Distribution and ecological relations among the alien crab, <Emphasis Type="Italic">Percnon gibbesi</Emphasis> (H. Milne-Edwards 1853) and autochthonous species,in and out of an SW Mediterranean MPA

The distribution of the allochthonous crab Percnon gibbesi and its relationships with other benthic invertebrate species was assessed inside the marine reserve of Cabo de Palos—Islas Hormigas (Mediterranean sea, Spain) and neighbouring non-protected sites. Although a significant spatial variability was detected at finer spatial scale, there was no influence of protection measures or insularity on the abundance of P. gibbesi. The presence of small holes, encrusting algae and low slope favour the colonization success of this crustacean, and the spatial distribution of these habitat features could explain the observed pattern. The abundance of P. gibbesi was similar to that of native crab species; however, a non-significant negative relationship between the abundance of P. gibbesi and native crabs (Pachygrapsus marmoratus and Eriphia verrucosa), urchins (Arbacia lixula and Paracentrotus lividus) and a snail (Phorcus turbinatus) was observed. This work highlights the importance of monitoring alien crab population densities taking structural habitat and other potentially influential factors into account and the likely effect of this alien species on the native ones.     

Molecular phylogeny of the crab genus Brachynotus (Brachyura: Varunidae) based on the 16S rRNA gene

The crab genus Brachynotus de Haan, 1833 is restricted to the intertidal and shallow subtidal of the Mediterranean and northeastern Atlantic. It is presently recognized to consist of four species, of which three (B. foresti, B. gemmellari and B. sexdentatus) are endemic to the Mediterranean. The fourth species, B. atlanticus, is found along the Atlantic coasts of northern Africa and southern Europe, but also extends into the western Mediterranean. This high level of endemism suggests that speciation within Brachynotus is strongly correlated with the geography and geology of the Mediterranean Sea. A molecular phylogeny based on the mitochondrial large subunit (16S) rRNA gene indicates that the four species of Brachynotus form a monophyletic group within Atlantic Varunidae. The DNA sequence data also show that the genus Brachynotus can be subdivided into two species groups, one comprising B. atlanticus and B. foresti, and the other one B. gemmellari and B. sexdentatus. While B. atlanticus and B. foresti are clearly genetically distinct, B. gemmellari and B. sexdentatus are identical in the studied region of the 16S rRNA gene, suggesting a recent separation or continuing gene flow.     

Preliminary Estimation of the Factors Influencing the Distribution of the Midlittoral Crab Portumnus lysianassa (Herbst, 1796)

In order to acquire information on the factors influencing the distribution of the Mediterranean endemic species Portumnus lysianassa (Herbst, 1796), which lives in the soft substratum midlittoral zone, 83 stations were selected along almost the entire Greek coast. In each sampling station, dredging was carried out, just above the rise of the surf zone, and sediment samples were taken with a core sampler. Two faunal samples were also taken by means of a quadrat from the lower midlittoral zone. The preliminary results of this study show that: P. lysianassa prefers to burrow in the rise of the surf zone; wherever the sediment becomes very coarse or very fine the crab populations decline; there is a correlation between the population abundance of the midlittoral bivalve Donacilla cornea (Poli, 1795) and P. lysianassa, and, moreover, this crab species is related to the composition of the midlittoral assemblage; also, P. lysianassa abundance is negatively correlated with the organic matter content of the sediment; in very exposed areas, D. cornea can be replaced or co-exist with the infralittoral species Donax trunculus (Linnaeus, 1758), and, in these cases, P. lysianassa can be replaced by the closely related infralittoral species Portumnus latipes (Pennant, 1777); when low temperatures or intensive wave action, as well as disturbance caused by swimmers in summer prevail, the population of this crab descends in the upper infralittoral zone.     

Distribution,abundance, and feeding of a disjunct population of lady crab in the southern Gulf of St. Lawrence,Canada

The lady crab (Ovalipes ocellatus) is one of the most common native species of swimming crab (Portunidae) of the Atlantic Coast of North America but most populations occur south of Cape Cod, Massachusetts. There is a disjunct population in Northumberland Strait (southern Gulf of St Lawrence), which was the focus of this study. Adult lady crabs were collected by trawling in water >4 m deep from May to October 1999 to 2005 to determine abundance, distribution, and diet. Lady crab occurred only in a small area (about 2,500 km²) in the central part of Northumberland Strait where bottom water temperature was >18°C during summer, and the substrate was mainly sand or sandy gravel. Male lady crab attained a maximum carapace width (CW) of 112 mm compared to 92 mm CW for females. The summer and autumn diet consisted mainly of infauna. The principal prey (each >5% of diet by weight) were: small bivalve molluscs (primarily Atlantic razor clam Siliqua costata and Macoma sp.; 43%), small rock crab (Cancer irroratus; 13%), polychaetes (11%), fish remains (9%), and small lady crab (9%). All stomachs collected during May (water temperature ≤10°C) were empty. There was little evidence of any difference in feeding intensity between 0700 h and 1900 h.     

