The adult S. carcini is extremely reduced. Because the female consists, literally, of only its root-system of tendrils which allow it to draw nutrients and influence its host and the external reproductive sac, S. carcini lacks any real sensory perception. However, they aer able to locate a host through chemical perception. Adult males have enough sensory perception to presumably allow it to find a female.
Communication Channels: tactile ; chemical
Perception Channels: tactile ; chemical
Because S. carcini is an internal crab parasite, its only predators are animals that predate on crabs.
Sacculina carcini differs greatly from other barnacles. While the larval form is typical of the barnacle cypris larvae, the adult form is extremely reduced. At first, the female adult form resembles a microscopic slug, but as it parasitizes the crab, it grows tendrils that allow S. carcini to obtain nutrients from the crab's tissues. As it develops, it becomes more of an ovoid sack hanging off the parasitized crab, essentially nothing but a mass of reproductive tissue enclosed in chitinous armor. The male S. carcini is extremely small and serves only to fertilize the female's eggs.
Range mass: <1 (low) g.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; radial symmetry
Sexual Dimorphism: female larger; sexes shaped differently
The lifespan of S. carcini is host-dependent, as its life-span matches that of the host. In many crabs this is 1-2 years.
Sacculina carcini lives in a marine environment. During the brief larval period, S. carcini is pelagic, but as an adult, it lives as a parasite within a crab. The crabs that S. carcini prefers to parasitize live in coastal waters with mud, rock, or sand substrates.
Range depth: 200 to 0 m.
Habitat Regions: saltwater or marine
Aquatic Biomes: pelagic ; benthic ; coastal
Other Habitat Features: estuarine
Sacculina carcini is a parasitic species, so its geographic range follows its host. Carcinus maenas, the green crab, is a major host. The green crab is considered a highly invasive species, so it is not clear where S. carcini's actual range is. Carcinus maenas has a native range of the upper European/North African coast, though it has since spread to most of the major coasts, including the United States' New England coast area, the western U.S. coast, some areas at the southern coast of South America, the southern coast of Africa, and the southeast coast of Australia. In addition, S. carcini is being introduced in areas to control C. maenas, so it is possible that the parasite extends to some of the crab's invasive range.
Biogeographic Regions: nearctic (Introduced ); palearctic (Native ); ethiopian (Introduced ); australian (Introduced ); atlantic ocean (Native ); pacific ocean (Introduced )
Sacculina carcini is entirely parasitic, relying on its host for nutrition. Its host secretes nutrients, which it absorbs.
Animal Foods: body fluids
Primary Diet: carnivore (Eats body fluids)
Sacculina carcini is a parasite on a wide variety of crab species, and causes decreased fertility in infected crabs. Since Carcinus maenas is a primary host, S. carcini works to somewhat control the green crab population. Currently S. carcini is being considered whether it is an effective invasive species regulatory control. In some populations, S. carcini can render up 50% of the crab population infertile, so in theory, S. carcini can have an important effect on the ecosystem balance.
Ecosystem Impact: parasite
Species Used as Host:
Sacculina carcini has been considered as a means of controlling invasive crab species, but due to low host specificity it also seems to damage non-invasive crab populations. As such, it is not yet known whether or not S. carcini will be an appropriate invasive species control.
Positive Impacts: controls pest population
Sacculina carcini causes economic damage to humans by decreasing the viability of crabs harvested for human consumption. Crabs infected with S. carcini cease molting, and so do not grow to a suitable size for eating. Carcinus maenas in particular is considered to be of gastronomic importance, and is frequently eaten in many European countries.
Negative Impacts: causes or carries domestic animal disease
The life cycle of S. carcini begins with a nauplius larvae being emitted from the mantle cavity of the host. The free-living nauplius larvae molts several times over five or six days, and then enters the cypris stage. Three days into the cypris stage, S. carcini attaches to its host's antenna. From there, it sheds its abdomen and thorax, and enters the crab as a mass of embryonic cells through its antennae. At this point, the mass of cells migrates to the mid-gut of the crab just below the heart and extends tendrils to secure itself and obtain nutrition.
Several weeks after it enters its host, Sacculina carcini extends a small knob through the abdomen of its host called an externa. This knob is where the male S. carcini enters the female.
Development - Life Cycle: neotenic/paedomorphic; metamorphosis
Sacculina carcini does not have any conservation status.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
The female S. carcini extends a small knob to the outside of a crab, through which a microscopic male larvae enters. Typically, a female S. carcini has two males which live off of it and constantly fertilizes it. The female then produces hundreds of eggs a day, which incubate in the abdomen of the host.
