Fish Habitat Research Articles

Fishing for more than shellfish: a systematic review of fish community monitoring of shellfish reefs

Shellfish reefs, characterized by habitat‐forming bivalves, are increasingly recognized as globally significant coastal ecosystems and valuable fish habitats. Shellfish reefs provide structural refugia, foraging grounds, and nurseries for diverse fish communities, including species with socioeconomic value. However, efforts to quantify the value of shellfish reefs as fish habitats are challenged by the limited and fragmented knowledge of published monitoring practices. Here, we systematically assess 116 peer‐reviewed studies to provide a global overview of literature evaluating fishes in these ecosystems. Research was unevenly distributed, with 67% of the studies concentrated in the United States, 61% on restored reefs, and 83% focused on oyster reefs. Few studies have directly compared fish communities between natural versus restored, or intertidal versus subtidal shellfish reefs. Methods to quantify fishes varied based on research objectives, tidal zonation, and targeted subsets of the fish assemblages. Gill nets, substrate trays, and underwater video stations were the most common methods, with 44% of studies deploying more than two methods to survey fish communities. Differences in the monitoring methods, research designs, and variables reported were also synthesized and discussed. From this review, we identified knowledge gaps and monitoring trends in fish community assessments that can guide future shellfish reef research and conservation efforts.

You shall (not) pass! Steep low-head ramps as potential selective barriers for fish movements

River fragmentation by instream barriers obstructs the movements of organisms, reducing the amount of available habitat for native fishes. However, instream barriers can also block the spread of non-native invasive ones. This study aimed to assess the selectivity of a small instream barrier, a steep (120%) low-head ramp, for successful movements of a native (the Iberian barbel, Luciobarbus bocagei), a non-native translocated (the Pyrenean gudgeon Gobio lozanoi) and a non-native invasive (the bleak, Alburnus alburnus) fish species, representing a harmfulness gradient to river ecosystems. Two variables were recorded: i) the number of attempts (AT) to negotiate the ramp and ii) the number of successful negotiations (S), which were used to calculate passage efficiency PE(%). Overall, AT was significantly higher for the barbel relative to the gudgeon and the bleak. PE(%) was also far superior for the barbel than for the non-native fishes: accordingly, thirty-four ramp successful negotiations were reported for the former – resulting in an overall PE (%) of 26.6 - whereas no gudgeon or bleak individuals were able to negotiate it (PE(%) = 0). The results of this study show that selectivity at small barriers can be achieved if properly designed, being useful in river management where non-native invasive species are a concern.

Hypoxia influences the extent and dynamics of suitable fish habitat in Chesapeake Bay, USA

Intra-annual patterns of hypoxia in Chesapeake Bay have been recorded since the mid-1900s, but anthropogenic inputs and climate change have exacerbated the volume and extent of hypoxic waters, which mobile marine fishes avoid. This estuary provides important habitat for many seasonally resident species but declines in relative abundance and relative habitat usage have been documented. An understanding of the relationship between environmental conditions and habitat suitability could assist in evaluating the stock status of these species. To characterize baseline habitat associations for Micropogonias undulatus, Leiostomus xanthurus, Paralichthys dentatus, and Cynoscion regalis, ecological niche models were developed relating catch-per-unit-effort data from a fisheries-independent trawl survey conducted within Chesapeake Bay to environmental covariates. Model output indicated that impacts of climate change on the environmental conditions, including continued increases in temperature and decreases in dissolved oxygen (DO) concentration, will likely further the decline in estuarine utilization of these species. The niche envelopes were then paired with hindcasts from an estuarine-carbon-biogeochemical regional model to derive estimates of spatiotemporal habitat suitability. The patterns in habitat suitability do not match those of declining abundance, indicating that dynamics outside of Chesapeake Bay are likely driving the shift. An auxiliary model was used to replace hypoxic DO concentrations with normoxic concentrations to evaluate the influence of hypoxia on habitat suitability. Both hypoxic severity and extent displayed significant associations with the quantity of suitable habitat available to each species in the bay. Results characterize the complexity of the dynamics underpinning observed trends in habitat utilization.

