Fish Biomass Research Articles

Environmental impacts on algal-bacterial-based aquaponics system by different types of carbon source addition: water quality and greenhouse gas emission.

Carbon source addition is an important way improving the carbon and nitrogen transformation in aquaculture system; however, its effectiveness of algal-bacterial-based aquaponics (AA) through carbon source addition is still vague. In this study, the influences of organic carbon (OC-AA system) and inorganic carbon (IC-AA system) addition and without carbon source addition (C-AA system) on the operational performance of AA system were investigated. Results showed that 10.1-19.5% increase of algal-bacterial biomass enhanced the purifying effect of ammonia nitrogen in OC-AA system and IC-AA system relative to C-AA system. Moreover, extra electron donor supply in the OC-AA system obtained the lowest NO3--N concentration. However, that was at the cost of aggravated N2O conversion ratio, which increased by more than 2.0-folds than other systems, attributing to 2.9-folds increase of nirS gene abundance. In addition, carbon source addition increased the pH and then decreased the fish biomass production of AA system. The results of this study would provide theoretical supports of carbon source addition on the performance of nutrient transformation and greenhouse gas effect in AA system.

Modeling the spatial distribution of numbers of coral reef fish species and community types in the Western Indian Ocean faunal province

Predicting and mapping coral reef diversity at moderate scales can assist spatial planning and prioritizing conservation activities. We made coarse-scale (6.25 km2) predictive models for numbers of coral reef fish species and community composition starting with a spatially complete database of 70 environmental variables available for 7039 mapped reef cells in the Western Indian Ocean. An ensemble model was created from a process of variable elimination and selectivity to make the best predictions irrespective of human influences. This best model was compared to models using preselected variables commonly used to evaluate climate change and human fishing and water quality influences. Many variables (~27) contributed to the best number of species and community composition models, but local variables of biomass, depth, and retention connectivity were dominant predictors. The key human-influenced variables included fish biomass and distance to human populations, with weaker associations with sediments and nutrients. Climate-influenced variables were generally weaker and included median sea surface temperature (SST) with contributions in declining order from SST kurtosis, bimodality, excess summer heat, SST skewness, SST rate of rise, and coral cover. Community composition variability was best explained by 2 dominant community richness axes of damselfishes-angelfishes and butterflyfishes-parrotfishes. Numbers of damselfish-angelfish species were ecologically separated by depth, and damselfishes declined with increasing depth, median temperature, cumulative excess heat, rate of temperature rise, and chronic temperature stresses. Species of butterflyfish-parrotfish separated by median temperature, and butterflyfish numbers declined with increasing temperature, chronic and acute temperature variability, and the rate of temperature rise. Several fish diversity hotspots were found in the East African Coastal Current Ecoregion centered in Tanzania, followed by Mayotte, southern Kenya, and northern Mozambique. If biomass can be maintained, the broad distributions of species combined with compensatory community responses should maintain high diversity and ecological resilience to climate change and other human stressors.

Variable forage fish biomass and phenology influence marine predator diet, foraging behavior, and species interactions in coastal Newfoundland, Canada

Abstract Forage fish species provide essential linkages for energy transfer within pelagic marine food webs. Capelin (Mallotus villosus), the focal forage fish in coastal Newfoundland, Canada, suffered a stock collapse in 1991 and has not recovered. Despite this collapse, capelin continue to provide locally abundant prey aggregations. Here, I synthesize the lessons learned from a long-term capelin-predator research program (2004–2022) on the northeast Newfoundland coast during the postcollapse period. I highlight the importance of simultaneously estimating forage fish biomass and predator responses in a multispecies and multiyear context. High interannual variation in capelin spawning timing and biomass was observed. Lower capelin biomass consistently resulted in predator species- and assemblage-level dietary shifts toward a higher diversity of lower trophic level, alternative prey. Energetic foraging costs of seabirds also increased under lower capelin biomass, but responses differed among species. Summer capelin consumption by dominant seabirds (9389 tonnes) and whales (778 tonnes) indicated predator energetic requirements and revealed higher natural mortality relative to fishery-based (1289 tonnes) mortality. Overall, this case study illustrated that, despite high observed behavioural plasticity, varying species-specific predator responses to changing capelin biomass integrated to increase potential competitive interactions under low capelin biomass, providing a basis for ecosystem-level change.

