Patrón de crecimiento de tres especies de Eufásidos (Crustacea: Euphausiacea) del área de Ensenada, Baja California, México

Se analizaron dieciseis muestras de zooplancton obtenidas frente a las costas de Ensenada, Baja California, Mexico. Se identificaron las especies de eufésidos asf como los estadios de desarrollo de cada una de ellas. Las cuatro especies más importantes según el fndice de valor biológico (IVB) fueron: Nyctiphanes simplex, Nematoscelis dificilis, Euphausia pacijica y Thysanoessa grrgtia. El anAlisis de frecuencia de tallas en los estadios de desarrollo nos da información para conocer el patrón de crecimiento de estas especies.


INTRODUCPION
One main reason to study the growth pattem of the organisms, could be to determine when they reach their sexual maturity, how and where to catch them and what kind of species are related to each other in each stage as well as to know more about the trophic relationships they support in their environment, besides the distribution and migration movements.

y Knight
The crustaceans are one of the most important groups, as they are useful to determine changes of hydrographic parameters due to currents or oceanic water masses, since some species can be considered as indicators of those changes (Brinton, 1957;1962;1979;Brinton and Townsend, 1980).
In some way the euphausiids, as other organisms, are related to environmental factors as temperature, since this varies accordmg to the circulation pattem of the water masses in which they are distributed. All euphausiid species are marine and holoplanktonic (Brinton, 1960).
In the present study, the size frequency distribution is determined for the different stages of Cnlypfopis jiudia, juvenile and adult in the sixteen samples analyzed for the station 100.29 and 100.30 from the CalCOFI basic plan for the year 1969.

