Egg Abundance Research Articles

Assessing the efficacy of two new formulations of larvicide pyriproxyfen for the control of Aedes aegypti using dissemination stations in two sites of Rio de Janeiro city.

BACKGROUND Aedes aegypti is the primary transmitter of several arbovirus with great impact in human health. Controlling vector mosquitoes is an essential and complex task. One promising control method is to use mosquitoes as a vehicle to disseminate tiny particles of juvenile-killing insecticides, such as pyriproxyfen (PPF), to breeding sites. OBJECTIVES We aimed to investigate the capacity of Ae. aegypti to disseminate two new formulations of PPF in two sites of Rio de Janeiro city for assessment of the efficacy of these products. METHODS Dissemination stations impregnated with powder and liquid new formulations of PPF were installed in two test sites. Ovitraps were used in the test sites and in a control site for monitoring the presence of Ae. aegypti throughout eggs collection. FINDINGS Entomological indices indicated that the new formulations of PPF were efficient in reducing eggs abundance. Liquid formulation performed better than powder formulation. Ready-to-use formulations of PPF can be quickly applied in the field and can be replaced after a few months.MAIN CONCLUSIONS New formulations of PPF associated with mosquito dissemination approach make a valuable vector control strategy, managing to cover places of difficult access for whatever reason. New formulations application requires less labour, being economically attractive.

Control strategies for a population dynamics model of Aedes aegypti with seasonal variability and their effects on dengue incidence

Aedes aegypti female mosquitoes are the principal transmitters of dengue and other vector-borne infections. This species is closely associated with human habitation, due to its blood-feeding habits and the presence of breeding sites widely available around households. In this paper, we introduce a mathematical model for the life cycle of Aedes aegypti mosquitoes comprising two stages, aerial and aquatic, that reflects seasonal changes in the mosquito abundance. This model is further amended by three season-dependent control actions. Two coercive actions are introduced during the hot seasons characterized by higher abundance and enhanced growth rates of mosquitoes. They consist in the application of two chemical substances, insecticide and larvicide, acting upon the aerial and aquatic mosquito stages, respectively. During the cool seasons, characterized by the slower growth rates of mosquitoes and abundance of quiescent unhatched eggs, we introduce a preventive vector control measure consisting in mechanical elimination of mosquito breeding sites. Using the framework of optimal control in combination with the cost-benefit approach and epidemiological assessment, we identify the most efficient strategy capable of essentially reducing the population of adult and immature mosquitoes during both seasons and provide a sketch for its modus operandi.

ИХТИОПЛАНКТОН АВАЧИНСКОЙ ГУБЫ В 2014–2017 ГГ.

Species composition of ichthyoplankton community was analyzed, relative abundance of eggs and fish larvae and seasonal changes in the qualitative composition of ichtyoplankton catches was estimated based on the data of the complex researches in Avachinskaya Bay in 2014–2017. In general 25 species from 11 famelies were found for the whole period of researches in the waters of Avachinskaya Bay. The eggs and the larvae revealed in our catches represented the families, including Pleuronectidae, Gadidae, Cottidae, Ammodytidae, Agonidae, Hexagrammidae, Liparidae, Osmeridae, Ptilichthyidae, Stichaeidae and Scorpaenidae. The ichthyoplankton in Avachinskaya Bay consisted in 92% of eggs and in 8% of larvae. The ichthyoplankton complex was the most reach and abundant in April and May.

Twenty-eight years of decline: Nesting population demographics and trajectory of the north-east Queensland endangered hawksbill turtle (Eretmochelys imbricata)

Globally, hawksbill turtles (Eretmochelys imbricata) are listed as Critically Endangered, the cause of which is largely attributed to excessive historical take by the tortoiseshell industry. Yet few long-term data analyses describing population trend or survivorship exist. Here we analyse a long-term dataset for a globally significant western Pacific E. imbricata nesting population on Milman Island, northern Great Barrier Reef. Three demographic indicators were used: (1) number of egg clutches laid, (2) nester abundance and survival, and (3) the body-size distribution of nesters (curved carapace length, CCL). Models were developed for a time series from the 1990–91 to 2016–17 nesting season that included 21 years of sampling, with predicted trends evaluated against samples from the 2017–18 nesting season. The number of clutches laid and nester abundance rate of decline varied over the study period, but the decline was markedly similar with a 58 and 57% overall reduction, respectively. Annual survival rate was high (0.972, 95% CI = 0.965 to 0.977), but was not estimated separately for all years. Models predicted that the current rate of decline would lead to nesting extirpation by 2036 (95% CI: 2026–2058) and 2032–2037 (95% CI: from 2020 to increasing), for the models of nester abundance and number of eggs laid, respectively; and aligned with the observed values for the test dataset (2017–18 season).The rate of decline of E. imbricata nesting at Milman Island highlights the urgency to understand and mitigate risks faced by this endangered population and more broadly across the western Pacific.

