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Temporal variations in the larval diet of Bregmaceros bathymaster on the coast of Jalisco and Colima during 1996 were analyzed. An increase in feeding incidence (from 10% in preflexion stage to 80% in transformation stage), in trophic spectrum (from 10 to 20 prey items), and in prey size (from 0.15 to 0.45 mm) was observed in relation to larval development. The index of relative importance showed that copepods in different stages of development dominated the larval diet with >80% of the total prey in preflexion larvae (nauplii and calanoids) and >60% in larvae in transformation (Euterpina spp. and calanoids). The Morisita index defined three groups of sampling stations based on larval diet and zooplankton environment. In the winter group, calanoid copepods, Euterpina spp., and Subeucalanus spp. dominated the diet, coinciding with the predominance of copepods in the environment. In the spring group, the cladoceran Penilia avirostris and ostracods dominated the diet and the zooplankton. In the summer/autumn group, calanoid copepods, Acrocalanus spp., and ostracods dominated the diet, whereas ostracods and copepods dominated the zooplankton. The results indicate that the temporal changes in the larval diet of B. bathymaster are associated with the variation in zooplankton, corresponding to three climate periods that affect the study area. [ABSTRACT FROM AUTHOR]

The purpose of this study is to analyse the spatial distribution of some groups of microzooplankton, including the more common potential prey of fish larvae (e.g. copepod nauplii and copepodites), in relation to oceanographic mesoscale processes in the vicinity of the Palamos Canyon (Catalan Sea, NW Mediterranean) as identified by a set of oceanographic and plankton data (60 μm mesh) obtained during a cruise in May 1992. The area was dominated by the Liguro-Provençal-Catalan current (slope current) that was influenced by the cold, fresh water discharged from the river Rhône and partial perturbations of its flow induced by the Palamos canyon. Spatial distribution of the plankton was examined by cluster analysis. Two main groups of stations and taxa were defined and named the “Oceanic group” and “Neritic group”, respectively. The Oceanic group was characterized by high concentrations of copepod nauplii and copepodites associated with slope current waters and its intrusions into the submarine canyon. In addition the presence of a large cyclonic eddy, detected by satellite data, at the eastern margin of the slope current could contribute to the concentration of organisms in this zone. The Neritic group was located on the shelf and slope areas and characterized by taxa of neritic–meroplanktonic habits together with copepod nauplii and copepodites. The latter were in lower abundances than recorded in the Oceanic group. The results suggest the microzooplankton groups analysed show well-defined distribution patterns related to the slope current and its interaction with the heterogeneity of the shelf. These in turn, affect the distribution of fish larvae and other predators. [ABSTRACT FROM PUBLISHER]

Larval diet and feeding habits of the marine fish Callionymus sp. Arnoglossus laterna larvae, two species co-occurring in the Catalan Sea (May, 1992), were compared. For the Callionymus sp. larvae, the dominant prey were Oithona spp. Oncaea sp. copepodites, and with less frequency Paracalanus sp. copepodites. For A. laterna larvae, the diet was composed only of Paracalanus sp. copepodites. Copepod nauplii were not important in the diet of these two species, although they were the most abundant zooplankter in the area. As larvae of both species grew, the size and number of prey increased. This tendency was more obvious in Callionymus sp. larvae, which reflected a greater prey diversity during all their early ontogeny. An analysis of covariance showed prey size increased with larval size in both species, but the prey consumed by Callionymus sp. larvae was larger than prey of A. laterna, corresponding to the larger mouth size (p<0.001). The results of this study show that these co-occurring species have different feeding strategies. [ABSTRACT FROM PUBLISHER]

This research study obtained the first morphological description of the Colorado snapper (Lutjanus colorado) larvae assisted by DNA barcoding as a molecular identification tool. Sixteen Lutjanidae larvae were separated from zooplankton samples and selected for this study. A fragment of the mitochondrial gene cytochrome oxidase subunit I (COI) of 658 bp was used in the analyses of intra- and interspecific genetic divergences; a neighbour-joining tree (NJ) of K2P distances was performed with reference sequences of 15 Lutjanidae species from the Northeastern Tropical Pacific. Genetic divergences and the NJ tree identified 16 larvae as L. colorado. Morphological investigations of larvae at different developmental stages were performed; similarities and differences are discussed in comparison to four species described previously for the Northeastern Pacific. Pigmentation patterns were the best diagnostic features, particularly the caudal melanophores, at least up to 12.4 mm body length., (© 2023 Fisheries Society of the British Isles.)

Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic-environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow.

Within the Sciaenidae family, the genus Micropogonias is composed of three recognized species along the Pacific coast of Mexico: Micropogonias altipinnis, M. ectenes, and M. megalops. These species exhibit overlapping diagnostic characters, which make species identification difficult. This study ties morphological differences (meristic, morphometry of body, and otolith) with DNA sequences (CO1 and 16S fractions of mtDNA and 28S of nDNA) among Micropogonias species in the Pacific. Meristic analysis showed a latitudinal variation among the three species in the number of rays, the number of gill rakers, and length of the longest spine of the dorsal fin. Discriminant analysis of morphometric characters (body and otolith) showed three morphological entities (p < 0.001). However, the mean genetic divergences among the three species with partial sequences of mtDNA (CO1 and 16S), and nuclear (28S) were lower than those reported at the interspecific level (>2%). Genetic results suggest that the three species are one species and that the differences in meristics and morphometry could be the result of phenotypic plasticity or incipient speciation. In this sense, M. ectenes and M. megalops are proposed as junior synonyms of M. altipinnis.

