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Del 29 de marzo al 30 de abril 2016 se realizó el Crucero de Evaluación Hidroacústica de Recursos Pelágicos 1603-04. 133 muestras de zooplancton fueron recolectadas utilizando una red Hensen de 300 µm de abertura de malla, operada en arrastres verticales con el buque parado desde 50 m de profundidad máxima a la superficie. Huevos y larvas de 44 familias y 66 especies de ictioplancton fueron determinados. Engraulis ringens fue la especie más abundante, cuyos huevos y larvas variaron entre 3 y 51.162 huevos.m-2, y de 3 a 936 larvas.m-2, con importantes concentraciones entre Pimentel y Pisco. Vinciguerria lucetia también presentó importantes concentraciones con valores de 3 y 4.272 huevos.m-2 y 3 y 261 larvas.m-2, los cuales se distribuyeron principalmente por fuera de la plataforma continental, con altas densidades entre bahía Independencia y Atico, y frente a Paita y Huarmey. Además del ictioplancton se determinaron 14 especies de eufáusidos, siendo Nyctiphanes simplex, la especie más abundante, representando el 49% del total de la abundancia, distribuido principalmente en la zona costera. Los biovolúmenes de zooplancton oscilaron entre 0,1 y 60,0 mL/muestra, con valores mayores a 10 mL/muestra ubicados desde Talara hasta San Juan de Marcona, principalmente por fuera de las 10 mn. La abundancia y distribución de los grupos reportados se asociaron a las condiciones ambientales registradas durante este crucero. ABSTRACT: The Instituto del Mar del Perú (IMARPE) conducted the 1603-04 hydroacoustic assessment cruise for pelagics between March 29 to April 30, 2016. We used a Hensen net with a mesh size of 300 µm for collecting 133 zooplankton. This net was deployed in vertical trawls with the vessel stationary from 50 m maximum depth to the surface. Eggs and larvae from 44 families and 66 ichthyoplankton species were determined. Engraulis ringens was the most abundant species, and its eggs and larvae ranged from 3 to 51,162 egg.m-2, and 3 and 936 larvae.m-2, respectively, with significant concentrations between Pimentel and Pisco. Vinciguerria lucetia also presented important concentrations with values of 3 and 4,272 egg.m-2 and 3 and 261 larvae.m-2, which were distributed mainly outside the continental shelf, with high densities between Independencia Bay and Atico, and off Paita and Huarmey. Besides ichthyoplankton, we determined 14 euphausiid species with Nyctiphanes simplex being the most abundant species (49% of the total abundance), distributed mainly in the coastal zone. Zooplankton biovolumes ranged between 0.1 and 60.0 mL/sample, with values greater than 10 mL/sample observed from Talara to San Juan de Marcona, mainly out of 10 nm. The environmental conditions observed during this cruise influenced the abundance and distribution of the aforementioned groups.

Seasonal distribution of biomass and somatic growth, molt, and egg production rates of Nyctiphanes simplex were estimated in the Gulf of California (November 2005, January 2007and July 2007) and associated with 12 environmental variables to define the conditions in which the higher biomass production rates occur. Daily growth rates, estimated from shipboard incubations, indicated that N. simplex did not grow or decreased in size in all the seasons, with higher proportions of animals in these 2 growth categories in July (21 and 52%, respectively) than in January (7 and 43%) and November (35 and 12%). Thus, the proportion of individuals that grew was higher in November (53%) and January (50%) than in July (27%). Mean juvenile and adult intermolt period (IMP) based on direct measurements was 5 d in January (range: 3 to 7 d), 3.8 d in July (2 to 8 d) and 4.4 d (3 to 7 d) for September to October 2010 (used as proxy for November, since not enough IMP data were available for that month). Calculations based on the inverse molting rate method estimated higher mean IMP (6.7 d; range 4 to 60 d). N. simplex mean (±SD) juvenile and adult daily total biomass production rate was 0.16 ± 0.13 mg DW m

