Paralithodes Platypus Research Articles

Survival, growth, and morphology of blue king crabs: effect of ocean acidification decreases with exposure time

Ocean acidification is an altering marine carbonate chemistry resulting in potential effects to marine life. In this study, we determine the effects of decreased pH on the morphology, growth, and survival of juvenile blue king crab, Paralithodes platypus. Crabs were reared at three pH levels: ambient (control, pH ∼8.1), pH 7.8, and pH 7.5, for 1 year and monitored for morphological changes, survival, and growth. Exposure to seawater at pH 7.8 had no effect on morphology or mortality and had only a minor effect on growth compared with the ambient treatment. However, exposure to seawater at pH 7.5 substantially increased mortality and decreased growth compared with the ambient treatment. The best fit model of mortality rate at pH 7.5 showed an initially high mortality rate, which dropped to become comparable to the mortality rate in the other treatments. This suggests phenotypic variability or plasticity in juveniles and may indicate acclimation by blue king crab to ocean acidification. As such, blue king crab may have scope for evolutionary adaptation in response to gradually changing pH levels. However, effects on other life-history stages, sub-lethal effects, carryover or transgenerational effects, and interactions with other stressors, such as increased temperature, still need to be investigated.

The bitter crab syndrome in commercial crabs in the Western part of the Bering and Chukchi Seas

We studied the distribution of the “bitter-crab” syndrome, a disease caused by the parasitic dinoflagellate Hematodinium sp., in eight commercial species of crabs in the west of the Bering and Chukchi seas. The crabs (25 388 individuals) were sampled during bottom trawl surveys of July‒September 2010 and October‒November 2012. The disease was first identified visually by a color change of the exoskeleton and the hemolymph of the animals and then using microscope analysis of hemolymph samples. Infestation was detected in crabs of three species, Chionoecetes opilio, C. bairdi, and Paralithodes platypus. The prevalence of the disease (the percent of infected individuals relative to all of those examined) in C. bairdi and P. platypus was very low, 0.1 and 0.3%, respectively. Infestation was widespread among C. opilio, its peak in the Bering Sea was in the fall. The average prevalence of the crab disease in different areas of the Bering Sea ranged from 0.8 to 10.8%. A high rate of crab infection was recorded in the Korfa Bay. In the Chukchi Sea, the average prevalence was 2%. Infestation by Hematodinium sp. was not revealed in the deep-sea snow crabs Chionoecetes tanneri and C. angulatus, and in three species of lithodid crabs, Paralithodes camtschaticus, P. brevipes, and Lithodes couesi. This can be explained by the small sample volume and/or ecology of these species, since the disease was registered in other areas in four of them.

Influence of temperature and congener presence on habitat preference and fish predation in blue (Paralithodes platypus Brandt, 1850) and red (P. camtschaticus Tilesius, 1815) king crabs (Anomura: Lithodidae)

Rebuilding fisheries is a difficult process and many stocks that are declared overfished fail to recover even in the absence of fishing pressure. The Pribilof Islands stock of the blue king crab ( Paralithodes platypus Brandt, 1850) in Alaska, USA is one of these recovery failures. To explore how environmental and ecological factors might interact to suppress this stock, we conducted a suite of laboratory experiments to assess the effects of temperature changes and the presence of red king crab ( Paralithodes camtschaticus Tilesius, 1815) on blue king crab habitat preference and fish predation survival. Age-0 blue king crabs exhibited plasticity in habitat preference mediated by changes in water temperature, as well as the presence and density of juvenile red king crabs. While blue king crabs are often associated with shell-hash habitat, increases in water temperature, as well as the presence of red king crab at high densities, caused blue king crab juveniles to shift into habitats with an algal mimic present, a habitat type shown to reduce the predation efficacy of red king crabs. In contrast, red king crabs exhibited fewer changes in habitat preference with changes in water temperature and the presence of a congener. Blue king crabs are therefore behaviorally plastic, switching from strategies of predator avoidance when predator encounter rates are likely low, to predator deterrence strategies when encounter rates are higher. Fish predation trials further support the idea that blue king crabs are more focused on predator avoidance than are red king crabs. In fish predation trials run separately for the two crab species, blue king crabs had higher survival (60%) than red king crabs (33%) when exposed to fish predators. Our results indicate that age-0 blue king crabs can be less vulnerable to fish predation than red king crabs, but future research should assess how fish predation rates change when presented with higher densities of red and blue king crab in mixed assemblages as the observed habitat shifts could affect predation survival.

