Physiology & physiological ecology
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  Diel, seasonal, & tidal movements/rhythms
 

The topic of physiology & physiological ecology is divided into a section on diel & seasonal rhythms considered here, and sections on pH & OCEAN ACIDIFICATION, CHEMORECEPTION, GAS EXCHANGE & METABOLISM, LOCOMOTION & TENACITY, OSMOTIC REGULATION & SALINITY TOLERANCE, and THERMAL STRESSES considered elsewhere.

This section is split into a part on diel & seasonal movements/rhythms and one on tidal rhythms of sand crabs Emerita analoga.

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Diel & seasonal movements/rhythms
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Research study 1
 

graphs showing activity during the day in shore crabs Hemigrapsus oregonensisA laboratory-based behavioral study on shore crabs Hemigrapsus oregonensis at the University of British Columbia shows that maximum locomotory activity in males is in early morning.  Females tend to be equally active during the 24-h period. The extent to which these diurnal rhythms in the laboratory reflect behaviour in the field is not known.  Symons 1964 Ecology 45: 580.photograph of shore crab Hemigrapsus oregonensis in a tidepool

NOTE  activity in this study is expressed as % change on the average of all experimental animals used.  How this translates into real activity is not known.  Data for several holding and experimental temperatures are combined here for each sex


Hemigrapsus oregonensis
in a tidepool 1.5X

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Research study 2
 

photograph of a kelp crab Pugettia producta, alive but temporarily strandedAlthough kelp crabs Pugettia producta give the impression of clinging to large kelps throughout the year, a study in San Pedro, California shows that this may be a seasonal activity.  By monitoring a bed of giant kelp Macrocystis pyrifera periodically over a 10-mo period the authors show that adult crabs migrate into the kelp canopy in late summer/autumn where they feed on the kelps, court, and mate in groups (2-5 individuals).  Only a single male is present in each group, while (subordinate?) males cling to separate kelp stipes and maintain distinct individual distances. After December the large crabs leave the kelp plants, perhaps to move into algal turf in shallow areas, and only a few small crabs remain. During the summer only a few crabs (of all sizes) are present. The reason for the migration is not known. Wicksten & Bostick 1983 J Crust Biol 3: 364.

NOTE  the authors check each plant in a 1-acre (0.4hect) area of transplanted kelp plants, using snorkelling equipment

Kelp crab Pugettia producta temporarily in air on the beach 0.5X

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Research study 3
 

photograph of a shore crab Hemigrapsus oregonensishistogram showing activity patterns of shore crabs Hemigrapsus oregonensis in relation to time of day and tidal height
Studies on diurnal locomotory activity in shore crabs Hemigrapsus oregonensis collected at Yaquina Bay, Oregon indicate that state of tide is a more important determinant of activity than any other factor, including light.  A possible exception to this, noted by the author, is that crabs are significantly more active during night-time high tides than during daytime high tides. Batie 1983 Northwest Sci 57: 49.

NOTE the crab shown above is likely a hybrid between H. oregonensis and H. nudus

NOTE  activity of individual crabs is measured using a small “desk-top” chamber balanced such that it tilts when a crab moves.  Each tilt is registered by micro-switches and transmitted to an event recorder for later analysis 

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Research study 4
 

photograph of kelp crab Pugettia richii courtesy Ron Long, SFU, Burnaby, B.C.In Pacific Grove, California spider crabs Pugettia richii tend to favour kelps Cystoseira osmundacea as habitat, and the fronds of the kelp are a preferred food.  Occupation of the upper parts of the plants, especially by males, follows a diel pattern, with the males moving up into the plants (more exposed) at nighttime and down (more protected) during daytime.  The females remain lower down on the plants.  The author suggests that the behaviour has evolved as a predator-avoidance mechanism.  At least 9 species of fishes in the area eat spider crabs and the fishes are apparently more abundant during daytime.  Avoidance of bottom-foraging octopuses is another possibility.  Aris et al. 1982 Bull Mar Sci 32: 243. Photo courtesy Ron Long, SFU, Burnaby, B.C.

 

 

Kelp crab Pugettia richii 1.5X

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Research study 5
 

photograph of a juvenile Cancer magisterObservations in Grays Harbor, Washington also show a diel cycle in activity with numbers of crabs Cancer magister being greater in subtidal areas during daytime and in intertidal areas during night-time.  The authors suggest that the response owes to greater presence of shrimp Crangon spp., a major food source of food especially for juveniles, in shallow waters at night.  Stevens et al. 1984 J Crust Biol 4: 390.

