Abundance of Petrolisthes armatus (Crustacea: Porcellanidae) on a tropical estuarine intertidal rocky beach, Gulf of Nicoya estuary, Costa Rica

Population of the porcellanid crab Petrolisthes armatus was studied on a rocky intertidal beach located at the Punta Morales peninsula in the mid upper Gulf of Nicoya estuary, Pacific coast of Costa Rica, from December 1997 to November 1998 (14 dates). Horizontal plankton tows (280 micron mesh net) were also made to verify the presence of P. armatus larvae. Crabs were collected every 3 m along three 18 m long transects, at two sites on the beach, by placing a bottomless bucket fringed with canvas to prevent the organisms from escaping under the rim. A total of 15,382 P. armatus were collected. Only 146 (0.95%) crabs had a carapace length longer than 10 mm, and 8995 (58.5%) were in the size range of 2 to 4.5 mm. The remaining crabs 6241 (40.5%) were in the size range of 4.6 to 10 mm. Male and female P. armatus were represented by 2777 and 3518 individuals respectively, with a sex ratio of 1:1.26. Ovigerous females were found at all dates and included 2937 individuals (83% of females). Plankton tows yielded only 73 larvae of P. armatus (Zoea 1), with a density of 1.2 larvae/m3. No statistically significant seasonal trends in the population of this species were detected. P. armatus appears to reproduce continuously the year around in Punta Morales, and some peaks of abundance were present during the dry and rainy seasons. These trends are similar to trends reported for other crustacean species in the Gulf of Nicoya.     

The phytoplankton community of Punta Morales, Nicoya Gulf, Costa Rica

Three daily samplings of the phytoplankton community were made at two consecutive days in March, April, May, September, October, November and December 1997, at Punta Morales, Golfo de Nicoya, Costa Rica. Samples were collected during each tide at depths of 50% and 10% of light penetration using a Niskin bottle. A total of 43 taxa were identified. Centric diatoms, pennates and flagellates represented 90% of total phytoplankton abundance. In the phytoplankton fraction (cells > 30 microm), diatoms were the most abundant group, and Skeletonema costatum (32%) dominated. In nannophytoplankton (cells < 30 microm), Chaetoceros (23.7%) was the most abundant taxon, followed by flagellates (23%) and Cylindrotheca closterium (13.1%). These results agree with previous surveys and suggest that a typical net phytoplankton community persist through time in the Punta Morales zone. The number of nannophytoplankton fraction cells varied seasonally and suggests quantitative changes in species abundance, with possible modifications of cellular size or chain length in filamentous species. The codominance between S. costatum and Chaetoceros spp. during the rainy season suggested the ocurrence of an early ecological sucession, and nutrients could be the factor generating such population changes.     

Feeding habits of sand smelt (Atherina boyeri, Risso 1810) in Trichonis Lake (Western Greece)

The feeding habits of sand smelt (Atherina boyeri, Risso, 1810) from Trichonis Lake (Western Greece) were investigated. Stomach contents were analyzed from 240 specimens with total lengths ranging from 35 to 112 mm. Samples were taken at monthly intervals (January–December 1997). Of the total number of stomachs examined, 53 were empty (22.1%). However, values varied greatly with season (maximum in January: 50%; minimum in August: 7.6%). Prey analyses of stomach contents identified 15 important items (%Rn > 0.05) belonging to six major groups: crustacean (copepods, cladocera), mollusca (bivalve: larvae), insects (larvae), cestode worms and finfish (fry and eggs). Dominant prey were larvae of the bivalve Dreissena polymorpha (%Rn = 33.8), the copepods Eudiadomus drieschi (%Rn = 26.4) and the cladocera Diaphanosoma brachyurum (%Rn = 24.2). The importance of cladocera and copepods decreased with increasing size of the sand smelt, while the importance of bivalve larvae, fish eggs and finfish fry increased with increasing sand smelt size. Seasonal changes in diet composition and prey abundance in sand smelt stomachs were recorded as coinciding with the seasonal composition and abundance of the zooplankton community in the surface layers of Trichonis Lake. Bivalve larvae were the dominant prey of A. boyeri during January to May, while copepods and cladocera dominated from June to December.     

