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Effects of the Toxic Dinoflagellate Heterocapsa circularisquama on Larvae of the Pearl Oyster Pinctada Fucata Martensii (Dunker, 1873)

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The effects of the toxic dinoflagellate Heterocapsa circularisquama on the activity rate, development rate, prevalence of damage, and survival rate of trochophore and D-shaped larvae of the pearl oyster Pinctada fucata martensii were studied in relation to H. circularisquama cell densities and exposure duration. In addition, larvae were regularly processed via scanning electron microscopy to investigate morphological damage. The activity rate of both larval stages was significantly decreased after 3–6 h of exposure to H. circularisquama at densities ranging from 100 to 2 × 104 cells/mL. The prevalence of damage was significantly high after 3–6 h of exposure to H. circularisquama at densities of 100 to 2 × 104 cells/mL and 5 × 103 to 2 × 104 cells/mL for trochophores and D-shaped larvae, respectively. Cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited mineralization of the shell, mantle protrusion, the appearance of abnormal masses in the velum, and the exfoliation of the larvae cilia coupled with epithelial desquamation were frequently observed. The activity rate of D-larvae transformed from trochophores exposed to H. circularisquama for 12–48 h at densities ranging from 10 to 2 × 104 cells/mL was significantly reduced. The survival of D-shaped larvae plummeted to less than 0.013 for densities ≥ 5 × 103 cells/mL. The results indicate that H. circularisquama blooms have detrimental impacts on bivalves at early life stages. Blooms of H. circularisquama occurring during the spawning periods will influence the natural recruitment in P. fucata martensii and will have profound impacts on its population biology. Therefore, shellfish farms should not be built in coastal areas where H. circularisquama occurs, or genitors should be relocated during potential blooming periods.
Light (LM) and scanning electron micrographs (SEM) of control and exposed P. fucata martensii trochophore larvae to H. circularisquama at 10 3 cells/mL. (A) Control trochophore 2 h postexposure (LM) showing normal body shape with the prototroch and apical tuft. (B) Trochophore exposed for 2 h (LM) showing cytoplasmic discharges. (C) Control trochophore (SEM) 3 h postexposure showing the animal pole developing into a sail of velum with the apical tuft in the center, and mineralization of the shell. (D, E) Trochophores (SEM) 3 h postexposure showing incomplete mineralization of the organic pellicle, abnormal masses in the velum, and H. circularisquama cells trapped in the detached cilia (F) Control trochophore (SEM) 6 h postexposure showing a fully developed velum and a further mineralized shell. (G, H) Trochophores (SEM) 6 h postexposure showing exfoliation of the velum cilia, epithelial desquamation, and hypersecretion of mucus entrapping H. circularisquama cell. (I) Control trochophore (SEM) 24 h postexposure fully developed into a perfectly shaped D-larva with a straight hinge and concentric growth rings. (J, K). Trochophores (SEM) 24 h postexposure showing heavier exfoliation of the velum cilia and epithelial desquamation, and abnormally shaped D-larva with incomplete mineralization of the shell. AM, abnormal mass; AS, abnormal shell; AT, apical tuft; Cd, cytoplasmic discharge; Ci, cilia; ED, epithelial desquamation; Ex, exfoliation; Gr, growth rings; Hc, H. circularisquama cell; Mc, mucus; MS, mineralized shell; OP, organic pellicle; P, prototroch; V, velum.
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EFFECTS OF THE TOXIC DINOFLAGELLATE HETEROCAPSA CIRCULARISQUAMA ON
LARVAE OF THE PEARL OYSTER PINCTADA FUCATA MARTENSII (DUNKER, 1873)
LEILA BASTI,
1,
* JIYOJI GO,
2
KEITA HIGUCHI,
2
KIYOHITO NAGAI
2
AND
SUSUMU SEGAWA
1
1
Laboratory of Invertebrates Zoology, Department of Ocean Science, Tokyo University of Marine
Science and Technology, Shinagawa, Tokyo 108-8477, Japan;
2
K. Mikimoto & Co. Ltd, Osaki Hazako,
Hamajima-Cho, Shima, Mie 517-0403, Japan
ABSTRACT The effects of the toxic dinoflagellate Heterocapsa circularisquama on the activity rate, development rate, prevalence
of damage, and survival rate of trochophore and D-shaped larvae of the pearl oyster Pinctada fucata martensii were studied in
relation to H. circularisquama cell densities and exposure duration. In addition, larvae were regularly processed via scanning electron
microscopy to investigate morphological damage. The activity rate of both larval stages was significantly decreased after 3–6 h of
exposure to H. circularisquama at densities ranging from 100 to 2 3 10
4
cells/mL. The prevalence of damage was significantly high
after 3–6 h of exposure to H. circularisquama at densities of 100 to 2310
4
cells/mL and 5310
3
to 23 10
4
cells/mL for trochophores
and D-shaped larvae, respectively. Cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited min-
eralization of the shell, mantle protrusion, the appearance of abnormal masses in the velum, and the exfoliation of the larvae cilia
coupled with epithelial desquamation were frequently observed. The activity rate of D-larvae transformed from trochophores
exposed to H. circularisquama for 12–48 h at densities ranging from 10 to 23 10
4
cells/mL was significantly reduced. The survival of
D-shaped larvae plummeted to less than 0.013 for densities $ 53 10
3
cells/mL. The results indicate that H. circularisquama blooms
have detrimental impacts on bivalves at early life stages. Blooms of H. circularisquama occurring during the spawning periods will
influence the natural recruitment in P. fucata martensii and will have profound impacts on its population biology. Therefore, shellfish
farms should not be built in coastal areas where H. circularisquama occurs, or genitors should be relocated during potential blooming
periods.
KEY WORDS: Heterocapsa circularisquama, Pinctada fucata martensii, larvae, activity, damage, survivorship
INTRODUCTION
Harmful algal blooms (HABs) often cause serious economic
loss worldwide as a result of the contamination and closure of
bivalve harvests (Shumway 1990). Among HABs, approximately
58 species of dinoflagellates are known to induce toxic red tides
associated with bivalve mortality (Burkholder 1998). Several
studies considering the relationship between toxic dinoflagellates
and the shellfish industry are available and deal mainly with toxin
uptake, anatomic distribution, and depuration (Bricelj & Shumway
1998), but they also have examined the direct effects of the toxic
algae on bivalve species. HABs producing dinoflagellates have been
shown to induce several detrimental effects in bivalves, interfering
with feeding activities (Cucci et al. 1985, Shumway & Cucci 1987,
Lesser & Shumway 1993), shell valve behavior (Gainey & Shumway
1988), burrowing abilities (Bricelj et al. 2000, MacQuarrie &
Bricelj 2008), and byssus production (Shumway et al. 1987), and
compromising growth and survival (Widdows et al. 1979, Nielsen
&Stro
¨
mgren 1991, Luckenbach et al. 1993).
A relatively new toxic dinoflagellate species, Heterocapsa
circularisquama, forms recurrent toxic efflorescences in Japan
and has been associated with mass mortality of natural and
cultured bivalves (Matsuyama et al. 1996), leading to serious
hardship for shellfish fisheries and aquaculture industries
(Matsuyama 1999). The dinoflagellate H. circularisquama was
shown to induce several deleterious effects in juvenile and adult
marine bivalves, ranging from behavioral alteration (Nagai
et al. 2006, Basti et al. 2009) and impairments of the basic
physiological functions of feeding and respiration (Matsuyama
et al. 1997, Basti & Segawa unpublished results) to death
(Matsuyama et al. 1992, Nagai et al. 1996, Yamatogi et al. 2004,
Basti & Segawa 2010).
Because H. circularisquama appears to have established itself
as a permanent resident of the Japanese central and western coastal
areas, where i t is formi ng r ecurrent, extensive toxic blooms
(Matsuyama 2003a, 2003b), it is plausible that native she llfish
species, including the commercially important pearl oyster
Pinctada fucata, could be exposed at any stage of their life cycle.
Red tides of H. circularisquama occur more frequently during the
summer and autumn seasons (Matsuyama 2003a) and fall along
the Japanese coasts at the time when the majority of bivalve
species spawn. The timing, density, and geographical extent of
H. circularisquama could play a role in the recruitment success of
bivalves if there are detrimental effects on any particular life
history stage.
The current study was designed to establish the causal re-
lationship between H. circularisquama densities and persistency in
the water, and potential toxic effects for Pinctada fucata martensii
TABLE 1.
Morphometric measures for Pinctada fucata martensii
genitors.
Sex n
Shell
Length (mm)
Shell
Height (mm)
Body Wet
Weight (g)
Male 4 78.42 ± 1.89 29.3 ± 2.76 63.4 ± 7.74
Female 4 79.45 ± 3.05 29.32 ± 2.34 65.72 ± 5.99
Data expressed as mean ± SD.
*Corresponding author. E-mail: bastileila@gmail.com
DOI: 10.2983/035.030.0125
Journal of Shellfish Research, Vol. 30, No. 1, 177–186, 2011.
177
trochophores and D-shaped larvae. The activity rate, develop-
ment rate, nature and prevalence of damage, and survival rate of
larvae were examined.
MATERIALS AND METHODS
Larval Rearing
Sexually mature adult pearl oysters, P. fucata (Table 1), were
reared at the K. Mikimoto & Co. Ltd farm, Ago Bay, Mie
Prefecture, Japan. Oyster shells were opened with a shell opener
and several incisions were made to the gonads. Gametes were
obtained by stripping the oysters and filtering the gonad spills
through gauze. Eggs and sperm were placed into 2-L and 1-L
beakers, respectively, containing 0.75 mM ammonia–seawater
solution for activation. The egg density in the suspension was
determined by taking 3 samples under agitation. The density
was then adjusted to 10
4
eggs/L. Only eggs showing a regular,
round shape were used. The sperm quality was checked under a
microscope and only those spermatozoa showing high swim-
ming activity were used for fertilization. Eggs were activated
for 45 min, and spermatozoa for 10 min. The eggs were then
fertilized with spermatozoa for 10 min, washed with filtered
(1.0-mm pore size) and UV-treated seawater, and transferred
to 30-L tanks maintained at 25°C. Trochophores (12 h post-
fertilization) and D-shaped larvae (24 h postfertilization) were
washed and used for the exposure experiments.