 

 

Juvenile Cancer magister 1X

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Research study 6
 

histogram of seasonal movements of Dungeness crabs Cancer magister at Trinidad Head, CaliforniaSeasonal movements of Dungeness crabs Cancer magister are monitored in a large-scale study at Trinidad Head, northern California. After 11,072 adult female crabs are tagged1, they are released from offshore positions.  Of the total released, 463 tags are recovered2 over the following 3yr.  Some 46% of these are recovered during the first year within 2km of the original release point, indicating remarkable site fidelity3.  Large numbers are recovered in inshore areas during springtime, confirming that the females move inshore for moulting, mating, and extrusion of egg masses.  Note in the histogram that some individuals have travelled up to 60km from their release points, most of these having been at large for almost 3yr.  The authors note that there is no significant tendency for north or south movements along the shore. Diamond & Hawkin 1985 Can J Fish Aquat Sci 42: 919.

NOTE1  tags are of the plastic anchor-type, inserted at the posterior epimeral suture to ensure high retention rates through moulting.  Other tags used with crabs are stainless-steel straps and suture tags. Gotshall 1978 Calif Fish Game 64: 234 and Diamond & Hawkin 1985 Can J Fish Aquat Sci 42: 919.

NOTE2  the incentive for crab fishers to return tags found in their catches is a once-yearly opportunity to participate in a single-prize draw for $500

NOTE3  the stay-at-home propensity of Cancer magister in northern California is documented in an earlier study in which 6209 males are tagged and released.  1434 tags are returned, 1073 with catch data.  These indicate that 204 (19%) come from within 2km of their release points.  The author suggests that in the northern California area the males may move offshore during Nov-Mar and return to inshore waters in Mar-Jun. Gotshall 1978 Calif Fish Game 64: 234.

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Research study 7
  Researchers from the Pacific Biological Station, British Columbia use several methodologies, including trap/mark/release and acoustic tags, to monitor seasonal movements of Cancer magister.  Mark-recapture results show that individuals don’t move far from points of release - less than 10-15km over the entire 18-mo study period.  Males retreat to deeper water in winter and return in spring to shallower water of about 10m depth, while maturing females move from locations in coastal inlets to ones on the exposed coast.  Acoustic tagging results show that daily movements average about 300m, but with some individuals moving up to 900m in a day.  The authors find no evidence of migratory movements.  Smith & Jamieson 1990 Fish Bull 89: 137.
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Research study 8
 

photographs of pods of juvenile red king crabs Paralithodes camtschaticus at Kodiak, Alaska courtesy C. Braxton Dew, Nat Mar Fish Serv, Alaska Studies on behaviour of red king crabs Paralithodes camtschaticus around Kodiak, Alaska show that juveniles (20-25mm carapace length) form large aggregations, or pods, during the day and disperse for foraging at night. Individuals smaller than this roam freely, often associating with sea stars Evasterias troschelii, which are common in the area and which appear to offer shelter to the juveniles. The crabs forage as a tightly knit group, typically occupying 10-16m2. Several hundreds or even thousands of individuals may be involved.  Nightly movements of pods studied in 3 habitats in Woman’s Bay, Alaska average only about 5-10m.  Pod depths in late winter when surface water temperatures are about 2-4oC range from 2-4m below MLLW, and in late spring when surface temperatures are 9-12oC , from 12-16m in depth.  The function of podding is unclear, but may relate to predator avoidance, similar to the way that schooling functions in fishes. The author notes that this is the first report of circadian rhythms within the Family Lithodidae.  Dew 1990 Can J Fish Aquat Sci 47: 1944. Photos courtesy C. Braxton Dew, Nat Mar Fish Serv, Alaska.

NOTE  other crustaceans such as certain spider crabs form similar “heaps” (for moulting/mating) and spiny lobsters form “queues” (involved in migrations) 

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Research study 9
 

maps showing seasonal movements of red king-crabs Paralithodes cantschaticus in Auke Bay, AlaskaStudies using ultrasonic transmitting devices in Auke Bay, Alaska on seasonal migration and distribution of red king crabs Paralithodes camtschaticus show that females move to deep water in spring after mating and egg extrusion, stay there until early November, and return to shallow water until early March (see maps). Moulting is during March-May in shallow water.  Females during their initial year of maturity move on average more in a year (12km) than ones that have previously reproduced (4km). Light and water temperature are implicated in these seasonal movements.  During winter when they are in large aggregations in shallow water, the females form pods, a behaviour not reported previously for adults of this species.  Stone et al. 1992 J Crust Biol 12: 546.