Seasonal Variation in Abundance of Dengue Vector in the Southern Part of the Baja California Peninsula, Mexico

Environmental factors that affect Aedes sp. mosquitoes should be considered to optimize control. The study assessed the association between the abundance of Aedes aegypti (L. 1762) (Diptera: Culicidae) and temperature, rainfall, and relative humidity of the State of Baja California Sur, Mexico. Total Mosquito eggs collected each week for 3 years from ovitraps at La Paz and Los Cabos was 3,129,203; mean number of eggs, ovitrap positivity index, and egg density index were calculated, showing the three entomological indices were greater at La Paz than at Los Cabos (P < 0.005). The means of eggs per month differed statistically only at La Paz (P < 0.0001), with less abundance in January and March but more in October. Although monthly differences were not detected from January to December at Los Cabos, increase occurred from September to November during the 3 years. Results showed statistical association between egg abundance and minimum temperature at both locations during the 3 years of study; more activity was observed during the summer and fall when more precipitation and thus greater relative humidity occurred, but they were statistically associated only with precipitation at La Paz (P < 0.01). The number of eggs was statistically significant with minimum temperatures at both locations (P < 0.01) and with rainfall only at La Paz (P < 0.01). Therefore, management should be more intense during winter-spring when insects were less abundant and hence management strategies used would be more effective.

Carcass additions increase juvenile salmonid growth, condition, and size in an interior Columbia River Basin tributary

Numbers of anadromous fish returning to freshwater ecosystems have declined precipitously across much of western North America, reducing a potentially important resource subsidy for juvenile salmonids. We added carcasses to three sections of a Snake River tributary and assessed juvenile Chinook salmon (Oncorhynchus tshawytcha) and steelhead trout (Oncorhynchus mykiss) growth, body condition, size, and diet responses in summer and early fall. Juvenile salmonids consumed an abundance of eggs and carcass tissue, which increased energy rations. Within 3 weeks of carcass additions, juvenile Chinook and steelhead growth rates were 1.1–5 and 6–23 times greater in treatment reaches relative to control reaches, respectively. We used long-term tagging and detection data from this system to assess the relationship between juvenile Chinook size and emigration survival for two different juvenile life histories. The increased growth rates and body size in response to carcass additions, coupled with a positive relationship between body size and survival, suggest that juvenile salmonid rearing productivity and emigration survival may be limited by depressed returns of anadromous fishes in this system and potentially other tributaries of the Columbia Basin.

Population dynamics of Rana sierrae at Dusy Basin: influence of non‐native predators, drought, and restoration potential

AbstractThe Sierra Nevada yellow‐legged frog (Rana sierrae) was once an abundant and widely distributed amphibian in California's alpine ranges. Rana sierrae is adapted to high‐elevation, fishless habitats. Its adaptions are reflected in a unique life cycle that involves a flexible, extended juvenile phase due to the short growing season typical of its alpine habitat. However, today this species is critically endangered, and most populations have been extirpated from their native range. Here, we present an 18‐yr‐long demographic study of a R. sierrae population in 15 lakes at Dusy Basin in Kings Canyon National Park. We focused on the period leading up to the arrival of the pathogenic chytrid fungus, Batrachochytrium dendrobatidis (Bd), and the subsequent local extinction of R. sierrae. We used N‐mixture abundance modeling, which accounts for detection probabilities, to quantify factors affecting frog abundance at different life stages. The abundance of subadult and adult frogs was negatively associated with the presence of introduced trout (Oncorhynchus mykiss and O. aquabonita). Frog abundance in all life stages was positively associated with lake surface area. The propensity of lakes drying correlated negatively with abundance of eggs, subadults, and adults in the following year. Moreover, drought years, characterized by longer summers and less winter snowpack, led to higher rates of lakes drying. Finally, our results suggest that the frequency of such droughts in the region has increased since 1937. Increased frequency or severity of droughts is expected to decrease the value of shallow lakes for Sierra Nevada yellow‐legged frogs because these habitats are prone to drying. We discuss our results in terms of future restoration strategies, including reintroduction and probiotic treatment, in this changed and changing ecosystem.

