Nursery Areas Research Articles

The need for constructing endangered fish habitats that conform to climate‐driven flow changes in a western U.S. river

AbstractWarmwater fish habitat in the San Juan River of the southwestern United States has been reduced by over 30% as a result of water depletion, reservoir inundation, and cold‐water dam releases combined with drought‐related changes in hydrology. This reduction and a suite of other factors have contributed to declines in native fish populations including the federally endangered Colorado Pikeminnow (Ptychocheilus lucius) and Razorback Sucker (Xyrauchen texanus). Conservation efforts for these species include determining flow needs; protecting, managing, and augmenting habitats; and stocking hatchery fish. But the young of stocked fish have low survival due largely to a paucity of nursery habitat not being reformed and maintained under current conditions. Flow recommendations for Navajo Dam releases designed to mimic the river's natural hydrograph have not been met due to water shortages, and the desired outcomes of increased channel complexity and enhanced fish habitat have not been observed. Forecasted hydrology that includes ongoing drought shows that achieving the flow targets through further dam reoperations is unlikely. Mechanical construction of early life‐stage habitats is a highly recommended complement to flow management for offsetting the effects of flow reduction and habitat loss. Habitats with features that are effective and resilient under a range of flows are important in counterbalancing the effects of climate change.

Non-Human Agency, Surprise Interventions, and Marine Futures. A Commentary on the ‘Whale’s Tail’ Metro Incident in Spijkenisse (NL)

In November 2020, a sculpture of a whale’s tail installed next to a metro station in Spijkenisse (NL) caught a derailed train falling from the overhead platform, preventing total catastrophe by saving the driver’s life. In this article, I argue that the sculpture’s unexpected intervention is emblematic of the entanglement between human beings and the natural and built environment in the Anthropocene, and provides new insight into the independent agency of non- and more-than-human beings. In particular, the incident reveals the capacity of other-than-human entities to impact human lifeworlds by rewriting existing social and material relationships. By acting so decisively in a situation spun beyond human control, the artwork both saved the day and created a novel configuration of heterogeneous elements, the train-wreck-on-a-frame. Following the incident, I suggest that the autonomy of ‘things’ requires humanity to start cultivating an attitude of receptivity: to learn to listen to unexpected expressions of agency, and follow their cues for the development of a more-than-human future. Building on these insights, I review various interactions between human beings and the coastal and marine environment, demonstrating that other-than-human actors already intervene in our lifeworlds more frequently than might be expected. Examples include newfound knowledge on ocean currents and gyres resulting from container spills and dumped plastics; the capacity of near- and offshore capital structures to act as nursery habitats; and demands for additional space by rivers and the sea itself. I conclude that surprise interventions by non- and more-than-human actors can help shape future marine environments, benefiting all involved.

Population structure discovered in juveniles of Greenland halibut (Reinhardtius hippoglossoidesWalbaum, 1792)

AbstractUnderstanding the genetic differentiation among populations of most marine fish requires investigating the differences among spawning grounds. However, this can be challenging as spawning grounds for some species are not well known, or spawning fish are difficult to collect. An alternative is to collect juvenile fish in nursery habitats closely associated with potential spawning grounds. Greenland halibut is a deep-dwelling, commercially important species with at least two identified major offshore spawning grounds in the North Atlantic and weak genetic differentiation across the Atlantic. In this study, we sampled juveniles from three sites representing the Davis Strait spawning area in the northwest Atlantic and one site in the northeast Atlantic representing the primary spawning area along the western slope of the Barents Sea. We applied genotype by sequencing and discovered 90 genetic markers that could be used to assess genetic differentiation among the four sites. The northeast and northwest Atlantic showed major genetic differentiation, supporting the existence of the two primary spawning clusters. Additionally, we found genetic differentiation between the three northwest Atlantic samples implying the existence of more than one spawning area in the northwest.

