Animal Diversity Web

Ge­o­graphic Range

The Cal­i­for­nia sea hare, Aplysia cal­i­for­nica, is found along the Cal­i­for­nia coast from Hum­boldt Bay in north­ern Cal­i­for­nia to the Gulf of Cal­i­for­nia, Baja Cal­i­for­nia, Mex­ico. (An­geloni, et al., 2003)

• Biogeographic Regions
• pacific ocean
  • native

Habi­tat

Aplysia cal­i­for­nica is in great­est abun­dance within shel­tered rocky shore coastal en­vi­ron­ments. Dis­tri­b­u­tion by depth de­pends on the spec­i­men’s age. Ju­ve­niles oc­cupy deeper wa­ters (up to 18 me­ters) whereas adults pri­mar­ily pre­fer shal­low water within the mid­dle and lower in­ter­tidal zones. ("Cal­i­for­nia Brown Sea Hare", 2014)

• Habitat Regions
• temperate
• saltwater or marine

• Aquatic Biomes
• benthic
• coastal

• Other Habitat Features
• intertidal or littoral

• Range depth

  18 (high) m

  59.06 (high) ft

Phys­i­cal De­scrip­tion

Aplysia cal­i­for­nica is a large mol­lusk, ca­pa­ble of grow­ing as long as 40 cm and weigh­ing as much as 2.3 kg; how­ever, most av­er­age 20 cm long and 1 kg in weight. Body col­oration is cryp­tic, and gen­er­ally ranges from red­dish-brown to green­ish-brown. Col­oration of A. cal­i­for­nica de­pends largely on the par­tic­u­lar species of algae fed upon by an in­di­vid­ual. The over­all body tex­ture is del­i­cately fleshy. The head re­gion bears four ten­ta­cles. Two are on the top of the head be­hind the eyes as well as two in front of the face slightly above the mouth. The species' nick­name (sea hare) is due to these ten­ta­cles which re­sem­ble rab­bit ears. On the dor­sum of the bi­lat­er­ally sym­met­ri­cal body are two wing-like folds called para­po­dia which cover the gills but allow water to pass through. As a type of large sea slug, A. cal­i­for­nica lacks a hard cal­ci­fied outer shell. How­ever, it does pos­sess a flat in­ter­nal shell which en­cases the in­ter­nal or­gans in­clud­ing the heart. On the un­der­side of the body is a large mus­cu­lar foot used for lo­co­mo­tion. ("Cal­i­for­nia Brown Sea Hare", 2014; "The Rosen­stiel School Of Ma­rine and At­mos­pheric Sci­ence", 2009)

• Other Physical Features
• ectothermic
• bilateral symmetry
• poisonous

• Sexual Dimorphism
• sexes alike

• Range mass

  2.3 (high) kg

  5.07 (high) lb

• Average mass

  1 kg

  2.20 lb

• Range length

  40 (high) cm

  15.75 (high) in

• Average length

  20 cm

  7.87 in

De­vel­op­ment

Aplysia cal­i­for­nica rapidly de­vel­ops over the course of a year. After lar­vae hatch from egg masses, each free-swim­ming mi­croor­gan­ism is known as a tro­chophore larva. These lar­vae swim with hair-like cilia. The lar­vae drift for 34 days or more until they set­tle on red algae and un­dergo meta­mor­pho­sis into the adult form. After meta­mor­pho­sis, the feed­ing ju­ve­niles rapidly grow in weight for three months. After 120 days, ju­ve­niles may be­come sex­u­ally ma­ture. (An­geloni, et al., 2003; "Cal­i­for­nia Brown Sea Hare", 2014; Paw­lik, 1989)

• Development - Life Cycle
• metamorphosis

Re­pro­duc­tion

Aplysia cal­i­for­nica is her­maph­ro­ditic, mean­ing each an­i­mal has both fe­male and male sex or­gans. Sea hares mate promis­cu­ously in mul­ti­ple events with con­specifics, when in­di­vid­u­als lo­cate each other through chem­i­cal cues, con­gre­gate, and form a “daisy chain”. Dur­ing a daisy chain, sev­eral sea hares line up and each an­i­mal may be ei­ther re­ceiv­ing or de­liv­er­ing sperm (or both) based on their cur­rent sex and po­si­tion within the chain. Mat­ing sea­son oc­curs dur­ing spring and sum­mer. ("The Rosen­stiel School Of Ma­rine and At­mos­pheric Sci­ence", 2009)

