Total Larval Density Research Articles

Loss of amphibian species alters periphyton communities in montane ponds

Amphibian larvae can affect the structure and functioning of freshwater ecosystems, but their effects have been little explored although amphibian biodiversity is rapidly declining. Given that larvae of different amphibian species belong to different trophic levels, their effects on freshwater communities and processes can be expected to differ, with herbivores likely having direct effects on algae and predators having indirect effects through trophic cascades. We explored this question through a mesocosm experiment conducted in montane ponds, using an anuran and a urodele species affected by emergent diseases. We used different scenarios of reduction and loss of one or both species, and compared them to a control scenario representing a typical amphibian community in the study area composed of four species, with total larval density held constant. Loss of the anuran resulted in lower chlorophyll concentration and algal density, likely due to replacement by more efficient grazers. Loss of the urodele produced similar trends but weaker, possibly due to an increase of invertebrate grazing activity in the absence of this predator. Our study shows how the loss of amphibian species can alter the structure of montane ponds, but also how the mechanisms involved and the intensity of effects differ for different species.

Entomofaunal survey and larvicidal activity of greener silver nanoparticles: A perspective for novel eco-friendly mosquito control.

The entomofaunal survey and its toxicity of Blumea mollis (Asteraceae) leaf aqueous extract-mediated (Bm-LAE) silver nanoparticles (AgNPs) were assessed against selected human vector mosquitoes (HVMs). A total of 1800 individuals of 29 species belongs to 7 genera were identified. Month-wise and Genus-wise abundance of HVMs larval diversity were calculated and one-way ANOVA statistically analyzed the average physico-chemical characteristics. The relationship between physicochemical characteristics and HVMs larvae in KWS was interpreted. The total larval density and container index were 23530.18 and 1961.85 examined against 10 different containers. Various spectroscopic and microscopic investigation characterized Bm-AgNPs. The Bm- AgNPs tested against HVMs larvae, the predominant LC50/LC90 values of 18.17/39.56, 23.45/42.49 and 21.82/40.43 μg/mL were observed on An. subpictus Cx. vishnui and Ae. vittatus, respectively. The findings of this investigation, improperly maintained drainages, containers and unused things in study sites, are engaged to HVMs development. This will be essential for designing and implementing HVMs control. The larval toxic potentiality of Bm- AgNPs had a prompt, inexpensive and compelling synthesis of multi-disperse action against HVMs.

Estimating densities of larval Salmonflies (Pteronarcys californica) through multiple pass removal of post-emergent exuvia in Colorado rivers.

Traditional methods of collecting, sorting, and identifying benthic macroinvertebrate samples are useful for stream biomonitoring and ecological studies, however, these methods are time consuming, expensive, and require taxonomic expertise. Estimating larval densities through collection of post-emergent exuvia can be a practical and time efficient alternative. We evaluated the use of multiple pass depletion techniques of the post-emergent exuvia of Pteronarcys californica to estimate larval densities at ten sites in three Colorado rivers. Exuvia density was highly correlated with both final-instar larval density (R2 = 0.90) and total larval density (R2 = 0.88) and the multiple pass removal technique performed well. Exuvia surveys found P. californica at three low density sites where benthic sampling failed to detect it. At moderate and high density sites the exuvia surveys always produced lower density estimates than benthic surveys. Multiple pass depletion estimates of exuvia proved to be an accurate and efficient technique at estimating larval densities and provided an effective alternative for traditional benthic sampling when objectives are detecting and monitoring P. californica, especially at low density sites.

Stream characteristics associated with feeding type in silver (Ichthyomyzon unicuspis) and northern brook (I. fossor) lampreys and tests for phenotypic plasticity

In most lamprey genera, “paired” species exist in which the larvae are morphologically indistinguishable but adult feeding type differs. The lack of diagnostic genetic differences in many pairs has led to suggestions that they constitute a single gene pool with environmentally influenced feeding types. To investigate whether stream characteristics are correlated with feeding type in the parasitic silver lamprey Ichthyomyzon unicuspis and non-parasitic northern brook lamprey I. fossor, eight variables (pH, alkalinity, conductivity, discharge, total dissolved solids, and density of larval sea lamprey Petromyzon marinus, Ichthyomyzon spp., and total larval density) were compared among eight streams with only silver lamprey, 10 with only northern brook lamprey, and 13 with both species, using classification tree analysis. The most parsimonious model had a 24% misclassification rate, with silver lamprey tending to inhabit streams with higher sea lamprey larval density and northern brook lamprey tending to inhabit streams with higher Ichthyomyzon larval density. We then conducted a pilot study investigating phenotypic plasticity in a lab-based common garden experiment and an in situ transplant experiment. These studies encountered myriad difficulties and were unable to demonstrate plasticity, but did identify challenges associated with culturing Ichthyomyzon larvae. Development of effective rearing procedures for Ichthyomyzon lampreys is essential for any future similar studies.

