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  Habitats, behaviour, & ecology
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  Mud shrimps

Much has been written on habitats, behaviour, and ecology of west-coast mud- and ghost-shrimps, but not so much on “true” or caridean shrimps.  Considered in this section are mud shrimps, while GHOST SHRIMPS and "TRUE" SHRIMPS are dealt with in their own sections.

photograph of mud shrimp Upogebia pugettensisEarly observations on the ecology of thalassinid shrimps by a researcher at the University of Washington, Seattle deal with both Upogebia pugettensis and  Neotrypaea gigas. Although the study  primarily focuses on the deleterious effects of these shrimps on the oyster industry of Puget Sound, there are some aspects of general interest.  The author notes a tendency for separation of the 2  types of shrimps, such that on beaches where Upogebia are present no Neotrypaea are found.  This relates, in part, to the preference of the former for harder, more compact sediments, and of the latter for looser, sand/mud substrata, especially the former.  A mud shrimp Upogebia excavates its burrow as follows.  The 3rd maxillipeds are used for scooping, while the juxtaposed chelipeds and 1st pair of walking legs form a carrier.  A load is scooped up by the maxillipeds and placed in the carrier, with the chelipeds forming the sides and the 1st walking legs the floor. When a full load is realised, amounting to about a teaspoonful, the body somersaults into the reverse direction with little loss of sediment, and the shrimp moves upwards to the burrow opening. Burrows are nearly vertical and generally Y- or U-shaped.  The author comments on the smooth plastering of the walls of the burrow, and later researchers determine that this is more common for Upogebia burrows than for Neotrypaea burrows (see photograph below).  The author notes that food is similar in both mud- and ghost-shrimps, consisting of plant debris and diatoms, but with the bulk of material in the digestive tracts of both species being comprised of fine sand.  Stevens 1929 Ecology ghost shrimp Neotrypaea californiensis in its burrow Dumbauld, Newport10 (4): 399. Photograph of Neotrypaea californiensis courtesy Brett Dumbauld, Newport, Oregon. 

NOTE  the article represents a presentation delivered at the 14th Annual Meeting of the Ecological Soc Amer, NY 28 Dec, 1928.

NOTE  descriptors such as “menace”, “worst enemy”, “pest”, “victims”, all relating to the well-being of the native oyster Ostrea conchaphila in face of shrimp excavating might have gone over well in a verbal presentation, but are unusual to see in contemporary scientific writing


Ghost shrimp Neotrypaea californiensis in its burrow.
The burrow opening is at the top of the photo 0.15X

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Research study 1

photograph of a preserved mud shrimp Upogebia pugettensis
Mud shrimps Upogebia pugettensis inhabit U- or Y-shaped burrows on intertidal mud- and sand-flats.  The burrows may extend to depths of 90cm, with sturdy walls consisting of sediment particles and other debris cemented together with mucus secreted by the shrimp.  Mud-shrimp burrows are not usually associated with a sediment mound (unlike ghost shrimps). 
Swinbanks & Murray 1981 Sedimentol 28: 201; Swinbanks & Luternauer 1987 J Paleont 61: 315; Griffis & Suchanek 1991 Mar Ecol Progr Ser 79: 171.


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Research study 2
  graph showing relationship of size to burrowing time in mud shrimps Upogebia pugettenis in different eelgrass habitatsThe effectiveness of burrowing in mud shrimps Upogebia pugettensis (and also ghost shrimps Neotrypaea californiensis) depends not only upon sediment type and compaction, but also the presence of other organisms.  Studies in the Gulf Islands, Washington and Fraser River tidal flats, British Columbia show that densities of both species are reduced in eelgrass beds.  In the Gulf Islands burrowing by Upogebia can take 3-7 times longer in the presence of eelgrass Zostera marina than in sieved mud (graph on Left)  Brenchley 1982 J Exper Mar Biol Ecol 60: 17; Swinbanks & Luternauer 1987 J Paleont 61: 315.
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Research study 3

map showing distributions of 18 species of mud-shrimps Upogebia on the west coast of North AmericaIf you are accustomed to thinking that only a single species of mud shrimp Upogebia pugettensis inhabits the west coast from Alaska to California, it may be a surprise to know that another 3 species live in southern California south of Point Conception and in the California Channel Islands U. onychion, U. macginitieorum and U. lepta, and even more of a surprise that another 14 species live from the northern Gulf of Mexico to south Central America (see map).   In comparison, only about 7 species inhabit the Atlantic coast of North America.  The author of a summary paper on Upogebia distributions notes that so far as is known, all members of the genus live in burrow systems, although possibly in different substrata.  The author provides a key and a wealth of morphological data for these 18 species plus an addition one in the Galapagos Islands. Williams 1986 San Diego Soc Nat Hist, Mem 14, 60pp.