Projecting contributions of marine protected areas to rebuild fish stocks under climate change

No-take marine protected areas (No-take MPAs) are considered as a major tool for conserving marine biodiversity and ecosystem services. No-take MPAs can also contribute to climate adaptation for exploited fish stocks. Meanwhile, many fish stocks in the world are overfished and management institutions are developing plans to rebuild them. Understanding the potential effects of no-take MPAs on fish stocks under climate change can help develop strategies for climate-resilient stock rebuilding. Here, using a linked climate-fish-fishing model, we undertake simulation experiments to examine the effects of no-take MPAs on biomass and potential catches of 231 exploited fish and invertebrate species in eight marine ecoregions in the Northeast Atlantic under climate change. The simulations include different levels of fishing, no-take MPAs coverage, atmospheric global warming levels, and account for the expected displacement of fishing to the area around the no-take MPAs. Average individual stock biomass is projected to decrease by 5–15% per degree Celsius atmospheric warming. Having 30% of the distribution of over-exploited fish stocks under no-take MPAs together with conservation-focused fisheries management of these stocks are projected to offset the negative impacts on their biomass under 2.6–2.9 °C global warming. Meanwhile, potential catches increase when a portion of the over-exploited fish stocks is protected from fishing as higher biomass in the no-take MPAs spills-over to the surrounding areas. Our findings highlight that no-take MPAs, combined with reducing fishing intensity, can help rebuild over-exploited fish biomass and benefit their dependent fisheries in the Northeast Atlantic under projected climate change in the 21st century.

Catalyzing Conservation: An Analysis of Fish Stock Dynamics in a Marine Protected Area before and after Artificial Reef Deployment

The marine ecosystem’s balance is crucial for sustaining biodiversity and supporting fisheries. Marine protected areas have been increasingly used to enhance marine habitats, yet their impact on fish populations remains a topic of debate. This study focuses on a marine protected area in Kitros, Pieria, in Greece, where an artificial reef was constructed, to understand its influence on coastal fish populations. The objectives were to investigate the changes in fish biomass and abundance, comparing the data from periods before and after the construction of an artificial reef. This research compares the data between 2007 and 2008 with the data between 2016 and 2017, collected with bottom trawl surveys strategically executed prior to and after the artificial reef’s installation. Fish species captured were identified, with their lengths and masses measured. The findings indicate an increase in the biomass and abundance of certain fish species after artificial reef deployment, notably the commercially significant Mullus barbatus and Pagellus erythrinus. The artificial reef in Kitros, Pieria, with its surrounding marine protected area appears to have had a positive impact on the local fish populations over the years, suggesting that it can contribute to marine conservation and fishery enhancement. These results underscore the potential of artificial reefs as tools for marine ecosystem management, offering insights for policymakers and environmentalists into coastal resource management.

Contribution of offshore platforms and surrounding habitats to fish production in the Bass Strait, south-east Australia