Mapping essential juvenile habitats of exploited marine fish: Complementary insights from a scientific survey-based model, fishers’ knowledge and fisheries-dependent data

In the Bay of Biscay (BoB, Northeast Atlantic), a preexisting habitat suitability model (HSM) fitted on ecological scientific trawl survey data with restricted partial coverage revealed the concentration of Young of the Year (YoY) common sole (Solea solea) on restricted coastal and estuarine nurseries. To extend the nursery map of sole in the BoB to zones where survey data are lacking and fit with the sole population and stock management extent, we crossed HSM, fishers’ ecological knowledge (FEK) and fisheries-based (FB) data. FB and FEK data also complemented knowledge on juvenile sole habitat and seasonal migration. Thirteen fishers with potential knowledge about the YoY sole distribution were directly interviewed. Direct interviews included both information about the location of juveniles and YoY distribution mapping. With good consensus among fishers, FEK allowed the identification of four new areas hosting essential juvenile habitat for the common sole, revealed the accuracy of the HSM model outside the spatial coverage of the ecological survey, and provided spatial refinement. The FB observation data confirmed the locations of the essential juvenile habitats given by FEK and the spatial distributions of YoY densities predicted from the scientific data. In addition, FB confirmed the seasonal migration of YoY sole, which was preliminarily hypothesized from a local and short-term survey-based study. Our results emphasized the local accuracy of FEK. These findings also underlined the interest in combining several sources of data and methods to map essential fish habitats outside areas well covered by ecological scientific surveys, on order to inform future spatial management measures.

Analysis of Heavy Metal Pollution in the Water of the Halda River: A Distinctive Breeding Habitat for Carp Fish in Bangladesh.

The present study aimed to assess the heavy metal concentrations in water from different sampling sites of the Halda River, the only natural breeding ground of Indian major carps. We have analysed the contamination level and seasonal variations of heavy metals (viz. Fe, Cu, Zn, Cr, Cd and Pb). The favourability of the breeding environment was assessed by different contamination indices. Samples were collected from six sampling sites for four different seasons, and the metal concentrations were determined for water samples using Flame atomic absorption spectrophotometer. The obtained order of mean concentrations of heavy metals for four seasons was winter>spring>monsoon>pre-monsoon, and the assessed mean concentrations (mg/L) of heavy metals follow the trend: Fe (9.129)>Pb (0.033)>Zn (0.024)>Cr (0.017)>Cu (0.012)>Cd (0.002). The concentration of Fe was found above the permissible limit set by the World Health Organization (WHO) (Guidelines for Water Quality) and ECR (1997), and the concentrations for Pb were found above the USEPA (2006) limit in all four seasons. Contamination indices (heavy metal pollution Index [HPI] and metal index [MI]) indicate that during winter and monsoon, the river water metal condition is critical (HPI>100) and the sites are moderately as well as slightly (1<MI<2) affected by the studied heavy metals. Contamination indices, such as contamination factors (Cf), degree of contamination (Cdeg) and the pollution load index (PLI), demonstrate the fact that Fe and Pb remarkably contaminated the studied sampling sites. The Pearson correlation matrix and the principal component analysis (PCA) revealed that the studied metals are connected by their sources, which can be geological or anthropogenic. Urgent initiatives need to be taken, and effective strategies must be implemented to control the different sources responsible for the entry of heavy metals into the Halda River water.

Nutrient fluxes, oxygen consumption and fatty acid composition from deep-water demo- and hexactinellid sponges from New Zealand

