Diet of European freshwater pearl mussels Margaritifera margaritifera (Mollusca: Bivalvia: Unionoida) in small river (Republic of Karelia, Russia)

The freshwater pearl mussel Margaritifera margaritifera (Linnaeus,1758) is endangered in Europe and is now listed in the Red Data Book of many countries and regions. The diet of the species in the Syskyänjoki River (a tributary of Lake Ladoga) has been studied. The contents of the intestine generally correspond to the composition of seston, and include organic detritus, filamentous and unicellular algae, fragments of invertebrates and macrophyte tissues mixed with silt and sand. The total biomass of the intestinal contents of varied from 0.8 to 30.6 mg per organism (absolutely dry weight). Margaritifera margaritifera consumes a wide range of particles, from 0.5 μm3 (bacteria and unicellular algae) to 200 000 μm3 (fragments of invertebrates and macrophyte tissues). About 90–95% (by volume) of the intestinal contents was consisted by fine organic detritus. The food composition did not differ significantly for mollusks of different sexes and size. In the intestinal contents, 63 taxa of algae were identified. The number of algal species in the content of one intestine varied from 3 to 17, with their abundance from 250 to 9560 cells per organism. The most abundant and constant in the contents of the intestines are unicellular algae. Diatoms are the most diverse, they make up 50.8% of the total number of species.

Deposit feeding of a foraminifera from an Arctic methane seep site and possible association with a methanotroph revealed by transmission electron microscopy

Several foraminifera are deposit feeders that consume organic detritus (dead particulate organic material along with entrained bacteria). However, the role of such foraminifera in the benthic food-web remains understudied. As foraminifera may associate with methanotrophic bacteria, which are 13C-depleted, feeding on them has been suggested to cause negative δ13C values in the foraminiferal cytoplasm and/or calcite. To test whether the foraminiferal diet includes methanotrophs, we performed a short-term (1 d) feeding experiment with Nonionellina labradorica from an active Arctic methane-emission site (Storfjordrenna, Barents Sea) using the marine methanotroph Methyloprofundus sedimenti, and analyzed N. labradorica cytology via Transmission Electron microscopy (TEM). We hypothesized that M. sedimenti would be visible, as evidenced by their ultrastructure, in degradation vacuoles after this feeding experiment. Sediment grains (mostly clay) occurred inside one or several degradation vacuoles in all foraminifers. In 24 % of the specimens from the feeding experiment degradation vacuoles also contained bacteria, although none could be confirmed to be the offered M. sedimenti. Observations of the area adjacent to the aperture after 20 h incubation revealed three putative methanotrophs, close to clay particles. These methanotrophs were identified based on internal characteristics such as a type I stacked intracytoplasmic membranes (ICM), storage granules (SG) and gram-negative cell walls (GNCW). Furthermore, N. labradorica specimens were examined for specific adaptations to this active Arctic methane-emission site; we noted the absence of bacterial endobionts in all specimens examined but confirmed the presence of kleptoplasts, which were often partially degraded. Based on these observations, we suggest that M. sedimenti can be consumed by N. labradorica via untargeted grazing in seeps and that N. labradorica can be generally classified as a deposit feeder at this Arctic site. These results suggest that if methanothrophs are available to the foraminifera in their habitat, their non-selective uptake could make a substantial contribution to altering δ13Ctest values. This in turn may impact metazoans grazing on benthic foraminifera by altering their δ13C signature.

Food Spectrum, Trophic and Length-Weight Characteristics of Nonindigenous Suckermouth Armored Catfishes Pterygoplichthys spp. (Loricariidae) in Vietnam

The food spectrum and trophic and length–weight characteristics of an invasive species, South American suckermouth armored catfishes Pterygoplichthys spp. (Loricariidae), from lotic and lentic inland waters of Vietnam have been studied. It is found that the diet of suckermouth armored catfishes consists of plant and animal food, as well as organic detritus. According to the predominant type and pattern of feeding, suckermouth armored catfishes can be classified as detritivore gatherers (janitor). Some specimens of catfish with a high consumption of animal food have been identified. It is noted that invasive suckermouth armored catfishes can be a significant food competitor for aboriginal fish species; detritivores; and, possibly, benthophages in the lotic and lentic inland waters of Vietnam.