Importance of Reservoir Tributaries to Spawning of Migratory Fish in the Upper Paraná River

AbstractRegulation of rivers by dams transforms previously lotic reaches above the dam into lentic ones and limits or prevents longitudinal connectivity, which impairs access to suitable habitats for the reproduction of many migratory fish species. Frequently, unregulated tributaries can provide important habitat heterogeneity to a regulated river and may mitigate the influence of impoundments on the mainstem river. We evaluated the importance of tributaries to spawning of migratory fish species over three spawning seasons, by comparing several abiotic conditions and larval fish distributions in four rivers that are tributaries to an impounded reach of the Upper Paraná River, Brazil. Our study confirmed reproduction of at least 8 long‐distance migrators, likely nine, out of a total of 19 occurring in the Upper Paraná River. Total larval densities and percentage species composition differed among tributaries, but the differences were not consistent among spawning seasons and unexpectedly were not strongly related to annual differences in temperature and hydrology. We hypothesize that under present conditions, densities of larvae of migratory species may be better related to efficiency of fish passage facilities than to temperature and hydrology. Our study indicates that adult fish are finding suitable habitat for spawning in tributaries, fish eggs are developing into larvae, and larvae are finding suitable rearing space in lagoons adjacent to the tributaries. Our findings also suggest the need for establishment of protected areas in unregulated and lightly regulated tributaries to preserve essential spawning and nursery habitats. Copyright © 2014 John Wiley & Sons, Ltd.

The importance of larval supply, larval habitat selection and post-settlement mortality in determining intertidal adult abundance of the invasive gastropod Crepidula fornicata

Understanding the processes that drive the recruitment of invasive non-native species is of critical importance in evaluating their potential to colonise previously unoccupied habitats. The slipper limpet Crepidula fornicata has spread rapidly into most European waters since its first introduction from the North West Atlantic in the late 19th century. Its invasion success is thought to have been aided by its long larval phase and its tolerance towards a wide range of environmental conditions. The Milford Haven Waterway in Wales, U.K. supports a population with highly variable densities in the intertidal as well as the subtidal zone. In the present study, we tested a series of existing models to investigate the roles of larval supply, larval habitat selection and post-settlement mortality in determining the final distribution of C. fornicata in the intertidal zone of the Milford Haven Waterway. During the main reproductive season of 2011, data on total settlement rates and recruitment were collected by deploying slate panels for varying durations in the low intertidal zone, and data on larval abundances were obtained by taking frequent plankton samples at two sites with contrasting adult densities: Beggars Reach (~15±13indm−2) and Pennar (~343±360indm−2). Total larval densities were much higher at Pennar, but densities of late-stage larvae (i.e. larval supply) were similar at both sites, indicating that local hydrodynamics may have resulted in the spatial homogenisation of supply of late-stage, metamorphically competent larvae, despite the higher larval production at the high adult abundance site. Settlement rates also did not differ between sites. Seasonal recruitment was overall low, indicating that post-settlement mortality, likely as a consequence of exposure to intertidal conditions, is very high. The lack of a relationship between adult abundance and settlement rates indicates that the final distribution of C. fornicata in the intertidal may be a result of differential post-settlement mortality. Understanding recruitment patterns in non-native species is essential for developing management strategies for potentially harmful invaders such as C. fornicata.

Microclimate and tree community linked to differences in lepidopteran larval communities between forest fragments and continuous forest

ABSTRACTAim We aim to assess the impact of forest fragmentation on lepidopteran larval community and study the associations of microclimate and tree community with lepidopteran assemblage.Location Kibale National Park, Uganda.Methods We investigated the effects of forest fragmentation on leaf herbivory, density of lepidopteran caterpillars, species richness and diversity as well as the composition of herbivorous lepidopteran larval community. Microclimate, size of the fragment, distance to the continuous forest, and tree diversity were studied as possible explanatory factors. We sampled 10 Neoboutonia macrocalyx Pax. (Euphorbiaceae) trees in each fragment during dry and rainy season, total of four times, in a year to cover the seasonal variation.Results The rates of herbivory, total larval density and species richness were significantly lower in the forest fragments than in the continuous forest but species diversity expressed as Fisher's alpha did not differ. The dominance structure and community composition of the larval communities in the fragments was different from that of the continuous forest. None of the differences we observed were related to the fragment area or distance to the continuous forest. Instead, we found an indication of association between the herbivore and the tree communities. The fragments had significantly lower humidity during most of the day and higher temperature during the afternoons (14–17 h), which might partially explain the differences in lepidopteran larval communities.Main conclusions Decreased larval density and species richness as well as differences in the community composition and structure all highlight the importance of large continuous forest areas for maintaining larval biodiversity.