Sponges are an important component of deep-water ecosystems enhancing eukaryotic biodiversity by hosting diverse endo- and epibiota and providing three dimensional habitats for benthic invertebrates and fishes. As holobionts they are important hosts of microorganisms which are involved in carbon and nitrogen cycling. While increasing exploration of deep-water habitats results in new sponge species being discovered, little is known about their physiology and role in nutrient fluxes. Around New Zealand (Southwest Pacific), the sponge biodiversity is particularly high, and we selected six deep-sea sponge genera (Saccocalyx, Suberites, Tedania, Halichondria/ Dendoricella, Lissodendoryx) and a member of the Sceptrulophora order for in-situ and ex-situ experiments.We investigated the biochemical composition of the sponges, measured oxygen consumption and inorganic nutrient fluxes, as well as bacterial and phospholipid-derived fatty acid (PLFA) compositions. Our aim was to assess differences in fluxes and fatty acid composition among sponges and linking their bacterial communities to nitrogen cycling processes.All sponges excreted nitrite and ammonia. Nitrate and phosphate excretion were independent of phylum affiliation (Demospongiae, Hexactinellida). Nitrate was excreted by Halichondria/ Dendoricella and Lissodendoryx, whereas Suberites, Tedania, and Sceptrulophora consumed it. Phosphate was excreted by Sceptrulophora and Halichondria/ Dendoricella and consumed by all other sponges. Oxygen consumption rates ranged from 0.17 to 3.56±0.60 mmol O2 g C d-1.The PLFA composition was very sponge-genera dependent and consisted mostly of long-chain fatty acids. Most PLFAs were sponge-specific, followed by bacteria-specific PLFAs, and others.All sponges, except for Suberites, were low-microbial abundance (LMA) sponges whose bacterial community composition was dominated by Proteobacteria, Bacteroidota, Planctomycetota, and Nitrospinota. Suberites consisted of high-microbial abundance (HMA) sponges with Proteobacteria, Chloroflexota, Acidobacteriota, and Actinobacteriota as dominant bacteria.Based on the inorganic nitrogen flux measurements, we identified three types of nitrogen cycling in the sponges: In type 1, sponges (Dendoricella spp. indet., Lissodendoryx) respired aerobically and ammonificated organic matter (OM) to ammonium, fixed N2 to ammonium, and nitrified aerobically heterotrophically produced ammonium to nitrate and nitrite. In type 2, sponges (Halichondria sp., Sceptrulophora, Suberites, Tedania) respired OM aerobically and ammonificated it to ammonium. They also reduced nitrate anaerobically to ammonium via dissimilatory nitrate reduction to ammonium. In type 3, ammonium was microbially nitrified to nitrite and afterwards to nitrate presumably by ammonium-oxidizing Bacteria and/ or Archaea.

Co‐production of a vulnerability assessment for aquatic and riparian ecosystems in the southwestern United States

AbstractTo address impacts of climate change and other stressors on stream ecosystems, managers must prioritize resources and locations for conservation actions to facilitate effective cross‐boundary solutions. Through a science management partnership, we co‐produced a spatially explicit landscape assessment framework for cold‐water fish habitat and riparian corridors in three large watersheds of the southwestern United States. Using literature review and stakeholder workshops, we developed indicators of vulnerability and built spatial datasets depicting areas of low to high vulnerability based on exposure, sensitivity, and adaptive capacity for each resource. We found that, in general, vulnerability was greater for cold‐water fish habitat than for riparian corridors. The Little Colorado River and San Juan River watersheds had the highest percentages of subwatersheds with high vulnerability of cold‐water fish habitat. Conversely, the Upper Rio Grande watershed had the highest percentage with high vulnerability of riparian corridors. Assessments like ours facilitate the management of water resources at the scale of watersheds or river basins and incorporate physical characteristics, land‐use history, current management practices, and status of imperiled species into actionable management plans.

Molecular identification and phylogenetic analysis of coral and megabenthic species from Gede Island, Central Java, Indonesia

Coral reef ecosystems are home to many organisms, including bivalves, gastropods, crinoids, and demersal fish, making biodiversity assessment crucial for effective conservation and management. This study aims to: i) apply DNA barcoding to identify coral and megabenthic species in coral reef ecosystems, and ii) construct phylogenetic tree to trace their evolutionary relationships. Using quantitative descriptive methods and purposive sampling, specimens were collected in July 2023. The study yielded one coral (R2), one hydrozoan (R3), and one gastropod (GP-1) sample were successfully barcoded. DNA barcoding through Cytochrome Oxydase I (COI) gene amplification revealed that sample R2 had a 98.70% similarity with Acropora hyacinthus, sample R3 had a 98.92% similarity with Zanclea galli, and sample GP-1 had a 91.19% similarity with Erronea errones. Phylogenetic analysis positioned R2 in the same clade as Acropora hyacinthus and related genera such as Montipora, Astreopora, and Alveopora, within the Acroporidae family. R3 clustered with Zanclea galli in the hydrozoan group, alongside Z. sesillis, Z. implexa, and Z. sango. GP-1 grouped with Erronea errones in the gastropod genus Erronea, showing relationships with other genera such as Blasicrura, Cribrarula, Bistolida, and Eclogavena within the subfamily Erroneinae. Species inventories like this are essential for the conservation and management of coral reefs, which are key habitats for fish and other marine life.

