Distribution of Japanese temperate bass, <Emphasis Type="Italic">Lateolabrax japonicus</Emphasis>, eggs and pelagic larvae in Ariake Bay

We collected eggs and larvae of the Japanese temperate bass, Lateolabrax japonicus, and present horizontal and temporal changes of distribution relative to development and growth during the species pelagic life history in Ariake Bay. Sampling was conducted from the inner to central region (11 sampling stations) of Ariake Bay using a plankton net (80 cm diameter, 0.5-mm mesh) from November 2000 to February 2001. Both eggs and larvae were collected most abundantly in mid-December. The CPUE of eggs in the surface layer was higher than the middle layer, which is in contrast to that at the larval stage. Most eggs were collected around the central and western regions of the bay. The distribution of eggs shifted vertically to the middle layer with development. Yolk-sac larvae were collected in the central region of the bay, and preflexion and flexion larvae were more abundantly collected in the inner region of the bay. The body length of larvae around the inner bay was larger than in the central region. The pelagic life history can be summarized as follows: eggs are distributed around the central region of the bay and eggs and larvae expand their distribution to the inner and shallower waters with growth. We conclude that the shift of vertical distribution in pelagic stages and the hydrographic features of the middle layer form one of the mechanisms enabling the inshore migration of L. japonicus.     

Spatio-temporal overlap of the alien invasive ctenophore <Emphasis Type="Italic">Mnemiopsis leidyi</Emphasis> and ichthyoplankton in the Bornholm Basin (Baltic Sea)

In 2007 the alien invasive ctenophore Mnemiopsis leidyi A. Agassiz 1865 was recorded for the first time in the Bornholm Basin, an area which serves as important spawning ground for Baltic fish stocks. Since M. leidyi is capable of preying upon early life stages of fish and further might act as food competitor for fish larvae, it is of major concern to investigate the potential threat that this non-indigenous species poses to the pelagic ecosystem of the Baltic Sea. The present study investigates the temporal and spatial overlap of M. leidyi with eggs and larvae of Baltic cod (Gadus morhua L.) and sprat (Sprattus sprattus L.) in order to assess the potential impact of this new invader on two of the most important Baltic fish stocks. Results show variable inter-seasonal distribution and overlap dynamics and thus different seasonal threat-scenarios for the early life stages of cod and sprat. The spatial overlap between M. leidyi and ichthyoplankton was low for most of the period observed, and we conclude that M. leidyi presently does not have a strong impact. However, we detected situations with high overlaps, e.g. for sprat larvae and cod eggs in spring. As the population dynamics of M. leidyi in the central Baltic are not yet fully understood, a future population explosion of the alien ctenophore with possible effects on fish recruitment cannot be ruled out. Furthermore, a possible shift in peak spawning of cod to the early season, when ctenophore abundances were relatively high, might increase the impact of M. leidyi on cod.     

Winter aspects of the ichthyoplankton community in Antarctic Peninsula waters

Summary Ichthyoplankton was sampled from the Antarctic Peninsula area of the South Polar Ocean in early winter (May and June 1986). A total of 153 eggs from two species and 1368 larvae or juvenile stages from 12 species were obtained. These included pelagic species, and demersal species with a long pelagic larval or juvenile phase. Most abundant were larvae of Pleuragramma antarcticum and Notothenia kempi, and eggs of Notothenia neglecta. The distribution of notothenioid and paralepidid larvae was apparently unaffected by ice cover, whereas myctophid larvae were confined to ice-free waters. Areas where newly hatched Chionodraco hamatus occurred coincided with dense aggregations of Euphausia superba (Krill) furcilia larvae which is a potential food resource during winter. The hatching of icefish larvae during winter is apparently independent of the seasonal production cycle. Epipelagic eggs of Notothenia neglecta were found during the spawning season, which suggests that eggs ascend to the surface after demersal spawning and that development takes place near the sea surface during winter. Larvae of Notothenia kempi were chiefly confined to shelf and slope waters to the west of the Antarctic Peninsula, with larger larvae found in coastal shelf areas. Pleuragramma antarcticum occurred in the coastal waters off the Biscoe Islands, in the Gerlache Strait, and in the northern Bransfield Strait. The smallest larvae were found in the northern Bransfield Strait, whereas those at the Biscoe Islands and in Gerlache Strait waters were larger and of a similar size. A cyclonic gyre to the west of the Antarctic Peninsula observed in the austral summer was likely to have affected the larval drift of Pleuragramma antarcticum and Notothenia kempi. Differences in the timing of spawning and hatching and the vertical distribution of these larvae will lead to different transport and spatial distribution patterns. It is hypothesized that early winter conditions do not imply severe limitations on the year-class success of larval fish. Dispersal and increased mortality may occur during the second half of the winter.     