Morphology of the early zoeal stages of Macropipus tuberculatus (Roux, 1830) (Crustacea, Brachyura, Portunidae)

The first three zoeal stages of the portunid crab Macropipus tuberculatus (Roux, 1830) are described and illustrated from laboratory-reared material obtained from one ovigerous crab captured in the western Mediterranean Sea. Zoeae of M.tuberculatus can be distinguished from other known polybiinid species from the northeastern Atlantic and Mediterranean waters by a combination of meristic and morphometric features, especially by the number of setae in the outer lobe of the maxilla endopod. Larval morphology presents additional evidence supporting the split of the genus Macropipus into the genera Liocarcinus and Macropipus sensu stricto based on adult characters.      

生态因子对红螯相手蟹捕食毛蚶苗种的影响

敌害生物的捕食在控制海洋底栖生物群落的丰度和组成中起着关键性的作用。以红螯相手蟹(Sesarma haematocheir)和毛蚶(Scapharca subcrenata)为试验对象,研究了红螯相手蟹的密度、规格、性别,以及毛蚶的密度、规格、海水温度和底质条件对毛蚶苗种存活的影响。结果表明,蟹表现出了第二种类型的功能反应,高密度底播毛蚶苗种可以显著提高成活率;当毛蚶苗种壳长达到20mm以上时,蟹的摄食速率显著下降;随着蟹个体的增大,其摄食速率显著增加,毛蚶的存活率下降;当蟹的密度逐渐增加的时候,同种个体之间的干扰竞争显著提高了毛蚶存活率;雄蟹凭借强有力的螯导致了更多毛蚶苗种的死亡;海水温度较低的春季和秋季底播毛蚶苗种可以显著提高成活率;底质条件的复杂性和异质性为毛蚶的存活提供了"庇护空间",从而减少了敌害生物捕食所带来的损失。     

Adaptations for feeding on rock surfaces and sandy sediment by the fiddler crabs (Brachyura: Ocypodidae) Uca tetragonon(Herbst, 1790) and Uca vocans(Linnaeus, 1758)

Two species of fiddler crab, Uca tetragonon(Herbst, 1790) and Uca vocans(Linnaeus, 1758), which belong to the subgenus Gelasimus, dwell on rocky shores and muddy–sandy tidal flats, respectively, in Phuket Is., Thailand. We investigated their feeding ecology in relation to the morphology of their feeding organs: minor food-handling chelipeds and maxillipeds. U. tetragononfed chiefly on rocks covered by filamentous green algae. U. vocansfed on the emerged sand and in shallow water along the shoreline and in pools. While feeding, both crabs made sand pellets beneath their mouthparts and discarded them, indicating that they divided the matter scooped up with their minor chelipeds into edible and inedible fractions by using the maxillipeds in the water passing through their buccal cavity. The morphology of maxillipeds hardly differed between the two species, which means that both species are flotation-feeders. The morphology of their minor chelipeds, however, differed: the tips of the dactyl and pollex were flat in U. tetragononand pointed in U. vocans.When the minor cheliped was closed, U. tetragononhad a hemispherical space in the distal one-fourth of the gape, which was closed by the framing keratin layers and a few setae of the dactyl and pollex. On the other hand, U. vocanshad an ellipsoidal space in the distal half of the gape. We consider these morphological characters to be adaptations to the different feeding substrates for retaining more food-laden sediment. We discuss the role of the setae on the minor chelipeds on the basis of the morphological differences between populations of U. tetragononin Phuket Is. and East Africa where the crab inhabits muddy–sandy tidal flats.     

