Mud shrimps Upogebia pugettensis are primarily suspension-feeders on fine organic particles and phytoplankton, but may also feed on organic deposits.  During suspension-feeding, the shrimp stands at one of the entrances to its burrow, holds its first pair of walking legs together, and pumps water backwards into the burrow by flapping its pleopods (swimmerets).  Suspended food is filtered from the water in the intermeshed bristles of the walking legs.  Periodically the 3rd maxillipeds brush food material from the bristles of the straining basket.  This material is passed to the 2nd maxillipeds and thence to the mouth.  MacGinitie & MacGinitie 1968 Natural history of marine animals McGraw-Hill, N.Y.; Feldman et al. 2000 Estuaries 23: 141.

In comparison, ghost shrimps Neotrypaea californiensis are sub-surface deposit feeders, but may also eat eelgrass and suspension-feed.  Their burrows are really mines within which the shrimps tunnel and extract food matter.  Edible material is sifted from the sediments by bristles on the 2nd and 3rd walking legs, then removed from these appendages by bristles on the 3rd maxillipeds and passed to the mouth.  MacGinitie 1934 Amer Midl Nat 15: 166; Swinbanks & Luternauer 1987 J Paleont 61: 315; Griffis & Chavez 1988 J Exper Mar Biol Ecol 117: 239; Feldman et al. 2000 Estuaries 23: 141; image from MacGinitie 1934 Amer Midl Nat 15: 166

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In what appears to be the first study of its kind on the west coast, researchers from University of California, Davis describe the feeding habits of 2 caridean shrimps Crangon franciscorum and Palaemon macrodactylus living in the Sacramento-San Joaquin Estuary of California.  The shrimps are similar in size and both are primarily carnivorous.  The frequency of occurrence (%) of various food items in the foreguts of both species throughout the year are shown in the accompanying histograms.  Overall, animal components exceed plant components by about 25%.  Principal identifiable animal components of the diet for both species are mysid shrimps Neomysis mercedis, with the addition for Crangon of gammarid amphipods, and for Palaemon of copepods.  Other prey for both species include sporadic numbers of worms, insects, bivalves, and shrimp and fish larvae.  The authors remark that some of the reported gut contents may have actually originated in the guts of consumed prey.  Both species undertake diel vertical migrations, so prey eaten is a combination of benthic and planktonic feeding.  The authors discuss possible food competition between the 2 species.  Sitts & Knight 1979 Biol Bull 156: 356.

NOTE  this non-indigenous species was introduced into the estuary in the first half of the 20th C.

NOTE  this obvious possibility is not always recognised by researchers doing such feeding analyses, or other types of analyses, such as tracking the origins of metabolites derived from an animal's diet to be possibly used in chemical defense by that animal

A determination of calorigenic effects of various diets on grass shrimps Crangon franciscorum by researchers at the University of California, Davis reveals highest effects on a diet of tubificids (43% elevation in metabolic rate), in comparison with diets of mysid shrimps and fish (14%) and 23%, respectively). The authors do not relate the scope of the effect to amounts eaten, but percentage nitrogen contents are listed as 9, 11, and 14%, respectively, for the 3 foodstuffs.  Other possible contributing factors such as increase in post-feeding activity and costs of muscular activity of the digestive system are not taken into account by the authors.  Mechanical costs of feeding are, however,  not an issue as the oxygen-consumption measurements are not made until 30min after feeding is completed.  Nelson et al. 1985 Comp Biochem Physiol 82A: 373.

NOTE  the effect, also known as specific dynamic action (SDA) is a post-ingestive increase in metabolic rate.  Long thought to be simply wasted heat through metabolic processing of foodstuffs, most notably protein, it is now believed to be an essential component of growth

A later and similar study of the feeding ecology of crangonid shrimps in San Pablo Bay over a 15mo study period provides the following dietary information:

Crangon franciscorum: diet partitioned more-or-less evenly among amphipods, bivalve, and foraminiferans.  Large individuals have more crangonid shrimp remains in their guts than small individuals, suggesting an ontogenetic shift in dietary preferences.

Crangon nigricauda: diet mainly of amphipods

The author remarks that the diets of both species are greatly influenced by prey availability.  For example, the mysids Neomysis spp. that feature so predominately in the diets of crangonids in the upper reaches of the Sacramento River-San Joaquin River estuary (see Research Study 1 above), are much rarer, and thus eaten much less by the crangonids, in San Pablo Bay itself. Wahle 1985 J Crust Biol 5 (2): 311.

NOTE  this location is more seaward than the estuarine location featured in Research Study 1 above (see map)