Two new cryptic and sympatric species of the king crab parasite Briarosaccus (Cirripedia: Rhizocephala) in the North Pacific.

Rhizocephalan barnacles have been reported to parasitize a wide range of king crab species (Lithodidae). So far all these parasites have been assigned to a single species, Briarosaccus callosus Boschma, 1930, which is assumed to have a global distribution. Here we investigate Briarosaccus specimens from three different king crab hosts from the fjord systems of Southeastern Alaska: Lithodes aequispinus Benedict, 1895, Paralithodes camtschaticus (Tilesius, 1815), and Paralithodes platypus (Brandt, 1850). Using molecular markers and by morphological comparison we show that Briarosaccus specimens from these three commercial exploited king crabs are in fact morphologically distinct from B. callosus, and further represent two separate species which we describe. The two new species, Briarosaccus auratum n. sp. and B. regalis n. sp., are cryptic by morphological means and were identified as distinct species by the use of genetic markers (COI and 16S). They occur sympatrically, yet no overlap in king crab hosts occurs, with B. auratum n. sp. only found on L. aequispinus, and B. regalis n. sp. as parasite of the two Paralithodes hosts.

Experimental infection of king crab hemocytes with a herpes-like virus in culture

To date, herpes-like viruses have been repeatedly found in wild king crab populations. In this study, freshly collected hemocytes of the red king crab Paralithodes camtschaticus have been experimentally exposed in culture to the herpes-like virus from thawed antennal gland samples from infected blue king crabs P. platypus. After 3–4 months of cultivation, significant differences in the pigmentation were observed between control and virus-infected hemocytes. Using Raman spectroscopy, we detected two obligatory peaks, characteristic for melanin identification, in the spectra of pigmented inclusions in harvested virus-infected hemocytes. These peaks are absent in the spectra obtained from control hemocytes. The cells of virus-infected cultures were viable after 10 months, while all control uninfected hemocytes were lost. As demonstrated by electron microscopic studies, virus-like particles become abundant at 7 days post-inoculation. Our results suggest that hemocytes could be used as a suitable model system for studies of crab pathogens. The in vitro studies confirm previous findings regarding the presence of viral infection in the natural population of king crabs.

A herpes-like virus in king crabs: Characterization and transmission under laboratory conditions

A herpes-like virus was found infecting the antennal gland and bladder epithelium in the blue king crab Paralithodes platypus from the eastern area of the Sea of Okhotsk. Electron microscopic analysis of antennal gland samples from blue king crabs with histologically confirmed signs of disease revealed virus particles, which were mostly hexagonal in shape and located primarily in the nucleus; these particles were rarely observed in the cytoplasm of infected cells. Most virus particles ranged in size from 115 to 125nm. Hemocytes of the red king crab Paralithodes camtschaticus in cell culture could be experimentally infected with virus from thawed antennal gland samples of the blue king crabs with histologically confirmed signs of viral infection. Clear signs of infection were observed in hemocyte cultures at 3–4days post-inoculation as small foci of highly vacuolated formations. These formations included several nuclei and were surrounded by a halo of small cytoplasmic bubbles containing actin and tubulin. As demonstrated by electron microscopic studies, no virus-like particles were found in the cells 1day post-inoculation, but particles become abundant at 7days post-inoculation. We developed a consensus primer PCR method for amplification of a region of the herpesviral DNA-directed DNA polymerase. Primers were designed to target sequences encoding highly conserved amino acid motifs covering a region of approximately 800bp. Thus, macroscopic, histological and ultra-structural examinations of blue king crabs infected with a virus and the molecular identification of the pathogen revealed the presence of herpesviruses. The frequency of the herpes-like viral infection in natural populations of blue king crabs in the Sea of Okhotsk ranged from 0% to 3% in different years.

Habitat, predation, growth, and coexistence: Could interactions between juvenile red and blue king crabs limit blue king crab productivity?