Subtropical water influences temporal fluctuations of early life stages of Vinciguerria lucetia (Osteichthyes: Phosichthyidae) in the Humboldt Current System (1998–2004)

AbstractIn the last decades, the fish Vinciguerria lucetia (Garman) has been of important interest to the fisheries sector; nonetheless, the spawning and nursery zones in the Humboldt Current System (HCS) have not yet been defined. By using a temporal series of 23 oceanographic surveys from austral spring of 1998 to autumn 2004 off northern Chile, the spatial and temporal distribution and abundance of eggs and larvae of V. lucetia were studied. The relationships with environmental conditions (sea surface temperature, water column stratification, salinity, dissolved oxygen) were modeled using generalized additive models (GAMs). Seasonal variations in eggs and larval abundances were recorded, and higher abundances were observed in spring and summer, respectively. The main spawning areas were located at approximately between 40 and 80 nautical miles offshore. The largest abundances of V. lucetia eggs were found during spring 2003; however, larval abundances reached the highest values following the strongest ENSO event 1997–98. GAMs predicted that offshore location, sea surface temperature, and the deepening of the oxygen minimum zone, characteristics of the subtropical waters (22–24°C, &gt;34.9, 3–6 ml/L) drove eggs and larval distributions of V. lucetia in the HCS during 1998–2004, toward areas with scarce food availability for larvae. These results suggest that spawning and larval development of this oceanic species occur in oligotrophic waters as a loophole strategy, in order to reduce predation risk during early life stages.

Essential roles of Windei and nuclear monoubiquitination of Eggless/SETDB1 in transposon silencing.

Eggless/SETDB1 (Egg), the only essential histone methyltransferase (HMT) in Drosophila, plays a role in gene repression, including piRNA-mediated transposon silencing in the ovaries. Previous studies suggested that Egg is post-translationally modified and showed that Windei (Wde) regulates Egg nuclear localization through protein-protein interaction. Monoubiquitination of mammalian SETDB1 is necessary for the HMT activity. Here, using cultured ovarian somatic cells, we show that Egg is monoubiquitinated and phosphorylated but that only monoubiquitination is required for piRNA-mediated transposon repression. Egg monoubiquitination occurs in the nucleus. Egg has its own nuclear localization signal, and the nuclear import of Egg is Wde-independent. Wde recruits Egg to the chromatin at target gene silencing loci, but their interaction is monoubiquitin-independent. The abundance of nuclear Egg is governed by that of nuclear Wde. These results illuminate essential roles of nuclear monoubiquitination of Egg and the role of Wde in piRNA-mediated transposon repression.

Paleoceanographic and paleoclimatic reconstruction based on marine palynomorphs in the period 1811–1907 CE in the Magdalena Basin, Baja California Sur, Mexico

Biennial variations of marine palynomorph concentrations mirrored oceanographic conditions in the Magdalena Basin, Baja California Sur (Mexico), in the period from 1811 to 1907 (common era, CE), for which the sea surface temperature index (SSTI) showed predominantly negative anomalies. We analyzed 49 samples of laminated sediments taken from a core extracted at a water depth of 520 m. Changes in dinoflagellate assemblages and copepod egg abundances were compared to SSTI records and to El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) reconstructions. Copepods were the most abundant and showed a significant correlation with SSTI. Among the dinoflagellates, heterotrophs were the most abundant and did not correlate with SSTI. The lowest concentration of autotrophs showed a significant and inverse correlation with SSTI. The canonical correlation analysis also indicated that copepods and autotrophs were modulated by variations in SSTI. Dinoflagellate richness and concentrations and copepod egg concentrations were low, indicating low productivity, and these values coincided with the negative SSTI anomalies. In contrast, the increase in concentrations from 1881 to 1907 CE coincided with positive SSTI anomalies. Also, even when marine palynomorphs showed no significant correlation with either ENSO or PDO, their concentrations increased during age intervals with combined negative conditions (La Niña, negative PDO) and decreased during combined warm conditions (El Niño, positive PDO).

