Unveiling the Relationship Between Sea Surface Hydrographic Patterns and Tuna Larval Distribution in the Central Mediterranean Sea

Thunnus thynnus (Atlantic bluefin tuna, ABT) and other tuna species reproduce in the Mediterranean Sea during the summer period. Despite the Central Mediterranean Sea, the Strait of Sicily in particular, being a key spawning site for many tuna species, little is known on the effects of oceanographic variability on their larval distribution in this area. The abundance and presence-absence of larval specimens for three tuna species (ABT, bullet tuna and albacore) were modeled in order to examine their relationships with environmental factors, by analysing historical in situ information collected during seven annual surveys (2010–2016). The results revealed that most tuna larvae for the three species were found in the easternmost part of the study area, south of Capo Passero. This area is characterized by a stable saline front and warmer nutrient-poor water, and it has different environmental conditions, compared with the surrounding areas. The models used to investigate the presence-absence and abundance of the three species showed that ABT was the most abundant, followed by bullet tuna and albacore. The presence and abundance data collected are comparable with those of other spawning areas in the Mediterranean. Regarding biological and physical parameters, the results suggest that temperature, salinity, and day of the year are the key factors for understanding the ecological mechanisms and geographical distribution of these species in this area. Temperature affects the presence of ABT larvae and salinity, which, with a physical barrier effect, is a key factor for the presence-absence of bullet and albacore and for albacore abundance.

Seasonality modulates the direct and indirect influences of forest cover on larval anopheline assemblages in western Amazônia

Serious concerns have arisen regarding urbanization processes in western Amazônia, which result in the creation of artificial habitats, promoting the colonization of malaria vectors. We used structural equation modelling to investigate direct and indirect effects of forest cover on larval habitats and anopheline assemblages in different seasons. We found 3474 larvae in the dry season and 6603 in the rainy season, totalling ten species and confirming the presence of malaria vectors across all sites. Forest cover had direct and indirect (through limnological variables) effects on the composition of larval anopheline assemblages in the rainy season. However, during the dry season, forest cover directly affected larval distribution and habitat variables (with no indirect affects). Additionally, artificial larval habitats promote ideal conditions for malaria vectors in Amazonia, mainly during the rainy season, with positive consequences for anopheline assemblages. Therefore, the application of integrated management can be carried out during both seasons. However, we suggest that the dry season is the optimal time because larval habitats are more limited, smaller in volume and more accessible for applying vector control techniques.

Assessing the distribution and abundance of larval Longfin Smelt: What can a larval monitoring program tell us about the distribution of a rare species?

Following its listing as threatened under the California Endangered Species Act in 2009, Longfin Smelt (Spirinchus thaleichthys) became a focus of resource managers in the San Francisco Estuary. Water exports were identified as one of the factors affecting Longfin Smelt abundance, and managers were challenged with balancing freshwater flows through the Sacramento-San Joaquin River Delta between human and ecosystem needs. This balance becomes especially challenging during the winter and spring when Longfin Smelt are spawning. Resource managers identified that the impact associated with entrainment of larval Longfin Smelt in the winter was uncertain, and to understand and manage this risk, new data was needed. In 2009 the Smelt Larva Survey was implemented and has since sampled newly hatched larvae from January–March. Here, I analyze this data and ask specific questions regarding distribution and densities of the larvae throughout five regions of the Upper Estuary – Napa River, Suisun, Confluence, Northern Delta, and Southern Delta – with the goal of understanding the spatial and temporal patterns of larval distribution since 2009. I found that larvae were most prevalent in the Suisun, Confluence, and Northern Delta regions, and less common in the Southern Delta and Napa River regions. Larval Longfin Smelt densities changed following a recent drought and record low population abundances. Median per-station averaged densities ranged from 154 to 274 fish per 1,000 m3 between 2009 and 2013 but declined to 1 to 65 fish per 1,000 m3 from 2014 to 2019. This survey data demonstrates that Longfin Smelt reproductive output has declined since their listing in 2009 and that their distribution into the Southern Delta is low relative to the rest of the Upper Estuary. These results reaffirm the species’ continued decline since its listing, and that improving the abundance of spawning adults is one of the many important steps needed for long-term recovery and resilience.

