Gonadal maturation and trace metals in the mangrove oyster Crassostrea corteziensis: seasonal variation

The Science of the Total Environment 231 Ž1999. 115]123

Gonadal maturation and trace metals in the mangrove oyster Crassostrea corteziensis: seasonal variation a,c b,U M.G. Frıas-Espericueta , J.I. Osuna-Lopez ´ ´ a , F. Paez-Osuna ´ a

b

Marine Sciences School, Autonomous Uni¨ ersity of Sinaloa, P.O. Box 610, Mazatlan ´ 82000, Sinaloa, Mexico Institute of Marine Sciences and Limnology, Mazatlan ´ Station, National Autonomous Uni¨ ersity of Mexico, P.O. Box 811, Mazatlan ´ 82000, Sinaloa, Mexico c Marine Sciences and Limnology Postgraduate Program, Mazatlan Station, National Autonomous Uni¨ ersity of Mexico, Mexico City, Mexico Received 20 September 1998; accepted 21 March 1999

Abstract The concentration of nine trace metals ŽCd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. associated with the gonadal and somatic Žnon-gonadal. tissues throughout the reproductive cycle of the oyster Crassostrea corteziensis ŽHertlein. have been studied. The metal concentration in this oyster exhibited significant seasonal variations. The highest concentrations of Cu, Ni, Pb and Zn occurred in November when the oyster was in the resting phase, while the maximum of Mn was recorded in March when the population was predominantly in gametogenic activity. The elevated values of Cd and Fe were presented in September during the post-spawning phase. Only Mn showed a good positive correlation with the maturation of the organism. This last result suggests that Mn may perform some function during the gonadal maturation or prespawning. Q 1999 Elsevier Science B.V. All rights reserved. Keywords: Bivalves; Crassostrea corteziensis; Trace metals; Mexican Pacific coast

1. Introduction It has been documented by several studies that trace metal pollution of coastal environments in

U

Corresponding author. Tel.: q52-69-85-2845; fax: q5269-82-6133. . E-mail address: [email protected] ŽF. Paez-Osuna ´

the temperate zones occurs near to industrialized areas or dense population centers Že.g. Goldberg et al., 1978; Phillips, 1980; Sericano et al., 1995.. Studies in tropical and sub-tropical environments have been limited, however, it has been assumed that a similar pattern of pollution exists ŽPhillips, 1991; Hunter et al., 1995.. Oysters, like mussels are widely used in biomonitoring of marine waters Že.g. Boyden and Phillips, 1981; Goldberg et

0048-9697r99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 Ž 9 9 . 0 0 0 9 7 - 2

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al., 1983; Lima et al., 1986.. As noted for the species of genus Mytilus, the bioaccumulation capacity of the oysters, their abundance, their wide distribution, makes them very suitable species for biomonitoring. Paez-Osuna and Marmolejo-Rivas ´ Ž1990a. showed that the levels of metals such as lead, chromium, nickel and cobalt in the mangrove oyster Crassostrea corteziensis were correlated with those in the particulate fraction of the lagoon water. These results, as well as the geographical distribution ŽKeen, 1971., long life, abundance, reasonable size and easy sampling provide evidence that C. corteziensis may be effective as a biomonitor of contamination in the coastal lagoons of the Pacific Latin America region ŽPaez-Osuna et al., 1993.. ´ The present study reports the trends of seasonal concentration for Cd, Cu, Fe, Mn, Ni, Pb and Zn in the gonadal and non-gonadal soft tissue of the oyster C. corteziensis from one station of the San Cristobal Estuary, Mexico, during 1 year ŽNovember 1989]October 1990..

2. Methodology 2.1. Area descriptions A population of Crassostrea corteziensis was sampled at intervals of 45 days to permit the analysis of specimens in different physiological states ŽLatouche and Mix, 1981. between November 1989 and October 1990 in the middle of San Cristobal Estuary in the Pacific coast of Mexico Ž218359N, 1058209W. ŽFig. 1.. The study area and the associated drainage basin are characterized by the absence of anthropogenic activity, only tropical fruit orchards and rural communities are present. The climate in the study area corresponds to the driest of the warm subhumids ŽGarcıa, ´ 1981.. Annual rainfall ranges from 500 to 1000 mm and is strongly seasonal with a pronounced dry season from November to May. The estuarine system is influenced by semidiurnal tides with a maximum range of 1.3 m. The supply of freshwater to San Cristobal Estuary is from land run-off and several streams. Lankford Ž1977. classified this lagoon as

