Spatial distribution of Euphausiids (Euphausiacea) off Malpelo Island, Colombian Tropical Pacific / Distribución espacial de Eufáusidos (Euphausiacea) en la Isla Malpelo, Pacífico Tropical de Colombia

Abstract Euphausiids migrate vertically in the water column as part of their diel cycle. These migrations make them a key element in the biological pump of the pelagic environment. In order to evaluate the vertical distribution of euphausiids around Malpelo Island (3.8 - 4.2 N & 81.4 - 81.8 W), we took stratified zooplankton samples (0-50, 50-100, and 100-150 m) during the Pacífico-ERFEN campaign in September 2012. A total of 10 species belonging to four genera were identified. Euphausia diomedeae was the most abundant species in the 0-50 and 100-150 m layers, whereas E. distinguenda was the most abundant species in the 50-100 m layer. Based on quasi-Poisson generalized linear distribution models we found that abundance in the 50-100 m layer was significantly higher than in the 100-150 m layer (t= 3.05, p < 0.05). There were no significant differences associated with sampling hour (diurnal/nocturnal) (t= 0.07, p = 0.94). We calculated a vertical distribution index (VDI) based on abundance, showed that euphausiid species were concentrated in the 50-100 m layer during day and night. Calyptopis larvae dominated in abundance at all depth layers, followed by furcilia larvae, juveniles, and adults. The abundance of the latter increased gradually from the most superficial layer to the deepest layer, whereas juveniles showed the opposite pattern. This is the first study to describe the taxonomic composition, and vertical and spatial distribution of euphausiids associated with Malpelo Island, Colombian Pacific.(AU)

Resumen Los eufáusidos son organismos que realizan migraciones verticales en la columna de agua como parte de un ciclo nictemeral, estas migraciones los convierten en un elemento clave del ambiente pelágico. Con el propósito de evaluar la distribución vertical de los eufáusidos alrededor de la isla Malpelo (3.8-4.2 N & 81.4-81.8 W), se tomaron muestras estratificadas (0-50, 50-100 y 100-150 m) de zooplancton durante la campaña Pacífico-ERFEN de septiembre 2012. Se identificaron un total de 10 especies pertenecientes a cuatro géneros, siendo Euphausia diomedeae la especie más abundante en los estratos 0-50 y 100-150 m, mientras que E. distinguenda fue la especie más abundante en el estrato de 50-100 m. Con base en modelos lineales generalizados con distribución quasipoisson se encontró que la abundancia del estrato de 50-100 m fue significativamente mayor que la del estrato de 100-150 m (t= 3.05, p < 0.05), sin embargo no se detectaron diferencias significativas asociadas con la hora del muestreo (diurna/nocturna) (t= 0.07, p= 0.94). Con base en la abundancia se construyó un índice de distribución vertical (IDV) encontrando que las especies de eufáusidos estuvieron concentradas en el estrato de 50-100 m durante el día y durante la noche. En los tres estratos de profundidad dominaron en abundancia las larvas calyptopis, seguido de las larvas furcilias, los juveniles y los adultos. Estos últimos incrementaron su abundancia gradualmente desde el estrato más superficial hasta el más profundo mientras que los juveniles tuvieron un patrón opuesto. Este es el primer trabajo que describe la composición taxonómica y distribución vertical y espacial de los eufáusidos asociados a la isla Malpelo, Pacífico colombiano.(AU)

Is vertical migration in Antarctic krill (Euphausia superba) influenced by an underlying circadian rhythm?

Antarctic krill (Euphausia superba) is a keystone species in the southern ocean ecosystem where it is the main consumer of phytoplankton and constitutes the main food item of many higher predators. Both food and predators are most abundant at the surface, thus krill hide in the depth of the ocean during the day and migrate to the upper layers at night, to feed at a time when the predatory risk is lowest. Although the functional significance of this diel vertical migration (DVM) is clear and its modulation by environmental factors has been described, the involvement of an endogenous circadian clock in this behaviour is as yet not fully resolved. We have analysed the circadian behaviour of Euphausia superba in a laboratory setting and here we present the first description of locomotor activity rhythms for this species. Our results are in agreement with the hypothesis that the circadian clock plays a key role in DVM. They also suggest that the interplay between food availability, social cues and the light:dark cycle acts as the predominant Zeitgeber for DVM in this species.

