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For many decades, the role of estuaries as important nursery areas for fishes was accepted as fact by scientists and environmental managers. At the turn of the 21st century, a question mark was raised in relation to the reduced predation component of the nursery function, with some scientists contending that both large and small piscivorous fish species had access to the estuarine habitats that juvenile fishes in estuaries occupied. If true on a global scale, the nursery designation for these habitats would be compromised and the long-held paradigm that estuaries are important nursery areas for fishes would need to be revised. In this review, I examine the nature of fish nursery areas in estuarine littoral habitats from a mainly predation perspective and, based on a variety of ichthyofaunal and avifaunal studies, come to the conclusion that apart from a few selected estuarine systems, there is limited predation on juvenile fishes in these particular areas. This, coupled with the abundant suitable food resources for juvenile fish from different trophic categories, shelter from high-energy marine wave action and biological connectivity between a variety of submerged and emergent macrophyte communities, renders shallow estuarine littoral areas ideal nursery areas for the juveniles of mostly euryhaline marine fish species, the dominant component of estuarine ichthyofaunas globally. In addition, there are strong indications from the fossil record that these littoral estuarine nursery areas have been functioning since the Devonian, more than 350 million years ago.

1. Nearshore ecosystems are increasingly recognized as critical habitats for fish of cultural, ecological and economic significance. These ecosystems are often densely inhabited by juvenile fish, highly productive and refuges from predation, leading ecologists to characterize them as nurseries. However, nearshore ecosystems are being transformed globally to support demands of growing coastal populations. Many shorelines are modified by armouring (e.g. seawalls, riprap) that minimizes erosion, and overwater structures (e.g. piers, docks) that facilitate waterfront use. These modifications affect the ecology of nearshore systems by restructuring, eliminating and shading shallow waters. 2. Here, we review literature examining effects of armouring and overwater structures on coastal and estuarine fishes, and discuss how research and management can coordinate to minimize negative effects. 3. Along armoured shorelines, fish assemblages differed from unarmoured sites, fish consumed less epibenthic and terrestrial prey, beach spawning was less successful and fish were larger. Under large overwater structures, visually oriented fish were less abundant and they fed less. Shade from overwater structures also interrupted localized movements of migratory fish. Thus, shoreline modifications impaired habitats by limiting feeding, reproduction, ontogenetic habitat shifts from shallow to deeper waters and connectivity. 4. Research suggests that restoring shallow waters and substrate complexity, and minimizing shading underneath overwater structures, can rehabilitate habitats compromised by shoreline modifications. 5. Synthesis and applications. Shoreline armouring and overwater structures often compromise fish habitats. These threats to nearshore fish habitats will become more severe as growing coastal populations and rising sea levels increase demands for shoreline infrastructure. Our ability to assess and rehabilitate nearshore fish habitats along modified shorelines will be enhanced by: focusing research attention on metrics that directly indicate fish habitat quality; implementing and evaluating shoreline features that repair compromised habitat functions within human-use constraints; collating natural history knowledge of nearshore ecosystems; and embracing the socio-ecological nature of habitat improvements by educating the public about conservation efforts and fostering appreciation of local nearshore ecosystems. Actions to reduce impacts of shoreline modifications on fish are particularly feasible when they align with societal goals, such as improving flood protection and providing spaces that facilitate recreation, education, and connections between people and nature.

In Kulisusu Bay waters, coastal ecosystem degradation caused by overfishing and destructive fishing gear has damaged critical marine habitats, including nursery grounds for juvenile rabbitfish (Siganus canaliculatus). These anthropogenic pressures have reduced both food availability and shelter for juvenile fish, threatening the species long-term sustainability. This study analyzes the habitat characteristics and the distribution of juvenile S. canaliculatus abundance across three distinct habitats (A, B, and C). Samples were collected four times in each habitat using modified juvenile nets in the seagrass ecosystem, with concurrent measurements of environmental parameters. Environmental parameters measured included current speed, water depth, salinity, total dissolved solids (TDS), seagrass density, and substrate. The results showed significant differences (p < 0.05) in habitat characteristics and juvenile abundance between habitats. The highest abundance was found in habitat C, which has low salinity (average 29.1 ppt), high TDS (47.0 mg Lİ), moderate current speed (average 0.34 т s!), high seagrass density (average 471.3 stands m2), and clayey sand substrate, with an abundance of 0.074 individuals m3. In contrast, habitat В, which has moderate salinity (average 31.2 ppt), low current speed (average 0.11 ms), low seagrass density (average 313.1 stands m\"), and sandy substrate, showed the lowest juvenile abundance of 0.030 individuals m3. The results of this study confirm the importance of habitat conditions, especially salinity, current speed, TDS, seagrass density, and substrate type, in supporting the abundance of S. canaliculatus juveniles. These findings provide a basis for habitat-based management and conservation strategies to support the sustainability of S. canaliculatus populations in Kulisusu Bay.

