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  Habitats, behaviour, & ecology
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  Ghost shrimps
  Much has been written on habitats, behaviour, and ecology of west-coast mud- and ghost-shrimps, but much less on “true” or caridean shrimps.  Considered here are ghost shrimps, while MUD SHRIMPS and "TRUE" SHRIMPS are dealt with in another section.
Research study 1

drawing of a burrow of a ghost shrimp Neotrypaea californiensis
photograph of a resin cast of a burrow of a ghost shrimp Neotrypaea Nickell & Atkinson 1995 Mar Ecol Progr Ser 128: 181. drawing of burrows of ghost shrimps Neotrypaea californiensis under crowded and solitary conditionsGhost shrimps Neotrypaea (Callianassa) californiensis inhabit U- or Y-shaped burrows, commonly on sand-flats.  One arm of the burrow complex is usually exhalent and is associated with the presence of a sediment mound (see drawing of side view of burrow on Left). 


Resin casts of burrow structure show several bulbs or chambers used for turning and for storing organic debris such as small pieces of eelgrass Zostera for food (photo on Right). 


Burrows in high-density beds show little inter-communication (see drawings lower Left). Drawings from Griffis & Chavez 1988 J Exper Mar Biol Ecol 117: 239; resin-cast photo from Nickell & Atkinson 1995 Mar Ecol Prog Ser 128: 181.

The apparent cavity at the top of the left cluster is
not a common chamber; rather, it appears to be just a
depression in the sand into which the liquid resin was poured

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Research study 2

In the Fraser River estuary in British Columbia, densities of Neotrypaea californiensis burrow-openings may reach 350-450 . m-2.  The burrows extend 20-50cm into the sediment and then branch horizontally for distances of up to 1m.  Each system usually has 2 exits, and contains numerous bulbous turn-arounds and blind alleys throughout.  There is no distinct lining to the burrow walls and they are thought to be temporary feeding burrows rather than permanent dwelling burrows.  Swinbanks & Murray 1981 Sedimentology 28: 201; Swinbanks & Luternauer 1987 J Paleont 61: 315.schematic showing positions of co-inhabiting clams Cryptomya californica in the burrows of ghost shrims Neotrypaea californiensis
In comparison, burrow densities of ghost shrimps N. californiensis may reach 50-170 . m-2 in Mugu Lagoon, California, 300-700 . m-2 in Oregon, 290-330 in areas of Washington, and 140-180 . m-2 in the Fraser River estuary.  Feldman et al. 2000 Estuaries 23: 141.

Several co-inhabiting clams Cryptomya californica are shown,
with their siphons opening into the shrimps' burrows

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Research study 3

graph of changing seasonal densities of mud- and ghost-shrimps in Willapa Bay, Washington

Numbers of both types of shrimps vary from year to year.  The graph shows yearly variation in shrimp densities in Willapa Bay, Washington over a 7yr period.  Dumbauld et al. 1996 J Crust Biol 16: 689.

NOTE  the data are based on counts of burrow openings, and a conversion factor of 1.5 burrow holes per shrimp for Upogebia and 1.2 burrow holes per shrimp for Neotrypaea

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Research study 4
  photograph of ghost shrimp Neotrypaea californiensis courtesy Dave Cowles, Walla Walla University, WashingtonReports in the literature differ as to whether mud-shrimp and ghost-shrimp burrows are inhabited by a single individual or a male and female mating pair.  Perhaps the 2 sexes only join up during reproductive time, or geographic differences may explain the differences.   MacGinitie & MacGinitie 1968 Natural history of marine animals McGraw-Hill, N.Y.; Swinbanks & Murray 1981 Sedimentology 28: 201; Griffis & Chavez 1988 J Exper Mar Biol Ecol 117: 239. Photograph courtesy Dave Cowles, Walla Walla University, Washington
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Research study 5

photograph of burrow openings of ghost shrims Neotrypaea californiensis showing aspects of age of burrow diggings
In comparison with the more firmly constructed and permanent burrows of mud shrimps, burrows of ghost shrimps Neotrypaea californiensis are unlined and often lack discernible openings to the sand surface during low tide.  For these reasons, plus the fact that mud shrimps ventilate their burrows, it is thought that ghost shrimps may be more exposed to hypoxic interstitial waters than mud shrimps.  Studies at Hatfield Marine Sciences Center, Oregon show that both species, but especially ghost shrimps, have low metabolic rates, and both tolerate low and even zero (anoxic) oxygen levels for several days if non-moulting. Thompson & Pritchard 1969 Biol Bull 136: 274.

