REPRODUCTION, DEVELOPMENT AND LIFE-HISTORY TRAITS
389
stalks) at both bathyal and abyssal depths. Meiofaunal
crustaceans, particularly harpacticoid copepods and ostracods, are very abundant in the deep-sea sediments.
Gonads, gametogenesis and reproductive
periodicity
The gonads of decapod crustaceans are discrete,
often paired or H-shaped organs that lie above the
stomach within the cephalothorax and extrude gametes
through gonopores on or near the bases of the
pereiopods. The gonads of peracarids originate under
the abdominal pereonites (Johnson et al., 2001), but
eventually may extend forward to the cephalothorax region as vitellogenesis proceeds (Bishop, 1994). Gonads
of barnacles lie at the proximal end of the visceral mass
in acorn barnacles and within the peduncle of stalked
barnacles (Green et al., 1994).
Most crustaceans brood their embryos either to the
juvenile stage or to a larval stage, so that reproductive
periodicity has often been documented by simply
noting the presence of brooded eggs or embryos. In
decapods, the egg mass or sponge is found attached
to the pleopods on the underside of the abdomen of
ripe “berried” females (Fig. 12.2). In barnacles, the
eggs are brooded as plaques or lamellae within the
mantle cavity, and in peracarids (including amphipods,
isopods, tanaids, mysids, cumaceans and a few lesser
known groups) they are brooded in a thoracic brood
chamber called a marsupium. The vast literature on
brooding in peracarids has been recently reviewed
by Johnson et al. (2001). In its most typical form,
the peracarid marsupium is formed by overlapping
plates (oostegites) which originate from the coxae of
the walking legs. Harpacticoid copepods carry their
embryos in a single brood sac attached to and trailing
behind the abdomen.
The gametogenic process of deep-sea crustaceans
appears identical to that of their shallow water relatives,
no special adaptations for deep-sea gamete formation
having been reported. The deep-sea red crab Geryon
quinquedens has an oogenic cycle illustrating the
general pattern seen in bathyal brachyurans that have
been studied (Haefner, 1977). The ovary begins as
a small colorless organ with no central lumen, and
consisting mostly of connective tissue. The germinal
epithelium is columnar and contains only small,
previtellogenic oocytes (Haefner, 1977). As it begins
to grow, the ovary becomes more opaque, and growing
oocytes replace the central connective tissue. The
early previtellogenic oocytes are small (14–53 mm) and
the nuclei are highly vacuolated. Vitellogenic oocytes
containing cytoplasmic yolk granules are larger (74–
278 mm) and have more compact nuclei. Each oocyte
is surrounded by a single layer of follicle cells. The
gonad grows and changes color as additional yolk is
added to the expanding oocytes. Eventually, the mature
ovum attains a diameter of 671 mm and the ovary fills
the dorsal side of the ovary, completely obscuring the
gut and hepatopancreas.
Wolff (1962) reported that the sex ratio of deep-sea
asellote isopods is often biased significantly in favor of
males. Indeed, of eleven families surveyed, all but one
had a significantly skewed sex ratio. Wolff suggested
that this pattern could be explained by gender-specific
survivorship, as is known for some shallow-water
isopods (Steel, 1961). Evidence for hermaphroditism
has been found in four hadal tanaids collected from a
depth of more than 6000 m (Wolff, 1956a), and Wilson
(1981) reported a case of facultative hermaphroditism
in a deep-sea isopod, Eurycope iphthima.
Table 12.3 gives a selection of studies of reproductive periodicity in deep-sea crustaceans. Although
continuous breeding was predicted for deep-sea isopods
early in the 20th century (Reibisch, 1927), the earliest
data bearing directly on the subject of reproductive
seasonality were anecdotal observations by Wolff
(1962) and others who participated in the Danish
Galathea Expedition between 1950 and 1952. In his
monograph on the asellote isopods, Wolff (1962)
noted that deep-sea asellote populations have fewer
incubatory females (i.e., those with marsupium present)
than did shallow-water isopods. Moreover, no brooding
females at all were found among the samples of isopods
(n = 40) and tanaids (n = 30) recovered from the hadal
trenches during this expedition (Wolff, 1956a,b). Wolff
(1962) considered several possible explanations for this
pattern: 1) mortality may be greater for brooding females than for non-brooding ones; 2) brooding females
may live deeper in the sediment, thereby avoiding the
sampling equipment; 3) breeding occurs only once
every few years; 4) the brooding period is much shorter
than the preparatory period (the preparatory period
is the moult stage when the marsupium is present,
but the eggs have not been deposited in it). Although
he had no access to seasonal samples from a given
locality, he guessed that brooding should occupy a
much longer period, perhaps 3–4 months, in deep
water than the incubatory periods of 30 to 40 days
known among shallow-water isopods, making the small
proportion of incubating females even more surprising.
