title for limpet section of the Odyssey
   
  Defenses & predators
 

Defenses of limpets include attachment strength, shell, escape crawling, and camouflage (both visual and chemical). Chief predators are crabs, fishes, and sea stars when the tide is in, and birds when the tide is out. There is overlap between defenses and predators. For example, attachment strength is useful against predation by both sea stars and birds, and shells provide protection against both crabs and fishes. For this reason, defenses and predators are intermixed in this overall section.

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  Defensive chemicals
  The topic of defensive chemicals is considered in this section, and topics of ATTACHMENT-STRENGTH PROTECTION, SHELL PROTECTION, ESCAPE-CRAWLING FROM SEA STARS, PREDATION BY BIRDS, and CAMOUFLAGE, are considered in other sections. DEFENSES OF KEYHOLE LIMPETS are dealt with separately and include camouflage, mantle response, and (sometimes) aggressive defensive activities of a symbiotic polychaete.
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Research study 1
 

There are few examples of defensive chemicals in limpets, even on a world-wide1 basis.  However, a novel triterpene called limatulone has been isolated from the foot of limpets Lottia limatula at the Scripps Institution of Oceanography, La Jolla, California.  Laboratory and field experiments suggest that the chemical acts in defense against some intertidal predators but not others.  Thus, tidepool cottid fishes Girella nigricans and hermit crabs Pagurus samuelis reject pieces of the foot of L. limatula, but readily eat foot tissue from co-occurring limpets L. scabra and L. gigantea.  In contrast, various sea stars2 (e.g., Pisaster giganteus) and sea gulls Larus californicus readily eat foot-portions of L. limatula.  The intertidal fish, Gibbonsia elegans, known to eat limpets in the photograph of Lottia limatula: tidepool cottid fishes Girella nigricans and hermit crabs Pagurus samuelis reject pieces of the foot of L. limatula, but readily eat foot tissue from co-occurring limpets L. scabra and L. gigantea courtesy Pawlik et al. 1986 Mar Ecol Progr Ser 30: 251field, reject food pellets containing approximately 0.5ppt of limatulone.  Limatulone is found only in foot tissue and not in viscera, shell, or foot mucus. 

In one boulder-field area, the risk of partial shell loss3 from impact damage in L. limatula, which results in loss of the outer ring of shell ("skirt") and which would otherwise expose the now-visible limpet’s foot to possible predation, may be mitigated by the presence of the defensive chemical. The authors note the absence of limatulone from gut tissue and conclude that it is most likely synthesised4 from related but inactive dietary precursors, possibly seaweeds. Albizati et al. 1985 J Org Chem 50: 3428; Pawlik et al. 1986 Mar Ecol Progr Ser 30: 251.

NOTE1 other world species of gastropods, most notably the pulmonate “limpet” Siphonaria spp. contain secondary metabolites known as polyproprionates but, at the time of the publication of these papers on L. limatula, the pharmacological significance of these metabolites had not been investigated

NOTE2 other defensive strategies, such as as fast escape crawling, may “kick in” with respect to sea-star predators.  This is considered elsewhere in this limpet section of the ODYSSEY: DEFENSES & PREDATORS: ESCAPE-CRAWLING FROM SEA STARS

NOTE3 occurrence of such limpet “skirts”, especially from L. limatula. in washed-up beach debris has been linked to predation by crabs Pachygrapsus crassipes.  Details of this work can be found elsewhere in this limpet section of the ODYSSEY: DEFENSES & PREDATORS: SHELL PROTECTION

NOTE4 in a later paper by researchers primarily in Japan, but also at the Scripps Institution of Oceanography, L. limatula is shown actually to synthesise 3 stereoisomers of limatulone. Mori et al. 1992 Nat Prod Lett 1 (1): 59.

 
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