Enhanced early detection and enumeration of zebra mussel (Dreissena spp.) veligers using cross-polarized light microscopy

Zooplankton with calcareous skeletons are birefringent under cross-polarized light, and thus this technique can be quite useful, indeed sometimes almost essential, for the detection and enumemeration of these types of organisms in plankton samples. A simple and inexpensive application of this technique is described and illustrated with quantitative examples from research on the veligers of the zebra mussel Dreissena polymorpha (Pallas). The time required to detect veligers in plankton samples was decreased by an order of magnitude; the accuracy of counts was substantially improved (15% more than controls), and the time required for counts was greatly reduced (41% of control times). This technique is especially useful in situations in which veligers are difficult to find or see (e.g., at low densities, in samples cluttered with extraneous organisms or material) or when the investigator is inexperienced with plankton sampling and planktonic organisms. The major limitations are its inability to discriminate among various bivalve species that have planktonic larvae and the similar appearance of ostracods which also have calcareous shells. Expanded use of this technique should (1) increase our ability to use plankton sampling for the early detection of veligers during range expansion and reproductive cycles and (2) permit more accurate estimates of veliger abundance.     

Downstream dispersal of zebra mussels (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>) under different flow conditions in a coupled lake-stream ecosystem

Dispersal, establishment, and spread of aquatic invasive species such as the zebra mussel (Dreissena polymorpha) can be influenced by riverine velocities and volumetric flows in invaded lake-stream ecosystems. Zebra mussels, which have a planktonic larval form (veliger), disperse rapidly downstream from a source population. Concentrations, dispersal, and body conditions of zebra mussel veligers were studied under different volumetric flow, or discharge, conditions in a coupled lake-stream ecosystem in northern Texas, USA. Veliger densities in lotic environments were strongly related to population dynamics in upstream lentic source populations. A strong exponential decrease in veliger density was observed through a 28-km downstream study reach. Increased water releases from the source reservoir increased veliger flux and dispersal potential, concomitantly increasing veliger flux and decreasing transit time. However, passage through release gates in the dam and increased turbulence in the river during high-discharge events could negatively affect body condition of veligers, and veliger body condition generally decreased from the source population to the farthest downstream site and was lower for veligers during periods of high discharge. Thus increased discharge appears to reduce the proportion of viable veligers because of increased turbulence-induced mortality. Colonization of distant downstream reservoirs can occur if discharge and propagule pressure are sufficient or if interim habitats are suitable for establishment of in-stream populations.     

Suppression of microzooplankton by zebra mussels: importance of mussel size

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22-mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments. 2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer-based clearance rates of large (22 mm) mussels approached published values for phytoplankton food. 3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.     

环境DNA技术在贻贝入侵监测中的应用挑战

沼蛤(Limnoperna fortunei)和斑马贻贝(Dreissena polymorpha)是淡水系统中常见的入侵贻贝物种,对其种群规模的持续监测是入侵贻贝防治管控中的关键环节。随着分子生物学技术的发展,入侵物种监测中逐渐尝试利用环境DNA(eDNA)技术实现快速、灵敏检测。然而,在入侵物种引入-定植-扩散过程的监测中,eDNA技术的灵敏度及定量效果受到诸多因素的影响,给实际应用带来挑战。系统梳理了国内外学者利用eDNA技术监测沼蛤、斑马贻贝等入侵物种的研究进展;分析了eDNA技术的采样方案、引物设计、定量分析、质量保证、原位便携仪器设计等影响监测效率与准确率的关键环节;进一步探讨了eDNA技术在贻贝入侵监测中的优势和局限性,以及未来的改进方向。     

Towards a ground pattern reconstruction of bivalve nervous systems: neurogenesis in the zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis>

Bivalvia is a taxon of aquatic mollusks that includes clams, oysters, mussels, and scallops. Within heterodont bivalves, Dreissena polymorpha is a small, mytiliform, freshwater mussel that develops indirectly via a planktotrophic veliger larva. Currently, only a few studies on bivalve neurogenesis are available, impeding the reconstruction of a ground pattern in Bivalvia. In order to inject novel data into this discussion, we describe herein the development of the serotonin-like and α-tubulin-like immunoreactive (lir) neuronal components of D. polymorpha from the early trochophore to the late veliger stage. Neurogenesis starts in the early trochophore stage at the apical pole with the appearance of one flask-shaped serotonin-lir cell. When larvae reach the veliger stage, four flask-shaped serotonin-lir cells are present in the apical organ. At the same time, the anlagen of the cerebral ganglia start to form at the base of the apical organ. From the apical organ, one pair of cerebro-visceral connectives projects posteriorly and connects to a posterior larval sensory organ that contains serotonin- and α-tubulin-like flask-shaped cells. Additional, paired serotonin-lir neurites originate from the apical organ and project into the velum. One unpaired stomatogastric serotonin-lir cell develops ventrally to the stomach at the veliger stage. The low number of serotonin-lir cells in the apical organ of bivalve veligers is shared with larvae of basally branching gastropods and scaphopods and is thus considered a feature of the last common ancestor of Conchifera, while the overall simplicity of the larval neural architecture appears to be a specific trait of Bivalvia.     