Correlation between transport and moulting of catadromous crab megalopae: The effects of starvation on rhythmic vertical migration

ABSTRACT Adopting circatidal vertical migration, catadromous crab megalopae use flood tide transport (FTT) to reach the settlement or nursery habitat and moult at a high rate that mismatches the low food-availability en route. To explain this “mismatch problem,” we hypothesize that besides development, starvation also affects megalopae’s transport so that the starved ones with low moulting possibility cannot succeed migration. The hypothesis was tested by studying how starvation affected rhythmic vertical migration of Chinese mitten crab (Eriocheir sinensis) megalopae. The findings support our hypothesis by showing that starvation weakened the vertical migration of the megalopae. The results also revealed that starvation caused the residual vertical migration of the megalopae to follow a circadian rhythm in addition to circatidal rhythm. We conclude that for catadromous crab megalopae, transport, just as development, is controlled by nutrition; and there exists a trade-off between the development and transport of Chinese mitten crab megalopae .

Atmospheric–ocean coupling drives prevailing and synchronic dispersal patterns of marine species with long pelagic durations

Dispersal shapes population connectivity and plays a critical role in marine metacommunities. Prominent species for coastal socioecological systems, such as jellyfish and spiny lobsters, feature long pelagic dispersal phases (LPDPs), which have long been overlooked. Here, we use a cross-scale approach combining field surveys of these species with a high-resolution hydrodynamic model to decipher the underlying mechanisms of LPDP patterns in northwestern Mediterranean shores. We identified basin-scale prevailing dispersal routes and synchronic year-to-year patterns tightly linked to prominent circulation features typical of marginal seas and semienclosed basins, with an outstanding role of a retentive source area replenishing shores and potentially acting as a pelagic nursery area. We show how the atmospheric forcing of the ocean, a marked hydrological driver of the Mediterranean Sea, modulates dispersal routes and sources of LPDP at interannual scales. These findings represent a crucial advance in our understanding of the functioning of metapopulations of species with LPDP in marginal seas and may contribute to the effective management of coastal ecosystem services in the face of climate change.

Ichthyoplankton and plastic waste drift in a river in the Amazon Basin, Brazil

Egg and larvae drift is a key mechanism for early fish stages to colonize nursery and growth areas and provides insights into ichthyofauna spawning times and spawning locations—crucial information for understanding fish biology. In the Tapajós River, Amazon Basin, no study has investigated the drift of ichthyoplankton along the hydrological phases nor the occurrence and dispersion of plastic waste associated with plankton. Thus, we aimed to present an overview of the spatio-temporal drift of ichthyoplankton and plastic waste in this river. Temporal sampling was carried out along a spatial gradient of approximately 300 km, covering different sectors of the river. Ichthyoplankton and plastic waste were captured through horizontal trawls on the subsurface of the water column for 10 min. Fish larvae belonging to 10 taxonomic orders and with an average size of 4.98 mm ± 3.14 mm were captured. Clupeiformes larvae occurred in all hydrological phases and reproductive peaks for other orders were recorded. Plastic waste was classified into 20 types according to color and shape and an average size of 1.55 mm ± 1.27 mm. Green fragments and blue filaments were the most abundant. We found the highest density of fish eggs and larvae drifting during the drought phase in stretches with greater environmental structure, whereas plastics were more abundant during the receding water phase in more turbulent stretches that have impacts from illegal mining. Simultaneous drift of ichthyoplankton and plastic waste was recorded in all hydrological phases and sampled sectors. This is worrying because, although we did not analyze the ingestion of plastics by fish larvae, plastic waste can enter the nursery areas of the Tapajós River and reduce the function of these areas for fish. Here we discover through the high densities of fish eggs and larvae deriving that the Tapajós River is an important reproduction site for ichthyofauna and that the presence of different landscape configurations prove to be a key factor in the dispersion, retention and development of ichthyoplankton and plastic waste.

Evidence for the first multi-species shark nursery area in Atlantic Africa (Boa Vista Island, Cabo Verde)

This study describes the first potential multi-species shark nursery area in Atlantic Africa (Sal Rei Bay – SRB, Boa Vista Island, Cabo Verde). From August 2016 to September 2019, 6162 neonates and juveniles of 5 different shark species were observed in SRB using beach gillnet-based bycatch surveys, namely milk (Rhizoprionodon acutus; n= 4908), scalloped hammerhead (Sphyrna lewini; n= 1035), blacktip (Carcharhinus limbatus; n=115), Atlantic weasel (Paragaleus pectoralis; n= 93) and nurse (Ginglymostoma cirratum; n= 12) sharks. Except for nurse sharks, significant seasonal variations in shark relative abundance were observed, with higher levels being recorded during summer and autumn. These findings, together with local knowledge (interviews to fishermen), denote the consistent use of SRB by juvenile sharks and its preference relative to other areas in the region. Ensuring the protection and conservation of SRB nursery area is especially relevant as, according to IUCN, all identified shark species are threatened with extinction over the near-future – in particular, scalloped hammerheads (critically endangered) and Atlantic weasel sharks (endangered). The effective protection of SRB will not only support the conservation of shark populations, but also of other charismatic fauna (e.g., loggerhead turtles) and broader benthic and pelagic ecosystems.

