Research Study 1:    Octopuses

Fig. 1.  Octopus bimaculatus

Courtesy Birch Aquarium, Scripps Institution of Oceanography, La Jolla, California

Fig. 2.  Seasonal haching success of eggs of Octopus bimaculatus 

A study on the reproductive biology of the two-spotted octopus Octopus bimaculatus (Fig. 1) in Catalina Islands, California is carried out over a 6yr period entirely and uniquely with the use of SCUBA. Matings occur May - July coincidental with increasing water temperatures (15 - 19°C).  Females lay their eggs in July - August and hatching is 50d later (at 19°C).  Clutch sizes can reach 20,000 eggs. The females tend the eggs by cleaning and ventilating, and die soon after the eggs hatch.  Females that lay their eggs too early in the season, for example, from Jan - Mar, generally do not complete the layings (Fig. 2).  The newly hatched octopuses spend several months in the plankton and then settle to the sea bottom Figs. 3 - 5).  Interstices in giant-kelp holdfasts Macrocystis pyrifera are attractive settling sites. The juveniles are most abundant during summer, with a second peak in winter representing the late hatchlings.  The juveniles remain in the holdfasts until attaining about 5cm mantle length. This occurs in late spring of the following year, at an age of about 8 - 10mo.  Adults are most abundant during late summer and autumn, but with considerable year-to-year variability.  Once adulthood is reached, an octopus' lifespan is approximately 8 - 10mo.  If the several months the juveniles spend in the plankton is included, the maximum life span is about 2yr. 

NOTE eggs of O. bimaculatus are 2 - 4mm in length, while those of the closely related O. bimaculoides are 10 - 12mm in length. The hatchlings of O. bimaculoides immediately assume a benthic way of life, with no planktonic stage (Forsythe & Hanlon, 1988)

Fig. 3.  Early development of Octopus bimaculatus

Fig. 4.  New hatchling, side view

Fig. 5.  Top view, note yolk supply

Research Study 2:    Octopuses

Fig. 1. The author provides this photograph of a Japanese ivory netsuke

Courtesy the author & The British Museum

Aging and death in octopuses is discussed by a biologist/psychologist at the University of Washington who likens an octopus' natural life to that of an octopus caught in a, a pot used both historically and even now to trap octopuses for consumption (Fig. 1¹).  The symbolism is that female octopuses especially, are destined to die naturally after a short life-span of perhaps less than a year, just as they would be destined to die after being caught in a pot and eaten.  Death of a female Octopus bimaculoides or Enteroctopus dolfleini² begins from the time the first egg is laid and by the time the eggs hatch the female is usually dead.  The author's point is that the death is programmed³, and it begins with a female fasting shortly after egg-laying.  For most of her remaining weeks of life the female tends to the egg mass, ventilating it and keeping it free from debris and predators (see Fig. 1 in Research Study 6 below).   In time the female's body begins to deteriorate and decline physiologically.   She may even eat her own arms, not so much for nutrition but symptomatic of her inevitable demise.  The process apparently is controlled by the optic gland, a neuroendocrine organ located in the brain, with function similar to the vertebrate pituitary gland.  Its secretions control reproductive and other life-history events.  Its experimental removal during the egg-tending period will cause a female octopus to abandon its eggs, resume feeding, and possibly to live for several months longer.  At this point the author waxes poetic with comments like, "Could the optic glands be an elegant octopus trap, carefully plotting the reproduction that ultimately ensures its death?".  Apart from nonsensical, this question and the study in general is rife with teleology and anthropomorphism. 

NOTE¹  netsukes are small toggle-like devices used to attach a small container (tobacco, medicine, and the like) to a sash wrapped around an otherwise pocketless kimono in the old days of Japan.   Despite being functional, netsukes are usually exquisitely crafted works of art that commonly depict everyday life in feudal Japan.  This one shows an octopus crawling into (or out of) a ceramic pot or takotsubo (est. 3 - 4cm in height).  Inscribed on the pot but not visible here, is a poem by the well-known haiku poet Basho (ca. 1866), "octopus traps fleeting dreams under summer moon", reminding us one guesses of life's fleeting joys and pain.  Is the octopus scratching its head over this?!

