Estuarine Fish Research Articles

Contrasting pollution responses of native and non-native fish communities in anthropogenically disturbed estuaries unveiled by eDNA metabarcoding

Understanding the influence of environmental pollutants on the assembly mechanisms of estuarine fish communities is vital for addressing conservation challenges in these biodiverse ecosystems. Although significant research has explored the toxic impacts of pollutants such as petroleum, heavy metals, and eutrophication on individual species and populations, their effects on community assembly processes and the differential responses of native versus non-native fish at the meta-community level remain inadequately understood. This study utilized environmental DNA (eDNA) metabarcoding to analyze fish community diversity across 28 subtropical estuaries in China, assessing how these pollutants affect community composition and assembly mechanisms. Results indicated that eDNA was 2.54 times more effective than traditional methods in species identification, while also enabling the detection of a higher number of non-native fish species and more diverse functional guilds within estuarine ecosystems. A significant distance decay pattern (p < 0.05) was observed among native fish, whereas non-native species exhibited non-significant patterns. Neutral and null models showed that non-native species had significantly higher migration rates (0.005939 vs 0.001757) and a greater contribution of stochastic processes (82.38% vs 70.59%) compared to native species. Additionally, distance-based redundancy analysis (db-RDA), variance partitioning analysis (VPA), and correlation analyses revealed that native species were strongly constrained by environmental factors, particularly oil, Hg, Zn, Pb, Cr6+, and NH4+, while non-native species displayed notable resilience to these pollutants. These findings highlight the potential for non-native species to disproportionately influence community dynamics and assembly through unrestricted random dispersal amid environmental disturbances. This research clarifies the contrasting ecological responses of native and non-native fish communities to anthropogenic pressures in estuarine environments, offering essential insights into ecosystem resilience and informing biodiversity conservation strategies in rapidly changing coastal ecosystems.

The Functional Response of Estuarine Fish Communities to Hydrologic Change in a Semi-Arid Ecosystem

Functional assessment approaches were used to identify the responses of fish to environmental change in the San Antonio Bay System (Texas, USA). Using a 26-year coastal fisheries dataset (1993–2018), multivariate analyses revealed relationships between functional group abundance and freshwater inflows in the upper segments (Hynes Bay and Guadalupe Bay), but the patterns were decoupled from inflows in the lower bay segments (San Antonio Bay, Ayres Bay and Espiritu Santo Bay). In Hynes and Guadalupe Bays, freshwater migrant carnivores accounted for a significant fraction of the community irrespective of the gear, year or flow. Freshwater stragglers (omnivores and carnivores) were often present in the upper reaches of the bay. In the lower reaches, marine migrant omnivores were present during high and low flows in Espiritu Santos Bay, but only during low flows in Ayres Bay. Marine migrant carnivores were more important in gill nets irrespective of the flow conditions. The five most abundant fish were estuarine resident carnivores and omnivores, accounting for 53.5% of the community. Declines in the abundance of functional groups occurred during the 2011–2014 drought, with rebounds in 2015–2018. Functional methodologies provide insights into estuarine ecosystems and can serve as management tools to assess changes in fish assemblages.

Landscape metrics predict habitat redundancy of restored oyster reefs for recruitment enhancement of dominant estuarine fish

