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Elysia chlorotica

By Chelsea Blanchet

Geographic Range

Elysia chlorotica, commonly known as the eastern emerald elysia, is found along the eastern coast of the United States, as far north as Nova Scotia, Canada and as south as southern Florida. (Rumpho, et al., 2001; Rumpho, et al., 2011)

Habitat

Elysia chlorotica is found in salt and tidal marshes, shallow creeks, and pools with depths of less than 0.5 m. The eastern sea slug is the most euryhaline osmoconformer known to date. The slug can survive salinity levels ranging from nearly fresh water (~24 mosm) to brackish salt water (~2422 mosm). Elysia chlorotica is generally found close to its main food source, Vaucheria litorea, an intertidal alga. The slug has an obligate relationship with the alga for both nutrients and physical development. (Green, et al., 2000; Pierce, et al., 1984; Rumpho, et al., 2011)

  • Range depth
    0 to 0.5 m
    0.00 to 1.64 ft

Physical Description

Elysia chlorotica has two main life stages: a juvenile stage which is defined as the time before the slug begins feeding on V. litorea, and an adult stage. The stages of development are distinguishable based on the slug’s morphology and coloring. The slugs start as veliger larva, meaning they are equipped with a shell and ciliated vellum used for swimming and obtaining food. After metamorphosing to juveniles, the slugs are normally brown with ventrally-located spots of red pigmentation. Elysia chlorotica only undergoes metamorphosis into the adult phase after exposure to and consumption of V. litorea, at which time its coloring and morphology also change. After the initial feeding, E. chlorotica sequesters chloroplasts obtained from the plant into its specialized digestive tract. The presence of the chloroplasts turns the slug from brown to bright green. Most adults lose the red spots. The green color persists only as long as the slug has functional chloroplasts in its cells. When the chloroplasts are expelled, the slug loses its bright green color and reverts to a gray color. Adults normally range in size from 20 to 30 mm but specimens of up to 60 mm have been documented. The eastern emerald elsyia obtains its name from its adult structure. Elysid refers to the adult slug’s leaf-like shape which is caused by two large lateral parapodia on either side of its body. This morphology is beneficial as both camouflage and allowing the slug to be more efficient at photosynthesis. Other members of this family are distinguished by their parapodia in addition to bright coloring. (Colin, 1978; Humann, 1992; Pierce, et al., 1984; Rumpho, et al., 2001; Rumpho, et al., 2008; Rumpho, et al., 2011; Rumpho, et al., 2000)

  • Range length
    20 to 60 mm
    0.79 to 2.36 in
  • Average length
    30 mm
    1.18 in

Development

The blastula of a developing Elysia chlorotica egg is holoblastic and spiral, meaning the eggs completely divide. At division, each plane is at an oblique angle to the animal's vegetal axis. Cells produce multiple tiers of cells with no clear center; this is referred to as a stereoblastula. Movements of cells occur by a process referred to as epiboly. Epiboly means that during development the ectoderm cells spread out to cover both the mesoderm and endoderm cell layers.

Elysia chlorotica has a veliger, juvenile, and adult stage of life. As a veliger larva, E. chlorotica has a shell and ciliated vellum, a common feature among a sea slug's developmental cycle. During the larval stage these cilia help the larva to swim in its aquatic environment. Coloration in the larva is different due to the lack of retained chloroplasts in their diverticula. Diverticula are essentially openings along the digestive tract that result in small pocket in which an animal can store food, or in this case stolen chloroplasts. Veligers will metamorphose into juveniles in one to two days after exposure to V. litorea. After 14 days of exposure to V. litorea and an additional two days of constant contact with this plant, E. chlorotica metamorphoses into the adult leaf-shaped sea slug. The adult sea slug is bright green in color due to chloroplast cells that have been sequestered into the complex diverticula of the animal. Adults die shortly after they lay their string of eggs. Researcher Sidney Pierce suggests mass death is due to the expression of an unknown retro acting virus. (Hoffmeister and Martin, 2003; Pierce, et al., 1999; Rumpho, et al., 2011; Rumpho, et al., 2000; Schmitt, et al., 2007)

Reproduction

The details of how E. chlorotica initiates mating and the techniques used during mating are not well known. In a similar species, the mating behaviors of Elysia timida are dependent on the responses generated by the potential partner. These slugs will approach each other head to head and feel the other’s head with their own. Then, one (no way of telling how they decide which begins to move) will proceed downward moving their head down along the other slug’s body. If the partner accepts the invitation to mate the slugs will align head to tail. When the proper alignment is established, mating begins where both slugs insert their penes into the other’s genital area.