We analyzed size-dependent variations in spatial patchiness of the eight numerically dominant euphausiid species in the California Current System (Euphausia pacifica, Nematoscelis difficilis, Nyctiphanes simplex, Thysanoessa gregaria, Euphausia recurva, Euphausia gibboides, Thysanoessa spinifera, and Euphausia eximia). Patchiness was measured by using a count-based statistic using euphausiid densities and applied to 11 yr of detailed size-specific enumerations from the California Cooperative Oceanic Fisheries Investigations program. We rejected the hypothesis of size-independent patchiness for seven of the eight species. The most common pattern observed was a "U-shaped" curve, showing elevated patchiness in the smallest size classes, a rapid decrease in patchiness of intermediate-sized euphausiids, and a later increase in patchiness of adults following the onset of reproductive maturity. These size-dependent changes parallel ontogenetic changes in spatial dispersion observed for some marine fishes. The initial descending limb of the patchiness curve appears to be caused by turbulent diffusion, while the later ascending limb of the curve is consistent with the onset of predator-induced aggregation behavior. The patterns were surprisingly consistent across years and different reproductive characteristics (egg-brooding vs. broadcast spawning euphausiids). © 2010, by the American Society of Limnology and Oceanography, Inc.

This essay attempts to summarize and hypothetically reconstruct the original condition for there productive strategy and hatching mechanisms of the family Euphausiidae (Order Euphausiacea). Comparison is made of the hatching mechanisms and hatching success rates among five broad cast-spawning ( Euphausia pacifica, Euphausia eximia, Euphausia distinguenda, Thysanoes saspinifera , and Thysanoessa inspinata ) and two sac-spawning euphausiid species ( Nematoscelis difficilis and Nyctiphanes simplex ) collected from the Oregon coast, Bahia Magdalena (west coast of Baja California peninsula), and Gulf of California. These along with the discovery of a novel source of embryomortality during hatching for broad cast-spawning species, and recently published genetic and phylogenetic information of the euphausiids, support the hypothesis that hatching as a free-living nauplius is a reversed character within the Order Euphausiacea in comparison with species be longing to ot her orders in the Class Crustacea. The hatching of embryosat nauplius stage, with distinct hatching mechanisms, appears repeatedly and intermittently in the Euphausiidae family phylogeny both in euphausiids with broad cast and sac-spawning reproductive strategy.This may represent a condition reemerging well back in crustacean phylogeny, even though it is not necessarily primitive among the Order Euphausiacea as a whole. Mecanismos de eclosion y muerte de embriones de eufausidos durante el proceso de eclosion ?Son estas evidencias que expliquen una reversion evolutiva de nauplios de vida libre? En este ensayo se intenta resumir y reconstruir la condicion hipotetica original de las estrategias de reproduccion y mecanismos de eclosion de la Familia Euphausiidae (Orden Euphausiacea). Se hace la comparacion de los mecanismos y tasas de exito de eclosion de cinco especies desovadoras externas ( Euphausia pacifica, Euphausia eximia, Euphausia distinguenda, Thysanoessa spinifera y Thysanoessa inspinata ) y dos especies desovadoras en saco ovigero ( Nematoscelis difficilis y Nyctiphanes simplex ) de la costa de Oregon, Bahia Magdalena en la costa oeste de la peninsula de Baja California, y Golfo de California. Esto, junto con el descubrimiento de mortalidad asociada al proceso de eclosion en especies con desove externo y la reciente informacion publicada sobre genetica y filogenetica de los eufausidos, apoyan la hipotesis de que la eclosion de nauplios de vida libre es una caracteristica revertida dentro del Orden Euphausiacea, en comparacion con especies de otros ordenes dentro de la clase Crustacea. La eclosion de los embriones en el estadio nauplio, con distintos mecanismos de eclosion, aparece intermi tentemente a lo largo de la filogenia de las especies de la Familia Euphausiidae, tanto en especies desovadoras externas como en desovadoras ensaco ovigero. Esta eclosion en estadio nauplio aparentemente representa una condicion reemergente de antepasados en la filogenia de crustaceos, y por lo tanto, no es necesariamente una condicion primitiva entre las especies de la Orden Euphausiacea.