Alga Culture
The toxic H. circularisquama (strain HC92) was isolated
from Ago Bay, Mie Prefecture, Japan, and cultured at 25°CinF/2
medium, under a 12-h light/dark photoperiod. After counting, the
alga cells were added to the experimental seawater at the desired
densities.
In Vivo Exposure of Larvae
Both trochophores and D-shaped larvae were exposed to H.
circularisquama in triplicate at 0, 10, 100, 500, 10
3
,53 10
3
,10
4
,
and 2 3 10
4
cells/mL in 6- or 12-well plates, depending on the
analysis to be performed. For each concentration of resus-
pended cell medium, 2 or 10 mL was transferred to each well
chamber, and the experiments were performed under a 12-h
light/dark photoperiod at 25°C for 72 h. The original volume of
H. circularisquama culture medium was diluted with seawater
several times before use. We assume that the alga culture
medium has no effects on the pearl oyster larvae (Nagai et al.
1996). The trochophore and D-shaped larvae densities were set
to 50 individuals/mL, and food was not provided.
Figure 2. Development rate of trochophore larvae of P. fucata martensii exposed to H. circularisquama for 24 h. An asterisk indicates a significant
difference from the relative control (ANOVA, Turkey-HSD, P < 0.01).
Figure 1. Activity rate of trochophore larvae of P. fucata martensii exposed to H. circularisquama. An asterisk indicates a significant difference from the
relative control (ANOVA, Turkey-HSD, P < 0.01).
BASTI ET AL.178
Effects on Trochophores
Trochophores exposed to H. circularisquama were regularly
observed or sampled and fixed in a 5% formalin solution to
determine the following:
Trochophore activity rate ¼ number of actively swimming
trochophores/total number of trochophores
Prevalence of abnormalities ¼ number of abnormal trocho-
phores/total number of trochophores
Figure 3. Light (LM) and scanning electron micrographs (SEM) of control and exposed P. fucata martensii trochophore larvae to H. circularisquama at
10
3
cells/mL. (A) Control trochophore 2 h postexposure (LM) showing normal body shape with the prototroch and apical tuft. (B) Trochophore exposed
for 2 h (LM) showing cytoplasmic discharges. (C) Control trochophore (SEM) 3 h postexposure showing the animal pole developing into a sail of velum
with the apical tuft in the center, and mineralization of the shell. (D, E) Trochophores (SEM) 3 h postexposure showing incomplete mineralization of the
organic pellicle, abnormal masses in the velum, and H. circularisquama cells trapped in the detached cilia (F) Control trochophore (SEM) 6 h
postexposure showing a fully developed velum and a further mineralized shell. (G, H) Trochophores (SEM) 6 h postexposure showing exfoliation of the
velum cilia, epithelial desquamation, and hypersecretion of mucus entrapping H. circularisquama cell. (I) Control trochophore (SEM) 24 h postexposure
fully developed into a perfectly shaped D-larva with a straight hinge and concentric growth rings. (J, K). Trochophores (SEM) 24 h postexposure showing
heavier exfoliation of the velum cilia and epithelial desquamation, and abnormally shaped D-larva with incomplete mineralization of the shell. AM,
abnormal mass; AS, abnormal shell; AT, apical tuft; Cd, cytoplasmic discharge; Ci, cilia; ED, epithelial desquamation; Ex, exfoliation; Gr, growth rings;
Hc, H. circularisquama cell; Mc, mucus; MS, mineralized shell; OP, organic pellicle; P, prototroch; V, velum.
HETEROCAPSA CIRCULARISQUAMA AFFECTS PEARL OYSTER LARVAE 179
Development rate ¼ number of D-shaped larvae/total number
of trochophores
Activity rate of transformed trochophores ¼ number of actively
swimming D-shaped larvae/total number of transformed
D-shaped larvae
Effects on D-Shaped Larvae
D-shaped larvae exposed to H. circularisquama were regu-
larly observed or sampled and fixed in a 5% formalin solution
to determine the following:
D-shaped larvae activity rate ¼ number of actively swimming
D-shaped larvae/total number of D-shaped larvae
Prevalence of abnormalities ¼ number of abnormal D-shaped
larvae/total number of D-shaped larvae
Survival rate ¼ number of alive D-shaped larvae/total number
of larvae
Scanning Electron Microscopy
Trochophores and D-shaped larvae samples were fixed with
4% glutaraldehyde solution in 0.15 M sodium cacodylate
trihydrate buffer, which contained 0.28 M sucrose (pH, 7.2),
for 2 h at room temperature (18–20°C). After fixation, samples
were dropped on 12-mm-round coverslips (Fisher Scientific,
Germany) coated with a 0.01% poly-
L-lysine solution (Sigma-
Aldrich, St. Louis, MO). Af ter the 30–40 min necessary for
larvae to adhere to the coverslips, the samples were dehydrated
in the following graded series of ethanol solutions for 30 min each:
25%, 50%, 70%, 85%, 90%, 95%, 100%, and 100%. The samples
were then washed for 15 min each in a 50:50 solution of 100%
ethanol and hexamethyldisilazane (HMDS; TCI, Japan). Last,
2 washes of 15 min each in 100% HMDS were conducted. Excess
HMDS was removed by gentle pipetting, and samples were
allowed to air-dry overnight at room temperature (16–18°C) (Dalo
et al. 2008). After coating with an ion sputter (E-1030; Hitachi,
Japan), samples were observed with a scanning electron microscope
(S-4000; Hitachi) for morphological abnormalities.
Statistical Analysis
The normality and homogeneity of variance were tested
a priori using the Kolmogorov-Smirnov test and Bartlett test,
respectively. Data expressed as a rate were transformed by the
angular transformation (arcsinOpercentage) to ensure normality.
The effects of H. circularisquama concentration and exposure
duration were tested using factorial ANOVA. To determine the
concentrations causing significant effects, the Newman-Keuls,
Turkey-HSD or Bonferroni post hoc tests were used.
RESULTS
Effects on Trochophores
The activity rate of the trochophores significantly decreased
after the 3-h exposure to H. circularisquama at densities $ 10
3
cells/mL (Fig. 1), and the development rate was inhibited by
exposure to the same densities for 24 h (Fig. 2).
The trochophores exhibited several anomalies, including
cytoplasmic discharges, mass mucus production, delayed or inhi-
bited mineralization of the shell, irregular shell shape, appearance
of abnormal masses along the trochophore body, and exfoliation
of the larval cilia with epithelial desquamation (Fig. 3). Cells of
H. circularisquama were frequently observed attaching to trocho-
phores, shedding their cell walls, and transforming into round,
temporary cysts. The algal cells formed a heavy load for the
trochophores, thereby altering their swimming behavior.
The prevalence of damage increased significantly after a 3-h
and 6-h exposure to H. circularisquama densities $ 10
3
cells/mL
and $ 100 cells/mL, respectively (Fig. 4).
The activity rate of the D-shaped larvae that were trans-
formed from the trochophores exposed to H. circularisquama
decreased significantly after 12 h of exposure to densities $ 10
3
cells/mL, 24 h of exposure to densities $ 100 cells/mL, and 48 h
of exposure to densities $ 10 cells/mL (Fig. 5).
Figure 4. Prevalence of damage among trochophore larvae of P. fucata
martensii exposed to H. circularisquama. An asterisk indicates a significant
difference from the relative control (ANOVA, Turkey-HSD, P < 0.01).
Figure 5. Activity rate of P. fucata martensii D-shaped larvae transformed from trochophore larvae exposed to H. circularisquama. An asterisk
indicates a significant difference from the relative control (ANOVA, Turkey-HSD, P < 0.01).
BASTI ET AL.180
A factorial ANOVA and a 1-way ANOVA showed that both
H. circularisquama concentration, exposure duration, and their
interaction had significant effects on the activity rate, develop-
ment rate, prevalence of damage, and activity rate of transformed
trochophores (Table 2). The experiment duration had no effects
on the control trochophores for any parameter of assessment.
Effects on D-Shaped Larvae
The activity rate of D-shaped larvae decreased significantly
after 3 h of exposure to H. circularisquama at densities $10
3
cells/mL. After 48 h and 72 h of exposure, the activity rate
decreased for densities $500 cells/mL and $100 cells/mL,
respectively (Fig. 6).
D-shaped larvae exposed to H. circularisquama showed
several anomalies, including abnormal protrusion of the velum
and mantle with H. circularisquama cells attaching to the velum,
an irregular shell shape and hinge, abnormal masses in the velum,
and exfoliation of the velum cilia with epithelial desquamation
(Fig. 7). D-shaped larvae typically closed their shells when
encountering H. circularisquama cells. However, the cells of H.
circularisquama were frequently observed attaching to the velum
or entrapped inside the shell, thereby altering the swimming
behavior of the D-shaped larvae.
The prevalence of damage among D-shaped larvae increased
significantly after 3, 12, and 24 h of exposure to H. circular-
isquama at densities $5310
3
cells/mL, $10
3
cells/mL, and $500
cells/mL, respectively (Fig. 8).
The survival rate of D-shaped larvae after 72 h of exposure
was significantly lower than the control value for the H.
circularisquama density of 10
3
cells/mL, but remained higher
than 0.8. For densities $5 3 10
3
, the survival rate plummeted
to less than 0.013 (Fig. 9).
A factorial ANOVA and a 1-way ANOVA showed that both
H. circularisquama concentration, exposure duration, and their
interaction had significant effects on the activity rate, preva-
lence of damage, and survival rate of D-shaped larvae (Table 3).
The duration of the experiment had no effects on the activity
rate or the prevalence of damage in the control D-shaped larvae.
DISCUSSION
Susceptibility to H. circularisquama Densities and Exposure Duration
In the current experiments, H. circularisquama induced
deleterious effects on the trochophore and D-shaped larva
stages of the pearl oyster P. fucata martensii. The effects ranged
from a reduced activity rate, to extensive damage, reduced or
inhibited development, and a reduced survival rate. These effects
were directly related to the cell densities of H. circularisquama
and the exposure duration, which had synergistic effects.