NOTE  telemetry devices are fixed to the crabs and monitored approximately weekly for 1yr

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Research study 10
 

An idea that movement of shore crabs Pachygrapsus crassipes within salt-marsh habitats can act as a bioindicator of habitat condition is tested by scientists at the Bodega Marine Laboratory, California in 2 marshes in California.  The researchers’ thinking is that significant shifts in distributions within the marshes may signify onset of unfavourable conditions.  Over 1100 crabs are captured in pitfall and minnow traps in different areas of the marshes, then tagged with glued-on numbered shellfish tags and released in these same areas.  During the next 3mo, crabs are recaptured at varying intervals (recapture success is about 18% for the 2 sites).  Over the 3mo study period, most crabs (75%) are photograph of shore crab Pachygrapsus crassipes courtesy Dave Cowles, Walla Walla Universityfound to have remained in the same area where originally tagged.  These crabs have moved less than 5m from the original tagging locations.  Only about 18% of the total have migrated between tidal creeks and marsh plains, and this seems to have mainly happened during spring tides, perhaps avoiding short-term inundation.  Results from stable-isotope analyses indicate that what movements occur may be associated with gradients in nutrient contamination.  Overall, the authors consider that P. crassipes can act as an effective indicator of small-scale variation in habitat condition.  Morgan et al. 2006 Mar Ecol Progr Ser 314: 271. Photograph courtesy Dave Cowles, Walla Walla University, Washington wallawalla.edu.

NOTE  a northern site is at Walker Creek, Tomales Bay, while a southern site is at Carpenteria Salt Marsh, Santa Barbara

NOTE  a stable-isotope study conducted at the same time as the mark-recapture study provides supportive evidence of Pachygrapsus’ “home-bodyism”

 

Shore crab Pachygrapsus crassipes 1.3X

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Research study 11
 

graph showing movements of king and tanner crabs from Muir Inlet into Glacier Bay seasonallymap showing geography of Glacier Bay, Alaska with marine protected areas shown (MPAs, no commercial fishing)Research on movements of red king-crabs Paralithodes camtschaticus and tanner crabs Chionecetes bairdi in Glacier Bay (see map), Alaska shows that to be effective at protecting broodstock from fishing mortality, marine protected areas (MPAs) must be much larger than is typical of MPAs worldwide.  The researchers use sonic tags to monitor movements over 0.7-1.3yr durations (about 30 individuals of each species are tagged). Average daily distances moved by both species range from 30-40m per day.  However, results of most significance relate to seasonal movement by both species out of Muir Inlet (one of the MPAs ) into the central part of Glacier Bay where fishing still occurs (see graph).  Reflected in the graph is a generally steady movement south out of the Inlet by Tanner crabs, but a seasonally related north-south-north cycle of migration by king crabs. After 350d from tagging, about 35% of tanner crabs have moved out of the Inlet, as compared with only 7% of king crabs.  Movements of king crabs may be less through seasonal concentration into breeding aggregations (see Research Study 9 above).  Of interest is the discovery of natural habitat barriers for Tanner crabs, of fairly large spatial scale, that could be incorporated into the design of more effective MPAs for the Glacier Bay area.  Taggart et al. 2008 Mar Ecol Progr Ser 365: 151.

NOTE  these species represent 2 of the most commercially valuable crab species in Alaska.  Harvest of both species peaked  in the 1970s, but stocks underwent massive declines over the next couple of decades accompanied by area-specific fishing closures.  In 1998 about half of Glacier Bay was closed by congressional decree to commercial fishing

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Tidal rhythms in sand crabs Emerita analoga
 
Research study 1
 

diagrams of beach orientation of sand crabs Emerita analogadiagram showing beach orientation in sand crabs Emerita analogaSand crabs Emerita analoga inhabit surf zones on sandy beaches.  In an early, if not the earliest, behavioural study on the species, a researcher at La Jolla, California performs some simple experiments on orientation to light and beach slope.  When placed on flattened areas of the beach either close to the water or up to 60m distant, the crabs invariably orientate to the water (see illustrations on Left).  If their view of the ocean is blocked, this orientation is disrupted.  Similarly, if their eyes are removed, the ability is lost even when tested close to the ocean (see illustration upper Right).  Beach slope is tested and also found to be involved in orientation.  Crabs move down slopes greater than about 7o, regardless of whether the ocean is visible or not.  On slopes less than 7o, movement direction is random. The study raises many questions and further research is justified. Mead 1917 Univ Calif Publ Zool 16: 431.

