Pathology of Hematodinium infections in snow crabs (Chionoecetes opilio) from Newfoundland, Canada

Bitter crab disease (BCD) of snow crabs, Chionoecetes opilio, is caused by a parasitic dinoflagellate, Hematodinium sp. The disease has shown an alarming increase in prevalence in the commercial fishery in eastern and northeastern areas of Newfoundland and Labrador since it was first recorded there in the early 1990s. We documented histopathological alterations to the tissues in snow crabs with heavy infections of Hematodinium sp. and during sporulation of the parasite. Pressure necrosis was evident in the spongy connective tissues of the hepatopancreas and the blood vessels in most organs. In heavy infections, little remained of the spongy connective tissues around the hepatopancreas. Damage to the gills varied; in some cases it was severe, particularly during sporulation, involving apparent thinning of the cuticle, loss of epithelial cells, and fusion of the membranous layers of adjacent gill lamellae. Affected lamellae exhibited varying degrees of distention with a loss of trabecular cells, hemocyte infiltrations, and swelling or "clubbing" along the distal margins. Large numbers of zoospores were located along the distal margins of affected lamellae suggesting that sporulation may cause a lysis or bursting of the thin lamellar cuticle, releasing spores. Pressure necrosis, due to the build up of high densities of parasites, was the primary histopathological alteration in most tissues. Hematodinium infections in the snow crab are chronic, long-term infections that end in host death, during sporulation of the parasite.     

Monitoring the prevalence of the parasitic dinoflagellate Hematodinium sp. in snow crabs Chionoecetes opilio from Conception Bay,Newfoundland

Bitter crab disease (BCD) of snow crabs Chionoecetes opilio is caused by a parasitic dinoflagellate, Hematodinium sp. In Newfoundland's commercial fishery, infected snow crabs are identified using visual, macroscopic signs of disease for separation prior to processing. We estimated the sensitivity and specificity of gross, macroscopic diagnosis of Hematodinium sp. by comparing these results with microscopic examination of prepared hemolymph smears. The sensitivity of a diagnostic test is the probability that the test will yield a positive result given that the animal has the disease. The specificity is the probability of a negative result given the animal is not diseased. In October 1998, we conducted a design-based survey using cluster sampling in 2 strata. Over 10 000 snow crabs from pot and trawl surveys were examined macroscopically for BCD. In addition, over 350 crabs were randomly examined microscopically for disease. The double sampling resulted in an estimated sensitivity of 52.7% and an estimated specificity of 100%. That is, a positive result from macroscopic examination is definitive, if the observer is well trained, but macroscopic examination will fail to detect infections in crabs with borderline clinical signs of disease. The prevalence estimated from macroscopic observations (p(st) = 2.24%) was corrected for misclassification by dividing p(st) by the estimated sensitivity (0.527), giving a corrected estimate of 4.25%. The use of double sampling provides for efficient estimation of prevalence in that large numbers of crabs can be quickly examined for gross signs of infection and the results corrected for misclassification based on a limited number of observations with a better, but time-consuming test. In addition, the prevalence of macroscopically infected male crabs was lower in a trap survey (0.57%) compared to a trawl survey (1.59%). In the trawl survey, female crabs had a significantly higher prevalence of macroscopically diagnosed infections than males (6.34%). The prevalence of BCD has shown an alarming increase since it was first detected in Newfoundland during the early 1990s. Transmission and mortality studies are warranted to better understand the effect of the disease on its commercially important host.     

A review of the parasitic dinoflagellates Hematodinium species and Hematodinium-like infections in marine crustaceans

Parasitic dinoflagellates in the genus Hematodinium are important parasites of marine Crustacea. Outbreaks of these parasites have damaged commercial stocks of Norway lobster Nephrops norvegicus, snow crab Chionoecetes opilio, Tanner crab C. bairdi, American blue crab Callinectes sapidus, and velvet swimming crab Necora puber. Species of Hematodinium can reach high enough levels to regulate their host populations, but mortalities are also centred on the unfished juveniles and females, hosts not normally sampled by fisheries; hence impacts are often underreported. Seasonal prevalences of up to 85 % occur annually in many host populations; in effect, these parasites form cryptic blooms in the water column with crabs and other crustaceans at risk of disease. We review the biology and ecology of Hematodinium spp. infections in crustaceans. Included is a comparison of the different infections, a synthesis of what is known, and an attempt to highlight fruitful areas for continued research.     