Our results showed that an H. circularisquama density of 10
3
cells/mL was critical for trochophore larvae, inducing decreased
activity after only 3 h and increasing damage, leading to the
inhibition of development. The lower densities of 100–500 cells/
mL had no effects on the activity and development, but induced
some damage within 6 h and altered the activity rate of the trans-
formed trochophores after 24 h. The lowest density of 10 cells/
mL appeared safe for the trochophores, but the activity rate was
altered for the transformed trochophores after 72 h.
For D-shaped larvae, an H. circularisquama density of 10
3
cells/mL was also critical and induced a decreased activity
rate (3 h), increased damage (12 h), and decreased sur vival ra te
(72 h). The lower density of 500 cells/mL had no effect on the
Figure 6. Activity rate of P. fucata martensii D-shaped larvae exposed to H. circularisquama. An asterisk indicates a significant difference from the
relative control (ANOVA, Newman-Keuls, P < 0.01).
TABLE 2.
Factorial ANOVA results for the effects of H.
circularisquama densities ( H) and exposure duration (E)
on the activity rate, the prevalence of damage, the development
rate, and the activity rate of transformed trochophores for
P. fucata martensii trochophores.
SS df MS F P
Activity rate
H 13.552 7 3.358 1.936 0.000*
E 0.025 1 0.043 0.025 0.000*
H 3 E 0.032 7 0.004 0.004 0.000*
Prevalence of damage
H 18.834 7 2.690 274.44 0.000*
E 0.425 1 0.425 43.39 0.000*
H 3 E 0.264 7 0.037 3.85 0.004*
Development rate
H 7.791 7 1.113 10,013 0.000*
Activity rate of transformed
trochophores
H 30.799 7 4.399 21,128.8 0.000*
E 0.0.24 3 0.008 38.2 0.000*
H 3 E 0.062 21 0.003 14.2 0.000*
* P < 0.01. SS, sum or squares; MS, mean of squares.
HETEROCAPSA CIRCULARISQUAMA AFFECTS PEARL OYSTER LARVAE 181
survival rate but induced some damage (24 h), thereby alter-
ing the activity rate of D-shaped larvae (48 h). Thereafter,
H. circularisquama densities of 100 cells/mL and 500–10
3
cells/mL were determined to be the critical concentrations
for P. fucata martensii trochophores and D-shaped larvae,
respectively.
Several studies previously established the deleterious effects
of some toxic dinoflagellates on marine bivalve larvae. For in-
stance, Alexandrium tamarense decreased the survival rate of
larvae of the Japanese scallop Chlamys farreri after 6 days of
exposure to 3310
3
cells/mL (Yan et al. 2001), and decreased the
activity rate of the bay scallop Argopecten irradians concentricus
D-shaped larvae after 48 h of exposure to 10
4
cells/mL (Yan
et al. 2003). Karenia brevis decreased the survival rate of larvae
of the northern quahog Mercenaria mercenaria, the Eastern
oyster Crassostrea virginica, and A. irradians, by exposure to
10
3
–53 10
3
cells/mL, and decreased the development rate of M.
mercenaria and C. virginica by exposure t o 10
3
cells/mL
(Leverone et al. 2006). Matsuyama et al. (2001) reported lethal
effects of A. tamarense, Alexandrium t aylori, Gymnodinium
mikimotoi,andH. circularisquama on larvae of the Pacific oyster
Crassostrea gigas over the cell density range of 100–10
3
cells/mL,
which is the same critical range of cell densities for H. circular-
isquama reported in this study. In a previous work, Nagai et al.
(1996) showed that densities of 23 10
4
cells/mL and 10
4
cells/mL
corresponded to the LD
50
levels for 2-mo postfertilization
juveniles of P. fucata martensii exposed to the same strain of H.
circularisquama used in our experiments. Therefore, the suscep-
tibility of P. fucata martensii early life stages to H. circularisquama
seems to decrease along the developmental process, making the
trochophore larvae the most susceptible to H. circularisquama
blooms.
Figure 7. Light (LM) and scanning electron micrographs (SEM) of control and exposed P. fucata martensii D-shaped larvae to H. circularisquama at
10
3
cells/mL. (A) Control D-shaped larva 6 h postexposure (LM) showing normal D-shaped body with velum cilia slightly extending from the shell. (B)
D-shaped larva exposed for 6 h (LM) showing abnormal protrusion of the velum and mantle, with H. circularisquama cells attached to the velum. (C, D)
Control D-shaped larva (SEM) 24 h postexposure showing perfectly shaped larva with a straight hinge, and normal velum with the outer and inner band
of cilia. (E, F) D-shaped larva (SEM) 24 h postexposure showing an abnormal shell, and H. circularisquama cells trapped inside the larva. (G, H) D-
shaped larva (SEM) 48 h postexposure showing abnormal masses in the velum, and exfoliation of the velum cilia with epithelial desquamation and
abnormal mineralization of the shell. AM, abnormal mass; AS, abnormal shell; Ci, cilia; ED, epithelial desquamation; Ex, exfoliation; Hc, H.
circularisquama cell; M, mantle; V, velum.
BASTI ET AL.182
The effects observed for both larval stages occurred rapidly
compared with the previously mentioned results of other studies
dealing with other toxic dinoflagellate species. These observed
effects prove that H. circularisquama is a highly potent HAB
species (Kim et al. 2002). The deleterious effects were observed
within a matter of a few hours, depending on the densities.
Blooms of H. circularisquama in nature reportedly last several
days, reaching up to 25 3 10
5
cells/mL (Matsuyama, 2003a).
Consequently, the effects of this toxic alga on the early larva
stages of bivalves could be extensive in the wild.
Harming Mechanisms
The toxic H. circularisquama may have affected both trocho-
phores and D-shaped larvae by 3 possible processes: internal
injuries resulting from consumption of the toxic alga (Wikfors
& Smolowitz 1995), contact with toxins excreted in the water
(Thain & Watt 1987, Yan et al. 2001), or direct cell-to-cell con-
tact with the alga (Kamiyama & Arima 1997, Matsuyama et al.
1997).
Because trochophore larvae are unable to ingest food
particles, only the effects observed for D-shaped larvae could
be explained by the consumption of the toxic alga cells. The D-
shaped larvae of Mytilus galloprovincialis were shown to ingest
several toxic dinoflagellate species (Alexandrium affine, Cochlodi-
nium polykrikoides, Lingulodinium polyedrum, Prorocentrum min-
imum, Prorocentrum micans,andScrippsiella trochoidea)with
mean equivalent spherical diameters of 12–38 mm. However, the
feeding began 9–13 days postfertilization (Jeong et al. 2004).
Similarly, early D-shaped larvae of the scallop species A. irradians
concentricus and C. farreri were unable to feed on A. tamarense
cells because of its relatively large size (Yan et al. 2001, Yan et al.
2003), which is similar to the H. circularisquama cell size of 20–28
mm (Horiguchi 1995). Consequently, the observed toxic effects
on P. fucata martensii larvae could not be related to the internal
toxicity arising from consumption of the alga, because trocho-
phores do not ingest food, and 1 to 3-day-old D-shaped larvae are
unable to graze on food particles as large as H. circularisquama.
The effects observed on the larvae could be related to toxic
mechanisms through the contact with exotoxins secreted by H.
circularisquama in the water. However, neither water filtrates of
H. circularisquama culture nor its suspension of lysed cells
induced any detrimental effect on marine bivalves (Matsuyama
et al. 1997, Matsuyama 2003b), even though potent cytotoxic
effects against mammalian cell lines were detected in the cell-
free culture supernatant of H. circularisquama (Katsuo et al.
2007). In fact, H. circularisquama have 2 flagella and a theca with
multiple cellulosic walls overlying the cell membrane (Horiguchi
1995). In this study, the cells of H. circularisquama were
frequently observed attaching to the body of trochophores or
the velum of D-s haped larvae. W hen the algal cells were
swimming in the seawater, the contact between larvae and algal
cells occurred. The algal cells then became inactive, liberated
their cell wall into the larvae, and transformed into temporary,
round cysts. These observations are supported by previous
studies that revealed that H. circularisquama toxins are located
Figure 8. Prevalence of damage among D-shaped larvae of P. fucata martensii exposed to H. circularisquama. An asterisk indicates a significant
difference from the relative control (ANOVA, Bonferroni, P < 0.01).
Figure 9. Survival rate of P. fucata martensii D-shaped larvae exposed to H. circularisquama for 72h. An asterisk indicates a significant difference from
the relative control (ANOVA, P < 0.01).
HETEROCAPSA CIRCULARISQUAMA AFFECTS PEARL OYSTER LARVAE 183
on the cell wall and are not excreted into the water, suggesting
that the alga induces toxicity by cell contact with bivalve soft
tissues (Matsuyama et al. 1997, Kamiyama & Arima 1997). In
addition, the results showing that the D-shaped larvae seemed
less vulnerable to H. circularisquama could be related to the
fact that their soft body is protected by the larval shell, thus
minimizing the chances of contact with the algal toxins. The early
trochophore larvae have no such protective shell, and the ciliary
apparatus augments the ratios of surface area to volume, thereby
increasing the chances for contact and adherence between the
toxic alga and larva. This might explain why the early trocho-
phores are more susceptible to the toxicity of H. circularisquama,
as suggested previously for the trochophore of A. irradians
exposed to Heterosigma akashiwo (Wang et al. 2006).
The damage, revealed in our study through scanning electron
microscopy, is proof of the cytotoxic effects of H. circularisquama
in P. fucata martensii trochophores and D-shaped larvae. For
both larval stages, there was a loss of the larval cilia, abnormal
masses growing along the trochophore body or in the velum of
the D-shaped larvae, and extensive exfoliation of the cilia with
epithelial desquamation leading to death. In 2002, a new diga-
lactosyl diacylglycerol was extracted from H. circularisquama
and shown to induce cytotoxicity in the heart cells of oysters
(Hiraga et al. 2002). In addition, the toxin Ha–2, extracted and
purified from H. circularisquama, was recently shown to induce
cytotoxicity against HeLa cells with high potency (Kim et al.
2008). Ha–2 tended to accumulate in the plasma membrane, and
necrosis was proposed as the most plausible mechanism leading
to cell death (Kim et al. 2008).
Many algal toxins are known to disrupt cellular ion homeostasis
by specifically binding to certain membrane receptors involved
in the regulation of cytosolic ions, notably Ca
2+
(Blumenthal 1995).
