Benthic Larvae Research Articles

Fluvial habitat associations of riverine dragonflies (Odonata, Gomphidae) in the Huron Mountains (Michigan, USA)

AbstractThe presence of sediment‐burrowing clubtail dragonflies (Gomphidae) may be directly related to riverine geomorphic properties. Their synchronous emergence behavior, marked by persistent exuviae, allows for the examination of emerging adult‐stage habitats. Here we explore how emerging adult and benthic larvae are related to hydrogeomorphic factors through regression modeling. Nine sites in two subwatersheds of the Huron Mountain region (Michigan, USA) were surveyed during two periods: May/June 2021 and August 2021. Temperature, pH, dissolved oxygen, conductivity, and discharge were measured concurrent with invertebrate surveys, and field samples of total suspended solids, nutrients, and substrate particle size distribution were also taken. In spring, 317 exuviae were collected, including 153 Gomphidae. In August, 45 larvae were collected including 22 Gomphidae. Spearman's rank correlations preceded robust regression analysis to aid variable selection. Although nonsignificant, Gomphidae exuviae were negatively correlated with conductivity, average water depth, and percent sand while non‐Gomphidae exuviae were positively correlated with the same variables. The model selection found the top models for Gomphidae and non‐Gomphidae exuviae abundance to relate to depth and conductivity, while the top model for Gomphidae larvae was with discharge. All single variable models (discharge, width, and percent sand) had similar AICc criterion values when examining their relationship with non‐Gomphidae larval abundance. Our study demonstrates that larvae of several riverine dragonfly taxa in the Huron Mountains co‐occur despite hydrogeomorphic variation, yet, at emergence, specific taxa may be responding to different stream properties. Understanding the habitat requirements of riverine dragonflies and how these potentially shift throughout development can support conservation efforts.

INVENTORY OF ZOOPLANKTON AND MACROINVERTEBRATES IN THE DAYA OF DAR BOUAZZA, CASABLANCA, MOROCCO

This study aims to contribute to the elaboration of an inventory of zooplankton and macro invertebrates in the daya of Dar Bouazza, Casablanca region, Morocco. The determination of macro invertebrates and zooplanktons was based on the study of benthic larvae sampled between March and June 2021 in 4 stations. In the 4 stations, the benthic macro invertebrates recorded are distributed over 4 major faunal groups, 27 families and 35 genera. Coleoptera are largely dominant with 7 families. Diptera are second with 5 families. The Hemiptera are in third place. The zooplanktonic fauna of the Daya is divided into 2 groups: Cladocerans which are represented by three genera (Bosmina, Daphnia and Diaphanosoma) and Copepods which are represented only by the genus Cyclops.The physicochemical results showed a strong mineralization in the Daya. This is probably the combined effect of the degradation of the waters of the Daya of Dar Bouazza and the water table of the coastal chaouia, of which Daya is part. These results are confirmed by bacteriological tests through the identification and enumeration of Coliforms and intestinal Streptococci. The presence of these bacteria translates a pollution of fecal origin making these waters unfit for human use.

Экология, биология и питание хариуса (Thymallus thymallus Linnaeus, 1758) р. Сотки Пинежского государственного заповедника

European grayling Thymallus thymallus (Linnaeus, 1758) is the most valuable nonmigratory species in the ichthyofauna of the Pinezhsky Reserve. The grayling’s habitat inside the specially protected natural area is the Sotka river - the main attraction in the Reserve - flowing through its karst gorges. There are presented the results of comprehensive ichthyological study of grayling population in the Sotka river. Data on the ecology, biology, linearly-weight characteristics and age structure of the population are given. It was found out that grayling prefers the water areas with a mountainous (fast) flow, where it dominates among the fish species and forms a core of the local ichthyocenosis. Specific features of nutrition and age-related changes in the grayling diet have been studied. The 18 taxonomic groups of invertebrates, vertebrates and aquatic vegetation were registered in the food spectrum. The nutrition grayling base in the summer was presented by benthic larvae of amphibiotic insects, planktonic and nektonic organisms. The older species had a narrower range of nutrition based on ground-air insects, while the juveniles' diet was dominated by aquatic insect larvae. By the nature of nutrition, graylings in the river Sotka are euryphages, whose basic diet consists of arthropods. The multi-age structure and abundant population indicates prosperous state of these species.

