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How do we know how long hermit crabs live in the wild?

How do we know how long hermit crabs live in the wild?


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This article states that hermit crabs in the wild are extremely difficult to track because they constantly change shells and even gender. Later in the article, they say that hermit crabs can live 4 decades in the wild. How can they know this if they can't follow a single crab for an extended period of time?


Hermit crabs increase in size over time and this is used to provide a minimum estimate for their age1.

You may also find this article interesting.


Reference:

SantAnna, Bruno Sampaio, Christofoletti, Ronaldo Adriano, Zangrande, Cilene Mariane, & Reigada, Alvaro Luis Diogo. (2008). Growth of the hermit crab Clibanarius vittatus (Bosc, 1802) (Crustacea, Anomura, Diogenidae) at São Vicente, São Paulo, Brazil. Brazilian Archives of Biology and Technology, 51(3), 547-550. https://dx.doi.org/10.1590/S1516-89132008000300014


Hermit crab

Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. [1] [2] [3] There are over 800 species of hermit crab, most of which possess an asymmetric abdomen concealed by a snug-fitting shell. Hermit crabs' non-calcified abdominal exoskeleton makes their exogenous shelter system obligatory. Hermit crabs must occupy shelter produced by other organisms, or risk being defenseless.

The strong association between hermit crabs and their shelters has significantly influenced their biology. Almost 800 species carry mobile shelters (most often calcified snail shells) this protective mobility contributes to the diversity and multitude of crustaceans found in almost all marine environments. In most species, development involves metamorphosis from symmetric, free-swimming larvae to morphologically asymmetric, benthic-dwelling, shell-seeking crabs. Such physiological and behavioral extremes facilitate a transition to a sheltered lifestyle, revealing the extensive evolutionary lengths that led to their superfamily success.


Plastic pollution has killed half a million hermit crabs, study says

The researchers said piles of plastic on beaches create physical barriers and "deadly traps" for the crabs.

The study looked at strawberry hermit crab populations on two remote tropical island locations.

The scientists say more research is needed into how plastic pollution is affecting wildlife populations worldwide, especially on land.

"The potential for plastics on beaches and in other terrestrial ecosystems to cause harm is under-acknowledged," said co-author Alex Bond, a senior curator in the department of life sciences at the Natural History Museum in London.

He says plastic in the ocean entangles and is ingested by wildlife, but on land it acts as a trap and a barrier to species going about their daily lives.

The researchers surveyed sites on the Cocos (Keeling) Islands in the Indian Ocean and Henderson Island in the South Pacific. They say both locations are littered with millions of pieces of plastic.

They say crabs had crawled into plastic containers and were unable to get out, eventually dying. The containers had openings that allowed the crabs to enter, but were positioned with the opening facing an upward angle, so that the crabs would have difficulty crawling back out.

The researchers counted how many hazardous containers there were and how many contained trapped crabs, and extrapolated their findings to estimate totals for the islands.

"These results are shocking but perhaps not surprising," said lead researcher Jennifer Lavers from the institute for marine and Antarctic studies at the University of Tasmania in Australia.

"It is inevitable that these creatures will interact with and be affected by plastic pollution," she said.

The problem is worsened by the fact that hermit crabs don't have a shell of their own. As they grow, they need to move into larger shells. When one crab dies, it emits a smell that tells another crab a new shell is available.

Meaning, "the very mechanism that evolved to ensure hermit crabs could replace their shells, has resulted in a lethal lure," according to the paper.

In one container, researchers found 526 hermit crabs. They also found containers with both dead and living crabs, the latter presumably drawn in by the former.

The authors say hermit crabs play an important role in the ecosystem. They fertilise and aerate soil, and disperse seeds. They also play a role in tourism - an important source of employment on the islands - by giving visitors a chance to observe native wildlife.

Though the study was conducted on remote islands, Mr Bond says plastic pollution is global, and that this is likely to be an issue anywhere hermit crabs live alongside debris.


Animal Diversity Web

Coconut crabs are terrestrial hermit crabs found widely throughout the tropical western Indo-Pacific Ocean, from Mauritius and the Aldabras Islands in the Indian Ocean to the Pitcairns, Tuamatus, and Easter Island in the Pacific Ocean, as well as on Madagascar and the Seychelles. There are also populations found in Tanzania. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993 McLaughlin, 2013 Morris, et al., 1988)

Habitat

Coconut crabs are found in coastal habitats on marine islands, or small islets near larger, continental islands, as much as 6 km from shore. They create burrows in the substrate, which provide protection and allow for food storage. These crabs may bury themselves completely in the soil while molting. Adult coconut crabs are primarily terrestrial eggs are released into the sea, where larval development occurs. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Eldredge, 1996 Lavery, et al., 1995)

