title bar for mussel section of the Odyssey
title for learn-about section of A SNAIL'S ODYSSEY
  Feeding & growth
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  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, equivalent to about 0.2 litres per hour per gram live mass. 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 3d 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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Research study 5

graph comparing pumping rates of 4 species of west-coast bivalves, including sea mussels Mytilus californianusPumping rates in bivalves will depend on several factors, among which are body size, relative surface area of the ctenidia, activity level, and habitat.  Continually submersed, larger-bodied species such as the bent-nose clam Macoma nasuta might be expected to have lower relative pumping rates, while intertidal forms such as sea mussels Mytilus californianus might be expected to have higher relative rates owing to limitations on submersion time.  But what about an actively crawling species like the cockle Clinodardium nuttallii, or a swimming species like the scallop Chlamys hastata?  Measurements made on these 4 species1 by a researcher from Northeastern University, Massachusetts show, in fact, that highest absolute rates (pumping rate to dry tissue mass; see graph) are exhibited by the swimming species C. hastata and the mid-intertidal inhabiting mussel21 M. californianus, with the burrowing clam M. nasuta, exhibiting the lowest rate.  As expected from predicted scaling relationships, slopes of these regressions are around 0.75 (0.71-0.94).  As for efficiency of the ctenidia at pumping (pumping rate per unit ctenidia area), the first 3 species form a statistically3 homogenous group ranging from 0.08-0.14 cm3 . dry g-1 . sec-1 with M. nasuta being an order of magnitude lower at about 0.007 (data not shown).  As predicted, slopes of regressions of pumping rate in relation to ctenidial area are isometric, ranging around 1.  The author does not attempt to correlate either absolute or relative pumping rates with behaviour or habitat of the test species, other than to mention that M. nasuta is primarily a deposit-feeding species that uses an extensible siphon to suction up food bits selectively from the substratum surface, rather than suspension-feeding like the other species.  Meyhofer 1985 Mar Biol 85: 137.

NOTE1  the bivalves are collected at San Juan Island, Washington

NOTE2  the rate measured here at 13oC is about 5-fold greater per live mass than that recorded in an earlier study in California at 22oC (see Research Study 2 above

NOTE3 sample sizes are unusually small in this study, so the reader should interpret any comments about statistical significance with caution

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