Larval Assemblages Research Articles

Sediment Core DNA-Metabarcoding and Chitinous Remain Identification: Integrating Complementary Methods to Characterise Chironomidae Biodiversity in Lake Sediment Archives.

Chironomidae, so-called non-biting midges, are considered key bioindicators of aquatic ecosystem variability. Data derived from morphologically identifying their chitinous remains in sediments document chironomid larvae assemblages, which are studied to reconstruct ecosystem changes over time. Recent developments in sedimentary DNA (sedDNA) research have demonstrated that molecular techniques are suitable for determining past and present occurrences of organisms. Nevertheless, sedDNA records documenting alterations in chironomid assemblages remain largely unexplored. To close this gap, we examined the applicability of sedDNA metabarcoding to identify Chironomidae assemblages in lake sediments by sampling and processing three 21-35 cm long sediment cores from Lake Sempach in Switzerland. With a focus on developing analytical approaches, we compared an invertebrate-universal (FWH) and a newly designed Chironomidae-specific metabarcoding primer set (CH) to assess their performance in detecting Chironomidae DNA. We isolated and identified chitinous larval remains and compared the morphotype assemblages with the data derived from sedDNA metabarcoding. Results showed a good overall agreement of the morphotype assemblage-specific clustering among the chitinous remains and the metabarcoding datasets. Both methods indicated higher chironomid assemblage similarity between the two littoral cores in contrast to the deep lake core. Moreover, we observed a pronounced primer bias effect resulting in more Chironomidae detections with the CH primer combination compared to the FWH combination. Overall, we conclude that sedDNA metabarcoding can supplement traditional remain identifications and potentially provide independent reconstructions of past chironomid assemblage changes. Furthermore, it has the potential of more efficient workflows, better sample standardisation and species-level resolution datasets.

Climate-driven shifts in decapod larvae assemblages in a temperate estuary

The study examines the complex impact of climatic patterns, driven by the North Atlantic Oscillation (NAO), on regional climate, hydrology, and sea surface temperatures. Focused on the period from 2003 to 2012, the research specifically investigates the influence of thermal variability on decapod larval communities. Monthly zooplanktonic sampling conducted at the Mondego Estuary, Portugal, entrance over a decade revealed the prevalence of Carcinus maenas, Diogenes pugilator, and Pachigrapsus marmoratus larvae. These assemblages displayed notable interannual and seasonal fluctuations, often corresponding with changes in sea surface temperatures. Significant system shifts around 2007, instigated by the large-scale NAO, led to subsequent modifications in sea surface temperature and decapod larvae communities' dynamics. Post-2007, there was an upward trajectory in both species’ abundance and richness. Phenologically during the former period, the community exhibited two abundance peaks, with the earlier peak occurring sooner, attributed to heightened temperatures instead of the unique peak exhibited before 2007. The research further elucidated the occurrences of Marine Heatwaves (MHW) in the region, delving into their temporal progression influenced by the NAO. Although water temperature emerged as a crucial factor influencing decapod larvae communities annually and seasonally, the study did not observe discernible impacts of MHW events on these communities. These communities represent essential trophic links and are crucial for the survival success of adult decapods. Given the rapid pace of climate change and increasing temperatures, it is imperative to assess whether these environmental shifts, particularly in thermal conditions, affect these meroplanktonic communities.