a ‘differential erosion’ type, which the depression was formed by non-marine processes during lowered sea level and inundated by Holocene transgression. 2.2. Techniques The oysters were sampled directly by hand from mangrove roots in the intertidal zone at the selected site ŽFig. 1., collecting from 41 to 70 specimens of similar size to minimize the effect of body weight ŽNAS, 1980; Marina and Enzo, 1983.. Wright et al. Ž1985. studied the intra-sample variability of metals in Crassostrea ¨ irginica and found considerable spread of concentrations. They used an empirical test and estimated that pooled samples of 15 and 20 oysters is a reasonable size sample. Daskalakis Ž1996. examined the variability of metal concentrations in Crassostrea ¨ irginica and found that the sampling error decreases significantly with increasing numbers of individuals per pool. The confidence interval of means for samples consisting of 20 oysters varied from "3% to "20%, depending on metal and site. The confidence interval of means decreased by a factor of 0.6 when 50 oysters were used per pooled sample. Such results indicate that increasing size of pooled samples is an option for detecting changes in environmental contaminants. In the laboratory, prior to analysis, the oysters were measured and freed of their shells to separate the tissues Žwere not depurated.. In Crassostrea iridescens ŽPaez-Osuna et al., 1995. and ´ Crassostrea corteziensis as Mytilus edulis ŽLobel and Wright, 1982., the gonad develops within the mantle and associated to the crystalline style sac, therefore, the gonad and some portions of mantle and style sac were taken to represent the gonadal tissue, while the remaining tissues were considered as somatic or non-gonadal. Each composite sample of 41]70 individuals of gonadal and non-gonadal tissue was weighed separately and then dried to constant weight at 708C. Pulverization and homogenization were achieved by grinding the tissue samples in a teflon mortar. Samples and blanks for analysis were prepared by digesting aliquots of dry material with concentrated quartz-distilled nitric acid using the multi-

M.G. Frıas-Espericueta et al. r The Science of the Total En¨ ironment 231 (1999) 115]123 ´

117

Fig. 1. Study area showing the location of sampling site Žw..

ple standard addition method and the metal concentrations were determined by flame atomic absorption spectrophotometry ŽPaez-Osuna et al., ´ 1993, 1995., and the confidence intervals Ž Ps 0.05. were calculated using the method described for Miller and Miller Ž1988.. All glassware and plastic devices used in the manipulation of the samples were completely acid-washed ŽMoody and Lindstrom, 1977.. The performance of the method was evaluated by analyzing a reference material mussel homogenate MA-M-2rMT. The concentrations found for Cd, Co, Cr, Cu, Ni, Pb and Zn were in the acceptable range reported ŽIAEA, 1985.. Fe and Mn were underestimated, being the recovery of 63.2 and 79.3%, respectively. More details about the accuracy of the method are given in Paez-Osuna et al. Ž1995.. All metal con´ centrations were expressed in terms of dry weight as micrograms per gram.

3. Results Table 1 lists size and tissue weights. Each value

is for a pooled sample of 41]70 oysters. The gonad index ŽGI. was adopted as the ratio of dry gonadal tissue weight Žmg. to dry somatic tissue weight Žg. ŽLatouche and Mix, 1981.. It was noted that the gonad index reached a maximum on 21 April, then it decreased, indicating that a major spawning occurred in the oyster population. Next, the gonad index increased again on 17 July and decreased on September and October indicating a continuous post-spawning. Table 2 shows the seasonal variations of Cd, Cu, Fe, Mn, Ni, Pb and Zn concentrations in C. corteziensis in gonadal, somatic and total soft tissues, collected from the San Cristobal Estuary inner. No values for Co and Cr were obtained because concentrations in the tissues were very close to the detection limit Ž0.2 and 0.6 mg gy1 , respectively.. The highest concentrations of Cu, Ni, Pb and Zn in total soft tissue, were found in November when the oyster was in the resting state, while the maximum of Mn was noted in March, when the population is predominantly in gametogenic activity. For Cd and Fe, the highest concentration occurred in September, during the post-spawning phase. Only

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Table 1 Crassostrea corteziensis: length, gonad index, and gonad and somatic weight Žvalues are expressed as mean " S.D.. Date

Length Žcm.

Gonad index Žmgrg.

Gonad weight Žmg.

Somatic weight Žg.