Observaciones sobre la larva del cangrejo marino tropical (Decapoda: Porcellanidae) Petrolisthes armatus en el Golfo de Nicoya, Costa Rica

During October and November 1998 (rainy season), and December, February and March 1999 (dry season), larvae distribution of Petrolisthes armatus and associated decapods were sampled in three different sites at the Punta Morales peninsula, Gulf of Nicoya, Costa Rica. A total of 6014 decapod larvae were collected, and 73 belonged to the genus Petrolisthes spp. No significant total larval density differences were found between seasons (p > 0.05); but there was a greater density of P. armatus and other decapod larvae (p > 0.05) during the dry season. In addition, no significant variations on temperature and oxygen concentration were observed. P. armatus larval abundance was higher during low tide, in contrast with other decapod larvae. Significant differences among sites were found for other decapod larvae, but not for P. armatus. The only parameter that varied significantly between seasons was salinity and results demonstrate that this factor regulates temporal concentration of larvae. Moreover, flow-tide oscillations were the most important spatial factor in larval dynamics. We propose this mechanism: P. armatus liberates larvae during high tide; these larvae leave the coastal area during low tide and return to the rocky intertidal ecosystem during high tide, when they are ready to settle as megalopa (pre-juvenile stage). Parallel laboratory observations showed higher survival rates at lower salinities (15 ups against 35 ups) and that the duration of the period from zoea I to megalopa was, in average, 19 days.

Relationship of water and leaf litter variability to insects inhabiting treeholes

I surveyed treeholes in central Pennsylvania for 7 mo in 1995 to investigate relationships among insect communities and water and leaf litter resources. I used water volume, essential to growth of treehole larvae, as an indicator of habitat size. Leaf litter is the basal food resource in treehole communities, and litter volume is related to the amount of energy available. Insect species richness and larval mosquito (Ochlerotatus triseriatus) and ceratopogonid midge (Culicoides guttipennis) densities were higher in treeholes that maintained high water volumes than those with low volumes throughout the study. Treeholes with high litter volume, irrespective of water volume, had the highest densities of C. guttipennis, and higher total larval densities than those with lower litter volumes; however, litter volume did not affect insect species richness. Scirtid beetle larvae were common in all treeholes, although their densities were unaffected by both litter and water volume. Insect species richness was not related to litter volume, unlike some other studies of phytotelmata. However, my study supported earlier conclusions that both habitat size and resource availability influence structure of treehole communities and maintain species populations. The influence of each resource on particular species presence and density may be related to physical aspects of treeholes, biotic interactions, and natural history of individual species.

Seasonal Dynamics of Pelagic Larvae and Settling of the Fouling Organisms in Conditions of Thermal Pollution

Year-round comprehensive study of fouling of the cooling system of the Vladivostok Heat Power Plant (VTETs-2) was carried out. The seasonal dynamics of pelagic larvae, their settling, and succession of fouling communities on test plates were analyzed in the intake scoop (Ussuriiskii Bay) and in Zolotoi Rog Bay (Amurskii Bay), which are subjected to thermal pollution by dump waters of VTETs-2. It was shown that the barnacles Balanus crenatus, B. improvisus, and B. amphitrite; bivalves Mytilus trossulus and Crassostrea gigas; polychaetes Polydora limicola and Hydroides ezoensis; and ascidians Molgula manhattensis and Diplosoma mitsukurii were background species in the plate fouling. A high correlation between the seasonal dynamics of larval plankton and the settling of spat was recorded only in some species. The total larval density in Zolotoi Rog Bay, despite the critical level of its pollution, more than 4 times exceeded that of the relatively clean Ussuriiskii Bay. The number of recorded species on the test plates was 2 times higher in Ussuriiskii Bay than in Zolotoi Rog Bay; however, the biomass and population density of settled spat of the dominant forms was several times lower in Ussuriiskii Bay. Thanks to thermal pollution, Zolotoi Rog Bay is an intermediate step for the introduction and acclimation of tropical species, such as B. amphitrite and M. manhattensis, brought by long-distance vessels. Measures aimed at the prevention of intensive settling of mytilids in the cooling system of VTETs-2 are suggested.

