Printer Friendly

Sand elimination by the Asiatic hard clam Meretrix meretrix (L.): influences of temperature, salinity and season.

ABSTRACT Clams, being filter-feeders that burrow into sand, tend to accumulate sand in their body tissues. Depuration reduces the clams' gut contents and eliminates sand from different body fractions, providing some cleansing and ensuring that they are safe for human consumption. The Asiatic hard clam Meretrix meretrix (Bivalvia: Veneridae) is a commercially important species inhabiting sand flats of Hong Kong and Southeast Asia. In this laboratory study, the effects of temperature and salinity on the rate and profile of sand elimination in M. meretrix were studied during winter and summer using a 2 x 2 factorial design (i.e., two temperatures 20[degrees]C and 30[degrees]C, and two salinities 15%and 30%). Sand removal rate was measured in terms of a decrease in inorganic content (i.e., ash) over a 72-h period. In general, sand was removed from the gut and body tissues and transferred to the external body fluid for subsequent discharge to the ambient water. Meretrix meretrix exhibited significantly lower sand removal rates in summer than in winter across all treatments, whereas the highest sand removal rate was observed at 20[degrees]C and 15% in both seasons. The sand removal rate of M. meretrix is, therefore, not only affected by temperature and salinity, but also strongly associated with natural, seasonal, effects. These findings have important implications for optimizing conditions for sand elimination of this species for the shellfish industry in Asia.

KEY WORDS: depuration, salinity, sand elimination, season, temperature


Sandy shore bivalves burrow into sand as an adaptation to protect themselves from wave impact, temperature fluctuations, desiccation, and predation (Nybakken 1997). As filter feeders, they feed during high tide using their siphons, which extend to the sand surface to collect microscopic organisms and particulates from the water column (Morton 1979). Ingested particles, containing both organic and inorganic matter, are either digested in the gut or expelled as faecal pellets (Hylleberg & Gallucci 1975, Ruppert & Barnes 1994). In addition sand particles, together with other unwanted particles such as viruses, bacteria, and pollutants, will be trapped in different organs such as the gills, gut, and adductor muscles (Richards 1988, Savari et al. 1991, Sobsey & Jaykus 1991, Somerset 1991, Ho & Kim 1995, Ariza et al. 1999). When the clams are sold for human consumption, the tissues that contain sand can be unpleasant to eat and also pose a health risk. As a common practice the clams are, therefore, allowed to clean themselves in clean seawater (i.e., depuration) to remove the sand in their body (Richards 1988, Savari et al. 1991).

In bivalves, significant effects of salinity have been reported on mortality (Mane 1978, Morton & Chan 1990), growth (Robert et al. 1988, Hutchinson & Hawkins 1992), and cardiac and siphonal pumping activity (Akberali & Davenport 1981). Salinity is especially important in controlling the effectiveness of depuration by sandy shore bivalves. Richards (1988), for example, demonstrated that salinities between 22% and 31% were optimal for microbial deputation by the hard clam Mercenaria mercenaria (L.), soft-shell clam Mya arenaria (L.), and hen clam Venus gallina (L.).

Apart from salinity, the depuration rate of bivalves is also influenced by water temperature, suggesting that it may be associated with temperature-dependent metabolic activities. Previous studies have shown that growth (His et al. 1989), respiratory responses (Hicks & McMahon 2002), and filtration rate (Walne 1972) of bivalves are temperature-dependent. Richards (1988) found that the depuration of viruses by the hard clam Mercenaria mercenaria (L.) was improved by increasing temperature, and a similar result was observed in a study on the elimination of coliphages by the mussel Mytilus edulis (L.) (Power & Collins 1990). Additionally, Richards (1988) investigated the seasonal variation of microbial depuration by temperate clams in terms of the combined effect of salinity and temperature and revealed that viruses were more effectively depurated from the clams during the summer and fail months than during the winter.

Although the depuration of pathogens (e.g., viruses; Carter & Cantelmo 1990, Ho & Tam 2000), soluble pollutants (e.g., hydrocarbons and heavy metals; Denton & Jones 1981, Jovanovich & Marion 1987, Savari el. al. 1991, Reinfelder et al. 1997, Ariza et al. 1999), and phytotoxins (Blanco et al. 2002) in bivalves has widely been studied, information on the elimination rate of insoluble, sand-like particles in clams and cockles is scarce. Indeed, there are only a few reports on sand elimination rates in mussel, clam, and cockle species in relation to their storage and handling in the shellfish industry (De Vooys 1987, Richards 1988, NSSP 1990. Somerset 1991).