Ant-mealybug mutualism modulates the performance of co-occurring herbivores

Mutualism between ants and honeydew producing hemipterans has been extensively studied. However, little is known on how ant-hemipteran mutualism impacts the co-occurring herbivores, which in turn affect the mutual relationship in ecosystems. Herein, we investigated the effect of ant-mealybug mutualism on the oviposition preference and spatial distribution of cotton leaf roller Sylepta derogata, a polyphagous herbivore, and in Apantetes derogatae performance, a larvae parasitoid of S. derogata. Leaf rollers constructed shelters for mealybugs to prevent them from enemy attack and preferred to lay eggs on plants with ant-mealybug mutualism. Egg abundance on mutualism-present plants was higher than on mutualism-absent plants. Leaf roller parasitoid A. derogatae showed higher parasitism on mutualism-absent plants. No obvious change in leaf roller egg abundance was observed when A. derogatae was excluded, suggesting that the parasitic pressure can also regulate the oviposition behavior of S. derogate. Apantetes derogatae showed higher aggressiveness in parasitizing leaf roller larvae at the absence of the mutualism. There was a definite correlation between leaf roller egg abundance and the number of patrolling ants on plants. Without ant-mealybug mutualism, S. derogata eggs showed a significantly aggregated distribution pattern, but a uniform distribution pattern was observed when the mutualism was present. Ant workers showed a consistently uniform distribution on plants. The results reveal a novel mediation effect of ant-mealybug association on the composition and structure of food webs in cotton field, which may contribute to a better understanding of the cascading effects of ant-hemipteran mutualism on other niche-related species in ecosystem.

Quantifying parasitoid and predator controls on rice hopper eggs using a dynamic stage‐structured model and field data

Abstract Rice hoppers can cause devastation to rice crops in SE Asia via disease spread and direct feeding. Current regulation is through pesticides; however, a more sustainable approach is to use the natural enemies of the hoppers. Here, we show how the combination of a process‐based model and field data can give insights into natural pest control, beyond those obtained through direct analysis of the field data. We use a stage‐structured host‐parasitoid model based on time‐delay ordinary differential equations (using the r package “stagePop”; Kettle &amp; Nutter, 2015; Methods in Ecology and Evolution 6:1484–1490) to investigate the interactions of four parasitoid genera and an egg predator on the eggs of two hopper hosts: the brown plant hopper (Nilaparvata lugens (Stål)) and the green leaf hopper (Nephottetix spp.). Model parameters are derived from 62 (×3) datasets from experiments in the Philippines. In these experiments, hopper eggs on rice plants were exposed in the field for 3 days and then taken back to the laboratory. The number of emerging hopper nymphs and parasitoid adults were then recorded. Single‐host and mixed host experiments were performed. The field data are not sufficient to fully constrain the model parameters so our results are given in terms of the value of an unknown parameter (γ; the number of hopper eggs killed per successful parasitism) which may be ascertained via future experiments. Synthesis and applications. Our model experiments suggest that although parasitoids are most likely the main control on hopper egg abundance, and despite the fact that the egg predator also consumes parasitoid eggs, the two‐enemy system (parasitoids and predators) is more effective at hopper egg control than if either enemy is present alone. Our results provide evidence in support of ecological engineering approaches that promote both parasitoids and egg predators.

Variation in the prevalence and abundance of acanthocephalans in brown-nosed coatis Nasua nasua and crab-eating foxes Cerdocyon thous in the Brazilian Pantanal.

Host infection by parasites is influenced by an array of factors, including host and environmental features. We investigated the relationship between host sex, body size and age, as well as seasonality on infection patterns by acanthocephalan in coatis (Procyonidae: Nasua nasua) and in crab-eating foxes (Canidae: Cerdocyon thous ) from the Brazilian Pantanal wetlands. Between 2006 and 2009, we collected faecal samples from these hosts and analyzed for the presence of acanthocephalan eggs. Prevalence, abundance and intensity of eggs of acanthocephalans were calculated. Egg abundance was analyzed using generalized linear models (GLM) with a negative binomial distribution and models were compared by Akaike criteria to verify the effect of biotic and abiotic factors. Prevalence of acanthocephalans was higher in the wet season in both host species but did not differ between host sexes; however, adult crab-eating foxes showed higher prevalence of acanthocephalan eggs than juveniles. In contrast, prevalence of acanthocephalan eggs found in coatis was higher in coati juveniles than in adults. Host age, season and maximum temperature were the top predictors of abundance of acanthocephalan eggs in crab-eating foxes whereas season and host sex were predictors of egg abundance in coatis. The importance of seasonality for abundance of acanthocephalan was clear for both host species. The influence of host-related attributes, however, varied by host species, with host gender and host age being important factors associated with prevalence and parasite loads.