Zooplankton inputs and outputs in the saltmarsh at Towra Point, Australia

The contribution made by saltmarsh to the production of estuarine zooplankton was examined through a comparison of inputs and outputs of tidal water at a site on Towra Point, NSW, Australia. Saltmarsh proved to be a net exporter of crab and gastropod larvae, although it functioned as a sink for copepods and amphipods. Further, the highest density of zooplankton in estuarine nearshore habitats (saltmarsh, mangrove, seagrass, and open water) during a high tide event was found in the saltmarsh. The presence of high concentrations of zooplankton, predominantly crab and gastropod larvae, in the saltmarsh and lesser extent in the mangrove represents a source of food for estuarine fish.     

Creating conditions for changes in prey community structure by Chaoborus spp. in a lake in Sweden

In Lake G»rdsjön (Southwest Sweden), liming as an experimental improvement of living conditions for pelagic algae, resulted in a significant increase of algal biomass and a reduction of mean cell size. The algal development was beneficial for small sized filter feeding zooplankton, particularly rotifers, which showed a significant increase. The increase in abundance of small sized zooplankton created better food conditions for the smaller instars, and thus a much better overall survival of Chaoborus larvae. The resulting, 6–7 times larger population of Chaoborus larvae significantly changed the structure of the crustacean zooplankton community. Bosmina coregoni, the fastest swimmer of the crustacean species suffered most and was strongly reduced by the increased predation from Chaoborus. The share of cladocerans decreased, while copepods increased in importance.     

Community structure and temporal variability of ichthyoplankton in North Brazilian mangrove creeks

The species composition and dynamics of fish larvae in three mangrove creeks located in the Caeté Estuary (north Brazil) were studied monthly using a trap net during diurnal ebb tides. A total of 109 954 larvae, representing 25 families and 54 species, were collected from October 1996 to October 1997. The community was dominated numerically by a few species, a feature common for other estuarine fish populations. The most abundant taxa were estuarine species, namely the eleotrid Guavina guavina (46·7%) and the engraulid Anchovia clupeoides (14·9%). The sciaenid Cynoscion acoupa was the only marine species that used the mangroves extensively as a nursery site, occurring mainly at the postflexion stage. The size distribution of G. guavina did not produce shifting modes, indicating continuous transport out of the mangroves by tidal currents. Significantly lower species richness was observed in the late rainy season, primarily due to the emigration of marine species. Intermediate seasons were characterized by more complex larval fish assemblages. The temporal trends of the dominant species was influenced to a great degree by their life history strategy.     

2016年夏季长江口邻近海域浮游动物群落结构

根据2016年8月长江口邻近海域27个站位的浮游动物样品数据,对长江口邻近海域的浮游动物群落结构和多样性进行分析,研究了浮游动物群落结构与环境因子的关系.结果表明: 该海区共鉴定出浮游动物93种,隶属于6门12大类群,另有浮游幼体及鱼卵仔鱼15种.其中,桡足类为绝对优势类群,共鉴定出48种,占44.4%;水母类为第二优势类群,共鉴定出12种,占11.1%.该海域出现的主要贡献类群为桡足类、海樽类、毛颚类、枝角类和水母类,平均丰度依次为273.9、115.0、67.1、63.6和61.1 ind·m^-3,其中绝对优势类群为桡足类,贡献率占20.3%.根据环境因子聚类结果,将该海区分为冲淡水影响区和外海水团影响区.单因子相似性分析检验发现,两个区域群落结构差异显著(平均差异性为4.0 %).SIMPER分析发现,对差异性的贡献比例依次是桡足类20.3%、海樽类18.0%、枝角类14.1%、毛颚类13.4%和水母类11.8%.     