Since the 1970s, dominance of the shallow water Pribilof Islands king crab populations has shifted from blue king crab (Paralithodes platypus) to red king crab (Paralithodes camtschaticus), potentially influenced by interactions at the juvenile stage. In laboratory experiments, we determined whether habitat and temperature could mediate competitive and predatory interactions between juveniles of both species. We examined how density and predator presence affect habitat choice by red and blue king crabs. Further experiments determined how temperature and habitat affect predation by year-1 red king crab on year-0 blue king crab. Finally, long-term interaction experiments examined how habitat and density affected growth, survival, and intra-guild interactions between red and blue king crab. Red king crabs had a greater affinity for complex habitat than blue king crabs and the presence of predators increased preference for complex habitat for both species. Predation on year-0 blue king crabs by year-1 red king crabs was lower in complex habitats and at colder temperatures. When reared alone, red king crab survival was higher at low densities and in complex habitats. When reared with blue king crab, survival of red king crab was higher in complex habitats and in the presence of blue king crab. Blue king crab survival was substantially lower in the presence of red king crabs regardless of habitat. In both rearing experiments, differences in changes in crab size appeared to be driven by mortality rates and size-selective predation. This demonstrates that interactions between juvenile red and blue king crabs are primarily driven by intra-guild predation and not competition for resources. These results, suggest that juvenile red king crabs have an advantage over blue king crabs which could lower productivity of the Pribilof Islands blue king crab stock since the former became dominant in that system.

Application of the virtual population model in the bio-economic model of long-term dynamics for exploited population of commercial invertebrates

The virtual population analysis is used for complex tasks of bio-economic modeling of long-term dynamics for exploited population of commercial invertebrates, as blue king crab in the western Bering Sea. This method is based on the data of landings for the period exceeding the life span for the studied stock and provides guaranteed estimations of the age cohorts abundance. The assessments of the blue king crab stock dynamics are used in the economic block of the model that provides market assessment of the resource for evaluation of final cost for the manufactured goods. Two blocks of the bio-economic model allow to calculate a future income from exploitation of the resource that is necessary for planning of economical activity in fisheries industry.

Inter-Cohort Cannibalism of Early Benthic Phase Blue King Crabs (Paralithodes platypus): Alternate Foraging Strategies in Different Habitats Lead to Different Functional Responses

Blue king crabs (Paralithodes platypus) are commercially and ecologically important in Alaska, USA, but population abundances have fluctuated over the past several decades likely resulting from a combination of environmental and biological factors, including recruitment variability. Cannibalism between cohorts may be a source of mortality limiting recruitment success in the wild, but the degree of inter-cohort cannibalism is unknown for early benthic phase blue king crabs. In laboratory experiments, we evaluated the effects of habitat type (sand and shell) on the predator functional response and foraging behavior of year-1 blue king crabs as predators of year-0 conspecifics and examined the effects of predator presence on crypsis of prey crabs. In sand, consumption rates increased with predator size and prey density until satiation, while predation rates in shell were low regardless of predator size or prey density. These differential predation rates yielded a type III functional response in sand but a type I functional response in shell habitat. Crypsis of prey crabs was generally high and did not change in the presence of predators. Predator foraging activity was reduced in shell and may be an adaptive behavior to balance foraging efficiency and susceptibility to larger predators. Our results demonstrate that early benthic phase blue king crabs are cannibalistic between cohorts in the laboratory and that shell material is extremely effective for reducing encounter rates with conspecific predators. The distribution and abundance of such habitat may be important for recruitment success in some populations. Future studies should compare benthic habitat and species assemblages in areas with variable abundances, such as the Pribilof Islands and Saint Matthew Island in the eastern Bering Sea, to better understand possible mechanisms for recruitment variability.

State of stock and assessment of stock abundance of blue king crab (PARALITHODES PLATYPUS, BRANDT) in the west Kamchatka subzone for fishery campaign 2013

State of stock and assessment of stock abundance of blue king crab (PARALITHODES PLATYPUS, BRANDT) in the west Kamchatka subzone for fishery campaign 2013

Storage and utilization of lipid classes and fatty acids during the early ontogeny of blue king crab, Paralithodes platypus

