The influence of environmental variability of a coastal lagoon ecosystem on genetic diversity and structure of white seabream [Diplodus sargus (Linnaeus 1758)] populations

As coastal lagoons serve as nursery areas for some marine and estuarine fish, selective pressures of these brackish or hypersaline lagoons may influence the genetic structure of species and populations. We examined spatial and temporal genetic patterns at eight microsatellite loci in white seabream [Diplodus sargus (Linnaeus 1758)] recruits from the Mar Menor (Southeast Spain) and compared these loci with those in coastal populations from the open sea, observing a high degree of genetic diversity and spatio‐temporal genetic stability. However, the results suggest the presence of subpopulations or genetic substructures in the Mar Menor D. sargus population that could be interpreted as a homogeneous mixture of individuals from three differentiated subpopulations in the Mediterranean and evidence of the Wahlund effect. It also suggests that D. sargus adults return to their original spawning habitat, thus conserving the genetic differences among the respective populations over time. Overall, this study demonstrates the importance of the Mar Menor coastal lagoon as a nursery area for the conservation of genetic diversity of D. sargus populations.     

Temporal and spatial variability in shallow- and deep-water populations of the invasive Caulerpa racemosa var. cylindracea in the Western Mediterranean

The invasive green alga Caulerpa racemosa var. cylindracea represents an important threat to the diversity of Mediterranean benthic coastal ecosystems by interfering with native species and modifying benthic assemblages. The present study deals, for the first time, with the temporal and spatial variability of the biomass and phenology of C. racemosa considering both deep- and shallow-water populations. Two sampling depths (30 and 10 m) were sampled at three different rocky bottom sites every 3 months in the Archipelago of Cabrera National Park (Western Mediterranean). All morphometric variables analysed showed a spatial variation and temporal patterns depending on depth. Between depths, C. racemosa biomass, stolon length, number of fronds and frond length were usually significantly higher at deep-water populations, suggesting that C. racemosa grows better in deep-waters. Deep- and shallow-water populations displayed a high temporal variation although no evidence of seasonal patterns was found, in contrast with what has been reported by other authors. The sources of this variability are still unknown but probably both physical factors and differential herbivory pressures display a key role.     

The genetic structure of the exotic ascidian Styela plicata (Tunicata) from Italian ports,with a re‐appraisal of its worldwide genetic pattern

The pleated ascidian Styela plicata (Lesueur, 1823) is a solitary species commonly found in ports and marinas around the world. It has been recorded in the Mediterranean region since the mid‐19th century. In the present work, the species’ genetic diversity was analysed, employing a 613‐bp portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene from 149 individuals collected in 14 ports along Italian coasts at spatial scales ranging from 1 to approximately 2200 km. Haplotype and nucleotide diversity values were h = 0–0.933 (total h = 0.789) and π = 0–0.145 (total π = 0.0094), respectively. A general southward trend of increasing within‐population genetic diversity was observed. Analysis of molecular variance revealed significant genetic structuring but no significant differences were detected among basins, and no isolation by distance was found. Our data were integrated with the COI sequences available from previous studies and re‐analysed in order to investigate the possible routes of introduction of this ascidian into the Mediterranean Sea. The presence of the two COI haplogroups detected in previous molecular investigations on S. plicata at intercontinental spatial scale was confirmed in the Mediterranean Sea. The results revealed multiple introductions of S. plicata, although some locations appear to have experienced rapid expansion from few founding individuals with reduced genetic diversity. However, continuous introductions would confound the pattern deriving from single founder events and make it difficult to estimate the time needed for gene diffusion into established populations. This mixing of effects creates difficulties in understanding the past and current dynamics of this introduction, and managing this alien invasive ascidian whose genetic structure is continuously shuffled by vessel‐mediated transport.     

