Reproduction
  Topics on reproduction include larval life, considered here, and COPULATION, EGG RELEASE, & LARVAL STAGES (separate sections for genus CANCER, GENERA A-L, and GENERA O-R), and SETTLEMENT, METAMORPHOSIS, & RECRUITMENT, considered in other sections.
  Larval life
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Research study 1
 

photograph of mole crab Emerita analoga
As is the case with most or all long-lived planktonic larvae of decapod crustaceans, offshore drift may be considerable.  This is shown in early collections of larvae of mole crabs Emerita analoga off the California coast from San Luis Obispo to San Diego, where zoeal Stage I larvae are found up to 32km offshore. Furthest from shore are zoeal stage III and IV larvae (up to 140km), while the settling stage V are only found close to shore.  In these early days of oceanographic studies along the west coast of North America, the author actually uses the larval stages as indicators of alongshore current flows in the region of southern California.  Johnson 1939 J Mar Res 3: 236.

 
Research study 2
 

drawings of swimming behaviour of megalopae of the crab Lophopanopeus bellusResearch on larvae of the pebble crab Lophopanopeus bellus in California shows that hatching is to a prezoea larva that lasts 0.5-2h in duration, followed by 4 zoea larvae and a megalops stage. The zoeae and photograph of crab Lophopanopeus bellusmegalopae (see drawings) swim either in a straight line using their maxillipeds as paddles, or in a “hop-up-and-sink” fashion where the body springs off the coiled abdomen aided by the maxillipeds thrusting downwards. Knudsen 1960 Pac Sci 13: 3.

NOTE  species featured in the study are Lophopanopeus leucomanus and L. bellus, but also included are less well-known species Cycloxanthops novemdentatus and Paraxanthies taylori

 
Research study 3
 

drawing of prezoeal stage of porcelain crab Petrolisthes pubescensResearch at Hatfield Marine Sciences Center, Oregon provides comprehensive information on behaviour of zoeae (including "prezoeae" = protozoeae), Zoea I, Zoea II, and megalopae larvae of 4 species of porcelain crabs, collected as gravid adults and reared in the laboratory.  Both of the later zoeal stages are strong swimmers drawing of 2nd zoeal stage of porcelain crab Pachycheles pubescens showing details of maxilliped morphologyand both are carnivorous.

The zoeae swim forwards by beating the maxillipedal exopods in a posterior direction with the telson extended posteriorly (drawings on Left).  Quick reversal is effected by snapping the telson forward and beating the maxillipeds in an anterior direction.  Prey capture is by contact, not visual, so there is no true hunting.  Prey is captured with the paired maxillae (not shown), and held for eating by the abdomen and telson, which flex forwards.  The mouth is used to clean the various appendages. 

drawing of megalopal stage of porcelain crab Pachycheles pubescensAfter moulting to the megalops stage, all species begin to filter-feed like adults using the 5 pairs of mouth appendages.  In laboratory culture the megalops eats only phytoplankton.  The particles are drawings of 2nd and 3rd maxillipeds of porcelain crab Pachycheles pubescensfiltered out by bristles of the 3rd maxillipeds, which are then combed by setal brushes of the 2nd maxillipeds and the particles moved to the mouth (see drawings below Left). The 3rd maxillipeds work alternately, one filtering while the other is being combed.  During the combing, inedible or undesirable particles are flicked away by the exopodites of the 2nd maxillipeds. The setal brushes on the 3rd maxillipeds are also used to clean the antennae.  Note in the drawing on the Right that the 5th pair of walking legs of the megalops are tucked along the carapace when not in use.  These are used to clean all parts in their reach, including abdomen, telson, and walking legs.  They are too short, however, to reach the claws and undersurface of the anterior body.  The megalopae swim by paddling with their abdominal pleopods, and older larvae may clap their abdomens to move backwards quickly.  In laboratory culture at 12-15o, the megalops float about for about 2wk after moulting from the 2nd zoeal stage, then begin to settle. Gonor & Gonor 1973 Fish Bull 71: 189; Gonor & Gonor 1973 Fish Bull 71: 225.