Growth and survival rates of dispersing free embryos and settled larvae of pallid sturgeon (Scaphirhynchus albus) in the Missouri River, Montana and North Dakota

We released nearly 1.0 million 1-day post-hatch (dph) and 5-dph pallid sturgeon (Scaphirhynchus albus) free embryos in the Missouri River on 1 July 2019 and sequentially captured survivors at multiple sites through a 240-km river reach to quantify daily growth and survival rates during the early life stages. Genetic analysis was used to assign captured fish to released family lots and known ages. Growth rate was similar (0.74–0.75 mm day−1) between the 1- and 5-dph age groups during the 3–4-day dispersal period when water temperature averaged 16.8 °C. Daily survival rate was 0.64 during 1–4 dph for the original 1-dph age group and 0.80 during 5–7 dph for the original 5-dph age group. Total survival during free embryo dispersal (hatch to 9 dph) was estimated as 0.0437. The transition from dispersing as free embryos to settling as benthic larvae was verified for fish originally released as 5 dph. Growth of settled larvae was quantified with a Gompertz model through 75 dph (9 September; 112 mm) when water temperature was 18.8–21.0 °C in the rearing areas. Settled larvae had an estimated daily survival rate of 0.96, and estimated total survival during 9–75 dph was 0.0714. This study provides the first empirical survival estimates for pallid sturgeon early life stages in natural settings and is one of few studies reporting similar information for other sturgeon species. Applications of this work extend to pallid sturgeon restoration programs where population models are being developed to predict recruitment potential and population responses to river management alternatives.

Sampling multiple life stages significantly increases estimates of marine biodiversity.

Biodiversity assessments are critical for setting conservation priorities, understanding ecosystem function and establishing a baseline to monitor change. Surveys of marine biodiversity that rely almost entirely on sampling adult organisms underestimate diversity because they tend to be limited to habitat types and individuals that can be easily surveyed. Many marine animals have planktonic larvae that can be sampled from the water column at shallow depths. This life stage often is overlooked in surveys but can be used to relatively rapidly document diversity, especially for the many species that are rare or live cryptically as adults. Using DNA barcode data from samples of nemertean worms collected in three biogeographical regions—Northeastern Pacific, the Caribbean Sea and Eastern Tropical Pacific—we found that most species were collected as either benthic adults or planktonic larvae but seldom in both stages. Randomization tests show that this deficit of operational taxonomic units collected as both adults and larvae is extremely unlikely if larvae and adults were drawn from the same pool of species. This effect persists even in well-studied faunas. These results suggest that sampling planktonic larvae offers access to a different subset of species and thus significantly increases estimates of biodiversity compared to sampling adults alone. Spanish abstract is available in the electronic supplementary material.

Hydrodynamic interactions with coral topography and its impact on larval settlement

Many benthic larvae rely on ambient flow and turbulence for their dispersal to settlement sites. After reaching the seafloor, larvae must prevent predation as well as overcome flow forces which act to dislodge them in order to achieve successful settlement. Most oceanic benthic habitats are topographically complex and are characterized by a combination of tidally driven currents and wave-driven oscillatory flows, which can exert substantial forces along settlement surfaces. In this study, computational fluid dynamics was used to numerically model both wave-dominated and unidirectional flows over surfaces of varying topography designed to mimic the surface roughness of corals. Near-surface hydrodynamic parameters, including velocities, turbulence statistics, and surface shear stresses, were computed, along with forces on simulated larvae settled on surfaces. It was found that widely spaced surface roughness (characterized as a k-type roughness with roughness width/height > 1) yielded 50–100% higher surface shear stress than tightly spaced roughness (characterized as d-type with width/height < 1), owing to eddy vortex ejection from k-type topographies. Results also found that a larva experiences up to two orders of magnitude greater mean fluid forces when settled on top of a roughness element rather than between roughness elements. Maximum drag and lift forces on a larva were two to three times greater in wave conditions compared to unidirectional flows. Our findings demonstrate that larvae have a higher probability to remain attached to surfaces when in less wavy environments and sheltered within coral crevices of d-type roughness.

