The influence of physical and biological processes on the ichthyoplankton communities in the Gulf of Sirte (Southern Mediterranean Sea)

This paper reports on the first study on the ichthyoplankton community structure in the Gulf of Sirte and its spatial distribution in relation to environmental conditions and zooplankton abundance. The results make an important contribution to the future management of fisheries in this unexplored, but much exploited, area. Biological samples were collected in July 2008 using a Bongo40 net. In total, 1914 larvae were found and 1652 of these were identified. In particular, bathypelagic taxa were the most abundant, followed by demersal, mesopelagic, pelagic and epipelagic taxa. The ichthyoplankton community had a patchwork distribution influenced by oligotrophic conditions, the bottom depth and oceanographical features. The results suggest that environmental forcings were able to transport the ichthyoplankton to productive areas. Indeed, maximum fish egg densities were found in coastal stations in correspondence with the Atlantic Tunisian Current inflow, whereas larvae were mainly concentrated in the east side of the Gulf, probably as a result of advection by the anticyclonic circulation. Additionally, the distribution patterns of the total larvae density and the different assemblages were well matched with the abundance of the zooplankton, probably determining final larval survival, growth and recruitment.     

Regional variation in springtime ichthyoplankton assemblages in the northeast Pacific Ocean

The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log₁₀ (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast.     

南海北部上层鱼类浮游生物多样性和丰度的季节变化

The objective of this study was to investigate the seasonal variations of ichthyoplankton diversity and abun-dance in the northern South China Sea based on the data collected during summer, winter and spring. In total, 95 taxa of larval fishes were identified. The greatest number of species was recorded in spring, followed by summer and winter. The number of species was distributed mainly in the coastal waters from the east of Leizhou Peninsula to the southeast of Hainan Island during the surveyed periods of summer and spring, but in the offshore waters during winter. The abundance of larval fish was lowest in winter, increased in spring, and reached the maximum in summer. High abundance of larval fish was generally restricted to coastal waters with the isobaths less than 50 m. Seasonal variations of larval fish richness, abundance and diversity index were significant （P〈0.001）. Carangidae was the most common and abundant taxon in summer and winter, whileSardinella sp.,Thrissa mystax andLeiognathus sp. were dominant in spring. High diversity and abundance of larval fish might be attributed to increased temperature and coastal upwelling in spring and summer.     

Evaluating the relationship between spatial heterogeneity and temporal variability of larval fish assemblages in a coastal marine ecosystem (Haizhou Bay,China)

In coastal marine ecosystems, spatial patterns of larval fish assemblages (LFAs) tend to exhibit geographic stability because of relatively stable spawning site selection and predictable oceanographic phenomena such as eddies. To evaluate the relationship between spatial heterogeneity and temporal variability of LFAs, we conducted a high spatiotemporal resolution ichthyoplankton survey from April to July in 2013 in the shallow waters (<20 m) of Haizhou Bay, China. Our analysis indicated three distinct assemblages, which were stable geographically but exhibited a gradual and directional change of species composition and abundance over our study period. Sea surface temperature was the most important environmental co‐variate for determining temporal variability of LFAs, likely owing to temperature effects of species composition and spawning period selection of adult fish, along with known temperature‐dependent survival rates of larval fish. Study of LFA spatiotemporal dynamics is essential for improved understanding of adult fish spawning behavior, and has potential to inform design and implementation of conservation and management measures (e.g. marine protected areas) in coastal systems.     

黑海西北部涡旋与环流对跨陆架水交换的影响

涡旋对海洋中的能量传递和物质交换有重要作用。黑海西北部陆坡边缘是长生命周期涡旋经常发生的海域,但涡旋引起的陆架和海盆之间水交换通量的季节性特征,以及海盆边缘环流对跨陆架水交换的作用等方面的研究还不是很充分。本文对黑海西北部陆架区与深海盆区间的跨陆架水交换进行了研究,利用高分辨率三维原始方程模式模拟的温、盐、流等资料,结合涡旋自动探测方法,统计了黑海西北部海域的涡旋活动,研究了涡致跨陆架水交换的季节性特征,计算对比了2002年到2010年间海盆边缘环流与涡旋对跨陆架水交换通量的各自贡献。结果表明:黑海西北部地区海盆边缘环流强度与跨陆架进、出通量的相关系数分别为0.57和0.67,海盆边缘环流位置与跨陆架交换量的相关系数为0.52;海盆边缘环流强度与位置的季节性变化导致了黑海西北部跨陆架通量的季节性变化。黑海西北部地区表层3月到8月之间涡旋所引起跨陆架交换量约占了跨陆架交换总量的16%~31%;涡致跨陆架通量也具有季节性特征。文中对单个涡旋进行了详细研究:2005年5月5日到2005年7月20日之间在黑海西北部存在一个直径最大值时达到120 km的反气旋式涡旋,涡旋存在期间完成了从陆架区向深海区的水体传输,相当于黑海西北陆架区水体积的30.9%。     