北部湾北部海域水体异养细菌的时空分布特征研究

为探讨环境因素对异养细菌丰度的影响,2016年9月至2017年8月通过月度航次调查对北部湾北部海域异养细菌丰度的时空分布特征进行了系统研究。结果表明,调查海区异养细菌丰度介于（2.75~56.86）×105 cell/mL,平均值为（11.01±6.31）×105 cell/mL。各季节细菌丰度从高至低依次为:夏季、春季、冬季、秋季。异养细菌丰度由近岸海域向西南深水区方向逐渐降低,在近岸浅水区垂直分布均匀,在水深大于20 m的海区出现季节性分层现象:表层细菌丰度较高,底层细菌丰度较低。主成分分析显示温度对异养细菌时空分布有重要影响,秋、冬季异养细菌丰度与温度呈显著负相关,在春、夏季呈显著正相关。细菌丰度与盐度呈显著负相关,说明海水盐度变化是细菌时空分布重要影响因素。异养细菌丰度与叶绿素a和溶解氧含量呈显著正相关,表明浮游植物初级生产过程影响了异养细菌的时空分布。在秋、冬和春3季异养细菌丰度与营养盐水平呈显著负相关,二者关系受浮游植物生物量间接影响。异养细菌时空分布差异取决于环境条件的变化,温度、盐度、叶绿素a和溶解氧含量是影响异养细菌丰度分布的主要因素。     

Assessing Cryptic Invasion State: Fine-Scale Genetic Analysis of Ciona savignyi Population in Putative Native Habitat of the Korean Coast

The solitary ascidian, Ciona savignyi (Ascidiacea, Enterogona) is a notorious marine invader still expanding its habitat range worldwide. This species is considered native to the North West Pacific, but its indigeneity in Korean coastal waters has been questioned because of outdated taxonomic records and its inhabitation of oceanographically marginal areas. To clarify their cryptic invasion state, 247 individual C. savignyi samples were collected from 12 harbors and marinas on the Korean coast, and a 744 bp region of mitochondrial DNA (mtDNA) cytochrome c oxidase subunit I gene was sequenced and analyzed. Our analyses of population genetic structure and demographic history provided considerable pieces of evidence supporting their long-term establishment on the Korean coasts: differentiated population genetic structure, sequentially arrayed star-shape haplotype network, neutrality test results of past population expansions, and post-glacial colonization pattern of demography. Consequently, we concluded that C. savignyi populations on the Korean Coast are indigenous rather than exotic. These results could be used as reference data for further phylogeo graphic and demographic studies of problematic Ciona species, and to clarify and resolve similar cryptic invasion states of the other Korean coastal marine organisms. This study is the first to resolve the cryptic in vasion state of Korean marine organisms using genetic analysis.

     

Matrilineal evidence for genetic structure and Late Pleistocene demographic expansion of the Ornate goby Istigobius ornatus (Teleostei: Gobiidae) in the Persian Gulf and Oman Sea

The Persian Gulf and Oman Sea are characterized by an interesting paleoclimatic history and different ecological settings, and offer a unique study area to investigate the genetic structure of marine organisms including fishes. The Ornate goby Istigobius ornatus is widely distributed throughout the tropical Indo‐West Pacific including the Persian Gulf and Oman Sea. Here, we present the population structure, genetic diversity, and demographic history of four populations of I. ornatus from the latter two regions using the D‐loop marker of mitochondrial DNA. The results reveal a shallow genealogy, a star‐like haplotype network, significance of neutrality tests, and unimodal mismatch distribution. This is concordant with a recent demographic expansion of I. ornatus in the Persian Gulf and Oman Sea at about 63,000–14,000 years ago, which appears to be related to Late Pleistocene sea level fall and rise. The results of the pairwise Fst estimates imply high gene flow along the coast of the Persian Gulf, which is probably due to larval dispersion, whereas the Oman Sea population clearly differs from all Persian Gulf populations. The AMOVA result indicates that 7.74% of the variation is related to differences among ecoregions, while inter‐ and intra‐population differences explained ?3.20% and 95.47% of the variation, respectively. The haplotype network depicts two groups of haplotypes, most of them were specific to the Persian Gulf. No further evidence for geographic lineage substructuring was evident. The Mantel test result indicates that isolation by distance is not the main mechanism that promoted the genetic differentiation among the studied populations of I. ornatus. We suggest that cumulative effects of ecological and geographic barriers such as salinity, oceanographic conditions, and the presence of the Strait of Hormuz have shaped the genetic structure of I. ornatus in the Persian Gulf and Oman Sea.     