Presence-only fisheries bycatch data produce biased species distribution predictions for Alcyonacean corals on British Columbia’s continental shelf and slope

Sedentary benthic species such as Alcyonacea corals form critical habitat for fishes and invertebrates. Assessing anthropogenic risks to these organisms requires unbiased, species distribution models (SDMs) that attempt to map probabilities of coral presence in relation to bio-physical ocean characteristics; however, in deep-water settings, the accuracy of SDMs is highly variable and dependent on spatial and taxonomic resolution. Here we investigated how data and model types affect SDM predictions of Alcyonacea probability of presence. We compared predictions from generalized additive models (GAMs) fitted to presence-absence observations over a stratified-random survey design with predictions from maximum entropy models (Maxent) fitted to presence-only bycatch records from commercial fisheries. We use a simulation analysis to show that both model types (i.e., GAM or Maxent) using presence-only bycatch data produced biased estimates of species distribution. Additionally, the maxent model fit using presence-only bycatch data produced biased estimates of performance metrics (AUC, TSS) that were overly optimistic. This study demonstrates a need for presence-absence data collected using a robust survey sampling design to fit SDMs that will better inform marine protected area placement while minimizing unnecessary economic losses, such as forgone fishing yield, due to sub-optimal placement.

Fishes Associated with a Vulnerable Marine Ecosystem Network in the Central Mediterranean Sea

In order to collect information on ichthyofauna of a deep-sea vulnerable marine ecosystem (VME) network along the Apulian margin (central Mediterranean Sea), two low-impact sampling tools were used in three VMEs characterized by cold-water corals (CWC), namely Bari Canyon (BC), off Monopoli (Mn), and off Santa Maria di Leuca (SML). Using an experimental longline, 53 deployments were carried out between a 314 and 650 m depth for a total of 217 fishing hours, whereas when using the baited lander MEMO (Marine Environment MOnitoring system), 31 deployments were carried out between 427 and 792 m, for a total of 223 h of video recordings. A total of 37 taxa were recorded, comprising 13 Chondrichthyes and 24 Osteichthyes. The similarities in species observed among the VMEs confirm the presence of a network of CWC-VMEs along the Apulian margin, whereas some differences detected are due to the different abundance of some species, such as Galeus melastomus, Helicolenus dactylopterus, and Phycis blennoides. The presence of commercial species, vulnerable/endangered cartilaginous fishes, and large and sexually mature individuals of G. melastomus, H. dactylopterus, and Pagellus bogaraveo in all the VMEs confirms that the network of CWC-VMEs along the Apulian margin can act as a network of refuge areas and an essential fish habitat (EFH) for species threatened by fishing activities.

Shifted Flood and Ecology Regimes Due To Channel Bar Greening and Increased Flow Resistance in a Large Dammed River

AbstractDamming profoundly affects downstream flow‐sediment regimes, altering channel bar dynamics and thereby affecting floods and riverine biodiversity. Here, we investigate the response of bars to upstream damming by examining patterns, mechanisms, and impacts in the Middle Yangtze River (∼1,000 km). Over a decade of post‐damming observational data reveal substantial increases in bar revegetation and Leaf Area Index. Shorter flood duration and stable bar size collectively drive bar greening. Consequently, denser vegetation has slowed flow velocity by 17% ± 2% and increased flow resistance by 21% ± 5%, offsetting the water‐level decrease from channel expansion due to scouring and even causing a slight rise in floodwater levels. Furthermore, damming has markedly altered river connectivity, thermal regimes, and solute dynamics, detrimentally affecting fish habitats and aquatic life. These findings, along with refined river stage simulation considering flow‐sediment‐vegetation interactions, facilitate sustainable reservoir operation and river management in big river systems.

Does the karst spring improve fish abiotic habitat in mountain streams?

