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Reproductive ecology, fecundity, and elemental composition of eggs in brown crab Cancer pagurus in the Isle of Man.

ABSTRACT The brown crab is an important fishery resource in northern Europe. Understanding factors that affect fecundity in this species is complicated by the fact that ovigerous females enter traps infrequently. This study aimed to understand factors that affect brown crab fecundity and egg quality for crabs sampled from the waters around the Isle of Man. The size-fecundity relationship for the Isle of Man matched closely with those published for other geographical areas where a fishery exists for this species. Ovigerous crabs varied in size from 134 to 215 mm carapace width and each individual carried an estimated 0.4-3.0 million eggs. Fecundity was not affected by factors such as sampling season, location, loss of chelae, or black spot disease. Egg volume was independent of the number of eggs per batch or female body size. Egg volume was reduced significantly in crabs that had lost chelae. Egg dry weight, C and N composition did not vary with body size or any other explanatory factors such as chelal loss or the occurrence of black spot disease. Although the importance of the effect of claw loss on egg volume remains unclear, it may be an important consideration in fisheries in which the landing of claws is permitted.

KEY WORDS: Cancer pagurus, Crustacea, reproductive ecology, fecundity, chela loss, egg size, elemental composition, sustainable fisheries


Sustainable fisheries management requires a full understanding of life history traits and environmental factors that influence reproduction, growth, and mortality of exploited species (Jennings et al. 2001, Ficker et al. 2014). Well-managed stocks are characterized by sufficient reproductive adults and egg production to maintain an adequate level recruitment (Carter et al. 2014). Understanding reproductive patterns, the size at maturity, the behavior of ovigerous females, fecundity, and egg/ larval quality all contribute to estimates of the turnover capacity of natural populations. Such information informs management recommendations and the use of appropriate technical measures [e.g., minimum landing size (MLS)] for exploited species (Pinheiro et al. 2003, Mente 2008).

Fecundity commonly refers to the number of eggs produced by a female in a single egg batch (Bourdon 1962, Sastry 1983, Pinheiro & Terceiro 2000, Pinheiro et al. 2003). Fecundity data should consist of three main parts: the unit counted (e.g., oocytes, eggs, embryos, and larvae); the individual in which the unit is counted (e.g., batch of eggs, female, and colony); and the timescale (e.g., spawning event, breeding season, year, and lifetime) (Ramirez-Llodra 2002). In the case of crabs, many studies indicate that their fecundity is affected by environmental factors: temperature, photoperiod and food availability (Hines 1988, Pinheiro et al. 2003, Verisimo et al. 2011), geographic area (Brante et al. 2004), season (Bas et al. 2007), chemicals (pollutants) and biological agents (bacteria, fungi) (Shields 1991), and species-specific factors such as body size (Hines 1991, Shields 1991), body weight (Haddon 1994), female age (Przemyslaw & Marcello 2013), moulting stage (Somerton & Meyers 1983), injury or damage, limb loss (Gardner 1997), and subsequent brood production (Verisimo et al. 2011).

In addition to the influence of environmental factors, some studies show that the reproductive patterns in oogenesis, embryogenesis, egg, and larval quality may be affected by factors such as female nutritional condition (Palacios et al. 1998, 1999, Wehrtmann & Kattner 1998), temperature (Paschke 1998, Gimenez & Anger 2001, Thatje et al. 2004, Fischer et al. 2009, Weiss et al. 2009), and salinity (Gimenez & Anger 2001, Torres et al. 2002). Moreover, some diseases in decapod crustaceans cause egg mortality and mortality of animals (Shields 2012) and limb loss negatively affects the reproduction, foraging efficiency, and growth of crustaceans (Juanes & Smith 1995, Mariappan et al. 2000, Patterson et al. 2009). Black spot disease is a bacterial infection that causes black lesions on the exoskeleton (Ayres & Edwards 1982). Exoskeleton lesions have been reported from many decapod crustaceans for three decades (Roald et al. 1981, Joseph & Ravichandran 2012, King et al. 2014). The potential impacts of the black spot disease and limb loss on the reproductive output and development of animals have not been investigated sufficiently yet. In crabs, the newly laid eggs contain all the energy necessary for embryonic development (Gimenez & Anger 2001). The quality of eggs (indicated by carbon (C) and nitrogen (N) content and/ or egg size) is important as larval survival and growth are affected by the amount of energy reserves that remain after hatching (Gimenez & Anger 2001, Churchill 2003, Ouellet & Plante 2004, Urzua et al. 2012). Thus, it is important to understand whether there are spatial, temporal, or other factors (such as limb loss or black spot disease) that might affect egg quality when attempting to estimate fecundity in the context of an exploited population.