• Mating System
• polygynandrous (promiscuous)

The eggs are fer­til­ized within a sperm stor­age cav­ity also known as the sem­i­nal re­cep­ta­cle be­fore they are laid in bright pink, long gelati­nous strings. These noo­dle-like egg masses may hold mil­lions of em­bryos. Eggs usu­ally hatch after ap­prox­i­mately twelve days, re­leas­ing plank­tonic lar­vae. Mat­ing oc­curs dur­ing spring and sum­mer. Egg lay­ing is ini­ti­ated by cop­u­la­tion. ("The Rosen­stiel School Of Ma­rine and At­mos­pheric Sci­ence", 2009)

• Key Reproductive Features
• semelparous
• seasonal breeding
• simultaneous hermaphrodite
• sexual
• induced ovulation
• fertilization
  • internal
• oviparous

• Breeding interval

  Aplysia californica mates once a year.

• Breeding season

  Mating takes place during spring and summer.

• Range number of offspring

  80 million (high)

• Range gestation period

  10 to 12 days

• Average age at sexual or reproductive maturity (female)

  1 years

• Average age at sexual or reproductive maturity (male)

  1 years

After an in­di­vid­ual A. cal­i­for­nica lays its egg mass, which likely con­tains pro­vi­sion­ing, there is no fur­ther in­vest­ment in the off­spring. ("The Rosen­stiel School Of Ma­rine and At­mos­pheric Sci­ence", 2009)

• Parental Investment
• pre-hatching/birth
  • provisioning

Lifes­pan/Longevity

Sea hares’ lifes­pans are usu­ally fairly short as they typ­i­cally live only a year. Most sea hares per­ish after re­pro­duc­tion. How­ever, be­cause water tem­per­a­tures delay re­pro­duc­tion, cooler wa­ters can some­what lengthen lifes­pan. ("Cal­i­for­nia Brown Sea Hare", 2014)

• Average lifespan
  Status: wild

  1 years

• Average lifespan
  Status: captivity

  1 years

Be­hav­ior

One of the more no­table be­hav­ioral as­pects no­ticed in sea hares is their abil­ity to re­lease a deep pur­ple ink from within the para­po­dia when threat­ened. The deep pur­ple color is de­rived from pig­ments within the red algae in their diet. The ink has been shown to be dis­taste­ful and acts as a de­fense mech­a­nism to ward off preda­tors. In order to avoid being at­tacked, sea slugs are mainly ac­tive at night. Sea hares give a cau­tion­ary avoid­ance re­sponse when in con­tact with cer­tain sea stars and preda­ceous opistho­branchs. This re­sponse con­sists of with­draw­ing the head rapidly and en­gag­ing in an es­cape re­sponse. (An­geloni, et al., 2003; "Opistho­branch par­a­sites - the cope­pod Is­maila", 2010; Nusnbaum and Derby, 2010)

• Key Behaviors
• nocturnal
• motile
• sedentary
• solitary

• Average territory size

  unknown cm^2

Home Range

Aplysia cal­i­for­nica has no spe­cific home range.

Com­mu­ni­ca­tion and Per­cep­tion

Sea hares con­gre­gate to mate, and thus they per­ceive con­specifics via tac­tile and chem­i­cal cues. These slugs have pho­tore­cep­tors that de­tect vari­ances in the in­ten­sity of white light. How­ever, they are less able to iden­tify red wave­lengths. Over­all, sea slugs re­spond more to chem­i­cal changes in sea­wa­ter. A sens­ing struc­ture lo­cated near the gills called the os­phra­dium de­tects dis­solved chem­i­cals and is the major organ of ol­fac­tion. (An­geloni, et al., 2003)

