We report the first results of a parasitological study of Dreissena polymorpha (zebra mussels) from the brackish Curonian Lagoon, SE Baltic Sea. Zebra mussels were collected monthly from May to October 2011 from a site near the mouth of the River Nemunas. Three types of endosymbionts were found in the mantle cavity and visceral mass of the molluscs during dissections, i.e. the commensal ciliate Conchophthirus acuminatus and parasitic ciliate Ophryoglena sp., and rarely encountered, unidentified nematodes. The abundances of C. acuminatus and Ophryoglena sp. were positively associated with host shell length and water temperature, but no effect of water salinity was detected. As the endosymbionts are either highly host-specific to zebra mussels (C. acuminatus and Ophryoglena sp.) or are probably free-living organisms that inadvertently infect the molluscs (nematodes), we conclude that the presence of D. polymorpha in the Curonian Lagoon does not pose any serious parasitological risk to native biota.We emphasize, however, that this conclusion should be treated with caution as it is based on a study conducted only at a single location. Our work extends the currently scarce records of D. polymorpha parasites and commensals from brackish waters, and adds to a better understanding of the ecological impact this highly invasive mollusc causes in the areas it has invaded.
Oceanologia 54(4): 701-713

The freshwater invasive mollusc Dreissena polymorpha and its host-specific commensal ciliate Conchophthirus acuminatus represent a convenient model to study various aspects of symbiotic relationships. This study was conducted to test whether the nutrient enrichment of waterbodies inhabited by D. polymorpha is associated with C. acuminatus infection. Three lakes differing in their trophic conditions were simultaneously sampled to estimate the levels of C. acuminatus infection in D. polymorpha (eutrophic Lake Batorino, moderately eutrophic Lake Myastro, and mesotrophic Lake Naroch, Republic of Belarus). Although the percentage of infected molluscs did not differ among these waterbodies, the average number of ciliates per host showed a significant increase with respect to the lake trophic status. This pattern could be explained by favorable feeding conditions experienced by D. polymorpha and its commensal C. acuminatus in waters of higher trophy. In particular, the average size of D. polymorpha (i.e., carrying capacity for the infection) significantly positively correlated with the lake trophic status. Higher trophy could also directly affect reproduction potential of the ciliate C. acuminatus, which supposedly feeds on bacteria, algae, and other organic particles filtered out from the water by its host. The results of this study may apply to a wider spectrum of similar commensal associations in fresh waters.
BioInvasions Records (2012) 1(3): 161-169

Aquatic organisms are exposed to pollution which may make them more susceptible to infections and diseases. The present investigation evaluated effects of nickel contamination and parasitism (ciliates Ophryoglena spp. and intracellular bacteria Rickettsiales-like organisms), alone and in combination, on biological responses of the zebra mussel Dreissena polymorpha, and also the infestation abilities of parasites, under laboratory controlled conditions. Results showed that after 48 h, more organisms were infected in nickel-exposed groups, which could be related to weakening of their immune system. Acting separately, nickel contamination and infections were already stressful conditions; however, their combined action caused stronger biological responses in zebra mussels. Our data, therefore, confirm that the parasitism in D. polymorpha represents a potential confounding factor in ecotoxicological studies that involve this bivalve.
Ecotoxicology (2012) 21, 538–547

The zebra mussel (Dreissena polymorpha) and its congener the quagga mussel (Dreissena rostriformis bugensis) are both invaders in freshwater, but have very different invasion histories, with zebra mussels attaining substantially faster rates of spread at virtually all spatial scales. However, in waterbodies where they co-occur, D. r. bugensis can displace D. polymorpha. To determine if the mechanisms for this displacement are associated with different survival and growth, we kept mussels in flow-through tanks for 289 days with two temperature regimes that mimicked the natural surface water (littoral zone) and hypolimnion conditions of Lake Erie. For the littoral zone regime, we used water directly from the surface of Lake Erie (range 4–25°C, average 11.9 ± 0.6°C). For the profundal zone treatment, Lake Erie surface water was chilled to about 6°C (range 5–8°C, average 6.2 ± 0.6°C) for the full duration of the experiment. For each of these temperature regimes, we used three replicate tanks with only zebra mussels present and three replicate tanks with only quagga mussels (150 ind./tank each), and three replicate tanks with both species (75 ind./tank of each species). Quagga mussels had higher survivorship and grew more than zebra mussels in all treatments. For both species, the size of the mussel entering the winter was critical for survivorship. Larger mussels had a higher survival over the winter in all treatments. For both species, there was a survivorship and growth tradeoff. In the warmer littoral zone treatment both species had higher growth, but lower survival than in the colder profundal zone treatment. Surprisingly, although quagga mussels outperformed zebra mussels, zebra mussel survivorship was better when they were faced with competition by quagga mussels than with just intraspecific competition. In addition, quagga mussels suffered size-specific mortality during the growing season only when facing interspecific competition with zebra mussels. Further experiments are needed to determine the possible mechanisms for these interspecific effects.
Hydrobiologia (2010) 668(1): 183-194

We report the first results of parasitological study of Dreissena polymorpha (zebra mussels) from Sweden. The samples of Dreissena were collected from Lake Erken in July 2007. The most common endosymbionts found in the mantle cavity of the mussels were the commensal ciliate Conchophthirus acuminatus and free-living nematodes Chromadorina bioculata and Laimydorus sp. Unidentified chironomid larvae and aquatic mites were also occasionally observed in the mantle cavity. The finding of host-specific ciliate C. acuminatus suggests that zebra mussels invaded Lake Erken at the juvenile or adult stage.
Aquatic Invasions (2008) 3(1): 83-86

Изучение некоторых сторон биологии дрейссены проводились в Кучурганском лимане-охладителе Молдавской ГРЭС в 1965-1968 гг. Ее размножение протекает здесь в течение всего вегетационного периода. Подтверждением этого служит одновременное обнаружение всех трех планктонных стадий личинок-велигеров с апреля по ноябрь при температурах воды не ниже 6°C. Численность личинок в течение вегетационного периода и по отдельным годам значительно изменяется. Из каждой тысячи личинок дрейссены, поступающей в охладительную систему ГРЭС, 600 обратно в лиман не возвращаются. Среди них примерно 12% составляют личинки на стадии оседающего велигера. Большая их часть закрепляется в системе водоводов. Рост всех возрастных групп дефинитивных особей дрейссены в камерах чистой воды ГРЭС в равной мере, как и сеголеток из нижнего плеса лимана, находящегося под постоянным воздействием работы станции, протекает намного интенсивнее, чем в других водоемах страны. Это дает основание считать, что при остальных равных экологических условиях температурный режим водоема играет решающую роль в лимитировании интенсивности роста дрейссены.

This is the first study to quantify the periodic emergence of a Conchophthirus sp. from its bivalve host. Emergence rates of C. acuminatus from Dreissena polymolpha over the entire 24-day experiment appeared to be directly correlated with infection intensity. The rate of ciliate emergence from individual mussels varied considerably throughout the experiment at both 14°C and 21°C. It was not uncommon to have a sampling period in which no emergence was observed immediately followed by a period of high emergence, e.g., at 14°Cfrom 0 to 25 ciliates and at 21°C from 0 to 720 ciliates. The total mean number of ciliates that were observed to have emerged from each mussel during the 24-day experiment was significantly higher at 21°C (207 ciliates/mussel) than at 14°C (29 ciliates/mussel). Our experiments suggested that C. acuminatus have a short survival period outside their host. Although we observed a maximum survival period of 144 hr (6 days), most ciJiates died within 48 h.
Journal of Shellfish Research (2003) Volume 22, Issue 1: 495-500