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Biochemical and energy dynamics throughout thereproductive cycle of the striped venus Chameleagallina (Mollusca, Bivalvia)Sandra Joaquima, Domitília Matiasa, Ana Margarete Matiasa, Paula Mouraa, Cláudia Roquea,Luís Chícharob & Miguel B. Gaspara

a Instituto Português do Mar e da Atmosfera, I. P., Av. 5 de Outubro, 8700-305 Olhão,Portugalb Centro de Investigação Marinha e Ambiental (CIMA) Faculdade de Ciências e Tecnologia,Universidade do Algarve, Campus de Gambelas, P-8005-139 Faro, PortugalPublished online: 28 May 2014.

To cite this article: Sandra Joaquim, Domitília Matias, Ana Margarete Matias, Paula Moura, Cláudia Roque, Luís Chícharo &Miguel B. Gaspar (2014) Biochemical and energy dynamics throughout the reproductive cycle of the striped venus Chameleagallina (Mollusca, Bivalvia), Invertebrate Reproduction & Development, 58:4, 284-293, DOI: 10.1080/07924259.2014.921646

To link to this article: http://dx.doi.org/10.1080/07924259.2014.921646

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Biochemical and energy dynamics throughout the reproductive cycle of the striped venusChamelea gallina (Mollusca, Bivalvia)

Sandra Joaquima*, Domitília Matiasa, Ana Margarete Matiasa, Paula Mouraa, Cláudia Roquea, Luís Chícharob andMiguel B. Gaspara

aInstituto Português do Mar e da Atmosfera, I. P., Av. 5 de Outubro, 8700-305 Olhão, Portugal; bCentro de Investigação Marinhae Ambiental (CIMA) Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, P-8005-139 Faro, Portugal

(Received 28 January 2014; accepted 1 May 2014)

The striped venus Chamelea gallina is an important commercial bivalve species in Europe. However, large inter-annualfluctuations in stock abundance and periodic recruitment failure threaten the biological and economic sustainability of thisfishery. This study aimed to improve the knowledge of the reproductive cycle and reproductive strategies of this speciesfrom the Algarve coast (southern Portugal) in order to contribute to the establishment of management measures and toassess its potential for aquaculture. The reproductive cycle of C. gallina followed a seasonal cycle, significantly influencedby sea surface temperature and food availability. Gametogenesis took place in winter, coinciding with the phytoplanktonbloom. Spawning occurred during summer, followed by a short period of sexual inactivity in autumn. Condition index didnot reflect the reproductive cycle of C. gallina and generally, followed the same trend of chlorophyll a. Glycogen was posi-tively correlated with gonadal index and chlorophyll a. High total lipid values were recorded throughout gonad ripenessand spawning, but decreased at the end of the spawning and in the rest period. The extended spawning period of C. gallinawill allow larvae to be obtained for much of the year by artificial spawning of wild broodstock.

Keywords: condition index; total lipids; glycogen

Introduction

The striped venus Chamelea gallina (Linnaeus 1758) isan infaunal bivalve species that occurs in the infralittoralzone. Chamelea gallina occurs on the eastern Atlanticcoast, across Norway and the British Isles, Iberian Penin-sula, Morocco, Madeira, and the Canary Islands (Gaspar& Monteiro 1998). It is also found in the MediterraneanSea and the Black Sea (Poppe & Goto 1993) and isabundant in the Adriatic Sea (Orban et al. 2006).Although this species lives in a variety of sediment typesit is preferentially distributed in the coastal well-sortedfine sand biocenosis (Perés & Picard 1964). Chameleagallina is an important commercial bivalve species inEurope, especially in the Iberian Peninsula and the Medi-terranean Sea. Along the Andalusia-Algarve coast,exploitation of this species supports one of the mostimportant fisheries (Gaspar & Monteiro 1999; Gasparet al. 1999; Chícharo, Chícharo, Gaspar, Alves, et al.2002; Chı́charo, Chı́charo, Gaspar, Regala, et al. 2002;Delgado et al. 2013). Officially, in this region the annuallandings of this species exceed 3000 tons (t) (Galisteoet al. 2012; DGRM 2012), with a market price between4 and 7€ per kg.

