392
Craig M. YOUNG
isopods in the Scotia Sea (George and Menzies, 1967)
and off North Carolina (George and Menzies, 1968).
The evidence has been considered equivocal by most
subsequent workers (e.g., Rokop, 1977b; Harrison,
1988; Bishop and Shalla, 1994), because many species
were pooled and there was limited seasonal coverage
of samples from any given region; nevertheless, the
work stimulated interest in the possibility of seasonal
reproduction in peracarids. Harrison (1988) pooled
data for 47 asellote species in the Rockall Trough
and concluded that there was no evidence for a
distinct seasonal breeding pattern, though he did
note a “fluctuating” breeding pattern in which more
brooding females were found in some seasons than
others. A fluctuating pattern of recruitment was also
found in the cumacean Diastylis stygia, a species
that recruits throughout the year in the northwest
Atlantic (Blake and Watling, 1994). Strong evidence
for seasonal breeding has been found at abyssal depth
only for the mysid Boreomysis tridens (Mauchline,
1986), the Antarctic amphipod Eusirus perdentatus
(Klages, 1993), and the cumacean Leucon profundus
(Bishop and Shalla, 1994).
The careful study of reproduction in Leucon profundus by Bishop and Shalla (1994) sets a high standard
that should be used in future studies of deep-sea
peracarids. In this study, females were classified not
only by the presence or absence of a brood, but
also by the size and stage of the gonad and the
developmental stages of brooded embryos. Leucon
profundus was shown unequivocally to have a seasonal
breeding cycle lasting approximately 14 months. This
finding raises the possibility that other species in
which brooding females have been found over much
of the year may in fact be seasonal breeders with
long reproductive cycles rather than aseasonal breeders
with short brood times. This work raises an important
challenge to virtually all previous studies; even though
there are perhaps more observations of reproductive
condition of peracarid crustaceans than most other
groups of deep-sea animals, one still has only a very
limited understanding of their breeding cycles and life
histories.
Of the various caridean shrimp and other crustacea
common at hydrothermal vents (Table 12.4), there is
little evidence for periodic reproduction (reviewed by
Tyler and Young, 1999). Rimicaris exoculata, probably
the most abundant metazoan at vents on the midAtlantic ridge, appears to have multiple cohorts of eggs
in its gonad, suggesting periodicity at the individual
level (Ramirez Llodra et al., 2000), but insufficient
seasonal coverage is available to infer any sort of
population-level synchrony. Extensive collections of
these abundant carideans have yielded a surprisingly
small number of berried females (P.A. Tyler, personal
communication). As with abyssal isopods, there is no
completely satisfying explanation for this pattern. One
hypothesis that remains untested is that females brood
their young far away from the vents in order to protect
the embryos from elevated temperatures (Tyler and
Young, 1999).
A number of crustaceans living at depths less than
1000 meters breed seasonally, as might be expected
(Table 12.4). These include bathyal dendrobranchiate
and caridean shrimps in the Mediterranean (Demestre
and Fortu˜ no, 1992; Company and Sard` a, 1997) and
some species of brachyurans in the northwest Atlantic
and the Gulf of Mexico (Haefner, 1977; Hartnoll and
Rice, 1984; Erdman et al., 1991). It is interesting
that various species of the slope crab genus Chaceon
found in the northeast Atlantic are seasonal breeders
(Haefner, 1977, 1978; Erdman et al., 1991), but the
congeneric C. maritae, living at comparable depths in
the Southeast Atlantic, is aseasonal (Melville-Smith,
1987). There are insufficient data to infer seasonal
reproduction in any abyssal brachyuran, though Wenner
(1980) suggested that Benthesicymus bartletti from
2000 m may have a synchronous breeding pattern.
Most species of pandalid shrimp in shallow water
are protandrous hermaphrodites, changing from male to
female as they grow. King and Moffitt (1984) presented
evidence that several species of deep-water tropical
pandalids are fully dioecious and that they never
undergo sex reversal. The reason for this difference
between deep-sea and shallow species is not known.
Gamete structure and fertilization
Spermatozoa of all crustaceans are aflagellate and
are modified for internal fertilization. There have
been no detailed studies at the ultrastructural level of
oogenesis or spermatogenesis in deep-sea crustaceans,
though the general structure of the reproductive system
is well known from gross dissections and paraffin
histology. Spermatozoa are often packaged into sperm
packets which are deposited in the oviducts of the female as sperm plugs. These have been commonly seen
in the hydrothermal-vent crab Bythograea thermydron
(G. Perovich, personal communication). The various
studies of gonad morphology that have been conducted
at the light-microscope level (e.g., Ramirez Llodra
Craig M. YOUNG
isopods in the Scotia Sea (George and Menzies, 1967)
and off North Carolina (George and Menzies, 1968).