Influence of reed beds (Phragmites australis) and submerged vegetation on pike (Esox lucius)

Eutrophication and reduced grazing have led to an expansion of the common reed (Phragmites australis) in archipelago areas in the Baltic Sea, while at the same time the composition of submerged vegetation has changed. Although reed is important as nursery habitat for many fish species, extensive emergent vegetation may reduce biodiversity and abundance of predatory fish. Pike (Esox lucius) is a predatory fish whose larvae and young-of-the-year find both food and shelter in reed but use different micro-habitats during different life-stages. Here we investigate the influence of reed and submerged vegetation on abundance and body size of adult pike during the spawning season. We predicted that coastal bays with extensive but heterogeneous reed beds with higher cover of submerged vegetation would have more and larger pike than bays with smaller, homogenous reed belts or with less submerged vegetation. To test these predictions, we estimated abundance and size-structure of adult pike from catches in angling fishing among 22 bays in the Stockholm archipelago at the Swedish Baltic Sea coast. Our analyses show that catches of adult pike were positively associated with both extensive reed beds and cover of rooted submerged vegetation. However, pike size was not correlated with any vegetation variable, but instead increased with wave exposure and bay area. Our study suggests that reed beds and submerged vegetation are important for adult pike during the spawning season, and even the most extensive reed beds had no evident negative effect on pike populations. We could not see any clear relationship between emergent reed habitat and cover of submerged vegetation among the studied bays, and conclude that to maintain pike population during the spawning season it is important that coastal bays have sufficient amounts of both reed beds and rooted submerged vegetation.

Trophic ecology of juvenile bull sharks (Carcharhinus leucas) in the Coyote estuary, Costa Rica.

Bull shark (Carcharhinus leucas) is a near-threatened elasmobranch species capable of moving between the fresh and salty waters of tropical and subtropical coastal areas, for which we still lack important ecological information. During their first years of life, bull sharks use estuarine systems as nursery areas, making them highly susceptible to environmental and anthropogenic pressures. We studied the trophic ecology of juveniles found in the Coyote estuary, a potential nursery area in Costa Rica, to understand the potential impact of further bull shark declines and gain knowledge that could aid in their conservation. We analysed the trophic ecology of juvenile bull sharks [81-103 cm total length (TL)] in the Coyote estuary, Costa Rica, using stable isotopes of δ15 N and δ13 C. Since one problem using this technique in juveniles is the confounding effect of the maternal signature, we sampled different tissues (muscle and plasma), verified the status of the shark's umbilical scar and identified the size at which the isotope signature is a result of the animal's current diet. The isotopic values of the muscle tissue reflected the maternal isotopic signature. In contrast, plasma values reflected the diet of juvenile bull sharks >95 cm TL and with a closed umbilical scar. Juvenile bull sharks fed primarily on teleost fishes of the order Anguilliformes and Siluriformes, and have a high trophic position (≥4.0) in the Coyote estuary. Our findings suggest that this estuary is an important feeding site for juvenile bull sharks of the Pacific of Costa Rica. Thus, the protection of essential habitats such as the Coyote estuary will benefit not only bull shark conservation, but also the conservation of an array of fish species that also use this habitat as a rookery, many of which are of commercial interest.

Can seamounts in the Gulf of Alaska be a spawning ground for sablefish settling in coastal nursery grounds?