The 'Botanical Triad': The Presence of Insectary Plants Enhances Natural Enemy Abundance on Trap Crop Plants in an Organic Cabbage Agro-Ecosystem.

Habitat manipulation through the incorporation of non-crop plants such as trap crops (to lure pests away from the cash crop) and insectary plants (to provide resources for natural enemies) into agro-ecosystems is an ecological approach to pest management. In a field-scale study, we quantified the effects of integrating the use of trap crops with insectary plants as a novel method to control pest herbivores in an organic cabbage agro-ecosystem. We hypothesized that pests would be concentrated in the trap crop habitat and suppressed by insectary-subsidized natural enemies in situ. We documented arthropod abundance (both adults and immature stages) associated with (1) two insectary plant species (sweet alyssum, Lobularia maritima, and buckwheat, Fagopyrum esculentum) either alone or in combination; (2) a trap crop mixture of mighty mustard (Brassica juncea), red Russian kale (Brassica oleracea var. acephala), and glossy collards (Brassica oleracea var. italica), and (3) cabbage cash crop (Brassica oleracea var. capitata). Trap crops were more attractive to pests than the cash crop. On a per-plant basis, densities of the herbivores Evergestis rimosalis, Trichoplusia ni, and Plutella xylostella were 154, 37, and 161× greater on the kale trap crop than on the cabbage cash crop, and 54, 18, and 89× greater on the collards trap crop than on the cash crop. Insectary plants contributed to the consumption of pests that aggregated on the trap crop. Parasitism of E. rimosalis by the braconid wasp Cotesia orobenae was significantly increased, and the abundance of eggs and larvae of the predatory coccinellid beetle Coleomegilla maculata was greater on the trap crop in the presence of insectary plants compared to trap crops that lacked insectary plants. The ‘Botanical Triad’ of cash crop, trap crop, and insectary plants represents a new type of agro-ecosystem manipulation that integrates ecosystem service providers (e.g., predators and parasitoids) within the cropping system.

Spatial and temporal variation in the distribution and abundance of pelagic fish eggs and larvae off Giresun, south-eastern Black Sea, Turkey

Background. Giresun Bay is an important spawning ground of many migratory fish species and hence it has been a major fishing area of pelagic fishes in the Turkish territorial waters of the Black Sea. However, this area has not been evaluated thoroughly for the abundance and distribution of pelagic fish eggs and larvae, which are prerequisite for understanding the dynamics of fluctuating fish populations. The presently-reported study aimed to fill this gap in the existing knowledge of spatial and temporal variation in the distribution and abundance of ichthyoplankton in the south-eastern Black Sea. Materials and methods. Bimonthly surveys were carried out from January through November 2009 at inshore and offshore sites (&gt;38&deg;E, &gt;40&deg;N). The samples were collected by horizontal tows with Manta nets. The mouth of the net was equipped with flowmeters to measure the amount of water passing through the net during each tow. Results. The horizontal tows returned a total of 13 556 eggs and 1304 larvae representing 26 species (from 22 families): Engraulis encrasicolus, Sprattus sprattus, Merlangius merlangus, Gaidropsarus mediterraneus, Atherina boyeri, Scorpaena porcus, Chelidonichthys lucerna, Dicentrarchus labrax, Trachurus mediterraneus, Diplodus annularis, Sciaena umbra, Mullus barbatus, Gymnammodytes cicerelus, Ctenolabrus rupestris, Symphodus ocellatus, Trachinus draco, Uranoscopus scaber, Parablennius sanguinolentus, Parablennius tentacularis, Blennius sp., Ophidion rochei, Callionymus pusillus, Gobius sp., Arnoglossus kessleri, Buglossidium luteum, Pegusa lascaris. Overall, the dominant species were E. encrasicolus with 89.8% of all collected eggs, followed by G. mediterraneus (7.0%). Similarly, 47.4% of the total larvae were represented by E. encrasicolus, followed by P. sanguinolentus (22.8%) and S. sprattus (13.2%). The colder months (January, March, and November) presented a total of four species: S. sprattus, B. luteum, Gymnammodytes cicerelus, and Gaidropsarus mediterraneus. The warmer months had a greater variety of different species than colder months. Of these, E. encrasicolus was the most dominant species, providing the maximum abundance of fish eggs and larvae in September. The abundance of E. encrasicolus eggs and larvae decreased from offshore toward inshore sites highlighting the preference of this species to deeper waters for spawning as well as for nursery purposes in Giresun Bay. Conclusion. The results of this study suggest that the length of the closed fishing season in the Black Sea should be reconsidered. We suggest that it should be extended to include also the last week of September in order to provide more time for pelagic fish (e.g., E. encrasicolus) to complete their spawning period. This could result in a healthier and more sustainable stock of E. encrasicolus in the Black Sea.