Larval fish distribution in shallow coastal waters off North Western Iberia (NE Atlantic)

Monthly sampling for ichthyoplankton was conducted at three stations very near to the coast (near to shore shallow stations before the surf zone in direction to the shoreline) of Atlantic northwestern Portugal within contrasting localities: rocky shore, in front of a sandy beach receiving an estuary and a fishing port with heavy anthropogenic impact. Sampling was conducted from August 2002 to October 2003, always at full moon, at low tide and high tide in daylight hours, at the water column using a 48 cm diameter plankton net with 335 μm mesh. Analysis of the physico-chemical parameters pointed out the spatial (horizontal) homogeneity of the sampling area. Fish larvae from 41 taxa belonging to 17 families were identified; Blenniidae, Labridae, Ammodytidae, Clupeidae, Gobiidae, Soleidae and Gobiesocidae were the most representative during the study period. Parablennius gattorugine, Ammodytes tobianus, Symphodus melops, Sardina pilchardus, Lipophrys pholis and Coryphoblennius galerita were the most representative species (percentage contribution to total abundance). Peak abundance of fish eggs occurred during May, June and August 2003 and fish larvae occurred during May and July 2003 and August 2002 and 2003; there was a pronounced winter/early spring (March 2003) peak in larval abundance dominated by the small sandeel A. tobianus. This study identifies the occurrence of a conspicuous assemblage of larval fishes at very nearshore shallow environments of a variety of species with different adult habitats: the fish larvae assemblage was dominated by intertidal species. The present study has shown that temporal and spatial variations in the larval fish assemblage are related to environmental conditions and biological dynamics: the results suggest that abiotic conditions mediate biotic parameters, and that both abiotic and biotic characteristics regulated the larval fishes at very nearshore shallow environments.     

Temporal occurrence of ichthyoplankton in relation to hydrographic and biological variables at a fixed station in the St Lawrence Estuary

Spring to autumn temporal distributions of ichthyoplankton and other oceanographic variables were measured at three nearshore stations in the lower St Lawrence Estuary in 1977 and 1978. The seasonal occurrence of various species of fish eggs and larvae was similar from one year to the next. Inshore-offshore gradients in abundance of eggs and larvae of different species appeared to be primarily related to the spawning location of each species. The semidiurnal variability was considerably less than the week-to-week variability in all physical and biological variables measured. The weekly variability is predominantly a function of spatiotemporal interactions, due to the geographic displacement of different water masses and their associated plankton in relation to the neap-spring tidal cycle. The timing and duration of spawning for each common species, inferred from ichthyoplankton distributions, suggest a unique combination of spawning and hatching times, ensuring a succession in the occurrence of larvae through time. Results of the temporal and spatial distributions of the different species of ichthyoplankton are discussed in terms of reduced competitive interactions. The relationship between ichthyoplankton distributions and the plankton production cycle in the St Lawrence Estuary is discussed in comparison with other areas.     

中国近海大气气溶胶的时间和地理分布特征

通过对中国近海10个航次气溶胶观测资料的统计分析得出:(1)从黄海、东海至日本以南海域气溶胶中地壳元素年平均浓度明显减小,在春季尘暴多发期间地壳元素浓度离到岸距离接指数规律递减.污染元素气溶胶浓度分布与陆源排放量和离岸距离有一定关系.(2)海上陆源气溶胶浓度的季节分布为:春季最大,秋冬次之,夏季最小.受日本排放源的影响,日本以南海域污染元素浓度最大值出现在冬季.(3)Se元素浓度与海洋源密切相关.海盐元素从黄海、东海至日本以南海域浓度逐渐增加,主要受周围海况影响,与风速呈现一定程度的正相关.影响近海气溶胶浓度的主要因素有陆源气溶胶排放量、降水分布和大尺度天气形势.     