Abstract Structured biogenic habitats in estuarine and coastal landscapes (or seascapes) augment nekton species' production; yet, landscape setting may make restored habitats functionally redundant to co‐occurring habitats for some species. Few relationships between recruitment enhancement and continuous landscape metrics have been quantified, limiting our ability to incorporate functional redundancy into restoration practice. To address this gap, we quantified two landscape metrics, per cent structure of proximal habitat and near distance to co‐occurring structured habitats, for experimentally restored oyster reefs in an intertidal landscape in Middle Marsh, North Carolina, USA. We then examined relationships between each landscape metric and recruitment enhancement of juvenile pinfish (Lagodon rhomboides), a species that uses multiple biogenic habitats and has high site fidelity as juveniles. We estimated that reefs with &lt;33% proximal structured habitat within 15 m and &lt;59% within 50 m contributed to recruitment enhancement, as defined by greater juvenile pinfish abundances at reefs than controls and no overlap in 95% confidence intervals. Additionally, functional redundancy, assigned according to per cent structure of proximal habitat within 15 or 50 m of restored reefs, reduced estimates of nekton recruitment enhancement in this experimental landscape by 58.3% or 33.3%, respectively. Estimates of nekton production augmented by restoration may be inflated if they have not been adjusted to account for habitat redundancy. Synthesis and applications. Landscape metrics offer some predictive capacity to help restoration practitioners avoid habitat redundancy for recruitment enhancement and extend beyond considering individual habitats toward integrating landscape scale processes into predictions and restoration practice. We demonstrated a straightforward process for restoration practitioners to identify where habitats may be redundant and incorporate the landscape into restoration siting decisions: delineate co‐occurring structured habitat with publicly accessible orthoimagery and model juvenile nekton relationships with proximal percent structure and near distance to other structured habitats.

Social and metabolic mediation of growth performance in a temperate estuarine fish

Despite the importance of juvenile growth to lifetime fitness, high variability exists within many fish species where some individuals grow markedly faster than others. Here, we explored whether social context mediated growth performance in n = 35 Galaxias maculatus by manipulating the social environment after identifying different growth phenotypes. We found that initially fast-growing fish slowed their growth rate when pooled with similarly fast-growing individuals, whereas none of the initially slow-growing fish markedly improved their growth when pooled with other slow-growers. We examined for any metabolic underpinnings to the findings by measuring standard, routine, and maximum metabolic rates (SMR, RMR, and MMR) at two time points separated by ~4 months. SMR and RMR positively correlated with growth rates when the fish were pooled into growth phenotypes, but not when they were returned to their original (mixed) social groups. We highlight research directions to further elucidate how social context and metabolism interact to govern growth phenotype.

An overview of the estuarine ichthyofauna from Bahia, Brazil: expanding the knowledge about the fish species of three important regions of the state

ABSTRACT The coast of Bahia state is the longest along the Brazilian coastline, and there are significant knowledge gaps concerning its estuarine fish fauna. Thus, there is a need to provide extensive coverage of the estuarine ichthyofauna of Bahia to provide an updated checklist of its fishes, which could function as a database for the management of such biodiversity. Therefore, this study aimed to characterize three different important estuarine systems (Camamu, Todos os Santos Bay, and Caravelas) in Bahia to contribute information on the ichthyofauna in shallow areas of the state. We recorded 29 orders, 54 families, 101 genera, and 147 species of fish. The families with the highest number of species were Sciaenidae and Carangidae, with twelve and nine species, respectively, followed by Gobiidae and Engraulidae, each with eight species. In terms of abundance in the northern region, the orders Atheriniformes (28.80%), Pleuronectiformes (15.92%), Clupeiformes (14.20%), and Gerreiformes (13.91%) predominated. In the Central region, Gerreiformes (21.55%), Tetraodontiformes (17.94%), Gobiiformes (12.83%), and Clupeiformes (8.94%) were the most representative. In the southern region, the orders Clupeiformes (57.48%), Mugiliformes (14.09%), Atheriniformes (4.10%), Lutjaniformes (3.97%), Gerreiformes (3.60%), and Carangiformes (2.23%) predominated. The region was characterized by a high representation of guilds of marine migrant species, followed by marine, estuarine, and freshwater visitors.