Physical Description

Coconut crabs are the largest terrestrial arthropods known, with a maximum carapace length of 200 mm (up to 1 m from leg tip to leg tip) and a maximum weight of 4 kg. Coconut crabs are hermit crabs, and juveniles use mollusk shells for protection until they grow too large for available shells. When an individual reaches this size, its abdomen partially tucks under its body and is protected by a series of hardened tergal plates. The remainder of the abdomen is covered with a leathery skin that has tufts of small bristles. Body color is variable, depending on the population and location most coconut crabs are deep blue in color, though some may have red tinges or be predominantly red or purplish-red. Like many other species of crabs, coconut crabs have asymmetrical chelae, with the left larger than the right. Additionally, they have two pairs of long periopods (walking legs) with pointed dacytls, which allow them to grip tree bark and other surfaces. They also possess a smaller pair of appendages with small claws females use these to tend to their eggs, while males use them in sperm transfer during mating. Coconut crabs exhibit sexual dimorphism males are larger than females (average carapace lengths of 75 mm and 50 mm, respectively) and females have three large, feathery pleopods located ventrally on their abdomens, used to carry egg masses. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993 Greenaway, 2003 Grubb, 1971 Lavery, et al., 1995 Wells, et al., 1984)

Coconut crabs have only vesitgal gills, which do not aid in oxygen intake instead, they have lungs that they use for gas exchange. Their lungs are located in the thoracic region, and are comprised of the inner lining of the gill chamber, which is well vascularised, with a thin ephithelium and large surface area. (Fletcher, 1993 Morris, et al., 1988)

  • Other Physical Features
  • ectothermic
  • Sexual Dimorphism
  • male larger
  • sexes shaped differently
  • Range mass 4 (high) kg 8.81 (high) lb
  • Range length 50 to 200 mm 1.97 to 7.87 in

Development

Eggs are carried on a female's pleopods until hatching. Egg maturation lasts 25-29 days, depending on tidal rhythms (developmental periods as long as 45 days have been recorded) these crabs time larval release to align with high tides. When embryos are mature, a gravid female moves from land to shallow intertidal water and releases her eggs by shaking them into the water. Upon making contact with the water, eggs hatch and larvae are released. Larvae undergo four or five zoeal stages, which last approximately 17-28 days total. Each stage requires a different amount of time: stage 1 lasts 5-6 days, stage 2 lasts 3-5 days, stage 3 lasts 3-18 days, and stage 4 lasts 6-12 days. Not much is known about the fifth larval stage. This larval period is followed by a glaucothoe (amphibious) stage, which lasts 21-28 days. Glaucothoes typically move into an empty gastropod shell before migrating onto land survival is highly unlikely otherwise. Upon reaching land, glaucothoes burrow into substrate and undergo metamorphosis into juveniles after 3-4 weeks. During this time they develop highly vascularized lungs. Juveniles continue to use gastropod shells for protection until developing protective tergal plates. There have been reports of crabs as large as 11.3 mm (carapace length) still utilizing shells, but also crabs as small as 8.4 mm (carapace length) without. Young crabs undergo a series of molts during which they increase in size but do not experience changes in overall morphology. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993 Greenaway, 2003 Morris, et al., 1988 Reese and Kinzie III, 1968)

Reproduction

Mating occurs on land, with neither individual needing to have recently molted. No significant courtship behavior has been observed for this species, unlike most hermit crabs. During mating, a male crab holds a female’s chelae with his and pushes her onto her back, with her abdomen flush to the ground. He transfers his spermatophore to her gonopore, located near the base of her walking legs, and sperm enters her spermatotheca. Ova are fertilized internally and pass out of her body onto her pleopods in an egg mass or egg ”sponge", containing tens of thousands of fertilized eggs which are orange in color. A female carrying eggs is known as berried or gravid. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993 Greenaway, 2003 Schiller, et al., 1991)

Females produce 50,000-138,000 embryos per spawn. Release of the eggs and hatching takes place in the evening and is thought to be tied to lunar and tidal rhythms. Females have been observed releasing eggs when tides are highest, within a few days after the new moon or full moon, allowing for the greatest number of larvae to be pulled away from shore and into the open ocean, where they will have the most food resources and lowest predation risk. Gravid females have been observed most often during summer months, with individuals previously observed as gravid no longer carrying eggs by October. On Christmas Island, spawning peaks coincide with peaks in the rainy season. Size at sexual maturity seems to vary by population, with median sizes ranging from 27 to 42.5 mm (total length). ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993 Greenaway, 2003 Schiller, et al., 1991)

