Individual Crabs Research Articles

Comparative analysis of nutritional and non-volatile taste components of the Chinese mitten crab (Eriocheir sinensis)

This study investigated the differences among 20–20 individual crab samples from Chongming (CM) and Taixing (TX) origin in china through proximate composition, taste composition, and sensory analysis evaluation, to find out the key factors and contribute to the realization of the high-quality mitten crab culture industry. The results showed that the overall performance of TX group was better, and the contents of Ala, Gly, Arg and AMP were 6.33±1.25 mg/g, 4.67±0.87 mg/g, 4.53±0.69 mg/g and 68.68±22.88 mg/100 g, respectively. The key taste amino acids, whose taste activity value was over 1.0, detected in TX (5 kinds) and CM (4 kinds). The umami and sweet sensory scores of TX were 0.52 and 0.50 higher than that in CM group. Cluster analysis and principal component analysis showed that TX and CM crabs could be distinguished to a certain extent.

Effects of Temperature and Diurnal Cycle in the Molting Schedule of Mangrove Crab, Scylla serrata (Forskål, 1775)

Soft-shell crab farming is gaining popularity since all crab parts can be eaten with almost no discards. However, its biggest challenge is the tedious monitoring every 4-hour interval to check for molting. A total of 90 mangrove crabs weighing 80-100 g were stocked in individual crab trays, recording 24-hour water temperature and incidence of hourly molting for 57 days to provide another basis for monitoring and cues in the molting schedule. Results showed that molting (82.24 %) happens at optimum temperature (Topt) levels, between 27–31°C, with a high incidence of molting (85.29 %) at nighttime when the water temperature is lower and within the Topt. Findings suggested that aside from 4-hour intervals, monitoring of molting for soft-shell crab farming is recommended at nighttime and early morning.

AssesSments of Vibrio parahaemolyticus and Vibrio vulnificus levels and microbial community compositions in blue crabs (Callinectes sapidus) and seawater harvested from the Maryland Coastal Bays.

Fluctuations in environmental physicochemical parameters can affect the diversity and prevalence of microbial communities, including vibrios, associated with aquatic species and their surrounding environments. This study aimed to investigate the population dynamics of two Vibrio species as well as the microbial community diversity of whole crab and seawater from the Maryland Coastal Bays (MCBs), using 16S rRNA sequencing. During this study, three crabs and 1 L of seawater were collected monthly from two sites for 3 months. Crab tissue was extracted and pooled for each site. Extracted crab tissue and seawater were analyzed for Vibrio parahaemolyticus and V. vulnificus using Most Probable Number (MPN) real-time PCR. For 16S rRNA microbiome analysis, three different DNA extraction kits were evaluated to extract microbial DNA from individual crabs. Also, 500 mL of each seawater sample was filtered for DNA extraction. Results indicated that sample types and sampling periods had a significant effect on the alpha diversity of the microbial community of crabs and seawater (p < 0.05); however, no statistical difference was found between DNA extraction kits. Beta diversity analysis also found that the microbial compositions between sample types and temporal distributions were statistically significant. Taxonomic classification revealed that Proteobacteria, Cyanobacteria, Actinobacteria, and Bacteroidetes were present in both crab and seawater samples. Vibrio parahaemolyticus and V. vulnificus were also detected in both crab and seawater samples, although crabs contained a higher concentration of the bacterium compared to the seawater samples. It was found that vibrios were not a dominant species in the microbial community of crab or seawater samples. Results from this study provide further insight into species diversity and phylogenetic compositions of blue crabs and seawater from the MCBs. These approaches will help in risk assessments that are essential in the overall advancement of public health.