Advances in our understanding of the global diversity and distribution of Hematodinium spp. - significant pathogens of commercially exploited crustaceans

Hematodinium species are parasitic dinoflagellates known to infect a growing number of marine crustacean genera from around the world, many of which support important commercial fisheries. Affected hosts undergo dramatic pathological alterations to their organs, tissues and hemolymph. There are no known control measures for this disease. Economically important wild fished hosts known to be susceptible to Hematodinium spp. include Tanner crabs Chionoecetes bairdi and snow crabs Chionoecetes opilio in the Northeast Pacific and Atlantic Oceans, blue crabs Callinectes sapidus from the Atlantic and Gulf coasts of the United States, and Norway lobsters Nephrops norvegicus and Edible crabs Cancer pagurus from European waters. In recent years, several farmed aquatic crustaceans in China have also been negatively impacted by Hematodinium-associated diseases, likely representing an emerging issue for that expanding industry. Molecular sequence data indicates that there are two species, Hematodinium perezi, and a second species, currently unnamed, infecting hosts from the Northern Hemisphere. Three subtly different H. perezi genotypes have been identified infecting hosts from different geographical locations: the English Channel, the eastern seaboard of the United States and Gulf of Mexico, and eastern China. Genotypic variability between isolates of the Hematodinium sp. infecting hosts from the North Atlantic and North Pacific has also been reported, though it is unclear whether there is any correlation with host or location. Identification of Hematodinium species (and genotypes of H. perezi) is largely dependent upon geographical location, rather than host species. However this is not exclusive, as both Hematodinium species can be found infecting multiple species from same location, as is the case in the English Channel.     

Infection by a Hematodinium-like parasitic dinoflagellate causes Pink Crab Disease (PCD) in the edible crab Cancer pagurus

The edible crab (Cancer pagurus) supports a large and valuable fishery in UK waters. Much of the catch is transported live to continental Europe in specially designed live-well ('vivier') vehicles. During the winter of 2000/2001, many trap-caught crabs from Guernsey, Channel Islands, UK, were reportedly moribund and pink in colour. These crabs generally died before and during vivier transportation. We provide histological, immunological, and molecular evidence that this condition is associated with infection by a Hematodinium-like dinoflagellate parasite similar to that previously reported in C. pagurus and to an infection causing seasonal mass mortalities of the Norway lobster (Nephrops norvegicus). Pathologically, every altered host bore the infection, which was characterised by very large numbers of plasmodial and vegetative stages in the haemolymph and depletion of reserve cells in the hepatopancreas. Due to the hyperpigmentation of the carapace and appendages, we have called this infection 'Pink Crab Disease' (PCD). Similar Hematodinium infections cause 'Bitter Crab Disease' in tanner and snow crabs, which has had a negative effect on their marketability. At present, little is known about the seasonality, transmission, and market impact of this infection in C. pagurus.     

Preliminary results on the seasonality and life cycle of the parasitic dinoflagellate causing bitter crab disease in Alaskan tanner crabs (Chionoecetes bairdi)

Tanner crabs (Chionoecetes bairdi) from the Sullivan Island area of southeast Alaska were sampled for 1 year to determine the prevalence and intensity of the parasitic dinoflagellate which causes bitter crab disease (BCD). The prevalence and intensity of infection were the greatest in the summer, declined in the fall and winter, and increased again in the spring. A possible relationship between softer, newer shells and higher levels of parasitism was also observed. In vivo transmission studies in the laboratory suggested there are several morphologically different forms of the vegetative cell of the BCD dinoflagellate which occur prior to sporulation of the parasite. In addition, it appears that both the two spore types produced by the parasite are infectious by injection and that there is no ploidy difference between the two spore types and the vegetative cell, suggesting that the two spore types may not represent separate sexes.     