NOTE as shown on the inset map of Baja California, these 3 species have localised distributions in the Channel Islands/N. Baja California/S. California (mcginitieorum), Santa Catalina Island/N. Baja California (lepta), and San Miguel Island (onychion)
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Research study 4
  drawing comparing features of burrows of mud- and ghost-shrimpsschematic showing comparative distributions of ghost shrimps Neotrypaea californiensis and mud shrimps Upogebia pugettensis in intertidal regions of the Fraser River mudflats in British ColumbiaOn the Fraser River tidal flats in British Columbia, mud shrimps Upogebia pugettensis are more common in mud/sand at intertidal levels where continuous exposure to air is less than 0.5d.  Burrow densities may reach 10-80 . m-2 in the Fraser River estuary, British Columbia and 200-700 . m-2 in Oregon.  Field studies on filtration rates of mud shrimps in Yaquina estuary, Oregon show that they are capable of filtering the entire body of overlying water each day (mean depth=1.1m). Note in the figure on the Left that the upper limit of Upodgebia is about +1.7m, or just below Mean Sea Level.

In comparison, ghost shrimps Neotrypaea californiensis are common in sandy sediments higher on the shore where continuous exposure to air may exceed 5d.  In the zone of overlap, Upogebia is vulnerable to being smothered by the large mounds produced by the ghost shrimps (see figure on Right). Swinbanks & Luternauer 1987 J Paleont 61: 315; Feldman et al. 2000 Estuaries 23: 141; Griffen et al. 2004 Mar Ecol Progr Ser 269: 223.
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Research study 5

histograms showing exclusion effect of mud shrimps Upogebia pugettensis on the presence of other mudflat-inhabiting invertebratesWhat effects do the activities of mud shrimps Upogegia pugettensis have on other mudflat macrofauna?  This is tested in Willapa Bay, Washington where mud shrimps are excluded from experimental arenas in areas where they are otherwise abundant.  Let’s repeat one set of experiments here.  First, we bury several 20-liter plastic tubs to the level of their rims in the mudflat.  We then fill the tubs with nearby sediment after screening it to remove all macrofauna.  To half the buckets we add 7 large (5-7cm) mud shrimps (Addition), and leave the other half shrimp-free (Exclusion).  A wire-mesh cage is placed on all the buckets for 48h to prevent access by predatory birds and fishes while the shrimps burrow into the sediment.  We then remove the cages and leave the buckets for 1yr.  After this time, and after a second (replicate) year, we sift out the macrofauna from several replicate areas (each 1/200 sq m) in each bucket and assess what effects on macrofaunal abundance the shrimps have had.  The sets of results for the 2 years are similar, so we combine them into grand means (see histograms).  Results show, firstly, that overall numbers of macrofauna (mainly sedentary tube-dwelling worms and crustaceans) are greater in the Exclusion tubs where mud shrimps are absent than in the Addition tubs.  Finer analysis shows that 4 species (2 polychaetes and 2 crustaceans, indicated in blue with asterisks), all sedentary tube-dwelling forms, are significantly more abundant in the absence of mud shrimps than in their presence.  Abundances of several other species, including the bivalve Macoma balthica, are not significantly affected.  Only one species, a tube-dwelling polychaete (Heteromastus filiformis), is significantly more abundant in the presence of mud shrimps than in their absence.  The authors conclude that mud shrimps have a significant negative impact on the mudflat macrofauna, likely owing to their large-scale digging and smothering activities.  Posey et al. 1991 J Exper Mar Biol Ecol 148: 283.

NOTE the tubs have mesh screens installed on the sides to aid in water circulation. 

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Research study 6

Burrowing activities of mud shrimps Upogebia pugettensis and, to a lesser extent of ghost shrimps, seriously interfere with bottom-culture of oysters – so much so, in fact, that since 1963 in Washington oyster-growers have been seasonally treating their oyster beds with a shrimp-killing toxin carbaryl.  Unfortunately, the toxin also kills other arthropods, including crabs, shrimps, and amphipods, as well as juvenile and sub-adult Dungeness crabs Cancer magister, and certain fishes such as English sole.  Use of carbaryl is opposed by crab-fishers, and has been banned in Oregon since 1984.  Dumbauld et al. 1997 J Shellf Res 16: 503; Feldman et al. 2000 Estuaries 23: 141; Dumbauld et al. 2001 Mar Pollut Bull 42: 826; for a review of the environmental ethics of use of carbaryl for controlling ghost- and mud-shrimp populations in Washington state see Feldman et al. 2000 Estuaries 23 (2): 141.