Morphometric Differentiation of the Swimming Crab Portunus sanguinolentus (Herbst, 1783) Populations in East Asia: Implications for Stock Identification and Management

Morphometric disparities were employed to characterize the geographical variations in and elucidate the phylogeography of Portunus sanguinolentus in East Asia. In this study, a comprehensive assessment was undertaken based on measurements from 833 individual crabs. These crabs were sampled from eight distinct locations, namely Kyushu (KS), Fuzhou (FZ), Yilan (YL), Xiamen (XM), Tainan (TN), Hong Kong (HK), Vietnam (VN), and Singapore (SG). Twelve morphometric measurements were standardized based on size using the allometric method. A cluster analysis and a canonical variate analysis (CVA) were then conducted for a data analysis. Randomization tests were subsequently performed to validate the morphometric differences observed among the groups. The analytical results classified the eight sampled populations into at least two distinct clusters. The first cluster included three samples from China (specifically FZ, XM, and HK), while the second cluster consisted of samples from East Asia (including KS, YL, TN, VN, and SG). The CVA revealed a tripartite division into three groups: the mainland China group (FZ, XM, and HK), the Kuroshio group (KS, YL, and TN), and the Southeast Asia group (VN and SG). The observed morphometric variations between these broad groups were statistically significant for both genders. These differences may be attributed to evolutionary origins, geographical events, or environmental adaptations. This study highlights the effectiveness of morphometric techniques in providing comprehensive insights into species delimitation and philogeographic relationships.

Population and spatial ecology of horseshoe crabs (Limulidae) in a nursery ground at Pulau Bedukang, Brunei Bay, Borneo

Abstract. Rozaini AF, Laurie KH, Marshall DJ. 2023. Population and spatial ecology of horseshoe crabs (Limulidae) in a nursery ground at Pulau Bedukang, Brunei Bay, Borneo. Biodiversitas 24: 4485-4492. Suitable nursery habitat to support populations of juvenile horseshoe crabs is becoming threatened globally. There are currently no formal studies on juvenile populations of the horseshoe crabs (Limulidae) for Brunei Darussalam (Brunei, Borneo). We investigated body size structure, population cohort and ecological distribution of juvenile horseshoe crabs associated with a mudflat on Pulau Bedukang, in Brunei Bay. Seventy juveniles were retrieved during four sampling days covering two seasons and four study sites. Carcinoscorpius rotundicauda and Tachypleus gigas were common, whereas only two individuals of Tachypleus tridentatus were found. Carapace width (size) was similar in the common species and there was no difference in juvenile size between the seasons and study sites. Body weight to carapace width relationships showed that the species grew at similar rates, although C. rotundicauda developed faster, producing 14 compared to the eight pre-migration mudflat instars produced by T. gigas. Species densities were similar, and there was no spatial separation of species or juvenile size across the mudflat or in relation to the mangrove forest edge. Nearest-neighbor (NN) analysis showed that individual crabs were generally dispersed. Their mudflat cohabitation suggests physiological and behavioral plesiomorphies for common optimal developmental salinity and temperature conditions. This study provides baseline information for comparison with other regional studies and for local conservation planning.

Distribution and Growth Patterns of Crab (P. pelagicus) Based on Environmental Characteristics in Candi Waters, Pamekasan Regency, East Java Province

Blue swimming crab (BSC) is a fishery commodity with high economic value and great demand in domestic and foreign markets. P. pelagicus swimming crabs are commonly found in Indonesian sea waters, one of the largest contributors to the country's foreign exchange after shrimp and tuna. The high demand for blue crab resources will trigger an increase in fishing efforts. If this is done continuously, it is feared that it could endanger the population structure. Moreover, disrupting the sustainability of blue swimming crab resources in the waters, this study examines the morphometric distribution and growth pattern of P. pelagicus crabs based on environmental characteristics in Candi waters, Pamekasaan Regency. Census sampling was carried out using the census method; the census method was carried out by taking all crab samples caught by fishermen. The results obtained found 33 individual crabs, which were divided into three classes, namely small (&lt;10 cm), medium (&gt;10 cm), and large (&gt;12 cm) size classes. Male crabs dominated the research locations with wider straps than female crabs. The analysis results show that the width-weight relationship's b values are 1.47 (males) and 2.00 (females). In addition, male and female crabs have a positive allometric growth pattern. Blue swimming crabs are often found in habitats with a substrate of dusty mud, high salinity and organic matter.