Life cycle of a torrenticolous Hawaiian chironomid (Telmatogeton torrenticola) : stream flow and microhabitat effects

In this study we documented the instar densities and life cycle of Telmatogeton torrenticola Terry (Chironomidae : Telmatogetoninae) from Kinihapai Stream, Maui, Hawaii. Greatest larval densities of this midge are found on substrates of high velocity, shallow flows of cascades, and splash zones of waterfalls, with lower densities in riffles. In the summer of 1994 we compared the effects of two microhabitats (termed optimal and suboptimal) on inter-instar density and relative abundance. In a second year (1995), we evaluated the effect of long-term reduced stream flow on these variables only in optimal microhabitats. A significant reduction in stream flow from 1994 to 1995 was correlated with a similar reduction in larval densities that precluded larval colonization of suboptimal habitats in 1995, thereby preventing sampling in this microhabitat during that summer. Depth of optimal habitats of 1995 were significantly shallower than both habitats of 1994, with suboptimal habitats of 1994 the deepest. Total larval density was significantly higher in 1994 optimal habitats, while 1994 suboptimal and 1995 optimal habitats were statistically similar. Individual instar densities showed variable differences among habitats and years, with the first three instars always highest in 1994 optimal habitats. All instars and pupae were collected on most sampling dates in both years ; however, pupae were only collected on a two dates in suboptimal habitats of 1994. Based on larval size frequency histograms, T. torrenticola has a multivoltine, asynchronous life cycle, with continuous reproduction, which is variable among microhabitats characterized by different flow velocity and depth, and between years of differing stream discharge. Reduced stream flow during the summer of 1995 had effects of reducing densities and changing life cycle features similar to those found in 1994 (a year of higher stream flow) suboptimal habitats.

Seasonal variation in the occurrence of planktic bivalve larvae in the Schleswig-Holstein Wadden Sea

In the late 1980s, recruitment failures of the musselMytilus edulis led to economic problems in the mussel fishing and cultivation industries of northwestern Europe. As part of a collaborative study to gain a better understanding of the mechanisms affecting recruitment processes of mussels, plankton samples were collected regularly over a four-year period (1990–1993) from three stations in the Schleswig-Holstein Wadden Sea. The bivalve component of the plankton was dominated by the Solenidae, which was almost exclusively represented byEnsis americanus (= directus). M. edulis was the second most abundant species. Abundances of mussel larvae peaked 2 to 4 weeks after spawning maxima in the adult populations. Although variations in timing and amplitude of the total larval densities occurred, annual abundances ofM. edulis larvae remained stable during the study period, and regional abundance differences were insignificant. A close relationship was found between peaks in larval abundance and phytoplankton blooms. Differences in larval concentrations in the ebb and the flow currents were insignificant. Planktic mussel larvae measured between 200 μm and 300 μm, and successive cohorts were recognizable in the majority of samples. Most larvae were found to originate from local stocks, although imports from outside the area do occur.

Coexistence of ecologically similar colonising species III. Drosophila aldrichi and D. buzzatii: larval performance on, and adult preference for, three Opuntia cactus species

Two Drosophila species, D. buzzatti and D. aldrichi, coexist on several species of Opuntia cacti in Australia, primarily on O. tomentosa and O. streptacantha in the northern part of the cactus distribution, and on O. stricta in the south. Thorax length of field-collected adults was less, and the variance in length greater, than that for flies reared on simulated rots in the laboratory, indicating that these species are affected by crowding in nature. A larval performance index, measured on simulated cactus rots at low, moderate and high densities in single-species cultures, and at moderate and high densities in mixed-species cultures, was used to compare the relative intensity of intra- and interspecific competition at the same total larval density per 5 g necrotic cactus. Larval performance of both fly species was greatest on O. streptacantha, intermediate on O. tomentosa, and least on O. stricta in both single-species and mixed-species cultures. On O. stricta, the performances of D. aldrichi and D. buzzatii were not different when in single-species cultures, but that of D. aldrichi decreased significantly in mixed-species cultures. On the other two cactus species, the performances of D. aldrichi and D. buzzattii were not different in mixed-species cultures. The order of preferences by adult females for the cacti differed from that for larval performance, with females of both species prefering O. stricta. Analysis of microbial numbers growing on the cacti showed little difference among cacti at the rot age used for testing adult preference, but later growth was greater on O. tomentosa and O. streptacantha, the cacti that best supported larvae. Differential larval performance on O. stricta may contribute to the rare presence of D. aldrichi in the southern part of the cactus distribution, while the superior quality of O. tomentosa and O. streptacantha (larger rot size and higher microbial concentration) may reduce competition and facilitate cocxistence of the fly species in the north.