The Biodiversity and Distribution of Abyssal Benthic Foraminifera and Their Possible Ecological Roles: A Synthesis Across the Clarion-Clipperton Zone

Benthic foraminiferal research in the North Pacific has a long history, with works published over a century ago providing important information about the taxonomy and distribution of morphospecies. These studies focused mainly on areas outside the Clarion-Clipperton Zone (CCZ). Our knowledge of foraminiferal faunas within the CCZ originates largely from recent baseline investigations related to likely future seabed mining of the polymetallic nodule deposits. These have revealed highly diverse assemblages of sediment-dwelling morphospecies among the meiofauna and macrofauna, as well as megafaunal xenophyophores and nodule-attached fauna. Morphological analyses have been complemented by metabarcoding studies that yielded even higher numbers of molecular species (Operational Taxonomic Units - OTUs). Monothalamids, the vast majority undescribed, constitute a substantial proportion of both morphological and molecular datasets, with multichambered agglutinated and calcareous foraminifera being less common. Their importance in this abyssal (>4,000 m depth) habitat likely reflects food limitation combined with carbonate dissolution close to and below the carbonate compensation depth. Literature records, supported in a few cases by genetic data, suggest that many morphospecies found in the CCZ have wide geographical distributions across the Pacific abyss and in other oceans. At smaller spatial scales (several 100s of kilometers) there is a general uniformity in assemblage composition. Nevertheless, many morphospecies are too rare to conclude anything about their geographical distributions. Similarly, the part played by benthic foraminifera in CCZ ecosystems is largely a matter of speculation, although their abundance across different size classes suggests that it is significant. Meiofauna-sized taxa that consume freshly-deposited organic detritus may be important in carbon cycling, particularly at the shallower, more eutrophic eastern end of the CCZ. Megafaunal xenophyophores can provide habitat structure for other organisms, potentially enhancing benthic biodiversity. Foraminifera of all sizes could be among the earliest recolonisers of disturbed or redeposited sediments. Their potential contributions in terms of both ecology and biodiversity make these protists significant members of benthic communities in the CCZ.

Mercury Distribution in an Upper St. Lawrence River Wetland Dominated by Cattail (Typha Angustifolia)

Legacy mercury (Hg) exists in Upper St. Lawrence River wetland hydric soils and is impacted by a new water level management plan (established in 2017) implemented to restore biodiversity and reduce the monotypic nature of riparian wetlands, currently dominated by Typha spp.. The distribution of Hg within the various components of a riparian wetland provides insight into potential impacts of water level fluctuations. Hydric soil represents 83% of the wetland Hg burden while wetland plant biomass contributed 17%, mostly due to organic detritus (13%). Although Typha roots had a bioconcentration factor of 1.2 (relative to hydric soils) and had the highest total Hg among living tissues (25 ± 9.3 ng/g dry wt.), detritus had the highest overall Hg content (110 ± 53 ng/g dry wt.). While root tissue Hg correlated significantly with soil Hg (p = 0.045), it was determined here that Typha spp. has limited use as a biomonitor in wetlands with low levels of Hg contamination, as in this ecosystem. Hg contained within the organic detritus contributed more to the overall Hg burden in these monotypic Typha wetlands than any other tissue or biomass component analyzed. Consequently, shifts in the plant community that are expected to result from a new water level management plan may alter Hg storage within these wetlands and affect its mobility in this ecosystem.