Strategic mowing of roadside milkweeds increases monarch butterfly oviposition

The eastern North American migratory population of monarch butterflies (Danaus plexippus) has declined precipitously due, in part, to the widespread decline of its obligate host plant, milkweed (Asclepias spp.). Linear right-of-ways (e.g. roadsides, power line corridors) are believed to be a significant source of milkweed and represent a valuable target for restoration efforts. Although many current mowing practices in these habitats are detrimental for monarchs because mowing occurs too frequently or is poorly timed, strategic mowing could be beneficial for monarch reproduction if it produces young milkweed at the right time of season. To address this, forty-nine paired experimental and control plots containing common milkweed (Asclepias syriaca) were established along habitat adjacent to a two-lane highway in southern Ontario. Experimental plots were mowed once per season and followed one of eight mowing treatments that occurred between mid-June and early August. Milkweed characteristics and the presence of monarchs at all life stages were monitored within plots from late June through September. Overall, mowed plots had higher egg abundance than unmowed controls. Within mowed plots, egg abundance/plant was highest in plots mowed between the 2nd and 3rd weeks of July. At this latitude (43°N), mowing past this window was less effective and would have resulted in high mortality of developing monarchs. Our results suggest that mowing common milkweed once before egg laying peaks could maximize monarch butterfly reproduction in managed landscapes.

Late Summer Oviposition of Green Lacewings (Neuroptera: Chrysopidae) on Olive Groves and Adjacent Trees.

In this study, we assess how chrysopids (generalist predators widely used as biological control agents) use olive, almond, oak, and pine trees for oviposition. We sampled clutches of chrysopids from tree canopies in August 2016 and 2017. Additionally, we checked the stage (alive, predated, emerged, or parasitized) and the site (upper side, edge, or underside of leaves) and mode (single and cluster clutches) for oviposition in every clutch. The clutches collected alive in August 2016 were raised in the laboratory and identified to species level. No differences in clutch abundance were observed amongst tree species, years and locations, suggesting that chrysopids are geographically well spread and that all of the tree species are equally suitable to support clutches of active chrysopids in this period. Additionally, chrysopids preferred to lay their clutches on the edge and upper side of the leaves and the single clutches were the most frequent. We collected clutches of 9 chrysopid species (Neuroptera: Chrysopidae) belonging to four genera, from which Pseudomallada prasinus (Burmeister, 1839), Cunctochrysa baetica (Hölzel, 1972), and Chrysoperla mutata (McLachlan, 1898) were the most abundant. The almond trees shelter the highest chrysopid species richness. We found C. mutata as the only Chrysoperla Steinmann, 1964 species laying on the olive trees and Chrysoperla lucasina (Lacroix, 1912) and Chrysoperla pallida Henry et al., 2002 on the almond trees. Although every tree species is able to shelter a similar abundance of eggs of chrysopids, conserving different trees ensures the existence of a diverse assemblage of chrysopids that might respond to periodical perturbations and moves to olive groves in the case of a pest outbreak.

Пространственное распределение ихтиопланктона у Крымского полуострова в летний сезон 2013 г.

