Sea cucumber, Apostichopus japonicus (Selenka), is a commercially important marine species in China. Among the differently colored varieties sold in China, white and purple sea cucumbers have the greatest appeal to consumers. Identification of the pigments that may contribute to the formation of different color morphs of sea cucumbers will provide a scientific basis for improving the cultivability of desirable color morphs. In this study, sea cucumbers were divided into four categories according to their body color: white, light green, dark green, and purple. The pigment composition and contents in the four groups were analyzed by high performance liquid chromatography (HPLC). The results show that the pigment contents differed significantly among the white, light-green, dark-green, and purple sea cucumbers, and there were fewer types of pigments in white sea cucumber than in the other color morphs. The only pigments detected in white sea cucumbers were guanine and pteroic acid. Guanine and pteroic acid are structural colors, and they were also detected in light-green, dark-green, and purple sea cucumbers. Every pigment detected, except for pteroic acid, was present at a higher concentration in purple morphs than in the other color morphs. The biological color pigments melanin, astaxanthin, β-carotene, and lutein were detected in light-green, dark-green, and purple sea cucumbers. While progesterone and lycopene, which are also biological color pigments, were not detected in any of the color morphs. Melanin was the major pigment contributing to body color, and its concentration increased with deepening color of the sea cucumber body. Transmission electron microscopy analyses revealed that white sea cucumbers had the fewest epidermal melanocytes in the body wall, and their melanocytes contained fewer melanosomes as well as non-pigmented pre-melanosomes. Sea cucumbers with deeper body colors contained more melanin granules. In the body wall of dark-green and purple sea cucumbers, melanin granules were secreted out of the cell. The results of this study provide evidence for the main factors responsible for differences in coloration among white, light-green, dark-green, and purple sea cucumbers, and also provide the foundation for further research on the formation of body color in sea cucumber, A. japonicus.

Marginal seas play important roles in regulating the global carbon budget, but there are great uncertainties in estimating carbon sources and sinks in the continental margins. A Pacific basin-wide physical-biogeochemical model is used to estimate primary productivity and air-sea CO₂ flux in the South China Sea (SCS), the East China Sea (ECS), and the Yellow Sea (YS). The model is forced with daily air-sea fluxes which are derived from the NCEP2 reanalysis from 1982 to 2005. During the period of time, the modeled monthly-mean air-sea CO₂ fluxes in these three marginal seas altered from an atmospheric carbon sink in winter to a source in summer. On annual-mean basis, the SCS acts as a source of carbon to the atmosphere (16 Tg/a, calculated by carbon, released to the atmosphere), and the ECS and the YS are sinks for atmospheric carbon (–6.73 Tg/a and –5.23 Tg/a, respectively, absorbed by the ocean). The model results suggest that the sea surface temperature (SST) controls the spatial and temporal variations of the oceanic pCO₂ in the SCS and ECS, and biological removal of carbon plays a compensating role in modulating the variability of the oceanic pCO₂ and determining its strength in each sea, especially in the ECS and the SCS. However, the biological activity is the dominating factor for controlling the oceanic pCO₂ in the YS. The modeled depth-integrated primary production (IPP) over the euphotic zone shows seasonal variation features with annual-mean values of 293, 297, and 315 mg/(m²·d) in the SCS, the ECS, and the YS, respectively. The model-integrated annual-mean new production (uptake of nitrate) values, as in carbon units, are 103, 109, and 139 mg/(m²·d), which yield the f-ratios of 0.35, 0.37, and 0.45 for the SCS, the ECS, and the YS, respectively. Compared to the productivity in the ECS and the YS, the seasonal variation of biological productivity in the SCS is rather weak. The atmospheric pCO₂ increases from 1982 to 2005, which is consistent with the anthropogenic CO₂ input to the atmosphere. The oceanic pCO₂ increases in responses to the atmospheric pCO₂ that drives air-sea CO₂ flux in the model. The modeled increase rate of oceanic pCO₂ is 0.91 μatm/a in the YS, 1.04 μatm/a in the ECS, and 1.66 μatm/a in the SCS, respectively.

