Hydrobiology, Volume 4, Issue 2 (June 2025) – 9 articles

Municipal wastewater effluent (MWWE) is a common source of nutrient enrichment and provides a route for emerging substances of concern (ESOCs) to enter aquatic systems. Community composition and abundance metrics of benthic macroinvertebrates are commonly utilized to assess ecological impacts associated with nutrient enrichment; however, the responses of these metrics in systems with diverse chemical mixtures from MWWE, are not well understood. This study specifically addresses the effects of cumulative loading of tertiary-treated MWWE through responses in benthic macroinvertebrate communities in experimental control and treatment streams. Treatment streams used source river water previously exposed to upstream wastewater treatment plants but with an additional 5% by volume tertiarily treated MWWE, while control streams used only source river water. Surbers and artificial substrate rock baskets were used to examine impacts on both established and colonizing benthic communities, respectively. No significant differences were observed between the control and treatment streams in any of the community metrics of well-established benthic communities. In contrast, significant decreases in colonizing taxon diversity and evenness were found between treatment and control streams. The dominant taxa (most abundant family, by percentage of sample) in the community, often filter feeders, significantly increased in percentage of the total community in treatment streams. This response was consistent with a nutrient enrichment effect, with no evidence of ESOC related toxicity. This study highlights the need for bioassessment programs to utilize approaches involving varied in-situ sampling methods and controlled exposure systems to gain a better understanding of how various stages of community-level development are impacted by urban pollutants such as MWWE. Full article

Intensive forestry, particularly the establishment of monospecific plantations with exotic species, can deeply impact the ecological functioning of forest streams, where riparian leaf litter is the primary source of energy. In this study, we investigated the effects of Eucalyptus globulus afforestation on macroinvertebrate communities in 20 streams in Galicia (NW Spain) with varying levels of accumulated eucalypt leaf litter. Sampling was done in autumn 2020 and spring 2021. In autumn, six streams had leaf litter composed of >50% of eucalypt leaves, a proportion that increased to 12 streams in spring. A total of 24,705 individuals were found in autumn and 12,529 in spring, belonging to 125 taxa. Although some taxa decreased their abundance with an increase in the proportion of eucalypt litter, variability in overall macroinvertebrate abundance was mainly explained by season, stream flow, and water temperature. However, species richness and diversity were significantly lower in streams mainly subsided by Eucalyptus litter compared to those dominated by native riparian vegetation. Macroinvertebrate abundance, richness, and diversity peaked in autumn, coinciding with the influx of deciduous litterfall and lower proportion of eucalypt litter. The lower quality, low-nutrient content, and presence of feeding deterrents in Eucalyptus leaf litter compared to native deciduous tree species likely drive these observed patterns, underscoring the importance of preserving native riparian forests to sustain stream biodiversity, even in managed landscapes dominated by Eucalyptus plantations. Full article

Understanding the factors influencing amphibian populations is essential for effective freshwater conservation, particularly for species with biphasic life histories. This study examined how pond- and landscape-level characteristics shape larval amphibian occupancy, abundance, and detection in a remnant Tupelo-Cypress wetland in southeastern Illinois. Given the small number of available ponds (n = 4), we standardized survey effort across sites and incorporated robust hierarchical Bayesian models to evaluate environmental effects at both community and species levels. Occupancy probabilities were generally high across species, with canopy cover significantly increasing both community and species occupancy, particularly for salamanders (up to 6.4-fold). Predatory backswimmers and fish substantially reduced occupancy (by 21.7-fold and 6.0-fold, respectively). Anurans, especially Pseudacris spp., were more abundant than salamanders, with abundance positively associated with canopy cover, leaf litter, and pond perimeter. Detection probabilities were generally low and varied by species, with predatory invertebrates reducing detection up to 83.3-fold. These findings underscore the importance of maintaining canopy cover while mitigating predation risks to support amphibian populations. The application of multi-species hierarchical models provides a nuanced understanding of species-specific responses, offering valuable insights for conservation strategies in regions affected by habitat loss and climate change. However, given the limited spatial replication, these findings should be interpreted cautiously and validated through additional studies across broader temporal and spatial scales. Full article

A field study on the biparental convict cichlids (Amatitlania siquia) in Lake Xiloá, Nicaragua was conducted to understand how the loss of a parent’s parental care affects the antipredator behavior of both parents and offspring during intruder events. We hypothesized that the combined efforts of two parents would result in increased intruder aggression and decreased offspring dispersion compared to single-parents of either sex, and that single-females and males would differ in their ability to deter predators and manage offspring dispersion. Both parents in a pair chased half the intruders that single-females did and the same number as single-males, suggesting that the presence of a partner deters intruders from encroaching and affords parents more time to engage in other parental care duties. Compared to single-parents, offspring accompanied by both parents were seldom left alone and showed greater shoal cohesion—both of which would presumably lower their risk of predation. Although there were sex differences between single-parents in terms of how often they left their offspring unattended and called to them using pelvic fin-flicks, neither sex was found to be more effective at managing the distribution of their offspring. This field study provides empirical evidence to support the need for biparental care in this species and gives insight into the selection pressures shaping parental investment. Full article

