Fixed-station sampling design was widely used in fishery-independent surveys because of its characteristics of convenient sampling station setting, but the non-probabilistic (fixed) nature made it more uncertainty of drawing inferences on population. The performance of fixed-station sampling design for multispecies survey has not been evaluated, and we are uncertain if the design could detect the temporal trends of different populations in multispecies fishery-independent survey. In this study, spatial distribution of abundance indices for three species with different spatial distribution patterns including small yellow croaker (Larimichthys polyactis), whitespotted conger (Conger myriaster) and Fang’s blenny (Enedrias fangi) were simulated using ordinary kriging interpolation as the “true” population distribution. The performance of fixed-station sampling design was compared with simple random sampling design by resampling the simulated “true” populations in this simulation study. The results showed that the fixed-station sampling design had the power to detect the seasonal trends of species abundance. The effectiveness of fixed-station sampling design were different in different species distribution patterns. When the species had even distribution, fixed-station sampling design could get high quality abundance data; when the distribution was uneven with heterogeneity or patchiness, fixed-station sampling design tended to underestimate or overestimate the abundance. Evidently, the estimates of abundance index based on the fixed-station sampling design must be calibrated cautiously while applying them for fisheries stock assessment and management. This study suggested that fixed-station sampling design could catch the temporal dynamics of population abundance, but the abundance estimates from the fixed-station sampling design could not be treated as the absolute estimates of populations.

The diversity, community composition and 16S rRNA gene abundance of bacterioplankton along a transect across an upwelling area off the eastern coast of Hainan Island (the Qiongdong upwelling) were investigated in August of 2016 using high throughput sequencing and quantitative PCR assay of 16S rRNA genes. Compared with the offshore stations, the inner-shelf stations had higher bacterial gene abundance (up to 3 fold) and operational taxonomic unit richness, a result of the influence of upwelled and fresher waters. Overall, a majority of the reads were affiliated with Gammaproteobacteria (11%–74%) and Alphaproteobacteria (14%–43%). The structure of the bacterial community was significantly affected by salinity, dissolved oxygen, ${\rm{NO}}_3^-$ and ${\rm{NH}}_4^+ $, which also defined the physicochemical features of the upwelled waters. Horizontally, the relative abundances and gene abundances of Rhodobacteraceae, SAR86, Cyanobacteria and Bacteroidetes in eutrophic zone decreased from the inner to outer shelves and slope, whereas Alteromonas, Vibrio and Oceanospirillaceae exhibited an opposite trend. This study stresses the riverine influence on the oceanographic condition and spatial variability of bacterioplankton diversity and distribution in the Qiongdong upwelling.

Marine microorganisms were considered to be important sources of marine bioactive compounds. The major objective of the study was to isolate and characterize bacteria with antimicrobial activities from the various marine environment of Egypt. In this respect, thirty-five bacterial isolates were recovered from sediment samples collected from different spots along the Egyptian Red Sea coastline and Alexandria coastline during the summer season of 2017 and 2018. According to the morphological, physiological, and biochemical characteristics, the bacterial isolates were clustered into 13 groups designated as A, B, ···, M. And, 14 Gram-negative and 21 Gram-positive bacteria were determined. The isolated bacterial strains were screened for their potentiality for antimicrobial agent(s) production against ten indicator strains. Strain Mo13 was showed high antimicrobial activity against all empirical strains. Subsequently, the most promising marine bacterial isolate with code MO13 was identified as Bacillus zhangzhouensis OMER4 according to the phenotypic characterization through morphological, physiological, and biochemical tests as well as genotypic characterization through the 16S rDNA technique. The bioactive components were extracted with ethyl acetate, then analyzed using GC-MS and the substantial component was recognized as phenol, 2, 4-bis(1, 1-dimethyl ethyl).

In contrast to typical planktonic hydromedusae, Cladonema medusae are mostly benthic, with specialised adhesive branches to adhere to the substrate. In this study, a Cladonema species discovered in a laboratory aquarium in Fuzhou, China, was confirmed as a new species, based on morphological and molecular analyses. The species was named Cladonema multiramosum sp. nov. Its medusa is distinct from that of congeners possessing substantially more adhesive branches (8–24, rarely 5–7), and tiny branches on the upper radial canals. The validity of C. multiramosumum sp. nov. was also supported by molecular phylogenetic analyses based on the mitochondrial 16S rDNA sequence. However, C. multiramosum sp. nov. medusa also displayed considerable phenotypic plasticity with respect to its radial canals, tentacles, stinging branches per tentacle, oral tentacles, manubrium, and gonads, hindering species identification based solely on morphology. Although some morphological characteristics of hydroids (filiform tentacles and medusa buds) and nematocysts could also be used as diagnostic characters in the genus Cladonema, this information is unavailable for some Cladonema species. Thus, the taxonomy within the genus Cladonema was re-evaluated based mainly on the morphological characteristics of the medusa. Further revision of the genus Cladonema should be made when supplementary information on the life cycle and DNA barcoding are updated.