Genetic diversity and population structure of the size‐selectively harvested owl limpet,Lottia gigantea

Size‐selective harvesting can elicit a genetic response in target species through changes in population genetic subdivision, genetic diversity and selective regimes. While harvest‐induced genetic change has been documented in some commercially important species through the use of historic samples, many commonly harvested species, such as coastal molluscs, lack historic samples and information on potential harvest induced genetic change. In this study, we have genotyped six microsatellite markers from populations across much of the California mainland range of the size‐selectively harvested owl limpet (Lottia gigantea) to explore the genetic structure and diversity of this species. We found no significant genetic structure or differences in genetic diversity among populations of L. gigantea. Our results suggest high gene flow among populations and that differences in life history, demography, and body size previously observed between protected and exploited populations is largely due to phenotypic plasticity. From a conservation perspective, if proper actions are taken to curb harvesting, then exploited populations should be able to return to their pre‐impact state given sufficient time.     

Changes in zooplankton community structure in Sanmen Bay, China

Seasonal variations in zooplankton abundance,biomass,species diversity and community structure were investigated in the Sanmen Bay,China.Samples were collected from 15 stations,on the seasonal basis,in April(spring),July(summer) and October 2005(autumn) and January 2006(winter),respectively.The results show that zooplankton species number,abundance and biomass varied widely and had distinct spatial heterogeneity in the Sanmen Bay.A total of 72 species of zooplankton belonging to 56 genera and 17 groups of pelagic larvae were identified.The zooplankton species richness was strongly related to salinity.Based on hierarchical cluster analysis,zooplankton in this study area were classified into three groups:coastal,neritic and pelagic groups,which corresponded to the upper,middle and lower portion of the Sanmen Bay,respectively.The coastal low-saline species were dominant in the study area.The zooplankton abundance and biomass reached a peak in summer,moderate in spring and autumn,and the lowest in winter.Zooplankton abundance decreased from the upper to lower portion of the bay in April,when the highest biomass occurred in the middle portion of the bay.There were the same spatial distribution patterns for the biomass and abundance in July,with the maximum in the middle of the bay.However,zooplankton abundance was the highest in the middle of the bay in October,when maximum biomass occurred near the lower of the bay.Zooplankton abundance and biomass were evenly distributed in the Sanmen Bay in January.Spatial and temporal variations in zooplankton and their relationship with environmental factors were also analyzed.The BIOENV results indicate that the combination of chlorophyll a(Chl-a),salinity,dissolved inorganic nitrogen(DIN),dissolved oxygen(DO) and silicate(SiO3) was responsible for the variations in zooplankton community structure in the Sanmen Bay.The environmental changes played an important role in changes in the zooplankton community structure in the Sanmen Bay.     

基于主成分分析法的闽江口及其近岸水域水质评价

选取2016年4月、7月和10月闽江口及其近岸水域7个调查点位的盐度、悬浮物、pH、溶解氧、化学需氧量、氮营养盐和重金属等15项监测指标数据,采取主成分分析法分析了该水域的水质,明确影响该水域水质的主要污染因子。结果表明：15项监测指标转换提取为4个主成分,解释82.153%的方差。从时间分布来看,闽江口及其近岸水域在4月份水质较差、10月份次之、7月份较好。从空间分布来看,近河口水质较差而远离河口水质较好。影响该水域污染水质的主要驱动因子是pH、COD、氮营养盐和Cd。研究结果对于进一步了解闽江口及其近岸水域水质情况具有重要意义,同时也为福建省海洋管理的科学决策提供支持。     

In two waters: contemporary evolution of lagoonal and marine white seabream (Diplodus sargus) populations