Zebra mussels and polystyrene

The growth of settled and metamorphosed larvae of the zebra mussel (Dreissena polymorpha) is clearly retarded when polystyrene plates are used as a substrate compared with the growth of those forms attached to PVC plates. Possibly, low molecular weight compounds are released into the aquatic environment by the polystyrene and these materials may have a strongly adverse effect upon the growth of young zebra mussels. There is no difference in colonization of young mussels between PVC and polystyrene plates if these plates are sufficiently overgrown with bacteria and algae.     

Filtering impacts of larval and sessile zebra mussels (Dreissena polymorpha) in western Lake Erie

Summary We assessed the feeding biology of veliger larvae of the introduced zebra mussel (Dreissena polymorpha Pallas) in laboratory experiments using inert microspheres as food analogues. Mean clearance rate on 2.87-m beads ranged between 247 and 420 L veliger^–1 day^–1. Clearance rate was unrelated to bead concentration up to 100 beads L^–1, but was positively correlated with veliger shell length. Clearance rates of Dreissena veligers are within the range of those reported for marine bivalve veligers of similar size and for herbivorous Great Lakes microzooplankton, but are orders of magnitude lower than those of settled, conspecific adults. The impact of settled zebra mussel grazing activities on phytoplankton stocks may be up to 1162 times greater than that exerted by veliger populations in western Lake Erie. Based on 1990 size-frequency distributions and associated literature-derived clearance rates, reef-associated Dreissena populations in western Lake Erie (mean depth 7 m) possess a tremendous potential to filter the water column (up to 132 m³ m^–2 day^–1) and redirect energy from pelagic to benthic foodwebs. Preliminary analyses indicate that chlorophyll a concentration is strongly depleted (<1 g L^–1) above Dreissena beds in western Lake Erie.     

Influence of toxic and non-toxic phytoplankton on feeding and survival of Dreissena polymorpha (Pallas) larvae

Grazing and survival of larvae of the zebra mussel, Dreissena polymorpha, on a green alga and cyanobacteria were studied in laboratory experiments. Clearance rates of the larvae were determined for Chlamydomonas reinhardtii (green alga), two non-toxic and two toxic Microcystis aeruginosa strains (Cyanobacteria). Clearance rates of larvae on non-toxic Microcystis were significantly higher than on toxic Microcystis. The clearance rate on Chlamydomonas reinhardtii was in between the clearance rates on toxic and non-toxic Microcystis strains and not significantly different from them. Effects of toxicity of Microcystis on the survival of zebra mussel larvae was investigated in a short-term experiment. Survival of larvae fed toxic Microcystis was lower than that of larvae fed non-toxic Microcystis, but higher than that of starved larvae. This may imply that, for survival of zebra mussel larvae, it is better to have bad quality (toxic) food than no food.     

Detection of DNA damage in haemocytes of zebra mussel using comet assay

The aim of the study was to use the comet assay on haemocytes of freshwater mussel, Dreissena polymorpha Pallas, for detection of possible DNA damage after exposure to pentachlorophenol (PCP) and to evaluate the potential application of the comet assay on mussel haemocytes for genotoxicity monitoring of freshwater environment. Zebra mussels were exposed for seven days to different concentrations (10, 80, 100, 150 μg/l) of PCP and in the river Sava downstream from Zagreb municipal wastewater outlet. Significant increase in DNA damage was observed after exposure to PCP at doses of 80 μg/l and higher and after in situ exposure in the river Sava as well. This study confirmed that the comet assay applied on zebra mussel haemocytes may be a useful tool in determining the potential genotoxicity of water pollutants.     

A developmental bottleneck in dispersing larvae: implications for spatial population dynamics

We found evidence for a critical population bottleneck at a developmental‐stage transition in larvae of the zebra mussel Dreissena polymorpha Pallas from field estimates of mortality. Identification of this critical period in the field was made possible by closely tracking cohorts of larvae over 5 days of development as they dispersed 128 km in a river system. The presence of a survival bottleneck during development was confirmed in laboratory studies of zebra mussel larvae. Development‐specific mortality has important implications for spatial population dynamics of the zebra mussel in particular, and all species with indirect development in general. Marine reserves that do not take development‐specific mortality into account may dramatically underestimate reserve size needed to protect rare and/or exploited marine populations. Conversely, for the zebra mussel, the lower contribution of dispersing individuals to population growth downstream of reserves can lead to more feasible control through the blocking of dispersal.     

Selective grazing by adults and larvae of the zebra mussel (Dreissena polymorpha): application of flow cytometry to natural seston

1. Selective grazing of adults and larvae of the zebra mussel (Dreissena polymorpha) on phytoplankton and detritus from both laboratory cultures and natural seston was quantified using flow cytometry. 2. Mean clearance rate of adult zebra mussels was higher on a mixture of the green alga Scenedesmus and the cyanobacterium Microcystis than when Scenedesmus was offered as single food, suggesting selective feeding by the mussels. 3. Feeding on lake seston both adults and larvae showed a higher clearance rate on phytoplankton than on detritus particles, suggesting that zebra mussels select for phytoplankton. Furthermore, it was noted that adults preferred seston particles in the 0–1 and 30–100 μm size ranges. 4. In our study, zebra mussels did not discriminate against cyanobacteria, and our results indicate that they may even ingest them preferentially.     

Space as a limiting resource in freshwater systems: competition between zebra mussels (Dreissena polymorpha) and freshwater sponges (Porifera)

Species interactions between two types of sessile benthic invertebrates, the zebra mussel (Dreissena polymorpha) and freshwater sponges (Porifera), were evaluated in Michigan City IN Harbor in southern Lake Michigan during 1996. The study objective was to define whether competition plays a role in structuring benthic communities using experimental techniques commonly employed in marine systems. Sponges were uninhibited by zebra mussel presence and overgrew zebra mussel shells on hard vertical substrata. In contrast, zebra mussels did not overgrow sponge colonies, but did show an ability to re-capture hard substrata if relinquished by the sponge. The negative affect of sponges on zebra mussels through overgrowth and recruitment suggests interactions that could eventually displace zebra mussels from these benthic communities. However, seasonal reduction of sponge biomass from autumn through winter appears to allow the zebra mussel a periodic respite from overgrowth, preventing exclusion of zebra mussels from the community and allowing these two taxa to co-exist.     

Effects of nonindigenous species on diversity and community functioning in the eastern Gulf of Finland (Baltic Sea)

An increase of xenodiversity in plankton and benthos in the eastern Gulf of Finland was observed from 1998 to 2004. Nonindigenous species account for 4.8% of all species found and up to 96% of total biomass. Invasive benthic omnivores, the alien amphipods Gmelinoides fasciatus and Pontogammarus robustoides and the predaceous fish Perccottus glenii with their versatile diets strongly affect the community structure. Invasive sessile seston-feeders that directly (through grazing and water clearance) and indirectly (through recycling of nutrients) interact with other ecosystem components, are mainly represented by the zebra mussel Dreissena polymorpha, which affect the structure of benthic and planktonic communities as well as benthic-pelagic coupling. The invasive predatory cladocerans Cercopagis pengoi and Evadne anonyx and larvae of D. polymorpha are only temporary components in the zooplankton, which is limiting their overall effect. Alien benthic bioturbators, the polychaetes Marenzelleria neglecta and the oligochaete Tubificoides pseudogaster account for a high proportion of total abundance and biomass but their effects on native species need further research.     

Experimental Pathogenicity of Aeromonas spp. for the Zebra Mussel, Dreissena polymorpha

Experiments were conducted to determine whether species of Aeromonas were pathogenic to the zebra mussel Dreissena polymorpha. A. jandaei, A. veronii, and A. media, identified with Biolog, were originally isolated from dead zebra mussels. When inoculated into living mussels, these bacteria resulted in the mortality of the bivalves. Two additional species, A. salmonicida salmonicida (ATCC 33678) and A. hydrophila (ATCC 7966), were also demonstrated to be pathogenic to the mussels. In addition to the pathogenicity, the data also suggest that the zebra mussels may be an important reservoir for these bacteria in freshwater environments. Received: 26 March 1997 / Accepted: 7 July 1997     

Characterization of zebra mussel (Dreissena polymorpha) sperm motility: duration of movement, effects of cations, pH and gossypol

We have examined effects of time after activation, pH, sodium and potassium, and gossypol concentrations on sperm motility of zebra mussel (Dreissena polymorpha). Zebra mussel spermatozoa appeared to have remarkable viability in the fresh water in comparison with freshwater fish sperm. Duration of sperm motility in fresh water is possibly one of the longest among freshwater animals, since it was not significantly changed 3 h after incubation at room temperature (20 °C) or 24 h of incubation at ±0 °C. High osmotic pressure suppresses sperm motility and effects of sodium and potassium are similar. Spermatozoa were inactive at acid pH and became gradually motile when exposed to pH 6.0–9.0. Gossypol appeared to be a very potent spermicidal agent and inhibited motility. This compound also inhibited fertilization. We observed some differences in gossypol effects on spermatozoa between North American and European zebra mussels. These data on zebra mussel sperm biology may be useful for better handling of gametes under laboratory conditions.     