Number of oysters

30 November 1989 16 January 1990 1 March 1990 21 April 1990 30 May 1990 17 July 1990 2 September 1990 21 October 1990

5.38" 0.96 4.62" 0.72 4.50" 0.74 5.37" 0.70 4.91" 0.61 4.69" 0.53 4.91" 0.76 5.17" 0.66

0 66 202 542 230 378 183 124

] 15.57" 15.3 8.82" 8.24 136 " 105 49 " 22 39 " 19 18 " 12 13 " 12

0.146" 0.15 0.235" 0.16 0.043" 0.02 0.251" 0.18 0.213" 0.08 0.103" 0.04 0.098" 0.03 0.105" 0.04

59 70 62 41 45 59 56 60

Table 2 Concentrations of trace metals Žmgrg dry wt.. in the gonadal Žg., somatic Žs. and total soft tissue Žt. of Crassostrea corteziensis from Nayarit Coast ŽMexico. during 1989]1990 Date

Tissue

Cd

Cu

Fe

Mn

Ni

Pb

Zn

Žg. Žs. Žt.

a

a

a

a

a

a

a

2.4" 0.30 2.4

28.5" 4.3 28.5

421 " 78 421

19.2" 2.3 19.2

5.1" 1.3 5.1

3.6" 0.2 3.6

768 " 45 768

Janr1990

Žg. Žs. Žt.

0.9" 0.03 1.0" 0.02 0.95

2.0" 0.5 15.8" 2.6 14.9

] 295 " 35 277

10.3" 2.0 13.3" 2.2 13.1

] 1.5 " 0.9 1.4

] 3.0" 0.2 2.8

81 " 7 391 " 22 372

Marr1990

Žg. Žs. Žt.

0.8" 0.08 1.8" 0.10 1.6

3.3" 0.9 15.3" 2 13.2

141 " 29 181 " 37 174

31.8" 1.1 22.4" 0.8 24

3.1" 1.1 3.0" 1.0 3

] ] ]

224 " 32 298 " 68 285

Aprr1990

Žg. Žs. Žt.

0.8" 0.04 1.7" 0.07 1.1

3.3" 0.9 15.3" 2.1 13.2

170 " 22 254 " 99 224

38.6" 1.2 14.9" 0.7 23.2

2.6" 0.8 3.1" 1.0 2.9

1.5" 0.1 ] 0.5

251 " 38 247 " 41 248

Mayr1990

Žg. Žs. Žt.

1.2" 0.10 1.6" 0.10 1.5

7.2" 1.5 13.6" 1.8 12.1

410 " 95 218 " 83 262

26.2" 0.9 13.2" 0.7 16.1

2.1" 0.8 2.3" 0.9 2.2

2.7" 0.2 ] 0.7

300 " 38 329 " 71 319

Julr1990

Žg. Žs. Žt.

1.1" 0.10 2.1" 0.14 1.8

15.0" 2.3 19.4" 2.2 18.2

264 " 7 194 " 22 213

17.9" 1.4 18.5" 1.9 18.3

3.0" 1.2 4.4" 1.2 4

] ] ]

439 " 20 553 " 41 521

Sepr1990

Žg. Žs. Žt.

2.1" 0.11 3.6" 0.16 3.4

17.2" 1.9 17.9" 1.9 17.7

372 " 11 475 " 18 459

16.1" 1.0 18.4" 1.4 18

0.7" 0.5 3.0" 0.9 2.6

2.1" 0.1 ] 0.4

470 " 28 482 " 26 479

Octr1990

Žg. Žs. Žt.

2.1" 0.16 2.1" 0.16 2.1

22.2" 2.5 32.2" 3.3 31.1

430 " 12 421 " 13 422

17.9" 1.1 17.3" 1.3 17.4

2.2" 1.0 4.3" 1.2 4

1.9" 0.1 ] 0.3

535 " 25 579 " 34 574

Novr1989

a

Individuals with gonad absent or poorly developed for effective separation; ], not detected Ž- 0.2 mg gy1 ..

M.G. Frıas-Espericueta et al. r The Science of the Total En¨ ironment 231 (1999) 115]123 ´

Cd and Cu showed consistently lower concentrations in gonadal than somatic tissue during the study period, while the remaining elements did not show a systematic variation between the two tissues. Correlations between GI and metal concentrations in gonadal, somatic and total tissues were not significant Ž P- 0.05. for the most elements, except for Mn, which was correlated significantly Ž r s 0.791, Ps 0.01. with the gonadal content, indicating that the bioaccumulation of this element is influenced by the reproductive cycle. Fig. 2 shows a significant relationship between the gonadal tissue and the Mn concentration associated with gonadal tissue; the regression analysis gave the following equation: y s 12.98q 0.196 X Ž r s 0.707, significant at 95%. where y is the level of Mn in the gonadal tissue Žmg gy1 . and X is the corresponding gonadal weight Žmg.. Significant correlations between gonadal and somatic content in most of the studied metals were not evidenced by a t-test ŽMiller and Miller, 1988.. However, an analysis of the linear correlation coefficient between Cu]Zn in gonadal, somatic and total tissues revealed a significant coupling: Cu gonadal]Zn gonadal Ž r s 0.90; P s 0.005., Cu somatic]Zn somatic Ž r s 0.82; Ps 0.05., and Cu total]Zn total Ž r s 0.88; Ps 0.05.; Cd gonadal]Cu gonadal Ž r s 0.88; Ps 0.01. and Cd gonadal]Zn gonadal Ž r s 0.87; Ps 0.01..