Stock enhancement, through the release of cultured juveniles, has been suggested as a possible recovery tool for depleted red (Paralithodes camtschaticus) and blue (Paralithodes platypus) king crab populations in Alaska, USA. Considerable progress has been made in the past decade in red king crab culture technology, but similar technologies are less developed for blue king crabs. We examined changes in organic content, lipid classes, and fatty acids (FAs) during the larval (zoeae), post-larval (glaucothoe), and first juvenile stages to understand energetics, nutritional requirements, and potential dietary deficiencies of this new aquaculture species. Total lipids increased throughout the larval stages and then showed a decrease in both total lipids and neutral storage lipids (triacylglycerols) during the non-feeding glaucothoe phase. The proportions of C18 polyunsaturated FAs (PUFAs) dramatically increased from the first zoeal (Z1) to the second zoeal stage (Z2), reflecting the uptake of enriched Artemia FAs. Both the selective retention of C20 & 22 PUFAs relative to their diet and the proportional increase in these PUFAs during the non-feeding glaucothoe stage suggest that they are essential for early growth and survival. Analytical measures of total lipids were highly correlated with a hatchery-based visual assessment of maximum lipid droplet size, an index of relative nutritional health. Formulated hatchery larval diets containing high levels of C20 & 22 PUFAs may optimize nutrition in early ontogeny for blue king crabs, but future research should refine specific ratios and absolute amounts.

Intra-guild predation among early benthic phase red and blue king crabs: Evidence for a habitat-mediated competitive advantage

The apparent shift in predominance of commercial crab species from blue king crab (Paralithodes platypus) to red king crab (Paralithodes camtschaticus) around the Pribilof Islands, Alaska, USA, may be driven by ecosystem-level processes such as competitive displacement or predation during early life stages. Specifically, intra-guild predation among species during the early benthic phase might be a source of mortality limiting blue king crab population recovery. In a laboratory experiment, we evaluated how varying ratios of prey species (year-0 blue and red king crabs) and habitat type (shell and cobble) affect prey preference of year-1 red king crabs. Year-0 red king crabs were preferentially consumed over blue king crabs in shell habitat, but not cobble, likely because the smaller interstitial spaces in shell reduced predator foraging efficiency and predator–prey encounter rates. Blue king crabs had high levels of crypsis regardless of habitat type or predator presence/absence, while red king crabs were less cryptic overall compared to blue king crabs, but crypsis increased when predators were present. Preference for red king crabs in shell may reflect divergent adaptations between species for minimizing predation. Blue king crab's light, mottled coloration and relatively smooth, flat carapace is well adapted for visual and physical crypsis in shell habitat, while the monochromatic, dark coloration and pronounced spination of red king crabs may make them more conspicuous. Our results show that habitat can mediate intra-guild predation between Paralithodes species and suggest that shell material may provide blue king crabs a competitive advantage over red king crabs. The extent of shell habitat may be an important factor regulating blue king crab distribution or the recovery of depleted populations around the Pribilof Islands.

High-density nursery culture of recently-settled blue king crabs (Paralithodes platypus): Comparisons to red king crabs (Paralithodes camtschaticus)

Stock enhancement through the release of cultured juveniles has been suggested as a possible recovery tool for depleted red (Paralithodes camtschaticus) and blue (Paralithodes platypus) king crab populations in Alaska, USA. Considerable progress has been made in the past decade in red king crab culture technology, but similar technologies are less developed for blue king crabs. As part of a stock enhancement feasibility study, hatchery-raised blue king crab juveniles were cultured from larvae of ovigerous females collected off Saint Matthew Island, Alaska. Juvenile instars were then cultured in indoor nursery containers for 42days at stocking densities of 500, 1000, 2000, 4000, and 6000crabsm−2 starting at metamorphosis to the first instar stage (C1). At day 42, survival was above 90% at all the densities, but had a slightly decreasing trend that ranged from 96% at 500crabsm−2 to 90% at 6000crabsm−2. The numbers of crabs cannibalized increased with density, but the overall increase in crab biomass offset the negative effects of cannibalism. Survival rates and biomass production for the first 42days post-settlement is much higher for blue king crabs compared to red king crabs reared under identical conditions. The low rate of cannibalism implies that blue king crabs are well suited for large-scale hatchery culture. Our results suggest that these two closely related crab species can be reared at different stocking densities immediately flowing settlement and that high densities will maximize hatchery efficiency for blue king crabs. Future studies should investigate longer term nursery culture, beyond 42days, to refine protocols for extended blue king crab rearing. Improving nursery techniques will boost the productivity and financial viability of a large-scale stock enhancement program.