  • Key Reproductive Features
  • iteroparous
  • seasonal breeding
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • fertilization
    • internal
    • Breeding interval Females likely only reproduce once per breeding season.
    • Breeding season Breeding occurs during summer months.
    • Range number of offspring 51,000 to 138,000
    • Average number of offspring 100,000
    • Range gestation period 25 to 45 days
    • Average age at sexual or reproductive maturity (female) 5 years
    • Average age at sexual or reproductive maturity (male) 5 years

    Females carry developing embryos on their pleopods and care for them, keeping them clean and aerated, until hatching. Males exhibit no parental investment. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993)

    Lifespan/Longevity

    Coconut crabs are long-lived, only reaching their maximum size after 40-60 years. (Greenaway, 2003)

    Behavior

    Coconut crabs are mainly nocturnal, though they may be active during the day as well on islands with high levels of human activity, they are exclusively nocturnal, to avoid predation. They are able to use their long legs to climb trees to find food, climbing to heights of two meters. These crabs do not engage in combat but do appear to have size-based dominance/submission relationships. Individuals are primarily solitary, venturing out of their burrows only to forage or mate. Crabs living on larger islands are nomadic, moving to new burrows frequently, while crabs on smaller islands tend to maintain one burrow. When it comes time to molt, coconut crabs dig burrows which may be up to 1 m long, staying in these burrows for 3-16 weeks larger crabs take longer to complete molting. In preparation for this time, crabs will overfeed and produce greater volumes of haemolymph. When molting is completed, a crab will feed on its shed exoskeleton. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993 Greenaway, 2003 Grubb, 1971)

    • Key Behaviors
    • terricolous
    • nocturnal
    • motile
    • nomadic
    • solitary
    • dominance hierarchies
    • Range territory size 40 to 250 m^2

    Home Range

    Depending on the size of the island, home range can vary from 40 to 250 m^2. (Greenaway, 2003)

    Communication and Perception

    Based on similarities in brain structure and neuropils, it is likely that coconut crabs have visual and mechanosensory abilities similar to those of other decapods. Coconut crabs have fully developed compound eyes on eyestalks. They perceive olfactory cues with their antennules and are able to differentiate between odors, allowing them to locate preferred food sources. The ways in which they process olfactory cues are very similar to those of insects. Bristles located on their claws function in tactile sensation. Communication between crabs is accomplished using visual cues for instance, up-and-down movement of claws and legs is a signal for a smaller crab to stand down when confronted with a larger crab. (Fletcher, 1993 Grubb, 1971 Krieger, et al., 2010 Stensmyr, et al., 2005)

    • Communication Channels
    • visual
    • tactile
    • Perception Channels
    • visual
    • tactile
    • chemical

    Food Habits

    As planktonic larvae, coconut crabs feed on other planktonic organisms. There is no information currently available regarding diet during the glaucothoe stage however, in an experiment studying the effects of enriched diets on the crab’s developmental stages, glaucothoes fed on shrimp and clam meat. Adults are omnivorous scavengers and have been observed feeding on carrion (including other crustaceans such as red crabs ( Gecarcoidea natalis )), molted exoskeletons of other crustaceans, tropical fruits (such as Pandanus fruits, one of their primary food sources in many locations), and coconut meat. These crabs use a variety of methods to obtain meat from a coconut. A crab may carry the coconut up a tree and then drop it, cracking it open by the force of its impact on the ground. Individuals have also been observed using their claws to poke the coconut in a soft spot (through one of the “eyes”), splitting it open. Alternatively, a crab may beat the coconut open using its claws. Coconut crabs will bring large food items back to their burrows to consume and store them. In captivity, coconut crabs are known to eat various types of vegetation, such as lettuce and cabbage, as well as live giant African snails (Achatina fulica), though it is unknown if they would consume these animals in the wild. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Fletcher, 1993)

    • Primary Diet
    • carnivore
      • molluscivore
      • scavenger
      • folivore
      • frugivore
      • Animal Foods
      • carrion
      • mollusks
      • zooplankton
      • Plant Foods
      • leaves
      • fruit
      • phytoplankton
      • Foraging Behavior
      • stores or caches food

      Predation

      The only documented predators of adult coconut crabs are humans. It has been suggested that juveniles and smaller invidiuals may be consumed by mangrove monitor lizards (Varanus indicus), cane toads (Rhinella marina), and feral pigs (Sus scrofa), but this has not been confirmed. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980)

      • Known Predators
        • Cane toads (Rhinella marina)
        • Human (Homo sapiens)
        • Pig (Sus scrofa)
        • Mangrove monitor lizards (Varanus indicus)