NOTE  trauma of eye excision is accounted for by testing one batch of eyeless individuals immediately, and keeping 2 other batches in an aquarium for 2 and 19d, respectively, and then testing them.  Results are similar to those of the first batch as shown

 
Research study 2
 

photograph of mole crabs Emerita analogaSand or mole crabs Emerita analoga feed on particulate food which they collect from the water washed down the beach after each incoming wave.  The crabs form aggregations that move up and down the beach en masse in accordance with the changing tides.  Observations of such aggregations by a researcher based at the Kerckhoff Marine Laboratory, Corona del Mar suggest that factors involved in keeping a crab a certain level on the beach appear to include current, water depth, beach slope, and light.  Other possible contributing factors are surf conditions, food availability, water temperature, and sand-grain size.  Although eaten by numerous species of birds, including sandpipers, curlews, scoters, and other types, predators appear to play a lesser role in regulating Emerita’s position on the beach than physical factors.  Sand-beaches are unique habitats that may be densely populated by organisms, such as E. analoga, that are themselves uniquely adapted to their conditions.  They feed mainly by filtering the backwash water with their large, feathery antennae.  Movements up and down the beach to attain best position for longest filtering time tend to occur by mass movement of the entire aggregation in just a few seconds (see photographs).   After such a movements the crabs dig in quickly.  MacGinitie 1938 Am Midl Nat 19: photographs of sand crabs Emerita analoga in aggregation and moving down the beach471.

NOTE  no data are presented by the author

NOTE  feeding of sand crabs is described LEARN ABOUT CRABS/SUSPENSON-FEEDING

Two sand crabs Emerita analoga sit in feeding
posture in a tank at the Monterey Bay Aquarium

 

 

 

Aggregation of sand crabs Emerita analoga: LEFT: feeding in
wave swash with antennae extended; RIGHT: mass movement
to a lower shore level. Photographed from 1.5m height

 
Research study 3
 

graph showing relationship of aggregations of sand crabs Emerita analoga to the daily tide cycle
On beaches around San Diego, California, aggregations of sand crabs Emerita analoga occur in densities averaging 4000 individuals . m-2.  Early studies by a researcher at the Scripps Instituion of Oceanography, UC La Jolla reveal that the aggregations move up and down the beach with the tides (see graph). The crabs also appear to have an activity rhythmn synchronous with the tides.  For example, in artificial light in the laboratory, adult females in particular exhibit endogenous activity rhythms with peaks at about high tide.  In one set of experiments, the author moves 9 aggregations each of several thousand crabs to new locations on the beach.  Three of these become well established, suggesting that the aggregations are principally biological in origin, arising from the behaviour of the crabs themselves rather than being a product of physical conditions.  The author suggests that the primary function of aggregations is to bring the 2 sexes into close proximity for reproduction.  Efford 1965 J Anim Ecol 34: 63.

NOTE  juvenile densities are usually much higher than this, with numbers sometimes reaching up to 20,000 individuals . m-2

NOTE  an earlier publication alludes to enhanced responsiveness to small pressure increases in sand crabs collected from the same geographical area, but no follow-up work seems to have been done. Enright 1962 Comp Biochem Physiol 7: 131    

 
Research study 4
 

The presence of large aggregations of sand crabs Emerita analoga on beaches around Santa Barbara, California has led to several investigations as to how distributions are determined, both vertically in the tidal zone, and laterally along the beaches.  These basically stem from the earlier work described in Research Study 1 above.  In one of these, a researcher from UC Santa Barbara proposes an interesting theory relating to avoidance by Emerita of areas of “puddled” sand.  The puddlings occur at the tops and bottoms of the wave swash, the fluidity of the sand being created by water movements.  The sand crabs do not like the liquefied sand and tend to burrow out of it, thus maintaining them within the boundaries of the wave swash.  As the tide moves in or out, the upper and lower boundaries of the swash shift, and the sand crabs move up or down  with them (see drawings below).  In the author’s view, lateral flows within the wave swash gradually move the crabs along the beach to areas where opposing waves converge or where an obstruction is met, and they accumulate to form their characteristic aggregations.  The study incorporates some of the ideas from the earlier studies (Research Studies 1 & 2 above), but adds the unique idea of “puddling avoidance”.  The author concludes that Emerita’s migrations up and down the shore do not originate with a “biological clock”; rather, they correlate with wave action and other water movements.  Cubit 1969 Ecology 50: 118.