An invasive crab alters interaction webs in a marine community

Over the last decade, the non-native, filter-feeding crab Petrolisthes armatus invaded oyster reefs of the South Atlantic Bight at densities of thousands m⁻². Mesocosm and field experiments demonstrated that P. armatus at ∼10–75% of mean summer densities: (1) suppressed growth of small oysters, biomass of benthic microalgae, and recruitment of native mud crabs, (2) enhanced oyster, mussel, and total bivalve recruitment, macroalgal cover, and survivorship of predatory oyster drills, but (3) did not affect native taxonomic richness. Laboratory feeding assays, field tethering experiments, and population changes in field and mesocosm experiments suggest that P. armatus is a preferred prey for native mud crabs and other consumers, thus relieving predation on native species and enhancing recruitment or survival of bivalves and oyster drills. In contrast, the invasive crab can consume crustacean larvae and via this feeding may suppress recruitment of native mud crabs. Our findings should be conservative given the low densities of P. armatus seeded into experimental plots and our inability to run longer-term experiments due to controls rapidly being colonized by non-native crabs recruiting from the plankton. Invasive crabs commonly impact native communities via predation, but community impacts of this invasive crab may be as much due to its role as a preferred prey of native consumers as to its predation on native prey. Given that oysters are foundation species for shallow reefs in the South Atlantic Bight, the long-term effects of this invasion could be considerable.     

Impact scenario for the invasive red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Tilesius, 1815) (Reptantia,Lithodidae) on Norwegian,native, epibenthic prey

Large invasive predators like the king crab, Paralithodes camtschaticus, deserve particular attention due to their potential for catastrophic ecological impact on recipient communities. Conspicuous, epibenthic prey species, such as the slow growing commercial scallop Chlamys islandica, are particularly exposed to the risk of local extinction. A research program integrating experiments and field monitoring is attempting to predict and track the impact of invasive king crab on scallop beds and associated fauna along the north Norwegian coast. The claw gape of the crab shows no limitations in handling the flat-bodied scallop. However, the potential impact of the crab on scallop may depend on the availability of other calcified prey associated with scallop beds, such as the sea star, sea urchin, and blue mussel, all species recorded in the diet of P. camtschaticus. To address this issue, a laboratory experiment on foraging behaviour of P. camtschaticus was conducted. The experimental results show that all size classes of red king crab prefer scallops, but small juveniles and medium sized crabs demonstrate active selection for starfish (Asterias rubens) that equals or surpasses the electivity of the large crab. The selection of sea urchin (Strongylocentrotus droebachiensis) and blue mussel (Mytilus edulis) is slightly positive or neutral for the three crab size classes. These results suggest that scallop beds with a rich associated fauna are less vulnerable to red king crabs predation and possibly more resilient than beds with few associated species. Also, crab size distribution is likely relevant for invasion impact, with increasing abundance of small and medium sized crabs being detrimental for alternative calcified prey associated with scallop beds. Successive stages of crab invasion will see an acceleration of scallop mortality rates associated with (i) decreasing availability of alternative prey, due to protracted predation pressure intensified by recruitment of juvenile crabs, and (ii) increased number of large crabs. Estimates of crab density and intake rates suggest that the accelerated loss rates will eventually endanger scallop beds persistence.     

Exotic Spartina alterniflora provides compatible habitats for native estuarine crab Sesarma dehaani in the Yangtze River estuary

Although the impact of plant invasions on benthic communities, especially burrowing crabs, has received increasing attention, the results from past studies are mixed. The exotic plant Spartina alterniflora has become the most abundant species in the salt marshes of the Yangtze River estuary since it was first found just over a decade ago, but its effects on crabs in the salt marshes is largely unknown. To examine whether the invasions of this exotic plant affected native crabs, we compared the biomass and abundance of the dominant burrowing crab Sesarma dehaani in an exotic Spartina marsh, native Phragmites australis marsh and mudflats of the Yangtze River estuary, China. To explain the differences of S. dehaani populations between different habitats, feeding preference of S. dehaani for Spartina and Phragmites was investigated. Results showed crab abundance and biomass in the Spartina marsh were significantly greater than those in the Phragmites marsh and mudflats. Soil water content and plant community characteristics in the Spartina marsh also significantly differed in the Phragmites marsh and mudflats. Moreover, the feeding preference experiment showed that crabs consumed Spartina more than twice as much as Phragmites. In summary, this study showed that Spartina provided compatible habitats for native crab S. dehaani through offering suitable food source and moderate environmental conditions.     

Atkinsiella dubia and its related species

Atkinsiella dubia, isolated from the mantle of abalone (Haliotis sieboldii), is described and illustrated as a new record from Japan. The fungus was also obtained from the gills of swimming crab (Portunus trituberculatus). Six other species of the genusAtkinsiella have hitherto been reported from various aquatic animals. The fungus is distinguished from the other six species by the morphology of its mycelia and the process of zoospore production. The most distinctive feature is that zoospores in the first motile stage ofA. dubia encyst in zoosporangia, unlike the other species. We therefore proposeHalocrusticida gen. nov. (Lagenidiales, Haliphthoraceae) for the other six species ofAtkinsiella. A key to species of the genusHalocrusticida is provided.     