In addition to their prevalence on the continental shelf, adult sablefish have been found over the chain of seamounts far offshore in the Gulf of Alaska (GOA). Many of the females that were observed had recently spawned or were ready to spawn. However, to date, it is not known what role the seamounts play in sablefish life history and there are no observations of sablefish eggs or larvae over the GOA seamounts. Due to their depth and remoteness, there are no suitable shallow nursery areas in the vicinity of the seamounts. For successful recruitment, individuals hatching from eggs spawned over seamounts would need to be transported hundreds of miles to suitable areas inshore. Using an individual-based model (IBM) of sablefish, we have demonstrated that if spawning occurs over any of the seamounts in the GOA seamount province it is likely that at least some individuals will be successfully transported to shallow inshore nursery areas in the coastal GOA. As our simulated individuals only exhibit vertical movement behavior this on-shore transport results from the prevailing currents to which they were subjected and not from any geographic or environmental homing capabilities. Our analysis indicates that the strength of the on-shelf velocity is not the primary factor in determining the likelihood of transport to nursery areas. We speculate that the size, strength, location, and direction of the eddies that populate the GOA in any given year could be important in determining transport success. This idea is reinforced by our path analysis which shows that there are markedly different pathways taken by successful individuals among years. Our findings suggest that it may be necessary to expand what is considered suitable habitat for young sablefish. With seamounts being a potentially important spawning site for sablefish, future research priorities should include ground-truthing with fishery or fishery-independent data collected from seamounts. Potential applications of this expanded sablefish IBM include testing for connectivity between seamount and slope spawning areas and the Aleutian Islands and Bering Sea and contributing to the development of spatially explicit assessment models of sablefish.

United States Gulf of Mexico Waters provide important nursery habitat for Mexico’s Green turtle nesting populations

Resolving natal populations for juvenile green turtles is challenging given their potential for extensive dispersal during the oceanic stage and ontogenetic shifts among nursery habitats. Mitochondrial DNA markers have elucidated patterns of connectivity between green turtle nesting populations (rookeries) and juvenile foraging aggregations. However, missing rookery baseline data and haplotype sharing among populations have often impeded inferences, including estimating origins of Gulf of Mexico juveniles. Here, we assessed genetic structure among seven foraging aggregations spanning southern Texas (TX) to southwestern Florida (SWFL), including Port Fourchon, Louisiana (LA); a surface-pelagic aggregation (SP) offshore of Louisiana and Florida; Santa Rosa Island, Florida (SRI); St. Joseph Bay, Florida (SJB); and the Big Bend region, Florida (BB). We estimated source contributions to aggregations with novel genetic data (excluding SP and BB) using a Bayesian many-to-one mixed stock analysis (MSA) approach. Haplotype frequencies for western (TX, LA, SP, SRI) and eastern (SJB, BB, SWFL) aggregations were significantly differentiated. The largest shift in haplotype frequencies between proximal nursery sites occurred between SRI and SJB, separated by only 150 km, highlighting the lack of a geographic yardstick for predicting genetic structure. In contrast to previous MSA results, there was no signal of Florida juveniles at any foraging site. Mexican contributions dominated in all aggregations, with strong connectivity between western Bay of Campeche (Tamaulipas/Veracruz) rookeries and western foraging aggregations. MSA indicated more diverse Mexican origins for eastern aggregations, with larger inputs from the eastern Bay of Campeche (Campeche/Yucatán), Campeche Bank, and Quintana Roo rookeries. These results demonstrate the significance of the Gulf of Mexico coast and offshore waters of the United States as important nursery habitat for green turtles of Mexican origin and highlight the need for international coordination for management of these populations.

