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Seasonal variations in gross biochemical composition, percent edibility, and condition index of the clam Ruditapes decussatus cultivated in the Ria Formosa (South Portugal).

ABSTRACT The grooved carpet shell clam Ruditapes decussatus (L. 1758) is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early 1990s. To understand the seasonality of its nutritional value, thus providing an improved basis for economic valuation of the resource, gross biochemical composition, percent edibility, and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam R. decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and nonprotein nitrogen covaried during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable with that shown by studies elsewhere at similar latitudes, and is underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks.

KEY WORDS: biochemical composition, condition index, percent edibility, Ria Formosa, Ruditapes decussatus, seasonal variations, grooved carpet clam


The grooved carpet shell clam Ruditapes decussatus (L. 1758) is one of the most popular and profitable molluscs of lagoon and coastal sites in the Mediterranean, having been used as a food source for centuries. Between 1996 and 2008, official statistics suggested an average pooled catch of 4 mt in Portugal, Spain, France, Ireland, and Tunisia (FAO 2010). In Portugal, the harvesting of bivalves--in particular, R. decussates--is central to aquaculture revenue. In 2007, the national annual production reported for this species reached 2 mt, representing 27% of total seafood cultured in Portugal, of which approximately 90% originated in the Ria Formosa (INE 2007). Here, clams are grown ("farmed") in plots exploited by clam farmers, locally known as "mariscadores," usually organized in professional associations. Clam farming involves seeding juveniles collected from natural beds into plots maintained in tidal flats and harvesting commercial-size animals (i.e., >20 mm). The culture of R. decussatus in the Ria Formosa is central to the local socioeconomic framework involving, directly or indirectly, more than 4,500 people (INE 2007). In 1996, there were 1,587 licensed clam farming plots in the intertidal area of the Ria Formosa, covering a total of 0.47 x[10.sup.6] [m.sup.2] (Cachola 1996), approximately 1% of the total intertidal area of the lagoon. More recently, the ICNB (2004) confirmed the existence of 1,290 plots in the Ria Formosa, a decrease in numbers but a 10-fold increase in the occupied intertidal area (about 4.76 x[10.sup.6] [m.sup.2]). In addition to the official catch figures, widespread illegal and largely opportunistic fishing and harvesting by elements foreign to the local associative system most likely doubles the official production estimates (Ant6nio Laboratory6ia, VIVMAR, pers. comm.).

Percent edibility (i.e., meat content/yield), physiological condition, and biochemical composition of bivalves vary seasonally with latitude and are strongly related to water temperature, food availability, and the gametogenic cycle (Beninger & Lucas 1984, Karakoltsidis et al. 1995, Okumus & Stirling 1998, Orban et al. 2002, Delgado et al. 2004, Ojea et al. 2004, Orban et al. 2006). Proteins, lipids, carbohydrates and minerals are major contributors to the nutritional value and organoleptic properties of clams (Orban et al. 2006), and justify the very high demand for this product in national and international markets. In R. decussatus, both stored and recently assimilated nutrients are used for gametogenesis (Perez-Camacho et al. 2003), characteristic of an intermediate strategy between opportunistic and conservative lifestyles (Rodriguez-Moscoso & Arnaiz 1998). During the reproductive cycle of this species, gametogenesis extends from the end of winter and spring; spawning occurs throughout the summer months, and a resting period occurs in autumn and early winter (Rodriguez-Moscoso & Arnaiz 1998).

Percent edibility or the condition index (CI) have long been used for biological and commercial purposes (Venkataraman & Chari 1951, Baird 1958). These are closely related to the gametogenic and nutrient reserve storage-consumption cycles, and thus to meat quality (Gabbott 1975). In industrial settings, CI has been adopted in international trade as a standard criterion to select the best product. It is also recognized as a useful biomarker reflecting the ability of bivalves to withstand adverse natural and/or anthropogenic stress (Mann 1978, Bressan & Marin 1985, Fernandez-Castro & de Vido de Mattio 1987). Hence, the CI may be considered a measure of "fatness" and "marketability" of a commercially exploited species and, together with proximate biochemical composition, is probably the most practical and simple method of monitoring gametogenic activity (Okumus & Stifling 1998).