NOTE  the authors provide behavioural observations for all 4 species but, as the behaviours are mostly similar, the information is presented here as a summary for Pachycheles pubescens.  The other species are Pachycheles rudis, Petrolisthes eriomerus, and Petrolisthes cinctipe

 
Research study 4
 

photograph of juvenile Dungeness crab Cancer magister
Preliminary research on offshore distribution of larvae of Cancer magister in central Oregon indicates that hatching is in January-March and the larvae remain in the plankton until late May (about 130d).  In this area the females carry their eggs from October-March and have a single brood per year.  The 1st zoeal larval stage or hatching stage is strongly photopositive and swims to the surface where the current is mainly onshore in winter.  The author is not able to identify food items in the guts of the larvae.  Lough 1976 Fish Bull 74: 353.

 

Juvenile Cancer magister 0.5X

 
Research study 5
 

photograph of shore crab Pachygrapsus crassipes courtesy Jackie Soanes, Bodega Bay Laboratory, Californiagraph showing number of megalopae of shore crabs Pachygrapsus crassipes caught in plankton tows in relation to daily maximum tidal ranges in La Jolla, CaliforniaAfter several months drifting in the plankton, most megalopae find themselves too far from shore and die. Others may be transported shorewards in internal waves generated by tidal movements. A study on the shore crab Pachygrapsus crassipes at the Scripps Institution of Oceanography, La Jolla, California explains how this might work.  Collections of larvae over a 3-mo period from the end of a pier and in nearby areas show that the megalopae may actually be carried ashore in surface slicks generated by tidally forced internal waves. Such surface slicks are commonly visible to the eye as lines of flotsam. The slicks precede the tide by a few days and will move drogues shorewards in 2-3h over a distance of 1-2km. Larvae, including other invertebrates and fishes, are 6-40 times more concentrated in the surface slicks than in the surface water between the slicks.  The data presented in the graph show a synchronicity between maximum tidal ranges (monthly springs and neaps) and presence of megalopae in shallow surface waters. The author suggests that such tidally driven transport may be an important means for onshore transport of P. crassipes and other species.  Shanks 1983 Mar Ecol Progr Ser 13: 311; for more on shoreward transport of crab larvae in foam slicks see Shanks et al. 2003 J Plankton Res 25: 1251. Photo courtesy Jackie Soanes, Bodega Marine Laboratory, California.

NOTE  the pier is 320m in length with a water depth of 6m at its end.  The larvae are collected on 1-m long bundles of hemp or surf grass suspended at standardised times and depths from the end of the pier

NOTE  the drogues are plastic cups weighted with sand so they float with their rims just at the surface. 

 
Research study 6
 

In a follow-up study at La Jolla, California, the same author of the foregoing Research Study observes megalopae of Pachygrapsus crassipes to swim to the surface both in open-water releases (monitored by SCUBA) and in controlled laboratory situations.  Their behaviour involves both positive phototaxes and negative geotaxes, and includes a strong tendency to cling to objects in the water (including SCUBA divers).  The larvae are quite speedy (mean swimming velocity of 9cm . sec -1) and can make positional adjustments quickly.  The author suggests that these observations are consistent with the hypothesis that P. crassipes megalopae inhabit the neuston and are transported shoreward in tidally forced waves.  Shanks 1985 Mar Ecol Progr Ser 24: 289.