The present investigation focuses on population structure analysis of the purple sea urchin Paracentrotus lividus across the African Mediterranean coast, with the main aim of assessing the influence of the Siculo-Tunisian Strait on gene flow disruption in this highly dispersive echinoid species. For this purpose, patterns of morphological and genetic variation were assessed among its populations from the western and eastern Mediterranean coasts. A total of 302 specimens from seven Tunisian sites were collected and examined for morphometric variability at twelve morphometric traits. Concordant results, inferred from CDA (canonical discriminant analyses), pairwise NPMANOVA (non parametric multivariate analysis of variance) comparisons and MDS (multidimensional scaling) plot, unveiled significant inter-population differences in the measured traits among the studied populations. Furthermore, the combined use of the one way ANOSIM (analysis of similarities) and the Discriminant/Hotelling analysis allowed unravelling two morphologically differentiated groups assigned to both western and eastern Mediterranean basins. The SIMPER (similarity percentages) routine analysis showed that total dry weight, test diameter and spine length were major contributors to the morphometric separation between locations and between groups. Pattern of phenotypic divergence discerned in P. lividus across the Siculo-Tunisian Strait is interestingly in congruence with that inferred from the genetic investigation of the purple sea urchin populations from the same region based on the analysis of the mtDNA COI (cytochrome oxidase I) gene in 314 specimens from nineteen locations covering a wider geographic transect, streching westward to the Algerian coast and eastward to the Libyan littoral. The specific haplotypic composition characterizing each Mediterranean basin, as inferred from the minimum spanning network, confirmed the geographic partioning of genetic variation, as revealed by F-statistics and AMOVA (analysis of molecular variance) analyses, yielding significant genetic differentiation between eastern and western Mediterranean populations. The newly detected phylogeographic patterns, observed for the first time in P. lividus throughout the explored distribution range, suggest the involvement of different biotic and abiotic processes in shaping such variation, and provide evidence that a large and geographically exhaustive dataset is necessary to unveil phylogeographic structure within widespread marine species, previously cathegorized as panmictic in part of their distribution range.

Maintaining stable water quality is one of the key processes for recirculating coral aquaculture. Traditional aquarium systems which mainly utilized a nitrification of nitrifying bacteria attached to the surface of massive artificial filter material are difficult to maintain the oligotrophic conditions necessary for coral aquaculture. This study investigated the removal effects of dissolved inorganic nitrogen (ammonia and nitrate) by live rock (LR), a key component in the "Berlin system" coral aquarium. The expression levels of bacterial functional genes, AOA3, amoA and nosZ, were measured on the exterior and interior of LR. The nitrifying and denitrifying bacterial abundance on LR was quantified and the nitrogen nutrient regulatory effects of LR were evaluated. The results demonstrated that LR mainly removed ammonium (NH₄⁺) from the water with a mean efficiency of 0.141 mg/(kg·h), while the removal of nitrate (NO₃^–) was not significant. Bacterial diversity analysis showed that ammonia-oxidizing bacteria (AOB) were the most common bacteria on LR, which accounted for 0.5%–1.4% of the total bacterial population, followed by denitrifying bacteria, which accounted for 0.2% of the total population, and the ammonia-oxidizing archaea (AOA) were the least common type (<0.01%). The low abundance of denitrifying bacteria may be responsible for the poor nitrate (NO₃^–) removal of LR. Thus, other biological filtration methods are needed in coral aquaria to control nitrates generated from nitrification or biological metabolism.

With the development of aquaculture, there is an urgent demand for an alternative antibacterial agent to reduce the drug resistance and environmental pollution caused by the abuse of antibiotics. Recently, silver nanoparticles (AgNPs) have been viewed as a novel type of antimicrobial agents due to their unique advantages. In this study, AgNPs were biosynthesized with the ginger rhizomes extract. The biosynthesized AgNPs were characterised by UV–visible spectroscopy, transmission electron microscopy, X-ray diffraction and fourier transform infrared spectroscopy. Furthermore, the antimicrobial activities of the AgNPs were fully analyzed against six typical aquatic pathogens. The results indicated that the components in ginger extract could function as the chemical reductant to synthesize AgNPs. Moreover, compared with the AgNPs synthesized by chemical methods, the biosynthesized AgNPs were smaller, and had higher stability and antibacterial activity. Therefore, the biosynthesized AgNPs using ginger extract may have prospective applications in aquaculture.