The synergistic action of fishing pressure coupledwith the rapid growth rate and short lifespan of C. gallinaleads to large inter-annual fluctuations in stock abundance

and periodic recruitment failure (Gaspar 1996). In someyears the abundance of this species decreases dramati-cally, threatening the biological and eventually, the eco-nomic sustainability of this fishery. The development ofrestocking programs supported by advances in C. gallinaaquaculture could be an efficient fishery managementstrategy to rebuild stocks. To follow these programs, adetailed knowledge of the reproductive cycle of this spe-cies and its reproductive strategies is crucial.

The reproductive cycle of C. gallina has been studiedin the Mediterranean Sea (Marano et al. 1980; Bodoy1983; Ramón 1993; Erkan & Sousa 2002; Erkan 2009),the Black Sea (Dalgic et al. 2009), the northern AdriaticSea (Salvatorelli 1967; Poggiani et al. 1973), theAndalusia coast, particularly, in the Gulf of Cadiz(Rodríguez de la Rúa et al. 2003; Rodríguez de la Rúa2008; Delgado et al. 2013), and in the Algarve coast(Gaspar & Monteiro 1998). However, no information onthe relationship between the reproductive cycle and thebiochemical and the energy dynamics was provided.Only Orban et al. (2006) studied the biochemicalcomposition of C. gallina, but from a nutritional andcommercial quality point of view.

The relationship between the reproductive cycle andthe energy storage and utilization cycles has beenreported by several authors for a wide variety of bivalves

*Corresponding author. Email: sandra@ipma.pt

© 2014 Taylor & Francis

Invertebrate Reproduction & Development, 2014Vol. 58, No. 4, 284–293, http://dx.doi.org/10.1080/07924259.2014.921646

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(e.g. Barber & Blake 1981; Fernández-Castro &Vido-de-Mattio 1987; Massapina et al. 1999; Pérez Cam-acho et al. 2003; Ojea et al. 2004; Joaquim et al. 2011;Matias et al. 2013). Energy reserves are of considerableimportance in reproduction and are closely correlated toenvironmental factors (e.g. Holland 1978; Delgado et al.2004; Ojea et al. 2004; Tlili et al. 2012). Thus, the tim-ing and rate of energy storage in bivalves are mainlyregulated by temperature and food availability (Joaquimet al. 2011). The accumulation of energy prior to game-togenesis synthesis during the period of high food avail-ability, called a conservative pattern, is the normal one.By contrast, in the opportunistic pattern, gametogenesisoccurs at the same time as energy storage, when foodavailability is enough to support the energy required bythe process (Mathieu & Lubet 1993; Darriba et al.2005). Carbohydrates constitute the most important andavailable energy reserve in bivalve adults, glycogenbeing the main component for supplying energydemands (Fernández-Castro & Vido-de-Mattio 1987)and, particularly used for the reproductive cycle (e.g.Newell & Bayne 1980; Pazos et al. 2005). Lipids playan important role in gamete formation being the mainreserve of oocytes and bivalve larvae (Labarta et al.1999; Matias et al. 2011). By contrast, many studieshave shown that proteins do not contribute significantlyto gametogenesis (Joaquim et al. 2008, 2011; Matiaset al. 2013).

This study improves knowledge of the reproductivecycle of C. gallina in the Algarve coast (southern Portu-gal) through the characterization of the nutrient storageand utilization patterns. This information could be usefulin the future for both the aquaculture production andrestocking programs.

Material and methods

Sample collection

Samples consisted of 60 adult C. gallina with a shelllength between 24 and 30 mm (see Gaspar 1996) werecollected monthly, during 2009, by dredge, from a natu-ral bed (3–10 m depth) located off Ilha da Culatra(36º98′42′′N and 7º83′36′′W), Algarve coast, southernPortugal (Figure 1).

Sea surface temperature and Chlorophyll a

Monthly data on sea surface temperature (SST) were col-lected from the Portuguese Hydrographic Institute buoynearest sampling area (http://www.hidrografico.pt/).Chlorophyll a (Chlo a) data were derived from satelliteremote sensing data, collected from the Giovanni onlinedata system (http://disc.sci.gsfc.nasa.gov/giovanni/overview/index.html) (Acker & Leptoukh 2007).

