Distribution and abundance of planktonic mollusks along a longitudinal gradient in the Southeastern Pacific off Chile

The objectives of this research were to estimate the abundance of the main groups of planktonic mollusks (meroplanktonic larvae, holoplanktonic gastropods and cephalopod paralarvae), and relate these groups to the physical-chemical water properties along a longitudinal gradient between Caldera, on the coast of mainland Chile, and the Easter Island ecoregion (Rapa Nui Island and Salas y Gómez Island), in the Southeast Pacific Ocean. Plankton samples were collected over the course of the CIMAR 21-Islas Cruise, from October to November 2015, at 33 oceanographic stations via vertical hauls of a WP2 net (180-µm mesh size) from a maximum depth of 300 m to the sea surface. Mollusks were sorted, counted and initially assigned to Class rank, later being identified to lower taxonomic ranks. Planktonic mollusks were obtained at all stations, and were composed of 92.7% of Gastropoda and 7.3% of Bivalvia. The total abundance of mollusks varied between 55 and 4,922 individuals 100 m-3.Euthecosomate gastropods exhibited the highest occurrence within the oceanic area. Meanwhile, no paralarvae were captured. Differences in the composition of planktonic mollusks between the continental and oceanic zones were evident. Bivalve larvae increased their abundance in warmer, salty and vertically mixed waters. These results are the first record of meroplanktonic mollusks in waters near the Chilean oceanic islands, and suggest that planktonic mollusks display spatial variation at the scale of the South Pacific Basin, which could be related to the hydrographic conditions and the water column structure.

Longitudinal gradient in the Camptocercus lilljeborgi Schoedler, 1862 species group (Cladocera: Anomopoda: Chydoridae)

A detailed study of morphology of the rare phytophilous cladoceran Camptocercus lilljeborgi Schoedler, 1862 revealed that populations from Eastern Siberia and Far East of Russia belong to a new species. C. smirnovi sp. nov. differs from C. lilljeborgi in body shape, morphology of ventral margin of valves, morphology of postabdomen, and length of IDL seta 1 of the thoracic limb I. C. lilljeborgi s. str. is distributed in Europe and Western Siberia, therefore, the lilljeborgi-group provides an example of the western-eastern differentiation in Northern Eurasia. Some characters of taxa from the lilljeborgi-group are convergently similar to the characters of the species of genus Graptoleberis Sars, 1862; both groups are adapted to a snail-like crawling on the surface of water macrophytes.

Occurrence and Habitat Characteristics of Aurelia sp. Polyps in a High-Latitude Fjord

Causes and consequences of jellyfish bloom formation are subject to controversial discussions worldwide. While medusae have been studied to a broader extent, the knowledge on polyp stages of scyphozoans is limited thus hampering reliable prediction of jellyfish bloom formation. This study describes the occurrence, abundance, habitat characteristics and interactions of scyphozoan Aurelia sp. polyp colonies with other fouling organisms in intertidal and subtidal sectors of Trondheimsfjorden (Norway). In total, 982 polyps were found on 70 substrata of varying material types during a field survey in spring-summer 2018 along a longitudinal gradient within and outside Trondheimsfjorden. The polyps were identified as Aurelia sp. based on molecular species identification. Most polyps were found in bays with macroalgae canopy on the down facing side of artificial and natural substrata (rocks, concrete, iron) and inside rock cracks. Polyp microhabitats included the surface of Ascidia mentula (solitary ascidian), increments of Pomatoceros triqueter (polychete) tubes and dead Balanus balanoides (barnacle) shells. Based on the deployment of settling plates, abundance of Aurelia sp. polyps ranged from 1.2 (± 0.7) to 0.12 (± 0.07) polyps cm–2. Settlement occurred either directly on the PVC settling plates or as epibionts on the ascidian Ascidia mentula and on barnacle shells of Balanus balanoides. This study provides insights into the potential of local Aurelia sp. polyps contributing to the seasonal occurrence and abundance of Aurelia sp. in fjord systems, where intensive blooms occur annually.