Predation by sprat and herring on pelagic fish eggs in a plaice spawning area in the Irish Sea

Predation on planktonic fish eggs was examined by stomach content analysis of sprat and herring sampled in a plaice spawning area to the east of the Isle of Man in March 1993. Plankton samples were taken to examine prey selection. The clupeids showed a selection for the later developmental stages of plaice eggs. Plaice eggs had a refuge in size from predation by sprat <80 mm total length which selected smaller non-plaice eggs. However, herring and sprat >80 mm total length showed a strong selection for plaice eggs, presumably due to their large size.     

中街山列岛海域鱼卵、仔稚鱼群落结构特征及其与环境因子的关系

为了解中街山列岛海域鱼卵仔稚鱼空间分布、种类组成及与环境因子的关系,于2010年5月—2012年2月在中街山列岛海域利用水平和垂直拖网开展了8个航次的鱼卵、仔稚鱼调查。运用非度量多维标度排序、聚类分析和典范对应分析(CCA)等方法对该海域鱼卵、仔稚鱼的空间分布进行了综合分析。结果表明:两年水平拖网共采集到鱼卵1783粒,仔稚鱼67尾;垂直拖网共采集到鱼卵576粒,仔稚鱼59尾。2010年平拖优势种为短吻红舌鳎(Cynoglossus joyneri),垂拖重要种为鲉形目未定种(Scorpaeniformes sp.)和扁舵鰹(Auxis thazard)。2011年平拖重要种为短吻红舌鳎、鰏属未定种(Leiognathuss sp.)、龙头鱼(Harpodon nehereus)和鳀(Engraulis japonicus);垂拖重要种为短吻红舌鳎、龙头鱼和中华小公鱼(Stolephorus chinensis)。经单因子相似性分析(ANOSIM),鱼卵仔稚鱼的优势种和重要种群落物种组成存在显著差异(P<0.01)。研究结果表明,温度和盐度对鱼卵仔稚鱼的影响较大,夏季是中街山列岛...     

Modelling population dynamics of the pelagic larval shrimp Metapenaeus ensis in the Osaka Bay estuary

Aiming at providing numerical tools useful to assess the impacts of coastal development pressures on marine life, a Lagrangian model for population dynamics of pelagic eggs and larvae of the greasyback shrimp, Metapenaeus ensis, in Osaka Bay was developed and improved based on laboratory experiments. The model was combined with a 3-D Eulerian numerical model that predicts physical and biological conditions of the habitat. A series of numerical experiments was done to investigate their transport processes from the spawning grounds, and the concentration process of full-grown larvae towards the mouth of Yodo River that flows into the innermost basin. Model results revealed, as a general tendency, that the early larval developmental stages through nauplius to zoea continue to drift like a passive tracer, and begin to concentrate at the river mouth area after the mysis stage, mainly avoiding low saline environment in the surface layer. This suggests that the full-grown larvae may be favored with chance to take advantage of the river-induced gravitational circulation that dominates the innermost estuarine basin. In addition, it was found that tidal condition around the spawning period also exerts a considerable influence upon the fate of pelagic larvae.     