Spatial and temporal variation in the abundance and composition of ichthyoplankton in a large South Island,New Zealand river estuary

Larval and juvenile fish drifting on ebb tides were collected from early summer to mid autumn at various locations in the Taieri River and Waipori River estuary, South Island, New Zealand. A total of seven species of fish were recorded, however only three species were regularly collected. These were the larval common bully (Gobiomorphus cotidianus McDowall), larval inanga (Galaxias maculatus Jenyns), and postlarval cockabully (Tripterygion nigripenne Valenciennes). Common bully densities were highest in mid January, with the highest densities being recorded drifting out of Lake Waihola. Inanga densities were highest in March and April, with the highest densities being recorded in the channels draining wetland areas where extensive tidal inundation of riparian vegetation occurred. Cockabully were recorded from February to April, mostly at more downstream sites. Inland penetration by marine species was considerable, with two marine species, clingfish (Trachelochismus pinnulatus Forster) and smooth leatherjacket (Parika scaber Forster), being recorded c. 12 km upstream in late summer.     

Abundance and distribution of ichthyoplankton in the upwelling zone off Oregon during anomalous El Niño conditions

The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engraulis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Niño could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.     

Larval fish assemblages in nearshore coastal waters off central Chile: temporal and spatial patterns

In this study we identified spatial and temporal patterns in the distribution and abundance of larval stages of several fish species in nearshore waters off central Chile. Larvae were sampled monthly at two close (20 km apart) but contrasting localities, El Quisco and Las Cruces. Surveys corresponded to standard plankton tows stratified according to bathymetry and distance from shore. Our results indicate that at both localities: (1) there is a seasonal reproductive pattern for most of the species studied; (2) there is a seasonal-related change in larval species composition and abundance, with austral Winter–Spring being the time of greatest diversity; (3) larval stages of several species that, as adults occupy intertidal, estuarine–riverine, subtidal, benthic-demersal, epipelagic or mesopelagic habitats, are found within these coastal environments; (4) there is a distinctive cross-shelf pattern of larval distribution, which seems to correspond, at least for the intertidal species, with the shallower (<30 m depth) portion of area surveyed; and (5) there is a coupling between the patterns of distribution and abundance of the entire ichthyoplankton assemblage with short-term physical features such as wind forcing, Ekman transport, and local currents. Our findings suggest that both the specific composition as well as the abundance of larval fish species varies spatially and temporally and that this variability may result from the interaction of physical and biological factors at different scales.     

春季东海有害藻华高发区仔稚鱼时空分布

根据2011年春季(3月29日—5月27日)海洋综合调查,对东海有害藻华高发水域(28°15′36″~30°30′16″N、121°52′36″~123°15′6″E)的仔稚鱼种类组成、时空分布以及主要优势种与环境因子的相关性进行了探讨。调查共采集到仔稚鱼27种,前几位优势种分别为日本鳀Engraulis japonicus、鰕虎科sp.(Gobiidae sp.)、六丝钝尾鰕虎Amblychaeturichthys hexanema、小黄鱼Larimichthys polyactis,该4种占据了总丰度的91.23%。优势种丰度和发育阶段组成的时空变化显示,日本鳀在调查期间有两次产卵小高峰,其仔鱼孵化后向岸漂流;小黄鱼和六丝钝尾鰕虎在此期间只有一次产卵高峰,其仔鱼在舟山群岛邻近水域进行保育。可以看出,调查水域及邻近水域是部分鱼类产卵,仔稚鱼保育、向岸漂流的场所或途径,是鱼类早期生活史中重要生境,一旦暴发有害藻华,补充群体将受到不良影响。多元分析结果显示,所选环境因子对几位优势种仔稚鱼的分布影响不大,推测产卵场位置和保育方式可能是更重要的原因。     