To understand the seasonality of R. decussatus nutritional value, thus providing an improved basis for its economic valuation, this study aimed to investigate the changes in grooved carpet shell clam gross biochemical composition in the Ria Formosa (southern Portugal). Moisture, ash, protein, total and nonprotein nitrogen, carbohydrates, and lipid contents, as well as percent edibility and CI were assessed with monthly periodicity for 1 y.


Environmental Data, Sampling, and Processing

The study was carried out between January and December 2006. Monthly average air temperature and precipitation recorded at a meteorological station (Faro International Airport) in the Ria Formosa were used to assess seasonality in climatic conditions. Samples of R. decussatus clams (~1 kg, about 140 individuals) were obtained directly from a farmer's plot belonging to VIVMAR Association on a monthly basis. This ensured that all tested biological material was of commercial value and was harvested from the same area of the Ria Formosa. Immediately after harvest, the samples were transported to the laboratory in a refrigerated box, washed, and placed in prefiltered (GF/C, Whatman Int. Ltd., UK) seawater for 3-4 h to purge pseudo feces and stomach content. Thirty individuals were then randomly selected for biometric measurements and for the determination of the percent edibility and CI. The remaining clams were stored at -20[degrees]C for later biochemical composition analysis.

Biometric Parameters, Percentage Edibility, and CI

Individual clams were weighed ([+ or -] 0.1 mg) and their maximum length measured using a precision caliper (to 0.05 mm). Clams were manually shucked by cutting the adductor muscle with a knife, and the meat was pressed with blotting paper to remove excess moisture before weighting. The meat and shells were subsequently dried at 105[degrees]C for 24 h and weighed again.

Percent edibility was calculated as

PE = (MWW/TW) x 100,

where PE is percent edibility, MWW is meat wet weight (measured in grams), and TW is the total clam weight including the shell (measured in grams) (Venkataraman & Chari 1951, Mohite et al. 2009). CI was calculated as

CI - (MDW/SDW) x 1,000,

where MDW is meat dry weight (measured in grams) and SDW is the shell dry weight (measured in grams), following Lucas and Beninger (1985) and Orban et al. (2006).

Biochemical analyses

Moisture and ash content of clams was determined for 30 individuals using the AOAC (2005) methods (Refs. 950.46 and 938.08, respectively). Total nitrogen (bulk protein content) was determined using the Kjeldahl method (Ref. 955.04 (AOAC 2005)). This was also used to determine nonprotein nitrogen content after precipitation of proteins with 10% (w/v) trichloroacetic acid. Net protein content was calculated as the difference between total nitrogen and nonprotein nitrogen multiplied by 6.25, the conversion factor used for meat and meat products (Pearson 1973). Carbohydrate and total lipids were determined according to Dubois et al. (1956) and Bligh and Dyer (1959), respectively. Biochemical analyses were carried out individually on 9 randomly selected clams.


Initially, l-way analysis ofcovariance was used to test whether putative seasonal variations (month) in the biological traits (response variables) covaried with individual size (length). Because no significant effects of length on biochemical composition were found (Table 1), 1-way analysis of variance and the Tukey honestly significant difference test were carried out to uncover any significant seasonal changes in biochemical composition, condition, or edibility. The lipid content values were log-transformed to correct for (severe) non-normality. In addition, relationships between monthly data on biochemical composition, CI, and edibility were investigated using Spearman's rank correlation coefficient. All statistical procedures were carried out at the 0.05 level of significance using R (R Development Core Team 2007).


Monthly average air temperature and precipitation for the Ria Formosa are illustrated in Figure 1. Higher temperatures were observed in summer (25[degrees]C in July and August) and the lowest in winter (<9[degrees]C). Monthly precipitation records showed an extreme value in November with 252 mm, which was much higher than the range observed throughout the rest of the year (15-40 mm).


Biochemical composition (Fig. 2), percent edibility, and CI (Fig. 3) varied with the season (Table 2). Average monthly moisture contents were significantly higher (P < 0.05) during autumn and winter (85.9% in March and 86.9% in November) than in June (82.6%). On the other hand, ash (which indicates the inorganic compounds content) was significantly higher (P < 0.05) during January and February (3.4% and 3.6%) compared with the rest of the year. Between March and August, a second period of intermediate values (~3.1%) was observed. From August to November, the clams had the lowest values of ash content (about 2.8%).

