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Pelagic development of juveniles

  Aspects of reproduction include pelagic development of juveniles, considered here, and COURTSHIP & COPULATION and EGG-LAYING & HATCHING, considered in other sections.
Research study 1
  graph showing growth of juvenile squids Doryteuthis opalescensSquids, especially pelagic species such as Doryteuthis opalescens, are notoriously difficult to keep in captivity, let alone rear to juvenile stage.  However, this has been accomplished at the Scripps Institution of Oceanography, California, with D. graph showing attacking success with age of juvenile squids Doryteuthis opalescensopalescens, using cylindrical rearing tanks and brine shrimp Artemia salina as food.  For the first 4wk the Artemia used as food are newly hatched individuals, while small adult Artemia suffice for the remainder of the rearing period.  Survival is poor over the first 4wk, better over the next 5wk, then poor again over the final 5wk, with only a handful surviving to 100d of age (see graph on Left). Attack success on Artemia prey is a function of age, as shown in the graph on the Right. Lack of success by young squids is attributed by the author mainly to prey escaping after being initially struck by the tentacles.  Oxygen-uptake measurements show that the daily maintenance energetic needs of a newly hatched squid could be met with 23 Artemia nauplii, while those of a 2mo-old squid (7mm mantle length) could be met with 225 nauplii.  However, actual consumption rates are estimated by the author to be considerably more than this, by a factor in each case of about 6.  Hurley 1976 Fish Bull 74: 176.
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Research study 2

In a later study at Galveston, Texas researchers culture eggs of Doryteuthis opalescens collected at Monterey Bay, California and grow the juveniles to a size of 17mm mantle length.  Success even to this small size is attributed to feeding them live copepods, rather than the commonly attempted diet of brine shrimps.  Hanlon et al. 1979 Veliger 21: 428. Photograph courtesy Southwest Fisheries Science Center, NOAA Fisheries Service, Fisheries Resource Div, La Jolla, California.

Female squid Doryteuthis opalescens with egg masses. A commercial fisheries has existed
in California for this species since 1850. On hatching, there is no larval stage and the
juveniles immediately adopt the adult way of life . Life span of D. opalescens is about 6-8mo

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Research study 3

photograph of Octopus bimaculatus courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, Californiadrawing of hatchling of an octopus showing chromatohore dispositionNewly hatched juveniles of Octopus bimaculatus are about 4mm in length and have 6-7 suckers on each earm. In the laboratory the juveniles will eat brine shrimp and net-plankton for a few days,  but then inevitably cease to eat and die.  During their early life they are positively phototactic, a behaviour that would ensure that they remain in upper positions in the water column while planktonic.  Ambrose 1981 Veliger 24: 139. Photograph courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, California.

Research study 4

map showing numbers of planktonic juveniles of octopus Enteroctopus dolfleini collected in plankton tows at night in the north Pacific Oceanphotograph of hatchling octopuses Enteroctopus dolfleini courtesy Shawn Robinson, Simon Fraser University, British ColumbiaAlmost nothing is known about the post-hatching life of any cephalopod, let alone octopus species that spend several weeks or months in the plankton.  For example, a Japanese oceanographic vessel has collected early juveniles of Enteroctopus dofleini in surface tows at night from areas 300-500km off the coasts of the Aleutian Islands, Alaska (see mapt). Most are collected during Apr-Sep at a size of 3-5mm in size, suggesting that they are no more than 1-2wk of age.  From their age and location of capture, the author suggests that they probably hatch in the coastal waters of the Aleutian Islands and are carried offshore in surface currents.  The author speculates on how the juveniles can be transported several hundred kilometers in just 1-2wk, and suggests that they may do so in a southward flowing component of the Alaska Stream.  As to how or whether they return to shore is anyone’s guess.  Kubodera 1991 Bull Mar Sci 49: 235. Photograph courtesy Shawn Robinson, Simon Fraser University, British Columbia.

NOTE  the author compares the netted specimens with Enteroctopus dofleini cultured in a fisheries lab in Hokkaido and concludes that they are the same species. The research interest in Japan relates, in part, to a fairly sizeable fisheries for E. dofleini in Hokkaido

Research study 5

Collections of post-hatching squids Doryteuthis (Loligo) opalescens in the Southern California Bight during the 3yr following a record El Niño event in 1997-98 reveal dramatic increases in abundance. The juveniles remain within 1-3km of the shore for several weeks after hatching, apparently entrained in a boundary layer of water created by tidally reversing currents.  Farther from shore, neritic currents disperse the juveniles throughout the Bight. The near-shore juveniles occur above 80m depth and undertake a daily vertical migration.  Zeidberg & Hamner 2002 Mar Biol 141: 111.

NOTE  the authors term these free-living juvenile life stages “paralarvae”, a term that appears in other fisheries-related publications on squids.  There is nothing inappropriate in this, providing it not be abbreviated to “larvae” as done in this present publication (and also in the following Research Study 6, as a larval life stage does not exist as a post-hatching stage in cephalopods).  The term paralarva is originally defined as “a cephalopod of the first post-hatching growth stage that is pelagic in near-surface waters during the day and that has a distinctively different mode of life from that of older conspecific individuals”.  See Young & Harman 1988 Malacologia 29 (1): 201 for further details

Research study 6

photograph of possible mating of jumbo squids Dosidicus gigasResearchers from California and Mexico team up to determine the identity of paralarvae collected in surface photographs of jumbo squids Dosidicus gigas paralarvaewaters in the Gulf of California. Molecular analysis of the mitochondrial gene cytochrome c oxidase I confirm the identity of all specimens collected as being jumbo squids Dosidicus gigas. Other observations of apparent mating behaviour of these squids in local waters confirm that the species is reproducing in the central region of the Gulf of California. Gilly et al. 2006 Mar Ecol Progr Ser 313: 125.