Information on the contribution of offshore oil and gas (O&G) platforms to fish productivity is required to contribute to the decision-making process to remove, partially remove, or retain these structures during decommissioning after petroleum production ceases. The present study assesses the biomass and fish production of one common and abundant fish species (Caesioperca lepidoptera – butterfly perch) and two commercially fished species (Helicolenus percoides – reef ocean perch; Nemadactylus macropterus – jackass morwong) on eight O&G platforms and in surrounding natural habitats in the Bass Strait, south-east Australia, where options for decommissioning are being assessed. High-definition stereo-video imagery was collected by remotely operated vehicle (ROV) from eight platform facilities, their immediate benthic surrounds, reference areas reflective of the likely pre-installation seabed state (sand-dominated) and a nearby natural ‘reef’ area referred to as south-east reef (some limestone foundation). The biomass of all three species was low in the benthic surrounds of platforms, at reference locations and at south-east reef where minimal cover by benthic organisms was recorded and, as such, there was little to no fish production for the three study species in these areas. We observed a total fish biomass of 2.85 tonnes across the eight platforms for the three fish species surveyed, with high variability across platforms. Total production (P) across all platforms was estimated at 1244 kg/year for the three species, with a mean fish production density of 82 g/m2/year. Approximately 79% of total production is considered ‘new’ production (984 kg/year i.e., the production attributed to the presence of the platforms; with a mean production density of 64 g/m2/year). The remaining 21% could be retained or redistributed into the surrounding area if platforms were removed. C. lepidoptera accounted for the majority (90%) of biomass and of total production for all three species across all locations surveyed. Despite only accounting for a small proportion of platform surface area, the bottom 5 m sections of platforms had 41% of the total biomass observed and accounted for 46% of total production of these three study species. Production measures for platforms surveyed here are relatively high compared to other artificial reefs and habitats around the world. Total removal of these platforms will likely result in a reduction of fish biomass and fish productivity (incl. several fishery species) in the immediate vicinity.

Temperature‐Dependence Assumptions Drive Projected Responses of Diverse Size‐Based Food Webs to Warming

AbstractFood web projections are critical for evaluating potential risks to ecosystems and fisheries under global warming. The temperature dependence of biological processes and regional differences in food web structure are two important sources of uncertainty and variation in climate forced projections of fish communities, but we do not know their magnitude or relative contribution. Here we systematically evaluated a range of different assumptions about temperature‐dependence on rates, including size‐dependent effects, controlling food intake, metabolism, and non‐predation mortality in fishes using species‐resolved size spectrum food web models that link individual‐level physiological processes to population and community dynamics. We simulated the physiological effect of warming in a range of size‐structured food web models calibrated to different marine ecosystems and in simplified trait‐based models. Higher food intake in warmed conditions increased total fish biomass, catches, and mean body weight, but these effects were offset by the negative effects of warming on metabolism and mortality, which combined resulted in lower total biomasses and catches for most food webs. These effects were enhanced when warming increased metabolic rates more than food intake, and the outcomes were also sensitive to size dependency of temperature responses. Importantly, these general patterns were not uniform across all food webs—individual functional groups and fish species within food webs responded to warming in different ways depending on their position in the food web and its structure. Hence, caution is warranted when generalizing food web or species outcomes to warming because they are mediated by community interactions. Uncertainty related to temperature dependence and ecological interactions will impact food web projections and should be represented in climate change projections.

Use of the raw material base of marine fish in Russian waters of the Far Eastern seas and adjacent areas of the open part of the Pacific Ocean in 2000–2020

The purpose of the work: characteristics of the raw material base of marine fish in the Far Eastern fishery basin and an assessment of the effectiveness of its use by domestic fisheries at the present stage (2000–2020).Methods used: to achieve this goal, data on biomass, catch and development of the main commercial marine fish were analyzed. Fish catches were reviewed based on operational information about the fishery based on daily ship reports from the industry monitoring system.Novelty: elements of novelty are generalized modern materials on biomass, catch and development of marine fish resources in the Far Eastern seas and adjacent waters of the Pacific Ocean. The current state of commercial fish stocks (walleye pollock, Pacific cod, saffron cod, Pacific herring, Righteye flounders, greenlings, Japanese pilchard, Chub mackerel, Pacific saury) in the Far Eastern fishing basin can be characterized as stable, and the distribution of the catch of these objects among individual fishing areas due to their significant volumes is practically determines the distribution of catch of both quota and non-quota species of marine fish. Scientific information support for the above-m entioned fish is at a high level, their biological condition is generally favorable, and the dynamics of their numbers is regulated mainly by habitat variability.Practical significance: the results of this study can be used in forecasting the dynamics of aquatic biological resources, and the results obtained on marine fish stocks and fisheries will improve the efficiency of using their raw material base.

