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Chitinase is a kind of glycoside hydrolase which is widely distributed in nature and encoded by multiple genes to catalyze the decomposition of chitin, which plays an important role in the molting and pathogen defense of crustaceans. However, the research on chitinase in crustaceans is mainly focused on a few species with economic value. In this study, full-length cDNA sequences of the HtCHT1, HtCHT3 and HtCHT4 genes were cloned from the mudflat crab Helice tientsinensis by RACE, and the sequences were analyzed. The results showed that the full-length 2,229 bp of HtCHT1 gene encoded 627 amino acids, while the full-length 2,191 bp of HtCHT3 gene produced 489 amino acids, and the full-length 3,312 bp of HtCHT4 gene encoded 664 amino acids. Bioinformatics analysis showed that all the obtained chitinase proteins had the glycosyl hydrolase family 18 (GH18) catalytic domain and chitin-binding domain (ChtBD2), furthermore, HtCHT1 and HtCHT4 proteins had signal peptide domains at N-terminal. Phylogenetic analysis showed that different types of chitinase were clustered, and HtCHTs were closely related to chitinases in the Eriocheir sinensis. Expression profile analysis showed that the HtCHT1, HtCHT3 and HtCHT4 were significantly expressed in hepatopancreas. Furthermore, the expression of three genes was significantly up-regulated in hepatopancreas after the Vibrio parahaemolyticus challenge. These results suggested that HtCHT1, HtCHT3 and HtCHT4 were belonged to the CHITINASE gene family in H. tientsinensis and were potentially involved in the antibacterial immune response. This study provides essential information for further research of chitinase in H. tientsinensis and even crustaceans. [ABSTRACT FROM AUTHOR]

Intertidal wetlands undergo dynamic water and salinity variations, creating both promising and challenging habitats for diverse organisms. Crabs respond strongly to these variations by means such as altering their movements, thereby restructuring their spatial distribution and influencing coastal ecosystem resilience. However, the movements of crabs under varying environmental conditions require further elucidation. We conducted a systematic mesocosm experiment using the ubiquitous intertidal crab species Helice tientsinensis with four amount levels and six salinity levels of sprayed water applied through a custom apparatus, with a primary focus on crab movement. Crab movement from the experimental side of the apparatus (with altered conditions) to the control side (resembling field conditions of the intertidal wetlands of China's Yellow River Delta) and vice versa was recorded. The results revealed significant differences in moving out of the experimental side and moving in among the different water and salinity conditions, both separately for the two factors and simultaneously. Decreases in water content had a more pronounced effect on crab movement, leading to an increased number of crabs moving out of the experimental side of the apparatus. Conversely, as the experimental side became wetter, crabs tended to move towards it, and this movement was intensified by increases or decreases in water salinity. A structural equation model revealed that the moving-out and moving-in played fundamental roles in determining the number of resident crabs at the end of each experiment. While crabs preferred moist sediment with lower salinity, changes in salinity alone had minimal direct effect compared to sediment water contents. Our results clarify crab movements under varying water and salinity conditions, offering valuable insights to support adaptive interventions for crab populations and inform adaptive conservation and management strategies in intertidal wetlands. • Crab movement plays a vital role in their survival and distribution. • We tested the effects of changes in sediment water content and salinity on crab movements. • Changes in sediment water content affected crab movements more strongly than salinity. • The crab Helice tientsinensis preferred moist sediment with low salinity. [ABSTRACT FROM AUTHOR]

Abstract For migratory birds that specialize on particular benthic macroinvertebrate species, the timing of migration is critical since prey availability may be temporally limited and a function of local ambient temperature. Hence, variation in local ambient temperature can influence the diet composition of migrant birds, and, consequently, they may be constrained by which stopover and wintering sites they are able to utilize during periods of colder temperatures. Here, we use fecal analysis, observer‐based population counts, digital video recordings, and temperature data to test five predictions regarding the influence of local ambient temperature on the activity and availability of mudflat crabs—a key prey resource at three staging/wintering sites in eastern China, for migratory Red‐crowned cranes (Grus japonensis) and how this subsequently influences crane diet and use of wetland sites. Pearson's correlations and generalized linear models revealed that mudflat crabs became significantly more surface active with increasing burrow ambient temperature. Piecewise regression analysis revealed that crab surface activity was largely limited to a burrow ambient temperature threshold between 12 and 13℃ after which activity significantly increased. Crab activity declining temporally during the crane's autumn migration period but increased during spring migration. Crabs accounted for a significant proportion of crane diet at two of three sites; however, the frequency of crab remains was significantly different between sites, and between autumn and spring migration. Analyses of crane count data revealed a degree of congruence between the migration timing of Red‐crowned cranes with periods of warmer ambient temperature, and a significant, positive correlation between the percentage of crab remains in crane feces and site ambient temperature. Collectively, our data suggest that temperature‐related mudflat crab activity may provide an important time window for migratory Red‐crowned cranes to utilize critical stopover sites and the crabs’ food resources.