Laboratory analysis

In the laboratory, clams were placed in 0.45 μm-filteredseawater at 20 °C for 24 h to purge their stomachs,before condition index, histological, and biochemicalanalyses. Afterwards, each clam was dissected and wetmeat weight (to nearest 0.0000 g) was determined.

Histology

Twenty individuals of each sex (when distinguishable)from each monthly sample were examined histologicallyto determine the gametogenic stages. First, the visceralmass was separated from siphons and gills and thenfixed in San Felice solution for 48 h. After fixation theywere transferred to 70% ethyl alcohol (ETOH) for stor-age. Posteriorly, tissues from these samples were dehy-drated with serial dilutions of alcohol and finallyembedded in paraffin wax. Thin sections (6–8 μm) werecut on a microtome and stained with haematoxylin andeosin. The histologically prepared slides were examinedusing a microscope at 400× magnification. Clam repro-ductive maturity was categorized into six stages usingthe scale proposed by Gaspar and Monteiro (1998)(Figures 2 and 3). When more than one developmentalstage occurred simultaneously within a single individual,the assignment of the stage criteria decision was basedupon the condition of the majority of the section.

A mean gonadal index (GI) was calculated using themethod proposed by Seed (1976):

GI ¼P

ind: each stage� stage ranking

total ind. each month

For each of the stages a numerical ranking was assignedas follows: inactive (0); early active gametogenesis (3);late active gametogenesis (4); ripe (5); partially spawned(2); spent (1). The GI ranged from 0 (all individuals inthe sample are in rest stage) to 5 (all individuals are inripe stage).

Figure 1. Map of the Algarve coast. Location of the Chameleagallina sampling site.

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Condition index

The dry meat (0.0000 g) and shell weights (0.0000 g) of20 clams from each monthly sample were determinedafter oven drying at 80 °C for 24 h. Meat samples werethen ashed at 450 °C in a muffle furnace, and the ashweight was determined. Organic matter weight was cal-culated as the ash free dry meat weight (AFDW). Thecondition index (CI) was calculated according to Walneand Mann (1975):

CI ¼ dry soft tissues weight ðmgÞ � ash ðmgÞdry shell weight ðmgÞ � 100

Whenever the gender could be determined for allindividuals analyzed in each sampling period byobservation of gonad smears under the microscope, theCI was calculated for females and males separately,otherwise sex was determined for the entire samplewithout distinguishing gender.

Figure 2. Gametogenic stages of female Chamelea gallina. (A) Inactive. (B) Early active; Og – Oogonia. (C) Late active; Vc –Vesicular cell. (D) Ripe; Oo – Oocytes; Po – Pedunculated oocyte. (E) Partially spawned. (F) Spent. Scale bar: 200 μm in A, B, C,and F; 100 μm in D and E.

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Biochemical composition

The meat of 10 clams (five females and five males,between March and July) from each monthly samplewas frozen and stored at −20 °C for biochemical analy-ses. For each specimen, glycogen content was deter-mined from dried (80 °C for 24 h) homogenates usingthe anthrone reagent (Viles & Silverman 1949). Total lip-ids were extracted from fresh homogenized material inchloroform/methanol (Folch et al. 1957). After charringwith concentrated sulfuric acid (Marsh & Weinstein1966), total lipids were estimated by spectrophotometry.Duplicate determinations were performed in all cases and

values were expressed as a percentage of AFDW. Caloriccontent of lipids and glycogen in tissues were calculatedusing the factors 33 KJ g−1 (Beninger & Lucas 1984)and 17.2 KJ g−1 (Paine 1971), respectively.

Statistics

Seasonal variations in histological parameters, conditionindex, and biochemical composition were analyzed byone-way ANOVA or Kruskal–Wallis ANOVA on ranks(K–W) whenever the assumptions of analysis ofvariance (ANOVA) failed. Percentage data were arcsine

Figure 3. Gametogenic stages of male Chamela gallina. (A) Inactive. (B) Early active; Sg – Spermatogonia; Fw - Follicle wall. (C)Late active. (D) Ripe. (E) Partially spawned; Sp – Spermatozoa. (F) Spent. Scale bar: 200 μm in A, B, C, D, and E; 100 μm in F.