Juvenile Dungeness crab foraging behavior and lipid composition is altered more by food quantity than seawater pH in a multi-stressor experiment

Increases in atmospheric, anthropogenic carbon are driving reductions in seawater pH, a process referred to as ocean acidification. Reduced seawater pH can influence behavior of marine animals, but little is currently known about how juvenile crustaceans will respond. We conducted lab experiments to improve our understanding of the consequences of pH exposure and food quantity on juvenile Dungeness crab (Metacarcinus magister, (Dana, 1852)) behavior and nutritional condition. To understand the foraging and pH sensing behavior of juvenile crab, and how this interacts with their nutritional status, we exposed recently settled second instar juveniles to either ambient pH or reduced pH for 42-d, crossed with either a ‘maintenance’- or low-quantity ‘challenge’ diet treatment. After the experimental exposure period, we introduced crab into foraging and sensing pH behavior experiments. In the foraging experiment, we placed crab in a behavior arena with unidirectional flow, where we measured the food discovery time and time allocation of activities in 300-s trials for all individual crab. Food quantity and pH exposure influenced both the speed with which juvenile crab identified and allocation of activities but there was no interactive effect of experimental factors. For our pH sensing experiment, we used a two-current flume plumbed with both ambient and reduced pH seawater. This flow-through flume provided a choice between the pH treatment waters and allowed us to measure the amount of time individuals spent on either side of the arena in 300-s trials. There was no effect of prior diet or pH exposure on the amount of time juvenile crab spent in either seawater pH condition. In addition to the behavior trials, we evaluated crab nutritional condition by quantifying the total lipid content of whole-body tissues and fatty acid profile composition of juvenile crab fed either the maintenance or low-quantity diet during the experimental pH exposure period. The proportional fatty acid profiles differed for crab based on their diet and pH exposure, with no interactive effects. However, we did not detect differences in the concentrations of key summary categories of fatty acids (e.g., saturated, monounsaturated, or polyunsaturated) based on pH exposure. Our results indicate that reduced food availability has a greater impact on juvenile Dungeness crab foraging behavior and nutritional condition than reduced seawater pH exposure representing the 0.3 pH unit decrease predicted by 2100.

A Part-based Deep Learning Network for identifying individual crabs using abdomen images

Crabs, such as swimming crabs and mud crabs, are famous for their high nutritional value but are difficult to preserve. Thus, the traceability of crabs is vital for food safety. Existing deep-learning methods can be applied to identify individual crabs. However, there is no previous study that used abdomen images to identify individual crabs. In this paper, we provide a novel Part-based Deep Learning Network (PDN) to reliably identify an individual crab from its abdomen images captured under various conditions. In our PDN, we developed three non-overlapping and three overlapping partitions strategies of the abdomen image and further designed a part attention block. A swimming crab (Crab-201) dataset with the abdomen images of 201 swimming crabs and a more complex mud crab dataset (Crab-146) were collected to train and test the proposed PDN. Experimental results show that the proposed PDN using the overlapping partition strategy is better than the non-overlapping partition strategy. The edge texture of the abdomen has more identifiable features than the sulciform texture of the lower part of the abdomen. It also demonstrates that the proposed PDN_OS3, which emphasizes the edge texture of the abdomen with overlapping partition strategies, is more reliable and accurate than the counterpart methods to identify an individual crab.

Metabolic rates in the squareback marsh crab Armases cinereum.

Metabolic rate is a basic individual metric that extends beyond the individual to link the ecology of populations, communities, and ecosystems via its role as a central component of energy budgets. Metabolic rates are often measured indirectly by quantifying respiration under simplified, standard laboratory conditions. This approach limits the application of these measurements to a small range of conditions that commonly do not reflect natural field conditions. We measured metabolic rates of the squareback marsh crab Armases cinereum under field conditions. Previous work highlights that movement of individual A. cinereum, especially females, provides a potential spatial subsidy of energy, as individuals consume foods in salt marshes and then transfer the resulting energy to upland forest ecosystems. We show that metabolic rate increases with size for both males and females and that metabolic rates are influenced by temperature and by whether females are vitellogenic. The metabolic rates that we measured more closely approximate field metabolic rates than standard metabolic rates and demonstrate that individual crabs experience high energy expenditures, reducing the amount of energy that may be transferred as a subsidy between marsh and forest as a result of the daily movements of individual crabs. Our measurements are therefore also a key component for the construction of an energy budget for this species.