        Ecosystem Roles

        The scavenging habits of these crabs assist in the dispersal of coconut seeds, as they may abandon the fruit before returning with it to a burrow to feed. Interspecific competition may exist between coconut crabs and other terrestrial crabs with similar diets, such as Coenobita sp., although competition is typically indirect and, if confronted, a Coenobita crab is likely to withdraw. Although few are known and infections seem to be uncommon, it is possible for coconut crbas to serve as hosts to some parasites. ("Biological studies on the coconut crab (Birgus latro) in the Mariana Islands", 1980 Alexander, 1979 Anderson, 2000 Carson and Wheeler, 1973 McDermott, et al., 2010)

        Economic Importance for Humans: Positive

        Coconut crabs are considered a delicacy in some cultures and are served at weddings or other ceremonies, as well as some restaurants. Many tourists are attracted to the unique experience of seeing and eating coconut crabs. The crabs are not difficult to catch and are an easy source of income for hunters. Their popularity as a food item has necessitated the import of larger crabs to some smaller islands. (Fletcher, 1993 Lavery, et al., 1995)

        Economic Importance for Humans: Negative

        There are no known adverse effects of coconut crabs on humans.

        Conservation Status

        Coconut crabs are currently listed as "data deficient" by the International Union for the Conservation of Nature and Natural Resources. It could be very easy to over harvest these animals, particularly due to their slow growth rate and the ease with which they are caught however, they are not currently considered threatened or endangered by any agency. (Eldredge, 1996)

        • IUCN Red List Data Deficient
        • US Federal List No special status
        • CITES No special status
        • State of Michigan List No special status

        Contributors

        Meaghan Ly (author), The College of New Jersey, Yesenia Werner (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Jeremy Wright (editor), University of Michigan-Ann Arbor.

        Glossary

        living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

        an animal that mainly eats meat

        uses smells or other chemicals to communicate

        the nearshore aquatic habitats near a coast, or shoreline.

        ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

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

        parental care is carried out by females

        union of egg and spermatozoan

        an animal that mainly eats leaves.

        A substance that provides both nutrients and energy to a living thing.

        an animal that mainly eats fruit

        An animal that eats mainly plants or parts of plants.

        fertilization takes place within the female's body

        offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

        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.

        eats mollusks, members of Phylum Mollusca

        having the capacity to move from one place to another.

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

        generally wanders from place to place, usually within a well-defined range.

        islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

        an animal that mainly eats all kinds of things, including plants and animals

        found in the oriental region of the world. In other words, India and southeast Asia.

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

        photosynthetic or plant constituent of plankton mainly unicellular algae. (Compare to zooplankton.)

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

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

        an animal that mainly eats dead animals

        breeding is confined to a particular season

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

        places a food item in a special place to be eaten later. Also called "hoarding"

        uses touch to communicate

        the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

        uses sight to communicate

        animal constituent of plankton mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

        References

        University of Guam, College of Agriculture and Life Sciences. Biological studies on the coconut crab (Birgus latro) in the Mariana Islands. Technical Report 66. Mangilao, Guam: University of Guam. 1980. Accessed August 12, 2013 at http://www.guammarinelab.com/publications/uogmltechrep66.pdf.

        Alexander, H. 1979. A preliminary assessment of the role of the terrestrial decapod crustaceans in the Aldabran ecosystem. Philosophical Transactions of the Royal Society of London: Series B: Biological Science , 286/1011: 241-246. Accessed October 22, 2012 at http://rstb.royalsocietypublishing.org/content/286/1011/241.

        Anderson, R. 2000. Nematode Parasites of Vertebrates: Their Development and Transmission (2nd Edition) . New York, New York: CABI Publishing.

        Carson, H., M. Wheeler. 1973. A new crab fly from Christmas Island, Indian Ocean (Diptera: Drosophilidae). Pacific Insects , 15/2: 199-208. Accessed August 13, 2014 at http://hbs.bishopmuseum.org/pi/pdf/15(2)-199.pdf.

        Eldredge, L. 1996. "Birgus latro" (On-line). International Union for Conservation of Nature and Natural Resources. Accessed August 12, 2013 at http://www.iucnredlist.org/details/2811/0.

        Greenaway, P. 2003. Terrestrial adaptations in the Anomura (Crustacea: Decapoda). Memoirs of Museum Victoria , 60/1: 13-26. Accessed October 21, 2012 at http://136.154.202.7/pages/4017/60_1_greenaway.pdf.

        Grubb, P. 1971. Ecology of terrestrial decapod crustaceans on Aldabra. Philosophical Transactions of the Royal Society of London: Series B, Biological Sciences , 260/836: 411-416. Accessed October 23, 2012 at http://rstb.royalsocietypublishing.org/content/260/836/411.