Potential for bowhead whale entanglement in cod and crab pot gear in the Bering Sea

AbstractBowhead whales (Balaena mysticetus) of the western Arctic stock winter in ice‐covered continental shelf regions of the Bering Sea, where pot fisheries for crabs (Paralithodes and Chionoecetes spp.) and Pacific cod (Gadus macrocephalus) pose a risk of entanglement. In the winter of 2008–2009 and 2009–2010 the spatial distribution of 21 satellite tagged bowhead whales partially overlapped areas in which pot fisheries for cod and blue king crab (Paralithodes platypus) occurred. However, these fisheries ended before whales entered the fishing areas, thus avoiding temporal overlap. A fishery for snow crab (Chionoecetes opilio) typically runs from January to May and provides the greatest potential for bowhead whales to encounter active pot gear. Tagged whales did not enter the area of the snow crab fishery during this study and generally remained in areas with >90% sea ice concentration, which is too concentrated for crab boats to penetrate. Pack ice sometimes overruns active fishing areas, resulting in lost gear, which is the most likely source of entanglement. The western Arctic stock of bowhead whales was increasing as of 2004; as such, incidental mortality from commercial pot fisheries is probably negligible at this time. Regardless, entanglement may increase over time and should be monitored.

Molting, growth, and energetics of newly-settled blue king crab: Effects of temperature and comparisons with red king crab

Populations of blue king crab (BKC) (Paralithodes platypus Brandt, 1850) have declined in Alaskan waters over recent decades, and substantial effort is being made to rehabilitate the once important fishery with releases of hatchery-reared juveniles. However, little is known about the species' first year of post-settlement life. This study was conducted to evaluate how temperature mediates growth and energy allocation beginning with the first benthic instar (stage C1). Juvenile BKC were reared in four temperatures (1.5 to 12°C) for a period of 60days in low-density populations (150crabsm−2) and 120days in individual cultures. Growth rate increased rapidly up to 8°C, and then leveled off. At 60days, most of the crabs in 1.5°C remained at stage C1, most in 4.5°C were C2, and most in 8°C were C3, while those in 12°C were highly variable and ranged from C2 to C5. Growth records for individuals revealed an inverse exponential relationship between water temperature and intermolt period (up to 8°C). A small decrease in molt increment at 12°C resulted in crabs 6% smaller than those at 8°C. Total lipid content increased with temperature in C2 BKC, but the response was variable and not significant in later stages. The proportion of storage class lipids (triacylglycerols) increased with an increase in temperature and polar lipids decreased. Concentrations of essential fatty acids were relatively constant over all temperature treatments, indicating that temperature and growth rate did not affect the biochemical condition of juvenile BKC. Survival rates of BKC (>95%) were similar across temperatures and were much higher than rates observed for red king crab (RKC) (Paralithodes camchaticus Tilesius 1815) (65–72%) in identical experiments. Growth rates of the two species were nearly identical up to 8°C, but RKC grew faster than BKC at temperatures greater than 8°C, with more molts resulting in larger individuals. Fatty acid (FA) signatures supported the lipid class data and showed that BKC had higher proportions of FA associated with energy storage while RKC had higher proportions of polyunsaturated FAs associated with membranes. These results indicate that BKC are the hardier species, and it shows little sign of cannibalism in culture (unlike RKC), but RKC grow faster at high temperature and are less vulnerable to warming climate. These data help to model temperature-dependent recruitment processes in the field and assist in the design of diets and hatchery conditions for production of seed stocks intended for field release.

Development of polymorphic microsatellite markers for blue king crab (Paralithodes platypus)

We isolated and characterized a total of 23 microsatellite loci from the blue king crab, Paralithodesplatypus. Loci were screened in 24 individuals from St. Matthew Island. The number of alleles per locus ranged from 4 to 17, observed heterozygosity ranged from 0.050 to 1.000, and the probability of identity values ranged from 0.015 to 0.339. These new loci will provide tools for examining the genetic population structure of the species throughout its range.