• Communication Channels
• visual
• tactile
• chemical

• Other Communication Modes
• pheromones

• Perception Channels
• visual
• tactile
• chemical

Food Habits

Aplysia cal­i­for­nica is a her­bi­vore and pri­mar­ily feeds on sev­eral kinds of red algae (Lau­ren­cia paci­fica, Plo­camium paci­fi­cum and Ce­ramium spp.) as well as sea let­tuce (Ulva spp.) and eel­grass (Zostera ma­rina) from within tide­pools in the mid­dle in­ter­tidal zone. Aplysia uses its toothed radula to graze at­tached algae. After the ma­te­r­ial has been tem­porar­ily stored in the esoph­a­gus, it is then passed through a mus­cu­lar stom­ach lined with pyra­mi­dal teeth which fur­ther grind up the food mat­ter. The food is then mixed with var­i­ous di­ges­tive flu­ids and wastes are ex­creted out the anus lo­cated near the para­po­dia. The lar­vae ob­tain nour­ish­ment by con­sum­ing phy­to­plank­ton. (An­geloni, et al., 2003; Win­kler and Daw­son, 1963)

• Primary Diet
• herbivore
  • algivore

• Plant Foods
• algae
• macroalgae
• phytoplankton

Pre­da­tion

Due to their lack of an outer cal­care­ous shell, sea hares uti­lize cryp­tic col­oration, noc­tur­nal be­hav­iors, and ink re­lease as de­fense mech­a­nisms. Sea hares are also dis­taste­ful to many preda­tors due to chem­i­cals known as sec­ondary metabo­lites which they cre­ate from chem­i­cals ob­tained from their algal diet. This chem­i­cal adap­ta­tion also makes sea hare tis­sue some­what toxic to cer­tain an­i­mals and fairly ef­fec­tive against most preda­tors. It has been dis­cov­ered that the mucus cov­er­ing the man­tle also acts a de­ter­rent against preda­tory crus­taceans and some fish. Two of the main preda­tors are the giant green sea anemone, An­thro­pleura xan­thogram­mica, and the ophis­to­branch slug, Na­vanax in­er­mis. (An­geloni, et al., 2003; "Opistho­branch par­a­sites - the cope­pod Is­maila", 2010)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • green sea anemone, Anthropleura xanthogrammica
  • sea slug, Navanax inermis

Ecosys­tem Roles

Aplysia cal­i­for­nica is a pri­mary con­sumer due to its her­biv­o­rous diet of algae. As such, it is a key or­gan­ism in the in­ter­tidal ecosys­tem, af­fect­ing the den­sity and abun­dance of its algal prey. There is lit­tle spe­cific in­for­ma­tion on par­a­sitic sym­bio­sis in A. cal­i­for­nica, other than one re­port of a mi­crosporid­ian pro­to­zoan in­fect­ing the nu­clei of its neu­rons. Other shell-less opistho­branchs are known to serve as hosts for cer­tain cope­pods in the fam­ily Splanch­notrophi­dae. ("Opistho­branch par­a­sites - the cope­pod Is­maila", 2010; Krauhs, et al., 1979)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Aplysia cal­i­for­nica is a highly valu­able lab­o­ra­tory an­i­mal es­pe­cially in the field of neu­ro­bi­ol­ogy and more specif­i­cally in study­ing mem­ory and learn­ing be­hav­iors. Sea hares pos­sess the largest neu­rons in the an­i­mal king­dom, as well as very few of them, so it is fea­si­ble to iden­tify the spe­cific nerve cells re­spon­si­ble for spe­cific mech­a­nisms. ("Cal­i­for­nia Brown Sea Hare", 2014)

• Positive Impacts
• research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known ad­verse ef­fects of Aplysia cal­i­for­nica on hu­mans.

Con­ser­va­tion Sta­tus

Al­though there is no cur­rent man­age­ment or con­ser­va­tion plan for this species, in­di­vid­u­als are pro­tected if they occur within the bound­aries of ma­rine pro­tected areas.

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Other Com­ments

The pur­ple ink re­leased by these an­i­mals smells pleas­antly of cedar (P. De­twiler, pers. comm.).