NOTE²  these two species are chosen because both are Pacific coast inhabitants and both have a semelparous type of reproduction; that is, they reproduce only once in a lifetime, then die.  This describes the majority of octopus species, but some few are iteroparous and breed multiple times throughout life.  Most other molluscs like snails and bivalves are iteroparous

NOTE³  this is in reference to the well-studied apoptosis, or programmed death of cells

Research Study 3:    Octopuses

Fig. 1.  Relationship of female live mass to fecundity in Octopus rubescens

Information on fecundity and embryonic development of octopuses Octopus rubescens in Monterey Bay, California is presented by a researcher at Moss Landing Marine Laboratories, California.  Mean numbers of eggs per brood range from 4,000 - 20,000 for females of 117 - 140g (Fig. 1).  Times to hatch in the laboratory range from 50d at 18°C to 90d at 15°C.  Selected developmental stages of the 31 “distinct” stages described by the author are shown in Fig. 2 - 5 along with their chromatophore patterns.  Hatchlings in laboratory culture are positively phototactic for just a few minutes.  Attempts to rear the hatchlings fail despite using many different combinations of rearing conditions and types of food. 

NOTE blastulation alone comprises 10 of these "distinct" stages, and gastrulation five.  Is this too much splitting, do you ask?  If in doubt, remember the expression of "not seeing the forest for the trees"!

Fig. 2.  Day 28 stage in embryonic development of Octopus rubescens at 18°C:  arms defined & suckers visible (sizes not given by the author)

Fig. 3.  Day 32: orange chromatophores are visible

Fig. 4.  Day 37: more chromatophores, including brown ones

Fig. 5.  Day 50: hatchlings are positively phototactic for the first 15min of free-swimming life. This takes them from the bottom to the sea surface where they disseminate

Research Study 4:    Octopuses

Fig. 1.  Octopus rubescens with agg mass

Courtesy Roland Anderson and Seattle Aquarium, Washington

Presented in Figs. 1 - 5 are photographs of developmental stages of a few west-coast cephalopods.

Fig. 2.  Late-stage embryo of Enteroctopus dofleini 

Courtesy Shawn Robinson, UBC

Fig. 3.  Newly hatched octopus Enteroctopus dofleini

Courtesy Shawn Robinson, UBC

Fig. 4.  Egg 'sausages' of squid Doryteuthis opalescens washed up on a B.C. beach

Fig. 5.  Egg and hatchling of stubby squid Rossia pacifica

Courtesy Roland Anderson, Seattle Aquarium

Research Study 5:    Octopuses

Fig. 1.  The relationship of fucundity with live mass of Enteroctopus dolfleini would be predicted to be linear, not curvilinear as shown here. This may be explained by the authors starting each axis at an arbitrary position instead of using 0-0 intercepts, and then eye-fitting a straight line

Fig. 2.  Seasonal gonad indices and egg sizes in Enteroctopus dolfleini

Researchers from the Alaska Fisheries Science Center provide life-history statistics for giant octopuses Enteroctopus dolfleini collected from sites around Kokiak Island in the Gulf of Alaska. Both sexes mature at about the same live mass of 14kg (but with high variability) and egg-laying takes place from Jan - Mar. These maturity sizes are apparently larger than other values reported for the species.  Mean fecundity, calculated as total number of eggs in the ovary, is 107,000 (again, with high variability; Fig. 1).  Measurements of gonadosomatic indices in females show increasing values from spring to highest values in winter, with comparably increasing egg lengths over the same period (Fig. 2).  Mating occurs predominately in spring/summer but, on the assumption that females are capable of storing sperm, the authors believe that mating may extend throughout the year. 

NOTE calculated as the ratio of reproductive-tract mass to total live mass (presumably including reproductive tract) in 14kg live-mass females

Research Study 6:    Octopuses

An interesting application of modern medicine to the study of reproduction in octopuses comes from the use of ultrasonic technology to measure gonad size in Octopus vulgaris.  The study is done in Spain using  27 wild and cultured females captured in artisanal fishing pots, and is included here in the hope of stimulating similar work on our own Pacific coast of North America species.  A female is anaesthetised in a 2% ethanol/seawater solution, mass and volume measured, and the body scanned with an ultrasonograph to determine its gonadosomatic index (= GI: gonad index).  Other invasive-type experiments show that such measurements provide a 75% correlation with GI data obtained from traditional dissecting methodology, a discrepancy owing basically to the squishyness of an octopus' body.  Researchers should be mindful of, and correct for, this potential error.  The ultrasound method, of course, has the advantage of being non-invasive, thus permitting time-based studies with potentially zero mortality. 