Saxitoxins, brevetoxin and its derivatives, and ciguatoxin bind to
different sites of voltage-dependant sodium channels, resulting in
either an inhibition or a persistent activation of the channels, with
consequent increase in intracellular calcium (Kao & Walkwe 1982,
Gutierrez et al. 1997, Hallegraeff et al. 1998, Dechraoui et al. 1999,
Mattei et al. 1999, Van Dolah 2000, LePage et al. 2003). Domoic
acid acts as an analog of the neurotransmitter
L-glutamate that
binds to the glutamate receptor, inducing a persistent activation
of the receptor and also resulting in elevation of intracellular
Ca
2+
(Hampson & Manalo 1998, Scholin et al. 2000, Berman
et al. 2002). In addition, both maitotoxin and azaspiracid-1 bind
to voltage-gated calcium channels, resulting in increased cyto-
solic Ca
2+
(Estacion 2000, Roma
´
n et al. 2002, James et al. 2003,
Alfonso et al. 2005, Kakizaki et al. 2006). Ye ssotoxin binds to
voltage-gated calcium/sodium channels, also resulting in in-
creased cytosolic Ca
2+
(de la Rosa et al. 2001, Perez-Gomez
et al. 2006). In addition, Perovic et al. (2000) showed that su-
pernatants of many species of Alexandrium induce an increase in
intracellular Ca
2+
.
Matsuyama (2003b) reported an influx of Ca
2+
in trocho-
phore larvae of the short-neck clam Ruditapes philippinarum
after exposure to H. circularisquama.Ca
2+
is a critical signaling
ion that plays a pivotal role in numerous physiological and
biochemical processes of the cell—notably, signal transduction
pathways, neurotransmitter release and synaptic plasticity, con-
traction of all muscle cell types, enzyme regulation, fertilization,
shell formation, and death through apoptosis/necrosis, with the
latter being associated with elevation of cytosolic Ca
2+
(McConkey
1998, Berridge et al. 2000, Berridge et al. 2003, Orrenius et al.
2003). The current study showed that shell formation and sur-
vival of the pearl oyster larvae are both severely compromised by
H. circularisquama, which further supports the hypothesis that
H. circularisquama toxins must affect, either directly or indirectly,
cell membrane integrity/permeability, thus interfering with the
regulation of intracellular ions—notably, Ca
2+
. This hypothesis
can explain the extensive physiological and pathological alter-
ations observed in the larvae, which ultimately die through apo-
ptosis or necrosis.
Ecological Implications
Recurrent toxic blooms of H. circularisquama form along
the western and central Japanese coastal area (Matsuyama et al.
1999) mainly during the summer–autumn season (Matsuyama,
2003a). These blooms coincide with the spawning period of
almost all bivalves, and the blooms reach high cell densities and
last for several days (Matsuyama 2003a, Matsuyama 2003b).
The extensive damage observed in this study occurred rapidly
and at lower densities than generally reported in the field.
Therefore, H. circularisquama blooms will potentially affect the
population biology of the pearl oyster, and possibly other
marine bivalves, along the Japanese coast. The toxic alga was
shown to induce the loss of ciliary structure and to cause ex-
tensive irreversible cytotoxicity to the larvae, thereby reducing
their activity and food intake, an d altering their sensory
abilities, which ultimately result in starvation, susceptibility to
predation, and death (Yan et al. 2003). It has been suggested
that several toxic HAB species might produce the toxic sub-
stances as a strategy to protect their population from grazing
species (Wang et al. 2006), to maintain their population at the
ultimate blooming conditions, and to contribute to the decline
of shellfish populations (Yan et al. 2001). In any case, H.
circularisquama could have extensive detrimental effects on the
recruitment of P. fucata martensii and other bivalves.
CONCLUSION
The toxic dinoflagellate H. circularisquama was found to
induce adverse effects in the trochophore larvae and D-shaped
larvae of P. fucata martensii at 100 cells/mL and 500–10
3
cells/mL,
TABLE 3.
Factorial ANOVA results for the effects of H.
circularisquama densities ( H) and exposure duration (E)on
the activity rate and prevalence of damage for P. fucata
martensii D-shaped larvae.
SS df MS F P
Activity rate
H 23.441 7 3.358 1,719.23 0.000**
E 0.171 4 0.043 22.04 0.000**
H 3 E 0.118 28 0.004 2.16 0.012*
Prevalence of damage
H 17.130 7 2.447 1,745.07 0.000**
E 14.293 4 3.573 2,548.12 0.000**
H 3 E 6.651 28 0.237 169.39 0.000**
Survival rate
H 4.963 7 0.709 2,282.23 0.000**
* P < 0.05. * * P < 0.01. SS, sum of squares; MS, mean of squares.
BASTI ET AL.184
respectively. The impacts ranged from decreased activity, to
inhibition of development, increased damage, and decreased
survival rate. The damage included exfoliation of larval cilia,
epithelial desquamation, abnormal shells, and delayed miner-
alization of the shell. The harmful mechanism is likely to be
direct cell contact.
Blooms of H. circularisquama are expected to have extensive
toxic effects on pearl oyster larvae and will affect the recruit-
ment of the species along the Japanese coast, causing further
hardship to shellfish fisheries and aquaculture industries. Ad-
ditional studies are required to assess the toxicity mechanisms in
larvae at the cellular and molecular levels.
ACKNOWLEDGMENTS
This work was supported by a grant from the Japanese
Ministry of Education, Culture, Sports, Science and Technology,
Japan (no. 17310027).
LITERATURE CITED
Alfonso, A., Y. Roma
´
n, M. R. Vieytes, K. Ofuji, M. Statake, T.
Yasumoto & L. M. Botana. 2005. Azaspiracid-4 inhibits Ca
2+
entry
by stored operated channels in human T lymphocytes. Biochem.
Pharmacol. 69:1627–1636.
Basti, L., K. Nagai, Y. Shimasaki, Y. Oshima, T. Honjo & S. Segawa.
2009. Effects of the toxic dinoflagellate Heterocapsa circularisquama
on the valve movement behaviour of the Manila clam Ruditapes
philippinarum. Aquaculture 291:41–47.
Basti, L. & S. Segawa. 2010. Mo rtalities of the short-neck clam
Ruditapes philippinarum induced by the toxic dinoflagellate Hetero-
capsa circularisquama. Fish. Sci. 76:625–631.
Berman, F. W., K. T. LePage & T. F. Murray. 2002. Domoic acid
neurotoxicity in cultured cerebellar granule neurons is controlled
preferentially by the NMDA receptor Ca
2+
influx pathway. Brain
Res. 924:20–29.
Berridge, M. J., P. Lipp & M. D. Bootman. 2000. The versatility and
universality of calcium signalling. Nat. Rev. Mol. Cell Biol. 1:11–21.
Berridge, M. J., D. M. Bootman & H. Llewelyn Roderick. 2003.
Calcium signalling: dynamics, homeostasis and remodelling. Nat. Rev.
Mol. Cell Biol. 4:517–529.
Blumenthal, K. 1995. Ion channels as targets for toxins. In: N.
Sperelakis, editor. Cell physiology source book. San Diego: Academic
Press. pp. 389–403.
Bricelj, V. M. & S. E. Shumway. 1998. Paralytic shellfish toxins in
bivalve molluscs: occurrence, transfer kinetics, and biotransforma-
tion. Rev. Fish. Sci. 6:315–383.
Bricelj, V. M., B. M. Twarog, S. P. MacQuarrie, P. Chang & V. L.
Trainer. 2000. Does the history of toxin exposure influence bivalve
population responses to PSP toxins in Mya arenaria?: I) burrowing
and nerve responses. J. Shellfish Res. 19:635.
Burkholder, J. M. 1998. Implication of harmful microalgae and
heterotrophic dinoflagellates in management of sustainable marine
fisheries. Ecol. Appl. 8:S37–S62.
Cucci, T. L., S. E. Shumway, R. C. Newell & C. M. Yentsch. 1985. A
preliminary study on the effects of Gonyaulax tamarensis on feeding
in bivalve molluscs. In: A. W. White & D. G. Baden, editors. Toxic
dinoflagellates. Amsterdam: Elsevier. pp. 395–400.
Dalo, D. T., J. M. McCaffer & J. P. Evans. 2008. Ultrastructural
analysis of egg membrane abnormalities in post-ovulatory aged
eggs. Int. J. Dev. Biol. 52:535–544.
Dechra oui, M. Y., J. Naar, S. Pauillac & A. M. Legra nd. 1999.
Ciguatoxins and brevetoxins, neurotoxic polyether compounds
active on sodium channels. Toxicon 37:125–143.
de la Rosa, L. A., A. Alfonso, M. R. Vieytes & L. M. Botana. 2001. Modu-
lation of cytosolic calcium levels of human lymphocytes by yessotoxin,
a novel marine phycotoxin. Biochem. Pharmacol. 61:827–833 .
Estacion, M. 2000. Ciguatera toxins: mechanism of action and phar-
macology of maitotoxin. In: L. Botana, editor. Seafood and
freshwater toxins: pharmacology, physiology and detection. New
York: Marcel Dekker. pp. 473–504.
Gainey, L. F. & S. E. Shumway. 1988. A compendium of the responses
of bivalve molluscs to toxic dinoflagellates. J. Shellfish Res. 7:623–
628.
Gutierrez, D., L. D. de Leon & L. Vaca. 1997. Characterization of the
maitotoxin-induced calcium influx pathway from human skin
fibroblasts. Cell Calcium 22:31–38.
Hallegraeff, G. M., B. L. Munday, D. G. Baden & P. L. Whitney. 1998.
Chattonnella marina raphidophyte bloom associated with mortality
of cultured bluefin tuna (Thunnus maccoyii) in south Australia. In: B.
Reguera, J. Blanco, M. L. Fernandez & T. Wyatt, editors. Harmful
algae. Vigo: Xunta de Galacia and IOC. pp. 93–96.
Hampson, D. R. & J. L. Manalo. 1998. The activation of glutamate
receptors by kainic and domoic acid. Nat. Toxins 6:153–158.
Hiraga, Y., K. Kaku, D. Omoda, K. Sugihara, H. Hosoya & M. Hino.