Brackish water ecosystems are often exposed to wide variations in environmental variables, including temperature and salinity, which may cause strong selective pressures on organisms modifying the genetic patterns of species. The aim of this work was to test whether there is a ‘divergence-with-gene flow’ in coastal lagoon populations of white seabream (Diplodus sargus) (Ria Formosa, S Portugal and Mar Menor, SE Spain) respect to four marine populations, by using partial sequences of cyt b mitochondrial gene and information from nine microsatellite loci. Genetic diversity was highest in both coastal lagoons (Mar Menor and Ria Formosa) considering mitochondrial and nuclear markers. Although some of F_ST population pairwise comparisons were not significant, analyses of molecular variance (AMOVAs) detected differences between groups (coastal lagoon and marine) close to significance. Also, only two haplotypes (Cytb-17 and Cytb-18) were detected in both coastal lagoon sampling sites and these localities (Mar Menor and Ria Formosa) showed the highest number of singletons, some of them with a high number of mutations, as has been already described for other Mar Menor populations (Pomatochistus marmoratus and Holothuria polii). Also, several tests detected significant positive and balancing selection considering mtDNA and microsatellite data. These data support the hypothesis of selection as one of the drivers of the genetic differences found between coastal lagoon and marine populations. The life strategy adopted by Diplodus sargus in coastal lagoons allows it to decrease its mortality rate and improve the heritability of its genes. Also, the increase time spent in coastal lagoons with different temperatures and salinities favours the fitness selection and the maintenance of exclusive haplotypes and genotypes in coastal lagoon inhabitants favouring the ‘divergence-with-gene-flow’.     

High nutrients in the coastal area after heavy rain observed in the central Seto Inland Sea in July 2012

Temporary enhancement of the nutrient concentrations in the coastal area was observed after heavy rain in the central Seto Inland Sea in July 2012. After passage of a stationary front accompanied by heavy rain, the river outflow was enhanced, and low salinity and high nutrient concentrations were detected near the mouths of rivers. The offshore salinity and nutrients increased and decreased, respectively, which suggested that a snapshot event, such as heavy rain, could influence the short-term variation of the coastal marine environmental conditions, such as the salinity and nutrient distributions.     

High gene flow promotes the genetic homogeneity of the fish goby Pomatoschistus marmoratus (Risso, 1810) from Mar Menor coastal lagoon and adjacent marine waters (Spain)

The extreme environmental variability of coastal lagoons suggests that physical and ecological factors could contribute to the genetic divergence among populations occurring in lagoon and open‐coast environments. In this study we analysed the genetic variability of lagoon and marine samples of the sand goby, Pomatoschistus marmoratus (Risso, 1810) (Pisces: Gobiidae), on the SW Spain coast. A fragment of mitochondrial DNA control region (570 bp) was sequenced for 196 individuals collected in five localities: Lo Pagan, Los Urrutias and Playa Honda (Mar Menor coastal lagoon), and Veneziola and Mazarrón (Mediterranean Sea). The total haplotype diversity was h = 0.9424 ± 0.0229, and the total nucleotide diversity was π = 0.0108 ± 0.0058. Among‐sample genetic differentiation was not significant and small‐scale patterns in the distribution of haplotypes were not apparent. Gene flow and dispersal‐related life history traits may account for low genetic structure at a small spatial scale. The high genetic diversity found in P. marmoratus increases its potential to adapt to changing conditions of the Mar Menor coastal lagoon.     

Striped weakfish (Cynoscion guatucupa) population structure in waters adjacent to Rio de la Plata,environmental influence on its inter-annual variability