Fish eggs and larvae in the diet of herring Clupea harengus membras Linnaeus, 1758 and the sprat Sprattus sprattus balticus (Schneider, 1904) (Clupeidae) in the Southeastern Baltic Sea

The qualitative and quantitative composition of fish eggs and larvae in the stomach contents of Baltic herring and sprat was examined. The occurrence of fish eggs and larvae in the diet of herring was markedly higher, compared to sprat. Eggs of four and larvae of nine fish species were found in the herring stomachs. The prey species composition of the herring and sprat diets was related to the ichthyoplankton composition and to the degree of overlapping of the prey and predator distributions. Sprat eggs were the predominant prey in the herring diet in May and sprat larvae prevailed in August. The daily ration estimates indicate that the sprat larvae consumption by herring in August exceeded the sprat egg consumption in May by many times. Cod eggs in the herring stomachs were only found at the optimal oxygen content and salinity for the cod eggs in the near-bottom water layer.     

The abundance and patterns of the egg and larval spatial distribution of Eastern Baltic cod Gadus morhua callarias (Gadidae) in 1931–1996

According to ichthyoplankton surveys of AtlantNIRO and published sources, the data on abundance of eggs and larvae of eastern Baltic cod Gadus morhua callarias at different spawning grounds of the Baltic Sea in 1931–1938, 1949–1956, and 1991–1996 are considered. We show that a similar type of spatial distribution of eggs and larvae of cod with localization of the greatest amount of its early ontogenetic stages in the Bornholm Basin in the southwest of the sea was observed in the 1930s and 1990s. The extension of the area of distribution was accompanied by an increase in the numbers of eggs and larvae of cod in all areas of the sea, and its decline was followed by a decrease in numbers, in the first turn, at northeastern spawning grounds in the Gotland Basin. The period of high numbers of eggs in 1949–1956 coincided with the century maximum of salinity of the near-bottom water layer.     

Eggs and larvae of the 'curvina' Plagioscion squamosissimus (Heckel, 1840) (Osteichthyes, Sciaenidae) in the Baia River, Mato Grosso do Sul State, Brazil

The aim of this work was to study the eggs and larvae of the‘curvina’, specifically the examination of spatialand temporal variation, location of spawning and dispersal groundsand verification of the relationship between occurrence andenvironmental variables. Sixteen collection sites were establishedin the Baía River, Brazil, and grouped into four areas.Collections were carried out between February 1999 and April2000. Spatial and temporal variations were analysed using ANOVA.Identification of the spawning and dispersal grounds was carriedout using development stage distribution. The relationship betweenoccurrence and the environmental variables was determined usingPrincipal Components Analysis (PCA) and Pearson correlation.The eggs were found in every area practically every month, almostexclusively in the initial embryo stage, while the larvae occurredin every area mainly between October and April. The correlationbetween PCA scores and organism occurrence demonstrated thatthe highest catches occurred when the values of temperature,water level and rainfall were high and those of dissolved oxygenand pH were low. This specie spawns and develops in lentic areas,and the lotic stretch serves as a dispersal route through whichthe eggs and larvae are transported.     

Distribution and abundance of coral plankton

High densities of eggs and larvae of scleractinian corals were found in plankton samples after mass, multi-specific spawnings on inshore high island fringing reefs in the central Great Barrier Reef region. Immediately after spawning, vertical stratification was observed with eggs concentrated on the surface. Larvae were found to be distributed vertically and horizontally within 12 hours of spawning. Larval development over the subsequent 6–7 days was associated with an increase in the length/width ratios of larvae and their volumes. Influxes of mature larvae onto the study reef were observed 3–6 days after spawning. The relative success of the sampling in relation to other reports in the literature, and the future for more informed work on the larval ecology of corals are discussed.     