Inferring habitat use of the Pacific White Shark using vertebral chemistry

The conservation and management of highly migratory sharks relies on understanding age-related movements and nursery habitat utilization. We reconstructed the habitat use and migratory history of young White Sharks (Carcharodon carcharias), a highly protected species, by utilizing natural chemical tracers (element:Ca ratios and stable isotope analysis, SIA) in vertebral cartilage growth bands. Two nursery areas in the northeastern Pacific are known, but migration patterns of immature White Sharks within the Gulf of California (GC) and natal philopatry are poorly understood. Vertebrae from coastal Mexican artisanal fisheries off central Baja California in the Pacific (12 neonates and juveniles; 139-280 cm total length) and the GC (3 subadults; 289-355 cm TL) were analyzed to characterize (1) trophic histories from collagen δ13C and δ15N values, and (2) in utero patterns and post-birth environmental histories from element:Ca time-series. Mean δ15N values from vertebral edges of GC sharks, representing the most recent feeding, was +5‰ higher than in the Pacific, reflecting the intense denitrification that permeates the regional food web and supporting SIA as tracers of migration between regions. A subadult from the GC likely resided within the system throughout its life, and two subadults migrated into the GC. Most neonate and juvenile sharks caught in the Pacific had SIA that did not overlap with those of the GC, but a single subadult likely migrated to the GC. Element:Ca ratios displayed ontogenetic trends, with Li:Ca, Zn:Ca, and Ba:Ca significantly higher before the birth mark in sharks captured in the GC. Edge values were significantly higher in Zn:Ca and Ba:Ca in the GC compared to the Pacific, suggesting elemental ratios may serve as tracers of migration between regions. Subadult sharks collected from GC displayed elevated maternal Zn:Ca and Ba:Ca, suggesting mothers may have resided in the GC for an extensive period pre-birth. Some White Sharks may reside within the GC from birth until at least the subadult stage (ca. 3 m TL), and there may be an unidentified nursery. Chemical tracers, coupled with genomic and tagging studies, should improve understanding of the importance of the GC to White Shark populations in the northeast Pacific.

Pelagic connectivity of European sea bass between spawning and nursery grounds

The sea bass stock around the UK (northern stock) has declined rapidly over the past decade, likely due to a combination of both overfishing and low recruitment. Understanding mechanisms that drive the number of young reaching nursery grounds is important for explaining observed recruitment variability and therefore developing effective management strategies. An individual-based model (IBM) has been developed here to investigate factors affecting sea bass settlement on nursery grounds for the northern stock. Simulations considered seven years with varying environmental conditions and year class strength, and outputs were compared to empirical data from monitoring of nursery areas in the UK and Ireland. The IBM includes hydrodynamics to simulate the drift of eggs and larvae, temperature-dependent growth and mortality, and behavior affecting position in the water column. Comparison between the model and ICES assessment abundance of age class zero fish showed similar temporal variability, but with higher recruitment predicted for 2018, and a lower peak recruitment in 1997. The model reproduced general patterns of interannual variability for the Thames estuary, but performed less well for some other regions. Further investigation is needed to understand differences between modelled supply and observations, as these could be due to uncertainties in reproducing the physical environment (e.g., currents, temperature) or biology (e.g., spawning, behavior, mortality), as well as uncertainty in recruitment derived from stock assessments or data collected from nursery grounds. Nevertheless, the model provides a useful demonstration of connectivity between spawning and nursery grounds, showing spawning regions that are likely to have greatest influence on recruitment in different estuaries, and how these may vary interannually. For example, sources from western Channel and Celtic Sea can supply larvae to many areas, leading to connectivity across the Channel and Celtic Sea, and into the Irish Sea. However, other regions may depend on more local areas. For example, with the Solent estuary dependent on sources within the Channel each year. With the temperature-dependence on growth, and therefore duration of the pelagic stage, results show the potential influence of spawning timing, in relation to ocean temperatures, for connectivity between spawning and nursery grounds.

Fishery Resource Evaluation with Hydroacoustic and Remote Sensing in Yangjiang Coastal Waters in Summer

Yangjiang coastal waters provide vital spawning grounds, feeding grounds, and nursery areas for many commercial fish species. It is important to understand the spatial distribution of fish for the management, development, and protection of fishery resources. In this study, an acoustic survey was conducted from 29 July to 5 June 2021. Meanwhile, remote sensing data were collected, including sea surface temperature (SST), chlorophyll concentration (Chla), sea surface salinity (SSS), and sea surface temperature anomaly (SSTA). The spatial distribution of density and biomass of fish was analyzed based on acoustic survey data using the geostatistical method. Combining with remote sensing data, we explored the relation between fish density and the environment based on the GAMs model. The results showed that fish are mainly small individuals. The horizontal distri-bution of fish density had a characteristic of high nearshore and low offshore. In the vertical direc-tion, fish are mainly distributed in surface-middle layers in shallow waters (<10 m) and in middle-bottom layers in deeper waters (>10 m), respectively. The deviance explained in the optimal GAM model was 59.2%. SST, Chla, SSS, and longitude were significant factors influencing fish density distribu-tion with a contribution of 35.3%, 11.8%, 6.5%, and 5.6%, respectively. This study can pro-vide a scientific foundation and data support for rational developing and protecting fishery re-sources in Yangjiang coastal waters.