Euphausiid abundance data from broadly based California Cooperative Oceanic Fisheries Investigation surveys in California and Baja California sectors of the California Current provided a time series distinguishing periodic, rhythmic and irregular species patterns. Comparisons with environmental indexes indicate significant correlations with warm-water species, most notably in coastal Nyctiphanes simplex. Oceanic warm-water species were similarly, but less extremely, allied with an index. Coastal warm-water N. simplex was uncommon off southern California before the atmospheric regime shift of the 1970s. It assumed a post-1978 pattern of rhythmic biannual abundance increases and decreases during 1981–2000. The near-tropical oceanic Euphausia eximia and Pacific Central subtropicals patterned similarly, but was more periodic than rhythmic. Euphausia pacifica, the most dominant and broadly ranging Euphausia species, peaked at irregular but distinct bi-decadal abundances during 6 strong La Nina episodes. The peaks uniformly collapsed by 90%, becoming El Nino-associated minima. The cold-water coastal northern species Thysanoessa spinifera frequently ranged far south off Baja California before 1960 but became limited to Central California in the 1980s. The importance of T. spinifera off the Californias is small compared with northern regions, but it extends to southern upwelling centers contributing to dominance, here, by cold-water euphausiids. Decadal periodicity of species abundances decreased in the 1990s, when trends became more common. Differences among sectors were minimal between the two Californias, but were often distinct between southern California and Central Baja California. Species abundances, comparing pre- and post-climate shift species averages, differed insignificantly for all species when logarithmic values were used. With arithmetic values, most 1977–1998 average values were the greater, but with large standard deviations.

Laguna Ojo de Liebre is part of El Vizcaino Biosphere's Reserve, one of the largest protected natural areas in the world. The contribution of seaweeds to the lagoons' total biomass had not been previously quantified. The purpose of this study was to evaluate the spatial and temporal variations of seaweed biomass in the lagoon. Seaweed samples were taken every season during 1995 at six sampling stations distributed throughout the lagoon. Total specific biomass of seaweeds was at its peak in the summer, and minimum in spring. The highest total annual biomass was found at Isla Brosa in the lagoon's central portion, and the lowest in El Datil at the head. The seasonal and spatial variation of biomass in the lagoon is related with species richness and environmental parameters. Potentially important species in terms of biomass, wide spatial and temporal distribution, and potential use were: Spyridia filamentosa, Entheromorpha clathrata, Dasya baillouviana, Hypnea valentiaeand Sargassum sinicola .Using PCA three groups of stations were defined: one chiefly at the lagoon's mouth, another comprised the islands in the central portion, and the last in the lagoon's head. Palabras clave: Tendencias espaciales, Laguna Ojo de Liebre, Nyctiphanes simplex, Seaweed, spatial, seasonal

We collected Nyctiphanes simplex in Barkley Sound, Canada (48°54′N, 125°6′W) between May and September 1998. This was during the most intensive ENSO (El Nino Southern Oscillation) event recorded and when southward current velocities were anomalously low. This is a range extension of about 330 km NNW of where N. simplex was collected previously by plankton sampling gear and about 65 km NNW of where it was found in fish stomachs. Animals ranged between 10 and 20 mm total length and were at various states of maturity. We present length-frequency and maturity stage distributions as well as length-mass relationships. Results from an ongoing herring diet monitoring programme showed that they did not feed on N. simplex.

"retrospeciive anaiysis oi zooplankton volumes (1951 to 1996) was performed for the area between Punta Baja (30°N) and Punta Abreojos (26 ?ON) in relatlon to the warming anomaly that has taken place in the California Current System during the last 2 decades. The seasonal cycle of median standing stock of zooplankton In this area showed a moderate alternation between h~gh values from June to October (median monthly volumes between 86 and 108 m1/1000 m") and low values from Kovember to May (58 to 77 m1/1000 m3). The quarterly long-term means of zooplankton volumes were the lowest in winter, as were wind speeds. The standard deviations associated with the long-term means indicated interannual variability was higher than seasonal variability. The time series showed an interval of high zooplankton volume between 1952 and 1957. Following the strong ENSO (El Nifio Southern Oscillation) of 1957-1958, a period of low values occurred which extended into the early 1960s. There was a slow recovery of zooplankton biomass through the rest of the 1960s, but it did not reach the earlier high values. Available data suggest the increasing trend reached a peak in 1975. Sub- sequently, from 1976 to the ENSO of 1982-1983, the biomass decreased. For the remainder of the 1980s, the few existing data showed an erratic behavior of the biomass. In the 1990s, there has been a decrease to values even lower than those observed durlng the 1957-1958 ENSO. Nonseasonal anom- alles for zoop1.ankton and environmental variables were significantly different (p < 0.001) anlong decades but not between the northern (30" to 28" N) and southern (28" to 26" N) areas. The decrease in zooplankton volume in this region over the last 2 decades is less than that reported for the Southern California Bight. This may be partly caused by seasonal northward movements of tropical zooplankton species along the Baja California coast, Mexico."