Increasing evidence shows that facilitative interactions between species play an essential role in coastal wetland ecosystems. However, there is a lack of understanding of how such interactions can be used for restoration purposes in saltmarsh ecosystems. We therefore studied the mechanisms of reciprocal facilitative interactions between native annual plants, Suaeda salsa, and burrowing crabs, Helice tientsinensis, in a middle‐elevation saltmarsh (with generally high plant density and moderate tides) in the Yellow River Delta of China.We investigated the relationship between the densities of the plants and crab burrows in different seasons. Then, we tested whether and how saltmarsh plants and crabs indeed facilitate each other in a series of field and laboratory experiments. Finally, we applied the results by creating a field‐scale artificial approach for microtopographic modification to restore a degraded saltmarsh.We found that the density of plant seedlings in spring was positively correlated with the density of crab burrows in the previous autumn; moreover, the density of crab burrows was correlated with the density of plants in summer. The concave–convex surface microtopography created by crabs promoted seed retention and seedling establishment of saltmarsh plants in winter and spring. These plants in turn facilitated crabs by inhibiting predators, providing food and reducing physical stresses for crabs in summer and autumn. The experimental removal of saltmarsh plants decreased crab burrow density, while both transplanting and simulating plants in bare patches promoted crabs. The microtopographic modification, inspired by our new understanding of the interactions between saltmarsh plants and crabs, showed that these degraded saltmarsh ecosystems can be restored by a single ploughing intervention.Synthesis. Our results suggest a reciprocal facilitation between annual plants and burrowing crabs in a middle‐elevation saltmarsh ecosystem. This knowledge yielded new restoration options for degraded coastal saltmarshes through the one‐time ploughing initiation of microtopographic variation, which could promote the re‐establishment of ecosystem engineers and lead to the efficient recovery of pioneer coastal vegetation and associated fauna. [ABSTRACT FROM AUTHOR]

For migratory birds that specialize on particular benthic macroinvertebrate species, the timing of migration is critical since prey availability may be temporally limited and a function of local ambient temperature. Hence, variation in local ambient temperature can influence the diet composition of migrant birds, and, consequently, they may be constrained by which stopover and wintering sites they are able to utilize during periods of colder temperatures. Here, we use fecal analysis, observer‐based population counts, digital video recordings, and temperature data to test five predictions regarding the influence of local ambient temperature on the activity and availability of mudflat crabs—a key prey resource at three staging/wintering sites in eastern China, for migratory Red‐crowned cranes (Grus japonensis) and how this subsequently influences crane diet and use of wetland sites. Pearson's correlations and generalized linear models revealed that mudflat crabs became significantly more surface active with increasing burrow ambient temperature. Piecewise regression analysis revealed that crab surface activity was largely limited to a burrow ambient temperature threshold between 12 and 13℃ after which activity significantly increased. Crab activity declining temporally during the crane's autumn migration period but increased during spring migration. Crabs accounted for a significant proportion of crane diet at two of three sites; however, the frequency of crab remains was significantly different between sites, and between autumn and spring migration. Analyses of crane count data revealed a degree of congruence between the migration timing of Red‐crowned cranes with periods of warmer ambient temperature, and a significant, positive correlation between the percentage of crab remains in crane feces and site ambient temperature. Collectively, our data suggest that temperature‐related mudflat crab activity may provide an important time window for migratory Red‐crowned cranes to utilize critical stopover sites and the crabs' food resources. [ABSTRACT FROM AUTHOR]

Crabs live at high densities in intertidal zones with various halophytes in salt marshes. However, the ecological relationships between crabs and halophytes as well as the impacts of herbivorous crabs on the plant distribution are not fully understood. In this study, we identified halophytic plant species consumed by crabs and determined the relative contributions of halophytes and other food sources to the diet. A DNA analysis of stomach contents was used to determine plant food sources for crabs. We found that the dominant crab species Helice tientsinensis consumed Suaeda japonica, even though several halophytes inhabited the study site. These results indicated that H. tientsinensis is a selective feeder. Based on a stable isotope analysis, we observed a dietary shift during crab development. Immature individuals mainly ate soil organic matter, whereas mature individuals showed more diverse food sources. We observed greater plant (S. japonica) consumption by middle-sized crabs than by crabs of other sizes. Our results for the feeding relationship between crabs and plants extend our understanding of the benthic food web in salt marshes. [ABSTRACT FROM AUTHOR]