NOTE  in Willapa Bay, Washington where 50% of the state’s oyster production occurs, about 95% of oysters are cultured directly on intertidal mudflats.  Dumbauld et al. 2001 Mar Pollut Bull 42: 826.

NOTE  a non-persistent organocarbamate pesticide (1-napthyl n-methyl carbamate) that is extremely toxic to arthropods (e.g., insects).  Its effect is to inhibit the activity of acetylcholinesterase, which itself functions to inactivate the neurotransmitter acetylcholine.  Death results from muscular and respiratory paralysis.  Carbaryl is applied in powder form during low tides in summer. It is not known whether the practise still exists in Washington

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Research study 7

histogram showing inhibitory effect of a layer of oyster-shell cultch on settlement of mud shrimp and ghost shrimp larvaeIs there an alternative to application of toxins to control the smothering activities of mud and ghost shrimps on oyster beds?  For example, might the presence of a dense layer of oyster shells (cultch) on top of the mud prevent settlement of the shrimps? Tests on mudflats bearing pavement layers of oyster shells (10-15cm thick) give a mixed answer:  'yes' for ghost shrimps, as settlement is much reduced, and 'no' for mud shrimps, as settlement is little affected.  The authors remark that such a pavement layer would greatly modify the ecology of the mudflat biota beneath, interfere with later harvest of the oysters, offer substratum for oyster spat-eating crabs, possibly turn ghost-shrimp beds into mud-shrimp beds and, by promoting large-scale natural settlement of oyster spat, perhaps ultimately convert the shell pavement into an oyster reef.  Feldman et al. 2000 Estuaries 23: 141.

NOTE cultch is used by oyster culturists routinely as a method to induce settlement of oyster larvae

NOTE the authors provide an excellent and comrehensive review of the past history of oyster culturing in Willapa Bay, Washington, use of toxins to control thalassinid shrimps, and the ecological ramifications of control procedures

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Research study 8
  photograph of a mud shrimp Upogebia pugettensis crawling near its burrow opening courtesy Santagata 2004 Biol Bull 207: 103.Mud shrimps Upogebia pugettensis rarely stray far from their burrow openings.  Feldman et al. 2000 Estuaries 23: 141; photo from Santagata 2004 Biol Bull 207: 103.
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Research study 9

The effectiveness of carbaryl in eliminating both mud and ghost shrimps in Willapa Bay, Washington is shown in these graphs.  The data show burrow counts monitored over a 3yr period after a single application of the toxin as compared with untreated CONTROL plots.  Both species are acutely affected, with numbers decreasing significantly by over 95% within 1-2mo.   The major difference in effect on the 2 species is that numbers of Upogebia remain low for at least 3yr after treatment, while numbers of Neotrypaea rebound after a year. Other parts of the study show high mortality graph of carbaryl effect on numbers of mud shrimps Upogebia pugettensis and ghost shrimps Neotrypaea californiensis in Willapa Bay, Washingtonof amphipods associated with application of the toxin, but little or no effect on polychaetes or molluscsDumbauld et al. 2001 Mar Pollut Bull 42: 826.

  treated with carbaryl at 5.6 kg per hectare in July (Day 0 on the graphs)

NOTE  numbers of the bivalve Cryptomya californica decrease significantly, probably owing to loss of the shrimp burrows in which they live

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Research study 10

An investigation of burrowing effects of mud shrimps Upogebia pugettensis in an intertidal mud flat in Yaquina River estuary, Oregon shows, not surprisingly, that carbon and nitrogen fluxing, and oxygen uptake, increases significantly with burrow density.  Burrowing by shrimps increases carbon cycling by 3-fold, ammonification by 7-fold, and nitrification by up to 9-fold.  Levels of cycling of pore-water dissolved inorganic nitrogen increase exponentially with burrow density up to 15 times that of control plots lacking shrimp.  Interestingly, the strongest relationships are with burrow-hole density rather than with shrimp numbers or biomass.  The paper is data-rich and this short account does not do it justice.  The authors term the process “geochemical ecosystem-engineering” to complement the already acknowledged role of U. pugettensis as “physical ecosystem-engineers”.  D’Andrea and DeWitt 2009 Limnol Oceanogr. 54: 1911.

NOTE  the researchers record densities in excess of 600 burrow-holes . m-2 in some areas of the estuary

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