Conservation in the first internal transcribed spacer region (ITS1) in Hematodinium species infecting crustacean hosts found in the UK and Newfoundland

Parasitic dinoflagellates in the genus Hematodinium infect a number of decapod crustaceans in waters off the UK, including the Norway lobster Nephrops norvegicus and the edible crab Cancer pagurus. This study investigated sequence variability in the first internal transcribed spacer (ITS1) region of the ribosomal RNA complex of Hematodinium spp. infecting N. norvegicus, C. pagurus, and Pagurus bernhardus from 4 locations in the UK and from the Hematodinium sp. infecting Chionoecetes opilio from the province of Newfoundland and Labrador, Canada. Phylogenetic analysis of the Hematodinium ITS1 sequences from N. norvegicus, C. pagurus, P. bernhardus and C. opilio suggest that these crustaceans are infected with the same species of Hematodinium. Length variability of the ITS1 region was observed (324 to 345 bp) and attributed to 4 variable microsatellite regions (CATG)n' (GCC)nTCCGC(TG)n' (TA)n' and (GAA)n(GGA)n within the sequenced ITS1 fragment. The observed variation may be due to co-infection of the host crustacean with several different strains of Hematodinium or differences among copies of ITS1 region within the genome of a single parasite cell. The Hematodinium ITS1 sequence from N. norvegicus, C. pagurus, P. bernhardus and C. opilio isolates was sufficiently conserved in primer binding regions targeted by previous molecular diagnostic assays; therefore, we suggest that this assay could be used to screen for Hematodinium infections in these crustacean hosts.     

Lack of transmission of Hematodinium sp. in the blue crab Callinectes sapidus through cannibalism

Hematodinium spp. are parasitic dinoflagellates of marine crustaceans. Outbreaks of Hematodinium sp. have impacted commercial landings of the blue crab Callinectes sapidus in the coastal bays of Virginia and Maryland (USA), with seasonal peaks in prevalence reaching 85%. The life cycle and transmission routes of the parasite in blue crabs are poorly understood. Cannibalism and waterborne transmission may be routes of transmission, although little conclusive evidence has been reported for these modes. We examined cannibalism as a route by a series of experiments wherein we repeatedly fed adult and juvenile crabs the tissues of crabs infected with Hematodinium. In each experiment, feeding was done 3 times over the course of 1 wk. Only 2 of 120 crabs were infected within 7 to 9 d after feeding, and these 2 were likely infected prior to the experimental exposures. Crabs inoculated with hemolymph from infected donors served as positive controls. They developed infections over 11 to 21 d, indicating that the Hematodinium sp. used in the cannibalism trials was infectious at the time of inoculation. Because amphipods also harbor Hematodinium-like infections, we fed tissues of infected crabs to the estuarine amphipod Leptocheirus plumulosus. Hematodinium DNA was detected in amphipods shortly after feeding, but not in animals held for longer periods, nor was it observed in histological preparations. Amphipods did not obtain infections by scavenging infected crab tissues. Our results show that Hematodinium sp. is not effectively transmitted through ingestion of diseased tissues, indicating that cannibalism may not be a major route of transmission for Hematodinium sp. in blue crabs.     

Epizootiology of the parasitic dinoflagellate Hematodinium sp. in the American blue crab Callinectes sapidus

Hematodinium sp. is a parasitic dinoflagellate that infects and kills blue crabs Callinectes sapidus. Periodic outbreaks of dinoflagellate infections with subsequent high host mortalities prompted a study of the epizootiology and distribution of the crab pathogen. Hemolymph samples from over 13000 crabs were assessed for infections over 8 yr. Moderate to high prevalences were found at several locations along the Atlantic and Gulf coasts of the United States. In the coastal bays of Maryland and Virginia, prevalence followed a seasonal pattern, with a sharp peak in late autumn. Infections were significantly more prevalent in crabs measuring less than 30 mm carapace width; host sex did not influence prevalence. Prevalences were highest in crabs collected from salinities of 26 to 30%o; no infected crabs were found in salinities below 11%o. Intensity of infection did not vary among crab sizes, molt stages, or sexes. Naturally and experimentally infected crabs died over 35 and 55 d in captivity, with a mean time to death of approximately 13 and 42 d, respectively. Several other crustaceans, including gammaridean amphipods, xanthid (mud) crabs, and the green crab Carcinus maenus, were found with Hematodinium-like infections. Considering its widespread distribution and high pathogenicity, we suggest that Hematodinium sp. represents a significant threat to blue crab populations in high salinity estuaries along the Atlantic and Gulf coasts of the USA.     