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transformed to normalize variance (Sokal & Rohlf 1981).Multiple pairwise comparisons were performed using thepost hoc parametric Tukey test or the non-parametricDunn’s test to detect significant differences betweenmonthly consecutive samples. The t-test, or the Mann–Whitney (M–W) test whenever the assumption of t-testfailed, was used to analyze the differences between sexesfor all the parameters studied. The Pearson or the Spear-man (when the residuals were not normally distributed)correlation coefficient were used to determine the degreeof association between parameters. Results wereconsidered significant at p < 0.05. The statistical analyseswere performed using the SIGMASTAT 3.11 statisticalpackage.

Results

Sea surface temperature and Chlorophyll a

The monthly SST and Chlo a values during the studiedperiod is shown in Figure 4. SST and Chlo a followed aseasonal cycle. SST ranged between 14.8 ± 0.4 °C inFebruary and 22.2 ± 2 °C in August. The lowest Chlo avalues were registered in September and October (0.5 ±

0.3 mg m−3 and 0.5 ± 0.2 mgm−3, respectively), coincid-ing with high SST values, whereas the highest value wasobserved in March (7.0 ± 4.0 mg m−3), before theincrease in SST. As expected, SST was negatively corre-lated with Chlo a (Spearman’s, r = −0.70, p < 0.01)(Table 1).

Gametogenic cycle

No hermaphrodites were found. Both sexes showed syn-chronism in gonadal development, and no significant dif-ferences were found between the GI of males andfemales (M–W, p > 0.05). The reproductive cycle ofC. gallina was characterized by a seasonal pattern(Figure 5). Gamete development took place in winter,coinciding with the phytoplankton bloom. BetweenMarch and May, the population reached the reproductivepeak, as represented by the highest values of GI (4.5 and4.6 in March for females and males, respectively, and4.2 in May for both sexes). In April, GI declined proba-bly following the abrupt decrease of Chlo a (Figure 6).After that, spawning began for both sexes and was inten-sified during summer as SST increased (Figure 4). Aftera short period of sexual inactivity, between October andNovember (which coincided with the decrease of SST),the onset of the phytoplankton bloom occurred andclams progressed to gametogenesis. GI correlated nega-tively with SST (Pearson’s, r = −0.76, p < 0.01) and posi-tively with Chlo a (Spearman’s, r = 0.80, p < 0.001)(Table 1).

Condition index

Between January and March, CI increased with the ripe-ness of the gonad and the phytoplankton bloom, andremained generally high until July, i.e. during most of thespawning period (Figure 7). Generally, CI followed thesame trend of Chlo a. A significant positive correlation(Spearman’s, r = 0.68, p < 0.01) was found between thesetwo parameters. Although the CI of females was lower

Figure 4. Monthly values (mean ± SD) of sea surface tempera-ture (SST) and chlorophyll a from the Algarve coast during2009.

Table 1. Results of Pearson and Spearman correlation coefficients between studied parameters (r, correlation coefficient, p, p value).

Chlorophyll a Gonadal index Condition index Total lipids Glycogen Energy

Temperature r = −0.70 r = −0.76 r = −0.22 r = −0.21 r = −0.62 r = −0.45p < 0.01 p < 0.01 p < 0.05 p < 0.05 p < 0.05 p < 0.05

Chlorophyll a r = 0.80 r = 0.68 r = 0.41 r = 0.58 r = 0.58p < 0.001 p < 0.001 p < 0.05 p < 0.05 p > 0.05

Gonadal index r = 0.48 r = 0.16 r = 0.60 r = 0.46p > 0.05 p < 0.05 p < 0.05 p > 0.05