The evidence has been considered equivocal by most
subsequent workers (e.g., Rokop, 1977b; Harrison,
1988; Bishop and Shalla, 1994), because many species
were pooled and there was limited seasonal coverage
of samples from any given region; nevertheless, the
work stimulated interest in the possibility of seasonal
reproduction in peracarids. Harrison (1988) pooled
data for 47 asellote species in the Rockall Trough
and concluded that there was no evidence for a
distinct seasonal breeding pattern, though he did
note a “fluctuating” breeding pattern in which more
brooding females were found in some seasons than
others. A fluctuating pattern of recruitment was also
found in the cumacean Diastylis stygia, a species
that recruits throughout the year in the northwest
Atlantic (Blake and Watling, 1994). Strong evidence
for seasonal breeding has been found at abyssal depth
only for the mysid Boreomysis tridens (Mauchline,
1986), the Antarctic amphipod Eusirus perdentatus
(Klages, 1993), and the cumacean Leucon profundus
(Bishop and Shalla, 1994).
The careful study of reproduction in Leucon profundus by Bishop and Shalla (1994) sets a high standard
that should be used in future studies of deep-sea
peracarids. In this study, females were classified not
only by the presence or absence of a brood, but
also by the size and stage of the gonad and the
developmental stages of brooded embryos. Leucon
profundus was shown unequivocally to have a seasonal
breeding cycle lasting approximately 14 months. This
finding raises the possibility that other species in
which brooding females have been found over much
of the year may in fact be seasonal breeders with
long reproductive cycles rather than aseasonal breeders
with short brood times. This work raises an important
challenge to virtually all previous studies; even though
there are perhaps more observations of reproductive
condition of peracarid crustaceans than most other
groups of deep-sea animals, one still has only a very
limited understanding of their breeding cycles and life
histories.
Of the various caridean shrimp and other crustacea
common at hydrothermal vents (Table 12.4), there is
little evidence for periodic reproduction (reviewed by
Tyler and Young, 1999). Rimicaris exoculata, probably
the most abundant metazoan at vents on the midAtlantic ridge, appears to have multiple cohorts of eggs
in its gonad, suggesting periodicity at the individual
level (Ramirez Llodra et al., 2000), but insufficient
seasonal coverage is available to infer any sort of
population-level synchrony. Extensive collections of
these abundant carideans have yielded a surprisingly
small number of berried females (P.A. Tyler, personal
communication). As with abyssal isopods, there is no
completely satisfying explanation for this pattern. One
hypothesis that remains untested is that females brood
their young far away from the vents in order to protect
the embryos from elevated temperatures (Tyler and
Young, 1999).
A number of crustaceans living at depths less than
1000 meters breed seasonally, as might be expected
(Table 12.4). These include bathyal dendrobranchiate
and caridean shrimps in the Mediterranean (Demestre
and Fortu˜ no, 1992; Company and Sard` a, 1997) and
some species of brachyurans in the northwest Atlantic
and the Gulf of Mexico (Haefner, 1977; Hartnoll and
Rice, 1984; Erdman et al., 1991). It is interesting
that various species of the slope crab genus Chaceon
found in the northeast Atlantic are seasonal breeders
(Haefner, 1977, 1978; Erdman et al., 1991), but the
congeneric C. maritae, living at comparable depths in
the Southeast Atlantic, is aseasonal (Melville-Smith,
1987). There are insufficient data to infer seasonal
reproduction in any abyssal brachyuran, though Wenner
(1980) suggested that Benthesicymus bartletti from
2000 m may have a synchronous breeding pattern.
Most species of pandalid shrimp in shallow water
are protandrous hermaphrodites, changing from male to
female as they grow. King and Moffitt (1984) presented
evidence that several species of deep-water tropical
pandalids are fully dioecious and that they never
undergo sex reversal. The reason for this difference
between deep-sea and shallow species is not known.
Gamete structure and fertilization
Spermatozoa of all crustaceans are aflagellate and
are modified for internal fertilization. There have
been no detailed studies at the ultrastructural level of
oogenesis or spermatogenesis in deep-sea crustaceans,
though the general structure of the reproductive system
is well known from gross dissections and paraffin
histology. Spermatozoa are often packaged into sperm
packets which are deposited in the oviducts of the female as sperm plugs. These have been commonly seen
in the hydrothermal-vent crab Bythograea thermydron
(G. Perovich, personal communication). The various
studies of gonad morphology that have been conducted
at the light-microscope level (e.g., Ramirez Llodra