Nearshore fish community changes along the Toronto waterfront in accordance with management and restoration goals: Insights from two decades of monitoring.

Aquatic habitat in the Greater Toronto Area has been subject to anthropogenic stressors. The subsequent aquatic habitat degradation that followed led to the Toronto and Region waterfront being listed as an Area of Concern in 1987. Thus, extensive shoreline and riparian habitat restoration have been implemented as part of the Toronto and Region Remedial Action Plan in conjunction with local stakeholders, ministries, and NGOs in an overall effort to increase fish, bird, and wildlife habitat. A key aspect of current fish habitat restoration efforts, monitored by Toronto and Region Conservation Authority, is to account for long-term community changes within the target ecosystem to better understand overall changes at a larger spatial scale. Here we use electrofishing data from the past 20 years with over 100,000 records and across 72km of coastline to show how declines and fluctuations in fish biomass and catch along the waterfront are driven by a few individual species across three main ecotypes, such as coastal wetlands, embayments, and open coast sites, with the remaining species showing a high level of stability. Using community traits and composition for resident species we demonstrate native warmwater species have become more dominant along the waterfront in recent years, suggesting that restoration efforts are functioning as intended. Additionally, piscivore and specialist species have increased in their relative biomass contribution, approaching existing restoration targets. Altogether this waterfront-wide evaluation allows us to detect overall changes along the waterfront and can be beneficial to understand community changes at an ecosystem level when implementing and monitoring restoration projects.

A diverse portfolio of marine protected areas can better advance global conservation and equity

Marine protected areas (MPAs) are widely used for ocean conservation, yet the relative impacts of various types of MPAs are poorly understood. We estimated impacts on fish biomass from no-take and multiple-use (fished) MPAs, employing a rigorous matched counterfactual design with a global dataset of >14,000 surveys in and around 216 MPAs. Both no-take and multiple-use MPAs generated positive conservation outcomes relative to no protection (58.2% and 12.6% fish biomass increases, respectively), with smaller estimated differences between the two MPA types when controlling for additional confounding factors (8.3% increase). Relative performance depended on context and management: no-take MPAs performed better in areas of high human pressure but similar to multiple-use in remote locations. Multiple-use MPA performance was low in high-pressure areas but improved significantly with better management, producing similar outcomes to no-take MPAs when adequately staffed and appropriate use regulations were applied. For priority conservation areas where no-take restrictions are not possible or ethical, our findings show that a portfolio of well-designed and well-managed multiple-use MPAs represents a viable and potentially equitable pathway to advance local and global conservation.

Spatial fish distribution in autumn in a shallow mesotrophic lake, assessed by hydroacoustic surveys, trawling, and beach seining.

Day and nighttime autumn fish abundance and biomass were studied in the pelagic and littoral zones of Lake Sauka in Latvia. Both pelagic methods (hydroacoustics and trawling) revealed significantly higher fish abundance and biomass during the day than at night, especially in deeper zones (below 3 m). Roach (Rutilus rutilus) and Eurasian perch (Perca fluviatilis) dominated the trawl catches during the day, while roach and ruffe dominated at night. Fish smaller than 14 cm strongly dominated in both the trawl catches and hydroacoustic observations. Our hydroacoustic sampling found inhomogeneous pelagic distributions of fish aggregated in big shoals during the day. In the littoral zone, which was sampled by beach seining, both the abundance and biomass were significantly higher at night than during the day. Roach, bleak, and European perch usually dominated in beach seine catches during the day and at night. The daytime pelagic biomass found by hydroacoustics was 62 kg/ha and it decreased to approximately 11 kg/ha at night. The littoral biomass found by beach seining was diurnally opposite, 4 kg/ha during the day and 37 kg/ha at night. It is obvious that diurnal horizontal migrations between pelagic and littoral zones, and shoaling behavior during the daytime are common patterns in the shallow Lake Sauka during the autumn. The study of the spatial distribution of fish is extremely important for the establishment of an appropriate monitoring plan for the purposes of the Water Framework Directive with regard to the morphometry of the lake, the geographical location, and the sampling period of the year. This study also shows that the combination of completely non-invasive hydroacoustic and other methods that are invasive (trawls, beach seines) but not as destructive as gillnets, which are normally used for scientific fish monitoring in Europe, could be a future way forward for fish monitoring.