A tiered toxicity testing strategy for assessing early life stage toxicity in estuarine fish (Mugilogobius chulae): A case study on tris (1-chloro-2-propyl) phosphate ester

The estuarine ecological environment faces significant threats from contaminants of emerging concern (CECs); yet, the risk posed by CECs to resident organisms remains poorly understood. Here, we employed tiered toxicity testing to investigate the adverse effects and potential mechanisms of tris (1-chloro-2-propyl) phosphate (TCPP) on the early life stages of an estuarine fish, Mugilogobius chulae. TCPP affected the development of M. chulae embryos, including survival, morphology, hatching, and behavior. A concentration-dependent transcriptomic analysis showed that TCPP disrupted 12 neurodevelopment-related KEGG pathways in M. chulae embryos, with five of the 30 % top-ranked pathways related to neurotransmitter signaling. Besides the cholinergic synapse signaling pathway, the glutamatergic signaling pathway (including NMDAR and AMPAR subtypes) may also mediate TCPP-induced neurodevelopmental toxicity. The NMDAR subtype GRIN2B was downregulated at high concentrations. Molecular dynamics simulations revealed a strong interaction between TCPP and GRIN2B, with TCPP binding to the residues Ile153 and Ile188. The results suggest that NMDARs play a crucial role in TCPP-induced neurodevelopmental toxicity toward M. chulae. AOP network analysis predicted that TCPP may impact cognitive functions and memory. Our study provides a novel testing strategy for identifying the mechanisms of toxicity of CECs, a crucial component of ecological risk assessment.

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.

Upper thermal limits are ‘hard-wired’ across body mass but not populations of an estuarine fish

Climate warming is seeing temperatures breach exceptional thresholds as the frequency and intensity of heat waves increase. Efforts to forecast species vulnerability to climate warming often focus on upper thermal limits threatening survival, overlooking the role of intraspecific variation in determining vulnerability. Using an estuarine fish (black bream, Acanthopagrus butcheri) as a model, we explore how intraspecific variation in body mass and among populations affects upper thermal tolerance. Upper thermal limits were quantified using critical thermal maxima (CTmax) of wild fish. We used a ∼500 g (mean = 52.4 g, range = 0.57–541 g) mass range to test the relationship between body mass and thermal tolerance. Four distinct black bream populations were chosen along a 5° latitudinal cline to explore population differences in thermal limits. Contrary to expectations, there was no effect of body mass on upper thermal limits. However, significant population differences in thermal tolerance were observed that correlate with mean habitat temperatures. Specifically, the southern population had a significantly lower CTmax (35.57 ± 0.43 °C) compared to northern (36.32 ± 0.70 °C) and mid-latitude (36.36 ± 1.15 °C) populations. These data underscore the importance of observing intraspecific variation in thermal limits to reveal the capabilities of individuals within a species to cope with climate warming and improve the management of at-risk life stages and populations.

Individual performance niches and responses to winter temperature change in three estuarine fishes from eastern Australia

Climate change may impact individual organisms in different ways, a consideration often overshadowed by predominant focus on population effects in studies. We examined three estuarine fish species to determine if individual fish performance, persisted across winter water temperatures. Fish performance at 16 °C (current Sydney winter estuarine water temperature) and 20 °C (predicted under climate change) with low and high food regimes was assessed using key physiological (growth, aerobic scope, burst speed) and behavioural parameters (foraging activity, boldness, shelter usage, predator escape response). We expected a strong positive relationship between performance at 16 °C and 20 °C for each parameter, and interactions with food level, however in general this was not found for any species. Relative performance was only maintained across temperatures for a few parameters, such as bite rate, boldness, and shelter response in one species (trumpeter Pelates sexlineatus), with aerobic scope in silver biddy Gerres subfasciatus, and boldness in fortescue Centropogon australis. Our results suggest that individuals’ fitness (directly via changes in growth, indirectly via behaviours) might be impacted by climate warming due to differences in relative performance among juvenile individuals across water temperatures. Changes in relative performance among individuals may initially compensate for a population-level response, thereby buffering the effects of climate change.

Is the diel cycle of routine metabolic rate in mummichog (Fundulus heteroclitus) affected by near-infrared lighting used for visualizing behavior of fishes at night?