Fig. 2. Crassostrea corteziensis: relationship between the Mn concentration of gonadal tissue vs. dry weight of gonadal tissue.

119

These correlations may be justified since C. corteziensis requires Cu and Zn in the same proportion during the reproductive cycle, and also because of the similar physicalrchemical properties of the elements involved ŽSzefer et al., 1994.. The existence of size-dependent metal accumulation by aquatic biota has been documented by numerous authors Že.g. Boyden, 1977; Phillips, 1980; Paez-Osuna and Ruiz-Fernandez, 1995., ´ ´ particularly in oysters, Boyden Ž1977. found that metal body burdens followed a power function of the form: Y s aW b. Where Y is the metal body burden, W is the body weight, and a and b are constants. The soft tissue metal concentration Ž YrW . of an oyster is simply the body burden divided by body weight, and using the Boyden equation ŽMo and Neilson, 1993.: YrWs aW by 1. When the size and whole total tissue measurements of metals obtained in C. corteziensis were fitted to this equation, b ranged from 0.64 for Cd to 1.01 for Fe, but the correlation coefficients never reached a statistical significance greater than 90%.

4. Discussion The reproductive cycle of Crassostrea corteziensis have been described previously by Stuardo and Ž1975. and Cuevas-Guevara Martınez-Guerrero ´ Ž1979.. Only the main and Martınez-Guerrero ´ characteristics of the seasonality of reproduction will be given here. The mangrove oyster C. corteziensis shows a predominant stage of spawning which is initiated when the water temperature is greater than 25.58C in the months of May or June and continues up to October or November. From then, a gradual succession of the other phases is initiated: post-spawning in December, undifferentiated sex stage in January, gametogenesis in February and maturation during March]April. Frıas-Espericueta et al. Ž1997. stud´ ied the reproductive cycle of C. corteziensis in the study area and found little variations: spawning in May, post-spawning in September]October, and a resting, gametogenesis and maturation phase in November, January]February and March]April occurred, respectively.

120

M.G. Frıas-Espericueta et al. r The Science of the Total En¨ ironment 231 (1999) 115]123 ´

As in Crassostrea iridescens ŽFrıas-Espericueta ´ et al., 1994., C. corteziensis incorporates predominantly Pb in the gonadal tissue when the oyster is in gametogenesis andror maturation phase, however, the gonad with portions of mantle and the stile sac were taken to represent the gonad tissue, and it is possible that Pb was really incorporated in the mantle Žandror the stile sac. instead of the gonad. Bevelander and Nakajara Ž1966., Fowler et al. Ž1975. and Lowe and Moore Ž1979. with Macrocallista macullata, Mercenaria mercenaria and Mytilus edulis, respectively, found the endocitosis action of Pb and other metals by the mantle in each case. The Mn behavior in similitude with the rock oyster Crassostrea iridescens ŽPaez-Osuna et al., ´ 1995., was the unique element that showed significant positive correlation with the gonad index, indicating that this metal is related to the reproductive cycle of C. corteziensis. Galtsoff Ž1964. reported that the distribution of this element in C. ¨ irginica is related to the female reproductive cycle, since its concentration in fully developed ovaries is several times more than the spermary and its total concentration decreases after the discharge of eggs. Marina and Enzo Ž1983. found that Mn and Zn presented higher contents during the period of gonadal maturation in Donax trunculus. Paez-Osuna et al. Ž1995. with C. iridescens ´ suggested that Mn plays an important role during the gametogenesis, possibly as an enzymatic catalyst. Gabbott and Bayne Ž1973. found that in Mytilus edulis an increased rate of gametogenesis was accompanied by elevations in energy demand and oxygen consumption. These processes, in turn, required an accelerated filtration rate and increases in phytoplankton ingestion ŽLatouche and Mix, 1981.. Khristoforova and Chernova Ž1990. concluded that the levels of Mn depend on its concentration and chemical form in the seawater, as well as for the development of phytoplankton for whose photosynthesis Mn is necessary. Although, the results obtained here suggest that Mn is preferentially incorporated in gonad than in the somatic tissue, particularly when the gonad weight is elevated ŽFig. 2.. Biochemical composition of the oysters vary with the reproductive cycle. Paez-Osuna et al. ´

