Hydrobiology, Volume 3, Issue 3 (September 2024) – 8 articles

Leaf litter is an important input to freshwater systems. Leaves provide carbon, nutrients, and secondary compounds. We examined the effects of tree leaf species on chlorophyll a concentration—a proxy for phytoplankton biomass. We found that an input of Chinese tallow (Triadica sebiferum, invasive in the southeastern USA) and red maple (Acer rubrum) leaves resulted in lower chlorophyll concentrations than controls and other native species. These leaf species also leached tannins, resulting in a darker water color, and either may have caused the patterns observed. To separate these potential mechanisms (darker water leading to light limitation and tannin toxicity), we conducted a second experiment with a fully factorial design manipulating tannins and water color. We found that darker water resulted in the lowest chlorophyll concentration, suggesting light limitation. In the clear-water treatment, the addition of tannic acid lowered chlorophyll concentrations but also resulted in moderately darker water by the end of the experiment. The tannic acid may have been toxic to the algae, or there may have been some light limitation. Our results suggest that tannins that darken water color may substantially suppress phytoplankton and that tree species composition may influence both phytoplankton and the brownification of freshwater. Full article

Harmful algal bloom events occur in salt, brackish, and fresh water. In bodies of water such as oceans and estuaries, diatoms or dinoflagellates form “tides” that produce toxins associated with seafood poisoning, including paralytic shellfish poisoning, or respiratory distress from inhalation of aerosolized toxins. Cyanobacteria predominantly bloom in fresh water; they can produce microcystins; cylindrospermopsin; and other toxins that humans or animals might be exposed to through water contact, inhalation, or ingestion. Animals that become ill or die can be sentinels for harmful algal bloom events. In a One Health approach, information about harmful algal bloom exposures and health effects support efforts to detect these events and mitigate and prevent associated illnesses. Human, animal, and environmental health partners can work together to document the occurrence and impacts of harmful algal bloom events and characterize associated illnesses. Full article

Winter ulcer disease (WUD) is widely recognized as a serious threat to animal welfare and a major contributor to revenue loss within the aquaculture sector, particularly affecting the salmon-farming industry. This highlights the significant impact of WUD on both animal well-being and the economic sustainability of fish farming. WUD causes hemorrhagic signs and results in dermal lesions and ulcers. This disease can lead to higher mortality rates and a considerable decline in the fish’s market value. Moritella viscosa, a Gram-negative bacterium, is predominantly, but not exclusively, correlated with the emergence of WUD, mostly during the colder seasons. Waterborne transmission is the primary way for spreading the bacterium within a population. However, there is remarkable variation in the prevalence and characteristics of WUD in different regions. In Europe, this disease often occurs in the winter, and the intensity and occurrence of outbreaks are influenced by water temperature and salinity. In contrast, outbreaks are typically observed in the summer and mid-autumn in Eastern Canada. Despite the administration of various polyvalent vaccines, outbreaks of skin ulcers have been documented in Canada, and studies have highlighted the possible roles of other bacterial pathogens in Atlantic salmon. This review discusses the etiology, pathogenesis, and potential mitigation or prevention strategies for WUD, mainly in Atlantic salmon. Moreover, it underscores the necessity of conducting further investigations to discover the potential unknown causative agents of ulcerative disease and design appropriate vaccines or preventive strategies for these pathogens. Full article

Large rivers are difficult to sample due to their size yet critical to monitor because humans heavily rely upon and alter them. Aquatic invertebrates are commonly used to assess the ecosystem quality of streams, but methods to sample large rivers are underdeveloped. We sampled aquatic invertebrates using a Hess sampler and rock baskets in the Snake River near Jackson, Wyoming, USA. Hess samples collected more aquatic invertebrate taxa and a higher proportion of Ephemeroptera, Plecoptera, and burrowing taxa. Rock baskets collected a higher proportion of Trichoptera, filterers, and clinging taxa. Bioassessment metrics differed between sampling methods; richness, diversity, evenness, Ephemeroptera, Plecoptera, and Trichoptera (EPT), and Hilsenhoff’s biotic index produced higher values in Hess samples, and percent EPT was higher in rock baskets. Non-metric multidimensional scaling and analysis of similarity indicated that the samplers collected different assemblages (p < 0.001). The standard error of total invertebrate density was smaller and most taxa were collected with seven replicate samples. Understanding how sampling methods alter the aquatic invertebrates collected will help managers develop monitoring protocols that are best suited to the river and collect the most unbiased invertebrate assemblages. Full article