The majority of fishery stocks in the world are data limited, which limits formal stock assessments. Identifying the impacts of input data on stock assessment is critical for improving stock assessment and developing precautionary management strategies. We compare catch advice obtained from applications of various data-limited methods (DLMs) with forecasted catch advice from existing data-rich stock assessment models for the Indian Ocean bigeye tuna (Thunnus obesus). Our goal was to evaluate the consistency of catch advice derived from data-rich methods and data-limited approaches when only a subset of data is available. The Stock Synthesis (SS) results were treated as benchmarks for comparison because they reflect the most comprehensive and best possible scientific information of the stock. This study indicated that although the DLMs examined appeared robust for the Indian Ocean bigeye tuna, the implied catch advice differed between data-limited approaches and the current assessment, due to different data inputs and model assumptions. Most DLMs tended to provide more optimistic catch advice compared with the SS, which was mostly influenced by historical catches, current abundance and depletion estimates, and natural mortality, but was less sensitive to life-history parameters (particularly those related to growth). This study highlights the utility of DLMs and their implications on catch advice for the management of tuna stocks.

A new spectrophotometric method based on a liquid waveguide capillary cell for an enhanced detection was developed to measure nanomolar iodate concentrations. This method has a detection limit and precision of 1–2 nmol/L, which is equivalent to 10% that of conventional methods, a recovery of 97.7%–104.0%, and a working range of 10–120 nmol/L. Water samples were collected from three estuaries and one coastal ocean for testing, and the proposed technique detected as low as 11 nmol/L and 18 nmol/L iodate in these samples. This newly developed method is helpful in understanding the biogeochemical cycle of iodine in nature.

With the development and deployment of observation systems in the ocean, more precise passive and active microwave data are becoming available for the weather forecasting and the climate monitoring. Due to the complicated variability of the sea ice concentration (SIC) in the marginal ice zone and the scarcity of high-precision sea ice data, how to use less data to accurately reconstruct the sea ice field has become an urgent problem to be solved. A reconstruction method for gridding observations using the variational optimization technique, called the multi-scale high-order recursive filter (MHRF), which is a combination of Van Vliet fourth-order recursive filter and the three-dimensional variational (3D-VAR) analysis, has been designed in this study to reproduce the refined structure of sea ice field. Compared with the existing spatial multi-scale first-order recursive filter (SMRF) in which left and right filter iterative processes are executed many times, the MHRF scheme only executes the same filter process once to reduce the analysis errors caused by multiple filters and improve the filter precision. Furthermore, the series connected transfer function in the high-order recursive filter is equivalently replaced by the paralleled one, which can carry out the independent filter process in every direction in order to improve the filter efficiency. Experimental results demonstrate that this method possesses a good potential in extracting the observation information to successfully reconstruct the SIC field in computational efficiency.

A large sand bar develops in the inner Qiantang River Estuary, China. It is a unique sedimentary system, elongating landwards by about 130 km. Based on long-term series of bathymetric data in each April, July, and November since the 1960s, this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project (LRNP) implemented in the last decades. The results show that three timescales, namely the seasonal, interannual and decadal timescales, can be distinguished for the sand bar evolution. The first two are related to the seasonal and interannual variations of river discharge. During high discharge seasons or years, erosion took place at the upper reach and sedimentation at the lower reach. Consequently, the bar apex shifted seaward. The opposite development took place during low discharge seasons or years. The decadal timescale is related to LRNP. Due to the implementation of LRNP, the upper reach has experienced apparent erosion and currently a new equilibrium state has been reached; whereas the lower reach has been accumulated seriously and the accumulation still continues. Nonlinear relationships for how the bar apex location and elevation depend on the river discharge over various stages of LRNP have been established. Compared with the earlier stage of LRNP, the bar apex at present has shifted seaward by about 12 km and lowered by about 1 m. The sand bar movement has significant feedback on the hydrographic conditions along the estuary and has practical implications for coastal management.

Empirical orthogonal function (EOF) analysis was applied to a 50-year long time series of monthly mean positions of the Kuroshio path south of Japan from a regional reanalysis. Three leading EOF modes characterize the contributions from three typical paths of the Kuroshio meander: the typical large meander path, the offshore non-large meander path, and the nearshore non-large meander path, respectively. Accordingly, the spatial variation characteristics of oceanic anomaly fields can be depicted by their regression fields upon the associated three leading principal components (PCs), which are well-matched with the results of composite analysis corresponding to each period of the three typical Kuroshio paths. A new index for the typical large meander is defined by using the second leading PC, which is highly correlated with the Kushimoto-Uragami index. Spectral analysis of this new index series shows variability of the Kuroshio path south of Japan at time scales of about 7–8 years and 20 years.