The metabolic rate of a freely moving fish (routine metabolic rate) is tightly coupled with volitional movement (spontaneous activity), both of which commonly show strong daily cycles linked to the species-specific diel activity pattern. Mummichog (Fundulus heteroclitus), an important estuarine fish in the north western Atlantic Ocean, are historically reported as diurnal (i.e., more active during daylight). Our recent laboratory studies on a Bay of Fundy population, however, showed a free-running (i.e., similarly active daytime and night-time) or even nocturnal (i.e., more active at night-time) diel activity pattern. In the laboratory, near-infrared (NIR) illumination is commonly used with a NIR-sensitive camera to visualize fish activity across the light-dark periods of the day. Because NIR light is close to the visible light spectrum and certain fishes show sensitivity to NIR, the use of NIR with mummichog possibly could disturb the animals and obscure the identification of their true diel activity pattern. We aimed to determine if NIR illumination (940 nm wavelength) influences the diel activity pattern of mummichog. We used measurements of routine metabolic rate (oxygen consumption rate, MO2) as a proxy for activity, as evaluating the effect of NIR requires treatments where NIR lights are off, which precludes visualization and direct assessment of fish activity at night-time. We measured routine MO2 of mummichogs over 6 days, exposed to either NIR off-on-off (2 days for each off or on period) or the opposite sequence of NIR on-off-on (to control for time-dependent effects). NIR lights did not influence the diel cycle of routine MO2, and activity by proxy, in mummichog. Thus, NIR illumination is a suitable method to visualize mummichog during light-dark diel cycles. Routine MO2, and presumably activity, was similar or higher during night-time periods compared to daytime periods, confirming a free-running or nocturnal activity pattern for at least certain populations of mummichog.

Estuarine ichthyofauna of Kamchatka: formation conditions, species diversity and ecological characterisation

Species composition of the estuarine ichthyofauna is described for the first time on a regional scale for Kamchatka Territory based on the materials of author’s field studies carried out in 2010–2022, as well as on the analysis of all available information (literature, archival, survey, fishery, etc.). Specific features of the conditions of formation of estuarine ichthyofauna of the region are revealed. Fish species dominating in abundance in Kamchatka estuaries are indicated. The main ecological groups (guilds) of estuarine fishes are outlined. It was found that 1 species of cyclostomes and 60 species of fishes belonging to 44 genera and 23 families can be attributed to the estuarine ichthyofauna of Kamchatka. All these species are, to varying degrees, euryhaline and therefore may utilize individual Kamchatka estuaries as habitats at various stages of the life cycle. The basis of species diversity of the ichthyofauna of Kamchatka estuaries is formed by marine fishes (at least 34 species), the second in importance are anadromous species (1 species of cyclostomes and 14 species of fishes), the minimum contribution belongs to freshwater resident fishes (13 species), which are found only in estuaries of some rivers of the region. Fish that can be referred to the ecological group of “solely estuarine” (i. e., those whose full life cycle takes place in estuaries) are probably absent in Kamchatka. The maximum species diversity of fish communutues is observed either in big Kamchatka estuaries that are largely open to the sea or in river basins with a diverse freshwater ichthyofauna. Environmental conditions in such estuaries are more favorable for the migrations and habitat of marine fish species (mainly coastal ichthyocene). At the same time, all anadromous or some freshwater euryhaline species may also use these same estuaries as temporary habitats at certain stages of the life cycle. Fish species diversity is significantly higher in the estuaries of the eastern coast of Kamchatka, which is explained by the milder climatic conditions of this area (compared to the coast of the Sea of Okhotsk), as well as by the greater typological diversity of estuaries. A separate section summarizes the currently available information on the biology and ecology of all species of fishes and fish of Kamchatka estuaries, which is presented in the form of brief species sketches (including, external view at individual stages of the life cycle; key morphological characters; maximum size and age; distribution over the territory of the region; habitat specifics, lifestyle and migrations; peculiarities of reproduction and development; feeding preferences; abundance in the region, commercial or economic importance).