The brown crab Cancer pagurus (Linnaeus, 1758) is one of the most important commercial species in terms of first-sale economic value (nearly 31 M [pounds sterling] in 2011) in the United Kingdom (MMO 2014). The fishery is prosecuted mainly by small-scale inshore fleets and larger-scale offshore vivier vessels. The present study focused on the brown crab fishery in the Isle of Man where the management measures include a current MLS of 130 mm carapace width (CW) and where the fishing of ovigerous crab is banned to protect egg production and to avoid overfishing. In addition, the landing of crab claws is prohibited which has stopped the practice of "declawing" by fishers that land their catches in the Isle of Man (Kaiser et al. 2008). Nevertheless, this practice remains prevalent in other parts of the United Kingdom and European Union.

Studying ovigerous brown crabs is complicated by sampling limitations that occur as a result of their behavior. In the autumn/early winter, ovigerous (berried) female Cancerpagurus migrate to deeper water where they remain hidden and half buried in the sand, gravel, or silt to incubate their eggs for periods to time up to 9 mo in duration (Nichols et al. 1982, Naylor et al. 1999, Woll 2003). During this egg-carrying period, ovigerous females either do not feed or they exhibit limited feeding activity and the large egg mass on the abdomen restricts their movement ability (Bennett & Brown 1983). As a consequence, these less-active female crabs rarely enter baited traps (Edwards 1979, Brown & Bennett 1980, Howard 1982, Bennett & Brown 1983, Bennett 1995, Karlsson & Christiansen 1996, Hunter et al. 2013). Traditional studies of brown crabs have relied mainly on trap-based surveys. For this reason, little is known about the distribution and abundance of ovigerous females and the factors that affect their fecundity (Howard 1982, Addison & Bennett 1992). In addition, there are few insights into how the elemental composition (and hence egg quality) of C. pagurus eggs may be influenced by environmental factors (Torres et al. 2002, Weiss et al. 2009).

The present study examined the fecundity of Cancer pagurus in the northern Irish Sea in the territorial sea of the Isle of Man. In addition, the study investigated whether egg size was affected by maternal factors (crab body size, chela loss, occurrence of black spot disease, etc.). Lastly, the possible effects of chela loss and occurrence of black spot disease on egg quality (dry weight, C, and N content) were examined.


Collection of Crabs

A total of 5,795 pots were hauled during fishery independent surveys in the Isle of Man from spring 2012 to summer 2013; however, only 16 ovigerous crabs were captured during this period. Additional samples of female ovigerous crabs were obtained from autumn 2012 until the early spring 2013 during scallop dredge fishery surveys and from commercial scallop fishing boats. The survey design was inevitably constrained by the need to work with existing commercial fishing activity, which was confined to specific areas. Although the samples size was relatively low (n = 78), it was greater than that reported for other studies (Williamson 1900, Edwards 1967, Cosgrove 1998, Tallack 2002, Ungfors 2007). Ovigerous crabs were placed in plastic bags separately to avoid the loss of eggs and appendages. These crabs were held on ice in insulated boxes at sea and returned to the laboratory for further analysis.

Environmental Data

A time series of seawater temperature data is maintained at three different sites around the Isle of Man territorial area (Resa, Targets, and Cypris). Monthly observations for the period between autumn 2012 and summer 2013 were extracted for bottom temperature (DEFA 2010, Shephard et al. 2010). The annual average water temperature values were 10.9 [+ or -] 2.8[degrees]C in Targets, 11.1 [+ or -] 2.7[degrees]C in Cypris, and 11.3 [+ or -] 2.9[degrees]C in Resa. To place the current study in a wider European context, the minimum, maximum, and average bottom water temperature values were calculated for the period between 1965 and end of 2013 obtained from the International Council for the Exploration of the Sea (ICES) data portal and compared with the mean value for the Isle of Man. Water depth across the areas sampled varied between 3 and 100 m, which reflected the distribution of the main commercial fishing activity in the Isle of Man.