NOTE  planktonic organisms associated with the air-water interface.  Collections by plankton net show that the megalopae are 10 times more abundant in the neuston than at depths to 6m

 
Research study 7
 

photograph of shore crab Hemigrapsus oregonensisWhat duration of feeding is required for a megalopa to attain metamorphosis?  This is investigated at Shannon Point Marine Center, Washington for megalopae of the shore crab Hemigrapsus oregonensis.  Rather than treatments involving diferent daily rations, which are often used for a study of this sort, the authors opt to feed the larvae ad libitum for different periods commencing from a Day 0 start time that begins with the appearance of the megalopa stage.  Results show that survival is good on the CONTROL and 10-Day-Fed treatments, but poor on the Starvation treatment (100% mortality by 20d post-megalopa).  80% and 85% of CONTROL and 10 Day-Fed megalopae, respectively, moult to the 1st-crab instar, while only 38% of 5-Day-Fed animals reach this stage.  These results do not differ significantly, prompting the authors to conclude that megalopal duration is not affected by total food deprivation imposed as early as 5d in the duration of the instar.  Clearly, though, there is a trend, and further research may be justified.  Farrelly & Sulkin 1988 J Crust Biol 8: 614.

NOTE  treatments are Starvation: No food (Artemia nauplii) over the entire 24-d study period; 5-Day Fed: fed for the first 5d, then starved; 10-Day Fed: fed for the first 10d, then starved; and CONTROL: fed for the entire 24d.  Megalopae vary in age by a few days

 
Research study 8
 

map showing location of study area Auke Bay, Alaska for work on growth of larvae of Alaska king crabs Paralithodes camtschaticaphotograph of Alaska king crab Paralithodes camtschaticaLab studies on nutrition in Stage I zoea larvae of Paralithodes camtschaticus in Auke Bay, Alaska show that different species of diatoms provide markedly different nutritional benefit.  Of 3 phytoplankton species tested, only Thalassiosira nordenskiodii sustain the larvae through the moult to the zoeal stage. Note in the graph that at high food levels almost 100% of the zoeae moult to the next stage. Although abundant in the plankton at the same time as Stage I zoeae are hatching, nauplii larvae of copepods and barnacles are not consumed.  The authors note that zoeal hatching concurrent with spring phytoplankton blooms may be an important factor affecting their survival.  Paul et al. 1989 J Exp Mar Biol Ecol 130: 55.

NOTE  species tested are those found to be present in the plankton at the time of the study, and concentrations provided in culture mimick natural concentrations.  Species used are diatoms Thalassiosira nordenskiodii, Chaetoceros debilis, and Skeletonema costatus.  Percentages of Zoeae I moulting to Zoeae II on these 3 diets are, respectively, 96, 5, and 27

NOTE  the researchers have fit a curvilinear line to their data, likely the best fit statistically, but perhaps not appropriate to scaling expectation. Shouldn't a linear increase in food particles lead to linear increase in growth and moulting? Note also that the curvilinearity of the data appears to largely depend upon an "outlier" point

 
Research study 9
 

photograph of female Pinnixa sp. nestles between the demibranchs of a sea mussel Mytilus californianus
Biweekly plankton-tow collections of brachyuran larvae in Elkorn Slough and 1km offshore in Monterey Bay, California provide data on seasonality of occurrence of species in 5 families, with the following species being most common: Pinnixa franciscana, Pinnixa weymouthi, Hemigrapsus oregonensis, Cancer gracilis, and Pachygrapsus crassipes. In general, zoea and megalopae larvae are most abundant in the plankton in late winter/spring.  An exception is P. crassipes, which is most abundant in late summer/early autumn.  Hsueh 1991 J Crust Biol 11: 546.

A female Pinnixa sp. nestles between the demibranchs of a sea mussel
Mytilus californianus. There are about a dozen species ofwest-coast
Pinnixa
that are parasitic on ( or commensal with?) various invertebrates
including worms, bivalves, sea cucumbers, and others 2X

 
Research study 10
 

Experiments on depth regulation in 1st zoeae larvae of Hemigrapsus oregonensis at Shannon Point Marine Center, Washington show that the larvae are negatively buoyant and will sink when they stop swimming.  When salinity is high, sinking rate decreases because of the increased buoyancy.  The larvae are negatively geotactic and tend to move to the surface as they swim.  Experiments show that there is no effect of incremental increase in hydrostatic pressure up to 0.8 atmospheres on swimming activity in the zoeae.  Arana & Sulkin 1993 Pac Sci 47: 256.