NOTE  lit. “low oxygen”; anoxic is “without oxygen”



The degree of "humped-uped-ness" of ghost-shrimp burrows relates to whether the digging is
fresh (top burrow) or older (bottom burrow), and also with the extent of wave action 0.3X

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Research study 6

schematic showing depths occupied by several potentially competing infaunal organisms including ghost shrimps Neotrypaea californiensisIn a study of space competition in sand-bottom habitats in Mugu Lagoon, California, 6 invertebrate species, including the ghost shrimp Neotrypaea californiensis, are found to account for almost 90% of the macrofaunal suspension-feeders present.  The 6 species (4 bivalves, one sand dollar, and one ghost shrimp) are stratified such that their vertical distributions overlap only slightly (see figure on Right).

graph showing densities of various infaunal organisms over several seasons in relation to their potential for space competition with ghost shrimps Neotrypaea californiensis
The 3 species that do overlap (the bivalve Nuttallia nuttallii1 and the ghost shrimp/bivalve pair N. californiensi/Cryptomya californica2, treated here as a unit because of their functionally related co-occurrence, are segregated horizontally.  The 6 species show relatively little temporal change in their densities over a 3-yr study period. Average density of all macrofauna species over this time is about 600 . m-2, but this rises to about 6000 . m-2 if all benthic fauna is included.

Another part of the study reveals a negative correlation between numbers of Neotrypaea californiensis/Cryptomya californica and the bivalve Nuttallia nuttallii, suggesting competitive exclusion graph showing potential competition between clams Nuttallia nuttallii with ghost shrimps Neotrypaea californiensis in Mugu Lagoon, California(see graph lower Right). The generally hyperbolic shape of the graph3 indicates that when either species is common, the other is rare, and only when each is rare are they found in nearly equal frequency.  Moreover, when all ghost shrimps and Cryptomya are removed from experimental plots, and then numbers re-assessed later, densities of bivalves Nuttallia and sand dollars Dendraster go up significantly. The author suggests that the ghost shrimps may exclude the clam and sand-dollar species by consuming their larvae and newly settled juveniles, and by burying the juvenile stages. 
Peterson 1977 Mar Biol 43: 343.

NOTE1 the small photo in the schematic on the Right is actually of the closely related N. obscurata

NOTE2  the ghost-shrimp burrows extend to 50cm depth and generally have 2 or more openings.  By living embedded in the wall of a shrimp’s burrow, Cryptomya effectively increases its depth distribution much more than its short siphons would otherwise allow

NOTE3  all densities are based on areas of 0.06 m2

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Research study 7

map of Coos Bay, Oregon showing study area for ghost shrimps Neotrypaea californiensisAnother way that ghost shrimps might exclude a bivalve species is by clogging their filtering ctenidia with sediments that they stir up when burrowing and deposit-feeding. Thus, one trophic group, the deposit-feeding shrimps, could inhibit the presence of another trophic group, the suspension-feeding bivalves, in a process known as “trophic-group exclusion”.

This concept is tested more generally in Coos Bay, Oregon by comparing abundances of 9 macrofaunal species of deposit-feeding invertebrates over a 2yr period in 3 adjoining areas: 1) within a dense intertidal bed of ghost shrimps Neotrypaea californiensis, 2) within a transitional zone characterised by spotty shrimp occurrence, and 3) outside the bed.  The 9 deposit-feeding graph showing changing densities of 9 macrofaunal species in relation to location within or without beds of ghost shrimps Neotrypaea californiensisspecies, representing over 95% of the non-shrimp macrofaunal individuals present, include 3 species of tube-dwelling spionid polychaetes, 3 species of tube-dwelling crustaceans (2 amphipods and one tenaid), and 3 motile species (cumacean, oligochaete, amphipod). 

The results of seasonal assessments of abundance over a 2-yr period show that 7 of the 9 deposit-feeding species have highest densities when numbers of ghost shrimps are low or intermediate, thus providing evidence of trophic-group exclusion. Results for all species cannot be included, here, but one species, the spionid polychaete Streblospio benedicti, exemplifies the general effects of the shrimips (graph on Right). As expected, because they can run away, the most variable results are shown by the 3 motile species. Otherwise, 5 of the 6 sedentary species solidly support the trophic-group hypothesis.  Posey 1986 Mar Ecol Progr Ser 31: 15.

NOTE  also known as “trophic-group amensalism”

NOTE  densities range from 70-130 individuals . m-2

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