Seasonal changes in the zooplankton community and population structure in the northern Bering Sea from June to September, 2017

Zooplankton community structure in the northern Bering Sea may change significantly over relatively short periods due to the inflow of different water masses and the seasonal release of meroplankton, although details of these changes are still unclear. We studied the zooplankton community in the northern Bering Sea from June to September of 2017 and examined seasonal changes in the community structure and stage structure of the dominant species. Zooplankton abundance ranged from 41,000 to 928,000 ind. m−2, with the greatest abundances near 174°W during July. Copepods were the dominant taxa, comprising 10–98% of zooplankton abundance, with benthic larvae such as bivalves dominant at some stations during July and August. Cluster analysis of abundances divided the station/zooplankton communities into seven groups. West of 172°W, clear seasonal changes were not observed, because the Bering Chukchi Winter Water persisted in the deep layer and sampling was only conducted in this region in July and August. In contrast, the community structures east of 172°W differed every month due to water masses changes, meroplankton release, and copepod production associated with the phytoplankton bloom. Despite the changes of water mass, development for the dominant large copepods (Calanus glacialis/marshallae, Eucalanus bungii and Metridia pacifica) was revealed from their population stage structures. Seasonal shifts in species within Neocalanus and appendicularians were driven by water mass exchanges. This study demonstrates that zooplankton community in the northern Bering Sea varies substantially on a monthly time scale. Therefore, to evaluate the impact of climate change on zooplankton, it is important to consider both the seasonal period and the dominant water masses present.

Exogenous Feeding in the Early Life Stages of Sturgeon (Acipenseridae) (Review)

Data on exogenous feeding in the early life stages of sturgeon in the wild and in aquaculture are analyzed. The data on food composition and feeding habits in sturgeon larvae at the stage of transition to exogenous feeding and some later in the wild are conflictive. Some data demonstrate that larvae, upon their transition to exogenous feeding, feed on zoobenthos; other data show that larvae at this stage of development feed on planktonic crustaceans and only in the fingerling period do sturgeons start feeding on benthic crustaceans and insect larvae. This contradiction has apparently resulted from different research conditions. As a whole, a high plasticity of the feeding pattern in the early life stages of sturgeons has been found. Under favorable conditions, sturgeon larvae, upon a transition to the external feeding stage and later stages, feed mainly on zoobenthos; the species composition of food and size of consumed organisms changes in the wake of larvae growth. Zooplankton is constrained food in the case of a deficit of available benthic forms. The predominance of zoobenthos in the feeding during the early life stages of sturgeon, including the transition to the external feeding stage, is connected with (a) the bigger calorie count when compared with zooplankton and (b) a higher accessibility for larvae at the stage of mixed feeding, depending on their morphology and sensory-system development, with a delay of olfactory when compared to gustatory, seismic sensorial, tactile, and electroreception systems.

Developing in a warming intertidal, negative carry over effects of heatwave conditions in development to the pentameral starfish in Parvulastra exigua

Ocean warming and increasing incidence of marine heat waves (MHW) are having far-reaching impacts on coastal ecosystems. The small intertidal asterinid starfish, Parvulastra exigua, in south-eastern Australia, occurs in a global warming hotspot. Development occurs in the intertidal as this species lays eggs and has benthic larvae. The impact of temperature on development to the juvenile was determined over a broad temperature range (12–28 °C) encompassing temperatures experienced during the breeding season (16–20 °C) and cool (- 4 °C) and warm (+10 °C) extremes with the higher temperatures (24–28 °C) simulating a MHW. As the larva to juvenile transition involves major body reorganisation, we determined the impact of temperature on metamorphosis and formation of the normal five-armed juvenile. Development was faster at the higher temperatures 24–28 °C, but survival decreased from 1 to 5 days post fertilisation (dpf). Mortality was evident from day 15 at 22 °C and no larvae survived to 20 dpf at 28 °C. Thermal tolerance decreased over developmental time and the thermal optimum for 95% survival to the 20 day old juvenile spanned from 12 to 20.0 °C with the lethal temperature for 50% survival being 23.5 °C (5.5 °C above ambient). Juveniles reared in 26 °C were smaller, suggesting application of the temperature size rule. Increased temperature (22–26 °C) perturbed pentamery with three, four, six and no-armed juveniles present, contrasting with the low level of non-pentamerous individuals (<3%) in the cooler cultures and in nature (five populations surveyed). Despite the high thermal tolerance in premetamorphic stages, negative carry over effects were evident in the juveniles. This shows the importance of considering the whole of development in climate warming studies. As sea surface temperatures increase and heatwaves become more prevalent, habitat warming will be detrimental to P. exigua populations.

