J. Mar. Biol. Ass. U.K. (2003), 83, 979^980 Printed in the United Kingdom
Fecundity of the arrow crab Stenorhynchus seticornis in the southern Brazilian coast Claudia Melissa Okamori* and Valter Jose¤ CoboO *Departamento de Biologia, Universidade de Taubate¤ UNITAU, Pca. Marcelino Monteiro, 63, 12030-010, Taubate¤, (SP) Brasil. E-mail:
[email protected] O Departamento de Biologia, Universidade de Taubate¤ UNITAU, Pca. Marcelino Monteiro, 63, 12030-010, Taubate¤, (SP) Brasil and Group of Studies on Crustacean Biology, Ecology and Culture NEBECC. E-mail:
[email protected]
The arrow crab Stenorhynchus seticornis (Brachyura, Majidae), is a common inhabitant of the rocky subtidal along the Brazilian coast. Fecundity and the in£uence of environmental variables on egg production are investigated in this study. Information on egg size and egg loss through incubation are also provided. Monthly samples were conducted using SCUBA diving, from January to December 1998 in the Ubatuba region (23825025@S ^448520 03@W), south-eastern Brazilian coast. Early broods were used for the estimation of size-speci¢c relationships of fecundity. Egg loss was assessed by comparing average egg numbers of early and late broods. The fecundity was estimated in 621.1 339.6 eggs, with an average diameter of 0.48 0.1 and 0.57 0.1mm for early and late eggs, respectively. The number of eggs produced was apparently constant year-round. No signi¢cant di¡erences were recorded among monthly fecundity values. The variation of abiotic factors did not show any relationship with temporal variability of fecundity, suggesting that the environmental e¡ect in egg production is slight at best.
Preliminary studies on the fecundity of crustaceans showed a positive relationship between fecundity and size of the parental female (e.g. Hynes, 1954). In fact, the size of the breeding female has been pointed out as a key variable determining the number of eggs extruded per batch and, thus, the reproductive output of brachyuran females. The weight of the egg mass is usually constrained to about 10% of the female’s somatic weight, since the space enclosed in the cephalotorax for the accumulation of yolk is limited (Hines, 1982). Fecundity is commonly measured as the number of eggs produced in each egg batch, and is described as a function of body size (Corey & Reid, 1991). Yet, it is convenient to distinguish fecundity estimates according to the stage of egg production, i.e. potential fecundity (number of oocytes stored in the ovaries), realized fecundity (number of extruded eggs attached) and actual fecundity (number of larvae released) (Steachey & Somers, 1995; Luppi, et al., 1997). The arrow crab Stenorhynchus seticornis is commonly found in the shallow subtidal on rock bottoms, corals, calcareous algae, and also on soft sediments, such as shelly gravel and sand. This species distribution is restricted to the western Atlantic from North Carolina (USA) to Argentina. It was reported from shallow waters to great depths (Melo, 1996). In spite of being a common inhabitant of hard bottoms, several aspects of its biology remain poorly studied. In this paper, the realized fecundity of the arrow crab is examined for a population from the south-eastern Brazilian coast. The role of temperature, salinity and luminosity is also assessed by sampling over a 1-y-period. In addition, we also report information on egg size and loss during incubation. This information may contribute to the understanding of the reproductive biology of the arrow crab in south-eastern Brazil. Monthly samples were obtained from January to December 1998 at Couves Island, Ubatuba, south-eastern Brazilian coast (23825025@S 448520 03@W). Crabs were collected by hand, using SCUBA diving with a monthly catch-e¡ort of approximately 4 h. Each crab was packed in plastic bags and transferred frozen Journal of the Marine Biological Association of the United Kingdom (2003)
to the laboratory of Zoology at the Universidade de Taubate¤ UNITAU. At the laboratory, each ovigerous female was measured (carapace width, CW) with a Vernier caliper, and sorted in 1-mm size-classes (CW). The egg mass of each ovigerous female was detached from the pleopods and the eggs were counted under a dissecting microscope with a manual counter. A sub-sample of ¢ve eggs was taken in each case and measured using a micrometric scale. Only counts of early eggs were used to estimate the sizespeci¢c fecundity relationship to avoid underestimation due to egg loss. Both early and late broods were used to assess egg loss. For this, median values were compared using the analysis of variance (ANOVA) and the Student’s t-test parametric procedures (Zar, 1999). The embryonic development stages were determined according to Boolootian et al. (1959), but adapted to this species as follows: initial stage ¼the egg is completely ¢lled with yolk; no sign of cleavage nor cellular di¡erentiation; ¢nal stage ¼the yolk is restricted to a reduced patch; the embryo is fully di¡erentiated, with clear segmentation of limbs and developed eyes. Average values of temperature and salinity were provided by the LabMet at the Instituto Oceanogra¤¢co da Universidade de Sa‹o Paulo USP. The section of climatology of the Instituto Agrono“mico de Campinas Base de Ubatuba, provided the light intensity data. The relationship between the seasonal variation of fecundity and the variation of environmental factors was tested using the Pearson’s coe⁄cient. The 5% statistical signi¢cance level was used. A total of 113 ovigerous females was measured, within an average size of 9.24 1.52 mm CW, spanning eight size-classes, from 6.0 to 14.0 mm CW. The number of eggs ranged from 69 to 1850 eggs. From the whole sample, 95 and 18 ovigerous females were found with initial and ¢nal broods, respectively.
