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title for learn-about section of A SNAIL'S ODYSSEY
  Feeding & growth
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  Feeding
  Little is published on feeding in west-coast mussels, perhaps because the process is generally so well known in bivalves.  The topic of feeding is presented in this section, while topics of GROWTH, and EFFECT OF PARASITES ON GROWTH & SURVIVAL are considered in other sections.
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Research study 1
 

In an early study of feeding in mussels Mytilus californianus at Corona del Mar, California the author employs a viewing window inserted into the front part of one shell valve.  This enables the author to describe in detail the process of rejection of inedible and/or undesirable material via ciliated grooves in the ventral mantle edge.  Thus, as mucus is moved from the edges of the ctenidia to the bases of the labial palps in particle-laden strings, if unwanted it is sent in these rejection pathways to be discarded as pseudofeces at the posterior end of the animal. MacGinitie 1941 Biol Bull 80: 18.

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Research study 2
 

photograph of tight cluster of sea mussels Mytilus californianusMussels filter-feed1 by pumping water through their ctenidia, collecting organic particles that impinge on the filaments.  Analysis of stomach and digestive-gland contents, and of feces of Mytilus californianus at Scripps Institution of Oceanography, La Jolla, California, reveal that a wide variety of living and dead particulate matter is eaten, including dinoflagellates, other protists, diatoms, bacteria, unicellular algae, algal spores, detritus, and invertebrate eggs and larvae.  Effectively, a mussel removes all particulate material entering its mantle cavity. The authors calculate that a large mussel (100mm in length) can filter about 22,000 liters2 of seawater per year.  From this it could obtain 4.9g of dry organic matter, split between dinoflagellates3 (22 million ingested = 4.2g), diatoms (=0.7g), and bacteria (=0.05g), but this is theoretically insufficient to satisfy yearly nutrient needs.  This is gross input and, at an estimated conversion efficiency of 10%, there exists a net shortfall of over 4g.  The authors suggest that the shortfall may be made up by ingestion of detritus particles and possible absorption of dissolved organic matter.  Fox & Coe 1943 J Exp Zool 93: 205.

NOTE1 a description of filter-feeding in bivalves can be found elsewhere in the ODYSSEY: LEARN ABOUT CLAMS & RELATIVE: FOODS & FEEDING 

NOTE2 the data on filtration rate in M. californianus is taken from an earlier paper that shows that an individual of 110mm shell length will filter 22.6 liters . day-1 at 22oC.  Fox et al. 1937 Biol Bull 72: 417

NOTE3  in an earlier article the same research group notes that food of M. californianus in the La Jolla, California area is represented by 98% diatoms and 2% dinoflagellates.  Clearly, food types will vary greatly with location and time of year.  Fox  et al. 1936 Bull Scripps Inst Oceanogr Tech Ser 4: 1.

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Research study 3
 

graph showing synchronicity between pumping rate in mussels Mytilus californianus and the high-tide cycleResearch on mussels Mytilus californianus at the Kerckhoff Marine Laboratory, Corona del Mar, California reveals an inherent tidal rhythm in their pumping. Note in the graph on the Left, representing a single individual mussel monitored over a 3-d period, that the daily pumping cycle coincides exactly with the daily tidal cycle. The rhythm is independent of temperature, occurs in intertidal as well as subtidal individuals, and persists in the laboratory in phase with the original tidal cycle for over 4wk. There is no evidence of a diurnal rhythm, and the original tidal rhythm is maintained in the laboratory in continuous darkness, continuous light, or in a natural daylight/night cycle.  Even more interesting is the fact that such a rhythm is present in mussels living on the underside of floats and therefore not subject to the direct physical effects of the tides.  Rao 1954 Biol Bull 106: 353.

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Research study 4
 

photograph of mussel Mytilus californianus half-eaten by an ochre star Pisaster ochraceusAn investigation on carotenoid pigments in sea mussels Mytilus californianus reveals the presence of 15 types, with alloxanthin being in highest concentration, followed by mytiloxanthin, and then several others, including ß-carotene, being present in lower concentrations.  The study is primarily on pigments of the European Mytilus edulis, but these seem not to differ markedly in type or quantity from those that the author has identified in M. californianus.  This is surprising because the 2 species differ greatly in the colour of their tissues, with the flesh of M. californianus being markedly more orange in comparison with that of M. edulis.  Feces of the latter species contain a range of carotenes, but in low concentration, and the phytoplankton foods of the mussels are, of course, rich in carotenoids.  The author does not comment on the significance of the different colours of flesh of the 2 species.  Campbell 1970 Comp Biochem Physiol 32: 97.

NOTE  other aspects on the biology of carotenoid pigments in  M. californianus can be found in Scheer 19-- Contr Scripps Instit Oceanogr No. 112: 275

Half-digested sea mussel Mytilus californianus showing orange flesh 1.5X

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