Exposure to Electromagnetic Fields (EMF) from Submarine Power Cables Can Trigger Strength-Dependent Behavioural and Physiological Responses in Edible Crab, Cancer pagurus (L.)

The current study investigated the effects of different strength Electromagnetic Field (EMF) exposure (250 µT, 500 µT, 1000 µT) on the commercially important decapod, edible crab (Cancer pagurus, Linnaeus, 1758). Stress related parameters were measured (l-Lactate, d-Glucose, Total Haemocyte Count (THC)) in addition to behavioural and response parameters (shelter preference and time spent resting/roaming) over 24 h periods. EMF strengths of 250 µT were found to have limited physiological and behavioural impacts. Exposure to 500 µT and 1000 µT were found to disrupt the l-Lactate and d-Glucose circadian rhythm and alter THC. Crabs showed a clear attraction to EMF exposed (500 µT and 1000 µT) shelters with a significant reduction in time spent roaming. Consequently, EMF emitted from MREDs will likely affect crabs in a strength-dependent manner thus highlighting the need for reliable in-situ measurements. This information is essential for policy making, environmental assessments, and in understanding the impacts of increased anthropogenic EMF on marine organisms.

High Potential for Secondary Metabolite Production of Paracoccus marcusii CP157, Isolated From the Crustacean Cancer pagurus

Secondary metabolites are key components in microbial ecology by mediating interactions between bacteria and their environment, neighboring species or host organisms. Bioactivities can be beneficial for both interaction partners or provide a competitive advantage only for the producer. Colonizers of confined habitats such as biofilms are known as prolific producers of a great number of bioactive secondary metabolites and are a potential source for novel compounds. We investigated the strain Paracoccus marcusii CP157, which originates from the biofilm on the carapace of a shell disease-affected Cancer pagurus specimen, for its potential to produce bioactive secondary metabolites. Its closed genome contains 22 extrachromosomal elements and several gene clusters potentially involved in biosynthesis of bioactive polyketides, bacteriocins, and non-ribosomal peptides. Culture extracts of CP157 showed antagonistic activities against bacteria from different phyla, but also against microalgae and crustacean larvae. Different HPLC-fractions of CP157 culture extracts had antibacterial properties, indicating that several bioactive compounds are produced by CP157. The bioactive extract contains several small, antibacterial compounds that partially withstand elevated temperatures, extreme pH values and exposure to proteolytic enzymes, providing high stability toward environmental conditions in the natural habitat of CP157. Further, screening of 17 Paracoccus spp. revealed that antimicrobial activity, hemolysis and production of N-acyl homoserine lactones are common features within the genus. Taking into account the large habitat diversity and phylogenetic distance of the tested strains, we hypothesize that bioactive secondary metabolites play a central role in the ecology of Paracoccus spp. in their natural environments.

High-Pressure Processing for the Production of Added-Value Claw Meat from Edible Crab (Cancer pagurus)

High-pressure processing (HPP) in a large-scale industrial unit was explored as a means for producing added-value claw meat products from edible crab (Cancer pagurus). Quality attributes were comparatively evaluated on the meat extracted from pressurized (300 MPa/2 min, 300 MPa/4 min, 500 MPa/2 min) or cooked (92 °C/15 min) chelipeds (i.e., the limb bearing the claw), before and after a thermal in-pack pasteurization (F9010 = 10). Satisfactory meat detachment from the shell was achieved due to HPP-induced cold protein denaturation. Compared to cooked or cooked–pasteurized counterparts, pressurized claws showed significantly higher yield (p < 0.05), which was possibly related to higher intra-myofibrillar water as evidenced by relaxometry data, together with lower volatile nitrogen levels. The polyunsaturated fatty acids content was unaffected, whereas the inactivation of total viable psychrotrophic and mesophilic bacteria increased with treatment pressure and time (1.1–1.9 log10 CFU g−1). Notably, pressurization at 300 MPa for 4 min resulted in meat with no discolorations and, after pasteurization, with high color similarity (ΔE* = 1.2–1.9) to conventionally thermally processed samples. Following further investigations into eating quality and microbiological stability, these HPP conditions could be exploited for producing uncooked ready-to-heat or pasteurized ready-to-eat claw meat products from edible crab.

Non-invasive MRI Studies of Ventilatory and Cardiovascular Performance in Edible Crabs Cancer pagurus During Warming Under Elevated CO2 Levels