Three new Luticola D.G.Mann (Bacillariophyta) species from Rapa Nui (Easter Island) found in terrestrial diatom assemblages dominated by widely distributed taxa

Background Rapa Nui (Easter Island = Isla de Pasqua) is of volcanic origin, best known for about 900 man-made stone statues known as moai. It is one of the most isolated inhabited islands on Earth and studies on the diatoms of Rapa Nui are very few. Methods Light (LM) and electron microscopic (SEM) observations of a single sample collected from Rapa Nui are presented. The samples (mix of soil and organic detritus) were collected from ground of cave entrance. Results The samples were characterized by low diatom diversity and strongly dominated by terrestrial (soil) forms. Among the taxa present in the material studied were cosmopolitan forms of the genera Humidophila, Nitzschia, Angusticopula, Orthoseira, Tryblionella and Luticola. Whereas most of taxa of the enumerated genera were identifiable, only one among four Luticola species distinguished in the samples studied was identified. This taxon was L. ectorii, a cosmopolitan species known previously from South America (Brazil) and Asia (China). The three remaining species could not be assigned to any established species. Therefore, based on external and internal morphological features from light and scanning electron microscopic analysis, we describe here three species new to science, including: L. georgzizkae, L. rapanuiensis and L. moaiorum. All three taxa new to science are compared to established Luticola species and their significance for the global distribution of the genus is discussed.

Feeding experiments of the seep-associated foraminifer Nonionellina labradorica with a marine methanotroph from the Arctic

<p>Foraminifera on the seafloor are known to have species-specific feeding habits. Among those are deposit feeders, eating organic detritus and bacteria. Little is known about the feeding habits of foraminifera from Arctic seep environments. That is, in particular, of interest as variable δ<sup>13</sup>C values in the tests of foraminifera have been suggested to be partly linked with a diet rich in bacteria, themselves lighter in δ<sup>13</sup>C values. As there is little information on the ecology of the foraminifer <em>Nonionellina labradorica</em> (Dawson, 1860), this study examined feeding habits on bacteria and compared them to in situ collected specimens, using Transmission Electron microscopy (TEM). As bacterial food, the marine methane-oxidizing bacterium <em>Methyloprofundus sedimenti</em> was chosen, which is an important representative of methanotrophs in the marine environment near methane seeps. Sediment samples containing living N. labradorica specimens collected in close vicinity(approx. 5 m) from an active methane seep in Storfjordrenna, Barents Sea (382-m water depth).  We performed a feeding experiment on <em>N. labradorica </em>(n=17 specimen), which were incubated in the dark at in situ temperature. Specimens were fed at the beginning of the experiment, except the un-fed controls, and incubations terminated after 4, 8 and 20 h. After fixation in epoxy resin the ultrastructure of all specimens and their food vacuoles was observed and compared using a TEM. All examined specimens were living at the time of fixation, based on observation of intact mitochondrial membranes. In all specimens, inorganic detritus was preserved inside food vacuoles. Closer observation of food vacuoles also revealed that in addition to inorganic debris, such as clay, occasionally bacteria were visible. This led us to conclude that our <em>N. labradorica </em>can  generally be classified as a deposit feeder, which is rather a generalist than a specialist. Regarding uptake of <em>M. sedimenti</em>, the timing of the experimentation seemed to be critical. We did not observe methanotrophs preserved in the resin at the 4 and 8 h incubations, but found two putative methanotrophs near the apertural region after the 20-h incubation. After closer observation, we could identify one of those two putative specimen as the menthanothroph <em>M. sedimenti</em> near the foraminiferal aperture, based on presence of a typical type I stacked intracytoplasmic membrane (ICM) and storage granules (SC). We concluded that <em>N. labradorica</em> may ingest <em>M. sedimenti</em> via “untargeted grazing” in seeps. Further studies must examine the exact relationship between diet and δ<sup>13</sup>C in foraminiferal test on several different paleo-oceanographically relevant species.</p>

Organic matter decomposition in subtropical South America aquatic environments: a systematic and scientometric review

Aim To evaluate the general situation of studies on the decomposition of organic matter in aquatic environments in the subtropical region of South America. Methods We compiled publications (1990-2018) with a combination of words referring to decomposition, debris, aquatic environments and South American countries with subtropical climate. The characteristics of the publications were analysed over time. Results A total of 1,042 publications were found, with 106 specifically addressing the purpose of this study. For subtropical climates in South America, this research topic is incipient. Most studies were carried out in streams (39.6%) and studied the decomposition process and associated invertebrates (42.5%). There is a great deficiency of studies in lentic environments (e.g. lakes, 10%). Conclusion Studies on the decomposition of organic detritus in aquatic ecosystems in the subtropical region of South America are still emerging. While the knowledge about the role of shredders is more or less understood, the importance of microorganisms on the decomposition process still needs to be better evaluated. Finally, our study demonstrated that scientific collaboration boosted publication on the topic.