The springtime temporal variations of striped weakfish (Cynoscion guatucupa) population structure available to the commercial fishery and its relationship to environmental factors were evaluated in the Uruguayan coastal zone (35° −33.4°S), from 86 stations sampled in 1994, 98, 99 and 2003. We examined the inter-annual variability of age-class structure over four years under different oceanographic conditions: (1) 1998 (El Niño year) was characterized by elevated water temperature; (2) 1999 (La Niña year) was characterized by decreased water temperature; and (3) 1994 and 2003 were ‘typical years’ with intermediate values in those parameters. To determine whether or not major shifts in population structure occurred between years we used ANOSIM and SIMPER analysis to determine which age-class typified and discriminated between years. A canonical correspondence analysis (CCA) was used to define the temporal pattern of age-class structure of C. guatucupa and to estimate its associations with environmental factors (depth, temperature, salinity, vertical stratification, and zonal and meridional component of the wind). The C. guatucupa population structure showed significant difference between 1998 and 1999 and 1994–2003. During 1998 and 1999, the population structure was dominated by adults (between 4 and >7 age-class), while that in 1994 and 2003 was dominated by juveniles (between 0 and 3 age-class). CCA results indicated that zonal wind and salinity has a major influence on the temporal pattern of C. guatucupa population structure. Juvenile population structure was associated with low salinities and occurred when the wind field forced an inflow of freshwater into the marine coastal area from the Rio de la Plata estuary, while the adult structure, associated with high salinities, occurred when the area was dominated by a wind driven inflow of higher salinity shelf water. These results support the hypothesis that the short-term environmental synoptic condition has a greater influence on the distribution and population structure of C. guatucupa than long-term environmental variability.     

Spatial and temporal variations of mesozooplankton in the Pearl River estuary, China

This paper examines spatial and temporal variations of mesozooplankton abundance, biomass and community structure during three cruises of July 2002 (summer), January 2003 (winter), and April 2003 (spring) in the Pearl River estuary, China. Zooplankton abundance and biomass fluctuated widely and showed distinct heterogeneity in the Pearl River estuary. A total of 154 species were identified during three surveys. The number of zooplankton species richness was strongly linked to salinity. Hierarchical cluster analysis identified three zooplankton groups during this study. Estuarine, neritic and pelagic groups corresponded to the upper, middle and lower reaches in the Pearl River estuary. The difference among groups could be mainly ascribed to changes in the relative contributions of the dominant species. The fluctuations in the zooplankton abundance, biomass and community structure were determined by the interactive effects of freshwater inflow, tidal and coastal currents, chlorophyll a, salinity and temperature. Significant spatial variability in the distribution of zooplankton species, abundance and biomass can be ascribed to the virtual presence of a horizontal gradient in salinity.     

Relationship between heavy metal accumulation and genetic variability decrease in the intertidal crab Pachygrapsus marmoratus (Decapoda; Grapsidae)

The “genetic erosion” hypothesis posits that heavy metal stress is related to a loss of genetic diversity at the population level. The genetic diversity of natural populations can, however, be affected by natural processes as well as by human impact. We studied the relationship between heavy metal bioaccumulation and genetic variability in the intertidal crab Pachygrapsus marmoratus. Tissue samples were collected from 40 individuals inhabiting four polluted and four unpolluted sites along the Tuscan coast (Mediterranean basin), and were examined for four heavy metals (arsenic, As, cadmium, Cd, lead, Pb, and copper, Cu). We also assessed the genetic variability of 235 crabs from the same localities using six microsatellite loci.Our results show that the bioaccumulation levels of these individuals accurately reflect the levels of pollution in their immediate environment, and that heavy metals accumulate more in the hepatopancreas than in the gills. Moreover, populations from polluted sites have significantly less genetic variability, measured as mean standardized d², and a significantly lower percentage of unrelated individuals, than populations from unpolluted sites. This evidence supports the “genetic erosion” hypothesis for metal heavy exposure in natural environments.     

Dynamics of pelagic variables in two contrasting coastal systems in the western Hokkaido coast off Otaru port,Japan