Larval dynamics suggest phenological strategies and positive effect of marine protected areas controlling indigenous and non-indigenous crab populations

The early life of most decapod crustaceans takes place in the water column as larvae before they settle in benthic habitats. The spatial and temporal variability in the settling of larval stages offers valuable insights into the potential recruitment of natural populations. To explore this, we studied megalopa assemblages at various segments of coastline on El Hierro and Lanzarote islands, both within and outside the Marine Protected Areas (MPAs) of each island. The study spanned four consecutive oceanographic periods in the Canary Islands (NW Africa), employing light traps for sample collection. The low number of recorded species suggested that light traps exhibit selectivity, particularly for megalopae belonging to Portunidae and Grapsidae. El Hierro, which experienced warmer sea surface temperatures, displayed higher megalopa abundance values than Lanzarote and distinct larval assemblages was observed between these two islands. Similarly, we identified significant variations in abundance and species composition between stratified and mixing seasons. These seasonal differences were influenced by the dominance of Achelous hastatus, Percnon gibessi, and Cronius ruber during the stratified season. In Lanzarote, C. ruber was not recorded during the mixing season, suggesting that the colder conditions there may constrain its reproduction. Interestingly, we observed that species traditionally harvested from the intertidal zone for human consumption (Plagusia depressa) or used as bait for recreational fishing (Pachygrapsus spp. and P. gibessi) exhibited higher megalopa abundances within the MPAs. In contrast, we noted lower megalopa densities of the non-indigenous species C. ruber within the protected areas. These results indicate a positive effect of MPAs controlling indigenous and non-indigenous crab populations. Moreover, the study provides novel data, showing that light traps are suitable for monitoring the temporal occurrence, abundance, and spatial distribution of non-indigenous and commercially exploited species. This is key for adopting an ecosystem-based approach to manage marine resources.

Estuarine front dynamics drive ichthyoplankton assemblage in the tidal freshwater zone of the Río de la Plata, South America

Frontal zones are critical in the retention and dispersal of ichthyoplankton. This study evaluates the response of ichthyoplankton assemblage to frontal zone dynamics in one of the world's largest estuaries, the Río de la Plata, South America. Surveys were conducted between October 2014 and December 2017 in a nearshore habitat of the tidal freshwater zone of the estuary. Ichthyoplankton was collected using conical nets, and physico-chemical variables were registered in situ. The frontal zone dynamics were evaluated through the turbidity front (TF) location, determined by satellite imagery. Although most larval taxa belonged to the freshwater category, the estuarine category had the highest abundances. The highest species richness and abundance occurred during spring and summer, linked to the season and proximity of spawning areas. The dynamics of the TF emerged as the primary driver of interannual variability in ichthyoplankton assemblages within the tidal freshwater zone. A seaward shift of the TF correlated with a reduction in total abundance and the prevalence of freshwater larvae, whereas a retraction of the TF location corresponded to an increased abundance of marine larvae in the tidal freshwater zone. These interannual shifts in TF location and fish larvae assemblages were closely tied to significant variations in river discharges resulting from the ENSO events during the study period. The findings suggest that marine and estuarine fish eggs exhibit effective retention near the frontal zone and the outer regions of the estuary. In contrast, larvae from these categories disperse along the main axis of the estuary in response to the displacement of the frontal zone. Finally, we discuss into the role of the frontal zone in the Río de la Plata as a pivotal environmental cue for fish larvae, influencing their behavior to regulate dispersal patterns.

Distribuição do ictioplâncton determinada por diferentes ambientes em uma lagoa costeira de água doce

Abstract Aim This study aimed to evaluate the spatial and temporal distribution of ichthyoplankton in the Peri Lagoon, a coastal freshwater lagoon in Brazil. Methods Ichthyoplankton samples were collected every two months from June 2008 to April 2010 with 500 µm conical-cylindrical planktonic nets at five sampling stations. Results In total, 181 fish eggs and 1,315 larvae, representing estuarine and freshwater species, were captured. The most representative species were Awaous tajasica, Ctenogobius sp1, and Platanichthys platana. Significant differences were found in temporal egg distribution and larval spatiotemporal distribution (Kruskal-Wallis test, p < 0.05). Eggs were predominantly captured during the autumn, winter, and spring Neotropical seasons. Geospatial analysis demonstrated spatial segregation in the distribution of larval assemblages, with higher abundances in areas adjacent to riparian forests, following stream mouths, and deeper areas with rocky substrates. Conclusions Proximity to streams and areas surrounded by dense forests is crucial for the spawning and development of fish species in the Peri Lagoon. The findings of this study provide valuable insights into the conservation of the ichthyofauna in this unique environment.