Resilience to changes in salinity and predator diversity in representative Gulf of Mexico estuarine fish predator-prey interactions

Predators strongly influence ecological communities and subsequent ecosystem function by directly consuming prey individuals and indirectly by inciting alterations in prey behavior, termed non-consumptive effects (NCEs). Gulf of Mexico estuaries support complex food webs structured by numerous species interactions maintained in constant environmental flux from variation in salinity. Environmental variation presents a source of physiological stress for estuarine fish and plays a role in their distributions and subsequent interactions. Here, we present the results of a mesocosm experiment examining if acute changes in salinity disrupt NCEs of different predators on estuarine prey. We exposed Gulf killifish (Fundulus grandis) to visual and/or olfactory cues from a common estuarine predator, red drum (Sciaenops ocellatus), and from a freshwater predator that is a transient species in lower portions of estuaries, largemouth bass (Micropterus salmoides), under either decreasing, constant, or increasing salinity. Killifish decreased shoal size and movement in response to olfactory cues or both visual and olfactory cues compared to when they were exposed to no cues or visual cues, demonstrating variable perceived risk dependent on cue type. Behavioral response did not vary by predator species, implying a generalized response to different fish predators. Prey did not change behavior when exposed to decreasing salinity compared to constant salinity. However, prey movement increased with increasing salinity, indicating that salinity changes may provide cues to search for different habitats instead of a stressor. Our experiment indicates that estuarine predator-prey interactions may be resilient to acute salinity changes given the broad tolerances of euryhaline species.

Unlocking the nutritional potential: amino acid profile of eight Indian food fishes and their role in meeting recommended dietary allowances

IntroductionProteins and amino acids, as vital biomolecules, are not only part of key metabolic pathways in the body but are also essential for tissue repair, enzyme function, and hormone regulation. They also serve as building blocks for the formation of signaling molecules, such as neurotransmitters and catecholamines. Additionally, amino acids are the primary building components of proteins. Fish serves as a vital source of high-quality animal protein and amino acids, playing a crucial role in supporting human nutrition.MethodsHigh-performance liquid chromatography (HPLC) using fluorescence detector was employed to investigated the amino acid content of eight food fishes from diverse aquatic habitats.ResultsThe study revealed that the small indigenous fish (SIF) Systomus sarana and the marine fish Sardinella melanura were rich sources of all essential amino acids. Furthermore, estuarine fish like Pisodonophis boro can be recommended for specific amino acids like arginine, histidine, leucine, and valine, while Setipinna phasa is suggested for cysteine.DiscussionThese recommendations rely on the possible contribution of these fishes to the Recommended Dietary Allowance (RDA) regarding each nutrient. The insights gained from this study could be utilized as recommendations to meet amino acid requirement using fish as a natural supplement.

Long-term trends in the functional structure of estuarine fish assemblages in a subtropical estuary and its relationships with local environmental variability, man-made changes, and climatic drivers

Climate and anthropogenic impacts are prevalent in marine and estuarine ecosystems. Rapid environmental changes have altered biological diversity and the ecological services associated with ecosystems around the world. The consequences of these impacts on estuarine ecosystems are worrying, given that estuaries are essential habitats for maintaining the diversity of species functions, as they act as sources for larger ecosystems through the recruitment and replacement of species. Through long-term standardized monitoring (1996–2019), we evaluated the temporal variability of the functional structure of fish species in a subtropical estuary using Principal Component Analysis (PCA), and their relationship with environmental, climatic, and anthropogenic variables using Generalized Additive Models (GAM). We investigate the hypothesis that natural disturbances associated with El Niño events and anthropogenic ones related with changes in the estuary morphology will lead to a decrease in the diversity of functions of the fish assemblage in the Patos Lagoon Estuary in south Brazil (32°S). Our findings suggest an overall downward trend in the fish functional structure, especially in the second half (2006–2019) of the time series, which seems to be associated with a combination of abiotic effects (salinity and temperature), global climate phenomena (ENSO phases) and anthropogenic impacts (changes in the morphology of the estuarine mouth and its connection with the sea). These findings rise concern considering the current climate change scenario, where phenomena such as El Niño may become more frequent and intense. Therefore, the evidence from this study suggests that extreme natural climatic events in synergy with anthropogenic disturbances may imply biodiversity losses over time and, consequently, loss of ecosystem processes in a subtropical estuary.