Production of the euphausiid Nyctiphanes simplex Hansen in Vizcaino Bay was 1,736 mg m-2 yr-1 as determined from size-class distributions through 9 sampling periods during 1966. The production : biomass (P:B) ratio for this period was 17.0. Production due to growth was 74.7%, exuviae 23.4%, and only 1.9% due to eggs. Most reproduction was in the fall. Maximal recruitment and spawning female aggregations (containing > 50 ind m-2) occurred in September, with a mean batch fecundity per spawner of 46 eggs. Maturation time for the eggs was estimated at 30 days, and 3 spawning events seem to be the usual quota per female. The reproductive pattern during fall in Vizcaino Bay seemed to be related to local eddy development in which adults were retained.

Distribution patterns and population structure of the euphausiids Nyctiphanes simplex and Euphausia eximia were examined In the Callfornia Current off the west coast of Baja California, Mexico with emphasis on the southern part near Bahia Magdalena, in relation to temperature zooplancton biomass, distance from the coast as a functlon of depth, and interannual variability. The data were collected in 6 surveys from May 1986 to October 1987. High densities of N. simplex were found in the shallow coastal waters ( E. eximia the maximum abundance occurred offshore at stations with depths of 200 to 3000 m. These distribution patterns (offshore-inshore) remained relatively constant throughout the surveys, but the latitudinal distributions showed important variations in relation to the current patterns of the region and seasonal differences in the upwelling events, particularly near Bahia Magdalena (24 to 25° N). Both species displayed continuous breeding, with 25 to 77% of the adult female N simplex in different fertilized stages. A slightly lower proportion of E. eximia females were reproductively active (37 to 48%). The breeding areas, indicated by early stages (calyptopes) and adults in the reproductive phase, showed that N. simplex is dependent on the upwelling system along Baja Callforia. High densities are maintained during spring and summer, then decrease during autumn as the physical environment changes. The population dynamics of E. eximia indicated breeding areas offshore with a continuous recruitment. Breeding areas were found in regions of relatively low biological production. Maximum abundance occurred during autumn.

Seasonal distribution of biomass and somatic growth, molt, and egg production rates of Nyctiphanes simplex were estimated in the Gulf of California (November 2005, January 2007and July 2007) and associated with 12 environmental variables to define the conditions in which the higher biomass production rates occur. Daily growth rates, estimated from shipboard incubations, indicated that N. simplex did not grow or decreased in size in all the seasons, with higher proportions of animals in these 2 growth categories in July (21 and 52%, respectively) than in January (7 and 43%) and November (35 and 12%). Thus, the proportion of individuals that grew was higher in November (53%) and January (50%) than in July (27%). Mean juvenile and adult intermolt period (IMP) based on direct measurements was 5 d in January (range: 3 to 7 d), 3.8 d in July (2 to 8 d) and 4.4 d (3 to 7 d) for September to October 2010 (used as proxy for November, since not enough IMP data were available for that month). Calculations based on the inverse molting rate method estimated higher mean IMP (6.7 d; range 4 to 60 d). N. simplex mean (±SD) juvenile and adult daily total biomass production rate was 0.16 ± 0.13 mg DW m−3 d−1 (DW = dry weight) and mean annual integrated production was 71 ± 58 mg DW m−3 yr−1. The greatest contribution to N. simplex biomass production was through somatic growth (46%), followed by molts (32%) and eggs (22%). N. simplex had high biomass and biomass production rates mostly in regions with