The carbohydrate content varied widely from 0.4% in January and July to 2.6% in September. Average log-transformed lipid content showed no significant seasonal variation despite the large variability on a monthly basis. The lowest lipid content was measured in April (0.07%) and the lowest total nitrogen content was measured between October and November (~1.2%). In contrast, total nitrogen content was significantly higher in June, August, and September (~1.5%). Despite null values of nonprotein nitrogen found in May and July, the total and nonprotein nitrogen contents evidenced complementary seasonal trends. The resulting protein content was significantly higher (P < 0.05) during early summer, averaging 8.5% from May to July, in contrast to winter values, which ranged from 5.9% in December to 6.7% in January.

Percent edibility of clams was significantly lower (P < 0.05) in January and February (-24%) compared with the April/June or October/December trimesters (30 32%). On the other hand, the CI of the clams was significantly higher (P < 0.05) from April to June (98.6-107.2) than from July to December, when intermediate values of 83.4-88.2 were recorded. Clams showed the lowest CIs (<77.2) in January and March.


Few pairwise correlation coefficients (Table 3) were judged to be significant (P < 0.05). Temperature and/or precipitation were associated with ash, total nitrogen and/or protein content, and CI. Moreover, CI and percent edibility were intercorrelated and associated with protein content and nonprotein nitrogen content.



Temperature and food availability have been considered the main factors conditioning the growth and hence production in bivalves. The effect of these variables is complex and depends on species-specific acquisition and expenditure of energy in the natural environment (Bayne & Newell 1983). In temperate tidal lagoons with considerable open-sea water exchanges and high primary production (e.g., Sufa Lagoon in Turkey or the Ria Formosa in Portugal), the food supply is not considered a limiting factor for growth and reproduction of bivalves (Serdar & Lok 2009), which feed mainly on microalgae (Delgado & Perez-Camacho 2005). Consequently, temperature is the key factor controlling the reproductive cycle of R. decussatus (Urrutia et al. 1999, Delgado & Parez-Camacho 2007, Matias et al. 2009), influencing seasonal biochemical composition and nutritional conditions (Gozler & Tarkan 2000, Perez-Camacho et al. 2003, Fernandez-Reiriz et al. 2007).

Seasonal biochemical composition followed the changes in percent edibility and CI, which indirectly reflect R. decussatus reproductive phases (Gozler & Tarkan 2000, Mohite et al. 2009). From January until June, the increasing temperatures induce gametogenesis (Delgado & Perez-Camacho 2007), resulting in an increase in percent edibility and CI. During this period, R. decussatus accumulated and used carbohydrates, lipids, proteins, and minerals, presumably for gonad development. The sudden decrease in all these parameters, which occurred between June and July, most likely coincided with spawning, and the phase may have lasted until September, when the species entered the resting phase.

Our results compare well with studies on the seasonality of clam physiology at other latitudes, including the Galician Rias in northwest Spain (Ojea et al. 2004), the Lagoon of Venice in Italy (Matin et al. 2003), Sufa and Cordak lagoons in Turkey (Gozler & Tarkan 2000, Serdar & L6k 2009), and Atlantic coast of Morocco (Shafee & Daoudi 1991), despite the differences in methodology. Overall, carbohydrates and lipids show complementary trends, with carbohydrates (and moisture levels) reaching minima during the summer, when lipid and protein content peaked. In addition, all previously mentioned study sites sustain similar seasonal trends of CIs, with small latitudinal changes. The more southern the location, the sooner gametogenesis, ripping, and spawning occur (Meneghetti et al. 2004), with spawning starting in August in northwest Spain (Perez-Camacho et al. 2003), in June/July in south Portugal, and in May in Morocco (Shafee & Daoudi 1991).