LENGTH-WEIGHT RELATIONSHIPS OF THE ESTUARINE FISH SPECIES IN THE SECOND LARGEST MANGROVE AREA IN THE WORLD, BRAZIL

Length-weight relationship (LWR) parameters are necessary to understand the life cycle of fish to describe the biological aspects of species. In this sense, LWRs were determined for 17 estuarine species from the second largest mangrove area in the world, Northern Brazil. The sampling was carried out during the dry and wet seasons of 2015 and 2018 in 3 estuaries described as conservation units in the rivers Pará, Caeté, and Parnaíba. Fish were collected by using manual beach seine, block nets and sieves. Overall 488 specimens were analyzed using the equation W = a TLb. The a values ranged from 0.000001 to 0.000019 and b values ranged from 2.7230 to 3.2821. This study brings new data on estuarine fish from Brazil with additional information contributing to the conservation and management of the fish stocks.

Trophic niches of estuarine fish and evidence of mangrove-fishery causal links in the Southern Caribbean (Colombia)

The trophic organization of estuarine fish communities is poorly known. We used Stable Isotopes (δ13C and δ15N) to classify the most abundant fishes of the Atrato River Delta (Colombia) into trophic guilds. We examined trophic niches and the relationships between the abundance of the trophic guilds (catch per unit effort) and environmental variables. The zoobenthivores were the dominant trophic guild. The isotopic niche width, based on Bayesian estimate of the standard ellipse areas, was more significant for carnivores (25.3‰2) and planktivores (24.4‰2) than for omnivores (7.8‰2) and phytobenthivores (3.1‰2). The overlap combinations showed a medium probability of isotopic overlap (≈50%) between carnivores and planktivores and between carnivores and omnivores. Isotopic niche size and overlap suggested diversity in food sources and considerable niche segregation of the fish community. Mangrove area was the main factor explaining the abundance of omnivores and zoobenthivores, supporting that the causal links between mangrove habitat and local fishery production may be explained through the trophic contribution of mangroves and mangrove-related sources. The results underscore the importance of mangrove areas in the trophic organization of fish communities and can inform strategies aimed at managing the ecosystem impacts of fishing and protecting extensive mangrove areas in the southern Caribbean.

Consistencies in the dietary and isotopic niche of spotted seatrout, Cynoscion nebulosus, across a salinity gradient within a coastal Louisiana estuary.

Estuaries are essential habitats for recreational and commercial fish that are shaped by both natural and anthropogenic processes. In Louisiana a combination of climate change and planned coastal restoration actions is predicted to increase freshwater introduction to coastal estuaries. As such there is a need to quantify the relationships between estuarine fish ecology and salinity to aid in predicting how species will respond to shifts in salinity. We investigated the relative abundance and dietary niches of adult (24.5 ± 5.4 cm standard length) spotted seatrout Cynoscion nebulosus across varying salinity regimes (oligohaline, mesohaline, and polyhaline) within Barataria Bay, Louisiana, using a combination of net sampling and gut content and stable isotopes analysis. We found that the relative abundance of C. nebulosus was lowest at the oligohaline site, translating to approximately five fewer fish captured for every single psu decrease in a site's average annual salinity. In contrast, we found that diets and, to a lesser extent, isotopic niches had a high degree of overlap across sites with differing salinity regimes. Fish and penaeid shrimp were the most common and important prey taxa recovered from guts at all sites. The small isotopic differences found among sites were likely due to spatial variation in hydrogeochemical baselines, and the observed isotopic overlap provides support for the idea that C. nebulosus move between adjacent salinity regimes and forage throughout Barataria Bay. Our results contribute to a greater understanding of the salinity preference and trophic ecology of C. nebulosus that can aid in predicting their responses to future salinity and habitat changes within Barataria Bay associated with predicted climate change and planned coastal restoration actions.

