Impact of the invasive parasitic copepod Mytilicola orientalis on native blue mussels Mytilus edulis in the western European Wadden Sea

Invasive species can indirectly affect native species by modifying parasite–host dynamics and disease occurrence. This scenario applies to European coastal waters where the invasive Pacific oyster (Magallana gigas) co-introduced the parasitic copepod Mytilicola orientalis that spills over to native blue mussels (Mytilus edulis) and other native bivalves. In this study, we investigated the impact of M. orientalis infections on blue mussels by conducting laboratory experiments using controlled infections with larval stages of the parasitic copepod. As the impact of infections is likely to depend on the mussels’ food availability, we also tested whether potential adverse effects of infection on mussels intensify under low food conditions. Blue mussels that were experimentally infected with juvenile M. orientalis had a significantly lower body condition (11–13%) compared with uninfected mussels after nine weeks of infection. However, naturally infected mussels from a mixed mussel and oyster bed did not significantly differ in body condition compared with uninfected mussels. Contrary to effects on mussel condition, we did not find an effect of experimental infections on clearance rates, shell growth or survival of blue mussels and no clear sign of exacerbating effects of food limitation. Our study illustrates that invasive species can indirectly affect native species via parasite co-introductions and parasite spillover. The results of this study call for the integration of such parasite-mediated indirect effects of invasions in impact assessments of invasive species.     

Moulting synchrony in green crabs (Carcinus maenas) from Prince Edward Island,Canada

The growth and spread of non-indigenous green crabs (Carcinus maenas) in Atlantic Canada is of concern to the sustainability of shellfish resources, particularly in areas recently invaded. Commercial green crab fishing has been initiated on Prince Edward Island to help control this species and provide a new resource for inshore fishermen. Developing a soft-shell crab product modelled after the Venetian ‘Moleche’ would provide an economic incentive beyond the existing hard-shell crab bait market. However, answers to questions such as the timing and characteristics of green crab moulting are required. A pilot study conducted in 2014–2015 collected seven groups of crabs and held them in individual compartments for 2–4 weeks to record moulting rates and physical characteristics. We found that a synchronized ‘moulting window’ occurs during July for male crabs. Field experiments in 2015 had an average moulting rate of 34%, with group-specific rates as high as 60%. The same cohort of crabs held in the laboratory had an average moulting rate of 48%, with group-specific rates as high as 75%. We observed a gradual increase in moulting rates from early to mid-July, after which all crabs caught had recently moulted, with evidence of new carapaces on all crabs. In 2015, the moulting window followed a 5°C increase in water temperature. Regarding morphology, the presence of a ‘halo’ on the episternites of the carapace was an indicator that a crab would soon moult. These promising results represent the first step in assessing the feasibility of a soft-shell, green crab industry.     

Size distribution,length–weight relationship and size at the onset of sexual maturity of the orange mud crab,Scylla olivacea,in Malaysian waters

The size distribution, length–weight relationship and size at the onset of sexual maturity of the orange mud crab (Scylla olivacea) from four geographically distinct locations (Taiping, Setiu, Kota Marudu and Lundu) representing Malaysian waters were analysed and estimated. Scylla olivacea was found in the size range of 47–134?mm carapace width. Males were significantly smaller in size but heavier than females. Geographical variation in carapace width and body weight were significant, but no interaction was found between sexes and locations. As shown by the length–weight relationships of S. olivacea, the males exhibited positive growth allometry whereas the females exhibited negative growth allometry. Males mature physiologically prior to attaining morphometric sexual maturity. Females, however, achieve physiological and morphometric sexual maturity in synchrony. No significant variation was found in the estimates of size at the onset of sexual maturity of males and females among different locations. We recommend the use of the third right walking leg merus length and carapace width to estimate the size at the onset of sexual maturity (morphometric maturity) for S. olivacea. Data obtained in this study serve as important baseline data for future mud crab resource management in Malaysia and were used to recommend minimum landing sizes for S. olivacea in each respective location based on the largest size at the onset of sexual maturity estimates were suggested.     

Population density and growth of the newly introduced Atlantic rock crab Cancer irroratus Say, 1817 (Decapoda,Brachyura) in Iceland: a four-year mark-recapture study

The Atlantic rock crab Cancer irroratus was discovered in Icelandic waters in August 2006 and spread rapidly along the coastline. The species has reproduced successfully in Iceland, and there have been strong indications that C. irroratus has become common on soft-bottom coastal habitats in south-western Iceland. To be able to evaluate the effect of such non-indigenous species on the ecosystem, population density estimates are required. In the years 2011 to 2014, a mark-recapture study was carried out on C. irroratus in a small inlet in the Kollafjörður fjord, south-western Iceland. In total, 6475 C. irroratus were captured and of them 4670 were tagged with sequentially numbered T-bar anchor tags. Of the crabs tagged, 155 were recaptured over the four years (3.3%), 34 had moulted and one of them presumably twice over the four-year period. The size range of recaptured crabs was 7.3–12.8?cm carapace width and the growth increment per moult ranged from 1.2 to 2.6?cm, with an average of 2?cm. Based on the mark-recapture analysis, the population at the study area in Kollafjörður was estimated to be about 107,000 individuals.     