Peaks and transient dynamics of ecological and biogeochemical variables following impoundment in boreal reservoirs

Across the globe, reservoirs represent nearly 10 % of the world's freshwater. River impoundment strongly alters the hydrological regime of aquatic ecosystems which subsequently affect the ecological (e.g., primary production, fish biomass) and biogeochemical variables (e.g., nutrient, mercury, and carbon cycles which includes Green House Gas emissions; GHG). We examined the transient dynamics and co-variation of biogeochemical and ecological variables from unique long-term time series (40 years of data) from Hydro-Québec boreal reservoirs, with data before and after impoundment. To do so, we applied curve fitting analysis on the data from eight plausible scenarios and model selection. Following impoundment, most variables increased, peaked, and then decreased over time (clear hump-shaped patterns; six over eight variables). Model predictions peaked between three- and 11-years post-impoundment and returned to pre-impoundment levels after about nine- to 40-years. Variables also followed a clear sequence where GHG emissions (CO2, CH4) peaked first, immediately after impoundment, followed by an increase in phosphorus and Chl-a. Total mercury in fish peaked a few years later for non-piscivorous fish and was followed closely by piscivorous fish. This work provides the first comprehensive and holistic description of the transitory nature and co-variation of ecological and biogeochemical variables following reservoir impoundment.

Biofloc supplementation improves growth performances, nutrient utilization, and histological status of Nile tilapia (Oreochromis niloticus) while enhancing zooplankton diversity, community, and abundance

The present work investigates the effect of biofloc supplementation, as an environmentally clean aqua-feed technique, on water quality, growth performance, feed utilization, and histological status of Nile tilapia (Oreochromis niloticus). Moreover, indicators of zooplankton diversity, community structure, abundance, similarities, and cluster analysis were studied during the experiment. A 60-day growth experiment based on biofloc supplementation was performed to evaluate, in addition to the control group (BF0), the effects of five groups of biofloc supplementation (BF1 = 14.20, BF2 = 28.40, BF3 = 42.60, BF4 = 56.80, and BF5 = 71.0 g L−1, respectively) on Nile tilapia juveniles (initial body weight: 13.30 ± 0.01 g fish−1). During the 15 days of acclimation, the juveniles in all groups were fed twice daily on the same control diet (a commercial diet containing 28% protein). Then, the juveniles were randomly distributed to 18 tanks (each 0.5 m3 with a stocking of 40 fish/tank). The feed rate was 3% of the total fish biomass, adjusted weekly. The water quality indicators were in the ideal range recommended for Nile tilapia culture. The results found that the highest weight gain, specific growth rate and survival rate, and the lowest feed conversion ratio of fish were reported in the BF5 group. Moreover, this group achieved the highest zooplankton abundance (20,706 Ind. L−1) compared to the control group (457 Ind. L−1). The results showed that sections of the muscles in the control group (BF0) revealed fibers arranged into bundles. Comparisons between the muscles in the control group (BF0) and the bioflocs groups (BF1–BF5) showed unclear differences. However, sections of the muscle group BF1 showed increased splitting of muscle fibers and the separation of individual muscle fibers into smaller units. The liver showed multiple pathological lesions in all experimental groups (BF0–BF5). Zooplankton diversity indicators and cluster analysis data also reported a significant difference between the control group (BF0) and the biofloc groups, especially the BF5 group. The present study concluded that the addition of biofloc (71 g L−1) to culture ponds significantly improves the growth, feed utilization, and survival rates of Nile tilapia while enhancing zooplankton diversity, community, and abundance.