Condition index r = 0.19 r = 0.46 r = 0.38p < 0.05 p < 0.05 p > 0.05

Total lipids r = 0.03 r = 0.91p < 0.05 p < 0.001

Glycogen r = 0.41p > 0.05

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than the CI of males, no significant differences were foundbetween sexes, except in July (t-test, t = 2.19, p < 0.04).Notwithstanding, the highest value of CI (5.00 ± 0.81) wasregistered for males in July, when all individuals werespawning while the highest value of CI (4.57 ± 0.81)found for females was recorded one month earlier. After

July, CI decreased reaching its lowest value in August(2.75 ± 0.37). At the end of spawning, this parameterstarted to increase again until the end of the year. Condi-tion index exhibited statistically significant differences(K–W., H = 109.2, df = 11, p < 0.001) only in the consecu-tive months of July and August. No significant correla-tions were found between CI and GI and SST (Table 1).

Biochemical composition

Glycogen increased between January and February as forthe phytoplankton bloom, and then decreased until April(Figure 8). In May glycogen rose again. Thereafter, gly-cogen reserves decreased at the same time that most ofthe population was at the spawning stage, and reachedthe lowest value in August (20.0 ± 15.1 μg mg−1 AFDW).In the following months and until the end of the year,glycogen showed an increasing trend following the tem-perature decrease and the phytoplankton bloom onset.Indeed, glycogen was positively correlated with Chlo a(Spearman’s, r = 0.58, p < 0.05) and negatively correlatedwith SST (Pearson’s, r = −0.62, p < 0.05) (Table 1). Nostatistical correlation was found between glycogen andCI; however, this biochemical content was correlatedwith GI (Pearson’s, r = 0.60, p < 0.05). The highest gly-cogen values were found in March (74.0 ± 14.2 μg mg−1

AFDW) and in May (95.8 ± 8.0 μg mg−1 AFDW) infemales and males, respectively. Significant differenceswere found between the sexes (M-W., t = 61.0, n (small)= 9, n (big) = 10, p < 0.03).

Total lipids peaked throughout gonad ripeness and thespawning period (in April and June) and decreased at theend of spawning and during the resting period. Total lipidfor females and males reached the highest values in April(98.5 ± 12.7 μg mg−1 AFDW and 83.4 ± 13.0 μg mg−1

AFDW, respectively). The lowest (24.0 ± 5.0 μg mg−1

AFDW) total lipid values were found in December(Figure 8). No statistical significant correlations werefound between total lipid and the GI or glycogen content,neither with CI nor with the studied environmental

Figure 5. Monthly variations in gonadal development ofChamelea gallina during 2009.

Figure 6. Monthly variations in gonad index (GI) of Chamel-ea gallina females and males (mean, n = 20) during 2009.

Figure 7. Condition index (mean ± SD) of Chamelea gallina,females and males during 2009.

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parameters (SST and Chlo a). Total lipid content differedbetween sexes in April (t-test, t = −2.41, df = 15,p < 0.03) and June (t-test, t = −3.20, df = 16, p < 0.01).

Total lipids contributed most to the energy contentwhich explains the positive correlation that was foundbetween these parameters (Pearson’s, r = 0.91, p < 0.001)(Table 1).

Regarding energy content, males reached the highest(4.2 kJ mg−1 AFDW) energy value in June, and femalesin April and June (3.6 kJ mg−1 AFDW). The lowest(2.0 kJ mg−1 AFDW) energy values were recorded inOctober/December (Figure 8). No correlation wasobserved between energy and the other studied parame-ters (except with total lipids). The energy of females dif-fered from males in June (t-test, t = −2.49, df = 16,p < 0.03). Statistically significant differences wereobserved between consecutive sampling periods for allthe biochemical constituents studied (glycogen: ANOVA,df = 11, F = 20.63, p < 0.001; total lipids: ANOVA,df = 11, F = 35.21 p < 0.001; energy: K–W., H = 101.5,df = 11, p < 0.001) (Figure 8).

Discussion

The reproductive activity of bivalves is controlled by theinteraction between endogenous and environmental fac-tors (Normand et al. 2008; Enríquez-Díaz et al. 2009).This study described the reproductive cycle of C. gallinathrough the characterization of the nutrient storage andutilization patterns, as well as their interaction with STTand Chlo a.