NOTE  it is too bad that the authors chose not to include a sample sonogram with their data.  It would be interesting to compare what we know of the fuzzyness of human embryos with the better/worse clarity of gonads of octopuses

NOTE  usually measured as a ratio of gonad mass/whole body mass including gonad X 100%.  However, because a sonogram shows only areas, the authors substitute volumes for masses using data on cross-sectional area, circumference, and diameter of ovaries to calculate volume-based gonadal indices

Research Study 1:    Squids

Fig. 1.  A female squid Doryteuthis opalescens holds the egg case (sheath) in her arms while she works on it.  Each case contains between 50-300 eggs.  It is not known how many cases a female will produce during a single spawning period.  Note  the protective gelatinous material surrounding the eggs. 

Courtesy Kevin Lee, Fullerton, California

A female squid such as Doryteuthis opalescens encases her eggs by first extruding a sausage-shaped sheath through the siphon and holding it between her arms (Fig. 1). She then pumps eggs into the case, closes the end in some way, and inserts it into the sand with a mucilaginous anchor, or attaches it to something firm on the sea bottom. As the embryos develop, the case absorbs seawater and becomes longer and thicker. The females dies shortly after producing the case(s), and the eggs hatch within a few weeks without parental care to a pelagic juvenile stage known as a paralarva.  During development the walls of the case weaken and degrade, allowing the juveniles later to emerge.

NOTE this is commonly referred to by fisheries-orientated researchers as a capsule or egg capsule. This is unfortunate in that the egg capsule, by dint of about 1.5 centuries of previous use, is actually the membrane layers that surround the egg.  Moreover, when a squid hatches, it does so from its egg capsule, not from the case (sheath). Another term, perhaps emergence, should be used for the young squid leaving its case (sheath). Paralarva is also a partial misnomer, as cephalopods do not have a free-living larval stage. There is nothing wrong in having a set of jargon terms specific to a subject, but not when it engenders confusion, as can be seen in some of the following studies

Research Study 2:    Squids

Fig. 1.  Copulation in Doryteuthis opalescens

Fig. 2.  Doryteuthis opalescens copulating

Squids Doryteuthis (Loligo) opalescens in Monterey Bay, California undertake their most intense spawning in April - July.  A unique SCUBA-diving observation of spawning Doryteuthis around La Jolla, California at 16m depth describes large masses of egg cases, some covering areas up to 3 - 4m in diameter, with many actively swimming squids nearby. The squids are about 15cm mantle length for males, and 14cm for females. The author describes their appearance as “spent”, with flaccid bodies and shreds of loose epithelium, especially on the females. Most of the egg cases are attached to other cases, rather than to objects on the sea floor. The juveniles hatch after about 7wk (14°C) at 4mm mantle length. The author comments that the most common copulatory behaviour is with the male below as shown in Fig. 1, although another another type of head-to-head behaviour may sometimes be used (Fig. 2).  

NOTE  incorrectly termed here "capsules" (this term is reserved for the membrane enclosing the eggs)

Research Study 3:    Squids

A description of squids Doryteuthis opalescens spawning on sandy bottom at 9m depth off Long Point, Santa Catalina Island, California goes as follows.  The male grasps the female from below and uses his left ventral arm, or hectocotylus, to transfer spermatophores from his siphon to the mantle cavity of the female. The female later deposits eggs, encased in 10cm-long gelatinous capsules (cases), onto the sandy bottom. The cases are most commonly deposited around the periphery of egg masses left by other females. The author notes the presence of many dead squids lying amongst and around the egg capsules. 

NOTE the author does not actually see the transfer, but presumes that it must have occurred

Research Study 4:    Squids

Fig. 1.  Mass laying of eggs by squid Doryteuthis opalescens in southern California. The photograph shows numerous cases containing egg capsules (inset photo) and a single, dead squid. The small size of the dead individual suggests that it may be a juvenile

Courtesy Kevin Lee, Fullerton, California diverKevin

Squids Doryteuthis opalescens spawn commonly in Barkley Sound, British Columbia.  A typical mass, consisting of an average of about 2,000 cases, each containing an average of 150 eggs, would therefore contain about 300,000 eggs (Fig. 1). The author estimates that 24,000 females may have been involved in a mass laying during a single night (31 May, 1982). 