The current study was therefore designed to investigate the rate of sand elimination by the commercially important, Asiatic hard clam Meretrix meretrix (L.) in clean seawater at four different temperature/salinity regimes during winter and summer, respectively. The results from such a study are important for optimizing conditions for sand elimination of this species for the shellfish industry in Asia.


Sampling and Experimental Design

Meretrix meretrix is one of the largest clam species among the Venus-shells (Veneridae) and very common on sheltered sand flats in Hong Kong, South China, India, Vietnam, Thailand, and the Saudi Arabian Gulf (Morton & Morton 1983, Jayabal & Kalyani 1986, Nhan et al. 1999, Vazquez el al. 1991). As a commercially important clam species in Asia, it has widely been cultured in China and Thailand (Ho & Zheng 1994, Ho & Kim 1995).

In the current study, adult M. meretrix were randomly collected from Shui Hau in Lantau Island, Hong Kong (Grid reference: 22[degrees]13'N, 113[degrees]55'E) during low tides in winter (24 February 2003; 75 individuals; shell length: 50.01 [+ or -] 4.13 mm, mean [+ or -] SD) and in summer (5 June 2003; 75 individuals; shell length: 54.9 [+ or -] 7.3 mm). Clams were collected using a specially constructed clam-rack commonly used by fishermen in Hong Kong and South China (Morton & Morton 1983).

Hong Kong has a strongly seasonal, monsoonal climate with a hot, wet summer and cool, dry winter (Kaehler & Williams 1996). Seawater temperature and salinity were measured using a thermometer and a refractrometer (ATGAO, S/Mill-E, Tokyo, Japan). The seawater temperature and salinity in the field were 15.0[degrees]C and 32.0 [per thousand], in winter and 29.0[degrees]C and 14.0 [per thousand] in summer. Such a considerable difference in salinity between the two seasons was mainly due to the close proximity of the site to the Pearl River estuary, which receives a huge amount of freshwater input during summer (Morton & Wu 1975). The collected clams were transferred to the laboratory within 2 h of collection. On arrival, the clams were divided into four groups and held in 1 L, aerated glass tanks filled with 500 mL of artificial seawater (Kent Marine Salt, Kent Marine Inc., Acworth, Georgia) at the same salinity level as measured at the collection site and at room temperature (20[degrees]C). The experimental ranges of temperatures and salinities were based on the natural ranges in the environment (Morton & Wu 1975, Morton & Morton 1983). The clams were acclimatized to four combinations of two temperatures (20 [+ or -] 0.2[degrees]C and 30 [+ or -] 0.4[degrees]C, mean [+ or -] SD) and two salinities (15 [+ or -] 0.8 [per thousand] and 30 [+ or -] 0.4 [per thousand]). The water temperature of the 30[degrees]C treatments was adjusted by increasing 4[degrees]C every 3 h using a water bath with a temperature controller, whereas the 20[degrees]C treatments were maintained at room temperature. Salinity was adjusted by decreasing or increasing values by 5 [per thousand] every 3 h until the desired levels were reached. This was achieved by renewing the seawater with artificial sea salts. A control group of 15 individuals was randomly selected at the beginning of the experiment to determine the initial inorganic content of the clams prior to depuration.

For each treatment group, there were three 1-L glass tanks, each holding 5 animals ([SIGMA]n = 4 treatments x 3 tanks x 5 clams = 60 clams). Water salinity and temperature were kept constant for each treatment and monitored twice daily. Experimental water was renewed daily. No food was provided and a 12-h light: 12-h dark cycle was maintained throughout the experiment. In a preliminary study, Lui (2003, unpublished data) observed that M. meretrix individuals removed >65% of sand from their body after 72 h in artificial seawater at 20[degrees]C and 32 [per thousand] (sand remaining [%] = 202.2 x [exp.sup.-4.5 x +] 34.2, where t is the duration of sand removal in hours). The clams were, therefore, allowed to depurate over 72 h in the current study, after which all animals were collected for dissection, condition index, and inorganic content measurements.

Dissection of Clams

To study the sand elimination profile and pathway, sand content in three different body compartments, namely the external body fluid, the gut, and the remaining soft body tissues, were determined. The animals in their shells were thoroughly scrubbed with a stiff brush in running tap water, rinsed with distilled water, and left to dry on clean paper towels. Shucking was achieved by inserting a dissecting knife at the site of the adductor muscle. After the shell valves were opened, any liquid was drained and collected in a preweighed aluminum container. This sample was designated as the external content (EC). The digestive tract was then carefully dissected and designated as the gut content (GC) and placed in a preweighed aluminum container. The remaining body tissues were also placed in another preweighed aluminum container and designated as the body content (BC).

