Dosidicus gigas (jumbo or Humboldt squid) is a semelparous, major predator of the eastern Pacific that is ecologically and commercially important. In the Gulf of California, these animals mature at large size (>55 cm mantle length) in 1–1.5 years and have supported a major commercial fishery in the Guaymas Basin during the last 20 years. An El Niño event in 2009–2010, was accompanied by a collapse of this fishery, and squid in the region showed major changes in the distribution and life‐history strategy. Large squid abandoned seasonal coastal‐shelf habitats in 2010 and instead were found in the Salsipuedes Basin to the north, an area buffered from the effects of El Niño by tidal upwelling and a well‐mixed water column. The commercial fishery also relocated to this region. Although large squid were not found in the Guaymas Basin from 2010 to 2012, small squid were abundant and matured at an unusually small mantle‐length (<30 cm) and young age (approximately 6 months). Juvenile squid thus appeared to respond to El Niño with an alternative life‐history trajectory in which gigantism and high fecundity in normally productive coastal‐shelf habitats were traded for accelerated reproduction at small size in an offshore environment. Both small and large mature squid, were present in the Salsipuedes Basin during 2011, indicating that both life‐ history strategies can coexist. Hydro‐acoustic data, reveal that squid biomass in this study area nearly doubled between 2010 and 2011, primarily due to a large increase in small squid that were not susceptible to the fishery. Such a climate‐driven switch in size‐at‐maturity may allow D. gigas to rapidly adapt to and cope with El Niño. This ability is likely to be an important factor in conjunction with longerterm climate‐change and the potential ecological impacts of this invasive predator on marine ecosystems.

Dosidicus gigas and Sthenoteuthis oualaniensis (Teuthoidea: Ommastrephidae: Ommastrephinae) are abundant, ecologically important squid that co-occur in the eastern tropical Pacific. Little is known about the genetic basis of population structure in either species, although the presence of 2 species within S. oualaniensis has been suggested. We report here on a comparative population genetic study of D. gigas and S. oualaniensis using the mitochondrial marker NADH dehydrogenase subunit 2. Despite the high potential for dispersal in these active swimmers, both species exhibit a distinct biogeographic break at 5 to 6°N. S. oualaniensis contains multiple deeply divergent, geographically segregated clades, whereas D. gigas shows only mild divergence between northern and southern hemisphere populations. We suggest that dispersal and genetic mixing across the eastern tropical Pacific may be impeded by both oceanographic and ecological factors. KEY WORDS: Biogeographic comparison · Eastern Pacific · Ommastrephid squid · Population genetic structure Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 418: [165][166][167][168][169][170][171][172][173][174][175][176][177][178] 2010 ML. Nigmatullin et al. (2001) suggested that the 3 sizeat-maturity forms may be incipient species, or at least distinct stocks. However, other researchers have proposed separating D. gigas into only 2 stocks, one 'northern' and one 'southern,' based on supposed migration patterns rather than size at maturity (Wormuth 1976, Nesis 1983, Clarke & Paliza 2000.Tagging studies on individuals of the large form of Dosidicus gigas have revealed that they make extensive use of the prominent oxygen minimum zone (OMZ) in the eastern Pacific, indicated with a white hashed line in Fig. 1. This zone provides a refuge from predators that cannot tolerate hypoxia, and also appears to be a favored hunting area of these large D. gigas (Gilly et al. 2006b).In the eastern tropical Pacific, the range of Dosidicus gigas overlaps with that of Sthenoteuthis oualaniensis (Lesson, 1830), the purpleback flying squid, a species of growing commercial interest (Zuyev et al. 2002, Xinjun et al. 2007). S. oualaniensis, however, does not extend into the temperate Pacific but it is found across the tropical and subtropical Pacific and Indian Oceans (Fig. 1). This transoceanic range is typical of the subfamily Ommastrephinae, to which both species belong. The northsouth distribution of D. gigas is unique and may belie an ecological connection between this species and the OMZ.Sthenoteuthis oualaniensis comprises multiple forms (Nesis 1983, Dunning 1998 These morphologies demonstrate 2 distinct gladius structures in western specimens Table 1. Dosidicus gigas and Sthenoteuthis oualaniensis. Size-at-maturity forms (Nesis 1983, Dunning 1998. ML: mantle length. nd: no morphological differences other than size at maturity are known for the forms of D. gigas with the photophore is found throughout the species range and co-occurs wit...