Application of radio frequency identification tags for marking of fish gillnets and crab pots: Trials in the Norwegian Sea and the Barents Sea, Norway

Marking of fishing gear is an important step in reducing abandoned, lost, and discarded gear, thereby reducing the amount of plastic pollution in the sea. With the help of fishers in their daily work on the Norwegian coast, we have performed several trials using radio frequency identification (RFID) tags to mark crab pots and gillnets. The results show that RFID tags are well suited to mark individual crab pots without affecting the daily work of fishers, and there is no evidence that the tags affect the catch. However, the trials uncovered that the tags easily entangle in the fish gillnets, creating much hassle for the fishers. Also, the heavy stress on the tags while hauling the gillnets damaged several tags. Therefore, we can not recommend marking gillnets with RFID tags before more appropriate tags have been identified and tested.

Effect of CO2 driven ocean acidification on the mud crab Scylla serrata instars

The decreasing ocean pH seems to adversely affect marine organisms, including crustaceans, which leads to potential threats to seafood safety. The present investigation evaluated the effect of seawater acidification on the edible marine mud crab Scylla serrata instars. The experimental setup was designed using a multi-cell cage based system assembled with 20 pre holed PVC pipes containing 20 individual crabs to avoid cannibalism. The crab instars were exposed to CO2 driven acidified seawater at pH 7.8 (IPCC forecast pH at the end of the 21st century), 7.6, 7.4, 7.2, and 7.0 for 60 days. The crabs reared in seawater without acidification at pH 8.2 served as control. The present study revealed a notable decrease in survival, feed intake, growth, molting, tissue biochemical constituents, minerals, chitin, and alkaline phosphatase in S. serrata instar reared in acidified seawater, denotes the adverse effect of seawater acidification on crabs. The significant elevations in antioxidants, lipid peroxidation, and metabolic enzymes in all acidified seawater compared to ambient pH indicates the physiological stress of the crabs' instars. The changes in the metabolic enzymes reveal the metabolism of protein and glucose for additional energy required by the crabs to tolerate the acidic stress. Hence, the present study provides insight into the seawater acidification can adversely affect the crab S. serrata.

Crab diversity and crab potential as support ecotourism in Teleng Ria, Grindulu and Siwil Beach, Pacitan, East Java, Indonesia

Abstract. Irwansyah RM, Azzahra SIN, Darmastuti SA, Ramadhandi AR, Firdaus O, Daeni F, Safitri N, Fajri OPA, Nugroho GN, Naim DM, Setyawan AD. 2021. Crab diversity and crab potential as support ecotourism in Teleng Ria, Grindulu and Siwil Beach, Pacitan, East Java, Indonesia. Intl J Bonorowo Wetlands 11: 75-83. The mangrove area in Pacitan District, Pacitan, East Java, Indonesia is generally not polluted. Therefore, the land is suitable for growing conditions from mangrove plants and has great potential as a mangrove area with ecotourism management in Indonesia. Ecotourism activities in mangrove areas, in principle, are the use of mangrove areas while maintaining the biological/ecological functions of mangrove areas that have social and economic value for local community. The mangrove ecosystem is a habitat of various species of Crustacea, such as the crab. Crabs are live in coastal/mangrove ecosystems and one of the key species that have a very important role in maintaining the balance of the ecosystem. The study about diversity of crabs in the mangrove area is very important because it will improve the quality of mangrove and potentially support ecotourism in the mangrove ecosystem. This study aims to determine the diversity of the crab and its potential to support ecotourism if the Pacitan Beaches will be ecotourism in the future. This research was conducted in Teleng Ria Beach, Grindulu Beach, and Siwil Beach, Pacitan, East Java, Indonesia in November 2021. Plots of 10 x 10 m2 are made to record the species and the number of individual crab species. The result found five species of crab,i.e. Austruca annulipes (H. Milne-Edwards, 1837), Coenobita perlatus (H. Milne-Edwards, 1837), Ocypode kuhlii (De Haan, 1835), Perisesarma guttatum (A. Milne-Edwards, 1869), and Scylla serrata (Forsskål, 1775). The total crab diversity index of 1.25 is included in the medium category. The morphology, activity, number of individuals and distribution of each crabs species in an ecotourism area will increase the attractiveness of tourists to visit. For example, the morphology of C. perlatus that has the red color as a strawberry sometimes has a home/the shells of the Mollusca which color and unique shape so that add appeal to be seen. Then, the crab A. annulipes that like to dance and play the violin with the claw can also be attractions drawing tourists. Hopefully, the data can be a reference for the managers of the mangrove area in developing ecotourism and conservation of mangrove forest.

