Predicting the impact of Lake Biomanipulation based on food-web modeling—Lake Kinneret as a case study

Low prevalence of Contracaecum third-stage larvae parasitizing Sea of Galilee fisheries: 1-year survey after 57 years of no information

Freshwater and marine ecosystems are a suitable habitat for parasitic nematodes of the genus Contracaecum (family: Anisakidae) to complete their complex life cycle. Several fish species of the Sea of Galilee (Lake Kinneret) were reported in 1964 as second intermediate/paratenic hosts of Contracaecum spp. larvae. The lack of taxonomically relevant morphological features of these larvae hindered their proper identification. Here we report the results of a 1-year survey conducted in 2021, 57 years after the first (and only) such survey. We analyzed 352 specimens from 10 fish species (native and non-native) of the Sea of Galilee (Israel) ichthyofauna. We compared our results with those of the first parasitological survey conducted by Paperna in 1964; the overall prevalence of nematodes referable to Contracaecum larvae was 16.8% and 0.85% in 1964 and in 2021, respectively. Different from the first survey that identified Contracaecum larvae morphologically, we used both morphological and molecular tools. Two wild native cyprinids-Jordan himri (Carasobarbus canis) and Jordan barbel (Luciobarbus longiceps)-were infected (a single specimen each) with Contracaecum quadripapillatum larvae in their abdominal cavity. A single specimen of blue tilapia (Oreochromis aureus) was infected with two larvae of Contracaecum multipapillatum E, localized in the pericardial cavity. The findings of our study, which is part of a large project focused on Contracaecum spp. infecting both piscivorous birds and fish collected in Israel, advance our knowledge about the distribution and host range of this potentially zoonotic parasite in fishery products of the Sea of Galilee.

Exploring multiple stressor effects with Ecopath, Ecosim, and Ecospace: Research designs, modeling techniques, and future directions

Understanding the cumulative effects of multiple stressors is a research priority in environmental science. Ecological models are a key component of tackling this challenge because they can simulate interactions between the components of an ecosystem. Here, we ask, how has the popular modeling platform Ecopath with Ecosim (EwE) been used to model human impacts related to climate change, land and sea use, pollution, and invasive species? We conducted a literature review encompassing 166 studies covering stressors other than fishing mostly in aquatic ecosystems. The most modeled stressors were physical climate change (60 studies), species introductions (22), habitat loss (21), and eutrophication (20), using a range of modeling techniques. Despite this comprehensive coverage, we identified four gaps that must be filled to harness the potential of EwE for studying multiple stressor effects. First, only 12% of studies investigated three or more stressors, with most studies focusing on single stressors. Furthermore, many studies modeled only one of many pathways through which each stressor is known to affect ecosystems. Second, various methods have been applied to define environmental response functions representing the effects of single stressors on species groups. These functions can have a large effect on the simulated ecological changes, but best practices for deriving them are yet to emerge. Third, human dimensions of environmental change - except for fisheries - were rarely considered. Fourth, only 3% of studies used statistical research designs that allow attribution of simulated ecosystem changes to stressors' direct effects and interactions, such as factorial (computational) experiments. None made full use of the statistical possibilities that arise when simulations can be repeated many times with controlled changes to the inputs. We argue that all four gaps are feasibly filled by integrating ecological modeling with advances in other subfields of environmental science and in computational statistics.

Piscivore stocking significantly suppresses small fish but does not facilitate a clear-water state in subtropical shallow mesocosms: A biomanipulation experiment

Biomanipulation by piscivore stocking has been widely used to combat eutrophication in north temperate lakes, but its applicability in warm lakes has not yet been well elucidated. Here, we used experimental mesocosms to test the effects of a native benthi-piscivore (snakehead, Channa argus Cantor) on water clarity under subtropical conditions where small omni-benthivorous fish like crucian carp (Carassius carassius L.) prevail. Our results showed that, despite of a great reduction of crucian carp biomass, snakehead stocking did not create a strong trophic cascade as neither (herbivorous) zooplankton biomass nor their grazing pressure, indicated by biomass ratio of (herbivorous) zooplankton to phytoplankton, changed significantly. Moreover, snakehead stocking significantly increased water non-algal turbidity as well as nutrient and chlorophyll-a concentrations, suggesting that these benthi-piscivores also disturbed sediments like crucian carp did. Our study showed that biomanipulation by stocking of snakehead does not facilitate clear-water state in warm shallow lakes, even on the short-term.

Combining lanthanum-modified bentonite (LMB) and submerged macrophytes alleviates water quality deterioration in the presence of omni-benthivorous fish