Sexually reproducing hermaphrodites may act only as female or male. Sperm are less costly than eggs, so functioning as a male may be more desirable energetically. Many species of sea slugs within the clade Sacoglossa practice hypodermic insemination, in which the sperm of one slug is injected directly into the surface of another slug. They penetrate directly into the mate’s body in the general area of the others gonads and release the sperm directly inside their partner. (Rumpho, et al., 2011; Rumpho, et al., 2000; Schmitt, et al., 2007)

These slugs are simultaneous hermaphrodites, capable of internal self-fertilization, although this particular species more commonly outcrosses. Out-crossing is essential sexual reproduction with another individual. Eggs are laid in long mucous-laden strings, hatching approximately in a week. The eastern emerald elysia breeds once a year in the early spring. (Rumpho, et al., 2011; Rumpho, et al., 2000)

  • Breeding interval
    Once annually
  • Breeding season
    Early spring
  • Range gestation period
    7 to 8 days
  • Average gestation period
    7 days

There are no documented incidents of parental care or investment in this species. Adults experience mass death both in natural and laboratory environments at approximately eleven months old. Pierce et al. (1984)suggest this is due to a viral expression, but little evidence exists. (Pierce, et al., 1984; Pierce, et al., 1999; Rumpho, et al., 2000; Schmitt, et al., 2007)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning

Lifespan/Longevity

Elysia chlorotica lives to be approximately 11 months old. Adults experience mass death after laying their string of eggs in the spring of each year both in the wild and when held in captivity. According to research done by Pierce this may be due to a viral expression not a biological clock. That means that although this death is synchronized among all adults it is due to the final stage of a disease that every slug inherits not an internal biological cue. Pierce et al. (1984) were unable to identify the pathogen but did find evidence of virulent DNA in the nucleus of all test subjects. (Pierce, et al., 1984; Pierce, et al., 1999; Pierce, 1982; Pierce, et al., 1996)

  • Average lifespan
    Status: wild
    11 months
  • Average lifespan
    Status: captivity
    11 months
  • Average lifespan
    Status: wild
    11 months
  • Average lifespan
    Status: captivity
    11 months

Behavior

Elysia chlorotica spend most of their time floating in the water or among V. litorea to obtain optimal sun exposure. These slugs are not social, and only join others for mating purposes. (Pierce, et al., 1999; Rumpho, et al., 2011)

Home Range

None documented (Schmitt, et al., 2007)

Communication and Perception

Little information is known on the techniques used by this species to communicate. Since the communication techniques of other sea slugs is variable, it is difficult to compare other species with E. chlorotica. The slug's eyes are not very developed. (Brandly, 1984; Rumpho, et al., 2011; Schmitt, et al., 2007)

Food Habits

Elysia chlorotica is a kleptoplastic member of the clade Sacoglossa, which are sap sucking sea slugs. This species feeds exclusively on V. litorea, and rarely feed upon Vaucheria compacta. The slug has an obligate relationship with its food source, requiring it for metamorphosis from the veliger to juvenile to the adult stage.

As an adult, E. chlorotica obtains nutrients by consuming chloroplast cells from the alga. Elysia chlorotica removes the chloroplast cells from the plant by projecting its radula, a scraping structure into the alga’s cell walls, and then sucking out the contents of V. litorea cells. The contents of these cells pass through the slug’s highly specialized digestive tract. Over time the chloroplast cells are sequestered into the diverticula of the slug’s digestive system, causing it to turn bright green. After the digestive tract projects green coloration, E. chlorotica is fully capable of photosynthesis for up to 10 months. Due to the slug’s photosynthetic nature, this species can often be found “sun bathing”, or laying with their parapodia extended to obtain maximum sunlight exposure. (Brandly, 1984; Mujer, et al., 1996; Pierce, et al., 1999; Pierce, et al., 1996; Rumpho, et al., 2001; Rumpho, et al., 2011; Rumpho, et al., 2000)

  • Primary Diet
  • herbivore
    • algivore
    • eats sap or other plant foods
  • Plant Foods
  • sap or other plant fluids

Predation

There are no known predators of E. chlorotica. The leaf like structure of its appearance allows it to blend amongst the algae and plants of its marine habitat. (Mujer, et al., 1996; Pierce, 1982; Pierce, et al., 1996; Rumpho, et al., 2008; Rumpho, et al., 2011; Rumpho, et al., 2000)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Elysia chlorotica has little impact on the environment because they are not predators of animals and are not known to be a prey of choice for any particular species. They interact with Vaucheria litorea, as all juveniles must feed on these plants before metamorphosis can occur. (Hoagland and Robertson, 1988; Hoffmeister and Martin, 2003; Rumpho, et al., 2011; Rumpho, et al., 2000)

Economic Importance for Humans: Positive

Although Elysia chlorotica does not directly benefit humans, members of the scientific community are very interested in this sea slug. Many studies about how this animal not only obtains the chloroplast from its algal food supply but also how they are able to maintain and utilize the complex structures. This species contains the blueprints to many of the required components of photosynthesis in their genome before even ingesting the chloroplasts of Vaucheria litorea. (Brandly, 1984; Kim and Archibald, 2010; Rumpho, et al., 2011; Rumpho, et al., 2000)

Economic Importance for Humans: Negative

There are no known negative effects to humans from Elyisa chlorotica.

