Observations on the incidence and seasonal fluctuations of certain crustacean larvae in the plankton of the South-West Coast of India

The seasonal fluctuations in the incidence of planktonic organisms and the larval forms of certain crustaceans such as crabs, barnacles and post larvae of prawns in the plankton of the south-west coast of India have been followed for a period of three years from 1963. South-west monsoon period is the least productive period for zooplankton in this area. Brachyuran zoeae, post larvae of prawns and barnacle nauplii occur in the plankton throughout the year with distinct peaks for different groups. The zoeae ofUca annulipes occur in the plankton from September to May with a peak during November–December. The zoeae ofPortunus pelagicus are present in the plankton from September to June and their abundance is in February–March. The post larvae ofMetapenaeus affinis are found in the inshore plankton from November to June with the peak in March. The nauplii ofBalanus amphitrite communis occur in the plankton in all the months of the year, the peak incidence has been during November January. The zoeae ofU. annulipes are found to tolerate better the medium saline conditions. Of the ecological factors, salinity of the ambient water and the availability of planktonic food for the larvae seem to influence the seasonal fluctuations of these crustacean larvae in this locality.     

On the life-history of Atractoscion aequidens, a migratory sciaenid off the east coast of southern Africa

East coast geelbek exist as a single stock comprising three distinct age/size structured subpopulations. The subadults (1-4 years) occur in the SW Cape, South Africa. They feed principally on anchovy Engraulis capensis , which they follow inshore in summer and offshore in winter. The adults (5-9+ years) undergo a seasonal inshore and longshore migration to Natal where they spawn offshore in spring. During this migration they feed mainly on the pilchard Sardinops sagax , which also move north-eastwards during this time, facilitated by regional oceanographic conditions. 'Adolescent' fish (4/5 years) appear to undergo limited gonadal growth and partially accompany the spawning stock on their migration. It is suggested that the eggs, larvae and early juveniles are transported southwards by the peripheral inshore waters of the Agulhas Current. Juveniles (<2 years) use the SE Cape region as a nursery area for about 1 year, initially feeding on mysids and then switching to anchovy, before moving south-westwards to join the Subadults in the SW Cape region.     

Primary production of plankton and decomposition of organic matter in saline lakes of the crimea peninsula

The lakes under study can be classified as eutrophic-hypertrophic waterbodies according to the level of primary production. High concentrations of suspended matter (up to 7326 g/m³) and total phosphorus (up to 5625 mg/m³) were registered in the lakes. The values of the primary production of plankton and the destruction of organic matter do not depend on the absolute concentration of salts in water. Unlike the destruction of organic matter, the primary production of plankton is higher in winter than in summer. Thus, the accumulation of organic matter in saline lakes occurs mainly in winter. The negative relationship between the primary production of plankton and the biomass of the filter feeder Artemia sp. has been determined.     

Planktonic larval stages of Brachyura in the Gulf of Tigullio (Ligurian Sea,Italy)

Summary

Horizontal planktonic catches made in the Gulf of Tigullio (Genoa, Ligurian Sea) have been analyzed with the aim of identifying the zoeae of Brachyura, whose knowledge is poor in all the northern Mediterranean Sea. Forty-four taxa (42 species plus Liocarcinus spp. and Brachynotus spp.) have been identified, 12 of which were present with all the larval stages. The seasonal distribution of the taxa has been analyzed, and it was possible to recognize species present throughout the year as well as spring/summer, summer/autumn, and winter/summer species. Problems regarding zoeae of dubious identification are discussed.     