        Krieger, J., R. Sandeman, D. Sandeman, B. Hansson, S. Harzsch. 2010. Brain architecture of the largest living land arthropod, the giant robber crab Birgus latro (Crustacea, Anomura, Coenobitidae): evidence for a prominent central olfactory pathway?. Frontiers in Zoology , 7/25: 1-31. Accessed October 24, 2012 at http://www.frontiersinzoology.com/content/7/1/25.

        Lavery, S., C. Moritz, D. Fielder. 1995. Changing patterns of population structure and gene flow at different spatial scales in Birgus latro (the coconut crab). Heredity , 74: 531-541. Accessed October 20, 2012 at http://www.nature.com/hdy/journal/v74/n5/pdf/hdy199575a.pdf.

        McDermott, J., J. Williams, C. Boyko. 2010. The unwanted guests of hermits: A global review of the diversity and natural history of hermit crab parasites. Journal of Experimental Marine Biology and Ecology , 394/1-2: 2-44. Accessed August 13, 2014 at http://www.sciencedirect.com/science/article/pii/S0022098110002273.

        McLaughlin, P. 2013. "Birgus latro" (On-line). World Register of Marine Species. Accessed August 12, 2013 at http://www.marinespecies.org/aphia.php?p=taxdetails&id=208668.

        Morris, S., P. Greenaway, B. McMahon. 1988. Adaptations to a terrestrial existence by the robber crab Birgus latro I. An in vitro investigation of blood gas transport. Journal of Experimental Biology , 140: 477-491. Accessed October 20, 2012 at http://jeb.biologists.org/content/140/1/477.full.pdf.

        Reese, E., R. Kinzie III. 1968. The larval development of the coconut or robber crab Birgus latro (L.) in the laboratory (Anomura, Paguridea). Crustaceana Supplement: Studies on Decapod Larval Development , 2: 117-144. Accessed November 14, 2012 at http://www.jstor.org/stable/25027392.

        Schiller, C., D. Fielder, I. Brown, A. Obed. 1991. Reproduction, early life-history and recruitment. Pp. 13-33 in I Brown, D Fielder, eds. The Coconut Crab: aspects of the biology and ecology of Birgus latro in the Republic of Vanuatu . Canberra, Australia: Australian Centre for International Agricultural Research. Accessed October 22, 2012 at http://aciar.gov.au/files/node/10585/mn8_pdf_11379.pdf.

        Stensmyr, M., S. Erland, E. Hallberg, R. Wallén, P. Greenaway, B. Hansson. 2005. Insect-like olfactory adaptations in the terrestrial giant robber crab. Current Biology , 15/2: 116-121. Accessed October 24, 2012 at http://www.sciencedirect.com/science/article/pii/S0960982204010486.

        Wang, F., H. Hseih, C. Chen. 2007. Larval growth of the coconut crab Birgus latro with a discussion on the development mode of terrestrial hermit crabs. Journal of Crustacean Biology , 24/7: 616-625. Accessed October 20, 2012 at http://www.bioone.org/doi/abs/10.1651/S-2797.1?journalCode=crus.

        Wells, S., R. Pyle, N. Collins. 1984. The IUCN Invertebrate Red Data Book . Gland, Switzerland: The International Union for the Conservation of Nature and Natural Resources.


        Research, Policy Development and Permitting

        While crab restoration projects are still in their infancy, research, policy development, and permitting are ongoing.

        In 2007, the Alaska King Crab Research, Rehabilitation and Biology (AKCRRAB) Program was formed to research red and blue king crab restoration possibilities. The AKCRRAB program is a cooperative effort of Alaska Sea Grant, the Alutiiq Pride Shellfish Hatchery, NOAA Fisheries, ADF&G, and the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. The program is guided by a steering committee, while a team of scientists and scientific advisors guide research efforts.

        ADF&G&lsquos role in AKCRRAB is advisory, and most of their focus is on permitting and policy development, which seeks to minimize the risks cultivated crab released into the wild might pose to wild stocks.

        &ldquoThere is a lot of life history information we don&rsquot know yet, so it&rsquos difficult to know the risk,&rdquo said Cynthia Pring-Ham, a fishery biologist with ADF&G. &ldquoRight now, there is nothing in our regulations dealing with invertebrates, so now it&rsquos more appropriate to develop policy, as there are already regulations in place that oversee management of resources.&rdquo

        Factors ADF&G considers when evaluating development or permitting of hatchery operations include the following:

        • Genetic risks, like inbreeding or hybridization
        • Risks from disease
        • Effects cultured releases might have on other species and their habitats
        • What evaluation tools are necessary to assess projects
        • Effects on other fisheries or user groups
        • Public review
        • Harvest management issues (all users &mdash subsistence, personal use, sport fishing, commercial fishing different harvest rates of wild and hatchery stock allocation stock recovery mixed stock issues and common property considerations).