 
Research study 11
 

photograph of juvenile Dungeness crab Cancer magisterAt the end of their larval lives, megalopae of Cancer magister swim to the sea bottom and actively seek out a spot to settle.  In Grays Harbor estuary in Washington the preferred substratum is oyster-shell deposits.  Natural current-flow rates in this area range up to 40cm . sec-1 and the question arises as to whether the megalopae are capable of making headway against these current velocities.  In the first study of its kind, researchers using a recirculating-flume apparatus determine that swimming speeds vary from 8cm . sec-1 in still water (about 8 body lengths . sec-1) to 45cm . sec-1 in current speeds of 40cm . sec-1 (about 44 body lengths . sec-1).  Megalopae spend a large proportion of time swimming against the current and the fact that they are able to make headway over the full range of natural current velocities tested suggests that they are capable of making active settlement-site choices over the range of current velocities found in Grays Harbor.  Fernandez et al. 1994 Estuaries 17: 271.

NOTE  studies on C. magister in Grays Harbor show that there is a 60-fold greater settlement on oyster shells than on adjacent mud

 
Research study 12
 

schematic of orientation of megalopae of shore crab Pachygrapsus crassipes while swimming Although crab megalopae are generally strong swimmers, it is mostly thought that in their later free-living stages when they are ready to seek out settlement sites they cling to floating debris and are driven close to shore by wind and waves.   A test of the alternative hypothesis, that the megalopae actually swim onto shore rather than clinging and floating, provides information on orientation and swimming depth for several west-coast species.  The tests mostly involve releasing megalopae from a 50-ml syringe at depths of 2-5m and about 150m from shore, and then visually monitoring their swimming direction for as long as possible.  On the west coast of North America, to gain the shore the megalopae would have to swim towards the east.  Results show that on release most magalopae swim towards the surface, level out at a certain depth, and swim straight courses.  In the case of Pachygrapsus crassipes, presented here as a typical example for most of the species, swimming orientation is either random, or toward the direction of the brightest underwater illumination or the sun, but not necessarily in a shoreward direction. Data for megalopae of Lophopanopeus bellus suggest that they are swimming in the direction of propagation of an internal wave (detected visually from a boat).  Megalopae of Cancer oregonensis and C. gracilis swim at about 3-5m depth in the direction of the sun’s bearing.  The author records wave and current directions (including an internal wave) as part of the data set, but it is unclear how a swimming larva, as it drifts with the current, could perceive any of these parameters, let alone use them for orientation, unless it were to be using some form of celestial navigation).  An idea not fully explored by the author is that, were swimming to be more prevalent in morning in the direction of the sun, then it would in fact be in a shoreward direction.  Conversely, if the larvae were to swim through the night, then a new set of hypotheses must be considered.  Shanks 1995 J Exp Mar Biol Ecol 186: 1.

NOTE  results of other experiments done using larvae in a clear plastic cylinder at 3m depth are not included here

NOTE  because megalopae of Cancer oregonensis in open-water tests swim towards the sun, in the morning its swimming orientation would be to the east but, in afternoon, it would be to the west