Is it stochastic? Chaoborus larvae bioturbation likely affect the timing of daily methane (CH4) ebullitive flux in a tropical reservoir

Controlling factors of CH4 ebullitive flux are still poorly understood within daily timescales in aquatic environments. Here, we explored if Chaoborus larvae bioturbation can influence the timing of daily CH4 ebullitive flux and how this emission pathway is affected considering direct observations in a tropical reservoir. For this, we collected CH4 bubbles on two different days and three sampling periods: 1–4 pm, 4–7 pm and 7–10 pm. In the middle of each period, we collected Chaoborus larvae, chemical, and environmental variables and acoustically surveyed the underwater environment. We found similar temporal patterns of CH4 emissions between the periods in both days. The intervals of higher CH4 ebullitive flux (1–4 pm and 4–7 pm) appeared to correspond with the exit period of Chaoborus larvae from sediment (2:30 pm to 5:30 pm). Furthermore, the density of benthic larvae, a proxy of the bioturbation intensity, was the only variable that significantly correlated with the ebullitive flux, presenting a high and positive relation. Our findings suggest that the stochastic nature of the CH4 ebullitive flux may not be absolute truth, and this emission pathway might be enhanced daily by a Chaoborus-driven physical disturbance.

Disturbance, dispersal and marine assemblage structure: A case study from the nearshore Southern Ocean

Disturbance is a key factor in most natural environments and, globally, disturbance regimes are changing, driven by increased anthropogenic influences, including climate change. There is, however, still a lack of understanding about how disturbance interacts with species dispersal capacity to shape marine assemblage structure. We examined the impact of ice scour disturbance history (2009–2016) on the nearshore seafloor in a highly disturbed region of the Western Antarctic Peninsula by contrasting the response of two groups with different dispersal capacities: one consisting of high-dispersal species (mobile with pelagic larvae) and one of low-dispersal species (sessile with benthic larvae). Piecewise Structural Equation Models were constructed to test multi-factorial predictions of the underlying mechanisms, based on hypothesised responses to disturbance for the two groups. At least two or three disturbance factors, acting at different spatial scales, drove assemblage composition. A comparison between both high- and low-dispersal models demonstrated that these mechanisms are dispersal dependent. Disturbance should not be treated as a single metric, but should incorporate remote and direct disturbance events with consideration of taxa-dispersal and disturbance legacy. These modelling approaches can provide insights into how disturbance shapes assemblages in other disturbance regimes, such as fire-prone forests and trawl fisheries.

Long-term studies reveal major environmental factors driving zooplankton dynamics and periodicities in the Black Sea coastal zooplankton.