Inorganic Content Analysis and Condition Index

Five empty, preweighed aluminum containers were used as controls for the weighing procedure. All samples, along with the empty shells, were dried in an oven at 80[degrees]C for at least 48 h until a constant dry weight was achieved. For each animal, dry weights of all the components (i.e., EC, GC, and BC) and empty shells were weighed using an electronic balance ([+ or -] 0.00001 g; OHAUS Analytical Plus, Nanikou, Switzerland). Dried samples were then ignited at 500[degrees]C in a muffle furnace for 4 h (Takada 1995) and the remaining ash content weighed. Three readings were taken for each sample to ensure a precise mean value for representing the dry ash weight. The inorganic content of each component was calculated as the percentage of the ash weight of the total dry weight of the whole soft body tissues. Total inorganic content percentage (TIC, %) of each clam was calculated using the following equation:

(1) TIC (%) = (Total Ash Weight/Total Dry Soft-Body Tissue Weight) x 100%

where total ash weight was calculated by summation of the ash weights from all of the three fractions (EC, GC, and BC) and total dry tissue weight was the sum of the dry weights of the gut and body tissues.

The condition index (CI) was calculated using the following equation described in Beninger and Lucas (1984) and expressed as g tissue per g shell weight:

CI = Dry Soft-Body Tissue Weight/Dry Shell Weight (2)

The Rate of Sand Elimination

The rate of sand elimination (mg [g.sup.-1] [h.sup.-1] for each species was calculated using the following equation:

(3) Rate = (TI[] - TI[C.sub.initial]/Depuration Time

where TI[] is the total inorganic concentration (mg [g.sup.-1] dry soft-body weight) at the end of the experiment over the total depuration time, and TI[C.sub.initial] is the initial total inorganic concentration (mg [g.sup.-1] dry soft-body weight) at time zero. The results were also expressed as percent sand remaining, which was a ratio of sand content between the control claims (i.e., initial) and each treatment group after 72 h depuration.

Statistical Analysis

Data were tested for homogeneity of variances using Levene's test (SPSS version 10.0). Two-way analysis of variance (ANOVA) was used to test the effect of the treatment (five levels: control and four temperature/salinity regimes) and season (two levels: winter and summer) on the condition index. To compare the inorganic content in each individual components (i.e., EC, GC, and BC) among the control and the four regimes in each season, one-way ANOVAs were used followed by post hoc Tukey's multiple comparison tests to identify significantly different means. Finally, a three-way ANOVA was used to test the significance of the effects of temperature (two levels), salinity (two levels), and season (two levels) on the sand removal rate.


Condition Index

As no food was provided during the depuration period, the condition index (CI) of M. meretrix decreased significantly after the 72 h depuration for the four treatments in both seasons (Fig. 1; two-way ANOVA: treatment effect, [F.sub.4, 19] = 35.64, P < 0.001). The CI values were significantly lower in summer than in winter across all of the control and treatment groups (Fig. 1; two-way ANOVA: season effect, [F.sub.1, 19] = 34.74, P < 0.001).


Inorganic Content in Different Body Compartments

Before depuration, the distribution of sand in the control group of M. meretrix followed the order external body fluid (EC) > body tissues (BC) > guts (GC) during the summer (Figs. 2a, 2c, and 2e). In contrast, higher levels of sand grit were found in BC than EC in the control M. meretrix group during the winter (Figs. 2b, 2d, and 2f). After the 72-h depuration period, the inorganic content in the gut decreased across all treatments in both seasons, although this decline in the clams exposed to 30 [per thousand] and 20[degrees]C was not statistically significant (Figs. 2c and 2d). For treatments under high salinity (30 [per thousand]) regardless of their water temperature and season, the amount of sand depurated was small, and the EC accounted for the largest proportion of overall inorganic content (Figs. 2a and 2b). Meretrix meretrix collected in winter and exposed to the two high-salinity regimes showed a significant increase in inorganic content in the EC over the deputation period (Fig. 2b). In terms of total inorganic contents (TIC) per individual clam (Figs. 2g and 2h), the two low-salinity (15 [per thousand]) treatment groups exhibited significant reductions in their sand contents, whereas the two high-salinity (30 [per thousand]) treatment groups did not show any significant decline in TIC. These results indicate that the speed of transportation of sand from the body tissues and gut to the external fluid for discharge was much slower in M. meretrix exposed to high salinities (30 [per thousand]) than for the other treatment groups at low salinity (15 [per thousand]).