An efficient and accurate prediction of a precise tidal level in estuaries and coastal areas is indispensable for the management and decision-making of human activity in the field wok of marine engineering. The variation of the tidal level is a time-varying process. The time-varying factors including interference from the external environment that cause the change of tides are fairly complicated. Furthermore, tidal variations are affected not only by periodic movement of celestial bodies but also by time-varying interference from the external environment. Consequently, for the efficient and precise tidal level prediction, a neuro-fuzzy hybrid technology based on the combination of harmonic analysis and adaptive network-based fuzzy inference system (ANFIS) model is utilized to construct a precise tidal level prediction system, which takes both advantages of the harmonic analysis method and the ANFIS network. The proposed prediction model is composed of two modules: the astronomical tide module caused by celestial bodies’ movement and the non-astronomical tide module caused by various meteorological and other environmental factors. To generate a fuzzy inference system (FIS) structure, three approaches which include grid partition (GP), fuzzy c-means (FCM) and sub-clustering (SC) are used in the ANFIS network constructing process. Furthermore, to obtain the optimal ANFIS based prediction model, large numbers of simulation experiments are implemented for each FIS generating approach. In this tidal prediction study, the optimal ANFIS model is used to predict the non-astronomical tide module, while the conventional harmonic analysis model is used to predict the astronomical tide module. The final prediction result is performed by combining the estimation outputs of the harmonious analysis model and the optimal ANFIS model. To demonstrate the applicability and capability of the proposed novel prediction model, measured tidal level samples of Fort Pulaski tidal station are selected as the testing database. Simulation and experimental results confirm that the proposed prediction approach can achieve precise predictions for the tidal level with high accuracy, satisfactory convergence and stability.

The South China Sea (SCS) and the Arabian Sea (AS) are both located roughly in the north tropical zone with a range of similar latitude (0°–24°N). Monsoon winds play similar roles in the upper oceanic circulations of the both seas. But the distinct patterns of chlorophyll a (Chl a) concentration are observed between the SCS and the AS. The Chl a concentration in the SCS is generally lower than that in the AS in summer (June–August); the summer Chl a concentration in the AS shows stronger interannual variation, compared with that in the SCS; Moderate resolution imaging spectroradiometer (MODIS)-derived data present higher atmospheric aerosol deposition and stronger wind speed in the AS. And it has also been found that good correlations exist between the index of the dust precipitation indicated by aerosol optical thickness (AOT) and the Chl a concentration, or between wind and Chl a concentration. These imply that the wind and the dust precipitation bring more nutrients into the AS from the sky, the sub-layer or coast regions, inducing higher Chl a concentration. The results indicate that the wind velocity and the dust precipitation can play important roles in the Chl a concentration for the AS and the SCS in summer. However aerosol impact is weak on the biological productivity in the west SCS and wind-induced upwelling is the main source.

The seasonal variability of the significant wave height (SWH) in the South China Sea (SCS) is investigated using the most up-to-date gridded daily altimeter data for the period of September 2009 to August 2015. The results indicate that the SWH shows a uniform seasonal variation in the whole SCS, with its maxima occurring in December/January and minima in May. Throughout the year, the SWH in the SCS is the largest around Luzon Strait (LS) and then gradually decreases southward across the basin. The surface wind speed has a similar seasonal variation, but with different spatial distributions in most months of the year. Further analysis indicates that the observed SWH variations are dominated by swell. The wind sea height, however, is much smaller. It is the the largest in two regions southwest of Taiwan Island and southeast of Vietnam Coast during the northeasterly monsoon, while the largest in the central/southern SCS during the southwesterly monsoon. The extreme wave condition also experiences a significant seasonal variation. In most regions of the northern and central SCS, the maxima of the 99th percentile SWH that are larger than the SWH theoretically calculated with the wind speed for the fully developed seas mainly appear in August–November, closely related to strong tropical cyclone activities. Compared with previous studies, it is also implied that the wave climate in the Pacific Ocean plays an important role in the wave climate variations in the SCS.