Comparison of Abundance and Structure of Larval Fish Assemblages between Autumn and Spring in the Waters Surrounding Taiwan Bank, Western North Pacific

The fluctuations in both time and space of larval fish assemblages in relation to hydrographic characteristics in the waters surrounding Taiwan Bank were studied in October 2021 (autumn) and March 2022 (spring). Throughout the study period, we identified a total of 149 taxa of fish larvae, encompassing 96 genera and 71 families. Engraulis japonicus, Diaphus slender type, unidentified Gobiidae, Apogon sp., unidentified Clupeidae, and Benthosema pterotum were the six dominant taxa and together constituted 47.39% of the total catch. There were no notable temporal variations observed in the abundance of fish larvae, but the species number of fish larvae was greater in spring than in autumn. Significant variations in species composition were observed between the different cruises, and the cluster analysis unveiled a distinct temporal structure of the assemblages of fish larvae. The dynamics of the prevailing currents induced by seasonal monsoons contribute significantly to the transportation of fish larvae. The distribution of fish larvae showed a good association with hydrographic characteristics, where seawater temperature and salinity emerged as the primary explanatory factors influencing the composition of larval fish assemblages in the waters surrounding Taiwan Bank. While the increased influx of nutrients from upwelling ensures abundant food availability, the hydrographic conditions may not be suitable for every fish larva.

Distribution and composition of Decapod larvae assemblages on the Berlengas archipelago and Peniche coast (western coast of Portugal)

For the first time, the decapod larval community in the Berlenga and coastal Peniche region have been investigated in detail, from a short-term time series (2015 – 2020). Sampling was conducted in two locations, at Berlengas archipelago, and near the coast, at Peniche. The communities found at both stations were revealed to be 80% different in terms of species composition, but species of Brachyura, Caridea, and Anomura were the most abundant in both locations. A marked seasonality, with abundance peaks during summer and autumn, was found for the assemblages near the coast, but absent in the assemblages of the Berlenga region. This suggests that factors other than the environmental variables examined in this study may play a crucial role in shaping the assemblages more offshore. Water temperature, upwelling index, salinity, and chlorophyll-a were the main factors dictating species abundance, especially at Peniche. This emphasizes the significant role of the Iberian upwelling productivity, which in turn influences decapod communities. Also, the progressive warming of coastal water will most likely have a negative impact on the decapod meroplanktonic life forms, with further consequences on recruitment and adult life stages.

Seasonality and hyphomycetes’ conidia conditioning affect the diversity of Chironomidae larvae associated with leaf litter in a tropical stream

This study aimed to evaluate the structure, taxonomic, and trophic composition of an assemblage of chironomid larvae associated with leaf litter in a tropical stream (Brazilian Cerrado biome) during different seasonal periods. Additionally, the study aimed to examine the relationship between the activity of decomposing microorganisms and the abundance and total richness of chironomids. To conduct the study, leaves were collected in buckets from the Boiadeiro stream at five sampling points over 30 consecutive days, resulting in a total collection of 12 months. Then, they were placed in litter bags (n = 3 per point) and incubated in the stream for 30 days to evaluate chironomid colonization and microbial activity. A total of 3,892 chironomid larvae were identified. Among the functional feeding groups (FFGs) of chironomid larvae, the food collector-gatherer group displayed higher diversity than other FFGs. The richness of chironomids was positively associated with the number of conidia produced by aquatic hyphomycetes' during leaf decomposition. We found that during the dry season (April–August), the highest values of abundance and total richness of chironomids were recorded, accompanied by the lowest taxonomic variability of chironomid larvae. Conversely, environmental variations in the rainy season contributed to greater taxonomic variability but lower abundance and total richness of chironomids associated with leaf detritus.