Mating System: polyandrous
A Sacculina carcini female is fertilized by microscopic males which live within it. The female releases fertilized eggs into the abdominal cavity of the host, where the eggs are incubated and develop into free-living larvae. About 6 weeks after finding a host, the young are capable of reproducing.
Breeding season: On Carcinus maenas June or July to September, on Portunus holsatus the breeding season is short and in the early spring
Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (Internal ); oviparous
While a female S. carcini provides no parental care, the hosts provide an efficient means of distribution for larvae. The behavior of both male and female infected crabs is modified so that they treat the externa from S. carcini like their own eggs. Infected crabs climb to high places with fast currents and disperse larval parasites like they would their own eggs, thus continuing the cycle of infection. At this point, the free-swimming S. carcini larvae are entirely independent.
Parental Investment: pre-hatching/birth
Sacculina carcini, the crab hacker barnacle,[2] is a species of parasitic barnacle in the family Sacculinidae, in particular a parasitic castrator, of crabs. The crab that most often is used as a host is the green crab, the natural range of which is the coasts of Western Europe and North Africa.[2] It can be found attached to the crab's abdomen and affect consumption rates by humans.[3]
The Sacculina carcini differ greatly between males and females. The female barnacles look like small slugs between entering the crab and infecting it. Once they have infected their host, they begin to develop and grow tendrils.[3] This allows them to get the nutrients that it needs from their host. Over time, it can be seen hanging off the crab's abdomen filled with reproductive tissue. The male parasites are much smaller and serve only to help the female Sacculina carcini reproduce.[3]
Sacculina carcini is a monoxenic parasite of crabs, most commonly the green crab (Carcinus maenas). They have also been found to infect the Carcinus aesturarii, Liocarcinus depurator (Harbour crab), Pirimela denticulata, Necora puber (Velvet crab), and the Liocarcinus holsatus (Flying crab).[2][3] The parasite's range largely coincides with that of this host, which is usually the coasts of Western Europe and North Africa. The green crab, however, has been expanding its range and has become established in both North and South America, Southern Africa and Australia, so it is possible that the parasite is now present outside its natural territory.[3] These crabs all live in shallow water over sandy, rocky, or muddy substrates.[2]
A female Sacculina carcini larva settles on a suitable crab host and crawls across its surface until it finds a suitable spot such as the base of a seta (bristle). It then develops into a form called a kentrogon, which inserts a stylet into the crab and pushes its way inside. In order to do this, she has to shed her outer hard shell first.[4] From there it moves through the inside of the crab, in due course pushing out a sac, known as an externa, on the underside of the crab's abdomen. The part remaining inside, the interna, develops tendrils which spread throughout the crab. They take over the stomach, intestines, and nervous system to absorb nourishment and enable the parasite to control the behavior of its host.[5][6]
The presence of the parasite inhibits the development of the crab's gonads, which eventually atrophy; it also prevents the crab from molting, consequently preventing it from regenerating lost limbs. The parasite causes a male crab to develop certain feminine characteristics including the broadening of its abdomen,[7] while in females, the abdomen becomes narrower and the pleopods degenerate. The eggs of the parasite develop in the externa and both male and female crabs carry these eggs around, secured under their abdomen, in the way that female crabs normally care for their own brood (but males never do). If the parasite is experimentally removed from the host, female crabs will usually regenerate their ovaries, but in males, sex change takes place and they develop ovarian tissue.[6]
The eggs inside the externa are fertilized by male larvae which enter the sac through a pore. These males are tiny, never become adults and soon die. However, the female, including the externa, can live for as long as the crab host survives, perhaps one or two years.[4] Hundreds of eggs are produced every day and remain in the sac for about six weeks. When the parasite eggs are ready for release, the crab will climb onto a rock, bob about to release them and waft them on their way.[4] The cycle then continues with each generation.
The Sacculina carcini is known to control the population size of their hosts, like the Green crab, by making many of them infertile. Without reproduction, the population cannot expand and can cause a shortage for human consumption. The parasite can also cause their hosts to stop molting once infected. This can cause the crab to stop growing before it reaches a size big enough for human consumption.[3]
Sacculina carcini, the crab hacker barnacle, is a species of parasitic barnacle in the family Sacculinidae, in particular a parasitic castrator, of crabs. The crab that most often is used as a host is the green crab, the natural range of which is the coasts of Western Europe and North Africa. It can be found attached to the crab's abdomen and affect consumption rates by humans.