The sand removal rate of M. meretrix was strongly affected by the different temperature/salinity regimes and season (Figs. 3a and 3b). In general, significantly higher sand removal rates (or lower sand remaining %) were observed at low salinity and low temperature (Fig. 3; Table 1), with the highest elimination rate at 15 [per thousand] and 20[degrees]C for both seasons (Fig. 3). The rate of sand removal was, however, significantly lower in the summer than in the winter (Fig. 3; Table 1). When comparing the magnitude of the differences among the four groups and the F values (Fig. 3b; Table 1), it was clear that salinity was a more important factor affecting sand elimination rates in M. meretrix than temperature and season. This was further supported by the absence of any significant interactions between temperature, salinity, and season on the rate of sand removal (Table 1).



Sand Distribution and Depuration

In this study, sand (as determined by inorganic content) was transported and accumulated in different body compartments. Sand particles either passed through the gut and were discharged as feces or pseudofeces or were transported from the tissues to the external body fluid for subsequent disposal from the edge of the shell. During a 72-h depuration period, a considerable amount of sand particles was defecated from the gut by M. meretrix in both seasons. The inorganic content remaining in the gut might serve several adaptive functions. First, inorganic matter might contain some essential nutrients that are assimilated through the gut or may have microalgal food items bound to their surface (Huz et al. 2002). Second, Chia (1973) demonstrated that sand grains could be used as a weight belt for juvenile sand dollars, Dendraster excentricus (Eschscholtz), that stored these grains in their intestinal diverticulum to help them settle on the sea floor. There is, however, much less information available on the adaptive function of sediment accumulation in burrowing clams.

Salinity Effect

Sand removal rate in M. meretrix was higher at low salinities (15 [per thousand]). A similar result has been reported for the blue mussel, Mytilus edulis, and the hard clam, Mercenaria mercenaria, concerning the depuration of coliphages and Escherichia coli (Richards 1988, Power & Collins 1990). Such an increase in depuralion rate may be attributable to an increase in filtration rate and pupming activity at low salinities. Nonetheless, Richards (1988) also reported that other species, such as the soft-shell clam Mya arenaria (L.), showed a greater depuration rate at higher salinities (25-30 [per thousand]), suggesting that the effect of salinity is species specific. Sobsey and Jaykus (1991) also reported that the range of optimal salinity for effective deputation varies among different bivalve species.

Variation in salinity affects bivalve physiology in a number of ways. Hutchinson and Hawkins (1992) demonstrated that the excretion rate of the oyster Ostrea edulis (L.) increased at low salinities, whereas the effect of salinity on their growth varied, depending on the level of food availability. Shell valve activity in response to variation in salinity may be another factor controlling the rate of sand elimination. Akberali and Davenport (1981), for example, showed that the exhalant siphon and valves of the clam Scrobicularia plana (de Costa) closed at low salinities and thus prevented their pumping activity.

In the current study, M. meretrix removed more sand at low salinities (15 [per thousand]), suggesting that they perform well under lower salinities. Meretrix meretrix occurs on shores in Hong Kong where surface salinities may tall to as little as 2 [per thousand] as a result of the summer monsoons and the influx of freshwater from the Pearl River (Morton & Morton 1983). This ability to survive in low salinities is important for infaunal species, as the salinity of estuarine and intertidal zones can fluctuate on an hourly, daily, weekly, and seasonal basis (Gainey & Greenberg 1977, Leung et al. 2002). This may explain why the effect of salinity on sand elimination in M. meretrix did not vary between winter and summer.

Temperature Effect

Sand elimination by M. meretrix is also temperature-dependent; higher removal rates of sand were generally found at lower temperatures (20[degrees]C). Some shellfish sellers in Hong Kong use lower water temperatures to achieve effective sand depuration by clams, as survival rates of the shellfish are generally higher al lower temperatures such as 17-18[degrees]C (Lui, personal communication). Matthews and McMahon (1999) also demonstrated that the zebra mussel, Dreissena polymorpha (Pallas), and the Asian clam, Corbicula fluminea (Muller), showed a higher tolerance to hypoxia at lower temperatures. In contrast, however, the West African clam, Galatea paradoxa (Born), showed a greater removal of sand at elevated temperatures (Ekanem 2000), whereas the deputation of" E. eoli also increased at higher temperatures in Mytilus edulis (Power & Collins 1990) and the king scallop, Pecten maximus, (L.) (Heath & Pyke 2001), suggesting that such temperature-dependent responses also vary between species.