First report of Cystoseira aurantia Kützing from the Mediterranean coast of Morocco

Algal diversity in aquatic environments can help assess the health status of ecosystems, provide information about invasions of new species and inform species diversity changes according to environmental conditions. An algal diversity survey (2016–19) of Nador Lagoon (northern Morocco) revealed the presence for the first time of the brown alga Cystoseira aurantia. Since 2015 this alga has been found in high abundance in the northwestern part of the lagoon, mainly around Attalayoun and Nador City. The thalli of larger specimens reached 60 cm in length, and all plants present were free-floating. The species was collected from the water surface to depths not exceeding 2 cm. Floating patches were usually found suspended above sandy and muddy substrates. Increased abundance of this species in the lagoon corresponds with new physico-chemical conditions and ecological parameters, principally resulting from increased water ventilation and improved water quality since 2012. The new communities of C. aurantia may offer a novel resource for the lagoon but high abundance could pose future threats to attached vegetation such as seagrasses and benthic algae by shading and the accumulation of organic detritus. Attention is drawn to taxonomic issues involving C. aurantia.

Impacts of bottom trawling on benthic trophic status and meiofauna in a deep-sea sedimentary environment (Gulf of Castellammare, southwestern Mediterranean Sea)

<p>The impacts of bottom trawling on the structure of benthic communities can be relatively non-selective, hitting biodiversity as a whole. This holds true also in the deep sea, where the impacts of trawling can be more severe and long-lasting than in shallow-waters, due to the reduced capacity for recovery and greater vulnerability of deep-sea organisms. For years, our knowledge of the impact of trawling on deep-water ecosystems has remained limited and has focused mainly on fish stocks and hard bottom systems. More recently, a number of studies have addressed the impacts of bottom trawling in the deep-sea sedimentary environments, and very few of them have focused on the impacts on meiofauna, though it is a key faunal component of deep-sea ecosystems.</p><p>We investigated the impact of bottom trawling on the quantity, biochemical composition and nutritional value of sedimentary organic matter and meiofauna along the Sicilian Margin (Gulf of Castellammare, southwestern Mediterranean) at ca. 550 m depth, during the summer of 2016. Amount, biochemical composition and freshness of sedimentary OM, as well as the abundance and community composition of meiofauna were determined in sediment cores taken at both trawled and untrawled grounds. The continuous erosive processes in the trawled site have led, generally, to the depletion of OM contents (20-60% lower than those in the untrawled site), as well as to statistically significant differences from the untrawled site in its biochemical composition. Nevertheless, the upper 2 cm of the trawled site consisted of recently accumulated sediments, enriched in phytopigments, and bulk OM contents similar to those in the untrawled one, interpreted as a very recent input of fresh OM from the upper water column. The abundance of meiofauna in trawled grounds was significantly higher than that in untrawled ones, whereas no differences were observed between trawled and untrawled grounds deeper in the sediment. Differences in the meiofaunal community composition among sediment layers in each site were larger than those among sites.</p><p>As previously reported, deep bottom trawling in the Gulf of Castellammare erodes large volumes of sediment, exposing old compacted sediment that is depleted in OM. This erosive action generally prevents the accumulation of fresh sediment. However, the episodic short-lived deposition of fresh organic detritus between hauls can lead to a temporary accumulation of fresh and bioavailable OM which, in turn, can induce a positive response in meiofauna abundance.</p><p>These results pinpoint the need of considering the impacts of bottom trawling on the benthic communities of deep-sea sedimentary environments at temporal scales shorter than previously done.</p>