        Care guide: How to look after pet hermit crabs

        Hermit crabs are best kept with their own kind. Introducing a new crab must be done with care because fighting may occur. Living together also ensures they have a wider variety of choices when moving shells. Parent more than one crab to prevent loneliness and improve your crabs’ chances of thriving in their new environment.

        Take your hermit crab out and enjoy time with them every so often. If you have kids, it’s important that everyone becomes familiar with your family pets. An interesting manoeuvre to try is lying on your stomach on the floor and making a circle with your arms for your hermit crabs to move around in.

        Setting up

        The ideal enclosure for your crab is a terrarium with a removable glass lid. It’s recommended to have 20 litres of space for every two crabs. You can find various options and sizes at your local Petbarn.

        Start by filling your tank with a substrate. The comfiest option is marine aquarium coral rock sand or a sand gravel mix. Find both at your local Petbarn. Also include rocks, safe climbing toys, dried choya wood, driftwood, coral and barnacles as these provide stimulating toys for hermit crabs.

        Create a space for your crab to hide and leave an area clear of obstructions for them to exercise in. Make sure food and water bowls are always accessible.

        Hermit crabs need an environment with high humidity to keep moist, which enables them to breathe properly. Purchase a humidity gauge to ensure your tank maintains a humidity level of 70–80%.

        To keep your tank humid, you will need a source of heat and water. You could use an under-tank heater or incandescent lights. If you’re using an under-tank heater make sure your substrate is at least 3cm thick so your hermit crabs aren’t sweating. Mist your tank with non-chlorinated water as needed to keep moisture high. Your tank will need to remain at a temperature of 21–24°C. You can use a thermometer to monitor this.

        Top tip: a natural sponge may help disperse humidity in the aquarium.

        Feeding

        Hermit crabs are omnivorous. Their diet consists of pellet food and veggies and fruits as treats. Find nutritious pellets at your local Petbarn. Make eating easier by crushing a teaspoon of pellets into their bowl or buying pellet powders.

        Mix up your pet’s diet with vegetables and fruits. Chop up kale or broccoli and fruits like apples or bananas. Leave these out overnight and remove any leftovers in the morning.

        Always provide your crabs with access to fresh water. Make sure you use filtered or dechlorinated water for their health.

        Travelling

        When taking your new pets home, set up a temporary tank in a small plastic container and include a substrate. Once established, don’t move your tank with your substrate and hermit crabs inside. This could cause water spillage and your pets’ burrows to collapse, which can be dangerous for them.

        Include holes for ventilation in your substitute tank. If any of your pets are happy in their burrows or shelters when you want to transport them, do not attempt to re-bury them in the substitute tank. Rather, place a bowl or hut over them.

        Grooming

        With the right tools, your crabs will groom themselves. Provide a conditioned freshwater bowl and saltwater bowl for them to bathe in. Put a sea sponge in the bowl so smaller crabs can climb out. Find sea sponges at your local Petbarn.

        Provide multiple shells for your pets to change into. We recommend at least two shells per crab. As they mature, provide bigger shells for them to grow into.

        Hermit crabs generally moult once every 18 months, becoming less active, burrowing more and drinking and eating less. Allowing hermit crabs to snack on their old skins will give them a calcium boost. Provide finely ground coconut fibre-based bedding for reptiles, such as forest bedding, to assist hermit crabs during moulting.

        Health care

        If your pet feels overcrowded, bullied or lonely, has been dropped or is too hot or cold, they may become sluggish, inactive or continue leaving shells due to stress. Provide sufficient space if you’re housing a lot of little crabs.

        Your pets are particularly vulnerable to chemicals, so make sure their tank is clear from any exposure. Only clean your tank with filtered water. If letting your crabs roam around your home, ensure they’re not exposed to chemicals.

        Check your hermit crabs regularly. Decreased appetite, lack of activity, staying outside of shells, excessive moulting, lost or damaged claws or limbs and strong odour from shells are all signs that your crab may be unwell. If you notice any of these signs or anything else peculiar about your crab, visit your local Greencross Vets for treatment.

        Pet safety tips

        If you’re a first-time crab parent try wearing thin gloves when handling your pet. Hold your crab over a bed or couch so if they make any sudden movements and you accidentally drop them they will land on a soft surface. Always supervise kids who are handling hermit crabs.