Generally, in bivalves, higher water temperatures result in increased feeding rates (in terms of filtration rates; Walne 1972) and higher metabolic rates (in aspects of growth; Robert et al. 1988) and oxygen consumption (Hicks & McMahon 2002). Some workers, however, did not find any significant effects of temperature at the organism level (Denton & Jones 1981, De Vooys 1987, Inza et al. 1998, Blanco et al. 2002), and they argue that the deputation process is independent of metabolic rates, as their target species still efficiently depurated over a broad range of temperatures (6.6 20.5[degrees]C). Whether depuration is a temperature-dependent physiologic process in all bivalves species has, therefore, yet to be confirmed.

Combined Effects of Salinity, Temperature, and Season

The effect of temperature on sand elimination by Meretrix meretrix was not as pronounced as the effect of salinity. Meretrix meretrix must tolerate a wide range of salinities on western shores of Hong Kong. The effect of temperature shock (either hot or cold) is, however, likely to be minimal on the shore because they burrow into the sediment where temperatures are more stable as compared with air temperatures (Yang et al. 2003).

In M. meretrir, oplimal sand elimination was achieved at low temperatures (20[degrees]C) and salinitics (15 [per thousand]) in both summer and winter. Although M. meretrix exhibited a higher rate of sand removal in winter than summer, the influence of temperature and salinity was similar between the two seasons. Interestingly, the significantly lower condition indices for M. meretrix in the summer (June) were probably associated with low food (i.e., particulate organic matter) availability in the water column (Wong & Cheung 2003), which may possibly be due to heat stress and the increase in freshwater input from rainfall and surface runoff. In contrast, micro- and macroalgae are more abundant during winter in Hong Kong coastal environments (Morton & Morton 1983, Hodgkiss 1984, Nagarkar & Williams 1999) and may considerably enhance the growth of the clams. In such favorable conditions in winter, the clams not only have better physiologic status to efficiently ingest and assimilate nutrients but are also able to excrete waste and depurate sand more effectively. Jovanovich and Marion (1987) also observed a seasonal variation in the deputation of anthracene by the clam Rangia cuneata (Sowerby); depuration rates remained low from March to August and rapidly increased to the highest levels during the fall spawning period. This seasonality was related to the reproductive cycle of R. cuneata and associated biochemical changes, which in turn affected the physiologic state of the clam.

The oyster Ostrea edulis (L.) shows physiologic variation according to seasonality (Hutchinson & Hawkins 1992). A "winter" physiologic state enables O. edulis to survive at low temperatures and salinites that are normally encountered during the winter months in its shallow coastal water habitat, whereas a reverse physiologic state was recorded in summer. Similarly, siphonal activity of the soft shell clam, Mya arenaria (L.), was higher during May September and then strongly declined from October (Thorin 2000). This variation was mainly attributed to seasonal changes in resource availability, water temperature, or individual reproductive state of M. arenaria. To our knowledge, the natural reproductive cycle of M. meretrix has yet to be established in Hong Kong and South China, although they have been artificially reared or cultured in Southeast Asia. As a result, we are unable to comment on the possible influence of their reproductive cycle on sand elimination.


Sand can be trapped in different body compartments in burrowing bivalves, and this needs to be eliminated for the clam to cleanse itself in the natural environment and for use in the shellfish industry to ensure safety for human consumption. Simple methods for sand elimination using clean seawater or freshwater are currently used by shellfish sellers and seafood restaurant owners worldwide (De Vooys 1987, Carter & Cantelmo 1990, NSSP 1990, Ho & Tam 2000, Heath & Pyke 2001). This pilot study investigated the effect of salinity, temperature, and season on sand elimination in the commercially important clam Meretrix meretrix. The rate of sand removal by M. meretrix was significantly affected by salinity and temperature. The highest rate of sand removal was found at low salinities (15 [per thousand]) and temperatures (20[degrees]C). These optimal depuration conditions were identical in both summer and winter, suggesting that lower temperature and lower salinity were physiologically more favorable regardless of seasonality. Depuration rates in the clams were, however, higher in winter for all treatment groups, and this is probably associated with seasonal variation in the climate, food availability, and reproductive cycle of the clam. Further investigation is, however, required to test whether factors other than salinity and temperature, such as reproductive cycle and food availability, could be important in regulating the rate of sand depuration in M. meretrix.
Results of three-way ANOVA on the sand depuration rate
(mg [g.sup.-1] [h.sup.-1]) of Meretrix meretrix exposed
to the four different salinity and temperature regimes
during the summer and winter.