BackgroundThe development and management of shelf-sea ecosystems require a holistic understanding of the factors that influence the zooplankton structure and ecosystem functions. The Black Sea is an example of such areas influenced by eutrophication, overfishing, climate variability, invasions of the ctenophores Mnemiopsis leidyi followed by Beroe ovata. Thus, there is a set of principal factors which may influence and explain periodicities in the Black Sea ecosystem.MethodsWe analysed a total of 918 samples taken from 1991 to 2017 with intervals of 10 days. Taxa were identified to species, their abundance and biomass were calculated. We tested 12 environmental factors, which may explain zooplankton distribution: temperature, productivity-linked factors (surface chlorophyll as a proxi), wind, turbidity, lowest winter temperature, and concentration of the ctenophore M. leidyi. We used canonical correspondence analyses to find the dominant environmental factors and further regression analyses to retrieve dependences of plankton biomass on the major factors. Periodicities were assessed with the use of the Continuous wavelet transform and tested with use of One-way ANOSIM and PERMANOVA. The distances between ecosystem states in different years were assessed using non-metric multidimensional scaling.ResultsCurrently, temperature and productivity are the major environmental factors driving zooplankton dynamics. Not long ago, before 1999, abundance of M. leidyi was one of the major factors explaining the zooplankton variance. Spectral analysis of species abundances revealed a 4-year transitional period in 1999–2002 (not reported before) when ecosystem adapted to a new invader B. ovata. Statistically robust 2- and 3-year periodicities were retrieved for most plankton taxa and some benthic larvae. We found robust correlations between temperature and surface chlorophyll concentration on one side and plankton abundances and biomass on the other, and retrieved multivariate regressions, which may have a prognostic value.

OBSERVATIONS OF CANOPY FLOW STRUCTURE AND FRICTIONAL VELOCITY OF CORAL COLONIES IN DONGSHA ATOLL

Understanding the hydrodynamics is important for biological, ecological, and biogeochemical processes in coral reef systems. The near-bed flow motion affects the benthic organism distributions, morphological evolution, larvae settlement, and nutrient uptake. The near-bed flow structures have been characterized as planar boundary-layer flows when the bottom roughness scale created by benthic organisms is much smaller than the water depth. On the other hand, when the bottom roughness scale becomes much larger, the resistance drag forces caused by these canopy elements should be considered (Rosman and Hench, 2011). The form drag of the multiple coral colonies generates turbulent wakes, enhances turbulent mixing, and changes the flow structure (Huang, 2015). Many laboratory and modeling studies have reported the drag parameterization and the flow structure for unidirectional flows through submerged canopy or vegetation (e.g., Finnigan, 2000; among many others). However, the vertical flow structures of the canopy layer caused by coral colonies (bommies) are rarely reported in fields. Here we present field measurements of flow structure over coral colonies using acoustic Doppler velocimetry (ADV) and pulse-coherent Doppler velocity profiler (PCADP) techniques. The measured current profiles and turbulence are used to study the flow dynamics in the canopy-layer created by coral colonies.

Contrasting life histories contribute to divergent patterns of genetic diversity and population connectivity in freshwater sculpin fishes

BackgroundLife history characteristics are considered important factors influencing the evolutionary processes of natural populations, including the patterns of population genetic structure of a species. The sister species Cottus hangiongensis and C. koreanus are small bottom-dwelling freshwater sculpin fishes from South Korea that display marked life history divergence but are morphologically nearly indistinguishable. Cottus hangiongensis evolved an ‘amphidromous’ life history with a post-hatching pelagic larval phase. They spawn many small eggs in the low reaches of rivers, and hatched larvae migrate to the sea before returning to grow to maturity in the river mouth. In contrast, C. koreanus evolved a ‘fluvial’ landlocked type with benthic larvae. They release a smaller number of larger eggs, and the larvae undergo direct development, remaining benthic in the upstream rivers throughout their entire lives. We tested whether there were differences in patterns and levels of within-population genetic diversities and spatial population structure between the two closely related Korean sculpins using mitochondrial DNA control region sequences and seven nuclear microsatellite loci.ResultsThe combined analyses of both marker sets revealed that C. hangiongensis harboured considerably higher levels of within-population genetic diversities (e.g. haplotype/allelic richness, heterozygosities) than C. koreanus. In contrast, the fluvial sculpin exhibited noticeably more spatial population structure than did the amphidromous sculpin, as suggested by pairwise FST statistics. The finding that C. hangiongensis individuals comprised a single random mating population across the east-flowing river basins in the Korean Peninsula, whereas C. koreanus individuals comprised genetically discrete individual populations, was further supported by an individual-based Bayesian population assignment and also factorial correspondence analyses.ConclusionsThe higher genetic diversity, but lower population structure, of the amphidromous sculpin relative to the fluvial sculpin may have resulted from its greater larval dispersal and also possibly, higher fecundity accompanied by an amphidromous life history. Hence, we conclude that contrasting early life histories – including the presence or absence of the pelagic larval phase – may have led to divergent patterns of within-population genetic diversities and spatial population structure between the sister Cottus species following speciation from a common ancestor of marine sculpin.