Species diversity and molecular taxonomy of symbiotic crustaceans on Portunus pelagicus (Linnaeus, 1758) in Vietnam, with remarks on host records and morphological variation

The blue swimming crab (Portunus pelagicus (Linnaeus, 1758)) is an economically and ecologically important species in Vietnam, and a potential subject for aquaculture as well. More than 400 individual crabs were collected along the Vietnamese coastline and examined for ectosymbiotic crustaceans. Two molecular markers (28S rRNA and COI mtDNA) were applied for species delineation. Seven species were reported and described, of which six are cirripede barnacles (Thecostraca, Thoracia); and one parasitic copepod Choniosphaera indica Gnanamuthu, 1954 (Copepoda, Podoplea). Four species (Chelonibia testudinaria (Linnaeus, 1758), Semibalanus sp., Octolasmis neptuni (MacDonald, 1869), and Dianajonesia tridens (Aurivillius, 1894)) were the first records for both host and location. The symbiotic crustaceans occupy specific niches on the crab body, and vary in their infestation status. Molecular taxonomy of symbiotic crustaceans was classified and confirmed based on sequence similarity and phylogenetic analyses.

Industrialization and food safety for the Tsleil-Waututh Nation: An analysis of chemical levels in shellfish in Burrard Inlet

While Indigenous food systems remain critical for community well-being, traditionally harvested foods are a potential source of toxic exposures. The Tsleil-Waututh Nation (TWN) is seeking to restore shellfish harvesting in Burrard Inlet (British Columbia [BC], Canada), where the cumulative effects of industrial activity have nearly eliminated safe harvesting. The Trans Mountain Expansion project would triple the capacity to transport oil through the inlet, threatening TWN's progress to restore shellfish harvesting. To inform ongoing efforts we assessed contamination by heavy metals (arsenic, cadmium, lead, and mercury) and 48 polycyclic aromatic hydrocarbons (PAHs) congeners in different shellfish species (Softshell clams, Varnish clams, and Dungeness crab) in three areas. We compared our results against local screening values (SVs) established by the TWN and BC Ministry of Environment and Climate Change Strategy, as well as provincial and national benchmarks. In total, we analyzed 18 composite samples of Softshell clams and Varnish clams (5 individuals per sample), as well as 17 individual crabs. We found chemical contamination in all species at all sites. PAHs were most frequently detected in Softshell clams, highest in the site closest to the pipeline terminus. Clams presented higher levels of contamination than crabs for PAHs, but not for heavy metals. For Softshell and Varnish clams, all heavy metals across study sites exceeded at least one of the population-specific SVs. Of the 14 PAHs detected, benzo(a)pyrene presented a median concentration in Softshell clams of 3.25 μ/kg, exceeding local SV for subsistence fisher. Our results call for further assessment of human health impacts related to food harvesting within Burrard Inlet and establishing a long-term coordinated program co-led by the TWN to monitor contamination and inform future harvesting programs. The study draws attention to the need to consider locally-relevant toxicity benchmarks, and include potential health impacts of food contamination in appraising development project proposals.