 
Research study 13
 

Zoea larvae of brachyuran crabs are carnivorous or omnivorous, depending on species, and eat small crustaceans, worms, larvae, and detritus in the plankton.  Feeding rates of zoeae are usually assessed in conditions of static prey density, which are not realistic given that the larvae undergo daily vertical migrations through varying plankton-prey densities, from low densities at depth to patches of higher densities at the surface at night.  Experiments at Shannon Point Marine Center, Washington on feeding and survival of Stage I zoeae of crabs1 Cancer magister and Hemigrapsus oregonensis show that survival in reduced densities2 and non-continuous contact with prey is as good as in high densities and continuous contact, suggesting to researchers that the larvae do not require continuous access to prey for optimal development.  Although the researchers find that the zoeae can feed equally well in the dark as in the light, the prey densities used to test this are quite high (20 Artemia nauplii . ml-1 . zoea-1), and accidental contact of larvae and prey, rather than actual hunting, may have been high.  The study has an interesting premise, but the results would be more convincing had it been possible to know what the baseline density3 for a “dense patch” of prey in the plankton was, in order to set levels in these laboratory tests.  For example, the fact that the zoeae survive as well in one-quarter density of prey (97% survival to Stage II) as in “control” density (92% survival), could suggest that the researchers’ estimate of what constitutes a control or "dense patch" of prey may be 4-fold too high.  The study is an interesting one and provides useful information on what constitutes a sub-optimal diet for these species for follow-up nutritional research.  Sulkin et al. 1998 Mar Biol 131: 515.

NOTE1  the species are selected for contrast in larval robustness with respect to dietary requirements and, thus, ease or difficulty in rearing (e.g., H. oregonensis is hardy; C. magister is more picky)

NOTE2  control densities are based on a “control” diet of 20 Artemia nauplii . ml-1, which is at the “high” end of levels used in other feeding studies on crab zoeae, while “reduced” densities are ¼ of this.  The authors also alternate ad libitum feeding with varying periods of starvation

NOTE3  the authors acknowledge that their control densities of prey are likely much higher than natural densities encountered in the plankton

 
Research study 14
 

graph showing survival of zoeal larvae of Dungeness crab Cancer magister on dites of brine shrimp and rotifersAn interesting and useful finding from studies at Shannon Point Marine Center, Washington is that a single prey species eaten by zoea larvae of crabs can vary greatly in nutritional value depending on what the prey species itself had been eating.  Thus, when zoea larvae of C. magister, C. oregonensis, C. gracilis, and C. productus are fed on rotifers Brachionus plicatilis that have been raised on the chlorophyte Dunaliella tertiolecta, they fail to attain the megalopa stage. If, however, the zoeae are fed on rotifers that have been raised on the chrysophyte Isochrysis galbana, those surviving all attain the megalopa stage.  In comparison, about 50% of zoeae feeding on freshly hatched nauplii of brine shrimp Artemia salina moult to the megalops stage. The authors attribute the difference in survival on the rotifer diets to the presence in Isochrysis-fed rotifers of an abundance of long-chain Ω-3 polyunsaturated fatty acids, known to be an important nutritional component for crab larvae.  In Dunialiella-fed rotifers these particular fatty acids are absent. The authors show that the value of heterotrophic microzooplankton as prey for crab larvae, either in laboratory culture or nature, may therefore depend upon the prey’s own feeding history. An interesting study, indeed. Sulkin & McKeen 1999 Mar Ecol Progr Ser 186: 219.

NOTE  survival to megalopa in laboratory culture is 1% only in Cancer productus, while in the other 3 species it ranges from about 10-30%.  Survival to the megalopa stage in all species is about 20-70% if fed on brine-shrimp Artemia nauplii

NOTE  the authors do not report what the source culture of adult brine shrimps is eating, but this might also be interesting to know. Brine-shrimp nauplii are often used as food for culturing crab zoea; hence, are considered a kind of control diet