After considering the various possibilities listed above,
389
stalks) at both bathyal and abyssal depths. Meiofaunal
crustaceans, particularly harpacticoid copepods and ostracods, are very abundant in the deep-sea sediments.
Gonads, gametogenesis and reproductive
periodicity
The gonads of decapod crustaceans are discrete,
often paired or H-shaped organs that lie above the
stomach within the cephalothorax and extrude gametes
through gonopores on or near the bases of the
pereiopods. The gonads of peracarids originate under
the abdominal pereonites (Johnson et al., 2001), but
eventually may extend forward to the cephalothorax region as vitellogenesis proceeds (Bishop, 1994). Gonads
of barnacles lie at the proximal end of the visceral mass
in acorn barnacles and within the peduncle of stalked
barnacles (Green et al., 1994).
Most crustaceans brood their embryos either to the
juvenile stage or to a larval stage, so that reproductive
periodicity has often been documented by simply
noting the presence of brooded eggs or embryos. In
decapods, the egg mass or sponge is found attached
to the pleopods on the underside of the abdomen of
ripe “berried” females (Fig. 12.2). In barnacles, the
eggs are brooded as plaques or lamellae within the
mantle cavity, and in peracarids (including amphipods,
isopods, tanaids, mysids, cumaceans and a few lesser
known groups) they are brooded in a thoracic brood
chamber called a marsupium. The vast literature on
brooding in peracarids has been recently reviewed
by Johnson et al. (2001). In its most typical form,
the peracarid marsupium is formed by overlapping
plates (oostegites) which originate from the coxae of
the walking legs. Harpacticoid copepods carry their
embryos in a single brood sac attached to and trailing
behind the abdomen.
The gametogenic process of deep-sea crustaceans
appears identical to that of their shallow water relatives,
no special adaptations for deep-sea gamete formation
having been reported. The deep-sea red crab Geryon
quinquedens has an oogenic cycle illustrating the
general pattern seen in bathyal brachyurans that have
been studied (Haefner, 1977). The ovary begins as
a small colorless organ with no central lumen, and
consisting mostly of connective tissue. The germinal
epithelium is columnar and contains only small,
previtellogenic oocytes (Haefner, 1977). As it begins
to grow, the ovary becomes more opaque, and growing
oocytes replace the central connective tissue. The
early previtellogenic oocytes are small (14–53 mm) and
the nuclei are highly vacuolated. Vitellogenic oocytes
containing cytoplasmic yolk granules are larger (74–
278 mm) and have more compact nuclei. Each oocyte
is surrounded by a single layer of follicle cells. The
gonad grows and changes color as additional yolk is
added to the expanding oocytes. Eventually, the mature
ovum attains a diameter of 671 mm and the ovary fills
the dorsal side of the ovary, completely obscuring the
gut and hepatopancreas.
Wolff (1962) reported that the sex ratio of deep-sea
asellote isopods is often biased significantly in favor of
males. Indeed, of eleven families surveyed, all but one
had a significantly skewed sex ratio. Wolff suggested
that this pattern could be explained by gender-specific
survivorship, as is known for some shallow-water
isopods (Steel, 1961). Evidence for hermaphroditism
has been found in four hadal tanaids collected from a
depth of more than 6000 m (Wolff, 1956a), and Wilson
(1981) reported a case of facultative hermaphroditism
in a deep-sea isopod, Eurycope iphthima.
Table 12.3 gives a selection of studies of reproductive periodicity in deep-sea crustaceans. Although
continuous breeding was predicted for deep-sea isopods
early in the 20th century (Reibisch, 1927), the earliest
data bearing directly on the subject of reproductive
seasonality were anecdotal observations by Wolff
(1962) and others who participated in the Danish
Galathea Expedition between 1950 and 1952. In his
monograph on the asellote isopods, Wolff (1962)
noted that deep-sea asellote populations have fewer
incubatory females (i.e., those with marsupium present)
than did shallow-water isopods. Moreover, no brooding
females at all were found among the samples of isopods
(n = 40) and tanaids (n = 30) recovered from the hadal
trenches during this expedition (Wolff, 1956a,b). Wolff
(1962) considered several possible explanations for this
pattern: 1) mortality may be greater for brooding females than for non-brooding ones; 2) brooding females
may live deeper in the sediment, thereby avoiding the
sampling equipment; 3) breeding occurs only once
every few years; 4) the brooding period is much shorter
than the preparatory period (the preparatory period
is the moult stage when the marsupium is present,
but the eggs have not been deposited in it). Although
he had no access to seasonal samples from a given
locality, he guessed that brooding should occupy a
much longer period, perhaps 3–4 months, in deep
water than the incubatory periods of 30 to 40 days
known among shallow-water isopods, making the small
proportion of incubating females even more surprising.
After considering the various possibilities listed above,