In the Mediterranean, the bluespotted cornetfish Fistularia commersonii Rüppell, 1838, presents a minor socioeconomic impact and the assessment of any environmental impact requires more relevant data. The congeneric red cornetfish Fistularia petimba Lacepède, 1803, has expanded its distribution range within the basin but only small numbers have been reported to date. A total of 207 individuals of F. commersonii were collected between April 2021 and March 2022 from the Levantine coast of Rhodes and 92 more from various locations. Additionally, 13 individuals of Fistularia petimba were caught in March 2024 from the Aegean coasts of the island. We aim to assess the current progression of the population of the two cornetfish, the possible further exploitation of F. commersonii to boost the local fishing economy, their possible dietary overlaps and to add valuable biological and ecological data. In F. commersonii, male to female ratio (1:1.33) significantly departed from 1:1, with length–weight relationships exhibiting positive allometric growth. Six age groups were identified. The highest reproductive intensity was observed during summer. The onset of sexual maturity was estimated at 65.52 cm in total length (1.8 years). Longevity was estimated at 11.1 years with females growing larger than males. The exploitation rate (E = 0.47) indicated that the population is underexploited. The optimum and target fishing mortality were higher in comparison with the present fishing mortality (F = 0.48), indicating a potential for commercial exploitation of the species. For F. petimba, the sex ratio was 1:2.25. The species preys on crustaceans, followed by fish and molluscs. The finding of Vanderhorstia mertensi (Klausewitz, 1974) in the stomach content of both cornetfishes constitutes the second published record for Hellenic waters and the first for the Dodecanese Islands. Full article

Many swimming protists travel by actuating whip-like flagella to generate thrust. While many organisms’ flagella have been observed to have hair-like protrusions called mastigonemes, the function of these mastigonemes is not known. In particular, however, although theory, numerics, and some experiments suggest that mastigonemes can initiate the reversal in direction of thrust generated relative to the direction of traveling waves propagated along flagella, other experiments have found that they do not have hydrodynamic effects. Thus, it remains unclear whether mastigonemes have a hydrodynamic effect and function; additionally, any hydrodynamic effects may be species-dependent, which calls for the investigation of additional species. In this work, we report experimental observations of the cryptophyte C. paramecium that obtain their cell body, flagellar, and mastigoneme geometries, as well as their swimming kinematics and behavior. We then use the observed geometries and kinematics to numerically simulate swimming trajectories for a particularly well-characterized reorientation event, with and without various configurations of the mastigonemes. The comparison of numerical and experimental results shows that a configuration of mastigonemes in the beating plane best reproduces the observed reorientation dynamics, suggesting that in C. paramecium, although mastigonemes do not lead to gross changes in motility, such as thrust reversal, they do exert important quantitative effects. Full article

Urban and agricultural runoffs can transport contaminants and pesticides into freshwater ecosystems, particularly in the developing tropics. For instance, organophosphate and pyrethroids pesticides, such as Roundup, Malathion, and Permethrin, have been found in tropical streams. The uncontrolled application of these pesticides has become a growing concern due to their adverse effects on various non-targeted organisms. Unfortunately, most studies have focused on a few selected model species, ignoring the effects on other non-target organisms, which may play an important role in tropical lotic ecosystems. In addition, the biological characteristics of aquatic crustaceans, including their morphology, physiology, and behavior, make them susceptible to toxic chemicals. For this reason, this study used the widely distributed freshwater shrimp Xiphocaris elongata as a model organism to determine the acute toxicity of Permethrin, Malathion, and Roundup. Our results show that the proportion of mortality of X. elongata in each concentration group became progressively higher as the concentration of exposure increased. We also found that the synthetic pyrethroid Permethrin was the most toxic pesticide tested, with a median lethal concentration (LC₅₀) value for 96 h of 3.96 × 10⁻⁶ µg·L⁻¹, followed by organophosphate Malathion (8.87 µg·L⁻¹) and Roundup (748.92 µg·L⁻¹). Experiments with this freshwater shrimp showed a good control performance and reproducibility for the tested pesticides. This study demonstrated that X. elongata is a suitable test organism that can be a representative bioindicator of pesticide toxicity in tropical streams. Full article

The family Eirenidae is one of the major taxa of the order Leptothecata, comprising approximately 80 species from ten genera. In this study, taxonomic investigations, including morphological observations and molecular 16S phylogenetic analyses, were conducted on unknown Eirenidae specimens collected off the coast of Iwaki, Fukushima Prefecture, eastern Japan, in June 2022. The specimens had the following morphological characteristics: marginal warts and tentacular bulbs with lateral cirri and without adaxial papillae, a mouth with simple lips, four simple radial canals, and eight statocysts common to the genus Eutima. However, this species can be distinguished from other species of Eutima by the number of tentacles, number and shape of marginal warts, position of the gonads, and gastric peduncle length. Moreover, the monophyly of the species was evident in the 16S rRNA phylogenetic tree (as indicated by the high bootstrap value of 100%), thereby supporting the validity of the new species. Based on these results, we describe it as a new species, Eutima onahamaensis, for taxonomic stabilization. We also made detailed observations of the morphology and molecular phylogenetic analyses of one of the species newly recorded in Japan: Eutima diademata. A comparative table of the primary diagnostic characteristics of Eutima has been provided. This study provided taxonomic keys for identifying species in the genus Eutima. Full article