Larval Fish Spatiotemporal Dynamics of Different Ecological Guilds in Yangtze Estuary

Estuaries, as important fish nursery habitats, usually include a variety of larval fishes of different ecological guilds and exhibit complicated changing environmental conditions. We carried out a survey to examine the spatiotemporal dynamics of different ecological guild larval fishes and their relationships with environmental factors in the springs and summers from 2018 to 2020 in the Yangtze Estuary (China). The aims of the study were to provide detailed information on the characteristics of the larval fish assemblage and to explore the spatiotemporal variation in different ecological guild species and the effects of environmental variables on assemblage structure. More than 140,000 fish larvae from 26 families and 99 species were gathered during the six cruises, with the spring being the most prolific. The assemblage was dominated by a few species and was divided into three ecological guilds. Engraulidae was the most abundant family, followed by Cyprinidae and Gobiidae. Hemiculter bleekeri (freshwater), Pseudolaubuca sinensis (freshwater), Coilia mystus (brackish water), and Engraulis japonicas (marine) were the predominant species. Seasonal variations in larval fish assemblage structure were closely influenced by temperature, and the fluctuation in salinity mainly determined the spatial distribution of the larval fish community. Freshwater flows also played an important role in shaping the larval fish assemblage structure and dynamics. The conclusions improve the understanding of the ecological dynamics of larval fish assemblages in environmentally heterogeneous areas and may be applicable to other estuary ecosystems.

Habitat use and movement patterns of adult male and juvenile scalloped hammerhead sharks Sphyrna lewini throughout the Hawaiian archipelago

Scalloped hammerhead sharks Sphyrna lewini are a circumglobal species found in tropical and subtropical waters. Globally, populations of S. lewini have undergone dramatic declines in recent decades, and 4 of 6 distinct population segments are at risk of extinction and listed under the United States Endangered Species Act. Despite this, limited data exist on movement behavior or habitat use requirements of S. lewini, especially in the Central Pacific region. In this long-term (2009-2020) telemetry study, 27 S. lewini (24 males [22 adults, 2 juveniles], and 3 juvenile females) ranging in size from 106 to 310 cm (total length) were tagged with a combination of acoustic and/or satellite tags in a known nursery area, Kāne‘ohe Bay, Hawai‘i. Acoustic data revealed repeated movements of adult male S. lewini to Kāne‘ohe Bay between May and September across multiple years. Horizontal movements away from the Bay indicate these individuals are highly associated with the Hawaiian Archipelago (i.e. Northwestern and main Hawaiian Islands), while vertical movements were dynamic, with repeated, nocturnal deep dives to depths beyond 800 m and temperatures as low as 5.0°C. We conclude that adult male and juvenile S. lewini tagged in Kāne‘ohe Bay exhibit fairly restricted movements throughout the Hawaiian Archipelago, and mature males specifically exhibit strong seasonal site fidelity to Kāne‘ohe Bay. These data add crucial baseline information on habitat preferences of S. lewini around the Hawaiian Islands, and can be used to help structure conservation strategies for a portion of the Central Pacific population.

Mangrove use by sharks and rays: a review

A wide variety of species depend on mangroves, making them essential habitats in tropical and subtropical regions. While the function of mangrove habitat is well studied for taxa such as teleost fishes, limited attention has been directed towards their value for elasmobranchs. Here, we review the available literature on how and why elasmobranchs use mangrove habitats based on 65 papers identified through literature searches. The use of mangrove habitat as nursery areas in combination with other coastal habitats has been well examined, although we found taxonomic and regional biases in research. Additionally, mangrove habitats are considered to offer elasmobranchs feeding opportunities and refuge from predators, yet such functions have rarely been tested. In particular, the ecological role of elasmobranchs within mangrove habitats is poorly known; as it is difficult to study their behaviour in complex mangroves, their feeding ecology is understudied as are trophic linkages between mangrove and adjacent ecosystems. For a greater understanding of the association between mangroves and elasmobranchs, direct observations of elasmobranch behaviour in mangrove habitats are needed. Given global concern regarding mangrove loss, understanding how this affects elasmobranch populations will require long-term studies, particularly in those regions where losses are greatest. We identify 8 key research questions that will help improve this understanding.