Chamelea gallina in the Algarve coast had a ripestage in spring, reaching its peak of maturation in March.After that, spawning events took place from the middleof spring to summer. Several studies have reported thatthe reproductive cycle of C. gallina was significantlyinfluenced by SST and food availability (e.g. Gabbott &Bayne 1973; Eversole 1989; Xie & Burnell 1994; Grant& Creese 1995; Gribben et al. 2004; Ojea et al. 2004;Albentosa et al. 2007). The SST and Chlo a patterns as

well as values observed in this study were typical ofthose from temperate climates and were similar to thevalues found in a nearby area (Gulf of Cadiz) as reportedby Delgado et al. (2013). The seasonal SST pattern wascharacterized by relatively low sea water temperaturesduring the winter that increased during spring and earlysummer, stabilized by the end of the season, anddecreased in autumn. The negative correlation foundbetween SST and Chlo a had already been reported byFalcão et al. (2007) for the studied area. According tothese authors, when SST is low, an upwelling eventoccurs, giving rise to the phytoplankton bloom registeredfrom late winter until early spring. In this study, the GIfollowed a seasonal cycle negatively correlated withSST. Besides, spawning onset may also be triggered bythe sharp decline of Chlo a in April, since a significantcorrelation was found between GI and Chlo a. Similarreproductive cycles were described for this species in thesame study area (Gaspar & Monteiro 1998) and in thenearby Gulf of Cadiz (Delgado et al. 2013). Thus, theextended spawning period and the gonadal developmentinterruptions observed in May, alongside with the re-ini-tiation of gametogenesis, were also observed in previousstudies (Delgado et al. 2013). However, these authorsreported that this event was not unique and intra-gonadaland inter-individual asynchrony in the spawning periodwas observed. In this study, although G. gallina had anextended reproductive period, there were no signals ofsuccessive asynchrony in spawning. Nevertheless, 20years ago Gaspar and Monteiro (1998) reported thatspawning of this population began in May and its gonadindex, once it fell in April, never rose again to a secondpeak in the same year. These small differences in thereproductive cycle of the species can be inherent to envi-ronmental factors associated with the different geographi-cal location in the first case, and with environmentalchanges over time in the other. The extended spawningperiod and the maintenance of synchronized gonadaldevelopment observed between males and females duringthe spawning period ensures the reproductive success of

Figure 8. Mean values (±SD) of glycogen, total lipids (μg mg−1 AFDW), and energy (kJ g−1 AFDW) of Chamelea gallina duringthe studied period (a, b statistically significant differences, p < 0.05 found between consecutive samples and between sexes,respectively).

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the species since gametes will be expelled into the watercolumn simultaneously for a long period, augmenting theprobability of fertilization. Such synchronization wasreported by Gaspar and Monteiro (1998) for this species.After a short period of inactivity between October andNovember, clams progressed to the onset of gametogene-sis that occurred in November and coincided with a SSTdecrease, and with the onset of the phytoplankton bloom.The development of gametes with the proliferation ofgonia intensified in winter following the phytoplanktonbloom, reaching the ripe stage in March. The gameto-genesis results were generally consistent with the previ-ous findings by Gaspar and Monteiro (1998) andDelgado et al. (2013).

Condition index is generally considered to reflect thereproductive activity of bivalves (Fernández-Castro &Vido-de-Mattio 1987; Massapina et al. 1999; Ojea et al.2004). This relationship has been observed in severalbivalve species from the Portuguese coast (e.g. Gaspar &Monteiro 1998; Moura et al. 2008; Joaquim et al. 2011).In this study, CI did not reflect the reproductive cycle ofC. gallina, since no significant relationship was foundbetween them. Thus, CI remained at high levels duringmost of the spawning period. In fact, CI followed the sametrend of Chlo a, as confirmed by the significant correlationfound between them. CI increased when clams were ingametogenesis and ripe stages following the phytoplank-ton bloom, but it also reflected the abrupt Chlo a decreasein April and re-initiation of gametogenesis in the followingmonth. Nevertheless, this phenomenon was not observedfor C. gallina by other authors (Gaspar & Monteiro 1998;Moschino & Marin 2006; Orban et al. 2006), who noticedthat CI only increased with gametogenesis progress, anddeclined during the spawning period.