Parasitism by isopods is a common phenomenon in marine fishes and may induce negative effects, especially in juvenile stages. The surf-zones of sandy beaches are an important nursery habitat for many fish species, including commercially important ones, and are structured by beach characteristics and human activities, which are suggested to influence the fishes’ susceptibility to parasitism. Here, we analyze the early infestation and prevalence of parasitism in surf zones fishes of 27 beaches in southeastern Brazil with different characteristics. Parasites were recorded in only seven of the beaches. A high infestation was found in a single site, the highly urbanized Itaguá beach, where the prevalence of parasitism on juveniles and early adults of the Atlantic anchoveta Cetengraulis edentulus was high (68.11%). Four species of parasitic isopods were found, all belonging to the Cymothoidae family, but Livoneca desterroensis was the most abundant (78.7%). No effects of parasitism were detected on the size, weight and physiological condition of fishes, but presence of parasites and prevalence of infestation were positively affected by urbanization. Overall, our results indicate that the surf-zones have low parasite infestation, yet, they suggest that anthropic effects such as urbanization may enhance the prevalence of isopod parasitism.

Loss of estuarine and coastal habitats worldwide has reduced nursery habitat and function for diverse fishes, including juvenile Chinook salmon (Oncorhynchus tshawytscha). Underutilized off-channel habitats such as flooded rice fields and managed ponds present opportunities for improving rearing conditions and increasing habitat diversity along migratory corridors. While experiments in rice fields have shown enhanced growth rates of juvenile fishes, managed ponds are less studied. To evaluate the potential of these ponds as a nursery habitat, juvenile Chinook salmon (~ 2.8 g, 63 mm FL) were reared in cages in four contrasting locations within Suisun Marsh, a large wetland in the San Francisco Estuary. The locations included a natural tidal slough, a leveed tidal slough, and the inlet and outlet of a tidally muted managed pond established for waterfowl hunting. Fish growth rates differed significantly among locations, with the fastest growth occurring near the outlet in the managed pond. High zooplankton biomass at the managed pond outlet was the best correlate of salmon growth. Water temperatures in the managed pond were also cooler and less variable compared to sloughs, reducing thermal stress. The stress of low dissolved oxygen concentrations within the managed pond was likely mediated by high concentrations of zooplankton and favorable temperatures. Our findings suggest that muted tidal habitats in the San Francisco Estuary and elsewhere could be managed to promote growth and survival of juvenile salmon and other native fishes.

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.

Increasing abundance of arborescent octocorals (often referred to as gorgonians) on Caribbean reefs raises the question of whether habitat structure provided by octocorals can mediate a transition between coral- and algal- dominated states by increasing fish abundance and herbivory. This study tested the hypotheses that feeding rates and densities of demersal reef fishes are affected by the habitat structure provided by dense octocoral communities. Surveys of fishes on coral reefs in St John, US Virgin Islands, found 1.7-fold higher densities, and 2.4-fold higher feeding rates within versus outside of dense octocoral canopies. This difference, however, was only seen at sites with octocoral densities > 8 colonies m−2. Furthemore, the proximity of octocoral colonies to fish had an effect on the grazing rate of key herbivores (surgeonfishes and parrotfishes), with a 53% higher feeding rate (1.90 ± 0.11 bites min−1 m−2) near octocorals (< 20 or 30 cm, depending on the site) versus farther from them (1.24 ± 0.09 bites min−1 m−2). Finally, within the canopy of dense octocoral communities (17 colonies m−2), reef fishes fed at a rate that was 2.2-fold higher within the community than at the edge of the community that faced an adjacent sand patch. Fish abundance, however, was not uniformly higher within versus at the edge of the octocoral community, as ecotone specialists such as gobiids, blennioids, ostraciids, holocentrids, labrids, and pomacentrids were 1.3—2.3 times more abundant at the edge. In contrast, other taxa of demersal fishes, notably herbivores, were twice as abundant within octocoral communities than at the edges. Together, these results reveal an association between habitat structure created by octocorals on shallow reefs and increased feeding rates of demersal fishes (including those of herbivores). The potential of octocorals to increase herbivory that could mediate stony coral recovery is therefore worthy of further study.

