Mudflats are hypoxic environments and oxygen availability may be a limiting factor to colonisation for many invertebrate species.  A study on respiratory adaptations in burrowing shrimps at Hatfield Marine Sciences Center, Oregon reveals that both Upogebia pugettensis and Neotrypaea californiensis are tolerant of conditions of low or zero oxygen content.  Under experimental conditions of anoxia Upogebia survives about 3d and Neotrypaea about 6d.  The difference may relate to the fact that Neotrypaea does not construct firm, lined burrows like Upogebia and, hence, is mor accustomed to hypoxic conditions of interstitial waters in mud/sand substrata. Thompson & Pritchard 1969 Biol Bull 136: 274.

NOTE  such conditions are created by bubbling nitrogen gas through seawater for 1-2h, which reduces oxygen content to “essentially zero”.  The tests are conducted in sealed jars at 10^oC

Burrow opening of a ghost shrimp Neotrypaea
californiensis in a bed of eelgrass Zostera sp. 0.6X

By definition, estuaries are brackish and usually subject to wide seasonal variation in salinity.  Studies at Hatfield Marine Sciences Centre, Oregon, where salinities in Yaquina Bay range from 21-34% over the year, show that the lower lethal salinity for mud shrimps Upogebia pugettensis is about 10% seawater, while that for ghost shrimps Neotrypaea californiensis is 25-35%.  Mud shrimps Upogebia regulate their blood osmotic concentrations strongly down to dilutions of about 20% seawater, while ghost shrimps Neotrypaea osmo-conform in dilute salinities.  In both species the urine is isosmotic to the blood, so regulation of blood osmotic concentration in Upogebia in dilute salinities is likely done by cation (and Cl^-) absorption by the gills as in crabs.  Thompson & Pritchard 1969 Biol Bull 136: 114.

NOTE  where 100% seawater is equivalent to 35‰ salt content

As concern grows over decreases in the stratospheric ozone layer, researchers are questioning the type of effects expected from increased UV exposure of planktonic organisms inhabiting the uppermost few meters of the sea surface.  This is investigated with larvae of shrimps Pandalus¹ spp. collected from Puget Sound, Washington.  Results of laboratory experiments show that zoea larvae of several shrimp species can tolerate UV-B² irradiance up to threshold³ levels with no significant reduction in survival or developmental rates. 

This is shown in the accompanying graph for the “lab-light only"-treatment (presumably indirect window sunlight?).  These data and the control data (“cool white”) for survival of zoea larvae of Pandalus platyceros can be compared with survival at 3 experimentally enhanced levels of UV-B irradiance. Note that survival over 7d, five of which with 3h of irradiation each day around noon, is poor for larvae exposed to experimentally enhanced UV-B levels.  Damkaer et al. 1980 Oecologia 44: 149; see also Damkaer et al. 1981 Oecologia 48: 178.

NOTE¹  species include Pandalus danae, P. hypsinotus, and P. platyceros, but only data for the last species is included here. Results for other shrimp species show similar trends.  The authors also provide data on euphausids and crabs, also not included here 

NOTE²   in comparison with UV-A, which is much less harmful, UV-B radiation is readily absorbed by proteins and nucleic acids, and induces photochemical reactions in plants and animals

NOTE³  levels close or equvalent to incident UV level

Do eye sizes in shrimps increase in size with depth of habitat?  A comparison of 19 benthic macrurans, including 5 species of pandalid shrimps Pandalus guernyi (9-95m), P. danae (0-180m), P. goniurus (7-180m), P. jordani (55-325m), and P. platyceros (45-1000m) shows trends in this direction for some groups (e.g., lobsters), but no obvious similar tendency in the 5 pandalids (see graphs). Hiller-Adams & Case 1985 Zoomorphology 105: 108.