Mountain streams constitute challenging habitat for many fish species due to rapid and variable flow, cool temperature, and limited food resources. Groundwaters recharge by karst spring may however mitigate harsh habit conditions of mountain streams providing niches for different fish species. This study aims to assess the suitability of mountain streams, replenished by karst springs, for various fish species like alpine bullhead, European grayling, brown and brook trout. The study was conducted in the Chochołowski Stream in the Western Tatra Mountains, Poland. The assessment of abiotic habitat is based on different characteristics of hydrological and thermal regimes as well as water chemical composition investigated between 01.09.2012 and 31.09.2014. The findings reveal that: 1) downstream variability of habitat abiotic conditions (such as water temperature, flow, water chemical composition) may affect the distribution of fish species, 2) karst springs contribute up to 100% of the stream’s recharge during periods of winter low flow, 3) karstic groundwater reduces the variability and amplitudes of stream water temperature and weaken the periodicity in water temperature associated with daily course of air temperature and solar radiation, 4) groundwaters prevent stream freezing in winter and moderate summer temperatures, 5) increasing mineralisation of water below the spring recharge may positively affect fish distribution. The findings underscore the importance of karst springs in modifying the abiotic conditions of fish habitat in mountain streams.

Mangroves as nursery habitats for Galapagos reef fishes

Mangroves offer key ecosystem services such as the provision of feeding, breeding, and nursery grounds to marine fish populations. The role of mangroves as fish nursery habitats is not ubiquitous and depends on factors such as species, geographic location, and environmental conditions. Studies of this nursery role for fish species are limited in the Tropical Eastern Pacific and particularly scarce for the Galapagos Islands. We used underwater visual censuses to survey fish species composition within mangrove forests and adjacent shallow rocky reefs across 6 of the Galapagos Islands. Adult densities of 3 commercially important reef fishes (Lutjanus argentiventris, L. novemfasciatus, and Mycteroperca olfax) were also surveyed in adjacent deep rocky reefs to investigate the relative importance and potential of mangroves in supporting their populations. Our study provides evidence that mangroves play a role as nursery habitats for reef fish species. Specifically, we identified Eucinostomus dowii, L. argentiventris, Mugil spp., Mycteroperca olfax, Sphoeroides annulatus, Stegastes arcifrons, and Scarus ghobban as mangrove nursery species, as their juvenile densities were significantly higher in mangroves than in shallow rocky reefs. Additionally, 19 other fish species, primarily juveniles, were exclusively observed within mangrove habitats. We found that the extent of mangrove perimeter within 10 km of deep reefs positively influenced the densities of adult L. argentiventris and M. olfax. Our results argue for the need to consider nursery ecosystem function in the design and management of the Galapagos Marine Reserve, since mangroves will directly contribute to the fisheries management of economically important species.

Important fish diversity maintenance status of the tributaries in a hotspot fish conservation area in the upper Yangtze River revealed by eDNA metabarcoding

This study employed Environmental DNA (eDNA) barcoding technology to delve into the influence of the tributaries and mainstem on fish diversity and spatiotemporal distribution in a hotspot fish conservation area in the upper Yangtze River. A total of 123 fish species were detected, belonging to 7 orders, 19 families, and 77 genera. The composition of fish species in tributaries is similar to that in mainstem, with higher fish community diversity in tributaries during the spring and summer. Exploration of fish ecotypes revealed significant differences between mainstem and tributaries. The fish community is mainly influenced by key environmental factors such as water temperature, dissolved oxygen, electrical conductivity, and ammonia nitrogen, with a higher impact of these factors on tributaries than on mainstem. In conclusion, while tributaries and mainstem in the Jiangjin section exhibit similarities in fish community composition, there are notable differences in community structure and diversity. Therefore, the protection of not only mainstem but also tributaries and their associated fish habitats is crucial for promoting the overall health and sustainability.