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Background: The mudflat crab Helice tientsinensis is one of the most commercially valuable species for crabmeat production due to its delicious taste. These crabs are mainly found in coastal wetland where they are seriously threatened by toxic heavy metal pollution. In crustaceans, the hepatopancreas is an important organ for detoxification, and metal toxic substances can be converted to non-toxic or less toxic compounds in this organ. Objective: To develop a better understanding of the molecular response of H. tientsinensis to the toxic metal cadmium (Cd) and provide a molecular basis for the toxic metal tolerance of H. tientsinensis. Methods: In this study, we performed comparative hepatopancreas transcriptome analysis between H. tientsinensis unexposed (as control) and exposed to the toxic metal Cd for 48 h. Results: We identified 1089 Cd stress significantly-upregulated and 1560 Cd stress significantly-downregulated unigenes. Functional categorization and annotation of these differentially-expressed genes (DEGs) demonstrated that the response to Cd stress in the hepatopancreas of H. tientsinensis mainly involves "antioxidant activity", "detoxification", "toxin degradation activity" and "immune system process". In addition, five genes (ABCC1, NDUFAF5, ASTL, DES1, CYP27A) were identified as possible major targets for toxic metal tolerance. Conclusion: This is the first time reporting that the response of H. tientsinensis to Cd exposure at the transcriptome level, and it lays the foundation for understanding the molecular mechanisms of the response of H. tientsinensis to environmental toxic metal stress. [ABSTRACT FROM AUTHOR]

Highlights • Seeds of Suaeda japonica were mostly dispersed within 1 m from the parent plants. • Plant biomass was significantly higher at distances >1 m from parent plants. • Crabs preferred a habitat with high plant cover. • The combined effects of plants and crabs increased spatial variability in soil properties. Abstract Crabs and halophytes are important indicators of soil composition and fertility in salt marsh ecosystems. Many previous studies have examined the effects of crab excavation on soil properties, but little is known about the combined effects of crabs and halophytes on salt marsh soils. The purpose of this study was to identify the distribution of halophytes and crabs in a macrotidal salt marsh, and to determine effects of the combination of crabs and halophytes on the physicochemical properties of soils. Vegetation structure and soil properties in relation to seed dispersion distance and habitat type were analyzed using Kruskal-Wallis tests, Cluster Analysis (CA), and Principal Component Analysis (PCA). Plant biomass and height of individual marsh plants tended to be higher at distances >1 m from stands of parent plants. Crabs preferred habitats with high vegetation cover. Low densities of burrowing crabs and halophytes also caused considerable changes in soil properties. The combination of crabs and halophytes increased the spatial variability of physicochemical parameters in these salt marsh soils. Thus these combinations may be important to a complete understanding of plant distribution and soil nutrient cycling in salt marsh ecosystems. [ABSTRACT FROM AUTHOR]

Abstract The mudflat crab Helice tientsinensis is one of the most economically important aquaculture species in China. Nevertheless, it is susceptible to various diseases caused by viruses, bacteria and rickettsia-like organisms. A better understanding of the immune system and genes related to the responses to bacterial and viral infection is required. Herein, the hepatopancreas transcriptome of H. tientsinensis was analyzed by comparing control and lipopolysaccharide (LPS)-stimulated RNA-Seq data, yielding 91,885,038 bp and 13.78 Gb of clean reads. Following assembly and annotation, 93,207 unigenes with an average length of 883 bp were identified, of which 31,674 and 13,700 were annotated in Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. Following LPS, 4845 differentially expressed genes (DEGs) were identified, of which 2491 and 2354 were up- and down-regulated, respectively. To further investigate immune-related DEGs, KEGG enrichment analysis identified immune response pathways, most notably the peroxisome and Toll-like receptor signaling pathways. Quantitative real time-PCR (qRT-PCR) confirmed the up-regulation of a random selection of DEGs. This systematic transcriptomic analysis of the innate immune pathway in H. tientsinensis expands our understanding of the immune system in crabs. Highlights • The LPS-challenged Helice tientsinensis hepatopancreas transcriptomes was determined. • Of 93,207 unigenes identified, 4845 were differentially expressed after LPS challenge. • Among the identified DEGs, 2491 and 2354 were up- and down-regulated, respectively. • Peroxisome and Toll-like receptor signalling were enriched in GO and KEGG analyses. [ABSTRACT FROM AUTHOR]

Understanding the relationships between nesting habitat quality and predation risk is essential for developing appropriate conservation management for threatened species. This is particularly relevant where anthropogenic pressures could decouple the environmental cues used by birds to assess nesting habitat quality from increased predation risk. In this study, we conducted a series of surveys and nest experiments to examine the nest predation rates of Reed Parrotbill (Paradoxornis heudei) a passerine bird between inland and tidal reed‐bed wetland habitats, at Yellow River Delta National Nature Reserve, Eastern China during 2008, and 2010–2012. We found significant differences in the habitat structural characteristics between the two adjacent wetland habitats that are critical for Reed Parrotbill nest‐site selection. Experimental trials using recently constructed and abandoned Reed Parrotbill nests as ‘artificial nests, quail eggs and predator‐exclusion measures, revealed that tidal mudflat crab (Helice tientsinensis) was the primary cause of Reed Parrotbill egg predation in tidal reed‐bed habitat. Annual predation rates of real nests from inland reed‐bed habitat varied from 35% to 68%, and predation rates of artificial nests were much lower than those from real nests. Pitfall sampling revealed that the abundance of tidal mudflat crabs was significantly higher in tidal reed‐bed habitat. Our data suggested that Reed Parrotbills breeding in tidal reed‐bed habitats may be highly vulnerable due to extremely high rates of nest predation (up to 100%), caused primarily by the high density of tidal mudflat crabs. The incongruence between nest‐site habitat preference and nest survival indicated an ecological trap scenario, which requires further studies on its proximate and ultimate causes as well as the development of effective conservation management for the Reed Parrotbill.

The mitochondrial genome (mt genome) provides important information for understanding molecular evolution and phylogeny. The further understand the molecular evolution and phylogeny of Helice tientsinensis , the complete mt genome was determined. It is 16,212 bp long and includes 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes and a control region. The genome composition of H. tientsinensis was highly A + T biased 69.0% and showed negative AT skew (− 0.017) and GC skew (− 0.289). One PCG, all rRNAs and 12 of the tRNAs appeared to be rearranged with respect to the pancrustacean ground pattern gene order. Tandem duplication, followed by random deletion, is widely considered to explain translocation of mitochondrial genes. Consecutive recombinations events could explain inversions of genes. The phylogenetic analyses showed that H. tientsinensis has close relationships with Eriocheir japonica sinensis , E. j. hepuensis and E. j. japonica ; this indicated that H. tientsinensis belongs in the Grapsoidea, part of the Varunidae family. This study provides evidence for a better understanding of gene rearrangements, as well as the evolutionary status of H. tientsinensis and related species. [ABSTRACT FROM AUTHOR]

Bioturbation by the burrowing crab Helice tiensinensis was investigated to determine its impact on polycyclic aromatic hydrocarbon (PAH)-contaminated estuarine sediments. The concentrations of 16 U.S. Environmental Protection Agency (U.S. EPA) priority PAHs in sediment and pore water from a crab bed (including surface and burrow samples) and a control area, as well as in crabs, were measured. The total concentration of the 16 U.S. EPA priority PAHs in surface sediment of the crab bed (average 2,772 ng/g dry weight) was significantly higher than in the control area (1,173 ng/g dry weight). In the crab bed, the total concentration of PAHs in burrow sediment (1,239 ng/g dry weight) was lower than in surface sediment, and a similar trend was found for most of the individual PAHs, except for indeno[1,2,3-cd]pyrene, and benzo[ghi]perylene. The enhanced PAH desorption in the burrow, which could be attributed to the increase in dissolved organic matter in pore water as well as the mechanical mixing by the crab, is expected to increase PAH flux to the sea. In addition to increased flushing to the sea, incorporation of PAHs in crab biomass and metabolism of PAHs by the crab, stimulated microbial degradation, was proposed as an ignorable factor that lowered the PAH concentration in burrow sediment, because crab bioturbation increases the abundance and activity of microorganisms through several means. Log KOW and log KOC correlated well for individual PAHs in sediment in the control area, although this correlation was poor for sediments in the crab bed. The log biota-sediment accumulation factor (BSAF) of PAHs exhibited a negative relationship with log KOW, suggesting that the bioaccumulation of sorbed PAHs was controlled primarily by their bioavailability. Environ. Toxicol. Chem. 2010;29:1248–1255. © 2010 SETAC [ABSTRACT FROM AUTHOR]

Investigating the composition of food sources with stable isotope method can provide direct evidence for the top-down control in the coastal wetland. In this study, we examined food source and feeding habit of Helice tientsinensis of common reed (Phragmites australis) vegetation in high marsh of Yellow River Delta. The results showed that the density of crab was (5.5±1.5) ind·m -2 , with the behavior of climbing P. australis to feed on the leaves at night. Under the same indoor experimental condition, H. tientsinensis showed feeding preference on fresh leaves of P. aus-tralis. The stable isotope food source analysis showed that the leaves of P. australis were one of the important food sources of H. tientsinensis in the field. There were temporal variations in the proportion of fresh leaves [May: (6.4±4.9)%, July: (5.8±4.9)%, September: (12.5±8.8)%] and dead leaves [May: (12.4±7.8)%, July: (15.5±9.9)%, September: (15.1±9.4)%]. Therefore, H. tientsinensis could inhibit P. australis's growth and affect litter decomposition through feeding disturbance behavior.