NOTE the authors remark that the depth data given in the paper are only approximate owing to the unreliability of collection data listed on the museum cards accompanying the preserved specimens

NOTE however, in no case is allometry shown in eye size relative to depth for a given species, nor are there consistent trends among related genera; rather, the authors have compared eye sizes across a broad range of taxa and show, for a few species (e.g., 3 unrelated lobsters: Homarus americanus, Panulirus interruptus, and Nephrops norwegicus), larger relative eye sizes in the deeper-dwelling species

A common open-water shrimp along the west coast, Sergestes (Eusergestes) similus, undertakes diel vertical migrations, spending night-time in shallower water near the surface where it feeds, and daytime at depth where it digests its food.  A shipboard study using specimens collected off the coast of southern California assesses the energetic costs of making 2 daily trips of 300m each (from a daytime depth of about 425m to a night-time depth of about 125m).  The author uses a swim-tunnel device that employs a torsion-needle attached to the shrimp that automatically assesses swimming orientation and swimming speed, and adjusts flow rates so that the shrimp is maintained in the same location in the swim chamber.  Temperatures are adjusted to a daytime temperature of 7^oC (equivalent to the temperature at depth) and a night-time temperature of 13^oC (equivalent to that at the surface), and oxygen uptakes are measured to enable metabolic determinations. 

Results show that the shrimps swim more or less continuously at routine rates of about 5cm ^. sec^-1 with burst speeds at about 17cm ^. sec^-1.  During simulated night-time they swim upwards at 6cm ^. sec^-1 and during daytime they swim downwards at a slightly slower speed.  Movement downwards is always active, never by passive sinking.  Swimming is by paddling with the abdominal appendages.  The focus of the study is on the energetic savings of a vertical-migration strategy.  Results show that of a total of 272µmoles O₂ ^. g live mass^-1 consumed daily, some 147µmoles is used at night (54%) versus 87µmoles during the day (32%), with the 2 migrations accounting for the remainder. As to the question of energy savings, a shrimp that stays in the warm surface waters would use the equivalent of 45cal ^. g live mass^{-1 .} d^-1, while one staying at depth would use 18cal ^. g live mass^{-1 .} d^-1.  However, a shrimp that migrates vertically would use 27cal ^. g live mass^{-1 .} d^-1, thus potentially saving energy while still being able to feed at the surface. Thus, a shrimp migrating daily from deeper water to the surface clearly will benefit in metabolic savings over  one remaining at the surface.  Whether this is true for other vertical migrators should provide much scope for research.  Cowles 2001 Pac Sci 55: 215. Photograph courtesy the author.

NOTE  the author discusses the inherent constraints of the system, for example, forward swimming only and no turning ability of a shrimp in the chamber, and how this might affect the quality of the data

NOTE  the idea that vertical-migration is an energy-savings strategy has been around for several decades – an organism feeds actively in warmer surface waters and then migrates to cooler, deeper waters to digest.  This, in theory, allows it to allocate a greater proportion of energy intake to growth and reproduction

Transportation of ghost shrimps Neotrypaea californiensis from Oregon and Washington into southern California for use as live bait¹ for fishing presents a risk of homogenising genetic variation in the species.  In fact, analysis of 2 mitochondrial DNA markers reveals little phylogenetic structure across this geographic range, owing presumably to widespread larval dispersal, and suggesting that the risk of homogenisation is low.  The study, done in Long Beach, California unexpectedly reveals the presence of a second² putative species of Neotrypaea in southern California intertidal habitats (shown as Clade A in the diagram).  The northern limit of range in this new species is Pt. Conception. Although genetic effects of the transport appear to be minimal, the authors note a more substantive risk – that of introducing a parasitic bopyrid isopod Ione cornuta³ into southern California waters, where it does not appear to be native.  Pernet et al. 2008 Mar Biol 153: 1127.

NOTE¹  such “bait-bucket transfer” is well known for freshwater habitats, but not so much for marine

NOTE²  a second known species in southern California is the less-commonly occurrring N. gigas (hard to distinguish morphologically from N. californiensis), but it is not apparently found intertidally in southern California

NOTE³  the authors report a 6% infestation in ghost shrimps purchased from bait shops