Evidence for a permanent establishment of the snow crab (Chionoecetes opilio) in the Barents Sea

In the Atlantic the snow crab (Chionoecetes opilio) is naturally distributed on the northwestern side, i.e. eastern Canada and west Greenland. Until recently, there have been no observations of snow crab in eastern Atlantic. However, in 1990s single and occasional reports were made of crabs captured in the eastern part of the Barents Sea, presumably introduced through ballast water. Special attention during the annual bottom-trawl surveys in the Barents Sea during February 2004–2006 were given to include recordings of snow crab to evaluate if the introduced species has succeeded to establish a self-sustaining population in this region. Recordings of snow crabs were systematically noted and biological measurements carried out. The results confirm previous Russian observations of snow crabs in the northern region of Gåsebanken. In addition, a significant number of crabs were also found in the central region of the Barents Sea, mainly in deeper waters from 180 to 350 m depth. The sizes ranged from 14 to 136 mm carapace width. All females above 70 mm were berried with fertilised eggs. A major fraction (31% in 2005; 76% in 2006) of the crabs consisted of juveniles below 50 mm CW, providing evidence for successful recruitment. The small-sized crabs were exclusively found in Gåsebanken, identifying the main recruiting area at present for snow crab in the Barents Sea. The results obtained show that the snow crab is now adapted to the northeast Atlantic.     

Effect of Eyestalk-Ablation on Circulating Ecdysteroids in Hemolymph of Snow Crabs, Chionoecetes opilio: Physiological Evidence for a Terminal Molt

Bering Sea snow crabs (Chionoecetes opilio) are a commerciallyimportant crab harvested in the Bering Sea. Optimal managementof this species requires an understanding of the biology ofthis crab that is currently incomplete. Fisheries managers applya continuous growth model in their management of snow crab,which assumes that male crabs increase in size throughout theirlifespan. Male snow crabs undergo a morphometric molt that leadsto a disproportionate increase in chelae size and it is stilldebated whether this molt is associated with a terminal molt.This study was conducted to determine whether adult male C.opilio are anecdysic. Using current knowledge of the hormonalregulation of crustacean growth, snow crab physiology was manipulatedto induce an increase in molting hormones (ecdysteroids). Sincefemale snow crabs are known to undergo a terminal molt afterattaining reproductive maturity, we compared ecdysteroid levelsin eyestalk-ablated terminally molted females, small-clawedmales and large-clawed males. Snow crabs were collected fromthe Bering Sea and maintained in circulating seawater at approximately6°C. Animals were either eyestalk-ablated or left intact.Ecdysteroid levels in hemolymph were quantified using an enzyme-linkedimmunosorbant assay (ELISA). Circulating ecdysteroids were significantlyhigher in small-clawed male crabs when compared to large-clawedmales or terminally molted females. Eyestalk-ablation increasedcirculating ecdysteroids in small-clawed males, but had no significanteffect on circulating ecdysteroids in large-clawed males orin terminally molted females.     

Important crab resources inhabiting Hokkaido waters

In this paper the fishing grounds, fluctuations in catches, history of exploitation, classification, distribution, migration, life history and resource trends of the edible crabs of the waters around Hokkaido are discussed. The Hokkaido crab fisheries developed along with the canning industry and there is now an increasing demand for boiled crab. At first, the most popular species was the king crab, Paralithodes camtschatica, but as its numbers declined other species such as the horsehair crab, Erimacrus isenbeckii, the banasaki crab, Paralithodes brevipes, the snow crab, Chionoecetes opilio, and the red snow crab, Chionoecetes japonicus, became popular. This report is based on the results of the latest research into the ecology and resources of the Erimacrus isenbeckii and Paralithodes brevipes species, which are currently the focus of resource conservation in Hokkaido.     