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.     

Learning in an invasive and a native predatory crab

The invasion of the green crab Carcinus maenas in the northeastern U.S. and its competition with the native blue crab Callinectes sapidus and other native crustaceans has been well-documented and researched. Various reasons for the invader’s success against native crabs have been examined (juvenile predation, food source flexibility, etc.), but another possibility is a difference in the learning ability of invasive versus native crab species. In this study, the learning ability of C. maenas and C. sapidus was tested by their increased speed in locating hidden food over successive days. The data suggest that C. maenas possesses a learning ability significantly greater than that of C. sapidus, which may partially contribute to its success.     

Epifauna associated with the northern stone crab <Emphasis Type="Italic">Lithodes maia</Emphasis> in the Barents Sea

Species composition, prevalence, and intensities of species colonizing the northern stone crab Lithodes maia in Dalnezelenetskaya Bay (Barents Sea) were examined. Sixteen species attached to the body surface or the host gills were identified. The most common associates were hydrozoans (100.0%), especially Obelia longissima, and the amphipods Ischyrocerus commensalis (93.8%). Species composition of the stone crab epifauna was similar to that observed for the Lithodid crab Paralithodes camtschaticus, except that tubular polychaetes Pomatoceros triqueter and Placostegus tridentatus were found only on the surface of the stone crab, while fish leeches Johanssonia arctica occurred on the red king crabs. Differences in percentage of infested hosts, and mean intensities of some associates are influenced by the conditions of carapace structure and size of both crab species.     

Feeding strategy of the sacoglossan opisthobranch <Emphasis Type="Italic">Oxynoe olivacea</Emphasis> on the tropical green alga <Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>

The feeding behaviour of the shelled sacoglossan Oxynoe olivacea was investigated to better understand the role and importance of this species in influencing encroachments of the alien alga Caulerpa taxifolia in the Mediterranean sea. We tested whether this slug preferred, as preliminary field observations suggested, an aggregative feeding behaviour and which part of the algal thallus, phylloid vs rhizoid, it preferred. Results showed that O. olivacea fed in groups and actively selected phylloid. This outcome poses important questions regarding the possibility that this species, fragmenting the alga thallus, could enhance dispersion and regeneration of C. taxifolia.     

Predation induced changes in behavior and growth rate in three populations of the intertidal snail, Littorina sitkana (Philippi)

We investigated the sublethal effects of a predatory crab, Cancer productus (Randall), on the behavior and growth of its snail prey, Littorina sitkana, by setting up controlled rearing and prey-size selection experiments. L. sitkana were collected from three sites on San Juan Island, WA, USA. These sites varied in snail size, abundance, and vertical distribution, and in the abundance of the crab predator C. productus. Snails from all three populations were raised for 34 days under the following treatments: no-crab control, a non-feeding C. productus encased in mesh box, and an encased C. productus feeding on L. sitkana. The non-feeding crab treatment did not affect snail foraging behavior or growth rate in comparison with the no-crab control. In contrast, the presence of a feeding crab elicited escape behavior in the snails, halted grazing, and consequently reduced growth rates. A population difference in escape behavior was observed: upward migration in snails from rocky shores and hiding in crevices in snails from a mud flat. It thus appears that chemicals leaching from crushed conspecific snails, rather than the presence of the crab predator, act as the “alarm substance” to which L. sitkana react. The magnitude of the growth depression in the presence of feeding crabs was 85%, with no difference among the three populations. Once the feeding crab stimulus was removed, snails in all populations resumed normal growth, suggesting that this response to feeding predators is reversible with changing environmental conditions. Laboratory experiments were set up to determine if all size classes of L. sitkana are equally susceptible to C. productus predation. C. productus consistently selected the largest of three size classes of L. sitkana. These results suggest that slow growth rate and small size in L. sitkana may actually be an adaptation for coexisting with high C. productus abundance, rather than simply a cost of escape behavior.     