Larval dispersal of Brachyura in the largest estuarine / marine system in the world

For the first time, this study monitored six sites in a wide transect with approximately 240 km radius on the Amazon Continental Shelf (ACS) every three months. The objective was to analyze the larval composition of Brachyura, its abundance in shallow/subsurface and oblique hauls, the extent of larval dispersion related to the estuary/plume, and to predict the probability of occurrence and abundance for the temperature, salinity, and chlorophyll- a profiles of the water column. A total of 17,759 identified larvae are distributed in 8 families and 25 taxa. The water salinity was the best predictor of larval distribution. The statistical models used indicated that Panopeidae and Portunidae larvae are more frequent and more likely to occur in shallow water layers, while Calappidae occur in deeper layers, and Grapsidae, Ocypodidae, Sesarmidae, Pinnotheridae and Leucosiidae occur similarly in both strata. The larval dispersion extent varies among families and throughout the year while the groups are distributed in different salinities along the platform. The probability of occurrence of Portunidae is higher in ocean water (> = 33.5); Grapsidae, Panopeidae, and Pinnotheridae is higher in intermediate and ocean salinity waters (25.5 to 33.5); Ocypodidae, Sesarmidae and Calappidae is higher in estuarine and intermediate salinity waters (5 to 25.5), whereas Leucosiidae, euryhaline, occur in all salinities (5 to 33.5). Furthermore, the Amazon River seasonal flow and plume movement throughout the year not only regulate the larval distribution and dispersion of estuarine species but are fundamental for the ACS species, providing the necessary nutrient input for larval development in the region plankton.

Larval distribution of the ocean sunfishes Ranzania laevis and Masturus lanceolatus (Tetraodontiformes: Molidae) in the Sargasso Sea subtropical convergence zone

Sunfishes or Molidae are a rarely encountered family within the teleost order Tetraodontiformes and most details of their reproductive biology including times and places of spawning and their larval ecology are rather unclear. Spawning of two species of Molidae was suggested in the Sargasso Sea before, yet comprehensive data on larval distribution from this area or elsewhere have never been published. Here we report on the abundance and size distribution of 383 sharptail mola (Masturus lanceolatus) and slender sunfish (Ranzania laevis) larvae, present novel information on their larval growth and development and test correlations with prevailing hydrographic data. Only 18 mostly larger Masturus larvae were caught evenly distributed over the study area and with no obvious hydrographic preferences. We conclude that there was no active spawning of M. lanceolatus in the area during the time of the cruise. In contrast, Ranzania larvae were caught primarily inside and south of a thermal frontal zone with increasing abundances toward warmer surface layers in the southeast of the study area. Due to the consistent presence of young Ranzania, it can be assumed that spawning activity was ongoing throughout the month of April, 2015. Our findings confirm the Sargasso Sea as a spawning area for R. laevis.

Helicoverpa zea (Lepidoptera: Noctuidae) Preference for Plant Structures, and Their Location, Within Bt Cotton Under Different Nitrogen and Irrigation Regimes

Helicoverpa zea Boddie is a common economic pest of cotton (Gossypium hirsutum L.), including transgenic cotton varieties that express Bacillus thuringiensis (Bt). Helicoverpa zea oviposition is similar in Bt and non-Bt cotton, but behavior of H. zea larvae can be different in the presence of Bt, with neonates moving away from terminals faster in single-toxin Bt than non-Bt cotton or avoiding Bt-treated diet in the lab. We quantified H. zea oviposition and larval distribution on structures within cotton plants in small plot experiments of Cry1Ac + Cry1F cotton for 2 yr under different irrigation and nitrogen treatments. More eggs were oviposited on plants receiving nitrogen application during 2016 and on leaves in the top section of irrigated plants during 2017, but other treatment effects on eggs or larvae were minimal. Helicoverpa zea eggs were most common on leaves in the top third of plants at position zero and middle section of cotton plants throughout the season, but some oviposition occurred on fruiting structures as well. First and second instars were more common on squares in the top section of plants during 2016 and bolls in the middle and lower sections during 2017 due to oviposition lower in the canopy during 2017. During both years, third through fifth instars were more common on bolls in the middle and lower section of plants closer to the main stem. These findings have resistance management implications as extended larval feeding on bolls could optimize nutrition, decrease Bt susceptibility, and potentially influence behavioral resistance.