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.     

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

Bowhead 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.     

Dynamics of snow crab (<Emphasis Type="Italic">Chionoecetes opilio</Emphasis>) movement and migration along the Newfoundland and Labrador and Eastern Barents Sea continental shelves

This study uses survey and tagging data and cluster analysis to interpret dynamics of ontogenetic movements and seasonal migrations in snow crab (Chionoecetes opilio) along the Newfoundland and Labrador (NL) continental shelves. Most historic literature from Atlantic Canada suggests snow crab undertake small-scale ontogenetic movements while observations of seasonal migrations had been near-exclusive to the inshore. Information on both types of movement in the most spatially expansive offshore region of Atlantic Canada, in NL, was lacking. We find that that both ontogenetic movements and seasonal migrations occur in most areas of the NL offshore, with ontogenetic movements generally down-slope and seasonal migrations generally up-slope. Conservative estimates of average ontogenetic movements range from 54 to 72 km for both males and females in the largest offshore regions while seasonal migrations are slightly smaller, with two independent studies on the Grand Bank producing average estimates of 43–46 km and an adjacent tagging study in a smaller inshore bay producing an average estimate of 25 km. Ontogenetic movements appear associated with a search for warm water while seasonal migrations appear associated with both mating and molting in shallow water. On average, morphometrically mature crab of both sexes move less vertical distance than morphometrically immature crab during seasonal migrations. We investigate plausible explanations for ontogenetic movements and spring migrations and detail how bottom temperature affects crab distribution and life history dynamics. We further document movement patterns from tagging studies on the burgeoning snow crab stock in the Eastern Barents Sea toward establishing consistencies in species behaviour on the global scale. Finally, we discuss explanations for historical disparities in the literature between scales of movement for snow crab in the Eastern Bering Sea of Alaska versus Atlantic Canada and advance perspectives on life history theory for the species.     

On the growth of the blue king crab (<Emphasis Type="Italic">Paralithodes platypus</Emphasis>) 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.     

The period of occurrence,density, and distribution of larvae of three commercial crab species in Peter the Great Bay,Sea of Japan

Based on materials from plankton surveys carried out in 2004–2009, the period of occurrence, density, and distribution of larvae of three commercial species of crabs in the Peter the Great bay and adjacent areas of Sea of Japan were studied. The larvae of the horsehair crab Erimacrus isenbeckii (Brandt, 1848) occurred in the plankton from mid-March to early June, within the range of water temperature from −1 to 10.8°C. The larvae of the helmet crab Telmessus cheiragonus (Tilesius, 1812) appeared in the plankton in mid-April and occurred to the end of June within the temperature range from 2.8 to 13.0°C. The larvae of the snow crab Chionoecetes opilio (O. Fabricius, 1788) appeared in the plankton in mid-April as well, but some individuals sporadically occurred until early August. All the species of crabs produced one generation of larvae for their reproduction season. The terms of larval stay in plankton depended on water temperature and the duration of the pelagic period increased in colder years. In that area, the larvae of C. opilio were the most abundant (up to 41 ind./m³) and the zoea density of horsehair and helmet crabs was significantly lower (no more than 2 ind./m³). The larvae of C. opilio occurred over the entire area of the Peter the Great bay; the greatest aggregations of their early stages were observed in its southwestern open part. The maximum density of E. isenbeckii zoea was recorded in the south of the Amursky bay and in the Posyet bay. Individual larvae of T. cheiragonus occurred in the Posyet bay and in the southern part of the Amursky and Ussuriisky bays. The late-stage larvae of all crab species were concentrated in areas of the coastal circulation.     

Development of an 18S rRNA gene-targeted PCR-based diagnostic for the blue crab parasite Hematodinium sp.

