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The underlying mechanism for sustaining the high productivity of coral reefs in nutrient deplete water, known as the Darwin Paradox, has long been debated. The input of new nitrogen, for example, derived from N2 fixation, and efficient nitrogen recycling are hypothesized as two critical factors in resolving the paradox. However, the source of new nitrogen and its connection to nitrogen recycling in the coral reef system remain poorly understood. We measured N2 fixation rates and investigated the diazotroph community in different components of a tropical coral reef system. Our results show that the reef‐building crustose coralline algae demonstrate a significantly higher N2 fixation rate than the overlying water or the coral holobiont, representing a large source of N2 fixation to the system. The associated diazotroph community was dominated by the non‐cyanobacterial Rhizobiales. 15N2‐based pulse‐chase incubation experiments revealed ~ 50% of the diazotroph‐derived nitrogen was released from the crustose coralline algae holobiont to the overlying water and coral holobiont within 48 h, which was five fold higher than the fraction of nitrogen released from nitrate‐based assimilation by crustose coralline algae. Furthermore, the released diazotroph‐derived nitrogen was rapidly transferred to the coral holobiont through grazing and was subsequently released back to the overlying water as dissolved organic nitrogen, revealing an efficient pathway that connects the new nitrogen input with the nitrogen recycling in the coral reef ecosystem. Our results provide new insights into the sources and fates of new nitrogen in the coral reefs, helping to resolve the Darwin Paradox in this unique ecosystem. [ABSTRACT FROM AUTHOR]

Computer vision plays an important role in scientific research, resource exploration, and other underwater applications. However, it suffers from the severe color distortion, which is caused by the scattering and absorption of light in the water. In this article, an underwater image color restoration network (UICRN) is proposed to obtain the real color of the image by estimating the main parameters of the underwater imaging model. First, an encoder neural network is applied to extract features from the input underwater image. Second, three independent decoders are used to estimate the direct light transmission map, backscattered light transmission map, and veiling light. Third, the loss functions and the training strategy are designed to improve the performance of restoration. As we know, the learning-based method would require a paired data set for training. An underwater image generation method is also proposed in this article to obtain the data set consisting of color-distorted images and corresponding ground truth. The method combines the inherent optical properties and apparent optical properties with structure information to generate the paired data set. More than 20 000 pairs of underwater images are generated based on the method. Finally, the UICRN method is quantitatively evaluated through various experiments, such as color chart testing in the South China Sea and natural underwater image evaluation. It demonstrates that the UICRN method is competitive with previous state-of-the-art methods in color restoration and robustness. [ABSTRACT FROM AUTHOR]

The diploid Poropuntius huangchuchieni in the cyprinid family, which is widely distributed in the Mekong and Red River basins, is one of the most closely related diploid progenitor‐like species of allotetraploid common carp, which was generated by merging of two diploid genomes during evolution. Therefore, the P. huangchuchieni genome is essential for polyploid evolution studies in Cyprinidae. Here, we report a high‐quality chromosome‐level genome assembly of P. huangchuchieni by integrating Oxford Nanopore and Hi‐C technologies. The assembled genome size was 1,021.38 Mb, 895.66 Mb of which was anchored onto 25 chromosomes with a N50 of 32.93 Mb. The genome contained 486.28 Mb repetitive elements and 24,099 protein‐coding genes. Approximately 95.9% of the complete BUSCOs were detected, suggesting a high completeness of the genome. Evolutionary analysis revealed that P. huangchuchieni diverged from Cyprinus carpio at approximately 12 Mya. Genome comparison between P. huangchuchieni and the B subgenome of C. carpio provided insights into chromosomal rearrangements during the allotetraploid speciation. With the complete gene set, 17,474 orthologous genes were identified between P. huangchuchieni and C. carpio, providing a broad view of the gene component in the allotetraploid genome, which is critical for future genetic analyses. The high‐quality genomic data set created for P. huangchuchieni provides a diploid progenitor‐like reference for the evolution and adaptation of allotetraploid carps. [ABSTRACT FROM AUTHOR]

Diver breathing sounds can be used as a characteristic for the passive detection of divers. This work introduces an approach for detecting the presence of a diver based on diver breathing sounds signals. An underwater channel model for passive diver detection is built to evaluate the impacts of acoustic energy transmission loss and ambient noise interference. The noise components of the observed signals are suppressed by spectral subtraction based on block-based threshold theory and smooth minimal statistic noise tracking theory. Then the envelope spectrum features of the denoised signal are extracted for diver detection. The performance of the proposed detection method is demonstrated through experimental analysis and numerical modeling. [ABSTRACT FROM AUTHOR]

The complete mitogenome of the brown-spotted grouperEpinephelus chlorostigmawas determined in this study. It is 16,894 bp in length, containing 37 genes with the typical order and transcriptional direction in the vertebrates. The overall nucleotide composition is: 28.7% A; 28.0% C; 16.3% G and 27.0% T. The lengths of 22 transfer RNA (tRNA) genes range from 67 (tRNA-Cys) to 76 (tRNA-Leu1) bp. Two start codons (GTG and ATG) and two stop codons (TAG and TAA/T) were found in the protein-coding genes. The nodes of phylogenetic tree were strongly supported based on the complete mitogenomes of available groupers. The phylogenetic results suggestedE. chlorostigmais the closest toE. areolatuswithin the genusEpinephelus. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome ofCarcharhinus maclotiwas determined in this study. It is 16,701 bp in length and contains 37 genes with the typical gene order and transcriptional orientation in vertebrates. A total of 29 bp overlaps and 29 bp short intergenic spaces located in 22 gene junctions. The overall base composition is 31.6% A, 26.2% C, 13.0% G and 29.2% T. Two start codons (ATG and GTG) and three stop codons (AGG, TAG and TAA/T) were found in 13 protein-coding genes. The length of 22 tRNA genes ranged from 66 bp (tRNA-Ser2) to 75 bp (tRNA-Leu1). The tRNA-Ser2(GCU) lacks the dihydrouridine arm by a simple loop and can not be folded into the typical cloverleaf structure. The control region is 1066 bp in length with high A+T content (68.2%). [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome (16,497 bp) of the humpback grouper Cromileptes altivelis is first presented in this study. The gene arrangement and translate orientation of C. altivelis is identical to most vertebrates, including 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes and a putative control region. The overall nucleotide composition of the H-strand is 29.80% A, 26.23% T, 15.67% G and 29.02% C. The origin of the light-strand replication was identified between the tRNA- Asn and tRNA- Cys genes, while the termination associated sequence (TAS) and conserved sequence blocks (CSB1-3) were identified in the control region. [ABSTRACT FROM AUTHOR]