        Your hermit crabs are extremely sensitive to metal, so ensure any objects in their tank, such as bowls, are ceramic or plastic. Always filter any water exposed to your crabs, just in case. If your crab has been exposed to an unsafe metal, visit your local Greencross Vets for treatment.

        Tip: Hermit crabs are very sensitive to metals. Be sure to use silicon, ceramic or plastic bowls.

        Hermit crab checklist

        Shop Petbarn online or in-store for all your hermit crab needs.


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        Identifying crab species

        Dungeness crab

        One of the most popular items on Washington seafood menus is the Dungeness crab. This hard-shelled crustacean is fished from the Aleutian Islands to Mexico. The shell is purple-tinged, gray or brown on the back and the tips of the claws are typically white. The Dungeness crab can reach 10 inches across the back, though 6 to 7 inches is more common. In Puget Sound this crab is most abundant north of Seattle, in Hood Canal, and near the Pacific coast. The Dungeness crab is frequently associated with eelgrass beds and prefers sandy or muddy substrates.

        Red rock crab

        The red rock crab (aka red crab, rock crab) is similar to -- but smaller than -- the Dungeness. This species usually measures less than 6 inches across the back and is characterized by large claws. Despite being less meaty than the Dungeness, red rock crab meat is also very tasty. It can be distinguished from the Dungeness by the presence of black on the tips of its claws and by its red coloration. The red rock crab also prefers rocky substrates, as the name implies.

        Box crab or king crab

        Two deepwater species that are occasionally seen in Puget Sound and also occur in deep water off the coast are the box crab and its close relative, the king crab. The latter is called the king crab because of its large size when fully grown (up to 10 inches wide) but is not to be confused with the commercial king crab of Alaska. These crabs are more apt to be seen by divers than fishers with pots. Both are covered with wart-like tubercles and spines and resemble a rough box when their legs and claws are folded against the body. The box crab gets its name from the opening or foramen formed from matching semicircular notches in the claws and first walking legs. When the legs are folded tightly, water enters the gill cavity through this round opening. In the king crab this opening is absent.

        Shore crabs

        Several species of tiny shore crabs can be found on Washington beaches. Contrary to what many believe, these are not the young of larger ocean crabs, but are simply small sized species. Under most rocks on Puget Sound shores you can find tiny black or gray hairy shore crabs ranging in size from smaller than a fingertip to about the size of a half-dollar. These are of two species, Hemigrapsus nudus and H. oregonensis.


        Hermit crabs grow ‘extra-long penises to have sex without leaving comfort of shell’

        Hermit crabs may have evolved to have extra-long penises so that they can have sex without fearing the loss of their home.

        According to a new study, crustaceans with valuable shell-homes are more likely to have larger genitals, some of which can grow to 60% of their body length.

        While even those with less precious ‘easily stolen property’ have larger penises than those carrying no property at all.

        In a new paper published in the Royal Society Open Science, Mark Laidre of Dartmouth College studied the ‘rarely explored’ relationship between the homes of creatures and penis size evolution.

        According to the ‘private parts for private property’ hypothesis, hermit crabs are extremely vulnerable when having sex.

        Reproduction requires both crabs to bring their shell openings face-to-face and they must come ‘at least partway’ out of their homes.

        The male then ejaculates into the female’s shell.

        Laidre goes on to predict that ‘enlarged penises evolved to prevent the theft of property during sex’, whereby the male can still participate while staying inside his shell.

        Hermit crabs ‘remodel’ the insides of their shells and without their home, they will dry up and die within 24 hours.

        To test the hypothesis, Laidre measured the penis-to-body ratio of more than 300 hermit crabs from a total of nine different species.

        All measurements were made of preserved museum specimens and no live animals were used.

        Laidre wrote in his paper that he had found the crabs’ relative penis size correlated to the value of their shell.

        ‘Species carrying more valuable, more easily stolen property had significantly larger penis size than species carrying less valuable, less easily stolen property, which, in turn, had larger penis size than species carrying no property at all,’ he said.

        He continued on to add that hermit crabs with longer penises likely evolved the trait to ‘facilitate safe sex,’ allowing them to hang onto their home ‘by extending a long penis outside the shell to copulate.’


        Facts About Horseshoe Crabs and FAQ

        The American horseshoe crab is a common sight on Florida's beaches. Horseshoe crabs are “living fossils” meaning they have existed nearly unchanged for at least 445 million years, well before even dinosaurs existed.

        Horseshoe crabs are not actually crabs at all, they are much more closely related to spiders and other arachnids than they are to crabs or lobsters!