Fouling of European freshwater bivalves (Unionidae) by the invasive zebra mussel (Dreissena polymorpha)

1. The zebra mussel (Dreissena polymorpha) is well known for its invasive success and its ecological and economic impacts. Of particular concern has been the regional extinction of North American freshwater mussels (Order Unionoida) on whose exposed shells the zebra mussels settle. Surprisingly, relatively little attention has been given to the fouling of European unionoids. 2. We investigated interspecific patterns in fouling at six United Kingdom localities between 1998 and 2008. To quantify the effect on two pan‐European unionoids (Anodonta anatina and Unio pictorum), we used two measures of physiological status: tissue mass : shell mass and tissue glycogen content. 3. The proportion of fouled mussels increased between 1998 and 2008, reflecting the recent, rapid increase in zebra mussels in the U.K. Anodonta anatina was consistently more heavily fouled than U. pictorum and had a greater surface area of shell exposed in the water column. 4. Fouled mussels had a lower physiological condition than unfouled mussels. Unlike tissue mass : shell mass ratio, tissue glycogen content was independent of mussel size, making it a particularly useful measure of condition. Unio pictorum showed a stronger decline in glycogen with increasing zebra mussel load, but had a broadly higher condition than A. anatina at the time of study (July). 5. Given the high conservation status and important ecological roles of unionoids, the increased spatial distribution and fouling rates by D. polymorpha in Europe should receive more attention.     

In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers

1. In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers. 2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six-sided, predator-exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers. 3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’). 4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size-selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size-selective predation on tightly packed zebra mussels in the Ohio would be difficult. 5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.     

Veliger larvae of dreissenids (Bivalvia,Dreissenidae) in the plankton foodweb of Rybinsk Reservoir

The abundance dynamics of adult dreissenids (Dreissena polymorpha (Pallas) and D. bugensis Andrusov) and of their larvae and the spatial distribution of the abundance of veligers and their role in the functioning of the plankton community have been analyzed on the basis of the data of original long-term monitoring (2004–2013) in Rybinsk Reservoir. The dreissenid veligers are most abundant in the summer time (July to August) when their number is comparable to that of the filter-feeding crustaceans and their biomass is close to that of rotifers. Before 2010 the production of veligers during the vegetation season comprised about 5% of the production of metazooplankton and the food consumption was about 1% of the primary production of phytoplankton. Pelagic invertebrate predators consumed about 90% of the production of veligers for the vegetation period. After 2010, the abundance of dreissenid larvae and their functional characteristics decreased by a factor of 5–6. Trophic relationships between zooplankton and veligers are discussed.     

Byssal proteins of the freshwater zebra mussel,Dreissena polymorpha

The freshwater zebra mussel (Dreissena polymorpha) is a notorious biofouling organism. It adheres to a variety of substrata underwater by means of a proteinaceous structure called the byssus, which consists of a number of threads with adhesive plaques at the tips. The byssal proteins are difficult to characterize due to extensive cross-linking of 3,4-dihydroxyphenylalanine (DOPA), which renders the mature structure largely resistant to protein extraction and immunolocalization. By inducing secretion of fresh threads and plaques in which cross-linking is minimized, three novel zebra mussel byssal proteins were identified following extraction and separation by gel electrophoresis. Peptide fragment fingerprinting was used to match tryptic digests of several gel bands against a cDNA library of genes expressed uniquely in the mussel foot, the organ which secretes the byssus. This allowed identification of a more complete sequence of Dpfp2 (D. polymorpha foot protein 2), a known DOPA-containing byssal protein, and a partial sequence of Dpfp5, a novel protein with several typical characteristics of mussel adhesive proteins.     

Epiphytic Refugium: Are Two Species of Invading Freshwater Bivalves Partitioning Spatial Resources?

Enumeration of benthic (bottom dwelling) and epiphytic (attached to plants) zebra and quagga mussels (Dreissena polymorpha and D. bugensis, respectively) at Lake Erie near-shore sites in fall of 2000 revealed an unexpected prevalence of the zebra mussel on submerged plants. Even at Buffalo, New York, USA, where benthic dreissenids have been 92–100% quagga mussel since 1996, zebra mussels constituted 30–61% of epiphytes numerically. This may reflect a partitioning of settling space consistent with interspecific competition. A seasonal epiphytic refugium might allow the zebra mussel to persist even where the benthos is almost exclusively quagga mussel. This revised version was published online in July 2006 with corrections to the Cover Date.