Factor df MS F P Value

Temp. 1 0.174000 8.625 0.010 *
Salinity 1 4.087000 202.487 <0.0001 ***
Season 1 0.135000 6.683 0.021 *
Temp. x Salinity 1 0.014140 0.701 0.416
Temp. x Season 1 0.057400 2.844 0.112
Salinity x Season 1 0.001029 0.051 0.824
Temp. x Salinity x Season 1 0.000383 0.019 0.892
Residual 15 0.020180

Asterisks denote significant factors at * P < 0.05: *** P < 0.001.


The authors thank Cecily Law. Laura Wong, and Lily Ng for their technical support and Cyrus Cheng and Shirley Lui for helping with collecting the samples. Special thanks are also extended to Gray A. Williams, Will Trewhella, Valerie Ho, Justine Tsui, Danny Lau, and Jasmine Ng for their critical reading of earlier drafts of this manuscript.


Akberali, H. B. & J. Davenport. 1981. The responses of the bivalve Scrobicularia plana (da Costa) to gradual salinity changes. J. Exp. Mar. Biol. Ecol. 53:251-259.

Ariza, J. L. G., E. Morales & I. Giraldez. 1999. Uptake and elimination of tributyltin in clams. Venerupis decussata. Mar. Environ. Res. 47:399-413.

Beningur, P. G. & A. Lucas, 1984. Seasonal variations in condition, reproduction activity, and gross biochemical composition of two species of adult clam reared in a common habitat: Tapes decussates L. (Jefreys) and Tapes philippinarum (Adams & Reeve). J. Exp. Mar. Biol. Ecol. 79:19-37.

Blanco, J., C. P. Acosta, M. Bermudez de la Puente & C. Salgado. 2002. Depuration and anatomical distribution of the amnesic shellfish poisoning (ASP) toxin domoic acid in the king scallop Pectin maximus. Aquat. Toxicol. 60:111-121.

Carter, T. H. & R. F. Cantelmo. 1990. Efficacy of commercial deputation in the elimination of enteric viruses and Clostridia from the hard clam. Mar. Tech. Soc. J. 23(1):14-20.

Chia, F. S. 1973. Sand dollar: a weight belt for the juvenile. Science 181:73-74.

Denton, G. R. W. & C. B. Jones. 1981. Influence of temperature and salinity on the uptake, distribution and depuration of mercury, cadmium and lead by the black-lip oyster Saccostrea echinata. Mar. Biol. 64:317-326.

De Vooys, C. G. N. 1987. Elimination of sand in the blue mussel, Mytilus edulis, J. Sea Res. 21(1):75-78.

Ekanem. E. O. 2000. Effects of shucking method on opening, meat yield and selected quality parameters of West African clam, Galatea paredoxa (Born). J. Food Process. Preserv. 24:365-377.

Gainey, L. F. & M. J. Greenberg. 1977. Physiological basis of the species abundance--salinity relationship in molluscs: a speculation. Mar. Biol. 40:41-49.

Heath, P. & M. Pyke. 2001. King scallop (Pecten maximus) depuration trials. J. Shellfish Rex, 20(1): 117-120.

Hicks, D. W. & R. F. McMahon. 2002. Respiratory responses to temperature and hypoxia in the nonindigenous Brown Mussel, Perna perna (Bivalvia: Mytilidae), from the Gulf of Mexico. J. Exp. Mar. Biol. Ecol. 277:61-78.

His, E., R. Robert & A. Dinet. 1989, Combined effects of temperature and salinity on fed and starved larvae of the Mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas. Mar, Biol. 100:455-163.

Ho, J. S. & G. X. Zheng. 1994. Ostrincola koe (Copepoda, Myicolidae) and mass mortality of cultured hard clam (Meretrix meretrix) in China. Hydrobiologia 284:169-173.

Ho, J. S. & I. H. Kim. 1995. Copepod parasites of a commercial clam (Meretrix meretrix) from Phuket, Thailand. Hydrobiologia 308:13-21.

Ho, B. S. W. & T. Y. Tam. 2000, Natural depuration of shellfish for human consumption: a note of caution. Water Resour. 34(4):1401-1406.

