Lottia gigantea, Owl Limpet

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Taxonomy

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Coelomata - Protostomia - Mollusca - Gastropoda - Eogastropoda - Docoglossa - Nacellina - Acmaeioidea - Lottiidae - Lottia - Lottia gigantea

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Brief facts

• Limpets inhabit wave-pounded rocks. They not only occupy one of the most physically stressful environments on earth but also have to undergo the heat and desiccation between tides.
• Lottia gigantea is common along the coast of North America from Washington state to Baja California. It can be found on vertical rocky shores firmly attached to the substratum with its muscular foot that fills most of the aperture area of its shell. Water currents apply huge multi-directional forces to inhabitants of the ecological niche. Still, limpets are very hard to dislodge. This ability of limpets was extensively studied. Secreted mucus as well as suction of the foot are believed to play a critical role in the attachement. Interestingly, it was found that in spite of millions years of evolutionary pressure the shell's shape is often is not optimal for withstanding the water forces. This is because the shell's shape helps the mollusks in other aspects of their survival.
• Lottia gigantea is a solitary limpet (as opposed to aggregating limpets). Algae that grow on the rocks are its main food source. Distinct behavioral characteristics of the Owl Limpet is that it is aggressively territorial and uses its shell as a bulldozer to clean the space for the algae to flourish. Mytilid mussels, barnacles, and anemones are Lottia's primary competitors for space. When faced with other herbivores, competitors for food, such as Acmaea, Tegula, or other limpets, Lottia tries destabilize the intruder by pushing and hitting it in the foot to increase the probability of the intruder getting washed off by a wave.
• It was found that mucus secreted by some limpet species, including Lottia gigantea, stimulates growth of the microalgae. It also serves as adhesive traps for the algae.
• Because of their large size and strong adhesive tenacity, adult L. gigantea appear to be immune to predation by birds and crabs.
• When confronted with a predator, such as predatory sea star Pisaster ochraceus, oyster Thais marginata, or sea snail (angular unicorn) Acanthina spirata, Lottia responds by a behavior known as mushrooming, which consists of raising its shell up and rocking it in a menacing manner, and later bringing the anterior end of the shell down on the foot of the predator so that the latter retracts its foot. In consequence, Lottia manages to weaken the attachment of the predator, making it more susceptible to dislodgement by waves.
• The shell of the Owl Limpets reaches 4-8 cm (up to 9 cm) in length. The Owl Limpet was harvested by humans as a food item since pre-historic times. The exploitation of natural populations (mostly illegal) continues today. It is believed that the excessive harvesting plays role in diminishing of the size of sexually mature limpets. An analysis of the life history and natural history of this limpet suggests that two factors in particular may be responsible for the species persistence: the small size at maturity and the pelagic dispersal stage.

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Life cycle

The following description is based on laboratory study of spawning of Lottia digitalis and Lottia asmi.

• gamete Male and female adults spawn (broadcast) their gametes into the water column where external fertilization occurs. Spawning is induced by vigorous bubbling of the water and might coincide with winter storms. Subsequent development usually occurs at 8-14°C. Approximate timing is given for ~13°C.
• fertilized egg
• embryo
  • cleavage Four rounds of cleavage occur within first 2-4 hours of development.
  • gastrula Ciliated gastrula.
• larval
  • trochophore Trochophore (ciliated blastula) larva hatches from the egg in ~14-16 hours after fertilizaion. The larva swims actively by using cilia.
  • lecithotrophic
    veliger Veliger developes gradually. Secretion of the shell begins as early as 28-30 h after fertilization. The shell surrounds the visceral organs of the larva (digestive tract, much of the nervous system, excretory organs). Ciliated velum extends beyond the shell and is used for swimming.
    • torsion Torsion (the rotation of the visceral mass, mantle and shell 180° with respect to the head and foot of that brings the mantle cavity and anus to an anterior position above the head) takes place over a 2-4 hours period. Soon after the torsion is completed, larva instead of flight as a defensive strategy, begins to withdraw into the shell. After operculum (the shell's lid) formation is completed, eyespots begin graduallly to develop concurrent with foot enlargement. The cephalic tentacles become visible at 3-3.5 days after fertilization.
    • metamorphic
      competence The state of readiness to adhere to the substartum and start metamorphosing is reached at 5-5.5 days. Veliger starts crawling ("behavioral competence") and ceases to develop new larval features.
• metamorphosis Velar loss is the first evidence of metamorphosis. Food is become visible in the gut in ~1 day after settlement. By second day after the settlement, the ribbon-like radula (mollusck's "teeth" used for rasping) is visible. Adult shell growth is initiated in 2-4 days after settlement. In 5-7 weeks, the postlarva reaches size of about 1 mm.
• juvenile Immature mollusk.
• adult Sexually competent mollusk.

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References

• Connor VM, Quinn JF. Stimulation of Food Species Growth by Limpet Mucus. Science. 1984 Aug 24
• Denny MW, Blanchette CA. Hydrodynamics, shell shape, behavior and survivorship in the owl limpet Lottia gigantea. J Exp Biol. 2000 Sep;203(Pt 17):2623-39.
• Kay MC. and Emlet RB. Laboratory spawning, larval development, and metamorphosis of the limpets Lottia digitalis and Lottia asmi (Patellogastropoda, Lottiidae). Invertebrate Biology 121(1): 11-24. 2002
• Smith AM. et al. Differences in the composition of adhesive and non-adhesive micus from the limpet Lottia limatula. Biological Bulletin. Vol. 196, No. 1 (Feb., 1999), pp. 34-44.
• Rojas J and Ojeda FP. TERRITORIALITY. Pacific Science (1996)

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