2004年秋季南海北部浮游植物组成及其数量分布特征

根据2004年9月18日—10月2日南海北部航次所获得的表层浮游植物群数据, 对其组成及数量分布进行了探讨分析。该次调查鉴定浮游植物共53属152种(含变种和变型), 分别属于硅藻门35属88种、甲藻门15属60种、蓝藻门1属2种及金藻门1属1种等; 优势种中分布较广泛的有柔弱伪菱形藻Pseudo-nitzschia delicatissima、反曲原甲藻Prorocentrum sigmoides、微小原甲藻P. mininum、锥状施克里普藻Scrippsiella trochoidea和红海束毛藻Trichodesmium erythraeum等; 浮游植物细胞丰度的数量范围为(0.11—23.61)×106cells•m-3, 呈现近岸区域高于远岸区域的平面分布格局, 最大值和最小值分别出现在海南岛东北部海域的E506站和海南岛东南部海域的B3站; 浮游植物物种丰富度也是近岸的站点较高, 以靠近珠江口E708站的51种为最多。硅藻类细胞丰度范围为(0.02—8.13)×106cells•m-3, 主要分布在高盐的外海水域, 其中产二甲基磺酸丙酯(DMSP)的小环藻Cyclotella spp.在多个站点出现; 甲藻类以近岸水域居多, 细胞丰度最高达15.67×106cells•m-3(E506站), 其中数量较多的赤潮种类主要有锥状施克里普藻、反曲原甲藻、微小原甲藻、环沟藻Gyrodinium spp.等; 固氮的红海束毛藻在调查海域广泛分布, 但主要集中于东部, 以E206站最多, 高达1.8×107cells•m-3。结合水文资料和其他层次的浮游植物资料进行对比分析, 结果表明, 红海束毛藻的分布与黑潮水的入侵存在一定关系, 其分布受水团和海流的影响。     

黄海中南部头足类的群落结构与生物多样性

为掌握黄海中南部头足类的群落结构及数量分布,作者根据2010~2011年间春、秋、冬3个季节的底拖网调查资料,对黄海中南部头足类的种类组成、生物量分布及生物多样性进行了研究。结果显示:3个季节共捕获头足类13种,隶属3目6科6属。各季节的优势种及其生物量比重分别为:春季——双喙耳乌贼(Sepiola birostrata)50.07%、秋季——针乌贼(Sepia esculenta)40.88%、冬季——枪乌贼(Loligo spp.)68.20%。各季节头足类平均资源密度分别为春季4.85 kg/km2、秋季2.52 kg/km2、冬季12.72 kg/km2,春秋两季间差异性不显著(P0.05),冬季与其他两季差异性显著(P0.05)。黄海中南部不同季节头足类的生物量分布变化较大,春季以西南及东北部密度最高,秋季以西南部密度最高,冬季以中部及东北部密度最高。头足类在各水深的垂直分布随季节变化。无论根据生物量还是丰度,种类丰富度指数、均匀度指数及Shannon-Wiener指数等多样性指数均以冬季最高,其次是春季,秋季最低。春季与冬季群落结构相似性较高,秋季与其他两个季节的群落结构相似性均较低。与1998~2000年同期相比,头足类种类数增加5种,相对资源密度增长了12%,枪乌贼类的生物量比重仍最高,耳乌贼类的比重提高,太平洋褶柔鱼的比重则大幅下降。     

东海、黄海浮游植物生物量的粒级结构及时空分布

浮游植物是海洋初级生产力的主要贡献者,初级生产过程是碳的生物地球化学循环的基础,它启动了海洋生态系统的能量流和物质流,支持着大量的渔业生产量.不仅如此,通过复杂的反馈机制,这一过程还对全球气候变化系统产生深远影响.沿岸海域只占全球海洋面积的8%,但却提供了26%的全球生物生产量和2/3到3/4的世界渔业产量.因此,许多重大的国际研究计划,如海岸带陆海相互作用(LOICZ)、全球海洋生态系统动力学研究(GLO-BEC)等,都将近海浮游植物研究作为非常重要的课题.     

南海中、东部海区发光细菌的生态分布与种类组成

初步研究了南海中、东部海区海洋发光细菌的生态分布与种类组成.对28个测站的表层水样和部分测站的水柱垂直分层(50、100、150和200 m)水样进行了发光细菌培养、计数、分离和菌种鉴定.结果表明,水体中发光细菌检出率达76.92%,检出率自表层向底层逐渐升高;观测海区表层海水中发光细菌的平均菌量为(8.60±15.57)CFU/dm3,深层海水的菌量较高,至150 m水层平均菌量达最高值,为(49.47±75.40) CFU/dm3,细菌丰度变幅为3～307 CFU/dm3,平均菌量的最高值和较大的变幅范围都出现在150 m水层;在200 m以浅水体中,发光细菌垂直分布趋势基本与深度的增加以及水温的降低相关联,高值大多出现在100～150 m水层;观测海区发光细菌主要由哈维氏发光细菌Lucibacterium harveyi、曼达帕姆发光细菌Photobacterium madapamensis、明亮发光细菌Photobacterium phosphoreum和费氏发光细菌Vibrio fischeri组成,分别占鉴定种群的42%、33%、19%和6%.