MATERIALS AND METHODS
The particular study area is located in front of Ensenada, Baja California, México, and forms part of the California Current. This is a well defined upwelling area mainly in June when northwest winds blow with high intensity, thus developing this nutrient rich zone (MoralesZúñiga, 1977).
The sampling stations were 29 and 30 from the 100 line of CalCOFI basic plan, which are located at 31o42.2'N , 116043.4'W and 31o406'N 116o466'W respectively (Fig.1). The samples were taken by oblique tows with a lm mouth in diameter and SOSmm mesh size net (Smith, 1974) from 157m at station 100.29 and 213m at station 100.30.
The samples were partitioned with a Folsom splitter (McEwen et al., 1954). Once separated all euphausiids were identified to species and development stage, according to Boden (1950;1951), Gopalakhrisnan (1973;1975) and Knight (1980). The total length of each individual has been taken from the top of the rostrum to the end of the telson. (1980). La longitud total de cada individuo se tomó del extremo final del rostrum hasta el extremo final del telson.
Analysis of size frequenciesand biological value index (BVI) were done, the former to know about the life histoty of the species, the latter summarizes the frequency of occurrence and abundarme for each species (Sanders, 1960;Dobbs, 1981 (Esterly, 1914;Boden, 1950;Brinton, 1962) in the particular case, its greater abundance concentrated in furcilia stage (three), which could be explained by the deeper distribution of juve nile and adult fonns . Because La fwra 3 muestra que N. difficilis alcanza su estado adulto a un ritmo más lento, ya que su intervalo de talla en estadio juvenil es m6s amplio, debido a su dimorfismo sexual, basado esencialmente en la forma y longitud del rostrum, considerándose adulto de los 15mm en adelante (A. Townsend, comunicación personal). Aparentemente esta especie realiza movimientos migratorios que obedecen a cambios de temperatura en el área; sin embargo, N. dificiiis es considerada endémica para esta zona (Gopalakhrisnan, 1974) por lo que el desarrollo de sus latvas debe realizarse dentro del Brea. Además al observar todos los estadios en cada mes y en todas las muestras analizadas, se infiere que existe reproducción continua.
of it this specie is omitted in the next analysis. The Size frequency analysis by stage for the year is summarized in  Figure 2 which corresponds to N. simplex, shows the growth pattem for the developmental stages of this species, which accordmg to Boden (1951), has three calyptopsis, six furciliae, one juvenile and one adult; the latter is considered so when it has reached 7mm in length (A. Townsend, personal communication). As can be observed, all stages of this species were found, which indicates that it has mainly coastal distribution.  considers it as a Baja Californian species whose northem limit is near Punta Concepci6n.
Pigure 3 shows that N.dificilis maches adult stage at a slower rate since its size range in the juvenile stage iswider because. of its sexual dimorphism, based essentially in the shape and length of the rostrum, considering it as adult from 15mm of length (A. Townsend, personal communication).
Apparently, this species displays migratory movements which obey to temperature changes in the area; however it is considered endemic for this zone (Gopalakhrisnan,l974) thus indicating that its larval development must take place witbin the area, being possible to fiid any stage at the same time ( as it was true in the present study ). rabia II. Talla promediox(mm), desviación tipica (S), intervalos de confianza al 95%, coeficiente de variación (CV), y número tota1 de organismos para cada estadio (n) de las tres especies más importantes según IVB. a) N. simplex, b) N. difficilis, c) E. pacifica. Table II. Average size X(mm), typical deviation (S), confidente intervals at 95%, coefficient of variation (CV) and total number of the organisms for each stage (n) of the three most important species according to the BVI. a) N. simplex, b) N. dificilis, c)  La distribucibn por talla para E. pacifica The size distribution for E. pacifica is se observa en la figura 4. Para esta especie, al showed in Figure 4. This species the same as igual que para la anterior, se observaron N. dijjicilis, experiences northerly movements movimientos en ciertos meses (octubre-enero) in certain months (October -January) tohacia áreas oceánicas y al norte del área de wards oceanic areas (Brinton, 1960); however, estudio (influenciados por las corrientes) the larval stages of these organisms are found (Brinton, 1960). Sin embargo, los estadios almost continuously in the coastal margins larvales de estos organismos han sido encon- (Knight, 1984). On the other hand Smiles and trados de continuo en los márgenes costeros (Knight, 1984). Por otro lado Smiles y Pearcy (1971) reportan un rhpido crecimiento y corto ciclo de vida para esta especie, a la que se considera adulto a partir de los llmm de longitud (A. Townsend, comunicación personal).
Pearcy (1971), reports a fast growth and a short life cycle for this species, which is considered as adult at llmm in length (A. Townsend, personal communication). Figura 3.-N. dificilis, tallas promedio, desviación típica e intervalos de confianza para cada estadio. Figure 3.-N. difficilis, average size, typical deviation and confidente intervals for each stage.
El patrón de crecimiento similar que se observa para las tres especies, se debe a que el Considering that the main environmental factors, as temperature and food availabiliúltimo estadio de la fase furcilia parece no ty, have a strong influente on the developcrecer considerablemente, sino que se diferenment and growth, particularly in crustaceans cia básicamente por características morfoló- Knight (1984), suggests that in general a poor gicas más que por la talla. A partir de aquí, se food ratio, both in quality as in quantity, has definen en juveniles y adultos solo por su effect on the intermoult period delaying it or incremento en talla.
accelerating it.
The similar growth pattem showed for the three species, is due to the fact that until the late furciliae stage apparently they do not grow considerably, as they differentiate basically by morphological characters rather than by size. From this moment on they are defined as juvenile and adult forms taking irtto account only their increasing size.
En relación a los adultos, su escasa aparición en las muestras puede deberse a dos causas: su distribución y el tipo de red utilizada en la toma de muestras.

AGRADECIMIENTOS
El presente trabajo es parte de una tesis de maestría realizada en el Centro de Investigación Científica y Estudios Superiores de As Table II shows, there are few adults for each species, which can be intetpreted as a less extensive dispersion of larvae than of adults, since spawning takes place near the coast, while the adult population disperses to oceanic waters (Brinton, 1960). Also, it has been considered that the lm CalCOPI net is not as efficient as the Bongo net to catch euphausiid adults.
The temperature and salinity ranges for the eight sampling months were 10.8 Oc to 17.5 oC and 33.4o/,, to 33.6o/,, for station 100.29 and 12.5 Oc to 18 Oc and 33.35 o/ooto 34.6 o/oo for station 100.30, these are within the normal range registered for this area (Wyllie and Lynn, 1971).

Euphasia pacifica, Nemetoscelis difficilis,
Nyeriphanes simpkx and Thysanoessa gregaria were the dominant species in the area for this sulvey.
The size ranges in the furciliae phase sometimes are overlapped since the morphological characters rather than size are determined to place them in one or another stage of this phase.
The limited number of adults may be because of their distribution and the net utilized in the samplings.

ACKh'OVVLEDGMENTS
This paper is part of a master thesis done at Centro de Investigación Científica y Estudios Superiores de Ensenada (CICESE). Thanks to Edward Brinton for his advice and Annie Townsend for her help. Also, to Miguel A. Cisneros for his contribution in the elaboration of this paper.
The author translated this paper to English.