NOTE the authors’ terminology throughout this account is unclear.  Use of “egg capsule mass”, “capsule mass aggregation”, egg number “per solitary mass”, and “number of eggs per isolated mass” without definition of each is confusing.  A better terminology, as used in the figure legend below, would be: a number of capsules, each containing a single egg, are contained within each case or sausage. A number of cases are laid by each female in large spawnings, leading to egg masses or egg mops

Research Study 5:    Squids

Fig. 1.  Stubby squid Rossia pacifica

Courtesy Roland Anderson and Seattle Aquarium, Washington

Stubby squids Rossia pacifica (Fig. 1) can readily be cultured in the laboratory.  At seasonally varying seawater temperature in the northern Washington area, embryonic development takes 5 - 6mo. From hatching to senescence takes another 18 -1 9mo, so the total life span is about 2yr.  Collections of Rossia in the Burrows Bay, Washington area reveal the presence of two distinct cohorts representing the 2yr of overlapping generations.  Release of hatchlings from an egg case, which occurs in the lab from late Oct – Dec, appears to be synchronised with the appearance of the new moon. The author suggests that the dark skies associated with declining daylight of late autumn and the new moon period may offer protection from predators. Additionally, the prolonged hatching period may be a strategy to spread out the appearance of the offspring in the plankton. 

NOTE  to see these data go to GROWTH

Research Study 6:    Squids

Fig. 1.  Copulating stubby squids Rossia pacifica. The male is the smaller of the two

Fig. 2.  Eggs of a stubby squid Rossia pacifica

Eggs of stubby squids Rossia pacifica have been found in the Puget Sound region in the months of February, April, June, and November, with one individual being observed laying in November.  Eggs require 6 - 8mo to hatch (Fig. 1). The eggs are large, up to 1cm in diameter, and the resulting hatchlings are about 1cm in size. Clutch sizes range from 50 - 75. The volume of eggs deposited represents about half the female’s live mass, and she dies a couple of days after laying. The eggs are usually deposited on underhangs of rocks, which perhaps keep them clean from “raining” sediments (Fig. 2).  Unlike with octopuses, there is no parental care of the eggs. The authors note that previous to their observations there have been no reports of egg-laying/egg cases for stubby squids in the field. 

NOTE in comparison, the eggs of Enteroctopus dofleini are about 6mm in diameter (Pickford, 1964)

Research Study 7:    Squids

An observation by researchers in California on a mass spawning of squids Doryteuthis opalescens in Monterey Bay following a 1997 El Niño event provides the following statistics.  In an area of about 1000m² there are some150 egg masses or “egg mops”.  Each egg mop contains an average of 259 cases, and each case contains an average of 164 eggs. The commonest predator eating the eggs is the sea star Patiria miniata.  

NOTE the terminology used in this paper has been modified to conform to that used in other Research Studies in this section

Research Study 8:    Squids

Fig. 1.  Egg mass of Dosidicus gigas, thought possibly to be from a single female

Fig. 2.  Developing embryo of a Humboldt squid Dosidicus gigas within its own protective chorion membrane and jelly envelope

A remarkable observation by researchers from educational institutions in California, Rhode Island, and Baja California is that eggs of Humboldt squids Dosidicus gigas are not deposited in the familar sausage-form of smaller, shallow-water species, but rather in a giant gelatinous, floating mass (Fig. 1).  Each egg is doubly protected by a chorion membrane and a jelly envelope (Fig. 2). The single egg mass featured here was observed off the east coast of Baja California, and was 3m in diameter, about 3 cubic meters in volume, and contained an estimated 1.3 million eggs. The eggs within are homogenously distributed and are over 99% fertilised. Although there is no obvious external barrier to maintain cohesiveness of the egg mass, any penetration as, for example, insertion of a collecting jar, immediately seals on withdrawal with no evident mark. Hatchlings from the mass appear healthy, swim about in laboratory dishes, and grow by 50% within the first 3d (at 20°C).  Following this, and at a size of about 1.5mm mantle length, they begin to decrease in size as their yolk supply beomes exhausted. The mass is neutrally buoyant and floats at a level presumably deep enough to be clear of surface wave disturbance, but shallow enough that the eggs experience good conditions of temperature and oxygenation for growth. The authors note that their paper is the first to document field- and laboratory-deposition of eggs in this species. 

NOTE this estimate is consistent with direct counts of eggs in oviducts of large female Dosidicus gigas reported by other researchers; hence, an egg mass of this size could have come from a single female

NOTE the mass is thought by the authors to be created by coatings (chorion and envelope, involved in later fertilisation) added to the eggs during passage through the oviducal gland. The eggs then pass through the nidamental gland where concentrated jelly is added (this later expands to form the watery, gelatinous matrix of the floating egg mass), and exit via the gonopore and siphon to be fertilised within the buccal area by sperm released from the male’s spermatophore (called a spermatangium by these authors) that has been left there after copulation

Research Study 9:    Squids

Fig. 1.  Effect of temperature on emergence success in squids Doryteuthis opalescens.  The apparently optimal range of 9 - 14^oC is indicated