Fish weight reduction in response to intra‐ and interspecies competition under climate change

AbstractAs described by the temperature–size rule paradigm, fish living in warmer temperatures grow faster but have a smaller mature body size. However, the changes in the body size of fish communities in the western North Pacific, which is one of the most active fishing grounds, remain unclear. This study aimed to investigate changes in the body size of fish assemblages in the western North Pacific and whether fish sizes were potentially driven by the temperature–size rule, bottom‐up effects and intra‐ and interspecies competition at a community scale. We evaluated the fish weight data of 6 stocks of 4 species from 1978 to 2018 and 17 stocks of 13 species from 1995/1997 to 2018. Weight reduction in the fish assemblage was observed in the 1980s and was associated with the biomass peak of the Japanese sardine (Sardinops melanostictus), indicating the effect of intra‐ and interspecies competition. Another weight reduction was observed in the 2010s, which was associated with a moderate increase in the biomass of the Japanese sardine and chub mackerel (Scomber japonicus). Our analyses indicate that stronger stratifications in the surface layers during the 2010s potentially reduced the nutrient supply from the subsurface to the surface layers. This limitation in food availability forced intra‐ and interspecies competition under a moderate increase in fish biomass. Our findings underscore the critical significance of integrating the impacts of species competition and climate change on fish sizes to improve fishery management at a community level.

An initial fish and megafauna biomass assessment from Tanjung Bira, a remote unprotected marine area

Indonesia is a part of the Coral Triangle, the global epicenter of marine biodiversity. As an island nation, fisheries are amongst the main sources of income for Indonesia’s economy, but overfishing has depleted fish stocks and degraded habitats, especially in unprotected marine areas. Tanjung Bira in South Sulawesi is an unprotected marine area that possesses understudied marine biodiversity and overlooked potential for sustainable tourism. Currently, research has only been done in a small area in Liukang Loe island, but we hypothesize that the habitats surrounding Bira east, Bira west, and Kambing island also harbor significant levels of marine biodiversity. In this study, we utilized a standardized citizen science effort to investigate the occurrence and to quantify the biomass of specific fish families (Lutjanidae, Serranidae, Carangidae, Scombridae, Sphyraenidae, Lethrinidae, and Scaridae), key fish species (large and vulnerable piscivores), sea turtles, elasmobranchs, and other megafauna in Tanjung Bira and its surrounding area. We discuss the species assemblages, their potential ecological roles, threats, and proposed management strategies for each region to foster coexistence between conservation and community livelihood. Implementing a measure of protection is imperative to ensure the conservation of reef ecosystems, commercially important fishes, vulnerable elasmobranchs, charismatic megafauna and nationally protected species such as the humphead wrasse, sea turtles, and cetaceans.