In the Ria Formosa, total nitrogen, nonprotein nitrogen, and thus protein contents show that the nitrogen metabolism in R. decussatus varies on a monthly basis. However, the lower nonprotein nitrogen registered during the summer, suggests that the majority of the clam nitrogen metabolism is being channeled to the spawning process during that period (Marin et al. 2003). Although the glycogen content is the parameter most often linked to seasonal variation in clam carbohydrate levels, direct determination of total carbohydrates not only allows the evaluation of the same type of seasonal changes, but also adds all the other types of mono- and polysaccharides involved in the clam's life cycle, thus becoming a more integrative parameter. In fact, the seasonal variation of glycogen and carbohydrates is strongly correlated, with the former being responsible for approximately 50% of the variance of the latter (Robert et al. 1993, Serdar & Lok 2009). In autumn and early winter, R. decussatus accumulates glycogen prior to gametogenesis, before it is used as an energy source for gonad development, in anticipation of the spawning period taking place during the summer (Ojea et al. 2004).

Lipids are the biomolecules that are more influenced by the clams" annual reproductive cycle because of their relationship with gonad maturation. The large variability of lipid content, evidenced by the SDs, may be related to the differential gender-related sexual dynamics of this species (Perez-Camacho et al. 2003). The link between the lipid and carbohydrate contents may thus be rooted in the assumption that many lipids accumulated by clams are sourced from glycogen reserves (Marinet al. 2003). This metabolic relationship underpins the opposite trends observed between the seasonal variations of these 2 parameters observed in the current study. This was particularly evident in July and August. During the remainder of the year, the clams attempt to accumulate lipid reserves through food ingestion in preparation for the next reproductive cycle (Marin et al. 2003).

Seasonal variations in the nutritional value can also be accessed, in a more global approach, using meat yield-related indices. In the Ria Formosa, the physiological condition of R. decussatus is higher between April and June, and lower during the rest of the year. Taking into account the physiological condition of the species and its nutritional value, in terms of protein content, the best period of the year to consume R. decussatus would be summer. However, this same period is understood to be the worst to do so from a toxicological point of view, because of the increased risk of poisoning by shellfish toxins (Vale & Sampayo 2002). In summer, consumers should exercise particular care when buying these bivalves, and always make sure to acquire depurated and certified products (Vale et al. 2008). On the other hand, the demand for R. decussatus and, consequently, its market value are also very high during the Christmas season. The product's "health threat" is not an issue at this time of the year (Vale & Sampayo 2003), but its physiological condition is at its worst, leading to a discrepancy between the nutritional value and the demand for this product, similarly to the case of R. philippinarum in the Lagoon of Venice in Italy (Marin et al. 2003).


The clam R. decussatus is an important natural resource and food product in the Ria Formosa, and its exploitation sustains an significant part of the local economy. Analysis of R. decussatus percent edibility and CIs allowed inference of its reproductive cycle: Gametogenesis started in January, spawning took place from June to September, and the resting stage occurred between October and December. The high seasonal variability observed in the biochemical composition of this species was most likely a result of the reproductive cycle, and it showed typical features of the life history of bivalve molluscs at temperate latitudes. Similarly to mariculture populations in Galicia (Spain), Lagoon of Venice (Italy), Turkey, and Morocco, the peak in nutritional value is observed during the summer, whereas the slump occurs during winter. Curiously, these two periods coincide with the peak of major commercial demand.


We thank Vera Francisco, Ana Sofia Viegas, and Andreia Geraldes for their contribution in laboratory processing of samples. We dedicate this work to the memory of Antonio Laboia, President of VIVMAR, a regional clam farmers association, who recently passed away. Work was funded in part by the project O-DOIS--Oxygen Dynamics coupled with Organic Carbon Mineralization in Intertidal Sandflats: Role of Porewater Advection (POCTI/CTA/47078/2002).


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* Corresponding author. E-mail:

DOI: 10.2983/035.030.0104


(1) CIMA-Centro de Investigacao Marinha e Ambiental, Universidade do Algarve, Instituto Superior de Engenharia, Campus da Penha, 8005-139 Faro, Portugal, (2) Centro de Ciencias do Mar CCMar AlgarveCIMAR Laborat6rio Associado and Universidade do Algarve, Instituto Superior de Engenharia, Campus da Penha, 8005-139 Faro, Portugal; 3School of Natural Sciences, Trinity College Dublin, College Green, Dublin 2, Ireland
Results of analyses of covariance per parameter studied in R.
decussates from the Ria Formosa (South Portugal).