Environmental changes and zooplankton temporal and spatial variation in a disturbed Brazilian coastal lagoon.

The Imboassica lagoon, located in the Municipality of Macaé (RJ), is separated from the sea by a sand bar, and its surroundings are partially occupied by residential areas. This coastal lagoon has undergone environmental degradation due to sewage input and artificial sand bar openings. The temporal and spatial variation of environmental variables and zooplankton were studied monthly for four years. There were five artificial openings of the sand bar during the period of study, mostly in the rainy season. Besides osmotic changes, these events caused the drainage of the water of the lagoon into the sea, loss of total organic nitrogen, and an increase of total phosphorus. The zooplankton community of Imboassica lagoon included freshwater and marine taxa, holoplanktonic, meroplanktonic and nectobenthonic forms. Polychaeta, Bivalvia and Gastropoda larvae, and the taxa of Rotifera Hexarthra spp., Lecane bulla, Synchaeta bicornis, nauplii of Cyclopoida and Calanoida copepods were considered constant taxa. Distinct zooplankton assemblages were found during zooplankton spatial surveys in oligohaline and mesohaline conditions. The successful zooplankton populations were either favored by the disturbance of the sand bar opening, such as the veligers of the gastropod Heleobia australis, or capable of fast recovery after the closing of the sand bar, during the succession from a marine into an oligohaline environment, such as Hexarthra spp.. Such populations seemed well adapted to the stress conditions usually found in the lagoon due to osmotic changes, column mixing, nutrient input, and high fish predation pressure. Rare species in the community, such as Moina minuta, presented population increases all over the lagoon under oligohaline conditions.     

Dietary shifts of a dominant reservoir planktivore during early life stages

We studied dietary shifts in the early life stages of gizzard shad Dorosoma cepedianum, a dominant forage species in North American reservoirs. Larval fish and zooplankton samples were collected weekly during spring in Sardis Reservoir, Mississippi, USA. Diet and prey electivity data suggested the existence of three dietary niches during early life stages: microzooplankton (larvae ≤10 mm total length) in which microzooplankters comprised over 90% by number; crustacean zooplankton (larvae 11–25 mm) in which larval gizzard shad consumed substantial numbers of crustacean zooplankton; and microplankton (larvae >25 mm) in which gizzard shad shifted to filtering protozoans, rotifers, and phytoplankton. There was a high overlap (84%) between the diet of larval gizzard shad and crappies Pomoxis spp. during early May. Larval gizzard shad can potentially reduce microzooplankton density through predation, then shift to crustacean zooplankton and drive their density to decline, then revert to filtration of microzooplankton and exploit phytoplankton. Although, gizzard shad have the ability to influence trophic interactions in reservoir ecosystems, their influence may sometimes be masked by the intensity of bottom-up and top-down effects, as well as population and community interactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

长江河口浮游动物的种类组成、群落结构及多样性

于1999年枯水期(2—3月份)、丰水期(8月份)、2000年枯水期(2—3月份)对长江河口浮游动物采样调查,研究了长江河口浮游动物的种类组成、群落结构及多样性并初步探讨了三峡工程对长江河口浮游动物的影响及长江河口水环境的生物监测。调查共发现浮游动物87种,甲壳动物占绝对优势,共59种。在所有浮游动物中挠足类31种。其次为水母类,有9种,此外,枝角类、毛颚类各8种。3次采样浮游动物的优势种主要有河口半咸水种和近岸低盐种类如华哲水蚤(Sinocalanus sinensis)、火腿许水蚤(Schmackeria poplesia)、虫肢歪水蚤(Tortanus vermiculus),真刺唇角水蚤(Labidocera euchaeta)等,还有长江径流带到河口的淡水种如近领剑水蚤（Cyclops vicinus vicinus)、英勇剑水蚤（Cyclops strenuus）、透明溞（Daphnia hyalina)等。一些浮游动物可作为水系指示种,其分布、数量反映了不同水系分布变化,长江河口浮游动物有;类水系指示种。通过对长江河口浮游动物群落聚类分析发现。1999、2000年枯水期浮游动物群落结构相似。可分为河口类群、近岸类群和近外海类群。1999年丰水期只形成近岸和近外海类群。浮游动物种类数由口门内向口门外方向有逐渐增加的趋势。浮游动物种类数由北向南变化趋势一致。大潮与小潮、涨憩与落强等潮汐作用对浮游动物影响往往因采样时间与区域等的不同而不同。对长江河口3次采样的物种多样性指数和均匀度指数进行了计算,结果表明：浮游动物多样性指数1999年枯水期最低,1999年丰水期最高。     