Dynamics of Decapoda larvae communities in a southwest Iberian estuary: Understanding the impact of different thermal regimes

Environmental conditions play a pivotal role in shaping the dynamics of meroplanktonic communities, which represent a vital life stage, crucial for successful recruitment. Specifically, temperature can impact the survival and duration of larval development in decapod crustacean species. The objective of this study is to analyze the community of decapod larvae in the Guadiana estuary, located in southwest Iberia. The analysis focuses on the community's taxonomic composition, temporal variability, and the influence of environmental factors. Particularly, the study emphasizes investigating the impacts of different thermal regimes on the abundance of these assemblages. A comprehensive zooplankton sampling program was conducted at a single station in the lower estuary, from 2014 to 2022. The decapod larvae assemblages are dominated by Upogebia spp., followed by Diogenes pugilator, Panopeus africanus, Afropinnotheres monodi, and Polybius henslowii species. The results of structural equation modeling unveiled a strong influence of water temperature and salinity on the community, while chlorophyll-a concentration, river runoff, and the large-scale climatic mode North Atlantic Oscillation (NAO) revealed no impact on the abundance of these assemblages. Overall, the community and the main taxa displayed a positive linear trend in response to increased salinity. However, the effect of increasing temperature varied among species. In the current climatic scenario, water temperature emerges as a critical factor in predicting seasonal variation of the assemblages' abundances, exhibiting a marked seasonality during spring and summer. Predictive models used to investigate future scenarios, Representative Concentration Pathway (RCP) 2.6 and RCP 8.5, defined by the International Panel on Climate Change (IPCC), where the temperature is expected to rise 2 °C and 4.3 °C by 2100, suggest the possibility for an alteration in assemblages' composition, where the abundances of D. pugilator, the second most abundant species, tend to decrease abruptly. Reported evidence, coupled with the typical Mediterranean climate of the region, where extreme climatic events, like marine heatwaves, are becoming more frequent, the high connectivity with the Mediterranean Sea, where invasion by non-indigenous species is increasing, also connected with changes in freshwater discharges, may trigger significant alterations in species dominance and abundance, with ecological and socio-economic implications.

Vertical variability in the diversity and abundance of fish larvae in a shallow tropical estuary in Southern Gulf of Mexico

Vertical migration in ichthyoplankton is relevant for its survive and it has been documented in estuaries with more than 10 m depth. In shallow estuaries this process is unknow or not supposed since no environmental stratification is assumed. The objective of this research is to investigate the vertical variability of fish larvae assemblages in shallow tropical estuarine zones. The model study site was the estuarine area of the San Pedro y San Pablo River located east of the Centla Wetland Biosphere Reserve in the Gulf of Mexico. The experimental design includes depth (bottom-surface), habitat type (coast-low complexity and mangrove-high complexity), circadian cycle (sunrise–midday–sunset–night), and season (dry-rainy). The ichthyoplankton were collected using a supporting net (150 cm in length, 50 cm mouth diameter, 400μm mesh size) device for simultaneous collection on the surface and bottom. Circular tows (2.7–4 km/h) were carried out for 5 min. A total of 40,968 fish larvae were collected, belonging to 13 orders, 26 families, and 38 species. The highest larval abundance expressed as mean density (693 ± 916 ind/m3), richness (4.57 ± 3.46), Shannon-Wiener diversity (1.05 ± 48.48), and Pielou evenness (0.88 ± 0.3) were recorded in the bottom. The variance component analysis indicated that the most important factors to explain the larval abundance was the depth (15.55%), the period of the day (11.20 %) and the interaction between all factors (10.51 %). Fish larvae species as Achirus lineatus, Trinectes maculatus, Etropus crossotus, and Symphurus civitatium occupied only the bottom. Despite the low depth, a vertical stratification was observed in the physicochemical parameters, especially in the salinity, being greater in the bottom than in the surface during the two seasons and habitat type and it was related with higher values of abundance, richness, and diversity of ichthyoplankton.

