Diversity and large-scale biogeography of Paramesochridae (Copepoda, Harpacticoida) in South Atlantic Abyssal Plains and the deep Southern Ocean

Multicorer samples for meiofaunal study were obtained within the framework of the international project CeDAMar, at 21 stations occupied during the DIVA and ANDEEP campaigns (2000, 2002 and 2005) to the southern Atlantic Ocean (Guinea, Angola and Cape Basins) and the Southern Ocean (Weddell and Scotia Seas), respectively. A total of 311 adult Paramesochridae Lang, 1944 (Copepoda, Harpacticoida) was extracted from 437 cores obtained during 83 deployments of the corer at depths between 1107 and 5655 m. All specimens were determined to species based on morphological characteristics. They belonged to 19 species and four genera (Kliopsyllus Kunz, 1962, Leptopsyllus T. Scott, 1894, Paramesochra T. Scott, 1892 and Scottopsyllus Kunz, 1962). Eleven species were restricted to single regions, whereas the others showed a much wider distribution. For example, Kliopsyllus andeep Veit-Köhler, 2004 and Kliopsyllus diva Veit-Köhler, 2005, were both collected from Guinea, Angola and Weddell Abyssal Plains, and Kliopsyllus schminkei Veit-Köhler & Drewes, 2009 occurred in the three West-African basins. This study provides a first insight into the large-scale biogeography of deep-sea harpacticoids, represented by the Paramesochridae, and indicates that distribution ranges, at least in this family, may extend across South Atlantic and Southern Ocean Abyssal Plains.     

Genetic stock structure of white steenbras Lithognathus lithognathus (Cuvier, 1829), an overexploited fishery species in South African waters

White steenbras Lithognathus lithognathus (Teleostei: Sparidae) is an overexploited marine fish species endemic to South Africa. Overexploitation in recreational, subsistence and commercial fisheries has resulted in stock collapse and the need for improved management of the species. Adults are thought to undertake large-scale annual spawning migrations, yet studies of their movement indicate low levels of connectivity among coastal regions. To address this, mitochondrial DNA sequencing and genotyping of microsatellite loci in the nuclear genome were conducted to determine the genetic stock structure and level of gene flow in this species. Genetic diversity was high throughout the species’ core distribution, with no evidence of isolation by way of distance or localised spawning. Low, non-significant pairwise fixation indices (F_ST, R_ST and Jost’s D_est) indicated low genetic differentiation and high levels of gene flow. The observed results, and agreement between mitochondrial and microsatellite DNA, confirm that white steenbras exists as a single genetic stock with high levels of gene flow throughout its distribution.     

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.     

气候变化对东北大西洋渔获物组成、多样性和营养级的影响

东北大西洋是世界上重要的捕捞海域,气候变化对该海域捕捞产生了重要的影响。本文基于联合国粮农组织所提供的1982−2016年东北大西洋渔获产量数据,对该海域渔获物组成、多样性、平均营养级及主成分变化特征进行时间序列上的分析,并结合东北大西洋海域气候、环境因子,应用广义可加模型探究渔获物组成与气候变化之间的关系。结果显示：渔获物多样性的变化总体上呈下降趋势,2002−2010年间处于较低水平;平均营养级在2002年之前呈平缓下降的趋势,2002年之后开始波动上升,相关性分析表明这两个指标与海域环境因子的变化较为相关。对渔获物组成进行主成分分析显示,第一主成份变化的方差解释率达到35.3%,且与海域气候、环境因素有较高的相关性,第一主成分变化能够较好地表征气候影响下渔获物组成变化的情况。广义可加模型分析结果显示,渔获物组成变化的影响因素按解释率由高到低分别为：海表温度、海平面高度、盐度、海冰和北大西洋涛动指数。该研究有助于认识气候变化对海洋渔业资源及其结构组成的影响。     