Fig. 2.  Penetration of capitellid worm Capitella ovincola into an egg case of Doryteuthis opalescens

An investigation of temperature effects on hatching (actually, emergence of paralarvae from the egg case) of squids Doryteuthis opalescens at Hopkins Marine Station, Pacific Grove, California shows that optimal emergence (96%) occurs in the dark within the range 9 - 14°C (Fig. 1).  Additionally, the authors find that a polychaete worm Capitella ovincola¹, long thought to be commensal with the egg cases, actually feeds² on the gelatinous matrix surrounding the egg capsules in the cases, but not on the eggs, embryos, or paralarvae.  In order to feed, the worms slice into the cases to gain entry, and several may form an intertwined clump within a case (Fig. 2).   Loss of matrix material caused by the worms, both in leakage via the slicings and by being consumed, and by the sliced opening itself, appear to provide easier egress by the paralarvae from their egg cases. In fact, emergence percentage is slightly elevated for egg cases in the presence of the worm as compared with when it is absent (3% difference; note: the authors report two contradictory p values related to the statistical significance of these data). For this reason and because the worms are provided nutrients and protection, the relationship is considered by the authors to be mutualistic³, rather than commensal or parasitic. The authors don’t consider predation as an option.

NOTE¹ this species and related capitellids are known to occur in other species of squids, but none has ever been reported from other types of cephalopods. The worms are commonly found in egg cases laid in the field, but not apparently in egg cases laid in the laboratory

NOTE² this is determined through stable-isotope analysis, using changing ratios of ¹⁵N and ¹⁴N in purported prey and predator to indicate consumption

NOTE³ the authors actually use the term symbiotic for the relationship, which seems to be more commonly used in Britain and Europe for what we in North America refer to as mutualistic

Research Study 10:    Squids

Fig. 1.  Female Doryteuthis opalescens with egg case. The egg capsules within the case are clearly visible 

Courtesy Kevin Lee, Fullerton, California

Fig. 2.  Different scales of resolution of egg-mops of Doryteuthis opalescens using side-scan sonar.  Inset:  expanded view of several clusters, along with a possibly predatory sea star Patiria miniata (bottom of photo)

In an interesting application of sidescan-sonar methodology, a group of California researchers map the distribution of egg cases of squids Doryteuthis opalescens in the southern part of Monterey Bay (Fig. 1). The method allows easy assessment of egg-mop densities over large areas with good resolution (Fig. 2).  The authors conclude that the method holds promise for determining site preferences for spawning squids and year-to-year egg-mop abundances for use in managing the fisheries. 

NOTE a spawning female will attach each case (or sausage) to something firm, like a rock in the sand, or to other egg cases.  When other females use the same attachment point, a flared-out “egg-mop” or mass is created. Many such egg-mops may be clustered in areas that provide good attachment points

Research Study 11:    Squids

Fig. 1.  Distribution of egg cases of Doryteuthis opalescens: red circles, cases present; white circles, cases absent

Similar scanning methodologies are used by another group of fisheries scientists to survey spawning activity of squids Doryteuthis opalescens in areas around Monterey, California and the California Channel Islands (Fig. 1). The researchers report densities of cases exceeding 1000 per m^-2 in some areas, deposited at depths of 10 - 60m in central California and 20 - 90m in the Channel Islands. Interestingly, 95% of the cases are found on sand.  Most favourable conditions for spawning in these areas, then, are sandy substrata, temperatures of 10 - 14°C, and depths of 20 - 70m. 

Research Study 12:    Squids

Fig. 1. Northwards expansion of distributional range of Humboldt squids Dosidicus gigas.  Historical range in light green; most recent extended range in dark blue

Recent northward range expansion by Humboldt squids Dosidicus gigas raises the question of temperature effects on their embryonic development. This is investigated by scientists at Hopkins Marine Station, California who capture live gravid squids, remove eggs and sperm, arrange in vitro fertilisation of the eggs, and culture the embryos over a range of temperatures from 5 - 30°C.  Results show that hatching occurs only between 15 - 25°C (maximal at 20°C) suggesting that this temperature range is optimal for early development. The researchers then review past oceanographic data and discover that a large area of inshore California coastline has seasonably suitable temperatures for the squid’s early development.  It is possible, then, that spawning by D. gigas populations in this area may have facilitated the invasive spread of the species into more northern areas during the last decade. 

NOTE the process seems straightforward as written here, but in practise requires some deft technical innovations

NOTE temperature effects on post-hatching development are not mentioned by the researchers, and it may be that the techniques for culturing the hatchlings or paralarvae are not yet perfected