Variation in Larval Fish Assemblage Dynamics Associated with Harmful Algal Blooms in a Temperate Estuary, South Africa

Eutrophication and concomitant harmful algal blooms (HABs) are on the rise globally and pose a threat to larval stages of fishes that rely on estuarine nursery habitats for growth and survival. The anthropogenically altered low inflow estuary (LIE), Sundays Estuary, South Africa, supports persistent and predictable HABs. This study investigated the effects of HABs on the environmental conditions and larval fish assemblage of this warm temperate nursery area. Sampling took place during the austral spring of 2016 and 2018 at three sites in the mesohaline zone where both larval fish abundance and HABs are known to reach maxima. Physico-chemical and phytoplankton data were collected during the day and night, while larval fishes were sampled after nightfall. Physico-chemical parameters and larval fish assemblages were compared by water column (surface and bottom) and sites within the mesohaline zone, years, and HAB intensity (hypereutrophic ≥ 2781 H. akashiwo cells•mL−1; standard ≥ 205 H. akashiwo cells•mL−1; none < 205 H. akashiwo cells•mL−1). A longer period of consecutive hypereutrophic bloom conditions was recorded during 2018 compared to 2016. Dissolved oxygen concentration was notably higher during hypereutrophic blooms (χ2 = 23.759, df = 2, P < 0.001) and reached a maximum of approximately 21 mg•L−1 during the day and 13 mg•L−1 at night. Density and similarity of estuarine resident larval assemblages were negatively correlated to supersaturated dissolved oxygen concentrations. Greater mean densities of estuarine resident larvae were recorded during hypereutrophic blooms compared to standard blooms and bloom absence and diversity was lower during 2018 when hypereutrophic bloom conditions were more persistent. These changes may have major implications for successful early development of fishes that rely on the Sundays Estuary and similar LIEs as a nursery.

Impact of transgenerational host switch on gut bacterial assemblage in generalist pest, Spodoptera littoralis (Lepidoptera: Noctuidae).

Diet composition is vital in shaping gut microbial assemblage in many insects. Minimal knowledge is available about the influence of transgenerational diet transition on gut microbial community structure and function in polyphagous pests. This study investigated transgenerational diet-induced changes in Spodoptera littoralis larval gut bacteriome using 16S ribosomal sequencing. Our data revealed that 88% of bacterial populations in the S. littoralis larval gut comprise Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. The first diet transition experiment from an artificial diet (F0) to a plant diet (F1), cabbage and cotton, caused an alteration of bacterial communities in the S. littoralis larval gut. The second transgenerational diet switch, where F1 larvae feed on the same plant in the F2 generation, displayed a significant variation suggesting further restructuring of the microbial communities in the Spodoptera larval gut. F1 larvae were also challenged with the plant diet transition at the F2 generation (cabbage to cotton or cotton to cabbage). After feeding on different plant diets, the microbial assemblage of F2 larvae pointed to considerable differences from other F2 larvae that continued on the same diet. Our results showed that S. littoralis larval gut bacteriome responds rapidly and inexplicably to different diet changes. Further experiments must be conducted to determine the developmental and ecological consequences of such changes. Nevertheless, this study improves our perception of the impact of transgenerational diet switches on the resident gut bacteriome in S. littoralis larvae and could facilitate future research to understand the importance of symbiosis in lepidopteran generalists better.