Artificial light at night (ALAN) mediates transient spatial aggregation of an ecosystem engineer, the crabNeohelice granulata(Dana, 1851) (Decapoda: Brachyura: Varunidae), under different ecological contexts

AbstractArtificial light at night (ALAN) alters natural light regimes in much of the world. The effect of ALAN has been studied in several organisms, although not so much in crustaceans, especially in adult stages. We evaluated the relationship between different intensities of ALAN and the abundance of burrows, and surface activity of the crab Neohelice granulata (Dana, 1851). The study was conducted in 2016 and 2017, in two salt marshes, San Antonio Oeste and Mar Chiquita, Argentina, both having different ecological contexts. During new-moon nights we counted the number of burrows and crabs on the surface and along a gradient of artificial light caused by street lighting with high-pressure sodium lamps. We found that the number of crabs on the surface increased with light intensity and that crabs were almost exclusively males. In contrast, we found that the number of burrows was not related to light intensity, suggesting that the increase of crabs on the surface was mainly due to an increase in their activity. We considered two main mechanisms causing the increase on surface activity of crabs: 1) an increase in the frequency of emergence and short-distance excursions around their burrow and 2) an increase of mobility with long-distance directional displacement from dark to lit areas. Overall, our observations suggest that the presence of ALAN can modify individual crab behavior (i.e., aggregation) and consequently effects on ecosystem functioning.

PENGEMBANGAN DESAIN PINTU MASUK BUBU LIPAT BERDASARKAN ASPEK TINGKAH LAKU RAJUNGAN

Blue swimming crab fishing using collapsible traps is widely used by fishermen because its caught live crabs and high selectivity. However, the passive fishing operation causes its low fishing productivity. The success of crabs fishing using folding traps is influenced by the suitability of the entrance design used. The size of the net and the inclination angle that are not by the crab's behavior will cause the crab to fail to be caught. This study aims to determine the more effective entrance design for catching crabs using the collapsible trap. The study was conducted in a laboratory using three mesh sizes, including 1.00, 1.25, and 1.50 inches with 30°, 40°, and 50° inclination angles. Each treatment combination uses different individual crabs. The study was conducted at night in an aquarium equipped with an infrared camera. Differences in mesh size and angle of inclination affect the crab's success rate and crawling speed in crossing the net field. The results showed that the highest percentage of crabs that successfully crossed the net field was obtained using a 1.25-inch mesh with an angle of 40°. The highest average crawling speed was also obtained at the same mesh size and angle of inclination. The use of a 1.25-inch mesh with an angle of 40° is expected to increase the effectiveness of catching crabs with folding traps.

Assessing the implications of live claw removal on Jonah crab (Cancer borealis), an emerging fishery in the Northwest Atlantic

In the Northwest Atlantic fisheries management is adapting to emerging fisheries. The fishery for Jonah crab (Cancer borealis) is rapidly expanding resulting in a quadrupling of landings over the past 20 years. In response to this increased fishing effort, management plans have begun adopting a suite of regulatory measures, one of which allows the live removal of claws at-sea. The overall goal of this project was to determine if claw removal has an impact on crab mortality. Results from a series of laboratory trials with individual crabs (n = 240) indicate that double-claw removal incurs markedly more mortality (70 %) compared with single-claw removal (51 %). Mortality was significantly correlated with wound size, temperature, and shell condition (GLM, p < 0.05), as well as elevated levels of glucose and lactate in the haemolymph of declawed animals. We also conducted a comparative claw removal trial (n = 40) using both manual- and mechanically-induced (using a declawing tool) methods and showed that mortality in manually declawed crabs (87 %) was much higher than when claws were removed mechanically (40 %, Wilcoxon pairs test, p < 0.0001). Finally, when claws were removed from tagged crabs released in the field (n = 464), four times as many control crabs were recaptured than crabs with claws mechanically removed, and none of the crabs whose claws were manually removed were recaptured (p = 0.0048). Overall, claw removal results in a significant number of mortalities. However, our findings also provide a foundation for future investigations on the sub-lethal effects of claw removal on Jonah crabs as well as the impacts of claw harvesting to improve fisheries management of this rapidly burgeoning fishery.