长江口浮游甲壳动物空间分布特征

2010年研究了长江口南、北支浮游甲壳动物的空间分布特征。共采集到浮游甲壳动物50种,其中桡足类39种,枝角类11种。种类数南支高于北支;平均密度北支高于南支,南、北支分别为1.7 ind./L和61.8 ind./L。基于群落相似性矩阵的CLUSTER聚类和MDS分析显示,在群落相似性为40%时,长江口区域浮游甲壳动物群落可分为北支组、南支组1和南支组2共3组。3组的优势种有差异。浮游甲壳动物的平均密度变化趋势为北支组（61.8±22.11 ind./L）〉南支组1（3.07±2.06 ind./L）〉南支组2（0.72±0.45 ind./L）。盐度、潮汐和径流量是影响长江口南北支浮游甲壳动物种类组成、密度和空间分布差异的重要环境因素。     

The dominant copepods <Emphasis Type="Italic">Senecella siberica</Emphasis> and <Emphasis Type="Italic">Limnocalanus macrurus</Emphasis> in the Ob Estuary: ecology in a high-gradient environment

Intensive transformation and sedimentation of suspended matter from riverine runoff occur in estuarine frontal zones. The mesozooplankton community plays an important role in these processes. In the Ob Estuary, the dominant copepods Limnocalanus macrurus and Senecella siberica form dense local aggregations, but only scarce data on the ecology of these species in the estuarine environment are available. We aimed at analyzing the main aspects of the ecology of the two species including their grazing impact on phytoplankton. The distribution (net tows), ingestion rates (gut fluorescence analysis), respiration and excretion rates (incubation experiments), diet composition, gonad development and size of the lipid sacs of these copepods in a high-gradient area of the Ob Estuary were studied during a cruise of the R/V Professor Stockman in September 2013. S. siberica predominantly inhabited the freshwater zone; L. macrurus was more abundant in the estuarine frontal zone. In L. macrurus, adult females and males dominated the population, the herbivorous feeding hardly met the metabolic demands, the specific lipid content was high, and the gonads were developed. In S. siberica, the fifth copepodite stage (CV) dominated. The feeding rate considerably exceeded the metabolic requirements, and the lipid content was variable. The gonads were undeveloped. The two species grazed one-fifth of the phytoplankton biomass and more than 100 % of primary production, with S. siberica responsible for the main part of the total grazing impact (up to 90 %). These results are discussed in connection with the hydrophysical parameters and phase of the population’s life cycle. The obtained results contribute to the knowledge about zooplankton ecology and the transformation of suspended matter in an estuarine high-gradient environment.     

Occurrence of Gobiidae larvae in a tropical Brazilian estuary,with particular emphasis on the use of size classes to categorize species guilds

The structure and seasonal dynamics of larvae of the Gobiidae family in the Mucuri Estuary (Bahia, Brazil) were studied for nine consecutive years. Sampling was conducted at three stations in the lower estuary channel, between 2002 and 2010, in relation to season, day and night and tidal variations. A total of 5802 Gobiidae larvae, representing 15 taxa (12 species and three morphotypes), were collected in the Mucuri Estuary during this time. The highest mean ± s.d. density of fish larvae, 54·7 ± 79·8 larvae 100 m^?3, was recorded during the flood tide and night sampling. Ctenogobius boleosoma was the most abundant species (68%), being dominant in the rainy and dry seasons and had a long reproductive period. This species was classed as a marine estuarine‐opportunist because it was observed at high frequencies and active larvae entering the estuary between 6·1 and 12·0 mm standard length (L_S). Gobionellus oceanicus, second in abundance (12%), occurred only in later larval stages but did not use the estuary as a preferred location for spawning, being classed a marine estuarine dependent. Microgobius carri (11%) was represented in all L_S classes and was resident in the estuary for spawning, remaining there throughout their life cycle. The other species were considered rare due to their low densities and could not be classified in any guild.     