The relative amounts of glycogen (20.0–95.8 μgmg−1 AFDW) measured in C. gallina were lower, interm of the proportions, to those previously described byOrban et al. (2006) for this species; however, the amountof total lipids (23.95 to 98.5 μg mg−1 AFDW) was simi-lar. Several studies on bivalves have shown that sexualmaturity is related to energy supply from previouslystored reserves or the ingestion of available food, andconsequently is closely linked to the biochemical compo-sition (Sastry 1979; Pérez Camacho et al. 2003). Thereproductive cycle translates a seasonal pattern of bio-chemical composition that can vary among populationsand species (Albentosa et al. 2007). Glycogen is one ofthe main energy reserves in adult bivalves. In this study,this energy reserve was positively correlated with GI, asobserved for other opportunistic species in which thegamete production occurs coupled with the phytoplank-tonic blooms. Indeed, glycogen was positively correlatedwith Chlo a and negatively correlated with SST. Delgadoet al. (2013) also referred to C. gallina as an opportunistspecies in terms of energy storage and utilization cycles.

Probably, the abrupt decrease of Chlo a in April hasforced the species to a remarkable consumption of glyco-gen reflecting its use in the formation of gametes. How-ever, in May glycogen content recovered, accompaniedby re-initiation of gametogenesis and consequent gonadrecovery. Thereafter, this content decreased graduallyduring spawning and the rise in SST, reaching the lowestvalue at the end of spawning. Throughout the extendedreproductive effort, C. gallina retained some glycogenreserves, probably as an energy source for the mainte-nance of their physiological state during the resting per-iod. This is an important strategy for survival of thespecies, since some bivalves, such as Ruditapes decussa-tus almost depletes its energy reserves in the reproduc-tive period, which leads to their debilitation andconsequent death (Matias et al. 2013). Several authors(e.g. Beninger & Lucas 1984; Ojea et al. 2004;Mouneyrac et al. 2008) have reported that lipid seasonalvariations are inversely related to glycogen owing to theconversion of glycogen into lipids, biosynthesized duringthe formation of gametes (Gabbott 1975). In conservativespecies, this process is detected by a negative correlationbetween total lipids and glycogen content, since thereserve accumulation lags behind gametogenesis. InC. gallina, an opportunist species, glycogen accumula-tion occurred simultaneously with the de novo synthesisof lipids during gametogenesis which justifies the lack ofa significant correlation between these two biochemicalcontents. Although the highest values of total lipids wererecorded throughout gonad ripeness and spawning,decreasing at the end of the spawning and in the restperiod, no significant correlations were found betweentotal lipids and GI, neither with CI nor with the environ-mental parameters (SST and Chlo a). By contrast, Orbanet al. (2006) found coincident fluctuations for the bio-chemical contents and the CI of C. gallina in the Adriat-ic Sea. The erratic variation of total lipids shown in thereproductive period may be related to production andsimultaneous release of gametes. Total lipids contributedmost to the energy reserves and therefore, these parame-ters showed the same trend during the year.

It is generally accepted that CI is influenced by theenergy storage and exploitation strategy of bivalve spe-cies (Delgado & Pérez-Camacho 2005; Joaquim et al.2008, 2011). However, in this study, no correlations werefound between energy and the other studied parameters.

This study has increased knowledge of the reproduc-tive biology of C. gallina, and provides the first data onthe storage and depletion of energy reserves in this spe-cies. This information could be helpful for establishingfishery management measures and for assessing thepotential of the species for aquaculture. The extendedspawning period of C. gallina will allow larvae to beobtained for most of the year, by artificial spawninginduction of wild broodstock.

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AcknowledgmentsWe would like to acknowledge Alexandre Pereira for his helpgathering the temperature and chlorophyll data. We also thankJ. Ramos for English editing. Sincere thanks are also due to A.Leitão and to the anonymous reviewers whose suggestionsgreatly improved this work. This study was funded by PRO-MAR Project (Interreg IIIA).

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