Morphological Characteristics

In the laboratory, for each crab, morphometric measurements were taken to determine which of these gave the most reliable estimate of fecundity, these were CW, carapace length (CL), 5th abdominal somite width (S5W), 5th abdominal somite length (S5L), 6th abdominal somite width (S6W), and 6th abdominal somite length (S6L) (all measured to the nearest mm). Based on Ungfors (2007), moult stage was classified into four classes: (1) early post moult (soft carapace), (2) late post moult (recently moulted, coloration still bright and no epifaunal growth), (3) intermoult (fully hardened carapace with some fouling organisms), and (4) late intermoult (evidenced from shell necrosis and the presence of many fouling organisms).


Fecundity was estimated using the methods in Tallack (2002, 2007). The wet weight of each egg mass was determined for each female. To avoid egg loss, the egg mass was carefully removed by cutting the pleopods from

the abdominal flap. Eggs were removed from the pleopods. A total egg mass weight was determined by weighing the entire egg mass to the nearest 0.001 g using an analytical balance. Three similar-sized separate subsamples of eggs were taken randomly from each brood, weighed to the nearest 0.001 g and the eggs counted under a stereo microscope. The weight of each individual egg was determined by dividing the mass of the subsample of eggs by the number of eggs in that subsample. The individual egg weights (EW) from the three subsamples (W1, W2, and W3) were then averaged to provide a mean individual EW. The total number of eggs per brood ([T.sub.eggs]) was calculated from Eq. 1.

[T.sub.eggs] = TEW/EW (1)

Egg Volume and Development Stages of Eggs

Ten eggs per brood were removed to measure their size and biomass. Egg volume was determined by measuring the mean egg diameter (measured to the nearest [micro]m) from two measurements (length [D.sub.1] and width [D.sub.2]) made with a stereo microscope (Kyowa, model SZM) equipped with a calibrated eyepiece micrometer. Diameter was then converted to a radius and this value was used to calculate the volume of each egg assuming it was spherical. Development stage was determined by removing the egg mass from the pleopods. Forty eggs from each brood were chosen at random and were investigated under a dissecting microscope to estimate their development stage based on Fischer (2009).

Elemental Composition of Eggs

The elemental composition (C and N content) of the eggs of a smaller number of berried females (n = 54) was determined to understand if the quality of the eggs varied in relation to loss of appendages or black spot disease. To determine the dry weight and elemental composition (C and N content) of the eggs within a single brood, the procedure outlined in Gimenez and Anger (2001) was followed. For each brood, three replicate samples of 40 eggs each were removed and rinsed for a few seconds in distilled water to eliminate residual seawater. Afterward, eggs were blotted dry on filter paper, and subsequently transferred to preweighed tin cartridges. Samples were dried for 48 h in a vacuum drier (Edwards Super modulyo 12K), weighed on a micro balance (Mettler Toledo, precision: 1 [micro]g) to obtain the dry weight. Immediately afterward, the C and N content was obtained by combustion of samples at 900[degrees]C in a CHNS-O Analyzer (Flash EA 1112).

Factors that Might Affect Fecundity or Egg Quality

Crabs that have lost appendages or that are infected with black spot disease may have incurred energetic costs that had a negative impact on fecundity. For this reason, the following parameters were recorded; leg loss, chelal loss, and the severity of black spot disease. When recording leg and chelal loss, only those crabs that had older wounds with evidence of melanization at the site of injury were considered. This was to avoid misreporting of instantaneous limb loss that occurred at the time of sampling. The severity of black spot disease was classified on a scale from 0 to 4: (0) no discoloration present; (1) one to five distinct spot, generally only on chelipeds; (2) the spot number varied between 6 and 10; (3) many distinct spots (more than 11), usually covering surfaces of chelipeds, abdomen, and carapace; (4) much discoloration; much of the surface of cheliped, abdomen, or carapace are affected, and solid black patches can be seen.