2002. A new digalactosyl diacylglycerol from a cultured marine
dinoflagellate Heterocapsa circularisquama. J. Nat. Prod. 65:1494–
1496.
Horiguchi, T. 1995. Heterocapsa circularisquama sp. nov. (Peridiniales,
Dinophyceae): a new marine dinoflagellate causing mass mortalities
of bivalves in Japan. Phycol. Res. 43:129–136.
James, K., M. D. Sierra, M. Lehane, A. Brana Magdalena & A. Furey.
2003. Detection of five newly hydroxyl analogues of azaspiracids in
shellfish using multiple tandem mass spectrometry. Toxicon 41:277–
283.
Jeong, H. J., J. Y. Song, C. H. Lee & S. T. Kim. 2004. Feeding by larvae
of the blue mussel Mytilus galloprovincialis on red tide dinoflagel-
late.
J. Shellfish Res. 23:185–195.
Kakizaki, A., M. Takahashi, H. Akagi, E. Tachikawa, T. Yamamoto,
E. Taira, T. Yamakuni & Y. Ohizumi. 2006. Ca
2+
channel activating
action of maitotoxin in cultured brainstem neurons. Eur. J. Pharmacol.
536:223–231.
Kamiyama, T. & S. Arima. 1997. Lethal effects of the dinoflagellate
Heterocapsa circularisquama upon the tintinnid ciliate Favella
taraikaensis. Mar. Ecol. Prog. Ser. 160:27–33.
Kao, C. Y. & S. E. Walkwe. 1982. Active groups of saxitoxin and
tetrodotoxin as deduced from action of saxitoxin analogs on frog
muscle and squid axon. J. Physiol. 323:619–637.
Katsuo, D., D. Kim, K. Yamaguchi, Y. Matsuyama & T. Oda. 2007. A
new and simple screening method for the detection of cytotoxic
substances produced by harmful red tide phytoplankton. Harmful
Algae 6:790–798.
Kim, D., Y. Miyazaki, T. Nakashima, T. Iwashita, T. Fujita, K.
Yamaguchi, K. S. Choi & T. Oda. 2008. Cytotoxic action mode of
a novel porphyrin derivative isolated from harmful red tide dino-
flagellate Heterocapsa circularisquama. J. Biochem. Mol. Toxicol. 22:
158–165.
Kim, D., Y. Sato, Y. Miyazaki, T. Oda, T. Muramatsu, Y. Matsuyama
& T. Honjo. 2002. Comparison of hemolytic activity among strains
of Heterocapsa circularisquama isolated from various localities in
Japan. Biosci. Biotechnol. Biochem. 66:453–457.
LePage, K. T., D. G. Baden & T. F. Murray. 2003. Brevetoxin
derivatives act as partial agonists at neurotoxin site 5 on the
voltage-gated Na
+
channel. Brain Res. 959:120–127.
Lesser, M. P. & S. E. Shumway. 1993. Effects of toxic dinoflagellates on
clearance rates and survival in juvenile bivalve molluscs. J. Shellfish
Res. 12:377–381.
HETEROCAPSA CIRCULARISQUAMA AFFECTS PEARL OYSTER LARVAE 185
Leverone, J. R., N. J. Blake, R. H. Pierce & S. E. Shumway. 2006.
Effects of the dinoflagellate Karenia brevis on the larval development
in three species of bivalve mollusc from Florida. Toxicon 48:75–87.
Luckenbach, M. W., K. G. Sellner, S. E. Shumway & K. Greene. 1993.
Effects of two bloom-forming dinoflagellates, Prorocentrum mini-
mum and Gymnodinium uncatenatum, on the growth and survival of
the eastern oyster Crassostrea virginica (Gmelin, 1971). J. Shellfish
Res. 12:411–415.
MacQuarrie, S. P. & M. V. Bricelj. 2008. Behavioral and physiological
responses to PSP toxins in Mya arenaria populations in relation to
previous exposure to red tides. Mar. Ecol. Prog. Ser. 366:59–74.
Matsuyama, Y. 1999. Harmful effect of dinoflagellate Heterocapsa
circularisquama on shellfish aquaculture in Japan. Jpn. Agric. Res.
Q. 33:283–293.
Matsuyama, Y. 2003a. Physiological and ecological studies on harmful
dinoflagellate Heterocapsa circularisquama. I. Elucidation of envi-
ronmental factors underlying the occurrence and development of
H. circularisquama red tide. Bull. Fish. Res. Agen. 7:24–105. (in
Japanese with English abstract).
Matsuyama, Y. 2003b. Physiological and ecological studies on harmful
dinoflagellate Heterocapsa circularisquama. II. Clarification on
toxicity of H. circularisquama and its mechanisms causing shellfish
kills. Bull. Fish. Res. Agen. 9:13–117. (in Japanese with English
abstract).
Matsuyama, Y., K. Nagai, T. Mizuguchi, M. Fujiwara, M. Ishimaru,
M. Yamaguchi, T. Uchida & T. Honjo. 1992. Ecological features
and mass mortalities of pearl oysters during red tides of Heterocapsa
sp. in Ago Bay in 1992. Nippon Suisan Gakkaishi 61:35–41. (in
Japanese with English abstract).
Matsuyama, Y., T. Uchida & T. Honjo. 1997. Toxic effects of the
dinoflagellate Heterocapsa circularisquama on clearance rate of the
blue mussel Mytilus galloprovincialis. Mar. Ecol. Prog. Ser. 146:73–80.
Matsuyama, Y., T. Uchida & T. Honjo. 1999. Effects of the harmful
dinoflagellates, Gymnodinium mikimotoi and Heterocapsa circular-
isquama, red-tide on filtering rate of bivalve molluscs. Fish. Sci. 65:
248–253.
Matsuyama, Y., T. Uchida, K. Nagai, M. Ishimaru, A. Nishimaru, M.
Yamaguchi & T. Honjo. 1996. Biological and environmental aspects
of noxious dinoflagellate red tides by Heterocapsa circularisquama
in west Japan. In: T. Yasumoto, Y. Oshima & Y. Fukuyo, editors.
Harmful and toxic algal blooms. Paris: IOC, UNESCO. pp. 247–250.
Matsuyama, Y., H. Usuki, T. Uchida & Y. Kotani. 2001. Effects of
harmful algae on the early planktonic larvae of the oyster, Crassos-
trea gigas. In: G. Hallegraeff, S. Blackburn, C. Bolch & R. Lewis,
editors. Harmful algal blooms. Paris: IOC, UNESCO. pp. 411–414.
Mattei, C., M. Y. Dechraoui, J. Molgo
´
, F. A. Meunier, A. M. Legrand
& E. Benoit. 1999. Neurotoxins targetting receptor site 5 of voltage-
dependent sodium channels increase the nodal volume of myelinated
axons. J. Neurosci. Res. 55:666–673.
McConkey, D. J. 1998. Biochemical determinants of apoptosis and
necrosis. Toxicol. Lett.
99:157–168.
Nagai, K., T. Honjo, J. Go, H. Yamashita & S. J. Oh. 2006. Detecting
the shellfish killer Heterocapsa circularisquama (Dinophyceae) by
measuring the b ivalve valve activity with Hall element sensor.
Aquaculture 255:395–401.
Nagai, K., Y. Matsuyama, T. Uchida, M. Yamaguchi, M. Ishimaru, A.
Nishimaru, S. Akamatsu & T. Honjo. 1996. Toxicity and LD
50
levels
of the red tide dinoflagellate Heterocapsa circularisqua ma on
juvenile pearl oysters. Aquaculture 144:149–154.
Nielsen, M. V. & T. Stro
¨
mgren. 1991. Shell growth response of mussels
(Mytilus edulis) exposed to toxic microalgae. Mar. Biol. 108:263–267.
Orrenius, S., B. Zhivotovsky & P. Nicotera. 2003. Regulation of the cell
death: the calcium–apoptosis link. Nat. Rev. Mol. Cell Biol. 4:552–
565.
Perez-Gomez, A., A. Ferrero-Gutierrez, A. Novelli, J. M. Franco, B.
Paz & M. T. Fernandez-Sanchze. 2006. Potent neurotoxic action of
the shellfish biotoxin yessotoxin on cultured cerebellar neurons.
Toxicol. Sci. 90:168–177.
Perovic, S., L. Tretter, F. Brummer, C. Wetzler, J. Brenner, G. Donner,
H. C. Schroder & W. E. G. Muller. 2000. Dinoflagellates from
marine algal blooms produce neurotoxic compounds: effects on free
calcium levels in neuronal cells and synaptosomes. Environ. Toxicol.
Pharmacol. 8:83–94.
Roma
´
n, Y., A. Alfonso, M. C. Louzao, L. A. de la Rosa, F. Leira, J. M.
Vieites, M. R. Vieytes, K. Ofuji, M. Satake, T. Yasumoto & L. M.
Botana. 2002. Azaspiracid-1, a potent, non-apoptotic new phyco-
toxin with several cell targets. Cell. Signal. 14:703–716.
Scholin, C. A., F. Gulland, G. J. Doucette, S. Benson, M. Busman, F. P.
Chavez, J. Cordaro, R. DeLong, A. De Vogelaere, J. Harvey, M.
Haulena, K. Lefebvre, T. Lipscomb, S. Loscutoff, L. J. Lowenstine,
R. Marin, P. E. Miller, W. A. McLellan, P. D. Moeller, C. L. Powell,
T. Rowles, P. Silvagni, M. Silver, T. Spraker, V. Trainer & F. M.
Van Dolah. 2000. Mortality of sea lions along the central California
coast linked to a toxic diatom bloom. Nature 430:80–84.
Shumway, S. E. 1990. A review of the effects of algal blooms on shellfish
and aquaculture. J. World Aquacult. Soc. 21:65–104.
Shumway, S. E. & T. L. Cucci. 1987. The effects of the toxic dino-
flagellate Protogonyaulax tamarensis on the feeding and behaviour
of bivalve mollusks. Aquat. Toxicol. 10:9–27.
Shumway, S. E., F. C. Pierce & K. Knowlton. 1987. The effects of
Protogonyaulax tamarensis on byssus production in Mytilus edulis
L., Modiolus modiolus Linnaeus, 1985 and Geukensia demissa
Dillwyn. Comp. Biochem. Physiol. A 87:1021–1023.