Microdebris Abundance, Distribution, and Ingestion by Sargassum-Associated Juvenile Fishes in the Gulf of Mexico

Holopelagic Sargassum is a critical nursery habitat for the early life stages of many marine fishes, including several federally managed species in the United States and Caribbean. Sargassum is often aggregated along surface convergence features where microdebris (synthetic, semi—synthetic, and naturally—derived particles size) have also been found in relatively high concentrations. In this study, we collected microdebris from Sargassum and adjacent open water habitats (in 2018), and juvenile fishes from Sargassum (in 2017 and 2018) in the northern Gulf of Mexico to quantify habitat—specific microdebris concentrations and the degree to which Sargassum—associated juvenile fishes ingest microdebris. Microdebris concentrations within Sargassum habitats were, on average, 180 times greater than those found within adjacent open water habitats. Microdebris concentrations decreased with distance from shore in both Sargassum and open water habitats, and generally increased with Sargassum biomass. Microdebris ingestion by juvenile (9–320 mm SL) fishes (n = 846) varied by year (all taxa: 24.7% in 2017; 14.7% in 2018) and by taxa, and generally decreased with distance from shore. Small fibers were the dominant type of microdebris observed in stomach contents. The structural complexity of Sargassum provides a mechanism for microdebris capture and concentration in surface waters. Since 2011, massive blooms of Sargassum have inundated regions in the central Atlantic Ocean and Caribbean Sea. The role of Sargassum as a microdebris “sink” has major implications for the transport of microdebris as Sargassum drifts within and across basins and eventually strands on beaches and coastal habitats, or subsides to benthic environments.

MANGROVE COVER-BASED VEGETATION INDICES MAPPING USING PLANETSCOPE DATA IN TIEN YEN DISTRICT QUANG NINH PROVINCE

This study focused on mangrove cover mapping by using vegetation indices in Tien Yen district. Mangrove ecosystems play a vital role in many coastal regions, protecting against erosion and storm surges, providing nursery habitats of aquatic organisms, and offering livelihoods to local communities. Besides, this study aims to evaluate the use of PlanetScope data based on vegetation indices for mapping mangrove cover. This study collected and analyzed high-resolution PlanetScope satellite imagery (3m x 3m) to calculate eight different vegetation indices, including CMRI, NDVI, NDWI, GNDVI, BNDVI, SAVI, IPVI, and EVI2. These indices were used to map the mangrove cover in Tien Yen District and to evaluate the accuracy of each vegetation index. The results showed that among all of the indices used, NDVI had the highest accuracy of 96.3% in mapping the mangrove cover in Tien Yen district, followed by CMRI. Besides, the study emphasizes the importance of utilizing remote sensing techniques in supporting conservation efforts and establish sustainable management practices for mangrove forests in Tien Yen district. Additionally, the study presents an overview of the current situation and policy recommendations for the integrated management of mangrove forests, and provides information on sustainable mangrove ecosystem management in the context of climate change adaptation and mitigation in Tien Yen district, Quang Ninh province.

Tidal migrations of juvenile Sillago spp. in a subtropical intertidal nursery seascape

Context Subtropical intertidal pools on depositional shores are important nursery habitats for smaller juveniles (10- to ~25-mm total length, TL) of commercially important smelt whiting (Sillago spp.), whereas larger juveniles >25 mm TL occupy shallow subtidal habitats at low tide. Aims We investigated the connectivity between lower and upper shore habitats in Moreton Bay. Methods We used funnel camera traps to assess tidal movements of juvenile whiting and compared harpacticoid copepod genera in small juvenile whiting guts caught post-foraging with those sampled from nearby sediments to infer patterns of foraging. Key results Smaller juveniles transited sandy upper-shore habitat at depths from 1.5 to <10 cm and avoided vegetated habitats, whereas larger juveniles moved into mangroves at depths of 15–30 cm on the rising tide. Coullana spp. harpacticoids were found in greater proportions in whiting guts of small juveniles than in the sampled habitats, but were abundant in intertidal pool and mangrove sediments. Conclusions Intertidal sandy habitats are seemingly an important high-tide habitat for smaller juvenile whiting, where they preferentially forage on Coullana spp. Implications Given the broad distribution of smelt whiting in the Indo-Pacific, the protection of such habitats must be addressed by fishery and habitat management agencies for species with similar early nursery requirements.