Examining the effectiveness of bored pile coral for coral rehabilitation

Abstract. Putri NP, Muharam MR, Ritonga A, Ruswanti CD, Arthen D, Munasik. 2024. Examining the effectiveness of bored pile coral for coral rehabilitation. Biodiversitas 25: 153-161. Semut Island is located in Kiabu Village, Anambas Islands, Riau, Indonesia, and has suffered significant damage to its coral cover due to blast fishing. To address this issue, Anambas Foundation initiated a coral reef rehabilitation on Semut Island using a customized artificial reef called Bored Pile Coral (BPC), a cylindrical structure made of concrete hammered into the seabed. This research aims to examine the effectiveness of BPC by monitoring its performance. Therefore, from February 2022 to January 2023, 1,500 BPCs were deployed and attached with corals covering an area of 170 m2. We quantified five ecological indicators, i.e., coral cover, survival rate, recruitment, growth rates, and fish biomass. Results showed an increase in coral cover from 3.8% to 8%. The survival rate was 64%, and the mean monthly growth rates varied among three genera: Pocillopora sp. (0.235±0.02 month-1), Acropora sp. (0.22±0.03 month-1) and Porites sp. (0.08±0.02 month-1). The monthly mean fish biomass data showed the biomass was 427,25 Kg/Ha and increased 3,9 times since the beginning of the research. BPC's structure has been proven to act as stable media for hard corals, although the modification may be necessary to enhance structural complexity and suitability for carnivorous fish habitats.

Herbivory through the lens of ecological processes across Pacific coral reefs

AbstractCoral reefs are in global decline primarily due to climate change. Herbivory is often viewed as key to maintaining coral‐dominated reefs, and herbivore management is gaining traction as a possible strategy for promoting reef resilience. The functional impact of herbivorous fishes has typically been inferred from total biomass, but robust estimates of ecological processes are needed to better inform management targets. Here, we provide a framework to calculate rates of herbivory across Pacific reefs. We synthesized available observations of foraging metrics in relation to fish body size and found considerable variation, even among closely related species. We then applied these allometric functions to survey data and calculated rates of herbivory for acanthurids and scarines, which make up the vast majority of herbivorous fish biomass in the Pacific. Estimated rates of algal consumption, area scraped, and bioerosion varied across islands, with noticeable differences that may align with the relative influence of human population density among underlying herbivore functional groups. We found no evidence of compensatory relationships among herbivore processes whereby decreasing rates in one type of herbivory is offset by increasing rates in another. We observed nonlinear, positive relationships between fish biomass and rates of herbivory. Yet, for a given biomass, the corresponding rates of herbivory varied among regions, and we observed instances where islands with the greatest biomass did not also have the highest rates of herbivory. Islands with the largest size classes of herbivores did not consistently exhibit greater rates of herbivory, and we did not find a clear, consistent pattern between the number of fish species and corresponding rates of herbivore processes. Cropping Acanthurus spp. provided the greatest proportion of algal consumption at every island, yet no single species accounted for the majority of this process, whereas we identified parrotfish species that provided >75% of scraping or bioerosion at certain islands. Our results emphasize the importance of considering the species and size composition of herbivore assemblages when estimating processes, rather than relying on total biomass alone. Lastly, we highlight gaps in foraging observations and additional work needed to further broaden our ability to quantify the ecological processes of herbivores.

Trophic lengthening triggered by filamentous, N2-fixing cyanobacteria disrupts pelagic but not benthic food webs in a large estuarine ecosystem.

Eutrophication, increased temperatures and stratification can lead to massive, filamentous, N2-fixing cyanobacterial (FNC) blooms in coastal ecosystems with largely unresolved consequences for the mass and energy supply in food webs. Mesozooplankton adapt to not top-down controlled FNC blooms by switching diets from phytoplankton to microzooplankton, resulting in a directly quantifiable increase in its trophic position (TP) from 2.0 to as high as 3.0. If this process in mesozooplankton, we call trophic lengthening, was transferred to higher trophic levels of a food web, a loss of energy could result in massive declines of fish biomass. We used compound-specific nitrogen stable isotope data of amino acids (CSIA) to estimate and compare the nitrogen (N) sources and TPs of cod and flounder from FNC bloom influence areas (central Baltic Sea) and areas without it (western Baltic Sea). We tested if FNC-triggered trophic lengthening in mesozooplankton is carried over to fish. The TP of cod from the western Baltic (4.1 ± 0.5), feeding mainly on decapods, was equal to reference values. Only cod from the central Baltic, mainly feeding on zooplanktivorous pelagics, had a significantly higher TP (4.6 ± 0.4), indicating a strong carry-over effect trophic lengthening from mesozooplankton. In contrast, the TP of molluscivorous flounder, associated with the benthic food web, was unaffected by trophic lengthening and quite similar reference values of 3.2 ± 0.2 in both areas. This suggests that FNC blooms lead to a large loss of energy in zooplanktivorous but not in molluscivorous mesopredators. If FNC blooms continue to trigger the detour of energy at the base of the pelagic food web due to a massive heterotrophic microbial system, the TP of cod will not return to lower TP values and the fish stock not recover. Monitoring the TP of key species can identify fundamental changes in ecosystems and provide information for resource management.