Efecto de la temperatura en el desarrollo embrionario y larval del mejillón, Mytilus galloprovincialis (Lamarck, 1819)Temperature effect in the embryonic and larval development of the mussel, Mytilus galloprovincialis (Lamarck, 1819) -10258) se evaluó el efecto de la temperatura sobre su desarrollo temprano para modular empíricamente las tasas de crecimiento larval. Los embriones y larvas se cultivaron a 12, 16 y 20ºC, en una unidad productora de semillas marinas en la bahía de Coliumo (36ºS), Chile, desde donde se extrajeron los reproductores. El desarrollo embrionario siguió la secuencia conocida para otros bivalvos. Las trocóforas se transformaron en velígeras, a las 45 h post fertilización, seguidas por las larvas D (longitud inicial 99 ± 6 μm), con velo ciliado, estómago bien definido y líneas de crecimiento concéntricas en la concha; las larvas umbonadas, a partir del día 15 post fertilización, desarrollaron manchas oculares y músculos aductores; las pedivelígeras (talla inicial 265 ± 2 μm) desarrollaron un órgano pedal y filamentos branquiales. Los estadios embrionario y larval fueron acelerados a mayores temperaturas. Las tasas de crecimiento larval a 20ºC (9,1 μm*día -1 ) fueron significativamente mayores que a 12 y 16ºC (6,7 μm*día -1 y 7,4 μm*día -1 , respectivamente). Comparado con Mytilus chilensis, M. galloprovincialis presentó mejores de tasas de crecimiento a iguales temperaturas. Esto sugiere que, en Chile, se puede producir semillas de M. galloprovincialis en condiciones controladas, para su cultivo masivo. MaryoriPalabras clave: Mytilidae, mejillón, embrión, larva, temperatura, tasa de crecimiento Abstract.-The Mediterranean mussel (Mytilus galloprovincialis Lamarck, 1819) has been recently registered for the Chilean coast, from Concepcion (36ºS) to the Magellan Strait (54ºS). To determine the feasibility of the massive culture of M. galloprovincialis in Chile, a study of the temperature effects on the early development was carried out. Embryos and larvae were raised at 12, 16 and 20ºC in laboratory facilities at Coliumo Bay (36ºS), Chile, from where adults mussels were collected. Embryonic development followed the common sequence exhibited by other bivalves. Trocophores turned into veligers at 45 h post fertilization, followed by D-larvae (99 ± 6 μm length, initial size), with a large ciliated velum, a welldeveloped stomach and concentric growth lines in the shell; 15 days post-fertilization, umbonate larvae developed eye-spots and adductors muscles; pediveliger larvae (265 ± 2 μm initial length size) developed a pedal organ and gill filaments. Both embryonic and larval stages were accelerated at higher temperatures. The larval growth rates at 20ºC (9.1 μm*d galloprovincialis seed can be produced under controlled conditions for its massive cultivation.

The clam Eurhomalea lenticularis may be parasitized by digenean trematodes of the family Plagiorchidae, specifically in the gonads (parasitic castration). A quantitative histological analysis of the parasitized gonads demonstrated a significant decrease in gonadal area, in the size of individual acini, and in the numbers of differentiated germ cells compared to unparasitized clams. Castration may be caused by mechanical compression due to trematode sporocyst growth. However, the uniform loss of germ cells in areas without sporocysts suggests that a more generalized mechanism is responsible. We suggest that parasitic castration has a primary effect on the host's neuroendocrine and gametogenic systems that regulate gamete production. KEY WORDS: Bivalve mollusc · Parasitic castration · Histological analysis · Eurhomalea lenticularis · Digenea · Trematode · Central Chile Resale or republication not permitted without written consent of the publisherDis Aquat Org 59: [151][152][153][154][155][156][157][158] 2004 of alteration in the neuroendocrinological system of the clam, we quantified the variation between germ cell number in the presence and absence of sporocysts. MATERIALS AND METHODSSample processing and histology. To determine the prevalence of the parasite, a total of 1702 clams was obtained from June 1995 to February 1998 by diving on a natural bank located at El Algarrobo inlet, central Chile (33°20' S, 71°40' W). They were transported live to the laboratory, and at least 1 random sample of 30 clams was processed each month (1034 in total; the remaining clams were dissected and observed under the stereoscopic microscope to determine the presence of the parasite) using routine histological techniques (Gabe 1968). After 1 h fixation in Bouin Hollande fluid to harden the tissues, serial transverse sections, 5 mm thick, were made of the visceral mass containing the gonad. After fixation in fresh fixative for 48 h, the thick sections were washed in tap water for 24 h, dehydrated in graded ascending concentrations of ethanol to 100%, cleared in butanol and embedded in Paraplast Plus (Oxford ® ). Histological sections of 5 µm thickness were made at different levels through the tissue at 300 µm intervals, deparaffinized, and rehydrated in a decreasing series of ethanol concentrations, and stained by a trichrome staining method. Briefly, the sections were stained in Harris hematoxylin solution for 75 s and rinsed in running tap water for 10 min, followed by a quick rinse in distilled water. Next, they were stained with a mixture of 0.5% Erythrosin-0.5% Orange G for 30 min, and quickly rinsed in distilled water. They were immersed in 0.5% phosphotungstic acid for 10 min, and again quickly rinsed in distilled water. Finally, they were stained in 1% Aniline blue for 75 s and immediately dehydrated in 3 consecutive baths of 95% ethanol followed by 3 baths in 100% ethanol (Arteta trichrome stain; López et al. 1982). After clearing in xylenes, the slides were coverslipped using Canada balsam (López et al. 1982...