Thain, J. E. & J. Watt. 1987. The use of a bioassay to measure changes
in water quality associated with a bloom of Gyrodinium aureolum
Hulbult. Rapport et Proce
`
s-verbaux des Re
´
unions Conseil Interna-
tional pour l’Exploration de la Mer. 187:103–107.
Van Dolah, F. M. 2000. Marine algal toxins: origin, health effects, and
their increased occurrence. Environ. Health Perspect. 108S:133–144.
Wang, L., T. Yan & M. Zhou. 2006. Impact of HAB species Hetero-
sigma akashiwo on early life development of the scallop Argopecten
irradians Lamarck. Aquaculture 255:374–383.
Widdows, J., M. N. Moore, D. M. Lowe & P. N. Salkeld. 1979. Some
effects of a dinoflagellate bloom (Gyrodinium aureolum) on the
mussel, Mytilus edulis. J. Mar. Biol. Assoc. UK 59:522–524.
Wikfors, G. H. & R. M. Smolowitz. 1995. Experimental and histological
studies of four life-history stages of the Eastern oyster, Crassostrea
virginica
, exposed to a cultured strain of the dinoflagellate Pro-
rocentrum minimum. Biol. Bull. 188:313–328.
Yamatogi, T., M. Sakaguchi, M. Matsuda, S. Iwanaga, M. Iwataki &
K. Matsuoka. 2004. Effect on bivalve molluscs of a harmful di-
noflagellate Heterocapsa circularisquama isolated from Omura Bay,
Japan and its growth characteristics. Nippon Suisan Gakkaishi 71:
746–754. (in Japanese with English abstract).
Yan, T., M. Zhou, M. Fu, Y. Wang, R. Yu & J. Li. 2001. Inhibition of
egg hatching success and larvae survival of the scallop, Chlamys
farreri, associated to exposure of cells and cell fragments of the
dinoflagellate Alexandrium tamarense. Toxicon 39:1239–1244.
Yan, T., M. Zhou, M. Fu, R. Yu, Y. Wang & J. Li. 2003. Effects of the
toxic dinoflagellate Alexandrium tamarense on early development of
the scallop Argopecten irradians concentricus. Aquaculture 217:167–
178.
BASTI ET AL.186
... Laboratory exposures to these HAB species were shown to differentially affect spermatozoa, eggs, fertilization, embryos as well as larvae of a few species of bivalves of ecological and economic importance (reviewed in Basti et al., 2018). These species include H. circularisquama, K. mikimotoi, K. papilionacea, C. marina, H. akashiwo and M. polykrikoides (Matsuyama et al., , 2003Banno et al., 2018;Basti et al., 2011b, 2015b, 2015c, (Basti et al., 2016b, Griffith et al., 2019b). Decreased egg viability, embryo development and motility with extensive cytotoxicity and high mortalities were reported for larvae of Japanese pearl oysters, following exposures to H. circularisquama (Basti et al., 2011b). ...
... These species include H. circularisquama, K. mikimotoi, K. papilionacea, C. marina, H. akashiwo and M. polykrikoides (Matsuyama et al., , 2003Banno et al., 2018;Basti et al., 2011b, 2015b, 2015c, (Basti et al., 2016b, Griffith et al., 2019b). Decreased egg viability, embryo development and motility with extensive cytotoxicity and high mortalities were reported for larvae of Japanese pearl oysters, following exposures to H. circularisquama (Basti et al., 2011b). Exposures of larvae of the same oyster species to K. mikimotoi, K. papilionacea, H. akashiwo and C. marina resulted in a decrease in their activity, with the first report of mortalities induced by C. marina (Basti et al., 2015b(Basti et al., , 2016b. ...
... Most studies on the effects of HAB on the early-life development of bivalve molluscs have focused on their larval stages. Low to high reduction in the activity of several larval stages, reduction of feeding activity, delayed to inhibited development, and low to high mortality rates were reported for several bivalve species following exposures to Alexandrium spp., Scripsiella trochoidae, H. circularisquama, Prorocentrum spp., Fibrocapsa japonica, M. polykrikoides, K. brevis, K. mikimotoi, K. papilionacea, C. marina, C. antiqua and H. akashiwo (Summerson and Peterson, 1991); Wikfors and Smolowitz, 1995;Matsuyama et al., 2001;(Wang et al., 2006); Basti et al., 2011bBasti et al., , 2015aBasti et al., , 2015b(Tang and Gobler, 2012); Rolton et al., 2014Rolton et al., , 2015. The dinoflagellate K. mikimotoi is known to produce several toxic agents and allelochemicals such as sterols, polyunsaturated fatty acids, and gymnodimine (Jenkinson and Arzul, 2001;Yamasaki et al., 2004;Satake et al., 2005;Gentien et al., 2007). ...
Article
Several species of harmful algae form blooms that are detrimental to aquatic organisms worldwide with severe economic loss to several industries. The cosmopolitan ichthyotoxic dinoflagellates and raphidophytes Karenia spp., Chattonella spp., Heterosigma spp., and Margalefidinium (Cochlodinium) polykrikoides are known to cause mass mortalities of fish and invertebrates, and the dinoflagellates Heterocapsa spp. are known to cause mass mortalities of shellfish, notably bivalve molluscs. The species K. mikimotoi, K. papilionacea, H. circularisquama, H. akashiwo, M. polykrikoides, and C. marina form recurrent harmful algal blooms (HAB) in coastal aquaculture areas of shellfish, coinciding with the reproduction seasons of natural and farmed bivalve molluscs. In the present study, their effects on eggs, fertilization, embryos, and three larval stages (D-shaped, umbo and pre-settling larvae) of a model bivalve species, the Japanese pearl oyster, Pinctada fucata martensii, are reported. The harmful algae had differential negative effects on each developmental stage, and had differential effects on larvae depending on their growth stage. Eggs were more affected by M. polykrikoides, K. mikimotoi and H. circularisquama than H. akashiwo and K. papilionacea. Fertilized eggs and developing embryos were more affected by M. polykrikoides and H. circularisquama than K. mikimotoi, K. papilionacea and H. akashiwo. Mortalities as well as abnormalities were not observed in any larval stage; however, motility of d-larvae and umbo larvae was more reduced by H. circularisquama and C. marina, than M. polykrikoides. In elder, 16 day-old larvae, all harmful algae induced a significant decrease in motility with the most severe effect observed during exposures to H. circularisquama, C. marina, H. akashiwo and M. polykrikoides. The superoxidase dismutase activity in larvae was not affected by exposure to any harmful alga; however, 6- and 16-day old larvae experienced a significant increase in GST activity following 48 h of exposures, with higher sensitivity of the elder larvae to C. marina, K. mikimotoi and M. polykrikoides. These results indicate that all tested harmful algae are differentially detrimental to the early-life development of the Japanese pearl oyster, with involvement of oxidative stress. Both M. polykrikoides and H. circularisquama were the most toxic followed by C. marina, K. mikimotoi, H. akashiwo and K. papilionacea. In addition, more developed larvae were most sensitive to these harmful algae in terms of motility-avoidance behavior and oxidative stress response, suggesting that ingestion of the harmful algae might enhance the toxicity of contact-dependent effects and dissolved extracellular compounds. The results also showed that superoxide anions were not associated with effects observed in larvae. Instead cellular detoxification was induced. The differential, stage-specific and growth-specific sublethal effects on bivalve development and recruitment also warrant further investigations of the oxidative stress and antioxidant enzyme activities in larvae of bivalves, to better address the toxicity mechanisms of ichthyotoxic HAB and their impacts on the reproduction, recruitment, and fitness of bivalve molluscs. Summary: The harmful algae Heterocapsa circularisquama, Chattonella marina, Hetrosigma akashiwo, Karenia mikimotoi, K. papilionacea, Margalefidinium (Cochlodinium) polykrikoides differentially affect early life stages of Japanese pearl oyster and activate detoxification enzymes in feeding larvae.
... HABs have also been reported to impact shellfish aquaculture worldwide (Shumway 1990, Matsuyama et al. 1997a). The dinophyte species Heterocapsa circularisquama Horiguchi, Gymnodinium aureolum (E.M.Hulburt) Gert Hansen, and the raphidophyte Chattonella marina (Subrahmanyan) Y.Hara & M.Chihara have been reported to kill shellfish (Matsuyama 1999, Basti et al. 2011, Kim et al. 2011b. However, to our knowledge, there is no information on the occurrence of this type of HAB species, particularly the species of Heterocapsa F.Stein, in Malaysian waters. ...
... Heterocapsa species that were associated with red tides were H. circularisquama and H. rotundata (Lohmann) Gert Hansen (Boonyapiwat 1999, Matsuyama 1999, Kamiyama et al. 2001, Iwataki et al. 2002, Litaker et al. 2002, Hernández-Becerril et al. 2010, Baek et al. 2011. These bloomforming species caused water discoloration, and some of the bloom events have been associated with mollusk kills (Matsuyama 1999, Iwataki et al. 2002, Matsuyama 2003a, Basti et al. 2009, Basti et al. 2011. For instance, a H. circularisquama bloom that reached up to 25 10 4 cells mL −1 resulted in the mortality of shellfish in Japan (Matsuyama 1999, Matsuyama 2003a, Basti et al. 2009). ...
... In a laboratory experiment, bivalves showed behaviors such as vigorous clapping and shrinkage of the mantle after exposure to H. circularisquama (Nagai et al. 1996, Basti et al. 2009, Kim et al. 2011a, Matsuyama 2012. Cells of H. circulariquama might cause damage to several organs of shellfish, thus leading to physiological stress and ultimately resulting in death (Kim et al. 2011a, Basti et al. 2011, 2016. Besides, H. circularisquama also adversely affects the development of larvae of several bivalves, and the reproduction of bivalves (Matsuyama 2003b, 2012, Basti et al. 2011. ...