The 18S rRNA gene from Hematodinum sp., a parasitic dinoflagellate that infects blue crabs, was amplified, cloned, and sequenced. The sequence showed a high similarity (95% at the nucleotide level) to sequences obtained from other dinoflagellate species, including both free-living and symbiotic species. Sequence similarity was much lower when compared with parasites of other marine invertebrates with similar life histories and with the 18S rRNA gene from the blue crab. Based on comparison of sequence alignments between Hematodinium, other dinoflagellate species, protozoan pathogens of oysters, and blue crab 18S rRNA gene sequences, 2 sets of PCR primers that specifically amplified fragments of the Hematodinium 18S rRNA gene were developed and tested. One of these primer sets (Hemat-F-1487 and Hemat-R-1654) amplified a 187 bp fragment that could be used routinely as a diagnostic test for the presence of Hematodinium in hemolymph from blue crabs. This fragment was consistently amplified from genomic DNA extracted from hemolymph of Hematodinium infected blue crabs. Comparison between the PCR technique and standard histological examination indicated that the PCR technique was reliable and provided 1000 times more sensitivity than the histological methods. The sensitivity of the PCR diagnostic was estimated to be one parasite cell among 300,000 crab hemocytes. Preliminary studies using the PCR diagnostic technique suggest that Hematodinium sp. is absent in crabs collected from waters with low salinity (5 to 10 ppt), but common in crabs from higher salinity environments in estuarine waters from southeastern Georgia (USA).     

First observations of temperature tolerances of adult male snow crab (Chionoecetes opilio) from the Barents Sea population and the effects on the fisheries strategy

This study investigates the effects of temperature on the survival, food intake, oxygen consumption and growth during long-term live holding of captive male snow crab (Chionoecetes opilio) (average?=?0.7?kg). The crabs were held at three different temperatures, 3, 6 and 9°C. The trials were done using groups of snow crabs held in nine land-based holding tanks (three replicates per temperature treatment). The results showed that temperature had a significant effect on survival. The survival rate at 3°C (61%) was significantly higher than at 6°C (33%) and at 9°C (28%). Specific oxygen consumption rates of unfed crab at 6°C were significantly higher than at 9°C and 3°C. In summary, the current study shows that the Barents Sea snow crab have a narrow temperature range in which they thrive compared with the Barents Sea red king crab (Paralithodes camtschaticus). Barents Sea snow crab has similar metabolic and physiological attributes to other major snow crab populations. In conditions when ambient temperatures are approximately 6°C, it may prove beneficial for animal welfare and also be financially advantageous to reduce ambient water temperatures in live snow crab holding facilities on boat or on land.     

Predation regulation of sedimentary faunal structure: potential effects of a fishery-induced switch in predators in a Newfoundland sub-Arctic fjord

The collapse of the cod fishery in Newfoundland has coincided with marked increases in abundances of snow crab, pandalid shrimp, and other crustaceans that prey on sedimentary infauna. A 3-year sampling program in Bonne Bay, Newfoundland indicates differences in composition and number of these predators in the two main arms of the fjord that coincide with strong differences in benthic community structure. To test whether predation pressure contributes to the observed patterns in sedimentary fauna, exclusion field experiments with full and partial cages were deployed in both arms at 30-m depth and sampled along with ambient sediments at 0-, 4-, and 8-week periods. Predation significantly influenced species composition, abundance and, in some cases, diversity. The most striking changes included increases in the polychaetes Phöloe tecta and Ophelina cylindricaudata in exclusions relative to controls, and concurrent declines in the polychaete Paradoneis lyra and the cumacean Lamphros fuscata. In laboratory experiments, fresh non-disturbed sediment cores from each experimental area were either protected or exposed to snow crab, the most abundant predator in the bay. A snow crab inclusion experiment was also carried out in the field, using cages similar to those used for exclusions. Despite differences in sedimentary faunas in the two arms, both types of experiments detected a predator effect that was very similar to that documented in exclusion experiments. Thus, despite differences in the scales associated with each type of manipulation, our results suggest that crab predation is a significant structuring force in Newfoundland sedimentary communities. Given the historical changes that have occurred in predator composition as a result of cod over-fishing, we hypothesize that broad-scale community changes may be taking place in North Atlantic benthic ecosystems.