Conservation Status

Elyisa chlorotica has no special status at this time. Populations are not in decline.

Other Comments

Members of this family are often brightly colored such as the Elysia picta which is known as the painted elysia. The main body of the painted elysia is green but laterally there are vivid bands of orange, blue, and neon green. The brown lined elysia, Elysia subornata has a bright green body and parapodia but also has a thin brown line along the very edge of its’ wing-like structures. (Colin, 1978; Humann, 1992)

Contributors

Chelsea Blanchet (author), Radford University, Karen Powers (editor), Radford University, Kiersten Newtoff (editor), Radford University, Melissa Whistleman (editor), Radford University, Renee Mulcrone (editor), Special Projects.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

vibrations

movements of a hard surface that are produced by animals as signals to others

References

Brandly, B. 1984. Aspects of the ecology and physiology of Elysia cf. furvacuda (Mollusca: Sacoglossa). Bulletin of Marine Science, 34/2: 207-219.

Colin, P. 1978. Marine Invertebrates And Plants of the Living Reef. Neptune city, /Nj: T.F.H Publications.

Green, B., W. Li, J. Manhart, T. Fox, E. Summer, R. Kennedy, S. Pierce, M. Rumpho. 2000. Mollusc-algal chloroplast endosymbiosis. Photosynthesis, thylakoid protein maintenance, and chloroplast gene expression continue for many months in the absence of the algal nucleus. Plant Physiology, 124/1: 331-342.

Hoagland, K., R. Robertson. 1988. An assessment of poecilogony in marine invertebrates: phenomenon or fantasy?. The Biological Bulletin, 174/2: 109-125.

Hoffmeister, M., W. Martin. 2003. Interspecific evolution: microbial symbiosis, endosymbiosis and gene transfer. Environmental Microbiology, 5/8: 641-649.

Humann, P. 1992. Reef Creature Identification. Jacksonville, Fl: New World Publications.

Händeler, K., Y. Grzymbowski, P. Krug, H. Wägele. 2009. Functional chloroplasts in metazoan cells - a unique evolutionary strategy in animal life. Frontiers in Zoology, 6/28: 1-18.

Kim, E., J. Archibald. 2010. Plastid evolution: Gene transfer and the maintenance of ‘stolen’ organelles. BMC Biology, 8/73: 1-3.

Mujer, C., D. Andrews, J. Manhart, S. Pierce, M. Rumpho. 1996. Chloroplast genes are expressed during intracellular symbiotic association of Vaucheria litorea plastids with the sea slug Elysia chlorotica. Cell Biology, 93/22: 12333-12338.

Pierce, S. 1982. Invertebrate cell volume control mechanisms: a coordinated use of intracellular amino acids and inorganic ions as osmotic solute. The Biological Bulletin, 1603: 405-419.

Pierce, S., R. Biron, M. Rumpho. 1996. Endosymbiotic chloroplasts in molluscan cells contain proteins synthesized after platid capture. The Journal of Experimental Biology, 199/10: 2323-2330.

Pierce, S., S. Edwards, P. Mazzocchi, L. Klingler, M. Warren. 1984. Proline betaine: A unique osmolyte in an extremely euryhaline osmoconformer. The Biological Bulletin, 167/2: 495-500.

Pierce, S., T. Maugel, M. Rumpho, J. Hanten, W. Mondy. 1999. Annual viral expression in a sea slug population: Life cycle control and symbiotic chloroplast maintenance. The Biological Bulletin, 197/6: 1-6.

Rumpho, M., K. Pelletreau, A. Moustafa, D. Bhattacharya. 2011. The making of a photosynthetic animal. The Journal of Experimental Biology, 214/2: 303-311.

Rumpho, M., E. Summer, B. Green, T. Fox, J. Manhart. 2001. Mollusc/algal chloroplast symbiosis: how can isolated chloroplasts continue to function for months in the cytosol of a sea slug in the absence of an algal nucleus?. Zoology, 104: 303-312.

Rumpho, M., E. Summer, J. Manhart. 2000. Solar-powered sea slugs. Mollusc/algal chloroplast symbiosis. Plant Physiology, 123/1: 29-38.

Rumpho, M., J. Worful, J. Lee, M. Tyler, D. Bhattacharya, A. Moustafa, J. Manhart. 2008. Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica. PNAS, 105/46: 17867-17871.

Schmitt, V., N. Anthes, N. Michiels. 2007. Mating behaviour in the sea slug Elysia timida (Opisthobranchia, Sacoglossa): hypodermic injection, sperm transfer and balanced reciprocity. Frontiers in Zoology, 4/17: 1-9.

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