Parameter             Factor            df          SS         MS

Moisture              Month              11      558.61      50.78
                      Length              1        0.18       0.18
                      Month X length     11       16.74       1.52
                      Residuals         335      396.44       1.18

Ash                   Month              11       19.70       1.79
                      Length              1        0.07       0.07
                      Month x length     11        1.05       0.10
                      Residuals         336       39.82       0.12

Carbohydrates         Month              11       45.98       4.18
                      Length              1        0.25       0.25
                      Month X length     11        0.93       0.09
                      Residuals          83       11.51       0.14

Logio(lipids)         Month              11       10.88       0.99
                      Length              1        0.47       0.47
                      Month X length     10        2.33       0.23
                      Residuals          27        6.20       0.23

Total nitrogen        Month              11        1.18       0.11
                      Length              1        0.00       0.00
                      Month x length     11        0.34       0.03
                      Residuals          81        1.67       0.02

Nonprotein nitrogen   Month              11        0.77       0.07
                      Length              1        0.00       0.00
                      Month x length     11        0.15       0.01
                      Residuals          82        0.72       0.01

Proteins              Month              11       76.64       6.97
                      Length              1        0.30       0.30
                      Month X length     11       16.44       1.49
                      Residuals          80       96.73       1.21

Condition index       Month              11   35,064      3,188
                      Length              1       19         19
                      Month X length     11    1,562        142
                      Residuals         335   53,717        160

Percent edibility     Month              11    2,451.8      222.9
                      Length              1       24.7       24.7
                      Month x length     11      102.9        9.4
                      Residuals         335    3,563.1       10.6

Parameter             Factor           F Value   P Value

Moisture              Month              42.91   [<10.sup.-6]
                      Length              0.15   0.6945
                      Month X length      1.29   0.2308

Ash                   Month              15.11   [<10.sup.-6]
                      Length              0.57   0.4526
                      Month x length      0.81   0.6317

Carbohydrates         Month              30.14   [<10.sup.-6]
                      Length              1.78   0.1857
                      Month X length      0.61   0.8153

Logio(lipids)         Month               4.31   0.0010
                      Length              2.06   0.1625
                      Month X length      1.01   0.4569

Total nitrogen        Month               5.20   [<10.sup.-5]
                      Length              0.15   0.7021
                      Month x length      1.51   0.1435

Nonprotein nitrogen   Month               8.04   [<10.sup.-6]
                      Length              0.03   0.8742
                      Month x length      1.57   0.1234

Proteins              Month               5.76   [<10.sup.-6]
                      Length              0.25   0.6211
                      Month X length      1.24   0.2777

Condition index       Month              19.88   [<10.sup.-6]
                      Length              0.12   0.7284
                      Month X length      0.89   0.5549

Percent edibility     Month              20.96   [<10.sup.-6]
                      Length              2.32   0.1285
                      Month x length      0.88   0.5605

MS, mean squares; SS, sum of squares.

Biochemical composition, condition index, and percent edibility of R.
decussatus from Ria Formosa: seasonal variation (mean [+ or -] SD)
for monthly samples of n individuals.

                            Month (2006)

Parameter        n             January

Moisture         30   85.96 [+ or -] 0.25 (de)
Ash              30    3.42 [+ or -] 0.58 (ef)
Carbohydrates     9    0.38 [+ or -] 0.13 (ab)
Lipids *          3    2.25 [+ or -] 3.57 (b)
Total nitrogen    9    1.31 [+ or -] 0.11 (a-d)
Nonprotein        9    0.25 [+ or -] 0.03 (b)
Proteins          9    6.67 [+ or -] 0.77 (ab)
Condition        30   72.80 [+ or -] 17.24 (de)
Percent          30    24.4 [+ or -] 3.69

                                      Month (2006)