基于线粒体控制区的中国东南沿海黄鳍棘鲷群体遗传多样性和遗传分化

本研究通过对线粒体控制区序列进行分析的技术手段,对中国宁德（ND）、厦门（XM）、漳浦（ZP）、南澳岛（NAD）、湛江（ZJ）、海口（HK）与北海（BH）的7个野生黄鳍棘鲷（Acanthopagrus latus）群体的遗传多样性和遗传分化进行比较分析。结果表明：中国东南沿海的野生黄鳍棘鲷群体呈现出中等以上的遗传多样性特征,48个黄鳍棘鲷样品的控制区序列长度为580 bp,单倍型数目为44个,总体的单倍型多样性指数（Hd）和核苷酸多样性指数（Pi）分别为0.996和0.017 30。7个野生黄鳍棘鲷群体间的遗传分化程度较低,各群体间的遗传距离为0.010 28~0.029 87。群体间的遗传分化系数（FST）为-0.068 41~0.545 86,北海群体和其他群体间存在一定程度的遗传分化。AMOVA分析显示群体内的遗传变异占比为83.34%,大部分遗传变异发生在组群内;但北海群体与其他6个群体分为两个组群后,组群间的遗传变异占比为42.66%,两个组群间存在较大程度的遗传变异。基于Kimrua距离法构建的系统进化树中显示北海群体聚为一个分支,另外6个群体聚为一支。基于TCS network构建的单倍型网络图中44个单倍型混杂在一起,未按照水系格局和地理距离进行分布,表明黄鳍棘鲷群体间未形成多个单系群。本研究可为中国东南沿海野生黄鳍棘鲷群体的种质资源利用和保护提供科学依据。     

Genetic diversity and population structure of the golden cuttlefish,Sepia esculenta (Cephalopoda: Sepiidae) indicated by microsatellite DNA variations

The golden cuttlefish, Sepia esculenta Hoyle, 1885 (Cephalopoda: Sepiidae) is a valuable and important fishery resource for China, Japan and Korea. This fishery has experienced severe population decline largely due to overexploitation in past decades. To provide guidelines for fisheries management, we estimated genetic diversity and population structure across four locations along the coast of Japan and one location in China (a total 281 individuals) using nine microsatellite DNA loci. Sepia esculenta showed high genetic variability with mean allele richness ranging from 15.8 to 21.4, and mean heterozygosity from 0.80 to 0.90. Weak but significant genetic differentiation was present and the F_ST value was 0.020 across all five populations. The useful information obtained in this study will offer insights into how to fine‐tune conservation and fishery management measures for this species and resource in the future.     

Lack of population genetic structure in the marine nematodes Ptycholaimellus pandispiculatus and Terschellingia longicaudata in beaches of the Persian Gulf,Iran

We investigated genetic diversity and population genetic structure of two common benthic nematode species, Ptycholaimellus pandispiculatus and Terschellingia longicaudata, from sandy beaches in the area of Bandar Abbas (Iran), Persian Gulf. Based upon partial mitochondrial cytochrome oxidase c subunit 1 (COI) gene data, 17 and two haplotypes were found for P. pandispiculatus and Te. longicaudata, respectively. Analysis of molecular variance did not reveal a significant population genetic structure for either species. The absence of genetic structuring indicates substantial dispersal and gene flow in our study area. To assess the species structure of Te. longicaudata at a larger geographic scale, we compared 18S rDNA and COI sequences from Iran and the Scheldt Estuary in The Netherlands to ascertain whether they truly belong to the same species. Our data confirmed previous studies that Te. longicaudata likely constitutes a complex of multiple cryptic species, with one of these species having a (near) cosmopolitan distribution.     

Regional variation in distribution pattern, population structure and growth rates of Meganyctiphanes norvegica and Thysanoessa longicaudata in the Irminger Sea, North Atlantic

Euphausiids are a key component of the northern North Atlantic marine ecosystem and Meganyctiphanes norvegica and Thysanoessa longicaudata are dominant both numerically and in terms of biomass. The Irminger Sea is remote and experiences often-hostile weather conditions. Consequently, few studies have been conducted there, and detailed information on the seasonal distribution, abundance and growth of euphausiids is limited. Here we explore patterns of abundance and spatial and temporal variation in length–frequency distribution in order to determine regional growth rates for both species in the Irminger Basin. Regional composite length–frequency distributions for spring, summer and winter were devised by aggregating discrete net haul data according to the results of a multivariate cluster analysis of length conducted on spring and summer net sample data. Three biologically distinct regions within the Irminger basin were apparent (Central Irminger Sea, Northern Irminger Sea and East of Greenland Shelf). These regions corresponded broadly with distinct physical zones within the basin. Modes in the composite length–frequency distributions were determined by fitting multiple normal distributions, and regional differences in growth were investigated by tracking modes between seasons. The results provide some evidence for regional variability in growth and population dynamics. The population structure and growth of M. norvegica was similar in the open ocean regions of the Northern and Central Irminger Basin, but different in the region around the East Greenland Shelf. There was a distinct absence of larger individuals (+I-group) in the open ocean regions compared to East Greenland Coast region, and growth rates were marginally higher. A similar pattern in population structure was also observed for T. longicaudata. Variability in growth and abundance are discussed in relation to prevailing environmental characteristics such as temperature and food availability.     

