrate Biology, 116: 243-247.

1997. [with P. S. Gross] The effect of eyestalk ablation on molting in larvae of the snapping shrimp Alpheus heterochaelis Say. Invertebrate Reproduction and Development, 32: 119-126.

1995. [with R. N. Khan and H. C. Merchant] Distribution of two sympatric species of grass shrimp, Palaemonetes pugio and Palaemonetes vulgaris, in relation to homogeneous and heterogeneous aquarium substrates. Journal of the Elisha Mitchell Scientific Society, 111: 83-95.

1995. [with M. R. Alavi] The larval morphology of Lysmata anchisteus Chace (Crustacea Decapoda) compared with other Lysmata species. Caribbean Journal of Science, 31: 289-310.

1995. [with R. N. Khan, P. A. Arguin, T. A. Aldaghlas, and R. Sivapathasundram] Factors determining distribution and abundance of Palaemonetes pugio and P. vulgaris (grass shrimp) along Delmarva shores. Virginia Journal of Science, 45: 231-247.

1994. Effects of larval eyestalk extirpation on morphogenesis and molting in the snapping shrimp Alpheus heterochaelis Say. Journal of Experimental Zoology, 270: 162-174.


Bisc 130 - Invertebrate Zoology, Fall
BiSc 167 - Marine Biology, Spring
BiSc 168 - Tropical Marine Biology, Spring, even years
BiSc 169 - Applied Marine Ecology, Spring, odd years

BiSc 204 -Seminar: Invertebrate Zoology, Fall, even years

Recent Graduate Students:

Daniel Marshalonis, M.S., 2003: “ Acute effects of Permethrin on four populations of grass shrimp, Palaemonetes pugio.”

Ronald B. Gallin, Ph.D., 2002: “Effects of salinity and temperature on survival and behavior of two sympatric species of grass shrimp, Palaemonetes pugio and Palaemonetes vulgaris, and implications of these effects on their distribution at Point Lookout State Park, Maryland.”