Conflict between two inshore fisheries: for whelk (Buccinum undatum) and brown crab (Cancer pagurus), in the southwest Irish Sea

Landings from the whelk fishery in the southwest Irish Sea rose from 63 t in 1990 to 6587 t in 1996 although landings declined to 2919 tonnes in 1998. Whelk are caught in pots baited with a combination of dogfish Scyliorhinus spp and brown crab Cancer pagurus. The input of bait crab is estimated at 7.2% of whelk landed. Most of the crab comes from southeast Ireland where some of it is a by-product of the claw fishery; some is targeted as bait crab, and this includes sub-size or recently moulted individuals. Fishing effort has been increasing on brown crab for human consumption also and there is concern about the sustainability of the crab fishery. Alternative bait trials examined a number of readily available fish species, some of them offals, whose attractiveness was evaluated by reference to crab and dogfish: whitefish (whiting and cod), pelagic species (mackerel and scad) and blue mussel. An artificial bait ration which included some crab meat, but 60% less than its natural equivalent, proved as effective as natural bait crab. A bait which consisted of a single species was less successful than two species fished together and some of the combinations (notably of whitefish) performed very effectively. Pelagic species performed poorly. The trade in brown crab for human consumption will always produce some form of discards which should be used; extending its use in an artificial bait is desirable.     

Population genetics,gene flow,and biogeographical boundaries of Carcinus aestuarii (Crustacea: Brachyura: Carcinidae) along the European Mediterranean coast

Carcinus aestuarii Nardo, 1847 is a widespread coastal crab species throughout the Mediterranean Sea with a pelagic larval phase. This species tolerates a wide range of environmental conditions and typically inhabits fragmented habitats, such as embayments, lagoons and estuaries. It is therefore a good candidate species for studying and testing different phylogeographical hypotheses in the Mediterranean Sea. By contrast to its Atlantic sister species, Carcinus maenas, studies on the population genetic structure of C. aestuarii in its native range are still scarce. In the present study, specimens from along the European Mediterranean Sea were collected and DNA‐sequenced and analyses were applied to discriminate between present day and historical factors influencing the population genetic structure of this species. The results obtained demonstrate the existence of two genetically distinct geographical groups, corresponding to the eastern and western Mediterranean, with further subdivision within the East Mediterranean Basin. A strong asymmetric gene flow was recorded toward the Eastern Basin, which may play a crucial role in shaping the present day biogeographical patterns of this species and potentially other sympatric ones with pelagic larvae. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 771–790.     

Life cycle and adaptive strategies of three non-annual,ruderalCardueae: Onopordum nervosum,Carthamus arborescens,andCirsium scabrum

The life cycle and autoecology of three Mediterranean thorny species,Onopordum nervosum (Iberian endemic),Cirsium scabrum (Western Mediterranean) andCarthamus arborescens (Iberian-North African), of potential use in agriculture as bioenergetic, forage or oil producing plants were studied. These threeCardueae spp. are good examples of ways in which Mediterranean plants adapt their typical annual cycle to avoid summer droughts.O. nervosum is a perennial, monocarpic, heliophilous species which flowers in early summer and grows even under the extreme xeric conditions of the Mediterranean summers. It is a basiphilous plant usually found in sandy-loamy and sandy-clayey-loamy soils with a marked geographical variability in its seed germination.C. scabrum is a perennial, monocarpic species which has a long life cycle, flowering in summer and growing only during the wet months. It is not well-adapted to droughts and is usually restricted to acid soils.C. arborescens is a perennial, polycarpic species which flowers in spring and dries up in summer. It is usually found in basic loamy-sandy or sandy-loamy soils poor in organic matter.     

Contrasting patterns of wetland use by sympatric larids in winter

The population dynamics and behaviour of the larid assemblage of a Mediterranean coastal wetland, the Vourkari inlet in Greece, were studied during the winter of 2008–2009. More black-headed gulls (Larus ridibundus) were seen in the inlet in December, more Mediterranean gulls (Larus melanocephalus) were present from mid-January to mid-February, while little variation was observed in yellow-legged gull (Larus michahellis) numbers throughout winter. Bird numbers remained stable through the day for the yellow-legged gull, but fewer black-headed and Mediterranean gulls were present in the late morning than the other periods. Diurnal activity patterns showed that feeding was the primary behaviour for yellow-legged gulls and resting and sleeping for black-headed and Mediterranean gulls, with locomotion being equally important for all species. All larids were primarily feeding in the late morning period, but yellow-legged gulls were doing so in much higher proportions. These contrasting patterns suggested that the Vourkari inlet was more important as a day roost for black-headed and Mediterranean gulls and a preferred feeding ground for yellow-legged gulls. Furthermore, results suggested that resting and sleeping were interchangeable activities and all other activities had more or less the same time demands on a daily basis, and also a consistent pattern across species in sleeping proportions that might indicate cross-species synchrony in sleep patterns; however future research is needed to resolve these issues. This study provided important new information on the winter ecology of three larids and revealed patterns of wetland use by these species that could help assess the importance of certain areas and improve coastal habitat management strategies to benefit birds.