The spatial and temporal variability in the dietary preferences of juvenile three-spined stickleback Gasterosteus aculeatus were studied across the typical coastal habitats of Keret Archipelago, Kandalaksha Bay(the White Sea). The sampling of fish using a beach seine was conducted in the late July–early August period and in late August. Additionally, zooplankton samples were collected to conduct a quantitative assessment of the abundance of potential prey items. The similarity percentage (SIMPER) analysis was applied to the data obtained from the stomach content and revealed the five planktonic taxa most prominently contributing to the diet of juvenile sticklebacks. Among these, the copepod Temora longicornis was the most important prey item at marine sites, while Acartia longiremis dominated the diet of fish in the marine lagoon. The calculation of the selectivity index revealed that some taxa (such as A. longiremis) were always avoided by juvenile fish, whereas the selectivity of some taxa increased in late August. In general, juvenile sticklebacks demonstrated a pronounced individual variation in their selectivity, even when a particular prey item was selected positively during the whole period of study. Our data highlight that despite the predominant consumption of easily available prey by juvenile sticklebacks, they demonstrate taxonomic- and size-specific prey selectivity.

Abstract On 11 March 2011, the Pacific coast in northeastern Japan was affected by the tsunami and land subsidence caused by the great east Japan earthquake. The disaster brought about various major environmental changes to the region. In our sampling site, examined over the period 2007–2015, the Zostera seagrass bed covered an area of approximately 3000 m2, but almost all of the shoots of the seagrasses were washed away by the tsunami. However, the seagrasses started to grow again in the summer of 2011, and the seagrass bed area expanded to approximately 3400 m2 by August 2014. Underwater observations revealed that the process of expansion resulted from regrowth from survived rhizomes and from seeds which were produced after 2012. A total of 28,969 fish larvae and juveniles, representing at least 65 species, were collected from 2012 to 2015, which showed a change in the composition of the dominant species. However, based on Jaccard’s coefficient of community, the species composition observed in 2015 returned to almost the same composition as observed before the tsunami. This implies that the seagrass formed a key habitat for the fish faunal recovery. Furthermore, it is implied that the occurrence of some transient species and casual (intermittent occurrence) species in the seagrass bed were associated with increase of these fishes in areas near to the seagrass bed. On the other hand, some species which occurred intermittently before the tsunami were not sampled or decreased after the tsunami.

Estuaries are important nursery areas for fishes worldwide but large-scale studies of spatial patterns of use are lacking. This study presents data on larval fish diversity, abundance and distribution within and among a range of temperate estuary types, spanning 25 systems sampled from 1998 to 2008 in South Africa. A standardized boat-based plankton towing technique was used. Estuary type and physico-chemical conditions played a defining role in the trends observed. Estuary resident Clupeidae and Gobiidae dominated the mid-channel larval catch, particularly the preflexion stages in permanently and intermittently open estuaries and in estuarine lakes. Permanently open estuaries were also characterized by high numbers of larvae and early juveniles of marine migrant fishes. Density was higher in warmer months (spring and summer), which coincides with peak spawning in coastal habitats coupled with zooplankton maxima in the warm-temperate region. A strong seasonal component was also evident in larval fish catches in cool-temperate systems, but this peak coincided with late winter rainfall. River inflow provides a strong influence on food availability and larval survival. Species richness and diversity was higher in estuaries with either extensive habitat variability and/or a strong, natural good supply of river flow. This was particularly evident in the higher numbers of marine migrant larvae in these systems. Freshwater deprived estuaries also displayed high species diversity due to the higher incidence of marine straggler species. Characterization of salinity into zones provided a valuable means to understand distribution and abundance dynamics. Mesohaline zones had the highest density of larval fishes, providing ideal food patches. A select suite of species dominate the larval fish assemblages in the various estuary types studied. These patterns persist but species abundance and rank may vary interannually based on productivity and larval fish survival.