Seasonal patterns in the structure of the fish larvae assemblages in the lower Amazon River

Abstract This study assessed the phenology and functional structure of parental stocks of fish larvae, and evaluated how the species modulate their reproductive activities as a function of natural hydrological regimes in the lower Amazon River, Brazil. Larvae were collected using conical plankton nets monthly over two hydrological cycles between January and December 2013, and between May 2017 and April 2018. The collections were conducted around an alluvial island located near the municipality of Santarém, Pará, Brazil. After identification, individuals were classified into four functional groups (e.g., life‐history strategy, feeding habits, type of migration, and swimming‐performance/microhabitat‐use in the water column) based on species traits. The relationships between seasonal hydrology, environmental variables and larval assemblage structure were evaluated using multivariate analyses. A total of 31,347 fish larvae were collected, from nine taxonomic orders, 26 families, 40 genera and 53 species. The larval assemblages showed highly variable taxonomic and functional composition between different phases of the hydrological cycle (rising water, high water, receding water and low water) and were strongly influenced by environmental variables. Fish reproductive phenology in the lower Amazon is complex and distributed among the hydrological phases. The different ecological characteristics allow the species to withstand specific environmental conditions during each phase. Changes in the structure of larval assemblages indicate that hydrological variability is a key ecological factor influencing the reproductive dynamics of fish and reflects adaptive strategies used to reduce interspecific competition for space and food, maximising recruitment. The variation of fish reproduction across the hydrological cycle that we observed is a result of different ecological characteristics enabling species and functional groups to adapt to environmental conditions of each phase.

Spatial distribution and seasonal variation of fish larvae in the upper 200 m of the Philippine Sea

The Philippine Sea, owing to its complicated circulation pattern and the presence of numerous seamounts, is considered to be a hotspot for biodiversity and an important fishing ground. However, to date, few studies on ichthyoplankton in the Philippine Sea have been conducted. During the summer, autumn, and winter of 2020–2021, a series of investigations were conducted to study the spatial and temporal structure of fish larvae in the Philippine Sea. A total of 65 samples were collected by vertical hauling from a depth of 200 m to the surface. A total of 882 fish larvae representing 81 distinct taxa, 49 genera, and 23 families were identified. A seasonal pattern was also observed based on the differences in abundance and dominant taxa. The abundance of fish larvae was 11.35 ± 12.46 ind./100 m3 (mean ± sd.) in summer, 5.83 ± 7.03 ind./100 m3 in autumn, and 2.57 ± 2.73 ind./100 m3 in winter. The dominant species were Vinciguerria nimbaria, Encrasicholina punctifer, and Cyclothone sp. in summer, V. nimbaria, and Ceratoscopelus warmingii in autumn, and Diaphus spp., D. garmani, and Sigmops sp. in winter. A significant latitudinal variation in fish larvae assemblages was found via cluster analysis, and two geographic groups were separated by the northern boundary of the North Equatorial Current. In addition, the fish larvae species diversity also showed a significant latitudinal gradient in autumn, which disappeared in summer. Canonical correspondence analysis indicated that the structure of fish larvae assemblages was affected by average temperature, salinity, and net primary productivity in the upper ocean and sea level anomaly. All dominant species were associated with specific niche environments. This study suggests that latitudinal zonation of fish larvae also occurs in the oligotrophic low latitude Pacific Ocean and is enhanced in autumn. These results provide multi-seasonal baseline data of fish larvae assemblage in the upper Philippine Sea, being an important reference for the planning of marine protected areas in the high seas.

Marine top secrets: Ichthyoplankton in surface water uncover hidden knowledge on fish diversity and distribution

Most marine fish species exploit the upper water layers during their early life stages, thus accounting for a considerable component of neuston communities. During this period, the early life stages of fish are subjected to coastal or oceanic currents, and developed and dispersed to ultimate adult habitats according to their specific ecological requirements. Despite the ecological importance of these pelagic communities, knowledge about species assemblages of fish eggs and larvae, particularly in an oligotrophic sea is scarce. To overcome this knowledge gap and to evaluate the contribution of such communities to invasive biology, we collected neuston ichthyoplankton above the coastal, shelf and bathyal waters of the Eastern Mediterranean Sea (Israeli coast), an oligotrophic basin prone to a dynamic invasion of tropical biota. To obtain species-level knowledge of fish diversity, we used DNA-based methods that uncovered the presence of 137 species which is one third of the total local Osteichthyes fauna, evidencing that neuston ichthyoplankton can be significantly diverse. In addition, we showed that neuston communities can provide new knowledge regarding cryptic or rare species, and have a potential to contain new non-indigenous species, by documenting fish larvae of three unreported species for the Mediterranean Sea. Last, we posit that ichthyoplankton biomonitoring in surface water layer can provide a holistic perspective regarding fish biodiversity throughout the marine environment.