Parasites as indicators of biodiversity and habitat complexity in coastal ecosystems

AbstractResearchers often use surrogate species for assessing biodiversity—organisms that can indicate the presence of additional taxa or provide insight into environmental processes. As indicators of anthropogenic impact, “cross‐taxon” surrogates are theorized to be effective shortcuts for determining how communities respond to environmental change. However, few studies have implemented cross‐taxon surrogates given the challenge of validating the strength of the relationship between surrogates and their target taxa. Trophically transmitted parasites require multiple invertebrate and vertebrate taxa to complete their life cycles (e.g., annelids, mollusks, fishes, shorebirds), making them ideal cross‐taxon surrogates of community diversity. By sampling for these parasite surrogates, it is theoretically possible to infer the composition of the overall host community based on the species of parasites present. In our study, we tested the use of parasites as cross‐taxon surrogates of biodiversity by sampling for digenetic trematodes in the mudsnail Ilyanassa obsoleta, collected from coastal shoreline environments with or without artificial structures (e.g., bulkheads, seawalls). We found that trematode richness, evenness, and diversity were all greater in snails sampled from natural shorelines versus those with artificial structures. While parasite communities clustered by shoreline type (with vs. without artificial structures), we found no differences in multivariate dispersion, or beta‐diversity, between groups in our system. At the species level, trematodes requiring polychaetes and estuarine fishes as downstream hosts dominated parasite communities at shorelines with artificial structures. These taxa are ubiquitous but more abundant in degraded environments. In contrast, trematode species requiring mollusks and shorebirds as hosts was only documented from shorelines without artificial structures (i.e., natural), which may indicate that these areas are less degraded and have greater overall host diversity. High parasite diversity in easily collected hosts (e.g., mudsnails) provides evidence that the secondary (polychaetes, crustaceans) and tertiary (fishes, shorebirds) hosts required by the parasites are present in the system. Our study also helps validate the concept of surrogate species by demonstrating how a single species can represent broader taxonomic groups.

Assessing the combined effects of catchment land use and runoff on estuarine fish assemblages

Connectivity between land and sea through the movement of species, energy and nutrients means that land-based impacts can affect the structure and functioning of nearby coastal ecosystems. As the interface between land and sea, estuaries are often faced with increasing pressures from catchment modifications (e.g. the removal of terrestrial vegetation) which can alter the overall health of estuaries (e.g. the degradation of coastal water quality due to an increase in terrestrial runoff) and change the value of habitat for many marine species. These landscape-scale impacts can, however, be mediated through variations in the context and connectivity of seascapes (e.g. greater extent of vegetated ecosystems help to filter nutrients). We surveyed fish across five estuaries over four years using underwater videography and sought correlations between fish biodiversity and abundance with variables indexing catchment land use, seascape connectivity, and coastal water quality. Fish assemblages were more abundant and diverse at sites which had lower chlorophyll-a concentrations and were nearer to the estuary mouth, in conjunction with catchments containing higher percent of natural land and heterogenous seascapes. Sites with lower concentrations of chlorophyll-a supported indicator species from more diverse functional groups that had greater fisheries values, in comparison to indicator species from sites with high concentrations of chlorophyll-a. This research can help direct coastal management to better prioritise management in coastal ecosystems, thereby enhancing fish richness and abundance, functional group richness and fisheries value.

Histological biomarkers and microbiological parameters of an estuarine fish from the Brazilian Amazon coast as potential indicators of risk to human health.

This study aimed to isolate and identify pathogenic bacteria in the intestinal tract, skin, and muscles of Sciades herzbergii; detect histopathological changes in the gill and liver; and use these biomarkers for the assessment of potential risks to human health. Fish were sampled during the rainy and dry seasons at two points in São Marcos Bay, Maranhão, Brazil: Ilha dos Caranguejos (IC) and Porto Grande (PG). Isolation and quantification were carried out using COLItest®. Colonies were subjected to identification and phenotypic investigation of antimicrobial resistance using Vitek®. Gill and liver samples were subjected to routine histological examination. The results indicated the presence of Klebsiella pneumoniae and Escherichia coli, the latter of which showed phenotypic resistance to norfloxacin and gentamicin. Fish caught at PG exhibited more extensive gill and liver damage than fish caught at IC. The findings suggest that histological changes in target organs of S. herzbergii may be influenced by infection with pathogenic bacteria.