Combined effects of salinity and temperature on grazing activity of invasive Gammarus tigrinus on charophytes

Charophytes are a refuge for zooplankton and stabilize sediments, but they are also a food source for various animal species (water birds, fishes, invertebrates). This grazing pressure may be an important factor prohibiting macrophyte re-colonization in eutrophic coastal waters. Especially the introduction of new species, like Gammarus tigrinus, into the Baltic Sea led to yet not understood changes in the food web. Furthermore, the occurrence of native and invasive species is determined by their capacity to acclimatize to changing abiotic factors. In this study we investigated the influence of temperature and salinity on the grazing pressure of Gammarus tigrinus on two charophyte species: Chara tomentosa and Chara aspera. The grazing experiments were conducted in a full factorial design with the factors salinity (3 – 13 PSU), temperature (5 – 30 °C), and charophyte species. Grazing rates were determined as mass deviation within 48 hours considering simultaneous growth of the charophytes. Experimental results were further used to determine gross macrophyte biomass within the ecosystem, using field data. Gammarids preferred C. aspera before C. tomentosa, but both were grazed within their respective growth optima. The potential grazing peak of 24 °C is not yet reached in these coastal waters. Furthermore, calculation of gross production revealed that macrophytes could show up to 60% and 15% more biomass without grazing in deeper light-limiting, and shallow, not light limited water depths, respectively. The impact of food web on coastal water restoration should therefore be equally considered, as the nutrient control.

Amphipods in estuaries: the sibling species low salinity switch hypothesis

A novel low salinity switch hypothesis is proposed to account for the speciation of an obligate estuarine (oligohaline) amphipod, Orchestia aestuarensis, from a closely-related one, Orchestia mediterranea, found in both estuarine and marine conditions (euryhaline). The underlying genetic mechanisms could involve: 1. A dimorphic allele, or linked set of alleles, carried by the euryhaline amphipod which controls the ability to breed in low salinity conditions in estuaries and which is selected for in these conditions, producing the oligohaline amphipod. 2. A genetically-assimilated gene or genes, controlling the ability to breed in low salinity conditions in estuaries, which is/are “switched on” by low salinity conditions. 3. Allopatric speciation from a euryhaline to an oligohaline amphipod species where low salinity conditions is the selective switch. It is possible that other estuarine, sibling, amphipod pairs have evolved by salinity switching. In the North Atlantic coastal region, this could include: Gammarus tigrinus/G. daiberi and G. salinus/G. zaddachi (Amphipoda, Gammaridae).

The invasive amphipod Gammarus tigrinus Sexton, 1939 conquering the north of Europe using a new pathway: the first recordings from Norway

The invasive amphipod Gammarus tigrinus has during the last decades spread to large parts of Northern Europe, mainly using pathways eastwards from The British Isles to Continental Europe and further northeast into the Baltic Sea. From the coastline it has to some extent spread further inland, especially in topographically low-relief landscapes with highly polluted rivers. This account reports another geographical direction of dispersal, towards north into Southern Norway. In coastal brackish-water regions G. tigrinus may displace other gammarids. Large parts of Norway consist of high-relief landscapes close to many estuaries, so the further spread into this country is doubtful. However, if the taxon can avoid the initial barriers using vectors and spread into new watercourses above such barriers and thrive in this new ambient water chemistry, it may have large negative influence on the other benthic fauna. But Norwegian lakes and rivers are most probably too electrolyte-poor to support this species. However, in estuaries and other brackish waters along the coast, at least in the southern part of Norway, the species will thrive. Gammarus tigrinus is the only known intermediate host for the native American acanthocephalan parasite Paratenuisentis ambiguus, which has the American eel as its main host. This parasite also infects the European eel, and this poses an additional threat to the already endangered eel in Norwegian rivers where G. tigrinus has been recorded.