Bonefish leptocephali of the genus Albula are difficult to identify to the species level due to morphological similarities between two different species present in the Northeastern Pacific Ocean, A. esuncula and A. gilberti. In this study, 22 bonefish leptocephali (premetamorphic and early metamorphic), collected from two locations in the southern Gulf of California were identified as Albula gilberti by comparing 459 bp of their mitochondrial cytochrome b gene sequences to those of four other species of bonefish. The characteristics of these A. gilberti leptocephali were compared to those of previously described bonefish leptocephali in the region. No distinctive morphological characteristics (meristic and pigmentation) were found that differentiate premetamorphic leptocephali of A. gilberti from those of other Albula species, making species identification by molecular-genetics a necessity. In early metamorphic leptocephali some differences in horizontal eye diameter-head length ratio, number of rays of pelvic and anal fins and myomere of pelvic-fin origin may help to differentiate A. gilberti from A. esuncula.

Sciaenidae fish larvae were collected from the upper Gulf of California during September 2012 using a conical net (505 μm) through surface tows. These were pre-classified into four larval morphotypes, based on external characteristics (mainly meristic and pigmentation). Partial sequences of cytochrome c oxidase, subunit 1 and 16S rRNA (16S) genes of mitochondrial DNA, were used in molecular genetic identification from each larval morphotype. Genetic results indicated the identification of four larval morphotypes as Micropogonias megalops, Cynoscion othonopterus, C. reticulatus and Menticirrhus nasus. Pigmentation patterns of larvae described after molecular genetic identification made it possible to distinguish between M. megalops, M. nasus and C. othonopterus (postflexion). However, pigmentation was not reliable for differentiating between preflexion larvae of C. othonopterus and C. reticulatus. From these results, both morphological and genetic approaches were proposed as complementary tools in taxonomic studies of ichthyoplankton, particularly in early fish larvae identification of congeneric species with similar morphological characteristics.

Effects of geostrophic kinetic energy flux on the three-dimensional distribution of fish larvae of mesopelagic species (Vinciguerria lucetia, Diogenichthys laternatus, Benthosema panamense and Triphoturus mexicanus) in the southern Gulf of California during summer and fall seasons of stronger stratification were analyzed. The greatest larval abundance was found at sampling stations in geostrophic kinetic energy-poor areas (<7.5 J/m3), where the distribution of the dominant species tended to be stratified. Larvae of V. lucetia (average abundance of 318 larvae/10m2) and B. panamense (174 larvae/10m2) were mostly located in and above the pycnocline (typically ~ 40 m depth). In contrast, larvae of D. laternatus (60 larvae/10m2) were mainly located in and below the pycnocline. On the other hand, in sampling stations from geostrophic kinetic energy-rich areas (> 21 J/m3), where mesoscale eddies were present, the larvae of the dominant species had low abundance and were spread more evenly through the water column, in spite of the water column stratification. For example, in a cyclonic eddy, V. lucetia larvae (34 larvae/10m2) extended their distribution to, at least, the limit of sampling 200 m depth below the pycnocline, while D. laternatus larvae (29 larvae/10m2) were found right up to the surface, both probably as a consequence mixing and secondary circulation in the eddy. Results showed that the level of the geostrophic kinetic energy flux affects the abundance and the three-dimensional distribution of mesopelagic fish larvae during the seasons of stronger stratification, indicating that areas with low geostrophic kinetic energy may be advantageous for feeding and development of mesopelagic fish larvae because of greater water column stability., Competing Interests: The authors have declared that no competing interests exist.

We report the distribution of major and trace element concentrations in epipelagic zooplankton collected in the Northern Gulf of California in August 2003. The Bray-Curtis index defined three element assemblages in zooplankton: (1) major metals, which included only two elements, Na (3.6-17.0%) and Ca (1.0-4.8%). Na had its highest concentrations in the shallow tidally mixed Upper Gulf, where high salinity, temperature, and zooplankton biomass (dominated by copepods) prevailed. Ca showed its highest concentrations south of Ballenas Channel, characterized by tidal mixing and convergence-induced upwelling, indicated by low sea-surface temperature, salinity, and zooplankton biomass; (2) Six biological essential elements, like Fe (80-9,100 mg kg(-1)) and Zn (20-2,570 mg kg(-1)), were detected in high concentrations in zooplankton collected near Guaymas Basin, which had high surface temperature and chlorophyll a concentrations. (3) Metals of terrigenous origin, such as Sc (0.01-1.4 mg kg(-1)) and Th (0.03-2.3 mg kg(-1)), and redox-sensitive metals, like Co (3-23.8 mg kg(-1)); this was the assemblage with the largest number of elements (15). Both types of elements of assemblage 3 had maximum concentrations in the cyclonic eddy that dominates the summer circulation in the Northern region. We concluded that sediment resuspension by tidal mixing in the Upper Gulf, upwelling south of Ballenas Channel, and the cyclonic eddy were key oceanographic features that affected the element concentrations of epipelagic zooplankton in the Northern Gulf of California. Oceanographic mechanisms such as these may contribute to element incorporation in marine organisms in other seas.