Moulting and growth of mangrove crabs Scylla olivacea (Herbst 1796) with injection of phytoecdysteroids and artificial feed

Moulting in crabs can be accelerated by adding moulting hormone. Phytoecdysteroids are an active compound found in certain plants, for example amaranthus, that are analogous to the moulting hormone in crustaceans. The aim of this study was to determine the effect of phytoecdysteroid administration through injection and artificial feed on moulting and growth of mud crabs (Scylla olivacea). Mud crabs with carapace width 61–62 mm and weight 50–51 g were reared in individual crab boxes with dimensions 25×20×20 cm. The selected crabs were injected with amaranthus extract at a dose of 1 mL/crab (I), then placed in the crab boxes and kept in a pond. Amaranthus leaves were dried in an oven at 60°C for 24 hours, ground using a hammer mill, and mixed with other feed ingredients. Different doses of amaranthus flour were applied: 0% (control), 10%. 12.5%, 15%, 17.5% and 20%. Moulting and growth data were analysed for a variance. The results showed that the administration of phytoecdysteroids from amaranthus by injection and through artificial feed had no effect on the percentage of mud crabs moulting, survival rate, growth, and feed conversion value. The mud crabs were not able to take full advantage of the artificial feed provided because of the inappropriate size of the feed and the fragile structure that cause wasted and uneaten feed.

Cannibalism as a potential factor affecting recruitment of the invasive Asian shore crab Hemigrapsus sanguineus

Cannibalism affects the population dynamics of many marine species, but its potential for influencing population sizes of non-native species is not well understood. A series of laboratory experiments was conducted in 2016 to examine the frequency of cannibalism in the Asian shore crab (Hemigrapsus sanguineus) and the factors influencing its rates of occurrence. Predators and prey varied in size from planktonic megalopae (the last larval stage) and the first benthic crab stage to small juveniles (3–6 mm carapace width, CW), large juveniles (7–10 mm CW), and adult crabs (12–15 mm CW). Individual crabs were paired with groups of smaller prey in glass culture dishes with sand and rocks as potential shelter for the prey, both with and without an alternative food source (commercial crab pellets). Adult and large juvenile crabs consumed megalopae, first-stage crabs and small juveniles, regardless of the presence of food. Megalopae were cannibalized the most heavily, and the size difference between predator and prey was an important factor determining cannibalism rates. Cannibalism of settling megalopae and newly settled juveniles by larger conspecifics could affect recruitment to benthic populations of this non-native crab species.

Sustainable co-location solutions for offshore wind farms and fisheries need to account for socio-ecological trade-offs

The spatial expansion of offshore wind farms (OWFs) is key for the transition to a carbon free energy sector. In the North Sea, the sprawl of OWFs is regulated by marine spatial planning (MSP) and results in an increasing loss of space for other sectors such as fisheries. Understanding fisheries benefits of OWFs and mitigating the loss of fishing grounds is key for co-location solutions in MSP. For the German exclusive economic zone (EEZ) of the North Sea we conducted a novel socio-ecological assessment of fisheries benefits which combines exploring potential spill-over from an OWF with an experimental brown crab (Cancer pagurus) pot fishery and an economic viability analysis of such a fishery. We arrayed a total of 205 baited pots along transects from an OWF located near the island of Helgoland. After a soaking time of 24 h we retrieved the pots and measured the carapace width (mm), weight (g), and sex of each individual crab. To conclude on cumulative spill-over potentials from all OWFs in the German EEZ and drivers of passive gear fisheries we analysed vessel monitoring system (VMS)-data and computed random forest regressions. Local spill-over mechanisms occurred up to distances of 300 to 500 m to the nearest turbines and revealed an increasing attraction of pot fishing activities to particular OWFs. This corresponds to the observation of constantly increasing fishing effort targeting brown crab likely due to both a growing international demand and stable resource populations at suitable habitats, including OWFs. Our break-even scenarios showed that beam trawlers have the capacities to conduct during summer an opportunistic but economically viable pot fishery. We argue that particularly in the North Sea, where space becomes limited, integrated assessments of the wider environmental and socio-economic effects of planning are crucial for a sustainable co-location of OWFs and fisheries.