Article
In November 2020, a high biomass multi-species algal bloom caused heavy water discoloration in the fish and mussel farm areas of the Johor Strait, Malaysia. A total of 19 microalgal taxa were identified from the plankton samples collected during the bloom event. Eleven genera were diatoms, and eight genera were dinophytes. The microalgal composition was dominated by the diatom Guinardia sp., with an average cell density of 1.7×10⁶ cells L⁻¹, making up 65–80% of the phytoplankton composition. Concomitantly, high densities of the dinophytes Heterocapsa minima (3.8–5.3×10⁵ cells L⁻¹) and Karlodinium spp. (3.5–6.6×10³ cells L⁻¹) were found. This is the first record of the occurrence of H. minima in Malaysian waters. Detailed morphological observations of H. minima based on scanning electron microscopy are presented in this study. To have a better insight into the Heterocapsa species assemblages in the Johor Strait, the diversity of Heterocapsa species assemblages along the strait was investigated based on a metabarcoding approach. Environmental DNA collected between 2018 and 2019 was used for high throughput amplicon sequencing targeting the small subunit (SSU) ribosomal RNA gene marker. The metabarcoding analysis detected three rare Heterocapsa species in the waters, H. niei, H. rotundata, and H. steinii. The results showed that Heterocapsa species assemblages varied temporally across the strait, with higher species diversity and amplicon sequence variant (ASV) read abundances detected in the Eastern Johor Strait. Although no fish/shellfish kills were sighted during the 2020 bloom event, the presence of harmful microalgal species, such as Heterocapsa minima and Karlodinium spp., urged the need for a comprehensive HAB monitoring program in the Strait to safeguard the aquaculture industry in the areas.
... Only invertebrates were affected at that time, and the cause appeared to be a labile protein-like complex on the cell surface which was causing the detrimental effect on bivalves. Further studies revealed mortalities in several commercially important bivalve species exposed to this microalga [29,85,179,180]. Five Heterocapsa species have been recorded in NZ, including H. cf. ...
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Harmful algal blooms (HABs) have wide-ranging environmental impacts, including on aquatic species of social and commercial importance. In New Zealand (NZ), strategic growth of the aquaculture industry could be adversely affected by the occurrence of HABs. This review examines HAB species which are known to bloom both globally and in NZ and their effects on commercially important shellfish and fish species. Blooms of Karenia spp. have frequently been associated with mortalities of both fish and shellfish in NZ and the sub-lethal effects of other genera, notably Alexandrium spp., on shellfish (which includes paralysis, a lack of byssus production, and reduced growth) are also of concern. Climate change and anthropogenic impacts may alter HAB population structure and dynamics, as well as the physiological responses of fish and shellfish, potentially further compromising aquatic species. Those HAB species which have been detected in NZ and have the potential to bloom and harm marine life in the future are also discussed. The use of environmental DNA (eDNA) and relevant bioassays are practical tools which enable early detection of novel, problem HAB species and rapid toxin/HAB screening, and new data from HAB monitoring of aquaculture production sites using eDNA are presented. As aquaculture grows to supply a sizable proportion of the world’s protein, the effects of HABs in reducing productivity is of increasing significance. Research into the multiple stressor effects of climate change and HABs on cultured species and using local, recent, HAB strains is needed to accurately assess effects and inform stock management strategies.
... Besides that, flagellated cells of the genus Pfiesteria have also reduced larval survival by attacking and consuming molluscan larvae (Shumway et al. 2006;Springer et al. 2002). Negative effects on larval growth, development, and lipid synthesis have been attributed to harmful algae exposure (e.g., Basti et al. 2011b;Mu and Li 2013;Rolton et al. 2014;Talmage and Gobler 2012;Wikfors and Smolowitz 1995). In addition, negative effects on embryo cleavage, inhibition of embryonic and newly hatched development, increased embryo abnormalities, damages to feeding and gut apparatus during embryonic development, reduction or interruption of embryo hatching, delay in metamorphosis of larval stages, and decrease in larval activity were shown in a few species of oysters and clams (e.g., Basti et al. 2013Basti et al. , 2014bBasti et al. , 2015aMu and Li 2013;Rolton et al. 2014Rolton et al. , 2015. ...
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Besides human health risks, phycotoxins may cause physiological injuries on molluscan shellfish and, consequently, damages to marine ecosystems and global fisheries production. In this way, this review aimed to present an overview of HABs impacts on marine shellfish by evaluating the effects of cultivated molluscs exposure to microalgae and cyanobacteria that form blooms and/ or synthesize toxins. More specifically, it was assessed the main molluscan shellfish responses to harmful algae, trophic transfer and dynamics of phycotoxins, and the risks for human health. Of the 2420 results obtained from literature search, 150 scientific publications were selected after thorough inspections for subject adherence. In total, 70 molluscan species and 37 taxa of harmful algae were assessed from retrieved scientific publications. A significant positive correlation was found between the marine production of molluscs and the number of available studies by molluscan category. Molluscan responses to HABs and phycotoxins were categorized and discussed in three subsections: effects on grazing and behavior, metabolic and physiological reactions, and fitness consequences. The main histopathological injuries and toxin concentrations in molluscan tissues were also compiled and discussed. Bivalves often accumulate more toxins than gastropods and cephalopods, occasionally exceeding recommended levels for safe consumption, representing a risk for human health. Harmful algae impact on molluscan shellfish are complex to trace and predict; however, considering the perspective of increase in the occurrence and intensity of HABs, the intensification of efforts to expand the knowledge about HABs impacts on marine molluscs is crucial to mitigate the damages on economy and human health.
... In particular, contaminants could 37 negatively affect their reproduction as demonstrated in oysters exposed to anthropogenic 38 pollutants (Akcha et al., 2012;Fitzpatrick et al., 2008;Mai et al., 2013;Vignier et al., 2017Vignier et al., , 39 2015. Experimental studies suggest that harmful algal blooms (HAB), often caused by 40 dinoflagellates, can affect marine bivalve reproduction by altering gamete quality and larval 41 development, growth, and survival (Banno et al., 2018;Basti et al., 2013Basti et al., , 2011Binzer et al., 42 2018;Bricelj and MacQuarrie, 2007;Castrec et al., 2020Castrec et al., , 2019De Rijcke et al., 2015;43 Gaillard et al., 2020;Rolton et al., 2018Rolton et al., , 2015Rolton et al., , 2014Tang and Gobler, 2012). In coastal 44 areas, HAB are a recurring phenomenon that can co-occur with the reproduction of free 45 spawning marine organisms (Gaillard et al., 2020). ...
Article
Dinoflagellates from the globally distributed genus Alexandrium are known to produce both paralytic shellfish toxins (PST) and uncharacterized bioactive extracellular compounds (BEC) with allelopathic, ichthyotoxic, hemolytic and cytotoxic activities. In France, blooms of Alexandrium minutum appear generally during the spawning period of most bivalves. These blooms could therefore alter gametes and/or larval development of bivalves, causing severe issues for ecologically and economically important species, such as the Pacific oyster Crassostrea (=Magallana) gigas. The aim of this work was to test the effects of three strains of A. minutum producing either only PST, only BEC, or both PST and BEC upon oyster gametes, and potential consequences on fertilization success. Oocytes and spermatozoa were exposed in vitro for 2 h to a range of environmentally realistic A. minutum concentrations (10-2.5 × 104 cells mL-1). Following exposure, gamete viability and reactive oxygen species (ROS) production were assessed by flow cytometry, spermatozoa motility and fertilization capacities of both spermatozoa and oocytes were analysed by microscopy. Viability and fertilization capacity of spermatozoa and oocytes were drastically reduced following exposure to 2.5 × 104 cells mL-1 of A. minutum. The BEC-producing strain was the most potent strain decreasing spermatozoa motility, increasing ROS production of oocytes, and decreasing fertilization, from the concentration of 2.5 × 103 cells mL-1. This study highlights the significant cellular toxicity of the BEC produced by A. minutum on oyster gametes. Physical contact between gametes and motile thecate A. minutum cells may also contribute to alter oyster gamete integrity. These results suggest that oyster gametes exposure to A. minutum blooms could affect oyster fertility and reproduction success.
... Following the success of French Polynesia and the Cook Islands in marine pearl oyster aquaculture, other island states in the Pacific have also developed their own pearl mollusk aquacultural setups (Tisdell and Poirine, 2008). Basti et al. (2011) revealed that Heterocapsa circularisquama blooms negatively influence the early life stages of P. fucata. Ocean acidification results in a reduced byssus diameter and amplified byssus nanocavity in P. fucata by altering the abundance and secondary structure of byssal proteins and affecting the metal ion content in distal threads (Li et al., 2017a). ...
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Article
Freshwater pearl mussels and marine pearl oysters are major producers of cultured pearls. With the development of pearl farming, pearl bivalve mollusks have attracted significant research attention over the past 25 years. To provide an overview of this research, we conducted a bibliometric analysis of publications from the Web of Science Core Collection database from 1995 to 2020. A network map generated by VOSviewer software was used to evaluate studies of pearl bivalve mollusks in terms of author, country, organization, journal, and keywords. A total of 2,288 publications were obtained, showing an annual increase in the number of papers. Researchers based in China were a major contributor to the field and there was active cooperation among authors. Research focused on mussel and oyster developmental biology, growth, culture mode, molecular biology, and ecological conservation. In recent years, hot topics, such as growth performance and traits, pearl formation and biomineralization, and immune response, have been widely discussed. Genomics, transcriptomics, proteomics, and metabonomics analyses were commonly used to analyze the regulatory mechanism of coding and non-coding genes. The interaction between the environment and farming activities showed the importance of sustainable development. Interdisciplinary research could solve some of the issues facing the pearl bivalve mollusk farming. In conclusion, our findings could serve as another way to understand research trends in pearl bivalve mollusks and contribute to future studies.
... Heterocapsa circularisquama is a bloom-former in many areas of oyster culture, particularly in Asia, and its detrimental effects have been well documented. It has been shown to cause cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited mineralization of shell formation, as well as other effects on pearl oysters (Basti et al., 2011). Clearly, the effects of H. rotundata on C. virginica are worthy of additional study. ...
