285
16 Loligo vulgaris and Doryteuthis opalescens
also evaluated the salinity tolerance of L. vulgaris eggs (stages 7–11) from the Izmir
Bay, Turkey in two experiments. In the first, egg capsules were introduced at salinities of 0, 28, 31, 34 and 37 psu under a mean temperature of 12.2 °C and in the
second, at 32–42 psu (mean temperature of 19.8 °C). The eggs developed normally
only within the range of 34–38 psu. These results suggest that salinity tolerance of
eggs decreased at lower temperatures, in accordance with the result obtained by
Nabhitabhata et al. (2001) for Sepioteuthis lessoniana. Nonetheless, in the experiments of Sen (2004, 2005b) eggs were transferred to different salinities without acclimatization and no information on hatchings competence was provided. There is a
good evidence that sudden temperature and salinity changes must be avoided, especially at early embryonic stages (D’Aniello et al. 1989; Boletzky and Hanlon 1983).
Changes in pH have the potential to cause a major impact on the physiological
aerobic performance of cephalopods (Pörtner and Zielinski 1998), particularly during late embryonic stages. D’Aniello et al. (1989) exposed L. vulgaris intermediate
stage eggs to pH levels between 7.1 and 9.1, observing no development at these extreme pH values. Eggs developed normally and hatching followed at pH 7.6 and 8.6,
but the paralarvae did not survive. Normal egg development and paralarval survival
was only found within a pH range of 7.8–8.4. Vidal et al. (2002a) observed that pH
below 8.0 produced abnormal development and high mortality of the newly hatched
D. opalescens paralarvae and recommended an even narrower pH range (8.1–8.4) for
egg incubation. More recently, Lacoue-Labarthe et al. (2011) evaluated the effects of
ocean acidification on accumulation of trace elements in embryos and hatchlings of
L. vulgaris. It was shown that the combined effect of low pH on the adsorption and
protective properties of the egg capsules during embryogenesis and of high CO 2 partial pressure on the metabolism of embryos and paralarvae resulted in changes to the
bioaccumulation of metals. These physiological responses were believed to be a result
of ionic and acid–base imbalance.
Eggs are incubated under constant low light intensities (1–6 Lx—Vidal et al.
2002a; 1.5µE m
−2
s
−1
—Villanueva 2000b) and also to a variety of manipulated (Paulij
et al. 1990; Vidal et al. 2002a, b; Villanueva et al. 2007) and natural photoperiods
(Boletzky 1979; D’Aniello et al. 1989). In any event, it is advisable to maintain light
at low intensities. Paulij et al. (1990) demonstrated that photoperiodicity has a major
influence on the timing of hatching of both L. vulgaris and L. forbesii. Independent
of the timing and duration of the dark period, the transition from light to dark conditions function as a synchronizer of hatching. This synchronization occurs only if light
and dark transitions are detected by the embryos, given that hatching could not be
stimulated by twilight (< 50 µE m
−2
s
−1
). Embryos exposed to constant light showed
random hatching, but when exposed to a dark shock hatched shortly after the onset
of darkness. It was also revealed that an endogenous hatching rhythm can only be
preserved after stage 15. Synchronous hatching seems to be very important to increase
the chances of hatchlings survival in the wild and could have a foundation on selective
intrinsic factors, such as light (L)–dark (D) cycles, although there are no field studies
to attest this argument. There seem to be no reports of the negative effect of light on
the embryonic development of the loliginid squid. However, reliable evidence suggest
that continuous illumination might lengthen the embryogenesis in Sepia officinalis by
16 Loligo vulgaris and Doryteuthis opalescens
also evaluated the salinity tolerance of L. vulgaris eggs (stages 7–11) from the Izmir
Bay, Turkey in two experiments. In the first, egg capsules were introduced at salinities of 0, 28, 31, 34 and 37 psu under a mean temperature of 12.2 °C and in the
second, at 32–42 psu (mean temperature of 19.8 °C). The eggs developed normally
only within the range of 34–38 psu. These results suggest that salinity tolerance of
eggs decreased at lower temperatures, in accordance with the result obtained by
Nabhitabhata et al. (2001) for Sepioteuthis lessoniana. Nonetheless, in the experiments of Sen (2004, 2005b) eggs were transferred to different salinities without acclimatization and no information on hatchings competence was provided. There is a
good evidence that sudden temperature and salinity changes must be avoided, especially at early embryonic stages (D’Aniello et al. 1989; Boletzky and Hanlon 1983).
Changes in pH have the potential to cause a major impact on the physiological
aerobic performance of cephalopods (Pörtner and Zielinski 1998), particularly during late embryonic stages. D’Aniello et al. (1989) exposed L. vulgaris intermediate
stage eggs to pH levels between 7.1 and 9.1, observing no development at these extreme pH values. Eggs developed normally and hatching followed at pH 7.6 and 8.6,
but the paralarvae did not survive. Normal egg development and paralarval survival
was only found within a pH range of 7.8–8.4. Vidal et al. (2002a) observed that pH
below 8.0 produced abnormal development and high mortality of the newly hatched
D. opalescens paralarvae and recommended an even narrower pH range (8.1–8.4) for
egg incubation. More recently, Lacoue-Labarthe et al. (2011) evaluated the effects of
ocean acidification on accumulation of trace elements in embryos and hatchlings of
L. vulgaris. It was shown that the combined effect of low pH on the adsorption and
protective properties of the egg capsules during embryogenesis and of high CO 2 partial pressure on the metabolism of embryos and paralarvae resulted in changes to the
bioaccumulation of metals. These physiological responses were believed to be a result
of ionic and acid–base imbalance.
Eggs are incubated under constant low light intensities (1–6 Lx—Vidal et al.
2002a; 1.5µE m
−2
s
−1
—Villanueva 2000b) and also to a variety of manipulated (Paulij
et al. 1990; Vidal et al. 2002a, b; Villanueva et al. 2007) and natural photoperiods
(Boletzky 1979; D’Aniello et al. 1989). In any event, it is advisable to maintain light
at low intensities. Paulij et al. (1990) demonstrated that photoperiodicity has a major
influence on the timing of hatching of both L. vulgaris and L. forbesii. Independent
of the timing and duration of the dark period, the transition from light to dark conditions function as a synchronizer of hatching. This synchronization occurs only if light
and dark transitions are detected by the embryos, given that hatching could not be
stimulated by twilight (< 50 µE m
−2
s
−1
). Embryos exposed to constant light showed
random hatching, but when exposed to a dark shock hatched shortly after the onset
of darkness. It was also revealed that an endogenous hatching rhythm can only be
preserved after stage 15. Synchronous hatching seems to be very important to increase
the chances of hatchlings survival in the wild and could have a foundation on selective
intrinsic factors, such as light (L)–dark (D) cycles, although there are no field studies
to attest this argument. There seem to be no reports of the negative effect of light on
the embryonic development of the loliginid squid. However, reliable evidence suggest
that continuous illumination might lengthen the embryogenesis in Sepia officinalis by