Field observations on the developmental ascent of larval Euphausia superba (Crustacea)

Summary Marr's (1962) hypothesis on the descent of eggs and ascent of early larvae of Euphausia superba is examined in the light of investigations prior to and including field investigations in January 1985. Two deep stations (4100 m) west of the South Orkney Islands yielded more than 6600 eggs and early larvae per 100 m³ in the 1000 to 2000 m layer; also below 2000 m eggs and naupliar stages occurred. Sinking speed and sinking depth of krill eggs are discussed in the light of laboratory experiments of Marschall (1983), Quetin and Ross (1984), and George and Strömberg (1985). Hatching depths calculated from the experimental data on sinking rate and incubation time tend to be shallower than the deep occurrence of krill eggs at sea. Possibly krill may spawn not only near the surface but also at depths of several hundred meters. The high abundance of naupliar stages in smaples from our deepest layer corrobrate the presumption of Marschall and Hirche (1984) that the nearly immobile nauplii still sink and that the larvae begin to rise only when they have reached the metanaupliar stage.     

Embryonic development,larvae and juvenile of elkhorn sculpin,Alcichthys alcicornis

The eggs ofAlcichthys alcicornis were spawned in tank at the laboratory and reared for the studies of embryonic, larval and juvenile development. This species takes place entosomatic fertilization, and females spawn fertilized eggs after copulation. The eggs are demersal and adhesive, released as a clump forming a thin layer on the bottom of tank. There was no significant difference in embryonic development between this species and other oviparous teleostean species. Hatching occurred between 17 and 18 days after spawning at a mean water temperature of 8.5?C. The newly hatched larvae averaged 4.44 mm in body length (BL). The larvae attained to post-larval stage at 5.80 mm BL, and juvenile stage at 10.2 mm BL. A specific feature of the post-larvae was the appearance of three lines of the melanophores on the caudal part of fin fold. Carotenoid first appeared on the nape at 8.70 mm BL, heavily emerged beyond 12.9 mm BL, and turned up on the back also beyond 15.2 mm BL. Scales on the lateral line were completed by 18.5 mm BL. Three pairs of flaps were observed on the dorsal surface of the head at 37.0 mm BL. External features of adult specimens are almost completed by 52.0 mm BL, yet the tip of the first preopercular was not branched but remained simple.     

山东半岛南部产卵场温跃层对鳀鱼鱼卵垂直分布的作用

2000～2004年5～7月"北斗"号生物资源调查船对山东半岛南部产卵场进行多学科综合调查期间,于2003年6月17～18日和6月27～30日分别在35°01.9′N、120°32.9′E海区和35°03.3′N、120°26.4′E海区进行了25 h和64 h的水团追踪观测调查,鳀鱼鱼卵的数量、垂直分布与水温的分布为重点调查内容.调查结果表明:水温垂直分布的变化、海水混合的强弱、水体的辐聚/辐散等物理过程对水体中鳀鱼鱼卵数量和鳀鱼鱼卵在不同水层的分布有很大影响.温跃层分布深度的波动引起水体的垂直交换(混合)、水平对流(辐聚/辐散)和跨跃层的物质交换.温跃层深度变浅时,上混合层水体的厚度变薄,跨跃层的向上混合,将下混合层水体中和温跃层中的鳀鱼鱼卵输运到温跃层和上混合层中,同时表层水体发生辐散现象,使得下混合层、温跃层和上混合层水体中鳀鱼鱼卵数量减少、密度减小,导致整个水柱内鳀鱼鱼卵的数量减少;温跃层深度加深时,上混合层水体的厚度增加,跨跃层的向下混合,将上混合层水体中和温跃层中的鳀鱼鱼卵输运到温跃层和下混合层水体中,同时表层水体发生辐聚现象,使得上混合层、温跃层和下混合层水体中的鳀鱼鱼卵数量增多、密度增大,导致整个水柱内鳀鱼鱼卵的数量增多;温跃层水体中鱼卵数量和密度的变化较上混合层和下混合层水体更为显著.水体中温跃层的存在、温跃层分布深度的波动及其波动的程度对上混合层和温跃层中鳀鱼鱼卵的数量和密度的变化起着主导作用,导致鳀鱼鱼卵数量垂直分布的剧烈变化.     