DISTRIBUTION OF DIATOMS IN THE PLANKTON OF YAQUINA ESTUARY,OREGON1

The distributional patterns of diatoms in the plankton of the Yaqnina Estuary, Oregon, were, investigated and related to selected climatic and hydrographic factors. Distribution was strongly influenced by seasonal patterns of rainfall resulting in the introduction of a large volume of fresh water into the estuary during fall and winter. Plankton assemblages in spring, summer and fall had fewer diatom species and exhibited a more rapid rate of change in species composition than in winter. Winter assemblages were further characterized by many pennate diatoms, apparently dislodged from the benthos during periods of high freshwater discharge and silt loads. A statistical measure of community difference indicated an increase in taxonomic homogeneity among assemblages throughout the estuary with the onset of the rainy season in late fall and a gradual transition to a more heterogeneous system again during late spring. Canonical correlation ordered 20 prominent diatom taxa along the salinity gradient and identified possible relationships among certain taxa and selected environmental variables, namely visible light energy and temperature. Redundancy in the species data given the environmental data was only 40%, emphasizing the difficulty in demonstrating a quantitive relationship between plankton dynamics in the field and concurrent measurements of chemical and physical variables.     

Larvae of uncommon caridean decapods in the German Bight: Species composition,distribution and abundance

Typically, the most abundant group of shrimp larvae in the German Bight is formed by representatives of the family Crangonidae. Larvae of the remaining species have been largely ignored, and only scarce information concerning their ecology is available. Thus, the purpose of the present study was to determine the species composition, distribution and abundance of noncrangonid shrimp larvae in the German Bight in July 1990, after the mildest winter of the century. The material is based upon plankton samples collected at 77 stations, covering the entire German Bight. Eight species were identified, as well as larvae of Palaemonidae andProcessa-juveniles.Processa nouveli holthuisi (53.0%) andP. modica (31.3%) were predominant in the collection. The distribution of the two species was clearly separated: the main concentration ofP. nouveli holthuisi (peak concentration of 1.94 larvae per m³) was confined to the northwest corner of the German Bight, while a majority ofP. modica larvae (peak concentration of 0.54 larvae per m³) occurred at the southwesterly stations. The spatial distribution ofCaridion steveni andEualus occultus around Helgoland indicates the presence of an adult population at the only rocky island in the study area. Other taxa, such as larvae of Palaemonidae and juvenilePandalina brevirostris were collected exclusively in estuarine habitats. Based upon both the results of the present study and comparable data, we conclude that developmental stages of ten non-crangonid species, as well as representatives of Palaemonidae, can be expected to occur in the plankton of the German Bight. The extremely mild temperatures of the preceding winter may have been, in part, responsible for the relatively high densities of some taxa encountered during our plankton survey. We assume that warm winter temperatures favour the immigration, reproduction and survival of cold-sensitive species.     

First record of picophytoplankton diversity in Central European hypersaline lakes

Our survey has revealed that the phytoplankton in the anthropo-hypersaline lakes of the Transylvanian Basin (Romania) was often dominated by photoautotrophic picoplankton (PPP, cells with a diameter <2?μm). Therefore, the aim of this study was to identify PPP members both in the summer and the winter communities using molecular biological techniques, denaturing gradient gel electrophoresis (DGGE) and sequence analysis. The applied PCR-DGGE methods were highly specific to cyanobacteria and green algae. A total of 11 different plankton taxa were identified that were related to several distant taxonomic groups. PPP were represented by a simple community and consisted of two major genotypes, one from the green algal species Picochlorum oklahomense and the other related to marine Synechococcus isolates (Cyanobacteria). These marine PPP species were recorded for the first time in inland saline lakes from Europe. Besides picoplankton, several additional marine taxa (e.g. cryptophytes and haptophytes) were detected among the nanoplankton species. The presence of the identified marine and hypersaline species could be explained by wind, precipitation or waterfowl transfer; however, this latter could have smaller importance.     

高原鼠兔肠道微生物中丰富及稀有类群的季节性特征

气候及食物是驱动植食性小哺乳动物肠道菌群产生季节性变化的重要因素。然而,此类研究很少涉及肠道丰富及稀有微生物类群。本文以高原鼠兔（Ochotona curzoniae）为对象,通过16S rRNA基因测序和分析,探讨丰富及稀有肠道微生物类群的结构组成、多样性指数及功能在春、夏、秋、冬四季的变化特征。结果显示,丰富类群对菌群主要门和功能的季节性变异贡献大于稀有类群,稀有类群对菌群OTU和alpha多样性的变异贡献大于丰富类群。丰富类群和稀有类群的香农指数均在冬季显著高于其他季节;丰富类群的ACE指数在秋季显著低于其他季节,而稀有类群的ACE指数则在冬季显著高于春季和夏季。丰富类群中拟杆菌门（Bacteroidetes）的相对丰度在冬季和秋季显著高于春季和夏季,但在稀有类群中,夏季和秋季的相对丰度显著高于冬季和春季。丰富类群中氨基酸代谢通路的相对丰度在冬季显著高于春季和夏季,而在稀有类群中,其相对丰度在春季显著高于夏季和秋季。气温、降水量和植被中的营养物质与肠道菌群中丰富类群和稀有类群的变化均显著相关,环境变量对丰富类群和稀有类群变化的总解释率分别为18%（气温：3%;降水：4%;植被营养成分：10%;联合：1%）和9%（气温：1%;降水：2%;植被营养成分：5%;联合：1%）。以上结果表明肠道微生物中的丰富和稀有类群具有不同的分布模式和季节性特征,二者对整体菌群变异的贡献存在差异,环境因素更多地影响丰富类群,反映了肠道微生物不同类群对季节变化响应的非一致性。本研究增进了我们对哺乳动物肠道菌群季节性变化过程及环境适应性的认识。     

Eukaryotic plankton communities across reef environments in Bocas del Toro Archipelago,Panamá

Variation in light and temperature can influence the genetic diversity and structure of marine plankton communities. While open-ocean plankton communities receive much scientific attention, little is known about how environmental variation affects plankton communities on tropical coral reefs. Here, we characterize eukaryotic plankton communities on coral reefs across the Bocas del Toro Archipelago, Panamá. Temperature loggers were deployed, and midday light levels were measured to quantify environmental differences across reefs at four inshore and four offshore sites (Inshore = Punta Donato, Smithsonian Tropical Research Institute (STRI) Point, Cristobal, Punta Laurel and Offshore = Drago Mar, Bastimentos North, Bastimentos South, and Cayo de Agua). Triplicate vertical plankton tows were collected midday, and high-throughput 18S ribosomal DNA metabarcoding was leveraged to investigate the relationship between eukaryotic plankton community structure and inshore/offshore reef environments. Plankton communities from STRI Point were additionally characterized in the morning (~ 08:00), midday (~ 12:00), and late-day (~ 16:00) to quantify temporal variation within a single site. We found that inshore reefs experienced higher average seawater temperatures, while offshore sites offered higher light levels, presumably associated with reduced water turbidity on reefs further from shore. These significant environmental differences between inshore and offshore reefs corresponded with overall plankton community differences. We also found that temporal variation played a structuring role within these plankton communities, and conclude that time of community sampling is an important consideration for future studies. Follow-up studies focusing on more intensive sampling efforts across space and time, coupled with techniques that can detect more subtle genetic differences between and within communities will more fully capture plankton dynamics in this region and beyond.

     

Variability in the inter-island environment of the Prince Edward Islands (Southern Ocean)

Variability in the oceanographic parameters and macrozooplankton and micronekton composition, densities and distributional patterns were investigated during a repeat survey conducted between the Prince Edward Islands in April 1998. Results of this study demonstrated the occurrence of pronounced water pulses along the inter-island trench. The location of the Subantarctic Front to the north of the island plateau, through its interactions with the island group, appeared to have a marked effect on the mesoscale dynamics of physical and biological parameters between and around the islands. Seawater temperature and salinity accounted for >40% of the variation in the zooplankton distribution during the trench studies. A total of 41 macroplankton and micronekton taxa, consisting of subantarctic, subtropical and Antarctic species, were identified. Numerical analyses revealed two major groupings of stations corresponding to an offshore and inshore region. Although there was no evidence for quantitative differences in macroplankton densities between the inshore surveys, offshore plankton biomass was at least three- to eightfold higher than during the trench surveys. The importance of water pulses in carrying stocks of large plankton between the islands appeared to be minimal, at least during the time when the investigation took place. Received: 1 November 1999 / Accepted: 12 February 2000     

Orthophosphate uptake of planktonic microorganisms in Lake Balaton

Seasonal orthophosphate uptake of natural plankton has been studied in hypertrophic and mesotrophic basins of Lake Balaton. Initial uptake of carrier-free labelled phosphoric acid followed first order kinetics in accordance with a single two-compartment model. In isotope equilibrium from 1.2 to 9.7 per cent of radioactivity was found in the filtrate. Turnover times of orthophosphate in water were some minutes in summer and two orders of magnitude longer in winter and April. Turnover time of phosphorus in microorganisms has been estimated on the basis of equilibrium isotope distribution between water and particular phases and turnover time in water. It ranged from 28 to over 1 000 min. The shortest times were found in summer, and the longest in winter. Turnover time of orthophosphate in water increased in relation to phosphate additions according to Michaelis-Menten kinetics. The values of Michaelis-constant plus the ambient orthophosphate concentration (K + S_n) suggested an overestimation of real phosphate concentrations by chemical measurements, being much lower than soluble reactive phosphorus contents in most cases, as it is well-known in many other lakes. Both K + S_n values and maximum uptake velocities (V) were significantly higher in the hypertrophic basin than in the mesotrophic one, in contrast to essentially similar values of turnover times. Maximum uptake velocity per unit chlorophyll-a P _opt:V ratio showed extreme to moderate phosphorus deficiency for Lake Balaton plankton, which seemed to decrease somewhat in the course of eutrophication.     

Comparison of inshore and offshore fish larval assemblages within the wider Yangtze River estuary (China)

It is hypothesized that fish larvae undertake vertical movements in estuarine waters. To test this hypothesis, a sampling period was selected during times when many spring‐spawning fish reach maximum abundance in coastal waters so that spring and summer variations in larval fish assemblages could be determined in the Yangtze River estuary. Six oceanographic surveys were conducted across the salinity gradient of an inshore (freshwater) and offshore area (brackish intersection) during spring (May) and summer (August) between 2010 and 2012. The fish larval community was dominated by species of Engraulidae, Gobiidae, Champsodontidae and Mugilidae. The pre‐flexion and flexion larval stages of euryhaline marine species, which are dependent on estuaries as nursery areas, were common. The brackish and marine larval assemblage was the most abundant with taxa such as Coilia mystus and Engraulis japonicus accounting for more than 57.3% of the total catch. Spatial differences in the taxonomic composition of larval fish assemblages were evident between the inshore and offshore areas. Additionally, the Yangtze River runoff regulatory functions as affected by the Three Gorges Reservoir operational mode (hydrological alternating operations) showed weak influences on fish and habitat environments. Low salinities from high freshwater inflow limited bay anchovy production in the inshore area.     

Early life history timings in marbled rockcod (Notothenia rossii) fingerlings from the South Shetland Islands as revealed by otolith microincrement

Although it has been reported that Notothenia rossii elsewhere hatches in spring, our daily increment back-counting from the capture date in otoliths of fingerlings caught in Potter Cove, South Shetland Islands, in the 2000s, showed two main periods of larval hatching, one in summer (February–March) and another in winter (July). In concordance, the simultaneous presence of two cohorts born the same year was identified in the age/length frequency distribution of fish sampled in spring 2010, which belonged to biological ages 0+ and 1+ and hatched, respectively, in summer and winter–spring. Maximum and minimum ages of pelagic blue-phase and demersal brown-phase fingerlings were, respectively, 227 and 240 days, indicating a demersal settlement after about 8 months from hatching. The estimated growth rate was 0.23–0.33 mm/day, equivalent to that of South Georgia fingerlings and higher than those of other nototheniids of similar size range. Based on early life events associated with the hatching periods, two types of life cycles are hypothesised for South Shetland fingerlings. The pelagic blue-phase fingerlings (6.5–7.6 cm TL, age group 0+) hatched in July (winter cohort), entering in Potter Cove in February–March. The brown-phase fingerlings (6.3–10.6 cm, mostly of age group 0+) hatched in February–March (summer cohort) and were collected in the cove in spring (the smaller specimens) or in summer (the larger ones). Finally, early juveniles (10.7–15.5 cm, age group 1+) hatched in winter, mainly in July (winter cohort), entering in the cove the following year to spend the second winter inshore.     

Contribution of biofilm‐dwelling consumers to pelagic–benthic coupling in a large river

1. Over the course of this 17‐month study, we assessed the potential loss of plankton (bacteria, algae, heterotrophic flagellates) to consumers (ciliates and rotifers) within mature biofilms established on natural substrata exposed to the main current of the River Rhine (Germany). Once a month, in flow cells in a bypass system to the River Rhine, we measured the clearance rates of the biofilm‐associated consumers on the different groups within the natural plankton. 2. Ciliates were the most dominant consumers, among which planktivorous groups, particularly peritrichs and (in spring and summer) heterotrichs dominated. Consumer biomass varied with season, with the highest density occurring directly after the appearance of the phytoplankton spring peak. 3. Clearance rates on plankton ranged from 96 to 565 L m^?2 d^?1 for bacteria and 66–749 L m^?2 d^?1 for algae, with a preference for algae in summer and for bacteria in winter. This pattern coincided with seasonal changes in the structures of the grazer communities. The consumers (both ciliates and rotifers with total standing stocks ranging between 19 and 572 mg C m^?2) imported a substantial amount of organic matter (between 15 and 137 mg C m^?2 d^?1) into the biofilm. 4. These results highlight the potential importance of consumers in the biofilm as a trophic link between the plankton and the benthos, a function that has hitherto mostly been attributed to filter‐feeding bivalves. In contrast to bivalves, the biofilm‐dwelling consumers show a more dynamic response towards the plankton density and composition. Such dynamic components need to be considered when estimating total plankton consumption by the benthos.     

Temporal patterns and variations in phytoplankton community organization and abundance in Narragansett Bay during 1959-1980

Incident irradiance, surface water temperature and phytoplanktonspecies abundances were measured at weekly intervals in NarragansettBay from 1959 through 1980. Stepwise discriminant analyses (SDA)of this 22-year data set indicate that fundamental ecosystemchanges occurred between the 1960s and 1970s, with 1969 beingthe key transitional year in these decadal shifts in phyto planktontaxonomic structure and seasonal abundance. This decadal shiftwas accompanied by the increased summer abundance of small Thalassiosiraspp., which first appeared in 1966 and by 1969 became the sixthmost important phytoplankton component in this bay. Decadaltrends in phyto plankton community organization and abundancewere also accompanied by distinct long-term climatological gradientsof temperature and light. The 1960s were generally colder andbrighter than the 1970s. Prior to 1969, the annual phytoplanktonmaximum occurred most commonly during winter; in the 1970s,the annual maximum generally shifted to a summer event. Three5-year phytoplankton cycles occurred between 1959 and 1974.During each pentade, the phytoplankton community returned toa similar taxonomic organization and abundance cycle after divergingin the intervening years. Pentade cycles did not occur after1974; the phytoplankton community thereafter diverged significantlyfrom each preceding year. Five species [Skeletonema costatum,Detonula confervacea, Asterionellopsis glacialis, Hererosigmaakashiwo (= Olisthodiscus lureus) and Thalassiosira nordenskioeldii]dominated the phytoplankton over the 22-year period. SDA revealeda high degree of similarity and constancy in the annual occurrencepatterns of these taxa. The decadal shifts revealed by SDA weremore directly related to the considerable interannual variabilitythat characterized the abundance and seasonality of the lessabundant species.     