NOTE the species supports large fisheries in Chile, Peru, and Mexico

Paralarvae of squids Dosidicus gigas. The fused
tentacles (proboscis) showin the above photo,
but these may have split in the older individual below. For more on the proboscis see RS8 below

Possible mating of a larger female
(above) with a smaller male (below)

Research study 6.1

graph showing speeds of proboscis extension and retraction in Humboldt squids Dosidicus gigas paralarvaeShipboard observation by American and Mexican researchers of hatchling paralarvae obtained from a naturally spawned egg-mass of a Humboldt squid Dosidicus gigas reveals some interesting behaviors. After escaping from the large, floating egg mass, which the 1.5mm paralarvae (3-6d post-hatching) seem to be able to do easily, behaviours such as proboscis extension, chromatophore expansion and contraction, and change in swimming speeds from motionless to 0.5cm . sec-1 are easily monitored. The proboscis can quickly (375msec) be extended about 2.5 times its original length (see graph) but, despite offering various types of plankton as food, there is no obvious attempt by the paralarvae to feed, with or without the use of the proboscis. Swimming is mainly upwards and when the paralarvae tire they sink down. It seems odd that the hatchlings would not be positively (or at least, neutrally) buoyant, but perhaps they need to feed to maintain a necessary level of lipids for buoyancy, especially when their yolk supply has run out. The authors do not mention whether sculling with fins is used to locomote in addition to jetting. Chromatophore activity is present, sometimes stimulated by surface or bottom contact, other times, just spontaneously. Staaf et al. 2008 J Mar Biol Ass UK 88 (4): 759.


Research study 7

photograph of a statolith of market squid Doryteuthis opalescensIn a first-of-its-kind study a consortium of researchers from the University of California and California Department of Fish and Game are able to match the trace-elemental composition of statolith cores of paralarvae of squids Doryteuthis opalescens with those of adults, and to show between-site differences for collection areas up to 100km apart. The photograph shows a statolith of a juvenile (paralarval) squid.  The pits represent the corings removed for analysis.  The core pit is the natal portion, that is, when the embryo is still in the egg capsule, while the 2nd pit is the paralarval or post-hatching portion.  The first represents a chemical signature of the birthplace, when trace elements are incorporated into the eggs by the mother, while the second represents environmental effects during early pelagic life. The study is valuable in that it presents a possible method for identifying the source populations for commercially important squid stocks and may answer the question as to whether squids when spawning have an affinity for natal areas.  Warner et al. 2009 Mar Ecol Progr Ser 379: 109.

NOTE  the technique, developed originally for fish otoliths, compares levels of various heavy metals, most notably Mg, Mn, Sr, and Ba, in fishes of different ages to determine natal origin.  It has been successfully applied to different types of west-coast invertebrates including crustaceans and gastropods, and is newly examined here for squids. The various hard parts represent natural tags enabling dispersal and movement patterns to be determined

Research study 8

drawing of paralarva of jumbo squid Dosidicus gigasParalarvae of squids in the Family Ommastrephidae uniquely possess fused tentacles known as a “proboscis1” until they reach a size of about 8-10mm mantle length (ML). Description2 of this unusual organ and other morphological features are provided for giant squids Dosidicus gigas by researchers in La Paz and Ensenada, Mexico. The proboscis has 8 suckers at its distal end. Each sucker has 2 concentric rings of knobs (about 10 inner and 12 outer at 3mm ML) that increase in size during growth presumably to become the hooks of the adult. The proboscis commences splitting at a size of 2-5mm ML, beginning with a ventral furrow that later splits completely to form 2 tentacles at about 10mm ML. A paralarva of Dosidicus can extend its proboscis by about 2.5 times its original length but, apart from that observation, the authors make no comment3 as to how or if it is used for feeding during juvenile life. Ramos-Castillejos et al. 2010 Invert Biol 129 (2): 172.

NOTE1 another name for this is rhynchoteuthis (“snout” “squid” G.), with the possessor being a rhynchoteuthion squid

NOTE2 the study ostensibly is to develop a handy “morphologic-morphometric” means to discriminate between paralarvae of squids Dosidicus gigas and Sthenoteuthis oualaniensis, two large commercially important species in the Baja California area; however, the description of the proboscis is, at least for Odyssey purposes, the more interesting part of the study. The paralarvae are initially identified to species through molecular analyses

NOTE3 an earlier author investigates this issue for 3 other ommastrephid species and notes inconsistencies among them with regard to proboscis transformation. The author suggests that the post-fusion tentacles are unlikely to be used for immediate prey capture because they end up shorter than the arms, they are often torn during splitting, and some species lose completely the terminal suckers. Also, the sucker buds that appear on the newly developing tentacle clubs may not be operational for some time. As for the proboscis itself, current thinking is that it may be involved in some sort of suspension-feeding, or perhaps even used for limited strikes on planktonic prey during the period from final yolk absorption to full use of the new attack tentacles. One wonders, perhaps naively, why someone can't just observe some new hatchlings and see what is going on. Shea 2005 Invert Biol 124 (1): 25.