Specific gravity and vertical distribution of sprat eggs in the Baltic Sea

During peak spawning of sprat Sprattus sprattus in the Baltic Sea in May–June egg specific gravity averaged ± s . d . 1·00858 ± 0·00116 g cm⁻³ but was significantly higher in the beginning and significantly lower towards the end of the spawning season. A close relationship was found between egg diameter and egg specific gravity ( r ² = 0·71). This relationship, however, changed during the spawning season indicating that some other factor was involved causing the decrease in specific gravity during the spawning period. The vertical egg distribution changed during the spawning season: eggs were distributed mainly in the deep layers early in the season, occurred in and above the permanent halocline during peak spawning, and above the halocline towards the end of the spawning season. Consequently, poor oxygen conditions in the deep layers and low temperatures in layers between the halocline and the developing thermocline may affect egg development. Thus, opportunities for egg development vary over the spawning season and among spawning areas, and depending on frequency of saline water inflows into the Baltic Sea and severity of winters, between years.     

Resistance to thermal stress in preadult Drosophila buzzatii: variation among populations and changes in relative resistance across life stages

Resistance to a short term exposure to a high temperature stress was examined in eggs, larvae and pupae of Drosophila buzzfltii from seven localities. Across development, pupae were most resistant, followed by eggs, and then first and third-instar larvae. Variation among populations for resistance to heat stress was significant in all life stages. However, there was much less variation among populations where measured as eggs and pupae than for both first and third instar larvae. Older larvae showed large changes both in viability and developmental time, while exposure of young larvae to heat stress led to a decline in viability without delayed development. Populations that had the shortest developmental time at 25^oC were relatively the most resistant to heat stress as larvae. High relative resistance at one preadult life stage was not necessarily associated with relatively high resistance at another, or with previous measurements of resistance for adults from these populations. Comparison of populations that were more similar in their pattern of change in resistance across development suggested a relationship with the climate of origin. The possibility that developmental variation in the expression of heat shock proteins may cause variation in resistance to thermal stress for different life stages is discussed.     

Larval retention and dynamics of the prawns Palaemon longirostris H. Milne Edwards and Crangon crangon Linnaeus (Decapoda,Caridea) in the Mira estuary,Portugal

Summary

Palaemon longirostris and Crangon crangon larval and post-larval stages were collected intensively in two 24-h cycles during neap and spring tidal periods in a fixed station located in the mid-Mira estuary (southwest Portugal). In each case, on the previous day, horizontal distribution of larval stages was studied in a series of 20 stations from the mouth of the estuary to near freshwater. Horizontal distribution of the discrete instars of both species were similar, suggesting larval retention. Results from the 24-h cycles indicate a semilunar cycle of larval release activity, and an initial displacement of the larvae from the parental stock, as newly-hatched larvae concentrate in the surface layer of the water column on post-crepuscular ebbing tides. The sequence of larval stages tends to be progressively more dependent of the bottom layers, and the whole larval and post-larval development is accomplished within the estuarine boundaries. Larval release cycles, coupled with duration of development and progressive change in vertical position, induce mutual exclusion of different aged larvae, which may minimise cannibalistic behaviour and competition between larvae with different capabilities.     

The choice of oviposition site and the effects of density and oviposition timing on survivorship in<Emphasis Type="Italic"> Rana japonica</Emphasis>

In species that lack parental care and whose larvae are restricted to a given space throughout development, choice of egg-laying or reproductive sites often greatly influences fitness. Furthermore, reproductive success of individuals may be affected not only by conditions of the breeding area but also by the time when they start to breed, because intraspecific variation in the timing of breeding may result in asymmetric competition between larvae. We addressed these issues in an experimental and field study of the Japanese brown frog, Rana japonica. We tested whether the survival success of larvae decreased with an increase in the number of deposited egg masses and with a greater delay in oviposition. We found that the number of egg masses and timing of oviposition together significantly predicted larval survival per clutch. Moreover, we observed the natural oviposition of R. japonica to examine the prediction that if the density of larvae and the timing of oviposition affect survivorship of larvae, R. japonica will avoid depositing eggs in pools in which egg masses have already been deposited. We found that for small pools only, R. japonica tended to favor oviposition at unoccupied pools (those lacking egg masses and larvae) in the spawning season. For large pools, however, adults favored those already occupied by egg masses in the spawning period. The density of egg masses and tadpoles or the timing of oviposition may have less effect on spawning or the survival of tadpoles in large pools than in small pools.     