The genetic diversity,individual relatedness and possible mating system of an isolated population of the Cyprinid species Megalobrama pellgrini in upper reaches of the Changjiang (Yangtze) River,China

Megalobrama pellegrini is a cyprinid fish endemic to upper reaches of the Changjiang(Yangtze)River,China,which is also an important economic species in the local area.In recent years,resources of this species have decreased sharply and its conservation has drawn great attention.In the present study,we collected 120 individuals from the Longxi River,a tributary isolated from the main channel of the Changjiang River,where M.pellegrini is still relatively abundant.Using two different molecular markers,mitochondrial cytochrome b(cyt b)gene,and nuclear microsatellite(simple sequence repeat,SSR),we analyzed the genetic diversity of this isolated population.The results show that sequence genetic diversity was low(Hd:0.290 and P i:0.000 77 for cyt b gene),while the SSR genetic diversity was high(Ho:0.824 4±0.147 2,He:0.823 5±0.145 1).Analysis indicated that this population had experienced a bottleneck,with inbreeding and small effective population size(around 50).Based on SSR data,relatedness analyzing revealed that the 120 samples were grouped into 10 completely independent clusters.It was inferred that the mating system of M.pellegrini was polygamy.We suggested that the low genetic diversity could be induced by the overfishing and inbreeding depression.Therefore,we suggested that the urgent conservation measures should be taken to control the overfi shing and give better conditions for the fish to grow and spawn,then to restore population size.     

Genetic diversity and population structure of three dominant myctophid fishes (<Emphasis Type="Italic">Diaphus theta,Stenobrachius leucopsarus</Emphasis>, and <Emphasis Type="Italic">S. nannochir</Emphasis>) in the North Pacific Ocean

We compared the genetic diversity of three dominant myctophid fishes in the North Pacific Ocean that have different diel vertical migration patterns on the basis of the nucleotide sequences of the mitochondrial gene for cytochrome b. No genetic structure was detected for each of these three species. The genetic diversity progressively increased for Diaphus theta, a diel migrant species showing clear diel vertical migration; Stenobrachius leucopsarus, a semi-diel migrant, in which only part of the population migrates vertically; S. nannochir, a non-diel migrant. All three species were suggested to have experienced a recent, sudden population expansion. Interspecific differences in genetic diversity might be attributable to differences in the degree of population size reduction during the glacial periods; this degree in turn corresponds to the energy demand of the fishes.     

Deep-water stands of Cystoseira zosteroides C. Agardh (Fucales,Ochrophyta) in the Northwestern Mediterranean: Insights into assemblage structure and population dynamics

Populations dominated by Cystoseira zosteroides, an endemic and threatened Mediterranean seaweed, colonize deep-water rocky habitats down to more than 50 m depth. Assemblages dominated by this species display high algal and invertebrate species richness. Algal biomass averages 1134 g dw m⁻². Erect and turf algae account for only 25% of total algal dry weight, while encrusting corallines are responsible for the remaining 75%. Sponges, bryozoans and ascidians constitute the dominant sessile macrofauna. Cystoseira zosteroides is the dominant erect algae, with a mean biomass of 60.6 g dw m⁻², and densities ranging from 4 to 7 plants m⁻². The alien turf alga Womersleyella setacea has a biomass of 104.2 g dw m⁻² and covers most of the understory substrate. The size-frequency distribution of C. zosteroides populations shows differences over time. Mean annual growth of the main axis is around 0.5 cm and mean annual mortality rate is lower than 2%. Recruitment was almost nil during the studied period of time (10 years). Processes structuring these deep-water Cystoseira stands must be driven by episodic disturbances, after-disturbance recruitment pulses, and long periods of steady growth that last at least 10 years. However, it is also possible that recruitment is irreversibly inhibited by the alien alga W. setacea in which case these old-growth stands are faced with extinction. The highly diversified assemblages and the low growth and low mortality rates of C. zosteroides indicate high vulnerability to natural and anthropogenic disturbances, and call for effective measures to ensure their conservation.