Predatory invertebrates indirectly impact leaf‐litter breakdown by different foragers in temporary wetlands

AbstractTemporary wetlands constitute a reservoir of fauna, many of which are endemic species well adapted to the typical dry–flooded cycle. The degradation of organic matter (both autochthonous and allochthonous) is an important process in temporary wetlands. Wetland animals like caddisfly and anuran larvae participate directly and indirectly in litter breakdown. Both groups also experience predation by invertebrates and vertebrates, which could alter the dynamics of litter breakdown. We used mesocosms to experimentally study the roles of caddisfly and tadpoles in leaf litter breakdown in the presence of a caged predator. We investigated how the presence of different types of forager (larvae of the caddisfly Verger vespersus and Batrachyla taeniata tadpoles) impacts leaf litter breakdown and also whether the presence of a caged belostomatid predator affected this process. Additionally, we investigated the behavioral response of B. taeniata tadpoles and V. vespersus larvae to predation risk cues from belostomatids previously fed on tadpoles or caddisflies. Our results indicated that only caddisfly larvae have a significant impact on litter breakdown. Predation risk did not influence the process, caddisfly larvae exposed to a caged predator reached the pupal stage more quickly than larvae that were not thus exposed, and tadpoles significantly reduced their activity in response to predation risk cues. None of the life‐history parameters of B. taeniata were affected by the predator, but tadpoles accelerated their development in warmer water. Our study is the first in South America to analyze the interactions between a common assemblage of tadpoles and caddisfly larvae and their impact on leaf litter breakdown when they experience predation risk. The model used here contributes to our understanding of ecosystem processes such as leaf litter breakdown and the impact of different biotic and abiotic variables when foragers co‐occur in the food webs of temporary aquatic systems.

Spatiotemporal and Environmental Dynamics of Abundances and Diversity of Larval Fish in Artificial Reef Edge Habitats of Kitros, Pieria (Northern Aegean Sea, Eastern Mediterranean)

Spatiotemporal and physiochemical influences on the abundances and diversity of ichthyoplankton were assessed in the Thermaikos Gulf and edge habitats surrounding the Pieria (Northern Greece) artificial reef complex. The collection of data was performed in edge habitats in the marine protected area near the artificial reef offshore of Kitros. Sampling trips occurred in each season of the spring, summer, and autumn in each year from 2015–2017. This artificial reef complex lies at a distance offshore of 11.5 km from Kitros and the delta of River Aliakmonas. A bongo net sampler was used to sample ichthyoplankton over a network of 16 sampling stations. Seventy species of larval fish were identified. The greatest measures of ichthyoplankton diversity were found during warmer seasons. Non-metric multidimensional scaling showed that seasons play a significant role in species assemblages, as months during the spring, summer, and autumn from different years clustered together. Ten groups of larvae were identified to the family or genus level, such as Arnoglossus spp., Callionymus spp., Crenilabrus spp., Gobius spp., Liza spp., Scorpaena spp., Solea spp., and Spicara spp. Overall, the species with the greatest abundance was the larvae of the European anchovy (Engraulis encrasicolus). The second genera (in order of highest abundance) were Gobius spp. followed by relatively abundant (but lesser numbers of) larvae representing the families Callionymidae, Centracanthidae, and Bothidae. The largest total abundances were found in July 2015 and September 2016. The biodiversity index indicated that measures of diversity were greater in July 2015, which was the only sampling performed in the middle of the summer, and indicated higher diversity in autumn 2015. The aim of this study was to present the assemblages of fish larvae in the marine protected area surrounding the artificial reef of Kitros Pierias as the result of a 3-year sampling program (2015–2017). The novelty of this study is that it is the only study of Ichthyoplankton ever performed in Greece with seasonal repetitions and densely located stations around a coastal marine protected area.