Hodgkiss, I. J. 1984. Seasonal patterns of intertidal algal distribution in Hong Kong, Asian Mar. Biol. 1:49-57.

Hutchinson, S. & K. Hawkins. 1992. Quantification of the physiological responses of the European flat oyster Ostrea edulis L. to temperature and salinity. J. Moll. Stud. 58:215-216.

Huz, R., M. Lastra & J. Lopez. 2002. The influence of sediment grain size on burrowing, growth and metabolism of Donax trunculus L. (Bivalvia: Donacidae). J. Sea Res. 47:85-95.

Hylleberg, J. & V. F. Gallucci. 1975. Selectivity in feeding by the deposit-feeding bivalve Macoma nasuta. Mar. Biol. 32:167-178.

Inza, B., F. Rbeyre & A. Boudou. 1998. Dynamics of cadmium and mercury compounds (inorganic mercury or methylmercury): uptake and depuration in Corbicula fluminea. Effects of temperature and pH. Aquat. Toxicol. 43:273-285.

Jayabal, R. & M. Kalyani. 1986. Biochemical studies in the hard clam Meretrix meretrix (L.) from Vellar Estuary, east coast of India. Indian J. Mar. Sci. 15:63-64.

Jovanovich, M. C. & K. R. Marion. 1987. Seasonal variation in uptake and deputation of anthracene by the brackish water clam Rangia cuneata. Mar. Biol. 95:395-403.

Kaehler, S. & G. A. Williams. 1996. Distribution of algae on tropical rocky shores: Spatial and temporal patterns of non-coralline encrusting algae in Hong Kong. Mar. Biol. 125(1):177-187.

Leung, K. M. Y., J. Svavarsson, M. Crane & D. Morritt. 2002. Influence of static and fluctuating salinity on cadmium uptake and metallothionein expression by the dogwhelk Nucella lapillus (L.). J. Exp. Mar. Biol. Ecol. 274(2):175-189.

Mane, U. H. 1978. Survival and behaviour of oysters in water of low salinities at Ratnagiri on the west coast of India. J. Moll. Stud. 44:243-249.

Matthews, M. A. & R. F. McMahon. 1999. Effects of temperature and temperature acclimation on survival of zebra mussels (Dreissena polymorpha) and Asian clams (Corbicula fluminea) under extreme hypoxia. J. Moll. Stud. 65:317-325.

Morton, B. & S. S. Wu. 1975. The hydrology of the coastal waters of Hong Kong. Environ. Res. 10:319-347.

Morton, B. & K. Y. Chan. 1990. The salinity tolerances of four species of bivalves from a Hong Kong mangrove. In: B. Morton, ed. The Marine Flora and Fauna of Hong Kong and Southern China II: Proceedings of the Second International Marine Biological Workshop: the Marine flora and fauna of Hong Kong and Southern China, Hong Kong, 2-24 April, 1986. Hong Kong: Hong Kong University Press, pp. 115-1122.

Morton, B. & J. Morton. 1983. The Sea Shore Ecology of Hong Kong. Hong Kong: Hong Kong University Press. 350 pp.

Morton. J. E. 1979. Molluscs. 4th ed. London: Hutchinson. London. 264 pp.

Nagarkar. S. & G. A. Williams. 1999. Spatial and temporal variation of cyanobacteria-dominated epilithic communities on a tropical shore in Hong Kong. Phycologia 38(5):385-393.

National Shellfish Sanitation Program (NSSP). 1990. Manual of Operations, Part II: Sanitation of the Harvesting, Processing and Distribution of Shellfish. Washington, DC: Public Health Service, U.S. Food and Drug Administration. 56 pp.

Nhan, D. D., N. M. Am, F. P. Carvalho, J, P. Villeneuve & C. Cattini. 1999. Organochlorine pesticides and PCBs along the coast of North Vietnam. Sci. Total Environ. 238:363-371.

Nybakken, J. W. 1997. Marine Biology: An Ecological Approach. New York: Addison-Wesley Educational Publishers Inc. 516 pp.

Power, U. F. & J. K. Collins. 1990. Elimination of coliphages and Escherichia coli from mussels during depuration under varying conditions of temperature, salinity, and toad availability. J. Food Protect. 53(3):208-212.

Reinfelder, J. R., W. X. Wang, S. N. Luoma & N, S. Fisher. 1997. Assimilation efficiencies and turnover rates of trace elements in marine bivalves: a comparison of oysters, clams and mussels. Mar. Biol. 129: 443-152.