Sustainable control of mosquito larvae in the field by the combined actions of the biological insecticide Bti and natural competitors

Integrated management of mosquitoes is becoming increasingly important, particularly in relation to avoiding recolonization of ponds after larvicide treatment. We conducted for the first time field experiments that involved exposing natural populations of the mosquito species Culex pipiens to: a) application of the biological insecticide Bacillus thuringiensis israelensis (Bti), b) the introduction of natural competitors (a crustacean community composed mainly of Daphnia spp.), or c) a combined treatment that involved both introduction of a crustacean community and the application of Bti. The treatment that involved only the introduction of crustaceans had no significant effect on mosquito larval populations, while treatment with Bti alone caused only a significant reduction in the abundance of mosquito larvae in the short‐term (within 3–10 days after treatment). In contrast, the combined treatment rapidly reduced the abundance of mosquito larvae, which remained low throughout the entire observation period of 28 days. Growth of the introduced crustacean communities was favored by the immediate reduction in the abundance of mosquito larvae following Bti administration, thus preventing recolonization of ponds by mosquito larvae at the late period (days 14–28 after treatment). Both competition and the temporal order of establishment of different species are hence important mechanisms for efficient and sustainable mosquito control.     

Spatiotemporal variability of demersal fish larvae assemblages in the southern region of the California Current

An analysis was conducted of the community structure variability of demersal fish larvae and its relationship with environmental forcing on the west coast of the Baja California Peninsula (25–31°N). The information comes from two data sets of oceanographic cruises in 1997–2000 and 2006–2010. From a total of 190 identified taxa, a high number of species (71) was shared throughout the peninsula. The spatiotemporal contrast in the community structure suggests the separation of two groups (northern and southern) whose boundary is located around Punta Eugenia. The northern group showed an alternate dominance of species with a subarctic-transitional faunistic affinity during the winter and spring and species of a subtropical affinity during summer–autumn. In contrast, the dominant taxa in the southern group have a tropical–subtropical affinity throughout the year, although some taxa of subarctic-transitional affinity also occur during winter–spring. In the spatiotemporal scale, these results suggest that the major cause that modulates the extension and structure of the assemblages is the seasonal oceanic dynamics. Moreover, the intensity of warming or cooling events (El Niño and La Niña) influences the structure of the community on an interannual scale by displacing the zonal boundaries of the groups’ distribution.     

Growth and sex maturation of a population of Saccostrea palmula (Mollusca: Bivalvia), Costa Rica

Growth and sexual maturity in Saccostrea palmula were studied between May 1998 and May 1999, in Morales estuary, Punta Morales, Puntarenas, Costa Rica (n = 540 individuals according to sample size equation). The weight-length relationship for the population was Pt = 2.13 x 10(-2) Lt1.6602 and von Bertalanffy growth function was Lt = 68.2 (l- e -0.1577 t). The mean sex ratio was 1.00 male: 0.92 females with sexually mature individuals found throughout the year. Spawning activity was highest between November and January. The mean condition index (IC = PCF/PV x 100) for the population was 121.53 +/- 2.24 and the mean meat yield was 10.32 +/- 1.64%.     