Statistical Analysis

Statistical analyses were performed with the SPSS software (Version 20). For the morphometric relationships, a linear regression (ln-transformed data) was used to determine: the relationship between fecundity and various external morphometric parameters. Similarly, a linear regression was used to determine the relationship between fecundity and CW of Cancer pagurus in this and other published studies. The data were tested for normality and homogeneity of variance using a Kolmogorov-Smirnov test and Levene's test, respectively, to determine whether they conformed to the assumptions of the statistical tests that were applied (Field 2005, Becerra-Jurado et al. 2014).

As the fecundity of crabs can vary seasonally (Samuel & Soundarapandian 2009), and there are distinctly different oceanographic regimes around the Isle of Man [stratified (west coast) versus mixed water masses (east and south coast)], a general linear modeling (GLM) approach was used to examine variation in fecundity with season (autumn versus winter-spring) and location (east and south versus west). The waters to the west of the Isle of Man are strongly stratified in the summer and autumn, which leads to strong differences in patterns of production (Dickey-Collas et al. 1996, Lambert 2011). Given the constraint of relatively low numbers of animals, it was necessary to group crabs into broad categories to examine the seasonal and spatial differences in fecundity. The following covariates were included in the model; CW, which is a proxy for crab size, egg volume, which may affect estimates of fecundity that are based on the weight of the egg mass, leg and chelal loss, which may incur energy costs that affect fecundity, and black spot disease, which may impair crab condition and moult stage. The effect of egg development stage was checked using a GLM procedure with CW as a covariate. In this model, the fecundity was chosen as dependent variable. When significant effects were revealed, these were examined using univariate analysis if appropriate.

A GLM was used to examine variation in egg volume with chela loss and severity of black spot disease.

Similarly, a GLM approach was adopted to examine whether the elemental composition of the eggs was affected by chelal loss and black spot disease (main factors). Egg development stage (stage 1 or 2), egg volume, and crab size (CW) were included as covariates in the analysis. Other factors were not included because of the relatively low sample size, which limited the number of degrees of freedom.

The relationship between the minimum size of egg bearing crabs around the fishing grounds of northern Europe and the minimum bottom temperature of these fishing grounds was tested using Spearman's rank correlation.



The 78 ovigerous females used for the counts of egg number varied in size from 134 to 215 mm CW, and they carried an estimated 0.4-3.0 million eggs each. The mean fecundity of the crabs in this study was estimated as 1.5 x [10.sup.6] [+ or -] 0.6 x [10.sup.6] eggs per ovigerous female. Statistically significant positive linear relationships were found between all of the morphometric measurements and the In fecundity (Table 1, Fig. 1). A GLM demonstrated that CW was a strong predictor of fecundity (Table 2). Fecundity did not vary between crabs sampled in the autumn versus winter-spring and there was no effect on fecundity of the area from which the crabs were sampled (Table 2).

Eggs were either in development stage 1 or 2. but there was no effect of egg development stage on the estimate of fecundity for the 54 crabs for which this was ascertained (GLM, [F.sub.(1,52)] = 0.18, P = 0.68).

Egg volume ranged from 15.8 x [10.sup.6] to 41.2 x [10.sup.6] [[micro]m.sup.3] in volume. Egg volume was independent of fecundity or female CW (Table 3, Fig. 2A) and it was clear that there was considerable individual variation in egg size for a given size of individual crab. The GLM demonstrated that egg size declined with when crabs had lost either chelae (note loss of one or two chelae was not differentiated because of the low number of crabs that had lost two chelae) (Table 3, Fig. 2B). There was no effect of black spot disease on egg volume (Table 3).

Elemental Composition of Eggs

Whole egg biomass ranged between 13.47 and 19.95 [micro]g dry weight, 6.96 and 10.03 [micro]g C, and 1.26 and 2.90 [micro]g N. The C:N ratio ranged between 3.32 and 6.10. Table 4 shows the mean, minimum, and maximum values (per individuals [+ or -] SD) of dry weight, C, and N in first two egg development stages. There was no effect of chelal loss or the severity of black spot disease on the elemental composition of the eggs. There was also no effect of any of the covariates (development stage, egg volume, or CW) on the elemental composition of the eggs (Table 5).

