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The microsporidium Nosema pontogammari Ovcharenko and Kurandina, 1987 was detected in the muscles of Pontogammarus robustoides collected in the stream of South Baltic Coastal Zone (sample site N 54°16', E 19°25') The parasite infects the cytoplasm of the muscle cells. The presence of remarkable intracytoplasmic vacuoles was noted inside of some parasite cells. Transmission electron microscopy showed that these intracytoplasmic vacuoles contained numerous microorganisms identified as rickettsialike prokaryotic cells. Groups of pleiomorphic in shape bacilliform and rounded cells were enveloped in electron-dense cover 20-30 nm wide. The prokaryotic cells wali was constructed out of triple layered coat of different electron density. The cytoplasm of infected cells was degenerated with weakly developed endoplasmic reticulum and undeveloped organelles. The obtained data demonstrate pathogenic nature of host-parasite relationship between endosymbiotic rickettsia-like organism and microsporidia.
In a small piece of Baltic amber several poorly preserved amphipod crustaceans were found. The most probable seems to be the affinity of these amphipods to the freshwater family Crangonyctidae.
The present paper reports for the first time on the occurrence of the parasite Maritrema subdolum in the amphipod Gammarus tigrinus, a non-native species in the Gulf of Gdańsk.
The North American gammaridean amphipod, Gammarus tigrinus, was found in the easternmost part of the Baltic Sea (Neva Estuary) near a new oil terminal. This species may well have been transported to the Neva Estuary with ballast waters from the Finnish area of the Gulf of Finland, where it was recorded recently. In 2005, the mid-summer density of G. tigrinus was 27 indiv. m−2. By 2006 this species had spread 100 km to the east from the first site, colonizing the northern coastal zone of the estuary. Its density reached 99–126 indiv. m−2. Fecund females and juveniles contributed about 50% to the entire population density, which testifies to the successful reproduction and establishment of G. tigrinus in the Neva Estuary. There is a high risk of further expansions of G. tigrinus from the new area to the various lakes of Eastern Europe via inland canal-river systems, which may lead to unforeseeable changes in aquatic communities.
Stream invertebrates use ‘drift’ or downstream transport in the water column to disperse, but they also actively move upstream against current. These movements have important role in re-colonization of empty stream reaches and in regulation of population size. For more than half a century, research of stream drift was stimulated by the problem of ‘drift paradox’, i.e. the question how upstream reaches of streams remain inhabited despite constant and often ample losses of individuals by drift. In this study we examined drift and upstream movements of the amphipod Gammarus fossarum through monthly sampling over one-year period at two sites in the upper and middle course of a small unaltered stream in the northwest Croatia. Differences in tendency to drift and to move upstream and effects of environmental factors (temperature, flow, population density and detritus dry weight) on the movement dynamics on both temporal and spatial scale were examined for three size categories (adults, subadults and juveniles). While seasonal variations of drift and upstream movements were similar at two examined sites, at the middle course we recorded higher density, and higher drift and upstream movement rates. In both drift and upstream movements, adults were the most represented size category. In subadults and juveniles, both type of movements depended on population density. Adult upstream movements peaked in November and May/June, with massive upstream movements in May in the middle course. Seasonality of diurnal and nocturnal drift was very similar at both sites, while seasonality of diurnal and nocturnal upstream movements differed between the sites. Out of four examined independent environmental factors, density and temperature had the most important positive effect on spatiotemporal variations of diurnal drift, while nocturnal drift was more strongly affected by density and flow. Temperature was the most significant driver of diurnal upstream movements, while nocturnal upstream movements were most significantly positively affected by density. Massive upstream movements were driven by overcrowding and enabled adults to colonize microhabitats where food is more abundant and competition is less severe.
Recently Pontogammarus robustoides, a Ponto-Caspian amphipod species that has invaded Baltic lagoons and lower Vistula River at the end of 20lh century, abundantly appeared in some water bodies of the Great Masurian Lakes area.
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