De novo transcriptome assembly and developmental mode specific gene expression of Pygospio elegans.

Species with multiple different larval developmental modes are interesting models for the study of mechanisms underlying developmental mode transitions and life history evolution. Pygospio elegans, a small, tube-dwelling polychaete worm commonly found in estuarine and marine habitats around the northern hemisphere, is one species with variable developmental modes. To provide new genomic resources for studying P. elegans and to address the differences in gene expression between individuals producing offspring with different larval developmental modes, we performed whole transcriptome Illumina RNA sequencing of adult worms from two populations and prepared a de novo assembly of the P. elegans transcriptome. The transcriptome comprises 66,233 unigenes, of which 33,807 contain predicted coding sequences, 26,448 have at least one functional annotation, and 3,076 are classified as putative long non-coding RNAs. We found more than 8,000 unigenes significantly differentially expressed between adult worms from populations producing either planktonic or benthic larvae. This comprehensive transcriptome resource for P. elegans adds to the available genomic data for annelids and can be used to uncover mechanisms allowing developmental variation in this and potentially other marine invertebrate species.

Coastal Ecosystem Effects of Increased Summer Temperature and Contamination by the Flame Retardant HBCDD

The combined effects of ocean warming and contaminants on marine ecosystems are poorly understood. In this study, we exposed model ecosystems comprising typical shallow coastal Baltic Sea communities to elevated temperature (+5 °C) and the flame retardant hexabromocyclododecane (HBCDD), both singly and in combination, for 13 days. Higher temperatures caused the release of PO4 from the sediment, which in turn stimulated the growth of the cyanobacteria Dolichospermum sp. This in turn led to an increase in the copepod Acartia bifilosa and other indirect effects in the plankton, interpreted as being caused by changes in predation, grazing, and competition. Elevated temperatures also stimulated benthic primary production and increased production of benthic mollusk larvae. Although increased temperature was the dominant driver of effects in these systems, HBCDD also appeared to have some effects, mainly in the zooplankton (both direct and indirect effects) and benthic meiofauna (an interactive effect with temperature). Although the study used model ecosystems, which are an approximation of field conditions, it highlights that interactive ecosystem effects between two stressors are possible and demonstrates the ecological and temporal complexity of such responses. Such unpredictable responses to warming and contaminants are a major challenge for ecosystem management to deal with multistressor situations in the Baltic Sea.

Population and reproductive dynamics of the polychaete Pygospio elegans in a boreal estuary complex

AbstractPygospio elegans is an opportunistic, wide‐spread spionid polychaete that reproduces asexually via fragmentation and can produce benthic and pelagic larvae, hence combining different developmental modes in one species. We documented the density, size distribution, and reproductive activity of P. elegans at four sites in the Danish Isefjord‐Roskilde Fjord estuary complex, where all modes of reproduction were reported. We compared population dynamics of this species to environmental parameters such as salinity, temperature, and sediment characteristics (grain size, sorting, porosity, water content, organic content, C/N). We observed that new cohorts—resulting either from sexual or asexual reproduction—appeared in spring and fall, and old ones disappeared in late summer and winter. Sexual reproduction occurred from September until May, and although their timing was variable, there were two reproductive peaks at three sites. At those sites, we also observed a switch in larval developmental mode. Asexual reproduction peaked in April. While the seasonal dynamics can be related to temperature to a large extent, the differences in population dynamics among sites also correlated with sediment structure and salinity. Populations from sites with coarse and heterogeneous sediment had high levels of sexual reproduction. At the site with lower salinity, intermediate and benthic larvae were present during winter in contrast to pelagic larvae found at the other sites. However, we could not identify one clear environmental factor determining the mode of development. At present, it remains unclear to what degree genetic background contributes to mode of development. Hence, whether the differences in developmental mode are the result of genetically different cohorts will be further investigated.