Results Compared in a Wider European Context

The size at which female brown crabs are first observed to carry eggs varies considerably across northern Europe and ranged from 113 to 144 mm CW (Fig. 3). There appears to be a significant increase in the minimum size of ovigerous crabs with the smallest females occurring off Sweden, Norway, and northeast England, and the largest females occurring in western waters (Fig. 3). Variation in the minimum size of egg bearing appears to be related to water temperature differences in the sampling areas (correlation coefficient = 0.75, P = 0.05, and n = 7).

Figure 4 shows size-fecundity relationships of Cancer pagurus in the present study compared with other studies in different European locations. Fecundity increased significantly with body size in all of these studies (Tallack 2002) except for Williamson (1900). The sample size in the Williamson (1900) study was too low for meaningful analysis. These studies included different methods (wet weight and dry weight).


There is considerable diversity in benthic habitats found around the Isle of Man (Hinz et al. 2010) and the areas sampled during the present study generally consist of sandy, muddy, and mixed gravelly habitats, providing suitable substratum in which ovigerous females can bury. Despite this high level of habitat variation, there were no effects of sampling location on fecundity in the present study. Sampling female crabs that are incubating eggs is problematic. Edwards (1979) and Brown and Bennett (1980) sampled 23,000 and 25,000 females, respectively, and found less than 1 % of animals bearing eggs in both cases. In the present study, 5,795 pots were hauled in the Isle of Man from spring 2012 to summer 2013, but only 16 ovigerous females were found in these pots. For this reason, the present study used bycatch of brown crab from scallop fisheries to supplement the sample size.

Based on previous published data and the present study, it appears that the minimum size at which female crabs are first observed to carry eggs varies significantly with minimum bottom seawater temperature. For the Isle of Man, the smallest female crab encountered with eggs was of 134 mm CW, which is above the MLS of 130 mm CW. Thus, future management may need to consider whether the current MLS is adequate to ensure that crabs have an opportunity to breed before they are removed by the fishery. As shown in other studies, female crab size was a strong predictor of egg-carrying capacity, which was strongly related to pleopod size and hence egg-carrying capacity. The importance of the size and functioning of crab pleopods are demonstrated by observations that crabs with damaged pleopods carry smaller egg broods (Hankin et al. 1989). Thus, protecting larger females by setting a higher MLS would seem a sensible management measure given the high survivorship of discarded crabs in pot fisheries. Such measures need to be given careful consideration because of changes in moulting frequency as crabs become larger. Shields (1991) reported that the moulting probability, the number of eggs per brood, and their survival rates decreased in older female crabs of the genus Cancer. More specifically, older Cancer pagurus individuals do not moult annually (Pearson 1908, Hankin et al. 1985, Shields 1991). This means that for a standard time, larger females may have lower fecundity compared with more frequently moulting smaller females.

The loss of legs and chelae will affect normal behavior during the period from autotomy to regeneration, which may take several moults to achieve. Growth and reproduction may be affected due to changes in energy budget because of the loss of chelae or energy directed to the regrowth of limbs (Juanes & Smith 1995, Lira & Calado 2009). For example, in the grapsid crab Cyrtograpsus angulatus (Dana, 1851), females that lost at least half of their pereipods, had significantly lower fecundity (Luppi et al. 1997). In the present study, although fecundity was not affected, egg volume decreased with increasing chelal loss. Water quality, parasites, predators, and damage are other important factors that can affect the ovigerous crabs, their eggs, and the mortality of the early development stages of larvae (Samuel & Soundarapandian 2009).