Utilisation of macroalgal habitats by juvenile rabbitfishes on an inshore reef

AbstractMacroalgal beds are increasingly recognised as nursery habitats for coral reef fish; however, the extent to which they are used as a source of food and/or a refuge from predation remains largely unexplored. Here, we investigate the distribution, feeding behaviour, diet, and predation risk for juvenile rabbitfish in macroalgal habitats on Orpheus Island, Great Barrier Reef. Visual surveys revealed that juvenile and adult Siganus doliatus had different among-habitat distributions with juveniles being largely restricted to the reef flat and positively associated with macroalgal cover, while adults were abundant on the reef crest. Focal feeding observations show that within macroalgal habitats, juvenile S. doliatus targeted epiphytes on Sargassum (80% of bites), with relatively few bites taken on turfs or the Sargassum itself (27% and 8%, respectively). These observations were supported by stomach content analyses with filamentous algae being the dominant item in the stomach content of both small (&lt; 4 cm total length, TL; 58%) and large juvenile S. doliatus (&gt; 4 cm TL; 47%). The stomach content of juvenile S. doliatus, S. canaliculatus, and S. spinus collected from macroalgal habitats was similar, consisting primarily of filamentous algae and detritus. We found no relationship between the abundance of potential predators and juvenile rabbitfishes across the study sites. Collectively, our results suggest that juvenile rabbitfishes are using macroalgal habitats on this, and potentially other, inshore reefs as a food source and add to a growing body of literature highlighting the importance of these habitats for the early life stages of reef fish.

Characterizing Juvenile Common Snook and Tarpon Habitat to Guide Conservation and Restoration of Coastal Wetlands

To conserve or restore juvenile fish habitat, resource managers, restoration practitioners, and engineers need fine-scale information to understand what conditions they need to preserve or what specifications are needed to create new habitat. The objective of this study was to develop statistical models using a dataset of 18 coastal ponds in Southwest Florida, USA, to predict the abundance of juvenile common snook Centropomus undecimalis (hereafter snook) and presence of juvenile tarpon Megalops atlanticus, both of which are flagship species used for conservation and restoration of subtropical and tropical wetlands. Model predictors included water conditions and characteristics of vegetation, sediment, and geographic position. Modeling results indicated that juvenile snook used coastal ponds that were directly connected to tidal creeks. In contrast, juvenile tarpon were more likely to be present in coastal ponds that were separated from tidal creeks by dense mangrove forest (e.g., elevation > 0.48 m above Mean Low Water) characterized by highly organic sediment and low dissolved oxygen, to which tarpon are well adapted. Overlap between snook abundance and tarpon presence was greatest where connections between ponds and the nearest tidal creek were at a relatively low elevation (e.g., -0.12 m relative to Mean Low Water). Although these findings are most applicable to management and conservation of populations in areas along the Gulf coast of Florida (i.e., in areas of similar tidal range and coastal geomorphology), incorporating more detailed habitat surveys to better capture landscape context, geomorphology, and connectivity into fish sampling designs should be broadly applicable to estuarine fish ecology.

The potential of oviduct tags and fine-scale acoustic telemetry to reveal the timing and location of spawning in Arctic salmonids (Salvelinus spp.).

Identifying and characterizing spawning locations are paramount for the protection of critical fish habitats but can be challenging, particularly in remote locations. Using the underexplored oviduct-tagging technique, we aimed to identify the timing and location of spawning for wild Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush) in two high-Arctic lakes in Nunavut. Specifically, Innovasea V7 acoustic telemetry transmitters were inserted into the oviducts of 13 Arctic char and 4 lake trout, and the timing and location of tag expulsion were determined using a fine-scale positioning system. Twenty Arctic char and 20 lake trout were also tagged with abdominal V16 transmitters, and 10 of them were paired with the oviduct tags, to further study the behavior of individual fish during the spawning season. Oviduct tags from four Arctic char and one lake trout could be used to assess the timing and location of spawning. Spawning anadromous Arctic char drastically reduced their activity and remained proximate to their presumed spawning location immediately before and for months after spawning. In contrast, a non-anadromous (i.e., freshwater resident) Arctic char and a lake trout showed little to no reduction in activity around presumed spawning events. Because of the highlighted sedentary behavior of inferred spawning anadromous Arctic char implanted with both abdominal and oviduct tags, we could also infer potential spawning based on the behavior of individuals equipped only with abdominal tags. Spawning areas identified via telemetry also aligned well with Inuit knowledge of those lakes. This is the first field study to use acoustic oviduct and abdominal tags coupled with a fine-scale positioning system. Despite a limited success rate of ejection, the study reveals the strong potential of the method to study spawning habitat and timing, particularly in remote areas.