Changes in the benthic fauna composition in the Upper Vistula over the last 50 years – the consequences of the water pollution reduction and alien species invasion

The organic pollution of the Upper Vistula waters has been significantly reduced since the mid-20th century. Also salinity has gradually decreased, following an increase observed until the 1990s. Furthermore, the number of alien species has systematically increased. The above-mentioned changes have affected the richness and composition of the benthic fauna. They are particularly remarkable in the river stretch between the town of Oświęcim and the city of Kraków. The improvement of water quality has resulted in the increased number of taxa, mainly those characteristic of moderately polluted water, and the disappearance of taxa typical of strongly polluted or deoxygenated water. Despite the increased salinity level persisting for many years, only three benthic species of brackish waters (Gammarus tigrinus, Paranais frici and P. litoralis) were found in the Upper Vistula. Taxa considered to be euryhaline or halophilous were more numerous. In the 1960s, only one alien species (Physa acuta) was found, but the increased number of non-indigenous species in the last decades is visible, particularly among gammarid crustaceans (Amphipoda, Gammaroidea). The presence of alien species has not caused any visible changes in the species abundance of oligochaetes and mollusks.

Macroinvertebrate communities on various microhabitats of a saline coal mine settling pond

To date, no studies have been conducted on macroinvertebrate communities in coal mine settling ponds used for temporary retention of saline mine waters. The objective of the research was to evaluate which habitat – Ruppia maritima, Phragmites australis or sediments without macrophytes – is the most favorable for the abundance and biomass of macroinvertebrate communities. The study was carried out in a hyposaline settling pond located in a mining and urban area in southern Poland. At this time, it is the only inland locality of R. maritima in Poland. In the studied coal mine settling pond, the non-native, euryhaline amphipod Gammarus tigrinus dominated in the communities on all the habitats. The abundance of other taxa was small and similar on each type of substrate; only Corixidae were much more abundant on the widgeongrass beds. The highest abundance and biomass of macroinvertebrates was recorded at the sites with R. maritima. Our study highlights the importance of coal mine settling ponds as a substitute habitat for salt-tolerant invertebrates.

The first records of the occurrence of a North American invader Gammarus tigrinus Sexton, 1939 in the tributaries of the upper Vistula River

The amphipod species Gammarus tigrinus, Sexton 1939 is native to the Atlantic coast of North America. The native range of its occurrence includes oligo- and mesohaline brackish waters with salinity of up to 14‰. Our survey was carried out in the tributaries of the upper Vistula River in Upper Silesia that is the most urbanised and industrialised region in Poland and constitutes one of the largest coal basins in the world. This survey uncovered the first occurrence of G. tigrinus with the maximum density of 1040 individuals m−2 in the tributaries of the upper Vistula River that have been polluted by coal mine water discharge. The occurrence of the invasive alien gastropod species, i.e. Potamopyrgus antipodarum (Gray, 1843) was also recorded in such salinised water. Our results showed that the anthropogenically salinised tributaries of the upper Vistula River constitute new habitats for euryhaline species and create new migration routes for alien and invasive species.

Non-indigenous amphipods and mysids in coastal food webs of eastern Baltic Sea estuaries

The study analyses the role of non-indigenous invertebrates in the food webs of two eutrophic brackish estuarine ecosystems of the Baltic Sea: the Neva River estuary and the Curonian Lagoon, with the aim of clarifying several questions such as what trophic levels were occupied by newly established species (mainly amphipods and mysids) and whether they can affect the native benthic invertebrates as a result of their possible carnivorous nature. Stable isotope analysis (δ15N values) and gut contents analysis of field-collected specimens were used to estimate trophic level and trophic links of the newly established malacostracan crustaceans, while their consumption rates when feeding as carnivores were measured experimentally. The δ15N analysis allocated four trophic levels (TL) in the coastal food webs of both studied ecosystems with the lowest δ15N (2–4‰) for detritus and algae and the highest for fish (12–14‰). Through their high abundance, non-indigenous crustaceans (Pontogammarus robustoides, Gmelinoides fasciatus, Obessogammarus crassus, Gammarus tigrinus, Limnomysis benedeni and Paramysis lacustris) have become important members of food chains of the studied ecosystems. Their trophic position varied significantly within species during ontogenesis. This suggests that they turned from being typically detritivores/plantivorous (TL 2–2.4) at juvenile stages to omnivores (2.5–3) or to carnivores (>3) as adults. Assessment of the predation pressure by the adult amphipods on other coexisting invertebrates (in the example of the Neva Estuary) showed a low or medium impact, depending on species of predator and productivity of its potential prey organisms.