Ž1993. studied the biochemical composition of mangrove oyster C. corteziensis and found that the amount of proteins and lipids increase with the gonadal cycle, while the amount of carbohydrates decrease. Gabbott Ž1983. found that this fact may be explained by the conversion of glycogen into lipid reserves of the developing eggs. Sidwell et al. Ž1979. who studied the protein, fat and glycogen content in Crassostrea ¨ irginica, found a fat peak during May and June, and after that this peak dropped. This increase in non-cellular material could tend to dilute the concentrations of metals in the tissues; however, such a tendency was not evidenced in the mangrove oyster C. corteziensis, contrarily, the concentrations of Mn were correlated positively with the total and gonadal tissues ŽFig. 3a,b.. In spite of organisms having a similar size, the somatic weight of the oysters changed substantially between months ŽTable 1.. From November to January somatic individual weight increased from 0.146 to 0.235 g, in this period, specimens were in resting phase, and a high demand of nutrient is necessary by the physiological effort that they had carried out Žspawning., this increased the weight of somatic tissue. From January to March Žgametogenesis phase., somatic weight dropped. Latouche and Mix Ž1981. found that in Mytilus edulis, a change of material from somatic to the gonadal tissues was carried out during gametogenesis for gonad development. Besides, seasonal changes in flesh weight have been documented in Mytilus edulis ŽDare and Edwards, 1975. and Donax trunculus ŽAnsell et al., 1980.. This phenomenon could have a strong effect on metal levels between gonadal and nongonadal tissues. Cu, Ni, Pb and Zn in the total soft tissue, showed their highest concentrations in autumn, when the oysters were in the resting phase, and Mn in winter. According to Marina and Enzo Ž1983., the influence of season can be seen in the biochemical composition of bivalve populations that show seasonal patterns in metal concentrations; and fluctuations with highest values in autumn or winter months have been found in other mollusks species: Chlamys opercularis and Pecten maximus ŽBryan, 1973., Mytilus gallopro¨ incialis

M.G. Frıas-Espericueta et al. r The Science of the Total En¨ ironment 231 (1999) 115]123 ´

121

Fig. 3. Crassostrea corteziensis: relationship between the Mn concentration of gonadal Žl. and total Žv. tissue vs. gonad index.

ŽMajori et al., 1978. and Mytilus edulis ŽLobel and Wright, 1982.. The causes of seasonal fluctuations have been related with the food supply, changes in fluxes of particulate and dissolved metals to the sea as a consequence of continental run-off ŽFowler and Oregioni, 1976., variations in the metal level in somatic and gonadal tissues, related to the reproductive cycle ŽLatouche and Mix, 1981. or simply seasonal size changes ŽPaez-Osuna ´ and Marmolejo-Rivas, 1990b.. An additional aspect that interferes with the interpretation of results for trace metals in bivalves, is the incorporation of gut contents in the soft tissue used for the metal analysis. Clearly, if

depuration is not carried out, somatic tissue measurements will include those metals associated with gut content. It is important to note that the amount of perturbation by particulate debris in the gut is not constant but varies ŽNAS, 1980.. Thus, in the study area the sediment suspended increased during August]September Žrainy season., consequently, the effects of gut contents probably will vary according to station, and could influence the trace metal fluctuations observed ŽPaez-Osuna et al., 1995.. ´ Regionally, the levels found here are lower than those reported previously for the same species in two coastal lagoons influenced by mu-

122

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nicipal and agriculture effluents, where concentrations more elevated particularly of Cd and Cu were detected ŽPaez-Osuna et al., 1991, 1993.. ´ The average metal concentrations in oysters of this study were comparable with those found in Choromytilus meridionalis from Saldanha Bay, a site relatively unpolluted with respect to trace metals ŽWatling and Watling, 1976.; higher in Cd and Cu and lower in Ni and Pb than values determined in Pinctada radiata from Halul Island ŽArabian Gulf. by Al-Madfa et al. Ž1998.. Inclusive lower than those values reported for Crassostrea ¨ irginica from the Atlantic coast ŽUSA. ŽGoldberg et al., 1978., Crassostrea angulata from Gerona ŽSpanish coast. ŽSchuhmacher and Domingo, 1996. and Crassostrea gigas from the east coast of Kyushu Island ŽJapan. ŽSzefer et al., 1997..

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