Проанализированы данные, полученные в пяти комплексных экспедициях НИС «Профессор Водяницкий», которые были проведены с мая по сентябрь 2013 г., в летний нерестовый сезон. Представлена динамика видового разнообразия и пространственного распределения ихтиопланктона в связи с особенностями гидрологического режима в различных районах шельфовых и открытых вод Чёрного моря у Крымского полуострова. В ихтиопланктоне идентифицированы 17 видов икринок и личинок рыб из 13 семейств. Количество видов в ихтиопланктоне было максимальным в июне. Средняя численность икринок и личинок за нерестовый сезон составляла 50,5 и 9,2 экз.·м-2 соответственно. Наибольшая численность икринок (109,9 экз.·м-2) и личинок (9,2 экз.·м-2) наблюдалась в июле. Преобладали икринки и личинки хамсы Engraulis encrasicolus (Linnaeus, 1758): их доля в открытых водах в разгар нерестового сезона достигала 96 и 94 % соответственно. Максимальные показатели индексов видового разнообразия и выровненности (значимости каждого вида) наблюдались в мае, когда доминантные виды только начинали нерест и их численность в ихтиопланктоне была сравнительно низкой. Индексы видового богатства достигали наибольших величин в июне, когда количество видов в ихтиопланктоне было максимальным. Видовой состав и пространственное распределение ихтиопланктона зависели от термогидродинамической структуры морских вод в районах исследований, а выживанию личинок рыб способствовало снижение прессинга желетелого планктона на их кормовую базу. Наиболее значимыми факторами, определяющими термогидродинамическую структуру моря в летний нерестовый сезон 2013 г., являлись: региональные особенности режима прогрева поверхности моря в весенне-летний период и его выхолаживания в осенний гидрологический сезон; адвективный вклад поверхностных течений (прежде всего Основного черноморского течения); сгонно-нагонные процессы в прибрежных районах; локальные термохалинные неоднородности в областях смешения распреснённых речных вод с шельфовыми в северо-западной части моря и азовоморских вод в Керченском предпроливье — с водами открытого моря.

Mosaic environments shape the distribution of Neotropical freshwater ichthyoplankton

AbstractDam presence results in heterogeneous aquatic environments that probably favour segregation of ichthyoplankton developmental stages. Therefore, the present study tested the hypothesis that dams in the Upper Uruguay River create heterogeneous aquatic environments favouring segregation of ichthyoplankton developmental stages and also separate species with different reproductive tactics. Ichthyoplankton were captured bimonthly during 2002–2015 in 25 sampling stations grouped by fluviometric characteristics. Sampling was performed at night, with cylindrical–conical plankton nets and light traps. After quantifying ichthyoplankton, we identified larvae to the lowest possible taxonomic level and classified them based on developmental stage and reproductive tactics. Egg abundance was higher in lotic environments, preflexion individuals were more abundant in transitional lotic/lentic environments, and the flexion stage was predominant in lentic environments. Larval assemblages consisted mainly of sedentary species or those with short reproductive migrations. Species with similar reproductive tactics occurred in different environments. In conclusion, we provided evidence demonstrating that mosaic environments in the Upper Uruguay River are important for life cycle completion of different fish species. These distinct habitat zones allow for successful spawning and offspring development, thus guaranteeing recruitment.

Assessing the spawning ecology of fish in situ using a benthic pump sampler

In situ observations of incubating fish eggs can identify spawning sites and spawning habitat preferences, informing the ecology of fishes with benthic eggs. Suction pumps have been used to sample benthic-incubating, non-adhesive fish eggs, yet their sampling efficiency is not well known. Imperfect or systematically variable egg detection could bias resulting ecological inference if left unaddressed. Here we present results from replicate field trials and examine the effects of varying substrate type, intake design, sampling effort, and egg density on the ability of a gasoline-powered diaphragm pump, rated for 66 gal/min (approx. 250 L/min), to detect egg presence and estimate relative or absolute abundance. A wider box-shaped intake was effective at detecting the presence of eggs on fine, silty substrates, but had limited effectiveness on larger-grained substrates. A narrower cone-shaped intake consistently detected the presence of eggs on silt, gravel, and shallow cobble, and demonstrated potential to measure relative and absolute egg abundance. Neither intake design was able to collect eggs from deep interstitial spaces (e.g. several layers of cobble), indicating that there are limitations to the types of substrates on which benthic sampling pumps can operate. Both intake designs often collected eggs from outside the edge of the intake opening. Most eggs were collected within a two minute period, but increasing pumping time to four minutes produced better egg detection outcomes. Our results suggest that stationary benthic sampling pumps are viable tools for directly sampling incubating eggs on most substrates, but have imperfect and varying sampling efficiency resulting from intake design and substrate type.