Effects of anomalous climatic events on the structure of fish larvae assemblages in the eastern Amazon

The reproduction of neotropical fish is linked to environmental stimuli that act as triggers in this process. Thus, it is possible to affirm that specific environmental changes can delimit most fish’s period and reproductive success. El Niño Southern Oscillation phenomena (ENSO) influence rainfall and, consequently, hydrological dynamics, affecting several fish population aspects, especially reproductive aspects. However, in the Amazon, empirical evidence of the effect of anomalous climatic events on fish reproduction is incipient. In this sense, we investigated the taxonomic and functional structure of parental fish larvae stocks and how species modulate their reproductive activities before (2013 and 2014) and during La Niña (2018) and El Niño (2019) events. The data evidence that the larval assemblages suffered alterations in the taxonomic and functional composition between the three analyzed periods and a pattern of temporal distribution with a high influence of environmental variables. Flow, pH, and electrical conductivity were the most important variables to modulate fish reproductive intensity between periods. The species seem to respond to combinations of these variables that reflect environmental conditions conducive to biological recruitment according to their ecological characteristics, allowing the perpetuation or decline of their abundance in each period. All species of commercial interest associated with the neutral period showed a sharp decline in the subsequent moments. These results suggest that the incidence of anomalous climatic events added to regional fisheries exploitation can negatively affect the phenology and demographic patterns of larvae assemblages on a short temporal scale. During the neutral period, the community was dominated by larvae of periodic large, herbivores, piscivores, epibenthic maneuverable, and nektonic burst swimmers. The decrease in the abundance of certain functional groups at the neutral and La Niña period favored an accelerated ecological succession during the El Niño period, due to the increase of species from basal trophic levels (planktivores), generalists (omnivores), highly resilient (intermediate strategists), sedentary, short-distance migrants and little commercially exploited. Thus, the results contribute to the understanding of the interactions between anomalous climatic events and the reproduction of fish with different ecological characteristics in the Amazon River.

Richness and structure of an Odonata larval assemblage of a cloud forest stream in western Mexico

Richness and structure of an Odonata larval assemblage of a cloud forest stream in western Mexico

Structural complexity of seagrass and environmental variables as a determinant of fish larvae assemblages in tropical coastal waters: Implications for seagrass management and conservation

Anthropogenic activities including climate change affect the development of structural complexity in seagrass and the state of environmental variables. It remains unclear whether these variables, alone or in combination, have an important influence on fish larvae assemblages. This study examined the influence of the structural complexity of seagrass meadows and various environmental variables on fish larvae assemblages in tropical coastal waters of Tanga, Tanzania. The study was conducted in four Thalassia hemprichii dominated seagrass meadows from June 2019 to January 2021. Multiple regression analysis indicated that the structural complexity of seagrass (canopy height, seagrass cover, and shoot density) and environmental variables (dissolved oxygen, temperature and salinity) were the foremost predictors for fish larvae assemblages; abundance and richness (R2 = 0.75, p = 0.0185, R2 = 0.54, p = 0.0396, respectively). Based on these findings, the structural complexity of seagrass and environmental variables are both important determinants of fish larvae assemblages in tropical coastal waters. The findings suggest that reducing anthropogenic activities that affect the development of structural complexity of seagrass and negatively impact environmental variables in seagrass meadows through more effective governance would result in increased production of fish larvae in meadows and, as a result, increased fish recruitment in tropical coastal waters.