Embryogenesis (single cell to twitching stage) and early larval stages (nauplius to calyptopis 3) internal morphology of the sac-spawning species Nyctiphanes simplex was investigated to explore its temporal association with gonad development and molt development cycles. Krill were collected and incubated shipboard in July 2007 and March 2010 in the Gulf of California. Cleavage patterns were similar to what is observed in broadcast-spawning species, suggesting a close phylogenetic consistency between krill species with distinct spawning strategies. Nyctiphanes simplex, like broadcast-spawning krill species, had eight Kranzzellen (K1–K8) cells during the blastula stage. The gonad of ovigerous females with embryos in the cell division stage is in the multiplication stage (Stage I). From the nauplius stage, most females are in previtellogenesis (Stage II). Only females with metanauplii occasionally have gonads in vitellogenesis (Stage III). Gonad maturity (Stage IV) occurs only after the release of the embryos from the ovigerous sac. Females with an ovigerous sac were invariably at the intermolt stage, suggesting a precise synchronization among processes of molting, gonad development and embryo release to produce consecutive broods. Lipid and carbohydrate storage decreased exponentially throughout embryonic and early larval development, depending on their endogenous reserves. When metanauplii leave the ovigerous sac, they have low storage lipid (,2%) and carbohydrate (,5%). These proportions suggest a theoretically short period-of-no-return (,2 days), when they transform into the first feeding stage (calyptopis 1).

The occurrence and causes of abrupt transitions, thresholds, or regime shifts between ecosystem states are of great concern and the likelihood of such transitions is increasing for many ecological systems. General understanding of abrupt transitions has been advanced by theory, but hindered by the lack of a common, accessible, and data-driven approach to characterizing them. We apply such an approach to 30–60 years of data on environmental drivers, biological responses, and associated evidence from pelagic ocean, coastal benthic, polar marine, and semi-arid grassland ecosystems. Our analyses revealed one case in which the response (krill abundance) linearly tracked abrupt changes in the driver (Pacific Decadal Oscillation), but abrupt transitions detected in the three other cases (sea cucumber abundance, penguin abundance, and black grama grass production) exhibited hysteretic relationships with drivers (wave intensity, sea-ice duration, and amounts of monsoonal rainfall, respectively) through a variety of response mechanisms. The use of a common approach across these case studies illustrates that: the utility of leading indicators is often limited and can depend on the abruptness of a transition relative to the lifespan of responsive organisms and observation intervals; information on spatiotemporal context is useful for comparing transitions; and ancillary information from associated experiments and observations aids interpretation of response-driver relationships. The understanding of abrupt transitions offered by this approach provides information that can be used to manage state changes and underscores the utility of long-term observations in multiple sentinel sites across a variety of ecosystems.

This study confirms the diet and determines the trophic position of the bentfin devil ray (Mobula thurstoni) and spinetail devil ray (Mobula japanica) in the south-west Gulf of California. There has been an active fishery in the area for these filter-feeding elasmobranchs, which are highly susceptible to exploitation due to low fecundity and long lifespan. However, information on their basic biology is scarce. δ13C and δ15N values of devil rays and zooplankton (sorted according to trophic level: herbivores, carnivores and omnivores) were determined over a period of 11 months, to allow for isotopic temporal variations in isotopic signals at the base of the food web. On the basis of fractionation factors we determined that bentfin and spinetail devil rays fed mainly on Nyctiphanes simplex, the most abundant euphausiid in neritic waters of the Gulf of California. The trophic positions obtained for the devil rays correspond to second level consumers.

Daytime surface swarms of the euphausiid Nyctiphanes simplex were observed during 9 spring seasons between 1984 and 1992 along the east coast of Baja California in the southwest part of the Gulf of California. Analyses of sex and maturity of surface patch samples showed that 57 % of the euphausiids were in breeding condition; males possessed developed spermatophores while females were carrying eggs and metanauplii. Sex ratios of female: male were between 1:1 and 2:1 Swarm samples contained high numbers of eggs and metanauplii. Both results suggest that this swarming phenomenon is related to reproductive activity. However, analysis of one particular swarm sample of N. simplex showed that only 8 % were in breeding condition. The highest biomass found was 32.6 g wet wt m-3, which is correlated with the high trophic activity observed in the sample area.