NOTE  this puddling, well familiar to beach-walkers, is called a thixotropic effect;  the opposite, or dilatantic effect, causes sand under pressure to become hard

NOTE  the author is able to re-create this behaviour in Emerita in several simple laboratory experiments, which lead to the following summary:

   
 
On an incoming tide:

drawing #1 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
Emerita feeding in the swash zone are struck by the incoming waves

drawing #2 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
The crabs are "puddled" by the waves & swim out of the disturbance
 
  drawing #3 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
The wave wash carries the crabs up the beach

drawing #4 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
The crabs burrow into the sand as the wave draws back. On subsequent waves they begin to feed again.

 
 
On an outgoing tide: drawing #6 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
As the tide falls, the thixotropic area reaches the crabs and they swim out into the water
drawing #2 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
The back-wash of the wave carries Emerita down the beach
 
 
  drawing #7 in a series of 7 showing how sand crabs Emerita analoga move up and down the shore with the tides
As the back-wash lessens, the crabs dig in and resume feeding
 
 
Research study 5
 

A later study on the beaches around Santa Barbara, California addresses the question as to whether the aggregations of Emerita analoga are static in position or whether they move along the shore, perhaps by current or wave action, or a combination of both.  Researchers from UC Santa Barbara test this idea by marking 2990 crabs, releasing them on the beach where they are collected, and then monitoring their positions on the shore on subsequent daily samplings over 27d total.  In all, 6 aggregations are monitored over about 900m of shoreline.  The along-shore drift is monitored with a plastic golf ball containing holes that floats just under the water surface.  Results show that the mean net drift along the shore during the period of study is 280m per hour in an eastward direction or 6700m per day, but with considerable variability. Over 27d of collection, 114 marked crabs are recovered, showing a mean eastward movement of about 15m per day.  Despite the apparent eastward movement of individual crabs, the 6 aggregations appear to maintain their positions along the beach “fairly regularly”.  The authors note, however, that the aggregations appear and disappear regularly throughout the study period.  Based on the general stability of the aggregations in terms of position despite the movements of individual crabs, the authors conclude that the aggregations must be made up of ever-changing sets of crabs.  Their data, in fact, suggest a physical basis for formation of aggregations, contrary to conclusions from an earlier study (see Research Study 2 above). In their summing up, the researchers question the validity of growth data sampled from sand-crab populations that are assumed to be stationary.  As for the crabs, are they fated to move steadily down the beach in conveyor-belt fashion and, if so, where do they pile up?  This is not discussed by the authors.  Dillery & Knapp 1970 Crustaceana 18: 233.

NOTE 2 methods of marking are used, including notching the carapace and sewing 0.3m threads onto the carapace as visual markers.  A third method, involving small buoyant corks attached to the threads, is tested but not used in the main part of the study.  The last method leads to best recovery (61% over 27d, as compared with 3 and 6%, respectively, for notching and threads) but, if used, could have biased the experiment owing to greater resistance in waves and currents.  The potential bias in this respect of thread plus cork, or even threads alone, is not discussed by the authors.  Tests using fingernail polish, vital stains, and waterproof felt-tipped pens are unsuccessful

 
Research study 6
 

A later study by a researcher from the Marine Science Institute, Santa Barbara on the causes of aggregated distributions in sand crabs Emerita analoga reveals significant day and night differences in overall abundances and in distributions of females.  First, densities of both sexes on the beach during the day is almost twice that during the night.  Second, large females are found at the lower edge of the population’s shore distribution during the day, but are more evenly dispersed during the night.  Finally, the entire population on Isla Vista Beach near Santa Barbara shifts seaward during the day and shoreward during the night.  The author remarks that these findings do not support an earlier hypothesis (see Research Study 3 above) that wave convergence alone is responsible for the aggregated distribution of mole crabs along Californian beaches.  Clearly, more research is needed on the subject.  Fusaro 1980 Crustaceana 39: 287.

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