Proteocephalidean larvae (Cestoda) in naturally infected cyclopid copepods of the upper Paran River floodplain,Brazil

The occurrence, prevalence and infection intensity of proteocephalidean larvae in naturally infected intermediate hosts of the Upper Paran River floodplain are reported. A total of 5,206 zooplanktonic and benthic organisms were analyzed, namely cyclopid (2,621) and calanoid (1,479) copepods, cladocerans (704), rotifers (307), chironomid larvae (41) and ostracods (54). Eight cyclopid copepods - two copepodids, one male and five females - comprising 0.3% of the cyclopid copepods examined, were naturally infected. The male infected belonged to a species of Paracyclops, and the females to Paracyclops sp., Thermocyclops minutus and Mesocyclops longisetus.     

Semiterrestrial meiofauna inhabiting a wet campo in central Brazil, with special reference to the Copepoda (Crustacea)

The wet campo (campo úmido) marsh type is widely distributed in the cerrado region of central Brazil. These marshes develop on slopes along margins of gallery forests where the water table persists at or near the soil surface year-round. Their grass and sedge vegetation covers spongy, highly organic (not peaty) soils. Ground and surface water seeping through the wet campos tends to be slightly acidic (pH about 5), ion-poor (conductivity less than 10 µS cm^–1) and well oxygenated.A typical freshwater meiofaunal community develops in those wet campos where soils remain moist throughout the year (moisture content more than about 60% of soil wet weight). Such a community was studied from 1979–1982 in a wet campo in a protected natural area on the Fazenda Água Limpa of the Universidade de Brasília. It was dominated by nematodes, rotifers and harpacticoid copepods, and included protozoans, turbellarians, cyclopoid copepods, cladocerans, ostracods, oligochetes, hydracarines and several families of aquatic insect larvae. This community was most fully developed in the wetter areas.Species richness of the copepod community is the highest yet recorded in a freshwater system. The 29 species of harpacticoid copepods and 4 species of cyclopoid copepods displayed pronounced zonation which seemed best correlated with soil moisture content and water regime.     

Seasonal and spatial variations of fish trophic guilds in a shallow,semi-enclosed tropical estuarine bay

A study on seasonal and spatial variations of feeding habits and trophic guilds of dominant fish species in Pattani Bay during March 2003 to February 2004 was aimed at classifying diet composition, identifying dominant food components of each species, categorizing trophic guilds of the community and evaluating effects of habitat characteristics and seasonality on guild organization. Most fishes showed high food intake, fed on a diverse range of food items but relied heavily on calanoid copepods and shrimps. All species, with the exception of Epinephelus coioides, were classified as specialist feeders. Four main dietary guilds were classified. Three of these were classified as the guilds dominated by at least two major food items. Significant variations in trophic guilds of 28 fish species based on habitat types and seasons were also identified. They could be divided into three seasonal groups and three site-groups and a single site. Trophic organization for each season and habitat ranged from two to four groups. This information identifies groups of fishes that seasonally and spatially utilize different food resources within a semi-enclosed estuarine bay ecosystem.     

生态育苗池中的桡足类与河蟹苗产量的关系

探讨了辽宁盘锦辽河三角洲地区中华绒螯蟹(Eriocheir sinensis)生态育苗池中出现的近亲真宽水蚤(Eurytemor affinis)和细巧华哲水蚤(Sinocalanus tenellus)与中华绒螯蟹幼体的关系.结果表明：近亲真宽水蚤和细巧华哲水蚤都严重地影响Ⅰ期中华绒螯蟹溞状幼体的成活率,其密度越大,Ⅰ期溞状幼体的成活率就越低(P＜0.01); Ⅲ期中华绒螯蟹溞状幼体可捕食桡足类无节幼体,且捕食量随着无节幼体密度增加而变大(P＜0.01);Ⅴ期中华绒螯蟹溞状幼体和大眼幼体容易捕食到近亲真宽水蚤而很难捕食到细巧华哲水蚤;蟹苗池中大眼幼体的产量与育苗初期池塘中桡足类的数量呈负相关关系,且不同桡足类密度下大眼幼体收获量差异极显著(P＜0.01).提出了控制和利用蟹苗池中桡足类的措施.