        There are four species of horseshoe crabs still around today. Only one species, Limulus polyphemus, is found in North America along the Atlantic and Gulf coasts from Maine to Mexico. The other three species are found in Southeast Asia.

        Despite existing for hundreds of millions of years, horseshoe crabs are nearly identical to their ancient relatives. This is because their body structure is extremely effective for survival, think, “if it ain’t broke, don’t fix it!”

        Horseshoe crabs have a tank-like structure consisting of a front shell called the prosoma, a back shell called the opisthosoma, and a spike-like tail called a telson. Some people think horseshoe crabs are dangerous animals because they have sharp tails, but they are totally harmless. Really, horseshoe crabs are just clumsy and they use their tail to flip themselves back over if they get overturned by a wave.*

        Though the horseshoe crab's shell is hard, it is very sensitive to the world around it. The crabs are especially sensitive to light. They have 10 eyes, a pair of compound eyes on the prosoma, and "photo receptors" in other areas, primarily along the tail.

        *Never pick up a horseshoe crab by its tail, as it can harm the animal. Instead, gently pick it up by both sides of the prosoma using both hands.

        Horseshoe crabs are known to gather in large nesting aggregations, or groups, on beaches particularly in the mid-Atlantic states such as Delaware, New Jersey and Maryland in the spring and summer, where their populations are largest. Horseshoe crabs can nest year-round in Florida, with peak spawning occurring in the spring and fall.

        When mating, the smaller male crab hooks himself to the top of the larger female’s shell by using his specialized front claws, and together they crawl to the beach. The male fertilizes the eggs as the female lays them in a nest in the sand.

        Some males (called satellite males) do not attach to females but still have success in fertilizing the female's eggs by hanging around the attached pair. Most nesting activity takes place during high tides around the time of a new or full moon.

        Horseshoe crab larvae emerge from their nests several weeks after the eggs are laid. Juvenile horseshoe crabs look a lot like adults except that their tails are smaller. The young and adult horseshoe crabs spend most of their time on the sandy bottoms of inter-tidal flats or zones above the low tide mark and feed on various invertebrates .

        Why are horseshoe crabs important?

        Horseshoe crabs are an important part of the ecology of coastal communities. Their eggs are the major food source for shorebirds migrating north, including the federally-threatened red knot. These shorebirds have evolved to time their migrations to coincide with peak horseshoe crab spawning activity, especially in the Delaware and Chesapeake Bay areas. They use these horseshoe crab beaches as a gas station, to fuel up and continue their journey.

        Many fish species as well as birds feed on horseshoe crab eggs in Florida. Adult horseshoes serve as prey for sea turtles, alligators, horse conchs, and sharks.

        Horseshoe crabs are also extremely important to the biomedical industry because their unique, copper-based blue blood contains a substance called "Limulus Amebocyte Lysate", or "LAL".

        This compound coagulates or clumps up in the presence of small amounts of bacterial toxins and is used to test for sterility of medical equipment and virtually all injectable drugs. That way, when you get a vaccine you know it hasn’t been contaminated by any bacteria. Anyone who has had an injection, vaccination, or surgery has benefited from horseshoe crabs! Additionally, research on the amazing and complex compound eyes of horseshoe crabs has led to a better understanding of human vision.

        Horseshoe crabs are also used in several fisheries. The marine life fishery collects live horseshoe crabs for resale as pets in aquariums, research subjects, or as educational specimens, and both the American eel and whelk fisheries use horseshoe crabs as bait along many parts of the Atlantic coast.

        Threats to horseshoe crabs and research efforts
        Horseshoe crab numbers are declining throughout much of their range. In 1998, The Atlantic States Marine Fisheries Commission developed a Horseshoe Crab Fishery Management Plan that requires all Atlantic coastal states to identify horseshoe crab nesting beaches. Currently, with the help of the public, biologists at the Fish and Wildlife Research Institute are documenting nesting sites of horseshoe crabs throughout the state. If you see horseshoe crabs mating and would like to report a sighting, please visit the Report Sightings page for more information.


        Should you really only eat oysters during the months with an "R" in their name?

        Fresh oysters are nutritious throughout the year. They do spoil rapidly at high temperatures, however. The belief that oysters were unsafe to eat from May through August arose in earlier days when refrigeration was less prevalent than it is today. Additionally, as high temperatures triggers reproductive spawning (release of eggs and sperm), meat content is low. They also look thin in warm months, resulting in what is considered as low oyster quality—and maybe the reason it would be avoided. However, many cultured oysters sold nowadays do not reproduce, so their quality is high and the meat looks plump throughout the year.


        Watch the video: Άνθρωποι και άγρια ζώα οι καλύτεροι φίλοι Beautiful moments with Wild Animals (July 2022).


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