Freshwater fish species play an important role in global aquaculture. Currently, sturgeon, carp, and tilapia are at the forefront of this industry. However, as human populations continue to grow, the demand for new sources of animal protein increases, making the use of other freshwater species in aquaculture essential. The pikeperch (Sander lucioperca) is one of the most promising fish species for European aquaculture, but its usage has been hindered by a lack of effective larval-rearing protocols. Most studies focus on using cultured or nutrient-rich zooplankton for larval cultivation, while natural zooplankton from the local environment are rarely used. In this study, we aim to investigate the nutritional requirements of pikeperch larvae by describing the taxonomic diversity and biochemical composition of zooplankton collected from a natural oligotrophic lake in Northwest Russia. The chemical composition of zooplankton is characterized by a high protein content (up to 70% of dry matter), a moderate lipid content (up to 25%), and a deficiency of certain fatty acids and amino acids. Specifically, there is a low concentration of docosahexaenoic acid and methionine. The dry matter content in the zooplankton averages 10%, with nitrogen-free extracts accounting for 4% and ash making up 4%. These biochemical parameters meet the nutritional requirements of freshwater pikeperch larvae, with the notable exception of the lower levels of DHA and methionine, which are typically characteristic of freshwater zooplankton. This information sheds light on the nutritional requirements of pikeperch larvae and the development of more efficient rearing methods. Full article

Dive fisheries are widely practiced in coastal areas worldwide owing to their minimal equipment requirements and extensive historical background. Female divers in Korea and Japan have extensive knowledge of the local coastal environment and engage in sustainable fishing practices. However, the number of divers and their catches has been declining. In this study, long-term catch and effort data were collected to investigate the reasons for the decline in the catch of the sea urchin, Hemicentrotus pulcherrimus, in Mikuni, Sakai City, Fukui Prefecture, Japan. A significant correlation was observed between catch and effort, and the main reason for the decline in catch was a reduction in fishing effort. Fishermen have voluntarily limited their fishing efforts to prevent the depletion of natural stocks, and a decrease in the number of fishermen has contributed to this reduction. In addition, regulations on catchable size and fishing season were implemented. However, natural stocks appear to have declined. Although sea urchin fisheries have been sustainably practiced for a long time, current fishery management and regulations appear inadequate. Therefore, sustainable fishing requires identifying the factors that affect stock fluctuations and updating management practices. Full article

Because animals threatened by visually oriented predators may respond in sun-lit daytime but not at night, invertebrate responses to predatory challenges may yield varying results based on the time period within the 24 h daily cycle. We predicted that in laboratory experiments aquatic isopods exposed to kairomones from predatory fish would spend more time immobilized in daylight to avoid detection than those not exposed to kairomones but that this difference would disappear under the cover of nighttime darkness. We further predicted that isopods in the absence of kairomones would move at elevated rates in the daytime compared with night, seeking a precautionary proximity to shelters. However, contrary to our predictions, Caecidotea communis isopods exhibited consistent activity (movement rate and proportion of time spent moving) when exposed to kairomones or in the absence of such cues, at all of the three diurnal cycle periods examined. Thus, Caecidotea communis displayed cathemerality (sometimes called metaturnality), the first documented case of this behavior in crustaceans. Full article

Cold-water lakes in high-latitude regions are experiencing rapid changes in community structure and functioning associated with local and global stressors (e.g., climate change, hydropower and invasive species). However, the long-term ecological responses of cold-adapted top predators are relatively poorly monitored despite their high importance for structuring ecological communities and for the provisioning of ecosystem services. We studied long-term changes (2010–2021) in the population structure and trophic niche of two cold-adapted coregonid fishes in oligotrophic Lake Osensjøen, southeastern Norway. Our gillnet surveys indicated that the whitefish (Coregonus lavaretus) population declines simultaneously with the increasing population density of roach (Rutilus rutilus), whereas vendace (Coregonus albula) showed more stable densities. Both whitefish and vendace became increasingly dominated by small-sized individuals following the increase in coexisting roach and perch (Perca fluviatilis) populations. Our stomach content and stable isotope data indicated a marked overlap in the trophic niches of whitefish and roach, with both species showing high among-individual variation in δ¹³C and δ¹⁵N values as compared to the more specialized zooplanktivorous vendace. Our study provides further evidence that the ongoing environmental changes in high-latitude lakes may induce rapid changes in community structures and lead to the population declines of cold-adapted fishes, likely associated with strong resource competition with warm-adapted cyprinid and percid fishes. Such shifts in fish community structure may, in turn, affect the benthic and pelagic food-web compartments and reduce valuable ecosystem services such as local fisheries targeting salmonids. Full article

Trace elemental water chemistry in aquatic systems is primarily derived from the underlying geology of surrounding watersheds. Trace elements can be absorbed from the environment and become permanently incorporated into certain calcified structures of fish. Comparison of the trace elemental chemistry of these structures with the chemical signature of water from the watershed in which a fish was captured can help identify movement patterns. The goal of this study was to create a relatively fine scale baseline for the trace elemental water chemistry of the Chattahoochee, Ocmulgee, Oconee, and Savannah rivers within the Piedmont ecoregion of Georgia, U.S., and to distinguish any trace elements that may be useful in delineating different reaches. Principal component analysis was used to analyze ratios of Ba:Ca, Mg:Ca, Mn:Ca, Na:Ca, and Sr:Ca from samples in each river. Results suggest that Ba:Ca and Sr:Ca ratios may be useful in delimiting river reaches in each system. In addition, Na:Ca and Mn:Ca ratios may have some utility in further differentiating reaches in the Chattahoochee and Savannah rivers, respectively. The ability of these elements to differentiate reaches within these rivers lends support for their utility in fish microchemistry studies to help better understand and manage fish in these systems. Full article