Richards, G. P. 1988. Microbial purification of shellfish: a review of depuration and relaying. J. Food Protect. 51(3):218-251.

Robert, R., E. His & A. Dinet. 1988. Combined effects of temperature and salinity on fed and unfed and starved larvae of the European flat oyster Ostrea edulis. Mar. Biol. 97:95-100.

Ruppert, E. E & R. D. Barnes. 1994. Invertebrate Zoology. 6th ed. South Melbourne, Australia: Brooks/Cole, Thomson Learning. 1056 pp.

Savari, A., A. M. P. Lockwood & M. Sheader. 1991. Effects of season and size (age) on heavy metal concentrations of the common cockle Cerastoderma edule from Southampton waters. J. Moll. Stud. 57:45-57.

Sobsey, M. D. & L. A. Jaykus. 1991. Human enteric viruses and depuration of bivalve mollusks. In: W. S. Otwell, G. E. Rodrick & R.E. Martin, eds. Molluscan Shellfish Depuration. Boca Raton: CRC Press, pp. 71-114.

Somerset, I. J. 1991. Current U.S. commercial shellfish depuration. In: W. S. Otwell. G. E. Rodrick & R. E. Martin, eds. Molluscan Shellfish Deputation. Boca Raton: CRC Press. pp. 25-29.

Takada, Y. 1995. Inorganic contents of faeces in molluscan grazers observed on a boulder shore at Amakusa. Japanese Journal of Malacology. 54(3):195-201.

Thorin. S. 2000. Seasonal variations in siphonal activity of Mya arenaria (Mollusca). Z Mar. Biol. Assoc. U.K. 80:1135-1136.

Vazquez. M. A., K. W. Allen & Y. M. Kattan. 1991. Long-term effects of the 1991 Gulf War on the hydrocarbon levels in clams at selected areas of the Saudi Arabian Gulf coastline. Mar. Pollut. Bull. 40:440-448.

Walne, P. R. 1972. The influence of current speed, body size and water temperature on the filtration rate of five species of bivalves. Z Mar. Biol. Assoc. U.K. 52:345-374.

Wang, W. H. & S. G. Cheung. 2003. Seasonal variation in the feeding physiology and scope for growth of green mussels, Perna viridis in estuarine Ma Wan. Hong Kong. J. Mar. Biol. Assoc. U.K. 83(3):543-552.

Yang, K. Y., S. Y. Lee & G. A. Williams. 2003. Selective feeding by the mudskipper (Boleophthalmus pectinirostris) on the microalgal assemblage of a tropical mudflat. Mar. Biol. 143(2):245-256.


(1) The Swire Institute of Marine Science and Department of Ecology & Biodiversity, The University of Hong Kong, Pokfulam, Hong Kong, China

* Corresponding author. E-mail:
COPYRIGHT 2004 National Shellfisheries Association, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2004, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Author:Leung, Kenneth M.Y.
Publication:Journal of Shellfish Research
Geographic Code:90ASI
Date:Aug 1, 2004
Previous Article:Herpes-like virus associated with eroded gills of the Pacific oyster Crassostrea gigas in Mexico.
Next Article:Surfclam histopathology survey along the Delmarva mortality line.

Related Articles
Surfclam histopathology survey along the Delmarva mortality line.
Reproductive cycle of the stout razor clam, Tagelus plebeius (Lightfoot, 1786), in the Mar Chiquita Coastal Lagoon, Argentina.
Impact of green crab (Carcinus maenas L.) predation on a population of soft-shell clams (Mya arenaria L.) in the Southern Gulf of St. Lawrence.
Effects of diets, their concentrations and clam size on filtration rate of hard clams (Meretrix lusoria).
Effects of salinity on sand burrowing activity, feeding and growth of the clams Mactra veneriformis, Ruditapes philippinarum and Meretrix lusoria.
Spatio-temporal variations in density of different life stages of a brackish water clam Corbicula japonica in the Kiso estuaries, central Japan.
A population dynamics model of the hard clam, Mercenaria mercenaria: development of the age- and length-frequency structure of the population.
Differences of Turkish clam (Ruditapes decussates) and Manila clam (Ruditapes philippinarum) according to their proximate composition and heavy metal...
Biotic and abiotic factors influencing growth and survival of wild and cultured individuals of the softshell clam (Mya arenaria L.) in Eastern Maine.
Trends in Maine softshell clam landings.

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters