Horseshoe crabs including Tachypleus tridentatus are a group of marine arthropods and living fossil species which have existed on the earth for ~500 million years. However, the genetic mechanisms underlying their unique adaptive ability are still unclear. Here, we assembled the first chromosome‐level T. tridentatus genome, and proved that this genome is of high quality with contig N50 1.69 Mb. By comparison with other arthropods, some gene families of T. tridentatus experienced significant expansion, which are related to several signaling pathways, endonuclease activities, and metabolic processes. Based on the results of comparative analysis of genomics and 27 transcriptomes from nine tissues, we found that the expanded Dscam genes are located at key hub positions of immune network. Furthermore, the Dscam genes showed higher levels of expression in the yellow connective tissue (the birthplace of blood cells with strong differentiation capability) than the other eight tissues. Besides, the Dscam genes are positively correlated with the expression of the core immunity gene, clotting factor B, which is involved in the coagulation cascade reaction. The effective and unusual immune ability endowed by the expansion and expression of Dscam genes in the horseshoe crab may be a factor that makes the species have a strong environmental adaptability within ~500 million years. The high quality chromosome level genome of a horseshoe crab and unique genomic features reported in this study provide important data resources for future studies on the evolution of marine ecological systems.

Trachidermus fasciatus is a small catadromous fish and has been listed as a second class state protected aquatic animal since 1988 in China due to the declines in its abundance. We describe the complete mitogenome of T. fasciatus in this study. The mitogenome is 16,536 nucleotides long and contains 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA genes, and two main noncoding regions. The overall base composition includes C (30%), A (26.3%), T (25.5%), and G (18.2%). Moreover, the 13 PCGs encode 3800 amino acids in total, all the PCGs use the initiation codon ATG except COI uses GTG. Most of them have TAA or TAG as the stop codon, except COII, ND4 and Cytb use an incomplete stop codon T. The phylogenetic tree based on the neighbour joining method was constructed to provide relationship within Cottidae, which could be a useful basis for management of this species.

Eelgrass beds in coastal waters of China have declined substantially over the past 30 years. In this study, a simple new transplanting technique was developed for eelgrass (Zostera marina L.) restoration. To assist in anchoring single shoots, several rhizomes of rooted shoots were bound to a small elongate stone (50–150 g) with biodegradable thread (cotton or hemp), and then the bound packet was buried at an angle in the sediments at a depth of 2–4 cm. This stone anchoring method was used to transplant eelgrass in early November 2009 and late May 2010 in Huiquan Bay, Qingdao. The method led to high success. Three month survivorship of the transplanted shoots at the two transplant sites was >95%. From April 20 to November 19, 2012, the following characteristics of the 2009 and 2010 transplanted eelgrass beds were monitored: morphological changes, shoot density, shoot height, leaf biomass, and sediment particle size. Results showed that the sexual reproduction period of the planted eelgrass was from April to August, and vegetative reproduction reached its peak in autumn. Maximum shoot height and biomass were observed in June and July. After becoming established, the transplanted eelgrass beds were statistically equal to natural eelgrass beds nearby in terms of shoot height, biomass, and seasonal variations. This indicates that the transplant technique is effective for eelgrass restoration in coastal waters.

Recent advances in high-throughput sequencing technologies have offered the possibility to generate genomewide sequence data to delineate previously unidentified genetic structure, obtain more accurate estimates of demographic parameters and to evaluate potential adaptive divergence. Here, we identified 27 556 single nucleotide polymorphisms for the small yellow croaker (Larimichthys polyactis) using restriction-site-associated DNA (RAD) sequencing of 24 individuals from two populations. Significant sources of genetic variation were identified, with an average nucleotide diversity (π) of 0.00105 ± 0.000425 across individuals, and long-term effective population size was thus estimated to range between 26 172 and 261 716. According to the results, no differentiation between the two populations was detected based on the SNP data set of top quality score per contig or neutral loci. However, the two analysed populations were highly differentiated based on SNP data set of both top FST value per contig and the outlier SNPs. Moreover, local adaptation was highlighted by an FST -based outlier tests implemented in LOSITAN and a total of 538 potentially locally selected SNPs were identified. blast2go annotation of contigs containing the outlier SNPs yielded hits for 37 (66%) of 56 significant blastx matches. Candidate genes for local adaptation constituted a wide array of biological functions, including cellular response to oxidative stress, actin filament binding, ion transmembrane transport and synapse assembly. The generated SNP resources in this study provided a valuable tool for future population genetics and genomics studies of L. polyactis.