Evaluation of the highly sinuous bend sequences using an ecohydraulic model to ascertain the suitability of fish habitats for river ecological conservation

The spatial and temporal patterns of river meanders play a crucial role not only in shaping the hydrogeomorphic properties of channels and floodplains but also in ascertaining the suitability of fish habitats for river ecological conservation. This study evaluates hydrodynamic features and fish habitat quality in six highly sinuous bend sequences along the Black River in China’s Qinghai plateau. The ecohydraulic model system was used to simulate hydrodynamics, habitat suitability, and sediment transport to determine the habitat quality of the highly sinuous bend sequences. The results have successfully identified differences in the suitability of various bends for fish spawning. Bend 1 was found to be the most suitable among all bends, while bends 5 and 6 were deemed unsuitable specifically during higher flood flows. Cases 3 and 4 were discovered to be highly suitable for fish habitat under normal discharge scenarios. Conversely, cases 5 and 6 were the least suitable, with cases 5 and 6 exhibiting the worst habitat quality, with HSI values nearing zero under high discharge. The study concluded that regulated discharge conditions could support fish spawning in these sinuous bends, with lower flood flows promoting habitat suitability and higher flood flows fragmenting habitat quality. The findings highlight the importance of diverse hydrodynamic and geomorphic conditions in creating suitable fish habitats across varying flow conditions, offering insights into the conservation and management of mountain rivers to protect endangered fish species and aquatic organisms.

Incorporating Implicit Information to Disentangle the Impacts of Hydropower Dams and Climate Change on Basin-Scale Fish Habitat Distribution.

The loss of freshwater fish habitats, exacerbated by climate change and dam constructions, poses a critical environmental concern. The upper Yangtze River basin, noted for its abundant fish fauna and concentrated dam development, serves as a crucial locale for investigating the impacts of climate shifts and dam construction. This study aims to disentangle the impacts of hydroelectric dams and climate change on fish habitat distribution by analyzing species presence data across different periods. Species distribution models were constructed using Maxent for Coreius guichenoti (a warm-water endangered fish) and Schizopygopsis malacanthus (a cold-water endangered fish). The model accuracy was assessed using the area under the curve of the receiver operating characteristic. Habitat distribution modeling and prediction for the pre-dam period (1970-2000) and post-dam period (2001-2020), as well as future climate change under two shared socioeconomic pathways scenarios, were conducted. The impacts of climate change and dam construction on the habitat suitability of two fish species were quantified. The results revealed dam construction predominantly diminished habitat suitability and range, with high-suitability habitats in the post-dam period decreasing by 56.3% (720.18 km) and 67.0% (1665.52 km) for the two fishes, respectively. Climate change would enhance the habitat suitability of Coreius guichenoti, while it would decrease the habitat suitability of Schizopygopsis malacanthus. The impact of dam construction is greater that of climate change for them. This study underscores the profound impacts of dam construction on fish habitats, particularly for cold-water species, and highlights the critical need for habitat restoration in sustainable hydropower development. Our method of disentangling these factors also provides a new approach to evaluating environmental impacts in large river basins.

Thermally Primed Zostera muelleri Seeds Exhibit Higher Germination Rates Than Those From Ambient Conditions.

Seagrasses provide critical ecosystem services such as carbon sequestration, sediment stabilisation and nursery habitat for juvenile fish. Zostera muelleri is ubiquitous within Australian and New Zealand estuaries, however, as a species is relatively understudied. We sourced seeds from a thermally affected east Australian estuary and investigated whether germination rates differed between ambient and thermally affected seeds over a variety of temperatures (16°C-28°C) to determine how seagrass systems might react in a warming climate. Germination for the experiment was low and totalled 5% of all seeds; however, similar numbers are typical in seed germination studies. Germination was highest at 16°C and was enhanced through the simulation of a 48-h freshwater pulse. Thermally affected sites germinated faster and had greater mean maximum germination when compared to control sites regardless of experimental temperature. These findings indicate that Z. muelleri in this system may be exhibiting transgenerational plasticity due to the thermal stress the parent experiences. This result provides an alternate viewpoint to the current literature by suggesting that unknown transgenerational effects may provide Z. muelleri with greater germination plasticity against temperatures expected under predicted climate change scenarios than previously expected.