Maternal influences on offspring quality could be a significant source of variation in crustacean recruitment (Moland et al. 2010) and the energy content per egg usually depends on egg size (Quellet & Plante 2004). Moland et al. (2010) reported that large females of Homarus gammarus (Linnaeus, 1758) produced large eggs. Hines (1991) noted that egg size of Cancer crabs did not differ significantly with female size. The variation in egg size among similar-sized females could be linked to heritable traits, their physiological condition, and/or previous growth history (Moland et al. 2010). In addition, inter annual temperature variation and regional variation in salinity can be considered as other factors that influence egg size (Bas et al. 2007). For example, Graham et al. (2012) suggested that the egg diameter of the blue crab Callinectes sapidus (Rathbun, 1896) was larger in spring than summer/autumn. Similarly, Urzua et al. (2012) suggested that eggs of shrimp Crangon crangon (Linnaeus, 1758) are larger and heavier in winter than in summer. According to the results of present study, egg size did not correlated with the female body size but egg size decreased with increasing chela losses.

In the present study, the first data concerning biomass and elemental composition of Cancer pagurus eggs were reported. Results here suggest the relationship between body size (CW) and initial egg biomass was not significant for dry weight, C, and N. Weiss et al. (2009) noted that elemental composition (C, H, and N) of zoea 1 larvae of C. pagurus varied significantly among the eight females. The present study showed that even though dry weight, C, and N contents decreased relatively from early stages to late stage, the relationships were not significant. Previous studies indicated that elemental composition (C, H, N, and dry weight) can change during embryonic development stages of eggs or the time of larvae early juvenile development patterns (Calcagno et al. 2003, Anger & Moreira 2004). Consequently, this study compares temporal and spatial variations in elemental composition of crab eggs. Any significant differences in dry weight, C, and N contents in different sampling periods and areas could not be found. According to Torres et al. (2002), dry weight, lipid, and protein contents of the zoea 1 larvae (C. pagurus) were affected by declined salinity. More importantly, results of this study suggest that elemental composition (e.g., N and C) did not increase with increased egg size.

In the present study, there were no significant temporal or spatial differences in fecundity. The patterns in sea water bottom temperature values had a similar trend at the Targets, Cypris, and Resa sampling stations during the sampling period. This similarity in bottom temperature may explain the lack of spatial variation in fecundity around the Isle of Man. This is contrast with the finding that minimum bottom temperature affected the size of first egg bearing in brown crabs across northern Europe.


As for other studies, there was a strong relationship between fecundity and increasing crab size. The smallest size of an egg bearing female encountered was higher than the current MLS, nevertheless, the sample size in this and other studies is low because of problems associated with sampling egg-bearing females. Egg volume was lower for crabs that had lost claws although the elemental composition (quality) of these eggs was not related to egg size. This also suggests that eggs size cannot be assumed to be an indicator of egg quality. Although it is unclear whether fecundity is related to egg size, it is an issue that warrants further investigation because of the potential for damage sustained by crabs taken as bycatch in mobile fishing gear (Ondes et al., unpublished data). Although declawing is not permitted in the Isle of Man, it is permitted in Scotland, England, Ireland, and Wales and may have potential negative effects in these fisheries (Patterson et al. 2007).


This study was funded by the Ministry of National Education, Republic of Turkey (awarded to F. O.), and the Department of Environment, Food and Agriculture (DEFA), the Isle of Man Government (awarded to M. J. K..). We gratefully acknowledge Dr. Luis Gimenez for his suggestions related to the elemental composition analysis. We gratefully acknowledge Prof. Yener Altunbas, Mr. Yurtsev Uymaz (Bangor University), and Mr. Hakan Ondes (Gazi University) for their suggestions about the statistical analyses. We are grateful to the Department of Environment, Food and Agriculture (DEFA) officers and Manx crab and scallop fishermen for their contributions.


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(1) School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey, LL59 5AB, United Kingdom; (2) Faculty of Fisheries, Izmir Katip Celebi University, Izmir, 35580, Turkey

* Corresponding author. E-mail:

DOI: 10.2983/035.035.0226

Linear regression of morphometric measurements (In CL, In
S5W and S5L, and In S6W and S6L) and the In fecundity of
brown crabs (Cancer pagurus) (n = 78) sampled from waters
around the Isle of Man.