980
C.M. Okamori and V.J. Cobo
Fecundity of the Stenorhynchus seticornis
Figure 1. Box^whisker plot of the fecundity average related to the crab size-classes.
According to Bryant & Hartnoll (1995), the terminal moult precedes the ¢rst oviposition in Inachus dorsettensis (Pennant, 1777). It is characterized by a high moult increment compared to the juvenile moults, and the gonads only ripen after moulting. There is thus a delay between ecdysis and brooding. Due to the high energetic cost of the terminal moult, the resources allocated for reproduction are limited and, therefore, the ¢rst brood is typically smaller. The egg increase during embryogenesis, as observed for S. seticornis, is a result of water uptake, a common feature in brachyurans (Wear, 1974). The eggs of S. seticornis are relatively large if compared to Pinotheres ostreum (Say, 1817), which produces the smallest eggs within the Brachyura (0.25 mm), but similar to the size observed in Geryon fenneri Manning & Holthuis, 1984, (0.56 mm) (see Hines, 1982). There is often an inverse relationship between size and number of eggs produced. The arrow crab S. seticornis produces large eggs and small clutches, a strategy directly related to the type of larval development. Choy (1988) points out that large eggs ensure a long incubation period and provide endogenous food resources for larvae, thus reducing early larval mortality. The authors are grateful to the Universidade de Taubate¤ UNITAU, for the ¢nancial support (P# 251/2001-PRPPG) and the OMNI-MARE Dive Center, for the logistical facilities during the samples programmes. Our special thanks to Dr Itamar Alves Martins, for his assistance during the dive sessions.
Figure 2. Relationship between egg number and crab size (carapace width).
Average fecundity for females carrying early embryos was 621.1 339.6 eggs. The values of mean fecundity in each sizeclass (Figure 1) and the regression analysis ¢tting the allometric model to data (E ¼1.27CW2.7, r2 ¼ 0.43) (Figure 2), show a close relationship between size and fecundity, despite the relatively low coe⁄cient of determination obtained. Average number of eggs in ¢nal clutches was 474.61 236.7, which did not di¡er signi¢cantly from initial clutches (Student’s t-test, P40.05). Yet, the average number of eggs in early egg batches was 23% higher than the mean number of eggs in late ones. During the sampled period, no di¡erences were found among monthly fecundity values (ANOVA, F ¼1.81; P40.05). No ovigerous females were collected in July. Initial eggs measured 0.48 0.1mm while the average diameter of late eggs was 0.57 0.1mm. This di¡erence was not signi¢cant (Student’s t-test, P40.05). The monthly variation of the environmental factors examined in this study, i.e. water temperature, salinity and luminosity, is not correlated with seasonal trends of egg production in S. seticornis (Pearson’s correlation coe⁄cient, P40.05). A lack of correlation was also obtained using a multiple regression analysis (F ¼1.131, P40.05). The variability of the number of eggs produced by S. seticornis, can be, in part, explained by size variation. The simultaneous occurrence of the puberty and ¢nal moult may result in a wide size range of primiparous females, and therefore in a large variation in fecundity.
REFERENCES Boolootian, R.A., Farmanfarmaian, A. & Turcker, J., 1959. Reproductive cycles of ¢ve west coast crabs. Physiological Zo˛logy, 4, 213^220. Bryant, A.D. & Hartnoll, R.G., 1995. Reproductive investment in two spider crabs with di¡erent breeding strategies. Journal of Experimental Marine Biology and Ecology, 188, 261^275. Choy, S.C., 1988. Reproductive biology of Liocarcinus puber and L. holsatus (Decapoda, Brachyura, Portunidae) from the Gower Peninsula, South Wales. Marine Ecology, 9, 227^241. Corey, S. & Reid, D.M., 1991. Comparative fecundity of decapod Crustacean. I. The fecundity of thirty-three species of nine families of caridean shrimp. Crustaceana, 60, 271^293. Hines, A.H., 1982. Allometric constraints and variable of reproductive e¡ort in brachyuran crabs. Marine Biology, 69, 309^ 320. Hynes, H.B.N., 1954. The ecology of Gammarus duebeni Lilljeborg and its occurrence in fresh water in western Britain. Journal of Animal Ecology, 23, 38^84. Luppi, T.A., Bas, C.C., Spivak, E.D. & Anger, K., 1997. Fecundity of two crabs species in the Laguna Mar Chiquita, Argentina. Archive Fishery and Marine Research, 45, 146^166. Melo, G.A.S., 1996. Manual de identi¢cac a‹o dos Brachyura (Caranguejos e Siris) do litoral Brasileiro. Sa‹o Paulo: Ple“iade. Steachey, D.P.M. & Somers, K.M., 1995. Potential, realized and actual fecundity in the cray¢sh Orconectes imunis from southwestern Ontario. CanadianJournal of Zoology, 73, 672^677. Zar, J.H., 1999. Biostatistical analysis, 4th edn. New Jersey: Prentice-Hall. Wear, R.G., 1974. Incubation in British decapod Crustacea, and the e¡ects of temperature on the rate and success of embryonic development. Journal of the Marine Biological Association of the United Kingdom, 54, 745^762. Submitted 2 December 2002. Accepted 22 July 2003.
Journal of the Marine Biological Association of the United Kingdom (2003)