Laguna Ojo de Liebre is part of El Vizcaíno Biosphere's Reserve, one of the largest protected natural areas in the world. The contribution of seaweeds to the lagoons' total biomass had not been previously quantified. The purpose of this study was to evaluate the spatial and temporal variations of seaweed biomass in the lagoon. Seaweed samples were taken every season during 1995 at six sampling stations distributed throughout the lagoon. Total specific biomass of seaweeds was at its peak in the summer, and minimum in spring. The highest total annual biomass was found at Isla Brosa in the lagoon's central portion, and the lowest in El Dátil at the head. The seasonal and spatial variation of biomass in the lagoon is related with species richness and environmental parameters. Potentially important species in terms of biomass, wide spatial and temporal distribution, and potential use were: Spyridia filamentosa, Entheromorpha clathrata, Dasya baillouviana, Hypnea valentiaeand Sargassum sinicola .Using PCA three groups of stations were defined: one chiefly at the lagoon's mouth, another comprised the islands in the central portion, and the last in the lagoon's head.

The brine shrimp, most probably Artemia franciscana occurs in the solar salt plant (`salina') of Pichilingue (24°15 N and 110°20 W, total area about 10 ha), Baja California Sur, México. During the periods September 1999 to March 2000 and June 2000 to March 2001, salinity and temperature were determined weekly in selected evaporation ponds, as were the biological parameters of Artemia biomass, size of adult females and males, and monthly the biochemical composition of dried Artemia biomass. An explosive growth of Artemia was observed during moderate salinity levels (80–120 g l–1), reaching a standing crop level of 300 kg wet weight ha–1. With increasing salinity, biomass production and the size, especially of the females, decreased drastically, probably due to limited availability of natural food and to environmental stress. Brine shrimp survived up to a salinity of 270 g l–1. Despite wide variations in the environmental conditions, the proximate analysis of Artemia biomass showed only small differences, with the exception of the crude fibre content.

On the west coast of Baja California, Nyctiphanes simplex is by far the most abundant euphausiid species. To determine its importance in terms of growth production (Pg), and its relation to physical changes in the southern region of the California Current System, a survey was made along the Baja California peninsula including intensive sampling areas on Bahia Vizcaino, south of Punta Abreojos and in front of Bahia Magdalena during February 1994. The results show high values for zooplanktonic volumes, chlorophyll a concentrations, and abundance of N. simplex along the peninsula associated to inshore areas from Bahia Vizcaino to the Golfo de Ulloa. Daily N. simplex growth production (Pg) values in Bahia Vizcaino and South Punta Abreojos were 0.215 and 0.440 mg dw m ‐3 day ‐1 respectively. In Bahia Magdalena the Pg value (0.014 mg dw m ‐3 day ‐1 ) was lower. Larvae (organisms ≤6 mm) showed the highest percentage of Pg. The Pg values recorded here, are nearly 3-fold the values registered previously in Bahia Vizcaino, and correlate well with those reported before at Bahia Magdalena. The region off Punta Abreojos proved to be the most important in terms of Pg of N. simplex for February 1994. Seasonal hydrographic conditions along the Baja California peninsula during winter may explain higher Pg values in South Punta Abreojos. The secondary production values of N. simplex produced in Bahia Vizcaino and Punta Abreojos contribute to maintain these important biological activity centers.

SUMMARY. The female of Nyctiphanes simplex carries her eggs in an egg sac. The eggs hatch in the nauplius stage and remain in the egg sac throughout that stage. The larva emerges from the sac as a pseudo-metanauplius and moults immediately into the metanauplius stage. This is followed by three calyptopis stages and the furcilia stages. There are probably nineteen types of furcilia larvae. Since six of these are numerically dominant, it is probable that the larvae “jump” stages in the furcilia series. The six dominant types are described as the six furcilia stages. A key to the furcilia stages is included.