Human impact on adjacent coastal waters, leading to alteration in nutritional environment and hence affecting phytoplankton biomass (Chlorophyll a), will probably be enhanced by the nearby presence of ports. The main goal of this study is to assess the influence of nearby presence of port on phytoplankton biomass build-up and the physical–chemical environmental characteristics in two contrasting coastal systems (Otaru port, S-IN and an exposed coastal area, S-OUT) in the western Hokkaido coast off Otaru port, Japan. Sampling was conducted on “bi-weekly and monthly” basis during the period of September 2006–December 2007 and data comprising 11 pelagic variables were obtained. In most instance, phytoplankton biomass, nutrients' (NH₄, NO₃, PO₄, and Si(OH)₄) concentrations and nutrients' molar ratios were higher at the Otaru port location. Physical parameters (temperature, salinity, hydrogen ion concentration (pH), photosynthetically active radiation (PAR) and dissolved oxygen, (DO)) were not significantly different (P > 0.05) between the two locations. With the exception of salinity, pH and DIC, all variables measured showed significant variation (P < 0.05) with season. While the coefficient of variation (CV) of physical parameters and phytoplankton biomass were relatively higher in Otaru port location (S-IN), the exposed coastal location (S-OUT) showed a higher variation in chemical parameters. Other variables showed different patterns between the two locations. We conclude that ports, due to its activities and restricted circulation favour high nutrient loading and phytoplankton biomass build-up in adjacent coastal systems, thus, suggesting the need for continuous field observation data in order to advance our knowledge on possible future human impact on coastal environment and the need to monitor and control port activities.     

Influence of environmental disturbances and reproductive strategy on genetic diversity and differentiation of Zostera marina populations on the southern coast of Korea

The genetic diversity and differentiation of four Zostera marina populations along the southern coast of Korea were estimated using random amplified polymorphic DNA (RAPD) markers to determine the effects of natural and anthropogenic stresses and reproductive strategy on within‐population genetic diversity. The mean number of alleles and gene diversities, indicating population genetic diversity, was highest in the Z. marina population that was exposed to repeated environmental disturbances, and lowest in the most undisturbed population. The higher genetic diversity in the disturbed population was associated with a higher contribution of sexual reproduction to population persistence. This suggests that both the level of disturbances and the reproductive strategy for population persistence contributed significantly to population genetic diversity at the study sites. According to the analysis of molecular variance (AMOVA), 76% genetic variation was attributable to differences among individuals within populations. The observed genetic differentiation (F_ST = 0.241) among Z. marina populations at the study sites appeared to result from reduced meadow size, increased genetic drift, and a high incidence of asexual reproduction. Increased population genetic diversity can enhance resistance and resilience to environmental disturbances; thus, this investigation of seagrass population genetics provides valuable new insights for the conservation, management, and restoration of seagrass habitats.     

Seasonal and depth variations of copper,iron and nickel in ligurian coastal waters

The aim of this work is to study the seasonal variation of iron, copper and nickel in connection with those of other environmental parameters which characterize the coastal system studied; in particular, the phytoplankton biomass. Sampling was carried out from January to October with monthly periodicity, at a station 2 miles offshore of Portofino, Italy, to depths of 200 m.The results indicate that the concentrations of copper, iron and nickel in particulate matter show a marked increase compared to values reported in the literature for the open seawater of the Mediterranean. It is also possible to determine a relationship between the three metals and the seasonal and depth variations. In the particulate matter, there is a direct relationship between the phytoplankton biomass and the heavy metals in the photic layer.     

我国东南沿海厚壳贻贝(Mytilus coruscus)4 个群体线粒体16S rRNA 序列及遗传结构分析

采用16S rRNA基因测序技术,对我国东南沿海4个地理群体的厚壳贻贝遗传结构及遗传变异进行研究。通过对4个厚壳贻贝群体共83个个体的线粒体16S rRNA基因进行测序,获得1个长度为305bp的同源序列,共检测到150个多态位点,多态位点比例达49.18%。83个个体中共检测到28个单倍型,单倍型多样性指数(Hd)为0.810,核苷酸多样性指数(Pi)为0.09602,平均核苷酸差异数(K)达27.846。结果表明,我国东南沿海厚壳贻贝群体具有较高的遗传多样性水平。遗传结构检测结果表明,舟山群体、温州群体、宁德群体间的遗传距离小,遗传分化系数(Fst)为-0.0141—0.0059之间,群体内部无显著分化(P>0.05),而福州群体与其它群体间遗传距离较大,为0.215—0.217之间,遗传分化系数(Fst)也较大,为0.6217—0.6319之间,存在极显著的遗传分化(P<0.001)。