 
Research study 15
 

photograph of lithode crab Rhinolithodes wosnessenskii courtesy Dave Cowles, Walla Walla U and http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/In a complementary study to Research Study 14 above, the same research group at Shannon Point Marine Center, Washington reports that brachyuran larvae in culture are able to discriminate among different species of dinoflagellates as food.  For example, zoea larvae of 4 crab species readily eat the dinoflagellate Prorocentrum micans, which is known to sustain survival of the larvae in laboratory culture, but reject 2 other species of dinoflagellates Alexandrium spp., which do not sustain survival.  However, when the zoea larvae are presented with mixed diets of all 3 dinoflagellate species, most larvae readily ingest both types of algal prey. When cells of the “good” species of dinoflagellate (Prorocentrum) are suspended in exudate of the “bad” dinoflagellate (Alexandrium) the larvae are still able to find the former and eat them.  When the reverse experiment is done, the larvae are able to identify and reject the Alexandrium cells.  Rejection is done at the level of the mandibles.  When feeding on a palatable dinoflagellate, the mouthparts swing rapidly outward, drawing a cell towards the graph showing % of zoeae feeding of 4 species of crab on different ratios of dinoflagellates in the labmouth, then rapidly draw in, enclosing the cell.  In comparison, an unpalatable Alexandrium cell is drawn in towards the mouth, then a moment later is pushed away by the mandibles.  The ingestion cue, possibly a coating of lectin molecules, appears to reside on the surface of the dinoflagellate cells.

In mixed algal assemblages, where at least some cells possess the ingestion cue, non-discriminate feeding occurs.  In one experiment, only when the ratio of  “good” (Prorocentrum micans) to “bad” cells (Alexandrium fundyense) becomes greater than 1:5 do the zoeae (in the graph on the Left these are H. oregonensis) begin to reduce their feeding. The authors suggest that this strategy of indiscriminate feeding may allow rapid ingestion of both “good” and “bad” particles by the larvae when dense prey patches are encountered in otherwise sparse feeding environments.  Hinz et al. 2001 Mar Ecol Progr Ser 222: 155; ; for more on feeding of zoea larvaesee Shaber & Sulkin 2007 J Exp Mar Biol Ecol 340: 149. Photo courtesy Dave Cowles, Walla Walla University, Washington www.wallawalla.edu.


NOTE
species include the brachyurans Cancer magister, C. oregonensis, and Hemigrapsus oregonensis, and the anomuran Rhinolithodes wosnessenskii

NOTE the species are A. tamarense (2 strains: one toxic in mouse bioassays and one non-toxic) and A. fundyense (toxic in mouse bioassays)

 
Research study 16
 

Zoeae and megalopae of crabs have abundant and obvious chromatophores1 distributed over their bodies.  The function of these chromatophores is not well understood, but one possibility is that they screen out damaging ultraviolet radiation.  This is tested at Friday Harbor Laboratories, Washington by exposing dark-adapted2 megalopae of crabs Cancer oregonensis and Telmessus cheiragonus to a range of light intensities in the lab, including UltraViolet Radiation (UVB + UVA: 280-400nm), UVAR (UVA: 320-400nm), and visible light (400-1700nm).  Within minutes in both of the potentially harmful treatments (UVR and UVAR) as well as in visible light the chromatophores of both species rapidly expand (see graph3).  The authors speculate that expansion of the chromatophores in both potentially harmful and benign wavelengths may owe to an inability to distinguish among different wavelengths.  Alternatively, they add that the chromatophores may have other functions, such as crypsis (both matching and disruptive coloration), and perhaps reducing the amount of reflected UVR to decrease their visibility to fishes that hunt by detecting UVR) and/or thermoregulation.  Miner et al. 2000 J Exp Mar Biol Ecol 249: 235.