DNA Methylation and Potential for Epigenetic Regulation in Pygospio elegans.

Transitions in developmental mode are common evolutionarily, but how and why they occur is not understood. Developmental mode describes larval phenotypes, including morphology, ecology and behavior of larvae, which typically are generalized across different species. The polychaete worm Pygospio elegans is one of few species polymorphic in developmental mode, with multiple larval phenotypes, providing a possibility to examine the potential mechanisms allowing transitions in developmental mode. We investigated the presence of DNA methylation in P. elegans, and, since maternal provisioning is a key factor determining eventual larval phenotype, we compared patterns of DNA methylation in females during oogenesis in this species. We demonstrate that intragenic CpG site DNA methylation and many relevant genes necessary for DNA methylation occur in P. elegans. Methylation-sensitive AFLP analysis showed that gravid females with offspring differing in larval developmental mode have significantly different methylation profiles and that the females with benthic larvae and non-reproductive females from the same location also differ in their epigenetic profiles. Analysis of CpG sites in transcriptome data supported our findings of DNA methylation in this species and showed that CpG observed/expected ratios differ among females gravid with embryos destined to different developmental modes. The differences in CpG site DNA methylation patterns seen among the samples suggest a potential for epigenetic regulation of gene expression (through DNA methylation) in this species.

Evaluation of Chironomidae Diversity in the Little Paint Creek Watershed, Pennsylvania

ABSTRACT The health of a watershed can be assessed by evaluating the benthic macroinvertebrates that are present in the waterways. Benthic chironomid larvae (Diptera: Chironomidae) are often used as a biological indicator of ecological health. The chironomid larvae are particularly tolerant to contaminants, with different taxa exhibiting different levels of tolerance. Thus, evaluation of the abundance and diversity of chironomids within a watershed can be an assessment tool for the biotic health of the watershed. Although several studies of Pennsylvania watersheds have identified the presence of Chironomidae, our study aimed to further understand chironomid diversity by assessing them to the subfamily and genus level. We surveyed eight sites over Little Paint Creek and three tributaries within the Little Paint Creek watershed in southwestern Pennsylvania. By comparing the chironomid abundance and diversity to previously published EPT data for the watershed, our data suggests that water quality of tributary UNT 45234 is better than previously predicted and may be better than that of tributary UNT 45242. The limited number of less tolerant subfamilies of chironomids in the Little Paint Creek samples suggests that this stream may have reduced water quality. We established a baseline of chironomid abundance and diversity within the Little Paint Creek watershed. Our future goal for the project will be to continue to monitor the chironomids at these sites and to compare our findings to areas within the watershed which have been reported to have higher rates of contaminants due to acid mine drainage and Marcellus shale drilling, to determine their effect on aquatic macroinvertebrate diversity.

Zoobenthos are minor dietary components of small omnivorous fishes in a shallow eutrophic lake

We examined whether small omnivorous fishes (smaller than ~100mm long) integrate littoral, pelagic and benthic pathways in a shallow, eutrophic lake (Lake Izunuma, Japan). The surface of the lake was covered by a dense vegetation of floating-leaved macrophytes, and small species dominated the icthyofauna. We determined the δ13C and δ15N ratios of five dominant species of small omnivorous fishes. Using a stable isotope analysis in the R mixing model, we determined the possible contribution of three potential food sources (epiphytic algae, zooplankton and zoobenthos (larval chironomids)) to omnivorous fish tissue compositions. Four omnivorous fishes (Gnathopogon elongatus elongatus, Pseudorasbora parva, Biwia zezera and Tridentiger obscurus) subsisted largely on epiphytic algae and zooplankton, whereas zoobenthos contributed little to their diets. Acheilognathus rhombeus subsisted mostly on epiphytic algae. Thus, in this shallow, eutrophic lake, omnivorous fishes incorporated both littoral and pelagic production into the food web, but rarely benthic production. The dominant benthic chironomid larvae often burrow several centimetres into the sediment, and the low dietary contribution of zoobenthos to small fishes may be due to inefficiency at foraging on buried benthos associated with fish body size.