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A 2-year study was undertaken to understand feeding preferences of the eastern oyster Crassostrea virginica in the eutrophic Rhode River, a tributary of Chesapeake Bay, Maryland, USA. A subset of experimentally suspended oysters was collected monthly and environmental parameters were simultaneously measured. Oysters were measured in height to determine growth, and the phytoplankton in their gut were examined both microscopically and using indicator pigments and compared with phytoplankton abundance and composition in the water column. Growth was higher in the second year of the study when flow was lower and salinity higher. Food selectivity was calculated using a modified electivity index (Ei), which relates phytoplankton composition in the gut to that in the water. Oysters appeared to preferentially graze–or at least preferentially retain in the gut–various (unidentified) flagellates, Ochrophyta (diatoms) and Myzozoa (dinoflagellates), and appeared to generally reject cyanobacteria, especially picocyanobacteria, from their diet. The Myzozoa included several common harmful algal bloom taxa, including Prorocentum minimum (=P. cordatum) and Heterocapsa rotundatum, that can detrimentally affect oyster growth. Reductions in eutrophication will likely be beneficial for oyster diets if such reductions result in fewer dinoflagellate blooms and in picocyanobacteria abundance during the critical feeding summer months.
... For example, in the Pacific oyster, Crassostrea gigas, change in valve activity behavior was observed with Alexandrium minutum exposure (Tran et al., 2010). In the pearl oyster Pinctada fucata martensii, the survival, activity, and development rates of trochophore and D-shaped larvae were decreased after exposure to Heterocapsa circularisquama (Basti et al., 2011). In the copepod Acartia clausi, hatching success and naupliar production were decreased in response to toxic dinoflagellate Alexandrium minutum (Frangópulos et al., 2000). ...
Article
s To understand how the marine copepod Tigriopus japonicus responds to the toxic marine dinoflagellate Gymnodinium catenatum, we assessed acute toxicity and investigated swimming behavior parameters (e.g., swimming speed, swimming path trajectory, and swimming distance) in response to G. catenatum exposure. In addition, the mRNA expression levels of detoxification-related genes (e.g., phase I cytochrome P450 [CYP] and phase II glutathione-S transferase [GST]) were measured in G. catenatum-exposed copepods. No significant change in survival was observed in response to G. catenatum, but swimming speed was significantly decreased (P < 0.05) at a high concentration of G. catenatum (600 cells/mL). Furthermore, the swimming distance was significantly decreased (P < 0.05) compared to that of the control at 600 cells/mL G. catenatum, while no significant change in swimming path trajectory was observed, suggesting that G. catenatum potentially has adverse effects on the swimming behavior of T. japonicus. In addition, the transcriptional regulation of T. japonicus CYPs and -GSTs were significantly upregulated and downregulated (P < 0.05), respectively, in response to G. catenatum. In particular, certain genes (e.g., CYPs [CYP307E1, CYP3041A1, and CYP3024A2] and GSTs [GST-kappa, GST-mu5, and GST-omega]) were significantly induced (P < 0.05) by G. catenatum, suggesting that these genes likely play a critical role in detoxification mechanisms and might be useful as potential molecular biomarkers in response to G. catenatum exposure. Overall, these results elucidate the potential impacts of the dinoflagellate G. catenatum on the swimming behavior and detoxification system of the marine copepod T. japonicus.
... H circularisquama dilaporkan boleh menyebabkan kerosakan pada tisu insang tiram yang membawa kepada tekanan fisiologi umum dan akhirnya mengakibatkan kematian (Kim et al., 2011). Basti et al. (2011) juga mendapati ledakan H circularisquama boleh memberi kesan buruk pada peringkat larva dan D-shaped larva tiram. Oleh itu, kajian ini dijalankan bagi mengenalpasti komposisi dan kepelbagaian fitoplankton sebagai sumber makanan kerang serta fitoplankton yang berpotensi bahaya di kawasan temakan kerang di Selangor. ...
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Abstrak: Kajian ini dijalankan bagi menyiasat kepelbagaian dan kelimpahan fitoplankton di sekitar kawasan temakan kerang (Tegillarca granosa) di Kuala Selangor, Perairan Selat Melaka. Persampelan telah dijalankan pada Julai, Ogos dan Oktober 2016 serta Januari hingga Mac 2017 di 16 stesen kajian. Fitoplankton telah dikenalpasti terdiri daripada 32 genera diatom (Bacillariophyceae), 15 genera dinofiagelat (Pyrrophyceae) dan dua genera alga hijau-biru (Cyanophyceae). Komposisi fitoplankton di semua stesen persampelan didominasi oleh diatom. Densiti sel fitoplankton adalah antara 3.09 x 10 4 sel L_l hingga 2.92 x 10 6 sel L_l. Lapan spesis fitoplankton berpotensi bahaya dikenalpasti seperti Alexandrium spp., Dinophysis caudata, Prorocentrum micans, Karlodinium spp., Pseudo-nitzschia spp, Ceratium furca, c. lusus, dan Noctiluca scintillans pada kepadatan se1 secara relatif adalah rendah. Fitoplankton berpotensi bahaya kepada kerang seperti Heterocapsa circularisquama, Gymnodinium aureolum dan Chattonella antiqua juga tidak dikesan sepanjang persampelan. Walaupun fitoplankton berpotensi bahaya didapati pada kepadatan yang rendah, namun begitu, kehadiranya masih boleh berpotensi memberi ancaman kepada kesihatan manusia dan keselamatan makanan laut jika ledakan sel berlaku. Oleh itu, pemantauan berkala fitoplankton adalah perlu bagi melindungi keselamatan manusia dan industri makanan laut di negara ini. Kata Kunci: Fitoplankton, temakan kerang, mikroalga berpotensi bahaya, Selat Melaka Abstract: A field survey was carried out in the cockle culture areas (Tegillarca granosa), Kuala Selangor, Strait of Malacca, to investigate the composition and abundance of phytoplankton. Sampling
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To investigate feeding by the larvae of the mussel Mytilus galloprovincialis on red-tide dinoflagellates, we measured grazing rates of M. galloprovincialis larvae as a function of larval age and prey concentration when feeding on several species of the red-tide dinoflagellates Alexandrium affine, Cochlodinium polykrikoides, Lingulodinium polyedrum, Prorocentrum minimum, Prorocentrum micans, and Scrippsiella trochoidea, as well as the flagellate Isochrysis galbana as a control species. The larvae were able to ingest all dinoflagellates offered in the current study; however, first feeding of the larvae on each species of the dinoflagellates occurred 9-13 days after fertilization, whereas that for I. galbana occurred after 5 days. Ingestion rates of the larvae on unialgal diets of the dinoflagellates and I. galbana increased with increasing larval age up to 17-21 days, but were saturated or showed a continuous increase thereafter. Ingestion rates of 25-day-old larvae feeding on unialgal diets of the dinoflagellates increased rapidly with increasing prey concentration up to 1000-2200 ng C mL-1, but were saturated at higher prey concentrations. The harmful alga C. polykrikoides, which has been responsible for great losses in the aquaculture industry, was the optimal prey. Maximum ingestion and clearance rates of the larvae on these dinoflagellates were 14-69 ng C predator-1 day-1 and 1.5-11.4 μL predator-1 h-1, respectively. M. galloprovincialis larvae, one component of microzooplankters, exhibited higher maximum ingestion and clearance rates than previously reported for other microzooplankters, such as Fragilidium cf. mexicanum (mixotrophic dinoflagellate), Protoperidinium cf. divergens, Polykrikos kofoidii (heterotrophic dinoflagellates), or Tiarina fusus (small ciliate), but lower rates than Strombidinopsis sp. and Favella sp. (large ciliates). The results of the current study suggest that dinoflagellates sometimes can be primary prey for the Mytilus larvae, and the grazers compete with other microzooplankters for dinoflagellate prey. Also, red-tide dinoflagellates can be used for culturing the Mytilus larvae as prey in the aquaculture industry.
Article
Effects of two harmful dinoflagellate blooms, Gymnodinium mikimotoi and Heterocapsa circularisquama on the clearance rate of the blue mussel Mytilus galloprovincialis and the pacific oyster Crassostrea gigas were studied during both red tide periods occurred in Hiroshima Bay, Seto Inland Sea, Japan, 1995. The mean clearance rate of mussel and oyster decreased to 19.8% and 14.4% of control in the G. mikimotoi red tide, respectively. In the oyster, red tide filtrate of G. mikimotoi slightly inhibited the filtration activity. The mean clearance rate of the mussel and the oyster decreased to the 8.8% and 1.5% of the control seawater in the H. circularisquama red tide, respectively. However, filtration rates of both mussels and oysters were not inhibited in the filtrate of H. circularisquama red tides. Both bivalves exposed to red tide exhibited various negative responses such as retraction of their mantles and gradual valve closure. The present study demonstrated that red tides of G. nikimotoi and H. circularisquama strongly inhibited the filtration rate of bivalves.
Article
Effects of two harmful dinoflagellate blooms, Gymnodinium mikimotoi and Heterocapsa circularisquama on the clearance rate of the blue mussel Mytilus galloprovincialis and the pacific oyster Crassostrea gigas were studied during both red tide periods occurred in Hiroshima Bay, Seto Inland Sea, Japan, 1995. The mean clearance rate of mussel and oyster decreased to 19.8% and 14.4% of control in the G. mikimotoi red tide, respectively. In the oyster, red tide filtrate of G. mikimotoi slightly inhibited the filtration activity. The mean clearance rate of the mussel and the oyster decreased to the 8.8% and 1.5% of the control seawater in the H. circularisquama red tide, respectively. However, filtration rates of both mussels and oysters were not inhibited in the filtrate of H. circularisquama red tides. Both bivalves exposed to red tide exhibited various negative responses such as retraction of their mantles and gradual valve closure. The present study demonstrated that red tides of G. mikimotoi and H. circularisquama strongly inhibited the filtration rate of bivalves.
Article
The marine dinoflagellate Heterocapsa circularisquama Horiguchi is the causal agent of red tide on the Japanese coast. In the last decade, H. circularisquama red tides have destroyed the shellfish aquaculture industries around the western part of Japan because this dinoflagel-late shows a detrimental effect on shellfishes particularly on bivalve molluscs. The current proliferation of H. circularisquama throughout western Japan is a cause for concern due to economic loss. The outbreaks of H. circularisquama are closely related to the environmental conditions: water exchange rate, water temperature, local and global climate changes. Administrative measures such as algal monitoring systems can be successfully utilized for the distribution and short-term prediction of red tide due to H. circularisquama in several locations. However, secondary damage, i.e. decline of demand due to misinformation and cost of measures to prevent the damage, adversely affects the development of shellfish aquaculture even if direct killing of the products can be avoided.