Born among the ice: first morphological observations on two developmental stages of the Antarctic silverfish Pleuragramma antarcticum, a key species of the Southern Ocean

The Antarctic silverfish Pleuragramma antarcticum is a keystone species in the Southern Ocean ecosystem, providing one of the major links between lower and higher trophic levels. Despite the importance of this species, surprisingly little is known of its early development. The first spawning area for the silverfish has been recently identified in the near-shore of Terra Nova Bay (Ross Sea). Evidence indicates that spawning and embryo development occurs in the cryopelagic environment, below the seasonal pack-ice. In order to contribute to the knowledge of the life cycle of this very important Antarctic species, we carried out the first histological characterization on pre-hatching embryos and newly hatched larvae. Embryonated eggs and larvae of P. antarcticum were collected between late October and November 2005 at TNB through holes drilled into the sea ice. Embryonic stage just before hatching and the first post-hatching stage were the most abundant within our samples and thus were analysed using both macroscopic and histological approaches. Early life stages of the Antarctic silverfish revealed interesting features: the sensory system, foraging apparatus and heart appeared well developed, whereas the liver and gills were underdeveloped. Morphological details of the organogenesis were performed, providing the first substantial information on the development of P. antarcticum and representing a further steps towards the knowledge of the life cycle of this important Antarctic key species. An erratum to this article can be found at     

Oxygen and salinity characteristics of predator–prey distributional overlaps shown by predatory Baltic cod during spawning

In the distributional overlap volume of Baltic cod Gadus morhua and its prey, studied in the Bornholm Basin in the southern Baltic Sea, only a fraction of the sprat Sprattus sprattus population vertically overlapped with the Baltic cod population. Sprat occurred in the intermediate water, in the halocline and in the bottom water, while herring Clupea harengus and Baltic cod occurred exclusively in the halocline and in the bottom water. Only parts of the sprat population were hence accessible for Baltic cod, and only a fraction of the sprat had access to the Baltic cod eggs below the halocline. Baltic cod–clupeid overlap volumes appeared to be determined by salinity stratification and oxygenation of the bottom water. Hydrography time series were used to estimate average habitat volumes and overlap from July to September in 1958–1999. In the 1999 survey spawning Baltic cod had greater ratios of empty stomachs and lower average rations than non-spawning Baltic cod. The average ration for Baltic cod caught within 11· 4 m from the bottom (demersal) did not differ from the average ration of Baltic cod caught in shallower waters (pelagic), because spawning and non-spawning Baltic cod in both strata were caught at equal rates. The diet of the Baltic cod caught demersally contained more benthic invertebrates, especially Saduria entomon, but Baltic cod caught pelagically also had fresh benthic food in their stomachs, indicating vertical migration of individual fish.     

Parasitism of Western Corn Rootworm Larvae and Pupae by Steinernema carpocapsae

Virulence and development of the insect-parasitic nematode, Steinernema carpocapsae (Weiser) (Mexican strain), were evaluated for the immature stages of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Third instar rootworm larvae were five times more susceptible to nematode infection than second instar larvae and 75 times more susceptible than first instar larvae and pupae, based on laboratory bioassays. Rootworm eggs were not susceptible. Nematode development was observed in all susceptible rootworm stages, but a complete life cycle was observed only in second and third instar larvae and pupae. Nematode size was affected by rootworm stage; the smallest infective-stage nematodes were recovered from second instar rootworm larvae. Results of this study suggest that S. carpocapsae should be applied when second and third instar rootworm larvae are predominant in the field.