NOTE1  large, dark chromatophores called melanophores seem to be often situated over vital organs, and the melanin pigments contained in them are known to absorb strongly both visible light and UVR.  The coloured pigments of other chromatophores (yellow, orange) may function similarly

NOTE2  megalopae are kept in the dark for 8h, which causes the chromatophores to contract

NOTE3  although differences are significant for Cancer oregonensis, they are not for Telmessus cheiragonus, owing to low sample sizes and high variability

 
Research study 17
 

Settlement of sand crabs Emerita analoga along the Oregon coast may depend upon northward drift of larvae from well-established populations of adults in California.  During El Niño events there is greater northward movement of the Davidson Current in winter, and the question arises as to whether larval recruitment in Oregon is enhanced during these periods.  This is tested by a consortium of researchers from various Oregon institutions by comparing recruitment between non-El Niño (1997) and El Niño (1998) years.  Although the data are variable and based upon just a single event, the researchers show significantly  greater abundance of E. analoga zoeae at several stations off the coast of Newport, Oregon during the El Niño event of 1998, as compared with the previous year, suggestive of transport in the Davidson Current.  The authors suggest in this regard that sand-crab larvae might even act as a bioindicator of north-south current fluctuations in the area.  Sorte et al. 2001 J Plankton Res 23 (9): 939.

NOTE  seawater temperatures are 4-6oC higher on Oregon beaches during 1997-98, also indicative of northward current flow

 
Research study 18
 

example of results obtained for tidal-simulation model of zoea larval movements out of San Diego Bay for crab Pachygrapsus crassipesMany types of marine-invertebrate larvae have evolved a strategy of vertical migration coordinated with tidal cycles that permit escape from embayment areas.  An investigation by southern-California researchers of crab species from 2 families in San Diego Bay shows, however, that such behaviour is not universal.  In one species, Pachygrapsus crassipes (F. Grapsidae) Stage 1 zoea larvae rise into surface layers on nocturnal ebb tides, and are carried out of the Bay (see simulation).  On subsequent flood tides, the larvae sink to the sea bottom and become entrained in low-velocity boundary layers or actually burrow into the sediments, such that their return into the Bay is retarded.  Although much of the study is done using hydrodynamic-model simulation and employment of “simulated” larvae, the authors remark that theirs is the first actually to sample the sediment-water interface to establish the presence of zoeae on the bottom during critical phases of the tides.  The effectiveness of the behaviour is evidenced by an eventual absence of later Stage zoeae within the Bay.  In contrast, early larval stages of Lophopanopeus spp. (F. Panopeidae) exhibit no clear pattern of tidally related vertical migration, and they tend to stay within the Bay.  DiBacco et al. 2001 Mar Ecol Progr Ser 217: 191.

NOTE  the strategy, known as selective tidal-stream transport, is more common in embayments where fresh-water input aids in horizontal transport, but the interesting feature of San Diego Bay for the purposes of study is that such freshwater input is negligible or seasonally absent

NOTE  laboratory swimming rates are measured at 20mm - sec-1, more than sufficient to allow a zoea to move up and down in the water column in the time required

 
Research study 19
 

Are seasonal appearances of crab larvae in Alaska uniformly delayed over their times of appearance in more southern west-coast latitudes?  Has there been an acclimatisation?  These questions are addressed by a researcher at Moss Landing Marine Laboratories, California in an investigation at Glacier Bay, Alaska of seasonal timing in appearance of 5 families of brachyurans.  Results for 5 species (highlighted in blue in the list below) for which good comparative data are available from the present study and from previously published work,  show that the initial appearance of zoea larvae is delayed by 3-4mo in Glacier Bay relative to times of appearance in California, Oregon, and Washington.  Moreover, the overall larval duration of at least one species, Cancer magister, is about 30d longer in Glacier Bay than in the lower-latitude states.  The author discusses possible reasons for the differences, and settles on cooler water temperatures in Alaska as being the most likely influence.  Fisher 2006 Mar Ecol Progr Ser 323: 213.

NOTE  species studied include Cancer magister, C. oregonensis, C. productus, and C gracilis (F. Cancridae), Fabia subquadrata and Pinnixia sp. (F.  Pinnotheridae), Pugettia spp., Oregonia gracilis, Hyas lyratus, and Chionoecetes bairdi (F.  Majidae), Telmessus cheiragonus (F. Atelecyclidae), and Lophopanopeus bellus (F. Xanthidae)

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