The thermal tolerance of marine decapod crustacea is defined through their capacities for oxygen uptake and distribution. High ambient CO2 levels were previously shown to reduce hemolymph oxygen levels at enhanced cardiac performance during warming. This study investigated the impacts of warming under two CO2 levels on ventilation and hemolymph circulation in edible crabs Cancer pagurus. It also highlights changes in the ventilatory and cardiac pauses displayed by Decapoda under routine metabolism. Animals were exposed to step-wise, sub-critical warming (12–20°C over 5 days) under control (470 μatm) and high (1,350 μatm) water PCO2. Flow-through respirometry was combined with magnetic resonance imaging and infra-red photoplethysmography to allow for simultaneous, non-invasive measurements of metabolic rates (M˙O2), ventilation and cardiovascular performance. Crabs spent significantly more time in a low M˙O2 state (metabolic pause), when experiencing high CO2 conditions above 16°C, compared to normocapnic warming. Heart rates leveled off beyond 18°C at any CO2 level. Cardiac output continued to increase with high-CO2-warming, due to elevated cardiac stroke volumes. Consequently, temperature-dependent branchial hemolymph flow remained unaffected by CO2. Instead, a suppressing effect of CO2 on ventilation was found beyond 16°C. These results indicate constrained oxygen uptake at stable cardiovascular performance in a decapod crustacean.Cancer pagurus: urn:lsid:zoobank.org:act:B750F89A-84B5-448B-8D80-EBD724A1C9D4

Factors contributing to the disease ecology of brown crab (Cancer pagurus) in a temperate marine protected area.

Marine ecosystems are affected by multiple, well-known stressors like fishing and climate change, but a less documented concern is disease. Marine reserves have been successful in replenishing stocks and aiding recruitment but studies have shown that high population abundances in marine reserves may lead to unwanted secondary effects such as increase in predators and competition, altering trophic webs, and disease. Here, we investigate factors contributing to disease prevalence in a brown crab (Cancer pagurus) population around Lundy Island (the UK's first MPA) after 7 years of no-take protection. Population parameters (size, sex, and abundance), disease (shell disease, Hematodinium spp. infection) and injury presence (a known precursor to some disease conditions) were assessed over two years in both fished and unfished areas of the MPA. We found no significant difference in prevalence between the disease prevalence in fished and unfished areas, however overall, the number of injured crabs increased significantly over the two years (12%), as did the prevalence of shell disease (15%). The probability of crabs having shell disease increased significantly in male crabs, and in those missing limbs. The probability of crabs being injured increased significantly in crabs below the minimum landing size. In terms of population parameters, crabs were more prevalent in the fished area compared to the unfished area, thought to be a result of an increase in the predatory European lobster. The findings of the present study highlight potential secondary community changes as a result of MPA implementation. Therefore, surveillance for such changes, as part of MPA management, would provide useful information on the health and overall function of the protected ecosystem.

Abundance and spatial distribution of brown crab (Cancer pagurus) from fishery-independent dredge and trawl surveys in the North Sea

Brown crab (Cancer pagurus) is a widely distributed crustacean that occurs around the British coastline supporting important commercial fisheries. The habitat preferences of brown crab around Scotland are poorly documented and for the purposes of stock assessment, the species is considered data-poor. Based on an analysis of dredge and trawl surveys taking place in the North Sea (2008–2018), we describe the spatial distribution of brown crab and for the first time, develop abundance and recruitment indices for the species. We make use of geostatistical methods and apply generalized additive models to model catch rates in relation to a number of explanatory variables (depth, distance to the coast, sediment type and year). The dredge and trawl abundance indices were correlated showing a similar trend of increasing catch rates in the early years of the time series up to 2016 and a subsequent reduction. The recruitment index showed a gradual increase in captured juvenile crabs up to 2014 followed by a steep decrease with 2018 being the lowest value estimated. The derivation of robust indicators of stock abundance will contribute to the stock assessment of this species and enable the provision of improved fisheries management advice for brown crab around Scotland.

Abundance and size of European lobsters (Homarus gammarus) and brown crabs (Cancer pagurus) inside and outside the Kåvra lobster reserve (west coast of Sweden)

The common method of using lobster-pot catch data for investigating relative abundance, sex and size distribution has serious disadvantages. This study estimates relative abundance and size of the European lobster Homarus gammarus and the brown crab Cancer pagurus using scuba diving techniques. The study areas were the Kåvra lobster reserve (Kåvra) on the Swedish west coast and three very different nearby areas where fishing for crustaceans is allowed: Gullmarsfjorden; the archipelago; and the offshore area. A total of 167 lobsters and 337 brown crabs were observed during 33 scuba dives (each 30 minutes long) in 2018-2019. The estimated mean abundance of lobsters was three to fifteen times as high at Kåvra in comparison with the other three areas (all exact showing that the statistical populations were distinct in comparison with Kåvra; Wilcoxon-Mann-Whitney Test). Dive sites in the outer part of the offshore area had the lowest abundance of lobsters although they had seemingly good lobster habitats and low fishing intensity. Large lobsters with a carapace length of ⩾15 cm were found only at Kåvra where they made up 24% of the lobsters. The proportion of large lobsters inside Kåvra continues to increase after 30 years of protection. Together, this emphasizes the impact of fishing on lobster abundance and size distribution, and indicates that limited recruitment and migration might possibly affect offshore lobster “sub populations”. Kåvra was the only area where the abundance of lobsters exceeded the abundance of brown crabs (). However, the abundance of brown crabs at Kåvra was as low as in Gullmarsfjorden () where fishing for crabs is allowed. Possible complex lobster/brown crab interactions together with other factors that might explain the low abundance of the protected brown crab at Kåvra, need to be investigated further.