Bioturbation by omni-benthivorous fish often causes sediment resuspension and internal nutrient loading, which boosts phytoplankton growth and may lead to a shift of clear water lakes to a turbid state. Removal of large-sized omni-benthivorous individuals is a lake restoration measure that may revert lakes from a turbid to a clear water state, yet the rapid reproduction of small omni-benthivorous fish in tropical and subtropical shallow lakes may impede such lake recovery. In lake restoration, also a combination of lanthanum-modified bentonite (LMB) and planting submerged macrophytes has been used that may synergistically improve lake water quality. How the combined effect works in the presence of small omni-benthivorous fish has not been studied, which is needed given the high abundances of small omni-benthivorous fish in (sub)tropical lakes. We conducted a two-by-two factorial mesocosm experiment with and without the submerged macrophytes Vallisneria natans and with and without LMB, all in the presence of small crucian carp. At the end of the experiment, turbidity in the V. natans, LMB and combined LMB + V. natans treatments had decreased by 0.8%, 30.3% and 30.9%, respectively, compared with the controls. In addition, the nitrogen (N) and phosphorus (P) release from the sediment in the combined LMB + V. natans treatments had decreased substantially, by 97.4% and 94.3%, respectively, compared with the control. These N and P fluxes were also significantly lower in the combined LMB + V. natans treatments than in the sole LMB treatment (88.1% and 82.3%) or the V. natans treatment (93.2% and 90.3%). Cyanobacteria in the overlying water in the combined LMB + V. natans treatments significantly decreased by 84.1%, 63.5% and 37.0%, respectively, compared with the control and the sole LMB and V. natans treatments. Our results show that LMB and submerged macrophytes complement each other in effectively improving the water quality, even in the presence of small omni-benthivorous fish.

Eco-bioengineering tools in ecohydrological assessment of eutrophic water bodies

Eutrophication of water bodies and deterioration of water quality are emerging environmental crises. The root causes and consequences of eutrophication are multidirectional. Thus, they provide a huge scope of risk-analysis and risk-assessment in the domain of remediation studies. However, recent restoration studies reveal a global trend of utilizing traditional restoration methods combined with advanced pioneer innovative techniques developed in the field of science and technology. This review introduces a novel approach to consider ecohydrological assessment of eutrophication by classical biomanipulation practices emphasising on their evolution into innovative 'eco-bioengineering' methods. The main objective of this study is to critically analyse and recognize the research gaps in classical biomanipulation and appreciate the reproducibility and efficacy of eco-bioengineering methods at micro- and macrolevel aquatic ecosystems. Comprehensive literature review was conducted on offline and online platforms. Our survey revealed (a) continuation of a historical trend in classical biomanipulation practices (61.64%) and (b) an ascending drift in eco-bioengineering research (38.36%) in the last decade (2010-2021). At a global scale, recent biomanipulation research has a skewed distribution in Europe (41.10%), East Asia (32.88%), North America (10.96%), South Africa (4.11%), South America (2.74%), Middle East (1.37%), Oceania (1.37%), and non-specific regions (5.48%). Finally, this review analysis revealed the comprehensiveness of eco-bioengineering methods and their strong ecological resilience to recurrence of eutrophication and fluctuating environmental flows in the future. Therefore, our review reinforces the supremacy of eco-bioengineering methods as cost-effective green technologies providing sustainable solutions to restore the eutrophic waters at a global scale.

Sustainable Restoration as a Tool for the Improvement of Water Quality in a Shallow, Hypertrophic Lake

Sustainable restoration treatments were implemented with the simultaneous application of pro-ecological methods that complement each other to improve water quality in the shallow and heavily polluted Raczyńskie Lake. Phosphorus inactivation with magnesium chloride and Phoslock® was introduced along with biomanipulation. Physico-chemical and biological parameters were studied in 2015 (before restoration) and throughout 2018 and 2019 (during restoration). Water quality improved in the first year of treatment. An increase in water transparency, oxygen concentration above the bottom, a decrease of chlorophyll-a concentration and a reduction in cyanobacteria were observed. In the second year of treatment, a slight deterioration of water quality was recorded, probably caused by fewer phosphorus inactivation treatments and a shortened period of application. However, the deterioration of conditions is also characteristic of sustainable restoration at the beginning of the restoration process. The obtained results showed that sustainable restoration requires more than two years, and its scope and intensity should strictly depend on the pace of changes, determined on the basis of monitoring. In addition, improved water quality will have a positive impact on the recreational use of this reservoir.

Effects of juvenile crucian carp (Carassius carassius) removal on submerged macrophyte growth-implications for subtropical shallow lake restoration

Rapid expansion of juvenile fish after biomanipulation can delay the successful restoration of submerged macrophytes, leading to a turbid water status in subtropical shallow lakes. Aimed to test the effects of direct removal of juvenile crucian carp (Carassius carassius) on water quality and growth of two submerged macrophytes Vallisneria natans and Hydrilla verticillate, a short-term outdoor mesocosm experiment was conducted in the Taihu Laboratory for Lake Ecosystem Research (TLLER). The results indicated that the concentrations of TN, TP, suspended solids, and chlorophyll a decreased significantly with increasing removal density of juvenile crucian carp, thus resulting in a clear status of the water. Additionally, the mean relative growth rate of V. natans and H. verticillata in the low- and high-density removal treatments were higher than that in the controls. Moreover, the removal of juvenile crucian carp also significantly increased the stem length of V. natans, but no significant effect on that of H. verticillata. Meanwhile, the total number of V. natans and H. verticillata in the low- and high-density removal treatments was higher than that in the controls, but all of H. verticillata were lower than the initials. Our results indicated that removing juvenile crucian carp could improve the water quality, increasing relative growth rate, height, and reproduction of V. natans, and improving the survival rate of H. verticillata. The promotion of fish removal on the V. natans growth was greater than H. verticillata. The results also implied that it was necessary to continuously remove the juvenile benthivorous fish several times for restoring the submerged macrophytes in shallow lakes.