Con­trib­u­tors

Saman­tha Dice (au­thor), San Diego Mesa Col­lege, Paul De­twiler (ed­i­tor), San Diego Mesa Col­lege, An­gela Miner (ed­i­tor), An­i­mal Di­ver­sity Web Staff.

Ref­er­ences

Aquar­ium of the Pa­cific. 2014. "Cal­i­for­nia Brown Sea Hare" (On-line). Aquar­ium of the Pa­cific. Ac­cessed Feb­ru­ary 17, 2014 at http://​www.​aquariumofpacific.​org/​onlinelearningcenter/​species/​california_​brown_​sea_​hare.

Aus­tralian Mu­seum. 2010. "Opistho­branch par­a­sites - the cope­pod Is­maila" (On-line). The Sea Slug Forum. Ac­cessed May 09, 2014 at http://​www.​seaslugforum.​net/​find/​ismaila.

Uni­ver­sty of Miami. 2009. "The Rosen­stiel School Of Ma­rine and At­mos­pheric Sci­ence" (On-line). The Na­tional Re­source for Aplysia. Ac­cessed April 01, 2014 at https://​cc1.​rsmas.​miami.​edu/​slugs/​.

An­geloni, L., J. Brad­bury, R. Bur­ton. 2003. Mul­ti­ple mat­ing, pa­ter­nity, and body size in a si­mul­ta­ne­ous her­maph­ro­dite, Aplysia cal­i­for­nica. Be­hav­ior Ecol­ogy, 14/4: 554-560.

Au­de­sirk, T. 1979. A field study of growth and re­pro­duc­tion in Aplysia cal­i­for­nica. The Bi­o­log­i­cal Bul­letin, 157/3: 407-421. Ac­cessed Feb­ru­ary 18, 2014 at http://​www.​biolbull.​org/​content/​157/​3/​407.​full.​pdf.

Krauhs, J., J. Long, P. Baur. 1979. Spores of a New Mi­crospori­dan Species Par­a­sitiz­ing Mol­lus­can Neu­rons. The Jour­nal of Pro­to­zo­ol­ogy, 26/1: 43-46.

Macgini­tie, G. 1934. "The egg lay­ing ac­tiv­i­ties of the sea hare Tethys cal­i­for­ni­cus" (On-line). Ac­cessed Feb­ru­ary 16, 2014 at http://​www.​biolbull.​org/​content/​67/​2/​300.​full.​pdf.

Mor­ris, R., D. Ab­bott, H. Eu­gene, R. Bee­man, G. Williams. 1980. In­ter­tidal In­ver­te­brates of Cal­i­for­nia. Stan­ford, CA: Stan­ford Uni­ver­sity Press.

Nusnbaum, M., C. Derby. 2010. Ef­fects of Sea Hare Ink Se­cre­tion and Its Es­capin-Gen­er­ated Com­po­nents on a Va­ri­ety of Preda­tory Fishes. The Bi­o­log­i­cal Bul­letin, 218: 282-292. Ac­cessed Feb­ru­ary 17, 2014 at http://​www.​biolbull.​org/​content/​218/​3/​282.​full.​pdf+html.

Paw­lik, J. 1989. Lar­vae of the sea hare Aplysia cal­i­for­nica set­tle and meta­mor­phose on an as­sort­ment of macroal­gal species. Ma­rine Ecol­ogy Progress Se­ries, 51: 195-199. Ac­cessed Feb­ru­ary 17, 2014 at http://​people.​uncw.​edu/​pawlikj/​1989MEPSPaw.​pdf.

Win­kler, L., E. Daw­son. 1963. Ob­ser­va­tions and Ex­per­i­ments on the Food Habits of Cal­i­for­nia Sea Hares of the Genus Aplysia. Pa­cific Sci­ence, 17: 102-105. Ac­cessed Feb­ru­ary 17, 2014 at http://​scholarspace.​manoa.​hawaii.​edu/​bitstream/​handle/​10125/​4930/​vol17n1-102-105.​pdf?​sequence=1.