Measurement   Intercept   Slope   [R.sup.2]    SE    Lower 95%

In CL           -2.430    3.603       0.71    0.26       3.08
In S5W           4.173    2.588       0.72    0.19       2.22
In S5L           7.109    2.645       0.63    0.23       2.18
In S6W           4.576    2.481       0.68    0.20       2.09
In S6L           5.834    2.534       0.61    0.23       2.08

Measurement   Upper 95%     r        P

In CL             4.13    0.85   <0.001
In S5W            2.96    0.85   <0.001
In S5L            3.11    0.80   <0.001
In S6W            2.87    0.82   <0.001
In S6L            2.99    0.78   <0.001

CL, carapace length; S5W, 5th abdominal somite width; S5L,
5th abdominal somite length; S6W, 6th abdominal somite
width: S6L, 6th abdominal somite length.

The GLM of possible explanatory variables for
variation in fecundity of Cancer pagurus.

Factors                 df         F         P

Season                   1      1.54     0.219
Area                     1      0.50     0.481
Season X area            1      2.12     0.150
In CW                    1    161.26    <0.001
Egg volume               1      0.12     0.734
Chela loss               1      0.51     0.478
Other pereipod loss      1      1.69     0.198
Blackspot disease        1      1.30     0.258
Moult Stage              1      0.16     0.686

GLM, general linear model. Factors: area, season, and area X
season; covariates: CW, egg volume, chela loss, other
pereipod loss, black spot disease, and moult stage.

The GLM of possible explanatory variables
for variation in egg volume of Cancer pagurus.

Factors        df       F         P

Blackspot       4    0.12     0.975
Chela loss      1    7.14     0.009
In CW           1    0.48     0.490
Fecundity       1    0.01     0.973

GLM, general linear model. In this model the factors are
blackspot disease and chela loss. The interaction between
blackspot disease and chela loss (black spot disease X chela
loss) did not show a significant effect on egg volume. Thus,
aforementioned interaction was removed from the model.

Changes in dry weight and contents of C, N, and C:N ratio
during embryonic development in Cancer pagurus; mean,
minimum, and maximum values per individual [+ or -] SD.

               dry weight
Stage          ([micro]g)      C([micro]g)     N ([micro]g)

Stage I
  Mean       17.30 [+ or -]   8.99 [+ or -]   1.69 [+ or -]
                  1.27            0.56             0.27
  Minimum-    13.47-19.95      7.34-10.03       1.40-2.50
Stage II
  Mean       17.23 [+ or -]   8.79 [+ or -]   1.67 [+ or -]
                  1.10            0.65             0.32
  Minimum-    15.19-19.20       7.66-9.82       1.26-2.90

                  C:N        n
Stage         ([micro]g)

Stage I
  Mean       5.42 [+ or -]   34
  Minimum-     3.44-6.07
Stage II
  Mean       5.37 [+ or -]   20
  Minimum-     3.32-6.10

C, carbon; N, nitrogen. Only eggs in Stage I (Blastula) and
Stage II (Gastrula) were encountered in this study.

The GLM of possible explanatory variables for variation
in dry weight, C, N of Cancer pagurus eggs.

Source                      dry weight

Factors                df    F       P

Chela loss             1    1.63   0.208
Blackspot disease      1    0.02   0.899
Chela loss x           1    0.26   0.613
  blackspot disease
Egg stage              1    0.02   0.890
Egg volume             1    0.42   0.519
CW                     I    0.17   0.685

Source                       C

Factors                df    F       P

Chela loss             1    1.01   0.321
Blackspot disease      1    0.10   0.755
Chela loss x           1    0.24   0.629
  blackspot disease
Egg stage              1    0.86   0.357
Egg volume             1    0.24   0.624
CW                     1    0.22   0.643

Source                       N

Factors                df    F       P

Chela loss             1    0.81   0.373
Blackspot disease      1    1.44   0.237
Chela loss x           1    0.03   0.855
  blackspot disease
Egg stage              1    0.07   0.792
Egg volume             1    0.17   0.678
CW                     1    3.29   0.076

GLM, general linear model. Factors: chela loss, black spot
disease, and chela loss x black spot disease; covariates:
egg stage, egg volume, and CW (n = 54).


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Author:Ondes, Fikret; Kaiser, Michel J.; Murray, Lee G.; Torres, Gabriela
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:4EUUI
Date:Aug 1, 2016
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