Larval stages of the crab Mithrax tortugae (Brachyura: Mithracidae) with comparisons between all species of Mithrax

The postembryonic larval stages of Mithrax tortugae are described, illustrated and compared with the described zoeae of other Mithrax species. Mithrax tortugae showed morphological features in all the stages of larval development that differed from those observed in other species of Mithrax, especially M. hispidus. In the Zoea I stage, M. tortugae and M. pleuracanthus lacked the minute spine on the dorsal spine observed in M. hispidus; M. tortugae exhibited a terminal spine on the inner lobe of the coxal endite of the maxilla, which was not observed in M. hispidus or M. pleuracanthus. Also, M. tortugae exhibited furcae with spines that are not spinulated, whereas in M. hispidus and M. pleuracanthus these spines are spinulated. In the Zoea II stage, M. tortugae showed a terminal spine on the coxal endite of the maxillula, whereas in M. hispidus and M. pleuracanthus this spine is absent. In the Megalopa stage, we also observed differences in the sternal plate setation between M. tortugae and M. hispidus, where M. tortugae had eight simple setae and M. hispidus showed two simple and four plumodenticulate setae. Partial sequences of the 16S rRNA and COI genes of the parental female were analysed, providing additional evidence for species identification. Together, our analyses of larval morphology and the results of the molecular analyses reinforced recognition of the relationships among M. tortugae, M. hispidus and M. pleuracanthus.     

Relative predation risk in two types of habitat for juvenile Australasian spiny lobsters,Jasus edwardsii

The decline in kelp habitat on coastal reefs resulting from changes in ocean climate and the distribution and abundance of herbivorous species is common in many temperate regions of the world. Kelp habitat is highly productive, biodiverse and provides a complex habitat into which many organisms recruit, including spiny lobsters, such as the Australasian red spiny lobster, Jasus edwardsii. The displacement of kelp habitat by less-complex barren reef habitat has the potential to influence the risk of predation for early juvenile lobsters. Therefore, relative predation risk on the juvenile spiny lobster, J. edwardsii, was compared for kelp and barren habitats on the northeast coast of New Zealand using juvenile lobsters held in transparent containers and recording predators with a video recorder. In total, 188 predation attempts were observed within 420?h of video recordings gathered over 3 weeks of sampling. There was an overall higher predation risk in barren habitats. Daytime predation attempts were higher in barren compared to kelp habitat; however, there was no difference between the habitats for night time, dawn or dusk observations, when juvenile lobsters are emergent from shelters and vulnerable to predation. Similar numbers of predatory species were identified in kelp (13) and barren habitat (12). Other factors, such as food availability and time spent away from shelter, especially during night and crepuscular periods, need consideration in future studies when investigating the cause of differences in juvenile lobster mortality among habitats.     

A new hermit crab of the Paguristes tortugae complex (Crustacea: Anomura: Diogenidae), with a key to the western Atlantic species

A new hermit crab species, Paguristes scarabinoi sp. nov. is described and illustrated based on specimens collected in Uruguay. The new species is assigned to the Paguristes tortugae species complex based on the characteristic dense fringe of long plumose setae present on ambulatory legs and dorsolateral margins of chelae. The new species can be differentiated from all other species currently placed in the P. tortugae complex by the combination of the following features: antennal flagellum with short and long setae on each article; antennular peduncles short to moderately long, not exceeding one-third of ocular peduncles including the corneas; dactyl of ambulatory legs long, slender, slightly convex and without a longitudinal sulcus flanked by corneous spines or spinules on the mesial face; and female brood pouch elongate, slender, blade-shaped. A key to the western Atlantic species of the P. tortugae complex is provided.

http://zoobank.org/urn:lsid:zoobank.org:pub:4B3298F3-D5DF-40E5-A2AB-9B457AB8BE0E     

Influence of fluoride on the uptake of 51Cr-chromate by human erythrocytes.

Uptake of 51Cr-chromate by freshly collected human erythrocytes was inhibited by 90 mM sodium fluoride only in cells preincubated with fluoride. In vitro storage also increased the sensitivity of the cells: 90 mM NaF clearly inhibited the uptake of chromate in cells stored in vitro for 5 weeks. Gel chromatography revealed two forms of 51Cr within the cells, one of small molecular weight, which thin layer chromatography indicated was unchanged chromate; the other form was apparently bound to macromolecules such as hemoglobin.