Relationship between Nitrogen Dynamics and Key Microbial Nitrogen-Cycling Genes in an Intensive Freshwater Aquaculture Pond.

Intensive aquaculture in high-density hybrid snakehead [Channa maculata (♀) × Channa argus (♂)] fishponds can lead to toxic conditions for fish. This study investigated nitrogen migration and transformation in these fishponds during different cultivation periods. Using qPCR technology, we analyzed the abundance variation of nitrogen-cycling microorganisms in water and sediment to reveal the nitrogen metabolism characteristics of hybrid snakehead fishponds. The results showed that fish biomass significantly impacts suspended particulate matter (SPM) flux. At the sediment-water interface, inorganic nitrogen fluxes showed predominant NO3--N absorption by sediments and NH4+-N and NO2--N release, especially in later cultivation stages. Sediments were rich in nirS and AMX 16S rRNA genes (ranging from 4.04 × 109 to 1.01 × 1010 and 1.19 × 108 to 2.62 × 108 copies/g, respectively) with nirS-type denitrifiers potentially dominating the denitrification process. Ammonia-oxidizing bacteria (AOB) were found to dominate the ammonia oxidation process over ammonia-oxidizing archaea (AOA) in both water and sediment. Redundancy analysis revealed a positive correlation between SPM flux, Chlorophyll a (Chl-a), and denitrification genes in the water, and between nitrogen-cycling genes and NH4+/NO2- fluxes at the interface. These findings provide a scientific basis for nitrogen control in hybrid snakehead fishponds.

The role of marine fish-produced carbonates in the oceanic carbon cycle is determined by size, specific gravity, and dissolution rate

Rising CO2 emissions have heightened the necessity for increased understanding of Earth's carbon cycle to predict future climates. The involvement of marine planktonic species in the global carbon cycle has been extensively studied, but contributions by marine fish remain poorly characterized. Marine teleost fishes produce carbonate minerals (‘ichthyocarbonates’) within the lumen of their intestines which are excreted at significant rates on a global scale. However, we have limited understanding of the fate of excreted ichthyocarbonate. We analyzed ichthyocarbonate produced by three different marine teleosts for mol%MgCO3 content, size, specific gravity, and dissolution rate to gain a better understanding of ichthyocarbonate fate. Based on the species examined here, we report that 75 % of ichthyocarbonates are ≤0.91 mm in diameter. Analyses indicate high Mg2+ content across species (22.3 to 32.3 % mol%MgCO3), consistent with previous findings. Furthermore, ichthyocarbonate specific gravity ranged from 1.23 to 1.33 g/cm3, and ichthyocarbonate dissolution rates varied among species as a function of aragonite saturation state. Ichthyocarbonate sinking rates and dissolution depth were estimated for the Atlantic, Pacific, and Indian ocean basins for the three species examined. In the North Atlantic, for example, ~33 % of examined ichthyocarbonates are expected to reach depths exceeding 200 m prior to complete dissolution. The remaining ~66 % of ichthyocarbonate is estimated to dissolve and contribute to shallow water alkalinity budgets. Considering fish biomass and ichthyocarbonate production rates, our results support that marine fishes are critical to the global carbon cycle, contributing to oceanic alkalinity budgets and thereby influencing the ability of the oceans to neutralize atmospheric CO2.