Octopuses & relatives
Reproduction: Pelagic Development Of Juveniles

Research Study 1

Fig. 1.  Survival of Doryteuthis opalescens in laboratory culture
Fig. 2.  Attack success of early juvenile Doryteuthis opalescens on brine shrimp Artemia salina in laboratory culture

Squids, 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. opalescens, 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 Fig. 1).  Attack success on Artemia prey is a function of age, as shown in Fig. 2.  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. 

NOTE  in excess of one thousand strikes per day seems a lot of work for a small yield;  would a larger-sized crustacean, such as shrimp, might have been a better alternative, perhaps also easier to catch?

Hurley   1976   Fish Bull 74: 176

Research Study 2

Fig. 1.  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
Courtesy Southwest Fisheries Science Center, NOAA Fisheries Service, Fisheries Resource Divisinon, La Jolla, California

In a study at Galveston, Texas, researchers culture eggs of Doryteuthis opalescens (Fig. 1) 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

Research Study 3

Fig. 2.  Juvenile Octopus bimaculatus
Fig. 1.  Octopus bimaculatus
Courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, California

Newly hatched juveniles of Octopus bimaculatus (Fig. 1) are about 4mm in length and have 6-7 suckers on each earm.  In the laboratory the juveniles (Fig. 2) 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

Research Study 4

Fig. 1.  Hatchlings of Enteroctopus dolfleini
Courtesy Shawn Robinson, Simon Fraser University, Burnaby, British Columbia
Fig. 2.  Catch statistics for juvenile Enteroctopus dolfleini in the North Pacific Ocean

Almost 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 Fig. 1). 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 (Fig. 2). 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. 

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

Kubodera   1991   Bull Mar Sci 49: 235

Research Study 5

Collections of post-hatching squids Doryteuthis (Loligoopalescens 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. 

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 earlier 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” (Young & Harman, 1988) 

Zeidberg & Hamner   2002   Mar Biol 141: 111
Young & Harman   1988   Malacologia 29 (1): 201

Research Study 6

Possible mating of a larger female Dosidicus gigas (above) with a smaller male (below) 
Fig. 1.  Paralarvae of squids Dosidicus gigas. Note the fused tentacles or "proboscis", visible in the upper photo, possibly now split in the older individual below.  The function of the proboscis is considered in Research Studies to follow

Researchers from California and Mexico team up to determine the identity of paralarvae (Fig. 1) collected in surface waters 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 (Fig. 2). 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.

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

Gilly et al.   2006   Mar Ecol Progr Ser 313: 125

Research Study 7

Fig. 1.  Extension and contraction of the juvenile feeding organ, the proboscis, in Dosidicus gigas takes about 1sec

Shipboard 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, thought to be a feeding organ, can quickly (375msec) be extended about 2.5 times its original length (see Fig. 1) 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, apparently just spontaneously. 

 

Staaf et al.   2008   J Mar Biol Ass UK 88 (4): 759

Research Study 8

Fig. 1.  Statolith of Doryteuthis opalescens showing sampling pits extracted for elemental analysis

In a first-of-its-kind study for cephalopods a consortium of researchers from the University of California and California Department of Fish and Game is 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. Fig. 1 shows a statolith of a juvenile (paralarva) 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. 

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.

Warner et al.   2009   Mar Ecol Progr Ser 379: 109

Research Study 9

Fig. 1.  Ventral view of a paralarva of squid Dosidicus gigas showing furrowing of the proboscis

Paralarvae of squids in the Family Ommastrephidae uniquely possess fused tentacles known as a “proboscis1” (Fig. 1) 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 two 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 (see Fig. 2) that later splits completely to form two 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. 

NOTE1 another name for this is rhynchoteuthis (“snout” “squid” G.), with the possessor being a rhynchoteuthion squid (fortunately this mouthful of syllables seems not to have gained popular acceptance by cephapodologists)

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 researcher investigates this issue for three 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, 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 (Shea, 2005) 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

Ramos-Castillejos et al.   2010   Invert Biol 129 (2): 172
Shea   2005   Invert Biol 124 (1): 25

Research Study 10


Fig. 1.  West-coast distribution of Octopus bimaculatus

Fig. 2.  Distribution of paralarvae of Octopus bimaculatus along the Mexican coast during summer/autumn
Fig. 3.  Early pelagic development of Octopus bimaculatus.  The photo appears to be a view from above, with perhaps part of the gut visible within the body mass

Two-spot octopuses Octopus bimaculatus are most abundant along the west coast from southern California to mid-southern Mexico (see Figs. 1 & 2). After hatching in late spring/summer they spend several weeks or months in the plankton before settling in nearshore habitats. Newly hatched individuals (0.5-0.7mm mantle length) are known as paralarvae up to a size up to about 3mm mantle length (see Fig. 3). Larger than this, up to about 10mm mantle length, they are referred to as juveniles, and retain this categorisation until settlement. Near- and offshore collections by Mexican fisheries scientists in the Pacific Ocean along the coasts of Oaxaca, and Chiapas in 2001 show that paralarvae are found mostly in nearshore waters during July-November, but some drift up to 600-700km offshore (see Fig. 2). By November the juveniles are about 0.5-1.0mm mantle length and 5-6mo of age. Of course, unless onshore currents sweep them back close to shore they will eventually die.  

Alejo-Plata et al.   2012   Revista de Biologia Marina Y Oceanografia 47 (2): 359