Parameter                February                      March

Moisture         83.84 [+ or -] 2.10 (bc)    85.87 [+ or -] 1.05 (d)
Ash               3.59 [+ or -] 0.51 (f)      2.99 [+ or -] 0.28 (a-d)
Carbohydrates     1.44 [+ or -] 0.81 (de)     0.84 [+ or -] 0.26 (ab)
Lipids *          1.71 [+ or -] 1.84 (b)      0.20 [+ or -] 2.38 (a)
Total nitrogen    1.37 [+ or -] 0.12 (a-d)    1.28 [+ or -] 0.07 (abc)
Nonprotein        0.23 [+ or -] 0.05 (b)      0.15 [+ or -] 0.12 (ab)
Proteins          7.13 [+ or -] 0.64 (abc)    7.11 [+ or -] 0.83 (abc)
Condition        73.37 [+ or -] 8.98 (bc)    77.17 [+ or -] 16.13 (d)
Percent           24.0 [+ or -] 5.5 (fg)      27.0 [+ or -] 3.9 (abc)

                                      Month (2006)

Parameter                  April                        May

Moisture         83.96 [+ or -] 0.84 (bc)    83.59 [+ or -] 0.85 (b)
Ash               3.11 [+ or -] 0.42 (cd)     3.10 [+ or -] 0.28 (bcd)
Carbohydrates     0.69 0.13  (ab)             0.79 [+ or -] 0.18 (ab)
Lipids *          0.07 [+ or -] 5.71 (a)      1.22 [+ or -] 10.13 (ab)
Total nitrogen    1.39 [+ or -] 0.17 (a-c)    1.35 [+ or -] 0.20 (a-d)
Nonprotein        0.17 [+ or -] 0.17 (b)      0.00 [+ or -] 0.00 (a)
Proteins          7.63 [+ or -] 1.41 (abc)    8.48 [+ or -] 1.24 (bc)
Condition        98.34 [+ or -] 13.52 (bc)   98.56 [+ or -] 12.83 (b)
Percent           30.6 [+ or -] 2.7 (ab)      31.9 [+ or -] 2.3 (b-e)

                                      Month (2006)

Parameter                  June                      July

Moisture          82.55 [+ or -] 1.54 (a)   84.51 [+ or -] 1.26 b,
Ash                3.21 [+ or -] 0.25 (de)  3.05 [+ or -] 0.356[degrees]d
Carbohydrates      1.91 [+ or -] 0.24 (e)   0.38 [+ or -] 0.21'
Lipids *           0.53 [+ or -] 1.53 (ab)  0.87 [+ or -] 2.25,b
Total nitrogen     1.52 [+ or -] 0.22 (d)   1.37 [+ or -] 0.14'-''
Nonprotein         0.13 [+ or -] 0.15 (ab)  0.00 [+ or -] 0.00,
Proteins           8.66 [+ or -] 1.56 (c)   8.52 [+ or -] 0.87 b'
Condition        107.21 [+ or -] 16.89 (a)  86.40 [+ or -] 9.92 b,
Percent            32.1 [+ or -] 4.0 (c-f)  28.3 [+ or -] 3.69

                                      Month (2006)

Parameter                 August                     September

Moisture         84.61 [+ or -] 1.2l (bc)    84.43 [+ or -] 0.83 (bc)
Ash               2.83 [+ or -] 0.08 (ab)     2.89 [+ or -] 0.09 (abc)
Carbohydrates     1.47 [+ or -] 0.42 (de)     2.62 [+ or -] 0.28 (f)
Lipids *          0.72 [+ or -] 1.09 (ab)     1.23 [+ or -] 4.36 (ab)
Total nitrogen    1.47 [+ or -] 0.11 (cd)     1.44 [+ or -] 0.18 (bcd)
Nonprotein        0.27 [+ or -] 0.1l (b)      0.22 [+ or -] 0.09 (b)
Proteins          7.47 [+ or -] 1.17 (abc)    7.60 [+ or -] 1.44 (abc)
Condition        85.43 [+ or -] 7.70 (c)     88.19 [+ or -] 9.98 (bc)
Percent           26.5 [+ or -] 2.l (a)       27.2 [+ or -] 2.5 (efg)

                                      Month (2006)