Diet and some ecological features of the most widespread commercial crab species in the northwestern Sea of Japan in early spring

Results of the study of feeding habits of the commercial crab species Chionoecetes opilio, Ch. japonicus, Paralithodes platypus, P. camtschaticus, and Erimacrus isenbeckii in early spring 2009 are presented. The composition, distribution, and quantitative characteristics of benthos in the areas of sampling are analyzed. The generalized pattern of distribution of the considered crabs is shown with the maximum and mean densities. These crabs were found to consume at least three to four single portions of food during 10–12 hours of daylight. The lowest feeding intensity was observed in the opilio snow crab in March and April. Cannibalism proved to be typical for all the studied crab species in the spring. It was most developed in the deepwater red snow crab, in whose diet representatives of the same species constituted a one-third share. It was also noted that the diet of the studied crabs included a major proportion of crabs and shrimps, which was unusual for the feeding habits of the same species in other Far Eastern seas.

Morphometrics, Fecundity, and Hatch Timing of Blue King Crabs (Paralithodes platypus) from the Bering Strait, Alaska, USA

Abstract The Bering Strait marks the northern species boundary for blue king crabs (Paralithodes platypus), but the life history of the population at this latitude has never been described in scientific literature. Blue king crabs were collected in shallow (10-23 m) waters near King Island (n: males = 199; females = 260) in July of 2005 and from near Little Diomede Island (n: males = 40; females = 19) in April of 2007 for morphometric, fecundity and hatch timing information. Crabs from Little Diomede and King Islands showed no significant difference in male carapace length (CL) by location and were smaller than blue king crabs from more southern parts of the state (mean CL ± SE: 108.45 ± 0.70 mm). Females from King Island (mean CL ± SE: 99.47 ± 0.52 mm) were significantly larger than female crabs collected from Little Diomede Island (mean CL ± SE: 93.11 ± 2.96 mm) and male crabs (mean CL ± SE: King = 107.98 ± 0.73; Diomede = 110.13 ± 2.24) were significantly larger than female crabs at both lo...

On the growth of the blue king crab (Paralithodes platypus) population in the Peter the Great Bay of the sea of Japan

The causes of the appearance of large blue king crabs (Paralithodes platypus) in Peter the Great Bay for the last decade are discussed. This species is an important commercial resource in the waters of Russian Far Eastern seas, and its general concentrations are related mainly to the sublittoral and upper bathyal zones of the northwestern Bering Sea and the northern Sea of Okhotsk. Until recently, this species has been observed in areas along the continental coast of the northwestern Sea of Japan up to the Peter the Great Bay, where it incidentally showed up in red king crab (P. camtschaticus) and snow crab (Chionoecetes opilio) catches but was also commercially used. This area was considered as the southern periphery of the species range. Since the late 1990s, both male and female blue king crabs have been recorded in trawl and trap catches during research works conducted within the Peter the Great Bay. Since 2002, any commercial catches of shelf crab species are prohibited in the waters south of 47°20′ N because of a dramatic decline in their populations. Since then all the illegally caught crabs, including blue king crabs that are seized live from poachers, are released back into the water in certain places of the bay. In total, at least 29 503 blue king crabs, including egg-bearing females, were released within the period from 2002 to November 2009. At present, the overall blue king crab abundance in Peter the Great Bay, estimated based on the trap catches over an area of 7048 km2, is 50500, the abundance of commercial-size males (with a carapace width over 130 mm) is 7500, and the male to female ratio is 1.00: 1.35. The increase in the blue king crab population observed in the bay is the result of the immigration of mature and viable individuals from other areas of its range. After this “uncontrolled introduction” blue king crabs adapted to new conditions, and then began breeding and spreading over the entire area of the bay.

Microsporidia of the genera Thelohania (Thelohaniidae) and Ameson (Pereziidae) in two species of lithodid crabs from the Sea of Okhotsk

Diseases caused by microsporidia were found in the red king crab Paralithodes camtschaticus and the blue king crab P. platypus that inhabit the Sea of Okhotsk. Based on the histological features of the invasion and data on the morphological structure of the parasites, the microsporidia were assigned to the genera Thelohania and Ameson. Infected crabs exhibited severe destructive changes of their internal organs along with sharply pronounced external signs of disease. During the observation period, the microsporidian invasion was only found in females and young (unmarketable size) males from August to mid-October. Later, until mid-December, no diseased crabs were found.