广州抽水蓄能电站蓄水库蓄水初期浮游生物调查

对我国首座核电站配套工程的抽水蓄能电站水库蓄水初期的浮游生物进行了调查。蓄水水库由上下两水库组成。两水库的浮游生物种类组成显著不同。上水库浮游植物共记录到３０种（属）,浮游动物１２种（属）;下水库浮游植物１９种（属）;浮游动物２５种（属）。上下两水库浮游生物数量均较贫乏,表明浮游生物群落尚处于初期发育阶段,但在局部浅水处已出现小规模的蓝藻水花,认为是水库蓄水初期必然的结果     

Phytoplankton in Two Ponds in Kathmandu Valley (Nepal)

A qualitative and quantitative analysis of the plankton of two ponds in Kathmandu Valley (Nepal) was made. Vertical and seasonal variations of the plankton of one pond were studied as well as physical and chemical properties of the water (temperature, visibility, electrical conductivity, pH-value, alkalinity). During the dry winter the number of plankton species and individuals was low. In summer, before the onset of the monsoon mass developments of different μ-algae and Ceratium hirundinella occurred.     

A phylogenetic analysis of the evolution of moult strategies in Western Palearctic warblers (Aves: Sylviidae)

Adult birds replace their flight feathers (moult) at least once per year, either in summer after termination of breeding or (in the case of some long-distance migratory species) in the winter quarters. We reconstructed the evolutionary pathways leading to summer and winter moult using recently published molecular phylogenetic information on the relationships of the Western Palearctic warblers (Aves: Sylviidae). Our phylogenetic analysis indicates that summer moult is the ancestral pattern and that winter moult has evolved 7–10 times in this clade. As taxa increased their migratory distance and colonized northern breeding areas, summer moult disappeared and winter moult evolved. Our data also allows us to trace the historical origins of unusual moult patterns such as the split-moult and biannual moult strategies: the most parsimonous explanations for their origins is that they evolved from ancestral states of summer moult. We briefly discuss our results in the light of recent criticisms against phylogenetic comparative methods and the utility of historical versus functional definitions of adapation.     

Observations on the hydrography and inshore plankton of the bay of Bengal of Balasore

The hydrographical features and the inshore plankton of the northern part of the Bay of Bengal was studied from the Balasore coast. The hydrology is mainly governed by the monsoons and river systems flowing into the bay. The surface temperature showed a bimodal pattern with a summer and autumn maximum. The salinity was below the oceanic average with the lowest value during October. The coastal water was found to be rich in nutrients, with peak values during the southwest monsoon. Three phytoplankton blooms followed by zooplankton maxima were observed between early spring and late fall.     

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

Longitudinal variations of phytoplankton biomass and composition were assessed in a 250 km-long section of the St.Lawrence River, which alternately runs through narrow (< 2 km) river cross sections and wide (up to 10 km) fluvial lakes. In the main river stem, concentrations of suspended matter and total phosphorus increased with distance downstream, whereas light penetration decreased. Seasonal changes in plankton composition and biomass were more important than those resulting from differences in water mass (tributary) of origin. Sampling at three cross river sections and in two fluvial lakes showed a progressive downstream decrease in phytoplankton biomass and changes in size structure and taxonomic composition. River plankton was primarily composed of small (< 10 µm equivalent spherical diameter), truly planktonic cells belonging to Cryptophyceae and diatoms, with Chlorophyceae in summer. Plankton sampled in summer among rooted macrophytes in fluvial lakes exhibited a higher biomass of resuspended periphytic algae than in the main river stem, which contributed slightly to downstream phytoplankton biomass.Successive river cross sections always shared about 50% of their taxa, indicating a rapid downstream transport of algae within the main water mass. However, the proportion of species common to all cross sections was highest during the spring freshet, and lowest during summer low discharge, likely resulting from the development of a distinct flora in fluvial lakes during summer. Conversely, about 30% of the identified taxa were exclusive to a cross section and were replaced by others occurring downstream. Overall, phytoplankton composition along the St.Lawrence River is primarily controlled by advective forces, which result in a homogeneous flora in the main river stem, with a local contribution of resuspended periphyton from fluvial lakes.