Gully controlling practices associated with soil geotechnical properties in the subhumid Ethiopian highlands

Check dams are business as usual practices used to avert gully erosion development and sedimentation in the downstream areas of the humid highlands of Ethiopia. We investigated the status of check dams and their relationship with geotechnical soil properties in the sub-humid Fogera floodplain. The density of gullies in the area was more sever having about 3.6 km km-2 which shows the severity of gully erosion. Thirty-two dams constructed and monitored over one rainy season. In the beginning of the rainy season, all the dams filled up with sediments, and at the end of the monitoring period ninety five percent of them had destroyed and the remainings had partially destroyed and had sediments accumulated on one side of the gully bank. The longitudinal gradient of streams above the dams decreased due to sedimentation. The morphological change of the gully showed an increase in width-depth ratio, gully bank erosion, and sediment aggradation in the gully bed. We found that the amount of sediments deposited behind the dams were higher than the amount of eroded material. The higher clay content and Atterberg limits increased soil erodibility once the gully channel formed. The erodibility and saturation in these soils were highly contributing to gully development and reducing the effectiveness of check dams. In conclusion, it is better to adopt an integrated novel practice to control gullying than solely using check dams.

Shift of seed mass and fruit type spectra along longitudinal gradient: high water availability and growth allometry

Propagule traits vary among biomes along geographical gradients such as longitude, but the mechanisms that underlie these variations remain unclear. This study aims to explore seed mass variation patterns of different biome types along a longitudinal gradient and their underlying variation mechanisms by involving an in-depth analysis on the variation of seed mass, fruit type spectra, growth forms and dispersal mode spectra in Inner Mongolia and northeastern China. Plant community characterization and seed collection were conducted in 26 sites spreading over five vegetation types and covering 622 species belonging to 66 families and 298 genera. We found there are significantly declining trends for mean seed mass, vertebrate-dispersed species richness and fleshy-fruited species richness along a longitudinal gradient from forests to desert grasslands. However, we also found the lowest average seed mass and the smallest proportion of species dispersed by vertebrates occurring at typical grasslands in the five biomes. The variations of average seed mass display high congruence with transition of growth form spectra. The selection for these propagule attributes is driven mainly by climatic factors such as precipitation, temperature, soil moisture and evaporation, as well as by internal biotic factors such as growth forms, canopy coverage and leaf area (Ackerly and Donoghue, 1998). A hypothesis was provided that environmental factors and botanical traits that favor greater water availability lead to emergence (or speciation) of species with large seeds or fleshy fruits with high water content. Due to greater water availability and increasing leaf area, much more photosynthate (photosynthesis production) and allometric growth then ultimately increase the biome average seed mass from west to east. Phylogenetic signal or diversity are not found to be significantly involved in the effect on the patterns. A novel mechanistic framework and mathematical model are provided to expound seed variation among species or biomes.

A cascade of dams affects fish spatial distributions and functional groups of local assemblages in a subtropical river

Dams reduce the longitudinal connectivity of rivers and thereby disrupt fish migration and the spatial distribution of species, impacts that remain poorly studied for some Neotropical rivers from mega-diverse basins. We investigated the spatial distribution of fish species with different trophic and movement/reproductive/size characteristics to assess how functional groups have responded to a cascade of dams on the Uruguai River in southern Brazil. Fish abundance, biomass, and species composition were evaluated at eight locations along the longitudinal gradient. The fish assemblage in the upper stretch was mainly characterized by small and medium-sized species at higher trophic levels, whereas the sites located furthest downstream displayed more medium and large-sized species, including many carnivorous species. Species with high fecundity, seasonal migrants, and catfishes with internal fertilization were common in the river´s middle and lower reaches. Detritivorous species dominated areas distant from the dams. Overall, functional diversity of local fish assemblages was greater in lower reaches. The cascade of dams has impacted the distribution of functional groups of local fish assemblages of Uruguai River. The alteration of functional groups in upper reaches of the river has potential consequences for ecosystem processes and services, such as nutrient cycling and fisheries.