Parameter                 October                    November

Moisture         86.37 [+ or -] 0.64 (de)    86.85 [+ or -] 0.57
Ash               2.88 [+ or -] 0.13 (abc)    2.74 [+ or -] 0.45 (a)
Carbohydrates     1.35 [+ or -] 0.25 (cde)    0.96 [+ or -] 0.38 (bc)
Lipids *          0.26 ([dagger] ab)          0.48 [+ or -] .30 (ab)
Total nitrogen    1.19 [+ or -] 0.15 (a)      1.21 [+ or -] 0.14 (ab)
Nonprotein        0.19 [+ or -] 0.08 (b)      0.14 [+ or -] 0.11 (ab)
Proteins          6.25 [+ or -] 1.25 (a)      6.69 [+ or -] 1.00 (ab)
Condition        85.08 [+ or -] 9.30 (de)    83.37 [+ or -] 14.31 (e)
Percent          30.2 [+ or -] 2.2 (d-g)      29.6 [+ or -] 2.7[pounds sterling]

                       Month (2006)

Parameter                December

Moisture         86.33 [+ or -] 0.81 (de)
Ash               3.13 [+ or -] 0.25 (cde)
Carbohydrates     1.88 [+ or -] 0.50 (e)
Lipids *          0.36 [+ or -] 2.85 (ab)
Total nitrogen    1.17 [+ or -] 0.08 (a)
Nonprotein        0.23 [+ or -] 0.03 (b)
Proteins          5.90 [+ or -] 0.48 (c)
Condition        84.84 [+ or -] 9.36 (de)
Percent           30.0 [+ or -] 2.5 (bcd)

Parameters are in percent except for condition index.

* These values are back-calculated from the log-transformed values
used in the analysis. The body mass of at least 3 individuals had to
be pooled to obtain each replicate.

([dagger]) Only one replicate available. Within a row, values not
sharing the same superscripts are significantly different (P < 0.05).

Matrix of Spearman correlation coefficients (R) and respective P
values for pairwise correlation analysis (n = 12) of  monthly mean
air temperature, precipitation, biochemical composition, condition
index, and percent edibility of  R. decussatus from Ria Formosa.

Parameter         Temperature   Precipitation   Moisture     Ash

Precipitation     -0.57
Moisture          -0.19          0.55
                   0.5486        0.0625
Ash               -0.59         -0.01           -0.50
                   0.0441        0.9828          0.1006
Carbohydrates      0.21         -0.06           -0.11      -0.09
                   0.5121        0.8629          0.7292     0.7787
Log(lipids)       -0.03         -0.26           -0.29       0.35
                   0.9225        0.4168          0.3541     0.2652
Total nitrogen     0.48         -0.45           -0.76       0.14
                   0.1114        0.1446          0.0040     0.6646
Nonprotein        -0.32          0.32            0.28       0.13
  nitrogen         0.3033        0.3126          0.3777     0.6881
Protein            0.57         -0.65           -0.83       0.11
                   0.0543        0.0220          0.0008     0.7292
Condition index    0.66         -0.64           -0.62      -0.10
                   0.0190        0.0261          0.0332     0.7456
Percent            0.28         -0.21           -0.24      -0.06
edibility          0.3839        0.5128          0.4433     0.8629

                                    Log       Total     Nonprotein
Parameter         Carbohydrates   (Lipids)   Nitrogen    Nitrogen

Log(lipids)        0.01
Total nitrogen     0.27            0.29
                   0.4038          0.3541
Nonprotein         0.32            0.25       0.03
  nitrogen         0.3126          0.4357     0.9225
Protein           -0.08            0.16       0.78      -0.56
                   0.8122          0.6175     0.0026     0.0562
Condition index    0.19           -0.17       0.55      -0.54
                   0.5567          0.5868     0.0666     0.0682
Percent            0.06           -0.49      -0.01      -0.66
edibility          0.8459          0.1063     0.9828     0.0190

Parameter         Protein     Index

Total nitrogen
Condition index   0.76
Percent           0.35      0.77
edibility         0.2652    0.0034

Significant (P < 0.005) coefficients are printed in bold type.
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Article Details
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Author:Anibal, Jaime; Esteves, Eduardo; Rocha, Carlos
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:4EUPR
Date:Apr 1, 2011
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