A short note on a euphausiid, Euphausia pacifica, an important food source to demersal fishes in Uljin area, the eastern coast of Korea.

Gut contents of two species of demersal fishes, Pleurogrammus azonus and Dasycottus steiger were examined to understand the importance of a euphausiid, Euphausia pacifica as prey of demersal fishes at coastal waters off Uljin, the eastem Korea where aggregations of large amounts of the euphausiids were found. Euphausiids were significantly important food source to the species of fishes examined. All of the stomachs of P. azonus examined contained euphausiids (% of a food item frequency occurred, F = 100%) in March and June 2003. Individual numbers of euphusiids in the guts ranged from 10 to 540 individuals per gut. Percents of individual number of food item were 99.60 and 99.96 for euphausiids in March and June 2003, respectively The guts of D. steiger also frequently contained euphausiids (F = 86.67 and 79.20% in October 2002 and June 2003, respectively), while amphipods (F = 36.67% and 16.17%,) and other fishes (F = 33.33% and 45.80%) were also often observed. Pleurogrammus azonus preferred larger euphausiids with size range 16.9-28.4 mm, while the range of euphausiids distributed in the ambient water column was much broader (from eggs to adults).

Sticholonche zanclea (Protozoa, Actinopoda) in fecal pellets of copepods and Euphausia sp. in Brazilian coastal waters / Sticholonche zanclea (Protozoa, Actinopoda) em pelotas fecais de copépodos e Euphasia sp. em águas costeiras brasileiras

Fecal pellets produced by mesozooplanktonic copepods (Centropages velificatus and Paracalanus parvus) and macrozooplanktonic Euphausiacea (Euphausia sp.) were examined using scanning electron microscopy. Fragments of the protozoan Sticholonche zanclea were found in both copepod and in Euphausia sp. fecal pellets, even when the abundance of the protozoan in the water was low. The results suggest that S. zanclea is an important food resource for different trophic levels, including meso- and macrozooplankton, in Brazilian coastal waters.

Pelotas fecais produzidas por copépodos mesozooplanctônicos (Centropages velificatus e Paracalanus parvus) e por Euphasiacea macrozooplanctônico (Euphasia sp) foram examinadas em microscópio eletrônico de varredura. Fragmentos do protozoário Sticholonche zanclea foram encontrados nas pelotas fecais dos copépodos e de Euphasia sp, mesmo quando a abundância do protozoário no ambiente foi bastante reduzida. Os resultados sugerem que S. zanclea pode representar um importante recurso alimentar para diferentes níveis tróficos, incluindo meso e macrozooplâncton, em águas costeiras brasileiras.

Eufáusidos (Crustacea: Malacostraca) del centro y sur del Mar Caribe mexicano / Euphausiids (Crustacea: Melacostraca) from the southern Mexican Caribbean Sea]

The composition, abundance and distribution of euphausiids from the southern part of the Mexican Caribbean Sea (August 1986) were sampled during the ARCOMM I cruise on board the R/V "Justo Sierra" of UNAM. Sampling was done using a Bongo-net (0.5 mm mesh size) performing oblique hauls from 200 m to the surface at 28 stations. Of the total euphausiid numbers, the most abundant species was Stylocheiron carinatum (49), followed by Euphausia americana (9.8) and E. tenera with (7.8). The highest total density and that of the three most abundant species occurred during the night sampling, and probably was related to vertical migration patterns. The Bray-Curtis index revealed three station assemblages, related to the day-night variations of the euphausiid community. Species were distributed mainly in the oceanic area, and were absent in the neritic zones. The local fauna shows a strong affinity for the euphausiid community of the Gulf of Mexico and other areas of the Caribbean Sea. Four species are considered to be new records for the western Caribbean Sea.

Two new species of Euphumosia from Papua New Guinea (Diptera: Calliphoridae)

Two new species of the calliphorid blow flies are described from Papua New Guinea under the names of Euphumosia lopesi and E. robertsi. Body coloration and mesonotal pattern are characteristic and differ from those of the closely allied species, E. evittata Togerson & James, 1967.